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DEPARTMENT OF THE INTERIOR bee

MONOGRAPHS

OF THE

UNITED STATES GEOLOGICAL SURVEY

VOe UNE VEE

ECIGIWS

WASHINGTON
GOVERNMENT PRINTING OFFICE
1884

UNITED STATES GEOLOGICAL SURVEY

J. W. POWELL DIRECTOR

SILVER-LEAD DEPOSITS

EUREKA NEVADA

By JOSEPH SEFORY. CURTIS

WASHINGTON
GOVERNMENT PRINTING OFFICE
1884

LETTER OF TRANSMITTAL.

San Francisco, Car., January 1, 1884.
Sir: I have the honor to transmit herewith a memoir on the Eureka
Mines by Mr. J. 8. Curtis. I visited the more important mines with Mr.
Curtis at the conclusion of his field work, and have carefully scrutinized ©
the conclusions drawn from it. So far as I am able to judge, the obser-
vations are correct and the inferences from them sound.
Very respectfully, your obedient servant,
G. F. BECKER,
Geologist in charge, Pacific Division.
Hon. J. W. Powe 1,

Director U. 8. Geological Survey.
(¥)

CONTENTS.

Page.

TDG} Tare GIP WIRE EL casa pnce co CRIDO nd BEdad Seeeae bcd cco s Qnanco noSoopendoAarcoscce sosueodcoc v
Contenteeieessaere seca a meer siteramsacercecenc seceiee salsa aaciene ee aniderereecccenssiceceieccces vii
LINTEIRSTUTOTIE) Coco86 GaS80g dd SOR EEE ESO CECE BORO SOLE CECE SOB OO HUES CRBES Shen sac Sonoda Seer aee ix
erelaGe wee cos= saeises eae cle tomer san else cbwereecaces Secwolesececissccas\aseuecissiscucoesaaceelessess xi
BrietiOntline of shesultsssacs-cSsssssseso tac cscs oease = sca concen cccs cesses eneseescsesceSeuaeus xiii
Chapter I.—General Description of Eureka District...... ..---. 02-220 woe won eee ene enone 1
ni Surtace Genlopyges=sescae seetemscetsee assistance eee as seaelsaciese/= sas ao sre a 5

iit —Stiractnrejof Prospect Mountain -s-e---o~/o252- a wacenmenaenc\eecmaronsassl-5-<5e ll

HiVe—SULU CLOTS Ole UO Vere lee srestenteate fo meteeemieiene = sa /s/eta onl aaelsteeeeiacestcemelasscinocia 19

V.—Ores of Prospect Mountain and Ruby Hill............-...-.------------------ 51

iVele—— he Orevh) GpOsttgieereeeet alesse wales eaeleceininia seine eclectic niaesine ciee se aes seine 64

Wilk hel Sourcerotet bor Ore sanee essere snes oe oscin ise cieisieeleiceioe fics es/eineeaitewiclee ais 80
VIII.—The Manner of Deposition of the Ore.... .-.. -...-.2.- ---0 2-5 ene one eee ones 93

IDC SVP sces coo conocs soneke Sotbod Cond 6608 co76 ceao teas cote cede onadibepoaceos conc 107

X.—Do the Ruby Hill Deposits form a Lode?.............-.------- Sepceccene DOCH 111

SESE ADS en Gene Beso oceocoSedo Sen p Gobo ced6 Hans Sag SSS HODScS cesbaceo co sSnkéose 120
OS ARE YG cans Sobods SASH OO odoaod NOLIN SooOsO Cees CobESS Snore Hoo ecetad ese 139

2.0 0 SIMS) TSM se 5 eee d0 S355 CaS NSS BOOS) BUDD EEIDOOOND NSEC DEC OSSO BenebE BSes 150
XIV.—Timbering in the Eureka Mines ....... 2222... 2202 eeenee eon ee cen eee = += 2 cee - 153

SVC SSNIG ATTA? po c6co GOSS HU SCOU CSO COO BASES C55 DES CHS EOS =HD0OSdS5 GSSOSEOS 3055 158

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Vil —Hutureiof hureks District)scc--cccccs ecesece=anewewccewacacn= cece mone sos6---= 169

2 UDR SN? Comsec ann n Og COSC 20 020A QUOI00 AO ECHIDE COG RES IcU ReacuoMbocoeToscnoCs 175

LNG? go aces Gaedas" 90885 2000 DISA ROEES 5 EROSOSSEROSEOU OSES OS HS SSbo core Saceso ca5> Ghossssces 195

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Pirate JI.—Surface geological map ---------------------- BSD E BS OSE CEOS SIIDONCG follows. --- ; 4
II.—Vertical cross-section of Prospect Mountain ...--..-----------------°> follows..--- 12
IIJ.—Elevation and plan of contacts of Ruby Hill mines --.---.------------ follows..-- 22
IV.—Ideal section of -Ruby Hill .--... ---------2---=---c 27 ocee eros faces...- 26
V.—Vertical cross-sections Nos. 1, 2, 3, and 4 ee ne conan neon ee faces.--- 29
ViI.—Vertical cross-section No. 5..--------------+-+-+0-0e0rrrr tt Aaancoe cate faces.--- 30
Vil.—Vertical cross-section No. 6 ..---- ------------27-rrr errs rrr err follows.-.--- 30
VIll.—Vertical cross-section No. 7 ..-------- ----2-s22r errors nee follows. --- 30
1X.—Vertical cross-section No. 8 .----. ----------+----2 errr rere serene nnn faces.... 32
X.—Vertical cross-section No. 9 ------------ +--+ sere rere n seer teres follows-.-- 32
XI.—Vertical cross-section No. 10 ...--..--------+---0serrr ree serene follows. --- 32
XII.—vVertical cross-section No. 11-..-.--------+ +--+ +22--+-77° BR Se re tects follows..--- 32
XII1.—Horizontal sections Nos. 1, 2, PG ay see See Coad Seep E CocebS Desa CRents follows..-- 34
XIV.—Horizontal sections Nos. 4, 5, and Gitte ere oeieee sarin seinen mcs follows-.-- 36
XV.—Ideal faulting of the two shale belts ---------+---++--220 2-77 srrrerer ree faces.... 39
XVI.—Projection of the hanging wall of the Ruby Hill fault..----------------- faces..-. 40
Fic. 1.—Relation of the formations to the main fissure .... ..---- ---- eee e eee e ee eens eee ee rn 31
2,—Plan of main drift and cross-drift 600-foot level, Richmond mine..-..------------+---- 82
aeposition of cupelsinmutile cs. ---tee~= 2m emi neminn ome = ooo ee SSS nT a 127
4,—Position of eupels in mufile ..--- oe EA Sa aaonn ces PaO SCO CEen LCbe PER OC RCeO OSE Sot 128
Re TORR OLIN socedo sper ac CIC Cee OGIO 20 I COR IES ata Se rai 144
6.—Assay curve ----.---- Sere SOG BODE ESO 0 CODSOS 9550C0 SORCE OC HOOLOCSIO ICG Sco neSnaS ese5cc 144
7,—IMustration of electrical activity .----.------++ --++--eer steerer centr nner 146
8,—Set of timbers ..------------------ BoOLCOOeeS RAE nS COSCEE COC DEC EES REDO DaGeLe COB CGQ5 154
9,—Richmond framing ----- Scoceo0 De eeeeeeeeesleseecessesiccenisn= ROB CDE UCOBAROGS HEECOS 155

10. —Eureka framing ....-..2css2eeeooee concen cccces cone cone cone cones cone cne enn ns eee" 157

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PREFACE.

The field work upon which the following report is based was begun in
July, 1881, and concluded late in 1882, the assays and many of the chem-
ical examinations being made during the progress of the field work, as occa-
sion required, in a temporary laboratory arranged for the purpose.

In 1879 Mr. George F. Becker made a preliminary examination of the
more important mines. My report was prepared under his supervision, and
I am indebted to him for much valuable advice and assistance. In 1880
Mr. Arnold Hague made a detailed survey of the general geology of the
district, an abstract of the results of which appeared in the Third Annual
Report of the Director. Upon this abstract I have relied for the determi-
nation of the stratigraphy and the relations of the district at large to the
ore-bearing formations. I also had the advantage of spending some days
in observations on the surface geology with Mr. Hague in 1881. The sur-
face geological map published with this report is taken from Mr. Hague’s
atlas, which will be published with his memoir.

Mr. C. R. Brown was my assistant during a great portion of the time
oceupied by the field work and rendered important services in collecting
specimens and in the laboratory. Mr. N. Wescoatt, formerly surveyor for the
Richmond company, gave me much information in regard to the workings
of the Richmond mine, furnishing maps upon which the drawings of that
mine are based, as well as drawing Plate III. To Mr. E. Probert, manager,
and Mr. R. Rickard, superintendent, of this company, I am also indebted for
many facilities, as well as to Messrs. Bryan, Longley, Morrison, and Davis,
employés. Mr. T. J. Read, superintendent of the Eureka Consolidated, not
only furnished me important maps and information, but gave me every

(si)

Xl PREFAOE.

assistance in his power in visiting the mines in his charge. Mr. Byce, fore-
man of the same mine, rendered me many facilities, as did also Mr. Stevens,
of the company’s reduction works. Mr. E. N. Robinson, superintendent,
and Mr. John N. Williams, foreman, of the Albion, showed me every cour-
tesy possible, and gave me free access to the mine Mr. Kermeen, of the
Ruby-Dunderburg, gave me every attention.

To superintendents and mine-owners too numerous to mention I have
to return thanks for the universally courteous treatment that I received at
their hands.

J. 8. C.
San Francisco, December 31, 1883.

BRIEF OUTLINE OF RESULTS.

From the year 1869 up to the present time (1883) Eureka District has produced about $60,000,000 gold and silver, and
about 225,000 tons of lead. Owing to the fact that the deposits of this district have been more completely developed than
any other of a similar character on the Pacific slope, they offer very complete opportunities for the scientific investigation of
the phenomena attending this class of deposits. In several respects they resemble those of Leadville, Colorado.

The structure of Prospect Mountain and Ruby Hill, the principal mining localities in the district, is explained in
detail in Chapters III. and IV. of this report. The investigation here described has resulted in showing that the dominant
factor of the structure of Ruby Hill is an extensive fault which has determined the present relations of the formations, the
aptitude of the ground for ore deposition, the ingress of ore-bearing solutions, and the fissure system by which the ore
bodies are connected. The presence of this fault, which has been called the Ruby Hill fault, is marked by a fissure filled
in places with rhyolite.

The sedimentary beds of the district are of the Cambrian, Silurian, Devonian, Carboniferous, and Quaternary periods.
Hitherto no deposits of value, with one exception in the quartzite of the Silurian, have been found outside of the limestones
of the Cambrian and Silurian, and they have been mostly confined to the limestones of the former age, though the deposition
of the ore took place without doubt in Tertiary or post-Tertiary times. The igneous rocks of the district occurring near
the mines are granite, quartz-porphyry, hornblende- and augite-andesites, rhyolite, and basalt. Granite-porphyry and dacite
occur, however, in this region.

The ore above the water-level is principally composed of the minerals galena, anglesite, cerussite, mimetite, and
wulfenite, with very little quartz and calcite; the gangue being for the most part hydrated oxide of iron. The ore also
carries considerable gold and silver, and zinc is present probably as carbonate and silicate. Below the water-level the ore
is chiefly composed of pyrite, arsenopyrite, galena, blende, and a few other sulphides, as well as silver and gold.

The ore deposits themselves are very irregular in form, sometimes resembling lodes, sometimes “stocks,” and
sometimes beds. Ore bodies of any size are always capped by caves or in some way connected with such openings in the
rock and with fissures. This connection of ore bodies with fissures is universal in the district. The caves were probably
formed since the deposition of the ore, partly by the action of water carrying carbonic acid, and partly by the shrinkage of
the ore caused by decomposition. Since this last action took place the ore has in many instances been redistributed by the
flow of underground waters. The former presence of these waters is shown by the stratification of portions of the ore
bodies, and by traces of aqueous action exhibited by the surrounding limestone.

It is likely that the constituents of the ore were derived from some massive rock by solution, the solutions being
due to the solfataric action incident to the eruption of large masses of rhyolite. They entered the limestone from below
through fissures, and the greater part, at least, of the ore was deposited by direct substitution for that rock. The lime-
stone was fissured and crushed in many directions by the various faulting movements and gave free ingress to the ore-
bearing solutions, which followed the channels of least resistance and deposited the ore in masses of very irregular form.

The assays of country rock show conclusively that the materials for the ore could not have been derived from any
of the sedimentary formations. The quartz-porphyry is the only igneous rock of the district in which anything but traces
of the precious metals has been found, and although it does not cover much ground on the surface it may be of much more
considerable extent below. The results obtained from its examination point to it as the source of the ore in its neighbor-
hood, at least. The granite which probably underlies the formations of Prospect’ Mountain and Ruby Hill may also have
been a source of the ore, but if such is the case the extraction of the heavy metals from it has been very complete, as when
found on the surface it contains scarcely a trace of silver, gold, or lead.

The process of determining the presence of an ore body by means of exact assays of the surrounding limestone has
as yet led to no practical application, although the results obtained by this method of prospecting coincide in a remarkable
manner with the electrical experiments made by Dr. Barus with a view to the same object. The methods used in assaying
are fully explained in the chapter on that subject.

The chances of finding ore in the deeper workings of Ruby Hill are considered to be favorable, though the quality
and size of ore bodies cannot be predicted with certainty.

(xiii)

ates

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SILVER-LEAD DEPOSITS OF EUREKA,
NEVADA.

BY J. S. CURTIS.

CHAP T ER. I;
GENERAL DESCRIPTION OF EUREKA DISTRICT.

Position. —Hureka Mining District is situated on the western side of the
Diamond Range in the eastern part of the State of Nevada and south of the
Central Pacific Railroad. The town of Eureka, which forms the business
center of this region, is about 90 miles south of Palisade, a station on the
above-mentioned railroad. Eureka is connected with Palisade by a nar-
row-gauge road. The town lies at an altitude of about 6,500 feet above
sea-level, in a cation, which, following a northerly course, enters Diamond
Valley. Ruby Hill, distant about two miles west of Eureka, is the mining
center of the district. On the hill which gives its name to the town are the
mines which, through their large production of lead, silver, and gold, have
given Eureka District a world-wide notoriety. The Ruby Hill mines are by
no means the only productive mines of the district, but they are those which
up to the present time have been most extensively worked and have afforded
the best returns for invested capital. On account of the facilities offered
for the study of mining geology, these mines are also the most interesting
from a scientific point of view. They have been examined by many able
geologists and mining engineers, among whom there has been great diver-
sity of opinion in regard to the nature of the deposit.

Topography— The surface of the country in which Eureka, Secret Cation,

and Silverado Districts are situated is broken up, by a series of canons, into
2654 L—L

a SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

narrow ridges or spurs which join either the Prospect Mountain ridge on the-
west or the main Diamond Range on the east. These spurs are separated
from each other by a main cafion running from Diamond Valley on the
north to Fish Lake Valley on the south. One of the principal of them, ex-
tending a little south of east from Prospect Peak, the central and highest
elevation of the Prospect Mountain ridge, divides the watershed of the east
side of that ridge so that the regions lying to the north and south of the-
crest of the spur are drained respectively by Diamond and Fish Creek Val-
leys. At the northern end of this canon, near its entrance into Diamond
Valley, is situated the town of Eureka. Silverado District lies a few miles.
east of the main cafion, in the hills south of the divide, and Secret Canon
District on the southern portion of Prospect Mountain, and its spurs west
of the before-mentioned main canon. The mines which will be described in
this memoir are confined to Eureka District, which includes the northerly
portion of Prospect Mountain and its spurs. Of these spurs Ruby Hill is.
the most important, and Adams Hill, though detached, is also to be regarded
as a member of the system.

Prominent elevations— Prospect Mountain is a narrow and steep ridge, some-
seven miles in length, extending from Diamond Valley to Fish Creek Valley.
The mountain itself consists of an anticlinal fold which at its greatest ele-
vation, Prospect Peak, is 9,600 feet above sea-level, and, with the exception
of Diamond Peak, is the highest point in the neighborhood. From this.
point it descends gradually, forming irregular and rugged peaks, and is lost
in the valleys on the north and south. The width of the uplift varies from
a mile to a mile and a half, and is greatest in the neighborhood of Prospect
Peak. The northern watershed is cut up by three long and deep canons,
Goodwin, New York, and the canon which connects with Secret on the
southern side of the divide and forms one of the principal canons which
empty into Fish Creek Valley. The western slope of Prospect Mountain is.
very much steeper than the eastern, and is divided into abrupt and rough
ridges by short canons which open into Spring Valley.

Ruby Hill forms the northern spur of Prospect Mountain, but the axis.
of its fold has a northwest direction from its junction with the main mount-

ain. At its highest point it reaches an altitude of 7,300 feet above sea-

GENERAL DESCRIPTION OF EUREKA DISTRICT. 3

level, or about 700 feet above Spring Valley, which divides the Prospect
Mountain ridge from the next succeeding one on the west. Although the
hill has a rather steep ascent it is by no means as rugged as many parts of
the mountain of which it forms a spur.

Adams Hill is a low hill, about 6,950 feet above sea-level, and is sit-
uated about half a mile north of Ruby Hill, from which it is separated by
a narrow ravine leading into Spring Valley. It is somewhat lower than
Ruby Hill, and présents no particular feature of topographical interest. It
may be regarded as the north end of the Prospect Mountain anticlinal, and
slopes off gradually toward Spring and Diamond Valleys.

Hoosae Mountain, somewhat noteworthy oan account of a mine in the

quartzite, lies just north of the divide between Secret Cation and the main
canon. Its altitude above sea-level is about 8,500 feet.

History—Ore was first discovered in this district in 1864, in New York-
Canon, near the present “‘76” mine, and a company was organized in New
York to work the mines, under the direction of Major McCoy, one of the
pioneers of this region. These discovery claims, although producing some
rich ore, were shortly abandoned, and the district remained uninhabited
until the latter part of 1868 or the beginning of 1869, at which time Major
McCoy recommenced mining operations on what is called Mineral Hill, an
elevation situated a short distance south of Ruby Hill. Subsequently, in
the same year, some men in his employ located the Champion and Buckeye
claims on the southwest side of Ruby Hill, and shortly afterwards the
Richmond and Tip-Top ground was taken up.

In Nevada in those days silver-bearing lead ores unless very rich were
considered of little value, and although the outcrops of these locations ex-
posed large quantities of such ore, little interest was taken in them until,
after several unsuccessful attempts by others, Mr. G. Collier Robbins in the
early part of 1870 succeeded in smelting ores from the Champion and Buck-
eye, if not with profit, at any rate with satisfactory metallurgical results.
This induced Messrs. Buel & Bateman to bond these mines and organize
the Eureka Consolidated Mining Company of San Francisco. Furnaces
were then built near what now forms the north end of the town of Eureka,
and active operations began upon the claims of the company.

4 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Still later the Tip-Top and Richmond claims were sold by Messrs.
Dunn & English to a company in London, and smelting works were erected,
under the supervision of Mr. English, at the south end of the town. The
Jackson and Phoenix companies were also incorporated in San Francisco
about this time, and the explorations, which have since resulted in the pro-
duction of such large amounts of lead, silver, and gold from these proper-
ties, were begun in earnest. The Maryland and other mines in Silverado
District, 16 miles southeast of Eureka, were being opened during this period
by an English company, and a large mill was being built at Pinto The
Page & Corwin and the Geddes & Bertrand mines in Secret Cation, south
of Eureka, had been producing rich ore since 1869, and a mill was also
built on the spot where the present leaching works stand. Secret Cation at
this time formed part of Eureka District, but has since been severed from it.
Mr. Robbins was also developing the Kentuck and Mountain Boy claims
in a range of mountains about fifteen miles west of Eureka.

It is not necessary to follow the history of Eureka through all the
vicissitudes which are incident to the growth of such towns, nor to describe
the different enterprises which have been undertaken and abandoned; suffice -
it to say, that in the course of twelve years this mining camp has been
twice partially washed away by floods, once ravaged by the small-pox, and
twice almost completely destroyed by fire, but remains to-day, after thir-
teen years of prosperity, one of the most productive mining towns on the
Pacific Slope.

The number of inhabitants of the district is at present in the neighbor-
hood of 6,000, but, as in other mining camps, a close estimate is very diff-
cult owing to the floating character of the population.

Production As nearly as can be estimated the production of the precious
metals up to the end of 1882 has been about sixty millions of dollars.
Probably about one-third of this amount, or twenty millions of dollars,
was gold. It is difficult to ascertain the quantity of lead produced, but
this is approximately 225,000 tons.

Silene Lae Rel ee —_—s oO eee! Oe oe oe ee a

GEOLOGICAL SURVEY

UNITED STATES

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SILVER- LEAD DEPOSITS PL.|

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CZOLOGICAL MAP OF. RUBY }EEMILL AND ADJACENT COUNTRY

Map extracted from the Report on the OY of Burch District by Arnold Hague

: — IGNEOUS
CAMBRIAN x ‘ EON
Se ~ Hornblende Quarte
Andesite Yorphyry

Mt Prospect Mc Pumice Granite
ab ace a Quarteire Basalt and Tufe Rhyolite

—

OHAPTER If.
SURFACE GEOLOGY.

General geology —Mr. Arnold Hague has described the general geology of
this mining district,” as well as that of the whole region lying within a radius
of ten miles from Prospect Peak, and little more is therefore necessary here
than a reference to his results. The Cambrian, Silurian, Devonian, and
Carboniferous are all represented in the formations of this district, though
it is only in the rocks of the first two that metalliferous deposits of any
kind have been found, and excepting the Hoosae mine, in the Eureka
quartzite of the Silurian, it is only in the rocks of the Cambrian period that
deposits of any great value have been discovered.

Formations —Mr. Hague distinguishes the following beds in the Cambrian,
beginning with the oldest: Prospect Mountain quartzite, Prospect Mountain
limestone, Secret Canon shale, Hamburg limestone, Hamburg shale. These
five formations have all been laid down conformably. The rocks of the
Silurian in the order of succession are Pogonip limestone, Eureka quartzite,
and Lone Mountain limestone. According to Mr. Hague, the first two of
these beds have been laid down conformably with the formations which
represent the Cambrian, but there appears to be a non-conformity between
the Lone Mountain limestone and the overlying quartzite. The rocks of
the Devonian in this neighborhood are the White Pine shale and Nevada
limestone, in the latter of which the mines of Alhambra Hill, in Silverado
District, are situated.

Relations of the mines to the formations. —With the exception of the Hoosac mine in
the Eureka quartzite, and the Bullwhacker and other mines in the Pogonip

aAbstract of Report on the Geology of the Eureka District, Nevada, by Arnold Hague; Third
Annual Report of the Director of the U. 8. Geological Survey, 1882. Mr. Hague’s full report is not yet
in print.

ce)

6 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

limestone on the slope north of Adams Hill, all the mines which will be
discussed in this report are found either in the Prospect Mountain or Ham-
burg limestones. No deposits whatever have been found in the Secret
Cafion shale which separates these two beds, and although it is true that
pyrite, both as impregnations and in masses, as well as distinctly defined
veins of quartz accompanied by calcite, has been found in the Prospect
Mountain quartzite, the lowest of the sedimentary beds of the district, it
has had no economic value. These occurrences moreover do not seem to be
in any way connected with the deposits in limestone. As far as is known,
there is no ore in the Hamburg shale.

Quartzite——The Prospect Mountain quartzite occurs on Prospect Peak,
and extends northerly, southerly, and westerly from this point, covering an
area of about a square mile. It is also found in the shape of a horseshoe
at the northern end of Prospect Mountain, where it divides Ruby Hill, of
which it forms the lower western portion, from the main mountain. There
is a third small outcrop of this rock on the west slope of Prospect Mountain,
between the two above-mentioned localities. These three places are the
only ones where this quartzite is found in the district. On the surface it is
of a reddish color, which is no doubt due to the oxidation of pyrite, but at
a depth of a thousand feet, or at a point where oxidation has not set in, it
is of a grayish-white color. It is brittle, particularly near the limestone,
where it is often possible to crush it in the hand. It breaks in sharp angu-
lar pieces, of which the faces of fracture have a somewhat vitreous appear-
ance. Aboveground it is usually harder and more compact. It is evi-
dently not even approximately pure silica, and is more or less associated
with clayey material.

Prospect Mountain limeston—T he Prospect Mountain limestone composes the
bulk of Prospect Mountain and Ruby Hill. It was laid down conformably
on the quartzite, and to subsequent upheaval and the erosion of overlying
formations owes its present prominence on the hill and mountain. Its strike
is northerly, following the ridge cf Prospect Mountain until it reaches Ruby
Hill, where it bends round to the west, following the quartzite horseshoe.
Its dip as exposed by the workings of the Ruby Hill mines is certainly much
less than 40°, but owing to the absence in most places of all signs of stratifi-

SURFACE GEOLOGY. K

‘cation, and to the occurrence of several faults, an exact statement of its
mean dip is impossible. This dip is, however, much less than it would at
first appear to be on an examination of its contact with the quartzite, as
that has apparently been moved upward along the plane of its contact with
the limestone, thereby crowding that rock outward. This is the case on the
northern portion of Prospect Mountain, as well as on Ruby Hill. On the
surface this limestone usually has a bluish-gray color. It weathers to a
chalky white, and is corrugated and roughened by the mechanical and
chemical action of water. In texture it is granular-crystalline, and it is
frequently hard and tough. . Underground it exhibits numerous varieties
of habitus and color. It appears as calcite, coarse marble, hard white and
black limestone, and in the neighborhood of ore bodies is usually stained
from a light and dirty yellow to a deep reddish brown by oxides of iron.
‘Considerable masses are often met with which have been crushed to a mere
powder, and in the neighborhood of ore bodies it is generally more or less
broken up. Numerous caves and vuggs occur in it, and it everywhere shows
the action of water. Breccias of different kinds of limestone, cemented to-
gether by calcite, are quite common, and occurrences of that mineral and
of aragonite are frequently met with in the openings in the rock. This
limestone is sometimes found distinctly stratified, and is then usually of a
dark bluish-gray color. It everywhere gives evidences of having been sub-
jected to immense pressure. es

Secret Cafion shale —''he Secret Cafion shale overlies the Prospect Mountain
limestone, and forms a narrow belt which follows the course of the ridge of
Prospect Mountain, and, like the above-mentioned limestone, bends round
to the west on reaching Ruby Hill. This shale is of a dull bluish color,
except where exposed to the atmosphere it has weathered to a dirty yellow,
or where it has been subjected to the action of surface waters through fis-
sures underground. It is often disintegrated to a mere clay. It is usually
argillaceous, though sometimes it alternates with thin layers of stratified
limestone, and the strata are much bent and twisted.

Hamburg limestone. —T'he Hamburg limestone does not differ so materially
from the Prospect Mountain limestone underground as it does on the sur-
face. As far as its physical properties are concerned, the limestone in the

8 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Ruby-Dunderburg mine, which is in the Hamburg limestone, might be mis-
taken for that of Prospect Mountain. It is only through its connection
with the well-established belt of Hamburg limestone that its relative age
can be decided. It is hard to say what the properties of the limestone in
the Hamburg mine are which make it easy to recognize the difference be-
tween it and the Prospect Mountain limestone, but they are characteristic
enough to render it evident even to the casual observer that it is a different
limestone. It breaks with a sharper fracture, which is probably due to the
larger quantity of silica that it contains; and one or two varieties resemble
quartzite in texture. The Hamburg shale differs in no essential respects
from the Secret Canon shale.

Pogonip limestone—The Pogonip limestone forms a nearly continuous belt
on the eastern slope of Prospect Mountain, and on the north and east sides
of Adams Hill where that elevation merges in the valley. In this lime-
stone the first discoveries in the district were made in New York Canon. In
it are also situated the Bullwhacker, Williamsburg, and other mines. In
color this limestone does not differ much from the two limestones before de-
scribed, except that it is of a brownish tinge, but it is softer, shows fewer
signs of metamorphic action, and is almost everywhere distinctly stratified.

Eureka quartzite — he Kureka quartzite composes Hoosac Peak and the en-
tire eastern half of the mountain of that name. It also occurs as a narrow
band on the west side of New York Canon and east of the main canon
where it enters Fish Creek Valley. Its color is white, reddish, or bluish,
and it is very hard and compact. In texture it is granular, and it is rarely
found stratified. It is apparently nearly pure silica.

Granite——The granite crops out at Mineral Hill at the north end of Pros-
pect Mountain, covering an area of but a few acres; and this is its only
occurrence in the district. It appears between the limestone and the quartz-

ite. It is coarse-grained, grayish in color, and very much weathered at the

SURFACE GEOLOGY. 9

surface. What its underground character may be is not known, as there
have been no explorations made in it.

Quartz-porphyry.— Quartz-porphyry appears in two places north of Adams
Hill. Mr. Hague assigns no definite age to this rock, but states that it is
post-Cambrian. From the manner of its occurrence in the Bullwhacker
mine it would appear to be of earlier origin than the ore. This rock has a
reddish color on the surface and a granular texture. Where exposed under-
ground it is white, shows considerable quartz, and contains cubes of pyrite.
Neither variety is hard.

Rhyolite—Rhyolite isabundant in the neighborhood of the mines as well as
in immediate proximity to the ore. In some portions of the district it covers
large areas, but in the mines it is only found in the form of dikes, which, so
far as is known, have never exceeded 20 feet in width. There are particu-
larly large outbursts of this rock at Purple Mountain near Ruby Hill and
at Pinto Peak. It is of a nearly white color, sometimes with a pinkish
tinge, and of various degrees of hardness.

Hornblende-andesite— Hornblende-andesite occurs near Hoosac Mountain,
where it covers a considerable territory. It is of a crystalline texture, dark
color, and is considerably weathered. The last two rocks are assigned by
Mr. Hague to the Tertiary age.

Peculiar formation in the Phenix mine—In the Phoenix mine there is an occurrence
of a peculiar rock, the exact nature of which has not been determined.
The position which it occupies can be seen on referring to vertical section
No. 3, Plate V. As far as known it lies wholly in the quartzite. It is
usually of a black color and contains large quantities of magnetite and
pyrite. It is everywhere penetrated by small seams of calcite, and some
specimens are composed almost entirely of that mineral and clay, which
latter substance often fills cracks and fissures in the mass of the rock.
Some pieces showing the least decomposition when treated with boiling
chlor-hydric acid give off a great deal of carbonic acid, and the iron and other
soluble substances are completely dissolved, while a white skeleton of some
siliceous material is left which exhibits a cellular structure. The mass
shows no signs of any stratification, and everywhere exhibits evidence of
the extended metamorphism to which it has been subjected. The form in

10 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

~which it occurs would indicate that it was an intruded mass of igneous rock,
and this theory is in a measure sustained by the fact that specimens closely
resembling rhyolite have been found in the mass. Other specimens are com-
posed almost entirely of calcium carbonate and have unquestionably the
-structure of limestone. In the upper levels of the mine this rock is so much
decomposed and mixed with quartzite that its boundaries are not distinct.
It is very possible that it was originally an intercalated bed of limestone and
has been metamorphosed by an intruded mass of rhyolite and the attending
-solfataric action.

CHAP TER EIT.
THE STRUCTURE OF PROSPECT MOUNTAIN.

Manner of upheaval— Prospect Mountain and its adjacent spurs form an anti-
clinal fold of which the axial plane is usually somewhat west of the crest of
the principal ridge. The course of this plane is nearly due north and south,
except at Ruby Hill, where it turns toward the west. At those places on
the western side of the mountain where the strata have been laid bare by
mining explorations, the traces of bedding are so rare that it is impossible
to form an accurate idea of the prevailing angle of dip.

When the alternating beds of shale and limestone, which at present
form the mountain, were folded and uplifted an enormous crushing and
grinding force was exerted upon the different members of the series. Those
rocks, such as the shales, which were flexible and would give, stood the
test of this great pressure with the least injury to their physical structure,
and, although they were much disturbed and flattened out, retained their
original character. With the limestones it was otherwise. Their hard and
compact nature and their tendency to break instead of bend when subjected
to great pressure caused the formation of numerous fissures and faults.
Most of these fissures were formed parallel to the axis of fold, though many
faults also occurred in every direction. As this uplifting and crushing con-
tinued great zones in the fold were ground almost to powder. Where the
limestone was the weakest or the pressure the greatest the first shattering
began, and as these breaks weakened the mass of the rock where they took
place, the grinding went on indefinitely until the uplifting force had spent
itself.

Influence of eruptive rocks. — Subsequently to the primal folding by which Pros-

pect Mountain was formed eruptions of rhyolite occurred, which had a fur-
ll

2 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

ther disturbing effect upon the structure of the country. There are no
large outbursts of this rock on Prospect Mountain itself, but it appears as
dikes in several places, and large masses of it, and hornblende-andesite, occur
in the immediate neighborhood. Many fissures and faults have unquestion-
ably been caused by the eruption of rhyolite, and as it is among the latest
disturbing agents which have entered into the formation of the country,
it is worthy of attention. It is also extremely probable that the eruption
of rhyolite and the solfataric action consequent upon it had an intimate
connection with, if they did not actually cause, the deposition of the ore.
Although the evidence found in the mines that the rhyolite preceded the
deposition of ore is not absolutely conclusive, it is strong enough to make
this order of succession almost certain. Where found in the mines the rhy-
olite is very much decomposed, being in places wholly changed to clay, but
still retaining enough of its original characteristics to permit of its determina-
tion with certainty. Ata distance from the ore bodies this rock, although
somewhat weathered, is much fresher. s

Relations of the granite to the other formations —It is not likely that the granite of
Mineral Hill, which is the only known occurrence of granite in the district,
broke through the quartzite and limestone, but that it originally formed a
submarine hill in the bed of the ocean upon which the quartzite, limestone,
etc., were laid down, and that its exposure in its present position is due to
erosion. Quartzite containing bowlders of a rock which was probably gran-
ite has been taken from the bottom of the Richmond shaft, which has
attained a depth of 1,230 feet, and is the deepest in the district. These
bowlders consist of granular quartz, mica, and a substance that appears to
be decomposed feldspar. It has not been possible to determine the nature
of this rock with certainty, but it is very probable that it is an altered
granite. Such being the case, it would indicate that the body of that rock
was at no great distance.

Direction of the dip of the various formations— "he strata of the formations which
compose Prospect Mountain do not always dip away from the axial plane
of the fold. There is a notable example of this occurrence in the Ruby-
Dunderburg mine, which is situated at the head of Goodwin Canon. The

principal shaft is sunk in the Hamburg limestone, but at a depth of 450

UNITED STATES GEOLOGICAL SURVEY

Silver Concur,
i

VERTICAL SECTION OF PROSPECT MOUNTS

Prospect Mt Limestone

Stratified See
Limestone Limestone Shale Ss
200 100 200 ~~ GOO

i020 180 160° 40 10 00 8 & H Bw O

SILVER=LEAD DEPOSITS PL. Il

= =]

Industr)
Mine yi

Alexandria
ine

JIS.Curtis, Geologist

TGH PROSPECT MT. AND EUREKA TUNNELS.

ourg Hamburg
stone. Shale. Rhyolite Ore
Inch .
1200 1400, 1600 1800 2000

— So ee TEE a ———— =
; : VERTICAL SECTION OF PROSPECT MOUNTAIN. THROUGH PROSPE\(

‘'T MT. AND EUREKA TUNNELS

Prospect Mt Limestone -
L : “ Na 4
Stratified a lineens Hamburg
Limestone Limestone Shale al E tone Shale ™ Khyolite

“ny M1 ineh

eh a

wee a.

fea.)

: Ag a Shs
ua ay y= J
FA ha inert me “EAs
. Peers aah

~ "| reales

STRUCTURE OF PROSPECT MOUNTAIN. 13

feet it intersects the Hamburg shale, which in this part of the mountain
dips west instead of east, as it should if it followed its normal pitch. Ata
depth of 800 feet it still dips west, and at an angle much less than it did
above, showing that this irregularity, which may be only local however, is
more considerable than was to be expected from the nature of the ground,
for the reason that the Secret Cafion shale which underlies the Hamburg
limestone dips to the east, and if the Hamburg shale should continue its
present pitch for some distance further it would come in contact with the
Secret Canon shale and shut out the Hamburg limestone altogether. There
is a strong rhyolite dike which cuts through the limestone and shale, pitch-
ing to the east, and it is very probable that it is not only connected with
the distortion of the strata, but also with the formation of the ore deposits
in this mine. Dikes of rhyolite, such as occur in the Ruby-Dunderburg
mine, will no doubt be found to exist in many places as mining explorations
lay bare the underground formations. As they are rarely but a few feet
wide, they may easily lie concealed in the surface débris in those places
where there has not been a large overflow of the lava.

Section of Prospect Mountain through Eureka Tunnel.— | he underground workings of
Prospect Mountain and its spurs, although they have now reached a con-
siderable extent, give by no means a perfect idea of the internal structure
of that region, as they expose but a relatively small portion of its rocks.
On the east side exposures have been made by the Eureka Tunnel, which
has been driven from a point near the head of the-west branch of Goodwin
Canon in a nearly due west direction into Prospect Mountain. It is now
over 2,000 feet in length, and has passed several hundred feet beyond the
ridge of that mountain, below which it attains a depth of about 800 feet.
The following are the different formations encountered, in the order of their
succession from the mouth of the tumnel:

85 feet mineral limestone’ (Hamburg limestone).
290 feet shale (Secret Canon shale).

«The name “ mineral limestone” has been given by the miners of the district to that limestone in
which the ore depositsoccur. Although the term “‘metalliferous” would be more scientifically correct as
applied to this rock, the word ‘‘mineral” is used not only by miners, but by writers on mining law,
and has in practice come to be synonymous with ‘“ ore-bearing”; there is abundant precedent, there-
fore, for the use of the term in this signification.

14 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

935 feet mineral limestone (Prospect Mountain limestone).
30 feet shale* (Prospect Mountain limestone).
51 feet mineral limestone (Prospect Mountain limestone).
460 feet shale (Prospect Mountain limestone).
90 feet stratified limestone (Prospect Mountain limestone).
50 feet mineral limestone (Prospect Mountain limestone).

‘The tunnel section, Plate I1., gives an excellent idea of the formations.
which compose the east slope of Prospect Mountain and its spurs. It is
true that in all probability no other section parallel to this one, and taken
at a considerable distance either north or south of it, would closely corre-
spond, yet it is safe #0 assume that there would be enough resemblance be-
tween them to permit of this particular one being taken as a type. Mr.
Hague, in his geological map of the district, has placed the mouth of this.
tunnel in the Hamburg limestone. The first belt of shale encountered is
therefore the Secret Canon shale.

The second belt of shale is probably nothing more than a fragment of
the third and widest, and has been brought into its present position in the
tunnel by movements of upheaval. If Plate II. is examined it will be seen
that the numerous faults which have occurred along the line of the Eureka
Tunnel have so displaced the shale beds that it is not possible to determine
with any certainty what was their original position. In drawing this sec-
tion it has been necessary to depend very much on probabilities in placing
the dividing lines between the different formations. The mass of shale
marked B, Plate II., does not appear in the tunnel, but it is exposed in the
incline winzes of the workings below the tunnel level from a distance 50
feet below that level down to the deepest excavations. As these incline
winzes are several hundred feet south of the tunnel, and as the strike of the
shale is east of north, it would appear in the tunnel section in the position
shown in the plate. There is only one boundary of this shale which has
been exposed, namely, that which is laid bare in the winzes, and the other

boundaries given it in the section must be necessarily of a very indefinite

«The term “ Prospect Mountain limestone” of course refers to a group of beds characterized by the
presence of certain fossils. Though limestone predominates, the intercalated shales which are charac-
teristic of this formation, according to-Mr. Hague, are necessarily classified as members of the same-
group of beds.

STRUCTURE OF PROSPECT MOUNTAIN. 15

nature. On Ruby Hill there are at least two beds of shale, one of which
is intercalated in the Prospect Mountain limestone, and it is certain that at
least that number can be found on Prospect Mountain.

Whether the third and widest belt of shale encountered in this tunnel
actually comes to the surface or not cannot be determined at present with
absolute certainty, but shale rock is found above the Industry mine, and it
is probable that it is a part of the third body of shale encountered in the
tunnel.

This third belt of shale is also somewhat different in character from the-
first, which seems closely allied to that found on the surface at Ruby Hill.
It consists of alternate strata of argillaceous shale and thin bands of stratified.
limestone, and, although considerably thicker than the lower shale of Ruby
Hill, is lithologically almost identical with it. The width of this shale in
the tunnel may be owing to the flatter position which it occupies or to local
expansion. The first zone of limestone has the usual appearance of the
mineral limestone of the district. It is crushed and broken, and all signs
of stratification have been obliterated. It is usually gray in color and
sometimes stained yellowish by iron oxide. It contains vuggs and numerous
séams. Where not too much crushed, it is crystalline in texture and some-
times brecciated, the different fragments being cemented together by calcite.
One of its peculiarities is the difference of the varieties which it presents.
within a few feet. The foregoing will apply to all the metalliferous lime-
stones of the district. It is difficult to state what the precise differences
are which distinguish the mineral limestone from the other limestones. It
is not the difference in geological age which distinguishes it, but rather
differences which are due to dynamical and chemical action. It is never
continuously stratified, and it is never found for any considerable distance
without a change in its physical characteristics. It always bears strong
evidences of metamorphism. The next zone of limestone is the largest,
extending 935 feet from the first to the second belt of shale. .It presents.
the usual characteristics of the mineral limestone, and owing to its great
extent offers almost all the varieties of that rock to be seen on any part of
the mountain. The narrow belt of mineral limestone found further on is.
similar to the main mass, from which it is separated by a thin belt of shale.

16 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

This thin band of shale most likely was at some time part of the third and
widest mass of shale, which lies to the west, and was separated from it by
a series of faults; at any rate faults are apparent along its contact with the
limestone. Alternating beds of shattered limestone and shale seem to be
characteristic of this portion of Prospect Mountain.

At various points along its course the tunnel cuts through seams and
fissures which generally cross it at right angles. Their usual pitch is east-
erly, though there are many exceptions to this rule. The most prominent
one of these fissures is at a point 840 feet from the mouth of the tunnel.

Its dip is nearly vertical, perhaps a little inclined to the east. It is
open in places and filled with sediment, bowlders, ete., which have been
washed in from above. At the point where it is encountered it is about 350
feet below.the surface, and it is a characteristic example of numerous occur-
rences of the same kind, both in the mountain and in Ruby Hill. Like
many others, it has been accompanied by ore, which was found on the north
side of the tunnel. The principal ore body yet discovered was found about
1,200 feet from the mouth of the tunnel, and was also connected with a fissure
which runs a little west of south, but pitches westerly. It did not extend
any distance above the tunnel level, but it was followed down about 100
feet, when a very considerable pipe of ore was encountered running under
the tunnel in a northerly direction. Most of these fissures and seams are
faults produced by the folding and upheaval of Prospect Mountain.

Although there have been local subsidences, it is safe to say that the
portions of country which lie west of the fissures upon the foot-wall side
have as arule been raised the highest. The strata have reached their great-
est relative height just over the axis of fold. The third belt of shale is over-
lain by black stratified limestone, which, at its contact with the shale, pitches
west at a steep angle until a little distance beyond the summit its stratifica-
tion is nearly horizontal. West of the stratified limestone the tunnel is in
mineral limestone.

The following is a list of specimens from the tunnel, and the points at
which they were taken:

430 feet from entrance.....- Black crushed limestone cemented by calcite, friable.
450 feet from entrance. .....Grayish crushed limestone, compact granular.

STRUCTURE OF PROSPECT MOUNTAIN. bid

990 feet from entrance. ....-Bluish-black limestone, compact granular.
1,010 feet from entrance...... White limestone, compact crystalline.
1,100 feet from entrance. ..... White limestone, compact crystalline, partly calcite.
1,200 feet from entrance. .....Gray stratified limestone, compact granular.
1,850 feet from entrance. .... Black limestone, compact granular.
1,900 feet from entrance ..... Gray stratified limestone, compact granular.

( First west cross-cut east side, bluish-gray limestone, com-
340 feet from entrance. .--.. pact, brecciated.
Sediment from fissure.
1,200 feet from entrance at discovery winze near ore. -..- - Yellowish-gray crushed lime-
stone, friable, crystalline.

1,200 feet from entrance... .-. Calcite, stained with manganese.

Section of Prospect Mountain through Prospect Mountain Tunnel | he Prospect Mountain
Tunnel, starting at a point about 2,700 feet west of the summit, nearly oppo-
site the Eureka Tunnel and several hundred feet below it, has been driven
2,350 feet into the mountain. For the first 1,400 feet it passes through a
hard compact white limestone, which in places resembles marble. This
limestone is not often fissured, but contains some cavities washed out by
water. There is nothing about it to indicate that it is mineral limestone.
At a distance of 1,400 feet from the entrance a fissure is encountered
at nearly right angles, which dips 80° to the west. From this point the
character of the limestone changes; it is much more broken, and many of
the ordinary varieties of mineral limestone are found, as well as seams
crossing the course of the tunnel. At 1,835 feet ore was discovered, but as
yet the deposit has not proved valuable. At a little over 2,100 feet strati-
fied limestone was encountered along a fault seam, which dips to the west
(see Plate IL). At 2,250 feet shale makes its appearance along a similar
seam. The twisting of the stratification of both the stratified limestone and
shale indicates that the portions of country east of these two seams were
raised relatively to the portion on the west. Although not absolutely cer-
tain, it is probable that the shale and stratified limestone encountered in the
end of the Prospect Mountain Tunnel is the same body as that encountered
in the end of the Eureka Tunnel.

General internal structure of Prospect Mountain.—I]t will be noticed that the west side
of the mountain differs greatly in the formations that compose it from the
eastern. This in some measure is owing to the fact that a larger portion of

the overlying rocks have been eroded, and that there has not been the same
2654 L——2

18 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

amount of faulting movement. It is possible also that the western side of
this portion of the ridge has not been tilted to the extent that the eastern
has, thereby leaving a broader mass of limestone along the line of the tun-
nel. The quartzite must lie at a very considerable distance below the tunnel,
but it is possible that the tunnel will strike it as it is driven to the east.

Distribution of ore in Prospect Mountain —'The largest portion of Prospect’ Mountain
and its adjacent spurs is composed of mineral limestone, and evidence of
the number of metalliferous deposits contained in it is offered by the
nunferous outcrops-of gossan, which occur along its whole extent, but
which are particularly numerous from Ruby Hill to the Secret Canon divide.
The mines on both sides of the mountain have produced considerable
quantities of ore, and there is every reason to believe that this region
when properly explored will produce important quantities for years to
come. With the exception of some few mines the properties of Prospect
Mountain have been but slightly developed. Those, however, that have
been opened to any great extent show that there are numerous masses of
ore contained in the Hamburg as well as in the Prospect Mountain lime-
stones, and that although no such large bodies as existed in Ruby Hill have
been discovered there are many of them. The ore, too, in general is per-
haps of a better quality.

CHAPTER IV.
THE STRUCTURE OF RUBY HILL.

Influence of granite on the Ruby Hill formations—The axis of fold of Ruby Hill, if
such a confusedly uplifted mass can be said to have an axis of fold, has a
northwest direction from its point of junction with Mineral Hill, as the
northern end of Prospect Mountain is called. Mineral Hill is composed in
part of an outcrop of granite. The quartzite overlies the granite on its
northern side and bends around it to the east and west in the shape of a
horseshoe. The limestone touches the granite on the south and overlies the
quartzite, separating it on the surface on the east and west sides from the
granite. Although the granite does not seem to have broken through the
overlying formations, its presence may have had some influence wm deter-
mining the present position of the quartzite and limestone on this part of
the mountain, and from indications observed in the Richmond shaft (see
page 12), it is possible that it underlies the quartzite at no very great depth
in the Ruby Hill mines. Ruby Hill is separated from Mineral Hill by a
narrow divide and a deep ravine which has been eroded in the quartzite.
This quartzite is found extending along the southwestern base of the former
hill and dips under it to the northeast; that is to say, it pitches northeast at
this point. On the east flank of Mineral Hill, on the other hand, the quartz-
ite dips to the east and on the western slope the quartzite also has a westerly
pitch. The limestone of Ruby Hill formed one and the same body with
that of Mineral Hill before erosion, and it is merely the continuation of the
long belt of limestone of which the greater part of Prospect Mountain is
composed. The bulk of Ruby Hill is made up of this rock, the shale only

making its appearance on the northeastern slope.
(19)

20 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Quartz-porphyry eruption—A bout a mile and a quarter to the north of Ruby
Hill, and beyond Adams Hill proper, there has been an eruption of quartz-
porphyry which covers many acres. If this eruption took place at the time
of the folding and upheaval to which Prospect Mountain and Ruby Hill
owe their origin, it would account for the deflection to the northwest of the
different formations found on Ruby Hill. Whether the eruption of this vol-
canic mass actually caused the bending and twisting before mentioned or
not, the fact remains that these formations were so deflected during the up-
heaval, or subsequent to it, that they lie nearly at right angles to the posi-
tion they would have occupied had they not been subjected to some other
force than that of simple upheaval along their axis of fold. That pressure
was exerted from some point to the north of Ruby Hill is clearly proved
by the marks of striation observable at various points on the walls of the
cross-faults, or those faults which in many places traverse the limestone of
Ruby Hill in a northerly or northeasterly direction. These striation marks
usually dip to the northeast, which would indicate that the lateral force had
been applied from that direction.

Faults—It cannot be said that all the fault-fissures occurring on Ruby
Hill have one general course, but they can be divided into two general sys-
tems; the first consisting of those which are approximately parallel to the
strike of the formations and which were produced entirely by the folding
and upheaval, and the second made up of those which were caused by the
same forces supplemented by a strong lateral pressure. These two systems
of fissures are mostly to be found in the limestone. To what extent they
occur in the quartzite cannot be determined, as the workings in that rock
are not very extensive, but it is probable from the nature of that formation
that they are not so frequent. There are numerous instances, however, of
cross-fissures faulting the quartzite, and this is particularly the case in the
Richmond, and will be more fully discussed when the quartzite in that mine
is examined. Cross-faults have been noticed in the shale, but they are not
so easily detected there, owing to its tendency to bend rather than to break.
There are several examples of fissures of the first kind which fault both
limestone and shale.

STRUCTURE OF RUBY HILL. Dil

Rhyolite eruption —T here has been another eruption of igneous rock in the
neighborhood of Ruby Hill, namely, the rhyolite of Purple Mountain,
which is situated about a mile and a half east of the mines, but this erup-
tion could not have caused the deflection of the Ruby Hill formations to
the northwest, as it occurred subsequent to the original upheaval, although
it was no doubt intimately connected with the subsequent phenomena which
accompanied the deposition of the ore.

Extent of the limestone on the surface—''he face of the quartzite mass which over-
lies the granite dips at an angle of about 40° northeasterly under the lime-
stone of Ruby Hill. The exposure of this belt of limestone on the surface
extends over 4,000 feet from the northwest to the southeast. On the north-
west end it is covered by the débris of Spring Valley, and on the southeast
is cut off by a fault which Mr. Hague has called the “Jackson fault” (Plate
I.). This brings it in contact with the Pogonip limestone lying to the east
of the Jackson hoisting works. Its width on the surface is from 800 to
2,000 feet. It shows few signs of stratification on the hill itself, and is
usually a compact highly crystalline limestone, gray in color and much
weathered.

Extent of the shale on the surface— Beginning at the northwest, the shale first
makes its appearance at the Albion mine, follows round a promontory of
limestone, which extends nearly 1,000 feet to the north, and narrows down
to a point in the lower part of the town of Ruby Hill before reaching the
fault to the east. The shape of this shale body is very irregular; it is widest
to the north of the Richmond hoisting works, where it attains a width
of 2,400 feet, and narrowest, except where it comes to a point, north of the
above-mentioned promontory. Its course is nearly east and west, and its
dip northerly. The angle of dip of its stratification varies greatly. It
sometimes reaches 45°, but is frequently as small as 25°.

Dip of the three formations—It may be as well to state here that nowhere on
Ruby Hill does the dip of the stratification of any of the three formations,
quartzite, limestone, and shale, correspond with the dip of their planes of
contact. In other words, the strata of these three formations do not con-
form to each other in their present position in the mines, though no doubt
they were originally laid down conformably. This lack of parallelism is

22 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

peculiar to the region of Ruby Hill* and Prospect Mountain, and is due to
faults which in many places have followed the contact of the different for-
mations. The local nou-conformity bears upon the ore bodies only as an
indication of structure.

Relations of the three formations underground— The subterranean structure of Ruby
Hill presents features of unusual interest to the geologist and miner. The
underground explorations have been very extensive, but they have not been
so complete that it has been possible to trace the contacts of the different
rocks in every instance, and in making the maps which accompany this
memoir it has often been necessary to calculate the position of points not
actually exposed. These calculations have been made with care and due
reference to the position which the different formations bear to each other
at all exposed points. The main beds of Ruby Hill are an underlying
mass of quartzite, a broad zone of mineral limestone, and an overlying
belt of shale, all of which have been tilted so that they stand at an angle
of about 40°; this angle being somewhat greater in the upper than in the
lower workings of the mines. That these strata should pitch at a smaller
angle as they approach the valley is naturally to be expected. Beginning
at the Jackson mine, the most southerly location on the mineral zone, the
strike of these formations is to the north, but their course is soon deflected
toward the west, until, in the Albion mine, the most northerly, they strike
nearly east and west. Their course underground resembles in its general
outlines that on the surface, though there are many irregularities and fre-
quent breaks caused by faults. As far as the deepest workings have pene-
trated (namely, to a depth of 1,230 feet in the Richmond shaft), the average
dip of the contact of the quartzite and limestone has been found to be
about 40°. Near the surface the angle of dip is much less, as the highest
point of the quartzite seems to be at the crest of an anticlinal fold. The
line of contact between quartzite and limestone on the southwest slope of
Ruby Hill would be very near the top of this anticlinal, which can be ob-

2Jt should be mentioned that Ruby Hill proper stops at the divide south of the Eureka hoisting
works, and that the Jackson and Phenix mines are on spurs of Prospect Mountain. The term “‘ Ruby
Hill mines,” however, will be used in this report as including the Jackson, Phenix, K. K. (now be-
longing to the Eureka Company), Eureka, Richmond, and Albion, the six mines that are situated on
that belt of limestone included between the quartzite and shale.

UNITED STATES GEOLOGICAL SURVEY

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SILVER - LEAD DEPOSITS PL.m

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IFFERENT FORMATIONS OF RUBY HILL

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UNITED STATES GEOLOGICAL SURVEY

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STRUCTURE OF RUBY HILL. 23

served in a tunnel which is run into the southwest side of Ruby Hill some
few hundred feet to the northeast of the Isandula shaft, a shaft sunk in the
débris of Spring Valley. In this tunnel the quartzite is cut through, and
there are signs of a flat undulation; the strata dipping to the northeast in
the face of the tunnel and to the southwest at its entrance. There is said
to be another locality where this can be observed, but it was not possible
to examine it, as the drift in which it occurs was inaccessible. It is ina
drift run to the west from the Buckeye shaft, and 30 feet below the first
level (Lawton tunnel) of the Eureka mine. The position of the quartzite
can be seen on vertical cross-section No. 6, Plate VII.

The quartzite and limestone contact—There is no regularity about the dip of the
quartzite and limestone contact, and there are but few places along its sur-
face where a cross-section would show that the dip remained constant for
any considerable distance. A glance at the various vertical cross-sections
and the plan of underground contacts (Plate III.) will show that both the
dip and the strike of the quartzite contact are very irregular. In some
places, though these are not frequent, this contact pitches back. This can
be observed on the plan of contacts (Plate III.), where the quartzite on the
fourth level of the Eureka projects out over that found below on the fifth.
It also pitches back at the end of a drift from the big cave situated nearly
on a level with the little tenth level of the same mine. This cave, which
will afterwards be described, lies west of the main incline from the ninth
level. Besides smaller irregularities in the quartzite, there are three large
protrusions along the course of this contact, which occur, respectively, in
the Pheenix, K. K., and Richmond mines. The first of these occurs in the
Pheenix and K. K. ground and extends from above the fourth level down to
the seventh of the latter mine with a northerly trend. The second begins
about 300 feet southwest of the Lawton or Eureka shaft on the third level
and extends with a northeasterly trend down to the tenth level. The third
begins on the surface near the ‘compromise line”* and trends in a north-
erly direction down to the ninth level of the Richmond, where it disappears.
Along the line of dip of this same contact there is a great depression sev-

2The “compromise line” is the line dividing the respective claims of the Richmond and Eureka
companies, and was established during the early litigation between those mines.

24 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA. ©

‘eral hundred feet in vertical extent, which occurs at about the same depth
in all the mines, and which, combined with the undulations along the line
of strike, forms large basins of an oval shape. These basins are intimately
connected with the ore bodies and will be referred to later.

The main fault The contact surface between the limestone and the shale,
like that between the quartzite and limestone, is very irregular, but there
seems to be little similarity between them, owing to the presence of a fault.
This fault, to which the name Ruby Hill fault has been given, has had a
very important bearing upon the structure of the mineral zone as well as
upon the ore deposits themselves. Beginning at the southeast, it is first to
be observed at the American shaft, which is about 25 feet deep, and is sit-
uated a few hundred feet south of the Jackson hoisting works. The course
of the fault from this point is a little west of north, and, although not per-
ceptible on the surface, passes west of the Jackson hoisting works, and can
be seen in the workings of that mine as well as in a tunnel near the Pheenix
line. From this shaft it changes its course to the northwest, and were it not
for the débris could no doubt be seen northeast of the Phcenix shaft. It
passes northeast of the Eureka and K. K. shafts, but must be very close to
the latter, and is plainly visible near the mouth of a tunnel run southwest-
erly to connect with the Bell shaft. The last place where it can be ob-
served on the surface is near the Richmond office. Although this fault is
not continuously traceable above ground, owing to the débris, its existence
is fully established by the fact that it is encountered at numerous points in
the underground workings of all the mines of Ruby Hill.

Dip and strike of the main fault——T'he average dip of the plane of this fault is
about 70° northeasterly, and it is of remarkable uniformity, scarcely ever

° one way or the other. Its course also is extremely direct, with

varying 5
the exception of the bend between the Phoenix and Jackson. This fault is
marked by the presence of a fissure filled with clay, which is widest in the
Jackson and Pheenix mines, where in places it measures as much as 15 feet.

The filling of the fissure——The filling or material contained in this fissure is
very different at different points along its course, although there is not

much change in it where it is followed along its line of dip.

STRUCTURE OF RUBY HILL. 25

In the Jackson and Phoenix mines it is rhyolite, which is usually much
decomposed, but owing to the mica and smoky quartz which it contains is
still easily recognizable. Ata place somewhere between the last point at
which it is seen in the Phcenix, and the first where it is encountered in the
K. K., positive evidences of its rhyolitic character are lost. It is likely that
the change is gradual, as there is something over a hundred feet of unex-
plored ground between where the rhyolite is last seen on the sixth level of
the Pheenix and the first place where it is encountered on the sixth level of
the K. K. It is possible, however, that this change may take place sud-
denly. Where the fissure is found in the K.-K. and Eureka mines, the fill-
ing is of a dull yellow, bluish, or occasionally white color, whereas in the
before-mentioned localities it was uniformly white, except where stained by
its contact with ore. In following the fissure northwest it becomes nar-
rower, until in the Richmond mine it is only a few inches wide, although it
is a distinct and well-defined seam, with a different character of limestone
on either side of it. The clay has here lost its plastic nature and is a calea-
reous product of the attrition of the two walls. Underground, as well as
on the surface, this fissure takes a northwest course, after leaving the Jack-
son, which it retains until it is last seen in the Albion ground.

General features of the main fissure —This fissure will hereafter be called the Ruby
Hill fault or main fissure, as to its formation are due the most important
features of the present structure of Ruby Hill, as well as the relations of
the ore bodies to each other. A careful description of its manner of occur-
rence and of the phenomena attending it is necessary for a complete under-
standing of the deposits of Ruby Hill; and although when examined in one
particular locality it does not seem to be of remarkable importance, taken
throughout its entire course it is found to be the key to the solution of the
structural problem of the mineral zone. A proof of its comparatively recent
formation is the fact that it faults all the formations with which it comes in
contact, but is itself nowhere faulted or dislocated. At various points in
the lower levels of all the mines southeast of the compromise line shale is
encountered on the northeast or hanging wall side of this fissure. This body
of shale, however, nowhere reaches the surface, as it is cut off by the fault.
As the workings in this shale are inconsiderable, it is impossible to tell what

26 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

- may be its angle of dip, but it is apparently less than 45°, and the shale pitches
to the northeast away from the fissure. As this formation will be described
at length hereafter, it is only necessary to mention it here in reference to the
fault. It is evident that the country southwest or on the foot-wall side of
this fissure has been raised many hundred feet relatively to the hanging
wall. Whether the former was raised or the latter subsided is immaterial,
as the same effect would be produced in either case. It is probable, how-
-ever, that there was both subsidence and upheaval, but that the latter
exceeded the former. In the Eureka mine the distance to which the south-
west wall has been raised relatively to the northeast wall is over 1,400 feet.
The faulting action is represented in PlateIV. Fig.1 is an ideal section of the
country through the junction of the Locan shaft cross-cut and the twelfth level
of the Eureka mine, on a line at right angles to the strike of the fault which
is represented by the line X Y. The order of succession of the formations,
beginning at the lowest, is: Prospect Mountain quartzite; Prospect Mountain
limestone, consisting of two beds of limestone, with an intercalated bed of
shale; Secret Cation shale; Hamburg limestone; Hamburg shale; Pogonip
limestone. Fig. 2 represents the position of the different formations after
the faulting and uplifting of the foot wall, and after the erosion of the over-
lying formations had given the country its present configuration. It will
be noticed that the intercalated belt of shale to the southwest of the fissure
has been eroded as well as the upper stratum of Prospect Mountain lime-
stone. In the Eureka mine the lower shale is not found much above the
little tenth level (830 feet below the top of the Lawton shaft), but in the Jack-
son it appears above the third level (315 feet below the top of the Jackson
shaft). In the Richmond mine it is exposed from the surface down to
nearly the deepest workings, but as the shale in the Richmond is of a com-
plicated structure its discussion will be postponed until the shale itself is
examined. One of the remarkable features of this widely extended Ruby
Hill fault, which runs in an unbroken line from beyond the Jackson to the
Albion, is its extreme regularity when compared with the contact planes of
the three formations, quartzite, limestone, and shale. In breaking through
these formations it seems to have been but little influenced by the difference
in their cohesion. In the Richmond mine, crushed limestone occupies the

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STRUCTURE OF RUBY HILL. AT

foot-wall side of the fissure and shale the hanging wall above the fifth level.
Below that level stratified limestone intervenes between the fissure and the
shale. In this mine the fissure is generally filled with a hard black clay,
and is often not more than an inch wide. It might be mistaken for an
ordinary slip, were it not for the differences in character everywhere exhib-
ited by the rocks on each side of it. Splices or small slips are of frequent
occurrence in connection with it, as is often the case with such fissures.
In this mine it appears at first sight to be of little importance, and has been
overlooked almost entirely by the engineers who have examined the under-
ground workings. When, however, it is taken in connection with its exten-
sion through all the mines to the southeast, and with the fact that it is a
fault plane along which the whole southwestern country has been raised
from 500 to 2,000 feet, it becomes of great importance as regards the struct-
ure of Ruby Hill.

Detailed description of the main fissure—I t will be seen on examining the plan of con-
tacts (Plate III.) and the various horizontal sections (Plates XIII. and XIV.)
of the different mines that there are a number of places on the various levels
where the distance between the points at which the fissure has been laid
bare is very considerable. ‘The usual method of prospecting in the mines
southeast of the Richmond has been to run a main level along the line of
contact between quartzite and limestone, sometimes. cutting through the
quartzite where its projections into the limestone are so great that the length
of the drift would be materially increased if this contact were followed; and
then if ore was not encountered along this line, to seek for it by driving
numerous cross-cuts towards what was supposed to be the shale, but was in
reality the Ruby Hill fault. Sometimes it was found to be more convenient
to keep the principal drift entirely in limestone and cross-cut in opposite
directions from it. Often these cross-drifts did not reach either the quartz-
ite or main fissure, though the mine superintendents were usually more par-
ticular about a thorough exploration of the quartzite contact than they were
about the fissure. Drifts along this fissure were uncommon, except in the
lower levels, where the quartzite and fissure came together. Owing to this
method of prospecting, the plane of the fissure was not as well explored as
was that of the contact of quartzite and limestone. There can be no rea-

28 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

sonable doubt, however, that the fissure, which in the Jackson and Phoenix
carries rhyolite, is identical with that which in the K. K. and the Eureka
carries calcareous clay. The fissure is intersected by drifts in over twenty
places, all of which correspond in position with that which the fissure would
be supposed to occupy from an examination of the exposures taken singly.
Better proof than this of the identity of a surface is rarely met with in
mines. When there are many fissures or slips it is not always an easy mat-
ter to distinguish one from the other, for one may have given out and
another one taken its place, or faults might have occurred which would
bring another fissure into the place where the first was to have been ex-
pected. This could not be the case in the present instance, as there is no
strong fissure within several hundred feet at any rate of the one in ques-
tion. This is shown by the explorations which have been carried on in the
‘front limestone” on the sixth level of the K. K. and in the cross-cut to the
Locan shaft in the Eureka mines. So, too, the contact of an irregular sur-
face, like the contact of quartzite and limestone, requires more proof than
that of a regular one. In the present case the evidence is amply sufficient
not only to prove the continuity of the fissure, but its unusual regularity.
If the change in the material composing the filling of the fissure had oc-
curred at the single bend of any importance in this fissure, which appears
in the Jackson, a drift along its course might have been necessary to estab-
lish the identity of the two branches. The rhyolite, however, gives out
between the workings of the Phoenix and K. K., and to the northwest of
this point is replaced by clay identical with that which fills the fissure in
the Eureka and K. K., so that the disappearance of the rhyolite forms no
argument against the continuity of the fissure. This clay also, as found in
the Eureka and K. K., is partly derived from the rhyolite, and is merely the
decomposed feldspar of that rock mixed with crushed limestone.

The main fissure at the American shaft— The first point where the main fissure is
noticeable at the southeast end of the Ruby Hill fault is at the American
shaft, which is situated over 400 feet south of the Jackson hoisting works.
The shaft, which is 25 feet deep, is sunk in Pogonip limestone. From near
the bottom of this shaft a cross-cut has been driven to the quartzite in a
southwesterly direction. In this cross-cut, 16 feet from the shaft, the main

Old
Jackson
Shaft

VERTICAL-CROSS-SEC TION Not VERTICAL-CROSS- SECTION No2-
JACKSON MINE,THROUGH A.B JACKSON MINE, THROUGH-C.D.

VERTICAL CROSS SECTION No.s . VERTICAL-CROSS SECILION No 4
PHOENIX MENE, THROUGH EF KK MINE, THROUGH GH

liu ien & Lith x 3 : - : <a a Ss IS. irlis Geologist
Prospect Mt. Limestone ora

Prospect Mt Crushed Magnetite Workings proyected
Quartzite Limestone Lime stone Shale Impregnation Ore Rhyolite Fissures on the Section

Secale 200 ft -1 Inch

wm 0 9 100 200 300 oo 500 660 760 oo *0 1000
Cietiis 4 4 A n 1 i —1_. ——— —
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METRES

STRUCTURE OF RUBY HILL. 29.

fissure, containing decomposed rhyolite, is encountered. On the west side
of the fissure, which pitches easterly, interstratified limestone and shale
are found, the strata of limestone becoming less numerous as the quartzite
is approached. These beds continue for a distance of 134 feet and to within
10 feet of the quartzite, this interval being occupied by crushed Prospect
Mountain limestone.

The main fissure in the Jackson —''he fissure containing rhyolite is also found in
the Jackson tunnel. In proceeding downward it is next to be found on the
third level of the Jackson mine, though it may possibly make its appear-
ance in some of the abandoned workings which are now inaccessible. It
crosses the new Jackson shaft somewhere above the third level and con-
tinues with its usual dip and strike down to the fourth and fifth. It appears
at numerous points on all these levels and is invariably filled with rhyolite,
which is more or less decomposed. It is 150 feet from the quartzite on the
third level in the cross-cut to the old Jackson shaft, is about 15 feet from it
on the fourth, and comes in contact with it somewhere between the fourth
and fifth. It is 60 feet west of the shale on the third, and lies on the foot-
wall side of it on the fourth, in the before-mentioned cross-cut.

The malin fissure in the Pheenix—In the Phoenix the main fissure, still filled with
rhyolite, is first noticed-on the fourth level and continues with its accus-
tomed pitch and strike down to the deepest workings on the seventh level.
It is over 200 feet removed from the quartzite on the fourth, but comes in
contact with it about 40 feet below the fifth near the Jackson line. On the
sixth level, farther to the northwest, it is but a few feet from the quartzite
at the end of the cross-cut from the main incline. It may be as well to
state here that the depth at which the main fissure comes in contact with
the quartzite increases as the fissure is followed westward. Three hundred
feet farther to the northwest, on this same level, it is 50 feet southwest of a
body of shale, probably the same which is encountered in the Jackson.
On the seventh level it is almost everywhere in contact with the quartzite,
and is also in all likelihood in close proximity to the shale.

Main fissure in the K. K.—The fissure is first encountered in the K. K. mine on
the third level and dips at its usual angle down to the deepest workings on
the ninth level. On the third it lies over 250 feet northeast of the quartz-

30 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

ite, and on the sixth it comes in contact with it. In the southeastern part
of the K. K. ground the quartzite face follows the course of the fissure, but
as the Eureka line is approached the quartzite bends westward. In the
lower levels the quartzite and the fissure are together for nearly the whole
of their extent, and the limestone is shut out from between them.

Main fissure in the Eureka—In the Eureka mine the Ruby Hill fault can be
noticed near the surface in the Bell shaft tunnel. This tunnel has been
driven in a southwesterly direction from a point 300 feet distant from the
compromise line to connect with the Bell shaft, and cuts through the fissure
about 50 feet from the mouth. The fissure can also be found in the Utah
tunnel near by, and is encountered in one or two other places, but it is not
an easy matter to trace it on the surface, as the seam is small and usually
covered with débris. At the surface it is about 700 feet from the quartzite.
Itis not again met with in the workings of the Eureka mine until it is encoun-
tered in several cross-cuts on the fifth level. Its dip and strike between
these levels seem to be normal and to conform with the dip and strike in all
other parts of the mine. It is first found in contact with the quartzite on the
twelfth level, 1,030 feet below the top of the Lawton shaft. Near the K.
K. line the junction takes place somewhat above the twelfth level. In the
cross-cut to the Locan shaft, 12 feet above the twelfth level, the fissure which
lies between quartzite and shale is very narrow, but contains a foot or so of
ore. As this level is followed toward the compromise line the quartzite bends
around towards the west, a block of limestone intervening between it and
the fissure. The fissure comes in contact with the shale nearly as high up
as the ninth level, but the developments made at this point are not sufficient
to determine at exactly what point the junction takes place. On the little
tenth (60 feet above the tenth), tenth, and eleventh levels the main fissure
lies under the foot-wall or southwestern side of the shale as the compromise
lme is approached. At or near this line on all these levels the shale bends
to the northeast, but the fissure continues its usual course. Its character in
this region can be best observed on the tenth level of the Eureka and the
seventh of the Richmond two corresponding levels. _While in contact with
the shale the usual clay filling of the fissure is much thicker and stained

SILVER-LEAD DEPOSITS PL.VI
=

UNITED STATES GEOLOGICAL SURVEY

[ sw. NE.

Lawton Shaft

— |

Julius Bien & Co Tith J.S.Curtis, Geologist

VERTICAL CROSS SECTION N° 5, EUREKA MINE, THROUGH I.J.

Prospect Mt Limestone

Prospect Mt. Crushed Workings projected.
Quartzite Limestone Limestone Ore Fissures-with Clay on the Sechon

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400

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UNITED STATES GEOLOGICAL SURVEY SILVER-LEAD DEPOSITS PL.Vil

SW. NE

Buckeye Shaf,

| awton Shaft

EE BUN L EVES

Julius Bien & Co. Lith

TS.Curks Geologist

VERTICAL CROSS SECTION N° 6, EUREKA MINE, THROUGH K.L.

Prospect Mt Limestone.

ns
Prospect Mt. Crushed Workings projected
Quartzite Limestone Fissures with Clay on the Section.
==
Scale 200 ft = 1 Inch
0 so 100 200 300 Oo eco. 7 e00 20 1000
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105100 9 80 7 GG 3 4 30 2% ° m0 200
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METRES

UNITED STATES GEOLOGICAL SURVEY

Windsail Shaft
Lawton Shaft

Julius

KCotth VERTICAL CROSS SHG

Prospect Mt Limestone

Prospect Mt. ° Crushed Stratified
Quartzite Limestone Limestone Shale Limeston
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SILVER-LEAD DEPOSITS PL Vil

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JS.Curus«

Workings projected
on the Section

2000,

Fissures

toLocan Shaft

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x =
Ore

Richmond. 1200 Leve

Hamburg
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UREKA MINE, THROUGH MN.

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WINS weD07

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STRUCTURE OF RUBY HILL. 3}

slightly yellow. Much of this clay is derived from the shale by attrition
and the decomposing action of waters passing along the fissure.

Main fissure in the Richmond— [he fissure leaves the shale at a short cross-cut
in the Richmond ground just after the compromise line is passed, and is here
very narrow, although it is plainly defined, and contains from a few inches
to a foot of clay. It continues its normal course, and is distinctly visible,
with its filling of clay, along the northwest drift in the southeastern portion
of the Richmond seventh level. After leaving the shale the space between
the latter and the fault is occupied by stratified limestone, while the rock
lying on the southwest of it consists of the usual broken and highly meta-
morphosed limestone. On the surface this fissure can be seen near the
Richmond office. On the first level of this mine it is in contact with the
shale, 94 feet west of the Richmond shaft. On the second level it is
35 feet west of the shaft, and is also in contact with the shale, and re-
mains so down to the fourth, where it is somewhat split up, and ex-
hibits a tendency to leave the shale. On the fifth level the fissure is found

SOTO

SSS .
Soy
SSN

Fic. 1.—Relation of formations to main fissure.

A, crushed limestone. B. main fissure. C, stratified limestone. D, contact of stratified E, shale.
limestone and shale.

in the first north cross-cut 182 feet from the main drift. Between it and
the shale the stratified limestone, which is here 30 feet wide, can be first
definitely distinguished. This band of limestone, which increases in width
as depth is attained, is always found on the hanging-wall side of the fissure,

32 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

between it and the shale below the fifth level. On the ninth it has been
cross-cut for over 100 feet without the shale being encountered. The
diagram, Fig. 1, represents the relative positions of the mineral-bearing
limestone, fissure, stratified limestone, and shale, as they are developed by
a cross-cut. The fissure is not often wide, but it exhibits unmistakable
signs of a great upward movement of the country to the southwest of it.
In places there are vertical striations, and the hard stratified limestone
which forms its hanging wall is often polished as smooth as glass. The
strata immediately adjoining the fissure are nearly parallel with it, but as
they approach the shale their angle of dip becomes less until it is frequently
as small as 20°. The contact of the stratified limestone and shale is very
irregular, the strata of the two formations being intermingled, so that there
is no well-defined line of demarkation between the two. This contact, as
far as can be determined by the examination of the limited portion exposed
in a drift, has less dip than the main fissure, but the dip of the bedding-
planes of the shale conform very nearly to those of the limestone. The
curvature of the planes of bedding in limestone and shale shows the upward
motion of the southwest country. The upper portion of the Prospect
Mountain limestone which underlay the shale retained its stratification, and
is now found to the northeast of the fissure, while the lower portion was
forced upward to the southwest of the fissure, its stratification being for the
most part obliterated by the crushing accompanying its translocation. This
stratified limestone is of dark color, and is similar in character to that com-
posing a large block which at the uplifting of the southwest country was
left in a comparatively undisturbed condition. This rock can be observed
on the sixth level of the Richmond, near the A. C. line (the dividing line
between the Richmond and Albion mines), in the widest part of the min-
eral belt.

The places where cross-cuts have been driven up to the shale are not
as numerous as could be wished, but there are enough of them to establish
the general relative position of the fissure and shale, and it cannot be rea-
sonably doubted that the fault is continuous between the points where it
has been laid bare. This fissure has very nearly the same dip and strike
that it had in the mines to the southeast. It extends through the Richmond

UNITED STATES GEOLOGICAL SURVEY

SILVER-LEAD DEPOSITS PL.Ix

Richmond
Shaft

lius Bien & Co Lith.

VERTICAL CROSS SECTION N° 8. RICHMOND MINE, THROUGH O P

Prospect Mt Limestone.

TS Gurls Geologist

— y. ;
Prospect Mt. Crushed Stratified Secret Ca Workings proyected
Quartzite Limestone Limestone Shale

Fissures on the Section

METRES

7
'
;

JNITED STATES GEOLOGICAL SURVEY SILVER-LEAD DEPOSITS PL. x

Richmond Shaft

—

fulius Bien & Co. Lith TS Curtis Geologist

VERTICAL CROSS SECTION N° 9. RICHMOND MINE, THROUGH Q.R:

.
Prospect Mt Limestone
nd
Prospect Mt Crushed Stratified Secret Cn
Quartzite Limestone Limestone Shale Fissures

pele 200 ft.= 1 Inch

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UNITED STATES GEOLOGICAL SURVEY SILVER-LEAD DEPOSITS PL.XI

Richmond
Shaf

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Julius Bien & Co. Lith

J.S.Curtis,Geologist
VERT CAt CROSS Sh CLvOn No lO: RICHMOND. MINE: THROU GH (S.—
Prospect Mt Limestone.
Prospect Mt Crushed Stratified Secret Cn Workings proyected.

Quartzite Limestone Limestone Limestone Shale Fissures on the Section

Scale 200 ft.-1 Inch
400

FEET

METRES

—

JNITED STATES GEOLOGICAL SURVEY

SILVER-LEAD DEPOSIT

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Julius Bien &Co.Lith.

VERTICAL

CROSS - SECTION

Prospect Mt. Limestone

N° ll RICHMOND

MINE THROUGH WV

Prospect Mt Crushed Stratified Secret Ca Workings proyected
BEB Lamestone Limestone Limestone Shale Ore Fissures on the Section
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METRES

STRUCTURE OF RUBY HILL. 33

into the Albion, where it is smaller and less distinct and probably disap-
pears altogether.

The Ruby Hill fault and the quartzite — Wherever the main fissure comes in contact
with the quartzite the dip of the face of the latter corresponds with the dip
of the fissure. The reason for this coincidence of dip is obvious. The
face of the quartzite when in contact with the fissure is no longer the orig-
inal contact of quartzite and limestone, but is the fault face of the south-
western uplifted country. The manner of this upheaval is explained in
Fig. 2, Plate IV. The change of dip of the face of the quartzite when it
comes in contact with the fissure can be noticed on the vertical cross sec-
tions (Plates V. to XII.). Up to the present time no signs of the fissure enter-
ing the quartzite have been observed, and it is not to be expected that it
will do so until a much greater depth is obtained. Nevertheless, as all the
shale and limestone beds and the quartzite pitch off flatter as the valley is
approached, it is but reasonable to suppose that the fissure will eventually
enter the quartzite unless the dip of the fissure also should decrease very
materially. From the fact that an important fault has taken place on the
fissure, it is not likely that depth will effect its dip in any marked degree.
Neither is it probable that it will disappear at any depth to which explora-
tions can be carried, as the fault which produced it is so widely extended.

Mr. Hague says that the thickness of the Prospect Mountain limestone
van be taken at 3,050 feet. As close a calculation as it has been possible
to make of the thickness of the bed of limestone between the lower or in-
tercalated bed of shale and the Secret Cafion shale gives this bed a thick-
ness of about 1,300 feet. Allowing 100 feet for the thickness of the lower
shale, there remain 1,650 feet of Prospect Mountain limestone. ‘This cal-
culation is based upon the measurements that have been made near the
Eureka main incline and the Locan shaft, and presupposes that the dip of the
strata is 40°. If there were no other factors to be regarded, the distance
at which the Ruby Hill fault could be expected to enter the quartzite would
be about 2,200 feet below the twelfth level of the Eureka, or 3,230 below
the top of the Lawton shaft. It is almost certain, however, that this dis-
tance will be very much decreased, owing to the fact that this lower bed
of limestone has been very much crushed and pressed together by the

2654 L—3s

34 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

quartzite moving upward along the Ruby Hill fault. It is very likely that.
this distance will be considerably less, though there is not much probability
that the fault will enter the limestone within 1,500 feet below the Eureka
twelfth level. These calculations are made for the portion of country from
which the ideal section, Plate IV., has been made.

Secondary fissure—At the time of the disturbance which produced the main
fault another and secondary fissure was formed along the contact of the
quartzite and limestone, and the quartzite was raised ‘higher than the lime-
stone, giving rise to the formation of a limestone wedge between the quartz-
ite on the one hand and the main fissure on the other. The dip of the
quartzite contact does not greatly exceed 40°, while the dip of the main
fissure is about 70°. The two surfaces of motion therefore approach each
other and must eventually meet. In some mines this has already been

shown to be the case, and the line of junction is exposed at various depths.
in the lower workings of those southeast of the compromise line. To the
northwest of this line the lowest workings have not reached the junction.

The crushed condition of the limestone wedge is due to the upward
movement of the southwestern country against the hanging wall of the main
fissure. This upward movement also accounts in some measure for the dis-
turbed nature of the contact between the quartzite and limestone, though
there is no doubt but that there were many irregularities in this contact
before the faulting took place. This is shown by the contact between shale
and limestone, which is also very irregular, but it could not have been pro-
duced by the fault, as it lies in an undisturbed region. The undulations
and protuberances in both quartzite and limestone were probably in the
main produced by the primary folding which formed the hill.

Up to the present time all the ore of any importance taken from Ruby
Hill has been extracted from the country southwest of the Ruby Hill fault,
between it and the quartzite. The limestone northeast of the fissure, or the
“front limestone,” as it has been called, although it has been considerably
prospected, has yielded no remuneration. An examination of the vertical
cross-sections of the Ruby Hill mines (Plates V. to XII.) will explain the
relative positions of the two fissures and of the limestone and ore between
them, and the elevation (Plate III.) exhibits the line of their junction. In

icra ttt by
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UNITED STAT

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GEOLOGICAL SURVEY

fies

a
Old Jackson Shaft

PHOENIX

Phoenix Shaft

_| JACKSON

Prospect Mt Limestone

Prospect Mt
Quartzite

lime stone

Crushed
Limestone

Stratfied
Limestone

Scale 400 ft = 1 Inch

Secret Cn
Shale

Magnetite
Impregnation

Rhyolite

Fissures

EUREKA

HORIZONTAL SECTION N

SILVER=LEAD DEPOSITS PL-XII

jon Shaft

s RICHMOND

{ILL MINES, THROUGH E F.

== i
IS Curbs, Geologist i

EUREKA <9 ne

HORIZONTAL. SECTION N®], RUBY HILL MINES. THROUGH AB

ze EUREKA re ; mcuonD
HORIZONTAL SECTION N° 2. RUBY HILL MINES. THROUGH CD

——————

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HORIZONTAL SECTIO

w ne 3 RUBY |}
TA NN . HILL MINES. "THROUGH EF.

——— — A

Dig th

STRUCTURE OF RUBY HILL. oD

some places the cross-sections show that the dip has again become slightly
flatter in the deepest workings, but this is probably not a permanent change.

Two belts of shale exist —It has already been mentioned that two belts of shale,
only one of which appears at the surface, exist on Ruby Hill. If the
geological map of the district (Plate I.) is examined, it will be noticed that
the shale and limestone contact on the surface lies at a considerable distance
northeast from the Jackson, Pheenix, K. K., and Eureka mines. Taking into
account the general dip of the Secret Canon shale on the surface and that of
the shale where it is encountered below, it is at once apparent that the two
must be distinct masses. On the third and fourth levels of the Jackson
mine, in the cross-cut to the old shaft, a body of shale upwards of 100 feet
thick is encountered, which lies on the east side of the main fissure and dips
away from it.

Lower belt of shale in the American and Jackson—'This lower shale has been faulted by
the fissure, and the western portion has been raised up and can be seen in
the American shaft cross-cut, described on page 28. Here it occupies the
position where it was to be expected, namely, on the west side of the Ruby
Hill fault. This is the only known place where this underground or lower
belt of shale is to be found on tie surface, the faulted portion having been
removed by erosion at all other points aboveground.

In the cross-cut on the third level of the Jackson it is about 50 feet
east of the main fissure and on the fourth it is in contact with it. It is
upwards of 100 feet thick on the third level and widens out somewhat as
depth is attained, so that in the cross-cut on the fourth it is 145 feet wide.
The dip of the contact of the shale with the limestone on the third and-the
rhyolite on the fourth is 70° toward the northeast. The dip of the stratiti-
cation, at its contact with the limestone or rhyolite, is very nearly the same
as that of the contact itself, but in proceeding toward the old shaft the
planes of bedding of the shale become flatter, though they again dip off
more sharply as a fault plane is approached, which separates the shale
from the black stratified limestone in which the old shaft was sunk. The
stratified limestone northeast of this fault plane exhibits the same phe-
nomena as regards dip as did the shale at its contact with the limestone or
the rhyolite. The dip of this fault plane is about 70° northeasterly, and it

36 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

has a northwesterly and southeasterly course. No rhyolite accompanies it,
but between it and the succeeding stratified limestone there is the ordinary
clay produced by attrition. The phenomena just described conclusively
prove the uplifting of this country in benches.

The quartzite was most raised, sliding along its contact with the Pros-
pect Mountain limestone; this limestone also being uplifted along the fissure
while the shale was raised along the fault between it and the stratified lime-
stone. During the upward motion of these different benches each rising
portion drew along with it more or less that which next succeeded. This is
visible in the present arrangement of the strata. In ascending it will be
observed that the main fissure, which faults or cuts off the shale, is no
longer in contact with this rock on the third level of the Jackson, Fig. 2,
Plate V. This is probably owing to the irregular form of the shale mass.

The lower shale in the Phenix—'T'he next place where the shale is encountered is
on the sixth level of the Phcenix. It is laid bare by a northeastern cross-
cut 50 feet long 300 feet northwest of the northeastern cross-cut from the
main incline. At the point where it is to be seen it is but 50 feet from the
main fissure, but as the drift does not pass through it it is not possible to
determine whether the same fault exists that is to be found on the north-
eastern side of the shale in the Jackson. It is altogether probable that it
does, however, and that this is the same body of shale that is exposed in
that mine, as its position is that which would be occupied by the Jackson
shale did it follow the course and dip which has been exposed in the cross-
cuts to the old Jackson shaft. Moreover it occurs on a line between the
next shale encountered in the Eureka and that found in the Jackson. The
Phoenix shale also does not appear on the surface.

Lower shale in the K.K.—"There is probably shale to be seen in the lower work-
ings of the K. K., but as everything in that mine has been flooded below
the sixth level for several years, it was not possible to examine the ground,
and information in regard to it was not reliable, as the clay in the main
fissure has often been described as shale. Still as shale is encountered in
the lower levels of the Eureka and Phenix mines, it is likely that it is to be
found in those of the K. K.

SILVER-LEAD DEPOSITS PL XIV

UNITED STATES GEOLOGICAL SURVEY

No. 4, THR O@@HSGree

HORIZONTAL SECTION

HORIZO

=
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=
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6
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Shaft

2
is
8
S.

No.6, THROUGH KL.

SECTION

|S
re

HORIZONTAL |

WOND

RICHM

EUREKA CON.

—

TS Curtis, Geologist

Julius Bien & Co. Lith

Mt Limestone.

Prospect

Cross Fissures

Fissures

Secret Cn
Shale

Shale

Stratified
Limestone

Prospect Mt. Crushed
Quartzite Limestone.

Limestone

i
hi
ll

isco

1600,

1200

1000

800

Scale 400 ft-1 Inch.

600

FEET.

210200 180 160 Ko 1 wo’ a & © Ww

METRES

STRUCTURE OF RUBY HILL. ot

Lower shale in the Eureka — This underground shale is exposed in the cross-cut
from the twelfth level of the Eureka mine to the Locan shaft. Vertical
cross-section No 7, Plate VIII, shows the position of this shale. At this
point it is very narrow, not exceeding 20 feet, and is more or less mixed
with stratified limestone. In this region it probably extends up as high as
the little tenth, and it forms the hanging wall of the main fissure, which
takes up the space between it and the quartzite. During the process of
upheaval which formed the main fissure and the secondary fissure at the con-
tact of the quartzite and limestone, there was considerable motion along
the face of the quartzite, and the shale which lay northeast of the fissure
was dragged upward, so that where it forms the hanging wall the dip of its
stratification is nearly parallel with that of the fissure. This can be noticed
in the cross-cut. The natural dip of the shale, however, is less than 40°,
so that as depth is attained it will gradually pitch off flatter and the lime-
stone will again make its appearance in the form of a wedge between the
fissure and the shale. This occurrence is already indicated on the thir-
teenth and fourteenth levels, where the limestone appears to be growing
wider. This limestone, having been subjected to a pressure similar to that
exerted in the upper wedge between the hanging wall of the main fissure
and the quartzite, will be found to be in a like crushed and broken state.
At a point on the tenth level just over the main incline, 140 feet above the
twelfth, the shale is found in contact with the main fissure, which is here
some distance from the quartzite. In going southeast from this point the
shale gives out, but in going northwest it is found in contact with the fissure.
Further along toward the compromise line the cross-cut passes through it
for 120 feet before reaching the limestone. Above this point the shale
reaches as high as the little tenth, always forming the hanging wall of the
fissure, but was not found where the fissure has been cut above it on the
ninth. Below the twelfth level it was not possible to inspect it, as the thir-
teenth and fourteenth levels have been under water for several years, but
from information obtained it must occupy about the position laid down on
the map.

This shale may or may not be the same as that which is found in the
Phoenix and Jackson, but the fact before mentioned, that it lies in a line

38 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

with those two belts and also that it is accompanied by a fissure on its
hanging-wall side similar to the one which occurs in a similar position with
it in the Jackson mine, would tend to prove that these three bodies of shale
were parts of a continuous belt. They are moreover identical in their
physical character.

Connection of the two belts of shale —If the shale is traced from the point where
it is found over the main incline on the tenth level of the Eureka past the
compromise line into the Richmond seventh, and from the seventh up to
the sixth, and so on up to the fourth, and thence through the shaft to the
surface, the continuity of shale from the lowest workings of the Eureka up
to the spot where it comes to the surface back of the Richmond hoisting
works is established. But, on the other hand, if it is followed upward from
the place where it is exposed in the cross-cut to the Locan shaft on the
twelfth level of the Eureka along the line of its contact with the main fis-
sure, it is lost sight of above the little tenth level of that mine. If it fol-
lowed the fissure, it would be found on the surface about 800 feet south-
west of the Locan shaft, and in the Bell shaft tunnel. But the shale on the
surface lies over 300 feet northeast of that shaft. There is no other shale
on the surface between the Locan and Lawton shafts, and none is found in
the former shaft until a depth of 1,020 feet is attained. The shale on the
surface, however, northeast of this shaft can be followed around to the
southwest of the Richmond hoisting works, so that the two masses of shale,
the upper and lower, must be connected somewhere below, the Locan shaft
being sunk inthe limestone between them. (See Plate I.).

Causes which produced the junction of the two shale belts —Through the faulting incident
to the upheaval the lower belt of shale has been brought into contact with
the upper or surface shale somewhere near the compromise line. At exactly
what point this junction takes place, it is a difficult matter to determine,
except on the tenth level of the Eureka and the seventh and eighth of the
Richmond, owing to the insufficiency of the explorations and the broken
character of the ground; but it is evident that there is a junction as will be
seen if the surface map is compared with the underground sections.

There is a sharp bend in the shale contact on the surface along the

compromise line. From observations made below on the sixth, seventh,

STRUCTURE OF RUBY HILL. 39

and eighth levels of the Richmond, it is almost certain that this bend in the
shale is not due to twisting and distortion, but was caused by a vertical
fault which followed very nearly the course of the compromise line. When
the country was raised up, the portion of it lying northwest of the compro-
mise line fault was not raised to the same height as the portion of country
lying on the southeast side of it. In other words, the block of ground just
described subsided either absolutely or relatively. It is almost certain that
in this manner the northwest end of the underground or lower body of shale
was brought in contact with the surface or upper belt of shale along this
compromise line fault. The position of the two bodies of shale southeast
of the compromise line favors this belief. Similar cross-faults noticed in
the quartzite in the Richmond mine also tend to prove the fact of a
frequent cross-faulting of the formations in this part of the hill. This being
the case, the lower belt of shale must underlie the stratified limestone in the
Richmond mine, and it will be encountered at greater depth. At this lower
level the ground must have very much the same appearance as the country
on the northeast side of the main fissure in the cross-cut to the Locan shaft.
The fissure, however, at the point where it cuts this lower belt of shale
might or might not be in contact with the quartzite. A calculation made
on the basis of the displacement of the shale on the surface would bring
the lower belt of shale in contact with the fissure at a point about 1,700 feet
below the top of the Richmond shaft, or about 500 feet below the present
lowest workings. Another proof that the lower belt of shale has been
brought into contact with the surface shale near the compromise line is fur-
nished by the fact that the surface or upper bed of shale is always under-
lain by distinctly stratified limestone whereas the lower shale is not. This
stratified limestone is not to be seen southeast of the compromise line or
fault, where the lower shale makes its appearance. It will be noticed that
this cross-fault does not in any way affect the course of the Ruby Hill
fault; it was, therefore, formed at the same time or prior to it.

lustration of the manner of faulting — Figures 1, 2, and 3, Plate XV., represent the
manner in which the two belts of shale were dislocated by the cross-fault
and the main fault. A B, Fig. 1, represents the upper or larger belt of
shale, and a b the lower, there being limestone between and on either side

40 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

of them, which, however, for sake of clearness, is omitted in the diagrams.
The point of view is in the Richmond ground looking towards the Eureka,
and the two bodies of shale dip easterly at an angle of 40°. The plane
MN OP, Fig. 1, represents the direction of the cross-fault, which was the
first one to occur. This fault takes place nearly on the compromise line,
and has a nearly vertical dip. When the faulting occurred the blocks B
and b, representing portions of the two shale belts, slipped down until they
occupied the positions relative to the blocks A and a shown in Fig. 2. The
plane Q RS T shows the direction of the main fault, and after it occurred
the pieces a’ b’ and B’ were raised above the present surface of the ground,
and have been removed by erosion. The piece @ corresponds to the shale
which was cut off from below the ninth level of the Eureka; the piece b’
is the corresponding portion of the lower belt of shale, supposed to exist
below the present workings of the Richmond, and B’ is the part of the
larger mass of shale, which was removed by the main fault. The face a,
Fig. 3, represents the shale as it now exists in the Eureka, and the face B
represents the shale in the Richmond. The irregular lines on the tops of
blocks A and B represent the surfaces of erosion as nearly as possible as
they exist at present. If the line e fg h is taken as representing the Rich-
mond seventh and the Eureka tenth levels, it will be seen that conditions
exist in these ideal beds of shale similar to those which actually occur in
the two mines. In the Richmond the contact between shale and limestone
is continuous to the surface, and it can also be traced in to the Eureka
ground along the tenth level of that mine, but cannot there be followed to
the surface.

Plate XVI. represents a projection of the different formations that are
found on the hanging wall of the main fissure upon a vertical plane par-
allel to its course. The point of view is from the mineral zone. The various
beds of shale are lettered to correspond with those in Fig. 3, Plate XV. As
the strata of shale and limestone were not only very much crumpled and
disturbed before the faulting took place, but during that dislocation as well,
the structure of this country is very complicated, and it isa matter of great
difficulty to trace the movements that have taken place.

UNITED STATES GEOLOGICAL SURVEY S!ILVER-LEAD DEPOSITS PL. xvi

Lawton Shaft!

(
Julius Bien & Co. Lith TS.Curus Geologist

VERTICAL PROJECTION -— HANGING WALL OF THE MAIN FISSURE
IN THE RICHMOND AND EUREKA MINES

Prospect Mt Limestone.

Crushed Stratified Secret Ca
Limestone. Lime stone Limestone . Shale

400

Scale 400 ft-1 Inch.
800 1000

oo 200 600 1200 1400 1600 2

FEET
210200 180 160 140 120 100 8 6 40 2 Oo 200 400
METRES

2000
——!

STRUCTURE OF RUBY HILL. 41

Shale in the Albion.— A large part of the work which has been done in the
lower levels northwest of the A C’ line has been performed by the Rich-
mond company.

On this end of the hill the shale does not present any remarkable feat-
ures. Its contact with the limestone is irregular, as usual, but its position
underground conforms very nearly with that which it occupies on the sur-
face, always allowing for the dip of the formations. There are occasionally
masses of it intruded in the limestone. South of the Albion shaft it is in
close proximity to the quartzite, touching it in places. The quartzite referred
to is a narrow belt of quartzite, which will be described hereafter. The
shale is shown in the various horizontal sections, and it retains its general
relations to the limestone down to the deepest point west of the A C line,
namely, at the end of the ninth level of the Richmond.

Front limestone — The time and manner of formation of the Ruby Hill fault,
and its subsequent filling either with rhyolite or clay, are matters of very
great importance as regards the history of the mineralization of the lime-
stone between the quartzite and the fault-fissure and the prospects of find-
ing ore either at a greater depth or by prosecuting developments in the
so-called front limestone. This body of rock lies northeast of the main
fissure, and although it has in many places the appearance of the ore-bear-
ing ground has hitherto been found unproductive, all the ore having been
obtained from the limestone wedge between the main fissure and the quartz-
ite. It is true that the prospecting done in the front limestone has not been
sufficient to prove that it contains no ore bodies, but it has been sufficient to
discourage search in that direction. It shows at any rate no such outcrops
as were apparent in the Champion, Buckeye, and Tip-Top claims (the orig-
inal locations of the Eureka Consolidated and Richmond companies), situated
in the southeastern slope of Ruby Hill, just above the quartzite and lime-
stone contact. If the theory, which will be discussed hereafter, is correct,
namely, that the ore was brought up in solutions from below through the
main fissure, the barrenness of the front limestone is easily accounted for

“The A C line is parallel to the compromise line, and is the dividing line between the Richmond
and Albion ground, which was established by the courts in the suits between the twocompanies. Prior
to the fixing of this line the Richmond company had explored a large portion of the ground which is
now held by the Albion.

42 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

by the presence of the lower belt of shale. The shale in general is unfavor-
able to the passage of solutions of any kind, as well as to the deposition of
ore, and in this particular instance (see Plate VIII.) it acted as a barrier to
confine the metalliferous solutions to the wedge of crushed limestone above
it, between the main and secondary fissures.

Front limestone in the Eureka — he explorations in the front limestone consist of
a few cross-cuts from the different levels of the K. K. and Eureka mines.
The principal of these cross-cuts is the one connecting the twelfth level of
the Eureka with the Locan shaft. This cross-cut is 508 feet long and is
driven from its junction with the twelfth level, near the station of the main
incline, in a northeasterly direction, through the upper belt of Prospect
Mountain limestone lying between the upper and lower belts of shale. The
rock through which it passes does not differ in any material respect from
the limestone which is found above between the quartzite and main fissure;
but it is harder and more compact, and does not show evidences of having
been crushed and disturbed to the same extent as the latter, except in the
immediate neighborhood of the fissure. It is dark colored, and shows some
slight signs of stratification.

Front limestone in the K. K.— The cross-cut on the sixth level of the K. K. (see
horizontal section No. 2, Plate XIII.) lays bare another portion of the front
limestone. This drift is over 300 feet long, and although the limestone is
different in color and texture from that in the cross-cut just described, there
is no greater difference than can be observed in varieties of limestone in
the mass between the quartzite and fissure. Samples for assay were taken
every 30 feet in this drift, and the results obtained will be discussed in the
chapter on assays. No signs of stratification were observed in this lime-
stone, and it was of a grayish-white color. It is harder and more compact
the farther it is removed from the contact with the fissure, and it is highly
crystalline in texture. It is considerably broken near this contact, and por-
tions of it are crushed and mixed with the clay. The limestone between
the fissure and this quartzite is crushed to a powder in many places, and
forms a narrow belt scarcely a foot wide, which is often stained with iron.
In another cross-cut, some 30 feet long, farther to the southeast, the lime-

stone is of a blackish color, and breaks in sharp angular pieces. Similar

STRUCTURE OF RUBY HILL. 43

material, however, can be found in many places in the mineral belt, and
this dark rock exhibits no characteristic features that would distinguish it as
coming from the front limestone.

Characteristics of the front limestone —It, has not been possible to find any charac-
teristic features in either of these two limestones which would distinguish
them from each other; and although the limestone southwest of the fissure
certainly belongs to the lower belt of limestone and that northeast of it to
the upper, yet there is nothing in the appearance of either that would indi-
cate that they belonged to different masses unless it is that the front lime-
stone is less disturbed and that its stratification is more frequently percep-
tible.

The quartzite southeast of the compromise line —’he quartzite in the four mines south-
east of the Richmond shaft appears to be substantially a solid mass many
hundred feet in thickness. Its contact with the limestone is very irregular,
and the rock near the surface is often displaced to a greater or less extent
by faults, but it is comparatively easy to explain these irregularities and to
account for the phenomena exhibited. Not so, however, with the quartzite
in the Richmond and Albion ground northwest of the working shaft of the
former mine.

The quartzite in the Richmond and Albion— The explanation of the occurrence of
this quartzite and of the manner in which it was brought into its present
position in this part of the hill is a matter of great difficulty, partly owing
to the absence of sufficient explorations in the neighborhood of the Rich-
mond shaft and partly on account of the complex character of the move-
ments which have taken place. The quartzite (see Plate III.) on entering
the Richmond ground from the Eureka bends toward .the west, as has
already been stated, and forms a promontory which pitches to the north.
This rock is first encountered in the Richmond shaft at a point about 30
feet above the seventh level and the shaft continues in quartzite down to
the deepest point reached, namely, a perpendicular distance from the sur-
face of 1,230 feet, which would give the quartzite a vertical thickness of at
least 580 feet. A cross-cut on the twelfth level, driven a little east of north,
passes through 360 feet of this rock before reaching the limestone. A cross-
cut on the 1,050-foot level driven a little west of north strikes the limestone

44 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

160 feet from the shaft. It will be seen that both of these cross-cuts are
run through the above-mentioned promontory, and that they give some idea
of its shape at the depth at which they were run. These cross-cuts and
other workings in the Richmond ground near the compromise line prove
that the quartzite in which the shaft is sunk is the main body of quartzite
which underlies the limestone of Ruby Hill. (See Plate XIV.)

The narrow quartzite —At variable distances, according to the depth attained,
northwest of the Richmond shaft, the secondary fissure, as the contact fis-
sure between quartzite and limestone has been called, leaves the main body
of quartzite and passes off into the limestone. It can be seen on all the
levels of the Richmond and Albion mines where the workings have been
pushed sufficiently to the south and west, but it is particularly well devel-
oped on the second and fourth levels of the former, where its course has
been followed by drifts until it disappears in the northwest portion of the
Albion ground. The most remarkable feature connected with this fissure is
the fact that it is accompanied by quartzite. In the upper levels this
quartzite is a very thin band, seldom exceeding 10 feet, and often much
less, but in the lower levels it is much wider, reaching a breadth of 80 feet
on the Richmond ninth level. Its junction with the main body of the
quartzite is not clearly shown on any of the levels, but it is considerably
northwest of the shaft in the upper levels, and gradually approaches the
shaft, as depth is reached, until on the ninth level it is at about the point
shown on the horizontal section No. 6, Plate XIV. The fissure is plainest on
the upper side of this narrow belt of quartzite, but a parting is nevertheless
distinguishable in many places on the under side. There are several cross-
faults and undulations in this quartzite, which were probably produced by
the primal upheaval. As the problem of the occurrence of the quartzite in
this portion of Ruby Hill is as complicated as that of the shale near the
compromise line, a detailed examination of its appearance is necessary to
a full comprehension of the phenomena attending the formation of the
mineral zone.

Description of the quartzite in detail—_In the Richmond the quartzite is first encoun-
tered on the second level, but it has not been as thoroughly explored on that
level as it has been on the fourth, 200 feet below it. It is not certain at

STRUCTURE OF RUBY HILL. 45

exactly what point on this latter level the quartzite begins to thin out, but
an alteration in its width is first noticeable about 800 feet westerly from the
shaft. (See Plate XIII.). Here the quartzite is but a few feet thick, and a
short distance farther to the west it is but a few inches, being scarcely more
than a seam filled with quartzite, limestone, and clay. This character it
retains in the continuation of this level, varying in thickness from a few
inches up to 20 feet or more until the extreme northwest workings in the
Albion ground are reached. Near the point where this thinning out of the
quartzite is noticed there are unmistakable signs of a fault. This fault is
of no great lateral extent, and forms one of a series of similar faults which
are found in this narrow strip of quartzite at various points on the different
levels. These faults have a general northerly course, and dip sometimes
easterly and sometimes westerly. What has been the extent of the faulting
in a vertical direction cannot be determined with any certainty, but in
some cases it has been considerable. At the point mentioned above, there
are two slips; but it is the one which has a westerly dip of 85° that seems
to displace the quartzite. One hundred feet beyond this point a drift has
been run into the ‘‘ back lime,” as the limestone is called which lies on the
southwestern side of this narrow strip of quartzite.

In proceeding along the fourth level from the shaft, the main body of
quartzite is left at some unknown point, the explorations that have been
made in the back lime not having been sufficient to discover it, and the
narrow band that is followed is but a splinter from the main mass. On the
Richmond fifth level the quartzite is to be found at two points. The first is
about 200 feet south of the shaft, and the second is at the end of the first
southwest cross-cut. In both places it appears to be the main solid body.
Still it is possible that at the last point it may be only 50 feet thick, for it
is found no wider than that on the sixth level 100 feet below and some little
farther west. ‘The explorations on the sixth level (Plate XIII.) lay bare the
contact of the quartzite and limestone for a long distance. The end of the
long southwest cross-cut, which is called the fissure drift, reveals the same
fault in the quartzite that is exposed on the fourth. In the southeasterly
branch of this southwesterly fissure drift the quartzite is found to be 50
feet thick. It is faulted and brought down to a seam by the fissure which

46 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

followed the southwestern branch of this drift, but in all probability it
widens out again in the manner shown on the map, a’s it is found at the south-
east on the first level of the Albion 30 feet above the Richmond sixth. It
there follows a course almost identical with that exposed above it on the
fourth. It seems to have the same bends and twists exhibited on that level,
and it is likely that its position at any intermediate point between the two
levels could be calculated within a few feet. Both in the Albion first and
in the Richmond fourth, 170 feet above it, the quartzite also comes in con-
tact with shale bodies, and the manner of occurrence in the two cases is
very similar. The quartzite on the Albion first is very narrow, and although
it lies along a well-defined fissure it is not an easy matter to obtain character-
istic specimens, as it is much mixed with limestone and clay.

On the seventh level of the Richmond there is a fault 190 feet from the
shaft, but it lies over 200 feet to the southwest of the point at which its
position above would indicate its reappearance. The quartzite and its
accompanying fissure is found at the southeast end of the Albion second
or intermediate level. At this point it has been cross-cut ten feet and the
back limestone has not been encountered. In following along this level,
the fissure, which is here nearly perpendicular, leaves the quartzite. It is.
true that this fissure contains more or less clay and quartzite for a consid-
erable distance, but the limestone on the southwest side of it does not seem
to have the usual characteristics of the back limestone. In passing along
the eighth level a fault is again noticeable, at a point where there is a sharp
bend in the drift 390 feet west of the shaft. The point is nearly directly
below the fault on the sixth.

As the seventh level does not extend far enough south to expose this
fault, were it in the position on that level indicated by its occurrence on the
sixth and eighth, it is impossible to tell whether the fault which is exposed
on the seventh, 190 feet from the shaft, is the same as the one on the sixth
and eighth. It possibly is another fault, but those exposed on the sixth and
eighth must be identical. Shortly after leaving this point nothing more is
to be seen of this quartzite on the eighth level until it is laid bare in the
south cross-cut west of this fault. It is here about 30 feet wide, and is

somewhat different in character from the ordinary quartzite. It is grayish

STRUCTURE OF RUBY HILL. ; AT

in color, rather slaty or laminated in texture, and sandy to the touch. <A
close examination, however, shows that it is quartzite. This cross-cut is run
some distance into the back lime, which has its usual habitus. The quartz-
ite is again laid bare on the third level of the Albion, which corresponds
with the Richmond eighth, in two westerly cross-cuts from the Albion shaft.
The quartzite has been faulted by a fissure near the winze which descends
from the Albion second, and is not visible along the southeasterly drift.

On the ninth level of the Richmond (Plate. X1IV.), which is run almost
entirely in back limestone, the quartzite, except near the shaft, is of the
same character as that which appears in the south cross-cut on the eighth.
Near the station, another fault is discovered. Again the question arises,
Can this fault be in any way connected with the others above it? It is
most likely a separate fault which here shows itself for the first time.
Southeast of the shaft, toward the compromise line, the quartzite retains
its normal character and apparently its normal thickness.

On the ninth level the narrow belt of quartzite must join the main mass
somewhere between the north cross-cut from the water drift and the shaft.
What the position of this dismembered mass may be on the 1,050-foot and
lower levels future developments alone will show. In descending, this belt of
quartzite widens until on the ninth level it reaches a width of over 80 feet in
places. On both its hanging and foot wall sides, but especially on its hang-
ing,
up with limestone at the planes of contact, and occasionally contains frag-

it exhibits signs of considerable motion, and it is more or less mixed

ments of the latter rock even at a considerable distance from the limestone.
Its lamination seems to be due rather to the effect of movement under im-
mense pressure than to the manner of deposition. Where the quartzite is
found unbroken and of the normal character it shows no such indications
of stratification.

Dip and strike of the thin quartzite——The dip of the contacts of this belt of quartz-
ite is much greater in many places than that of the main mass, although its
irregularities are such that it is impossible to make an exact determination.
The average dip in the levels above the Richmond ninth is about 45°, but
_ in the lower levels it would correspond more nearly with that of the main
fissure. ‘The course of this quartzite is very tortuous, as a reference to the

48 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

various horizontal sections will show; but it is remarkable in this respect,
the irregularities nearly correspond on all the levels.

Relations of the quartzite and secondary fissure — I'he motion of this quartzite upward
along the plane of its contact with the limestone has already been men-
tioned. It is a difficult matter to tell what has been the extent of the up-
ward motion, but that it has been very considerable is shown by the com-
minution of the quartzite and limestone at their contact, and the numerous
striation marks where either of these rocks have remained in a solid con-
dition. When the main fissure was made and the faulting took place which
raised that portion of country lying southwest of the fissure, the quartzite
was moved up, not only along the fissure, but also along the plane of its
contact with the limestone, and the limestone wedge between the quartzite
and the fissure slid back against the limestone hanging wall. The upward
motion of the quartzite crushed and otherwise dismembered the limestone
lying between it and the solid northeastern wall. When the fissure between
the quartzite and limestone reached a point southwest of the present Rich-
mond hoisting works, it shot off into the limestone instead of following
around the contact plane of these two rocks, which turns towards the south.
The continuation of this quartzite fissure is the fissure which is found in
the Richmond and Albion mines accompanying the narrow band of quartz-
ite, and which has been described in detail. The Ruby Hill fault fissure
lies much farther to the northeast, near the shale, and has also been de-
scribed in detail. The positions of these two fissures and their relations to
each other can be observed in the different maps and diagrams. They are
designated by heavy black lines.

The manner in which the narrow band of quartzite found its way into
its present position seems to admit of but one solution, namely, that its oc-
currence is due to a succession of faulting movements which followed the
line of the accompanying fissure, and that it originally formed part of the
main body of quartzite which must here underlie the limestone. It is alto-
gether improbable that it constituted a distinct bed of quartzite laid down
upon the back limestone. In this case some indications of its existence
would have been noticed in other parts of Ruby Hill. It is not possible

STRUCTURE OF RUBY HILL. 49

either that it is quartz, and was deposited after the formation of the fissure,
as under the microscope it exhibits the structure of quartzite.

Relation of the two fissures to the country rock The two fissures, the secondary and
main fissures, do not exhibit a width which is in any way proportional to
the amount of movement which has taken place along their planes. The
main fissure in the Eureka, and other southeastern mines, is very strong,
often having a width of 12 feet or more, but in the Richmond and Albion
it is scarcely more than a seam, and would naturally not be considered
of much importance if the great difference in the country rock on each
side of it was not taken into account. The secondary fissure, although it
is always accompanied by more or less clay, does not always exhibit abso-
lute proof of its nature, and in some places might be mistaken for the
ordinary contact of two dissimilar rocks, but when considered as a whole
and in conjunction with the narrow strip of quartzite in the Richmond mine
the fact that it is a distinct rent in the earth’s crust can hardly be disputed.

Back limestone—This term is used in reference to the limestone which is
found on the foot-wall side of the narrow band of quartzite, which in the
Richmond and Albion ground accompanies the secondary fissure. In the
cross-cut run into the limestone at the point on the fourth level already
mentioned (page 45), the quartzite appears in the roof of the main drift, and
is scarcely more than a foot wide. Except that it is mixed more than usual
with clay and limestone, it differs in no way from the ordinary quartzite.
It has the same pinkish color and friable nature. The back limestone is
pulverized almost to a powder at the contact, but becomes more compact as
the drift penetrates farther from the fissure. This limestone differs in a
great many respects from the limestone which is encountered between the
quartzite and shale. It is blackish, breaks with an angular fracture, has a
somewhat glassy appearance, and its planes of fracture are lined with quartz
or calcite. It isa highly metamorphosed and somewhat silicified limestone,
and contains some bituminous matter. As yet no ore of any kind has ever
been found in it. Its peculiarities are very characteristic, and it is easily
recognizable wherever found. Specimens taken at a depth of 900 feet are

not distinguishable from those that have been taken at four.
2654 L—4

50 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Relation of the Ruby Hill fault to the Jackson fault——If the surface-map, Plate IL, is
examined an extensive fault will be noticed just east of the Jackson hoist-
ing works. This fault extends a considerable distance to the north and
south, and has been called by Mr. Hague the Jackson fault. The main
fissure of Ruby Hill, the one containing rhyolite, joins the Jackson fault
somewhere south of the American shaft, but at exactly what point has not
yet been determined, the surface of the ground being covered by débris,
while the underground developments are inconsiderable. It has bzen stated
that the limestone in which the American shaft is sunk is the Pogonip lime-
stone. It is therefore possible that the main fissure of Ruby Hill is identical
with the Jackson fault at this point, though the fault laid down by Mr.
Hague runs nearly due north from the American shaft. That there is
another fault parallel to the main Ruby Hill fissure is clearly shown on the
cross-cuts to the old Jackson shaft, and it is probable that this other fissure
is no other than the one which Mr. Hague has called the ‘‘Jackson fault.”
There seems to be very little doubt that the eruptions of rhyolite which
occur in this neighborhood, of which Purple Mountain is a prominent
example, are intimately connected with all these faults.

CH AP TE, V-

ORES OF PROSPECT MOUNTAIN AND RUBY HILL.

Classification of the Prospect Mountain and Ruby Hill ores.— The ores of Ruby Hill are to
be classed under the head of argentiferous-auriferous lead ores. They are
of two classes, oxidized and unoxidized, though up to the present time
almost all the ores produced by the mines of Ruby Hill have been of the
former character, sulphurets being only found in a very few places in a
region two or three hundred feet above the water level and in some locali-
ties below it. As might naturally be expected, the line which divides the
oxidized from the unoxidized ores is not sharply defined, and the transition
is a gradual one.

Influence of the water-level on oxidation—Jn some places where ore is found at a
considerable distance below the water-level, it is in an altered condition,
which would seem to point to the fact that the present water-level is some-
what higher than it has been at some previous time. This is probably the
case, as it is not possible that oxidation could have taken place at any con-
siderable depth below the surface of the water. The workings of the mines
of Ruby Hill have at present reached a depth of over 1,200 feet, the deep-
est point being the bottom of the Richmond shaft. The greatest depth at-
tained in the old workings of the Eureka is 200 feet higher than the bottom
of this shaft. From the lower workings of the Eureka up 200 feet the
ground has been flooded for several years. The water rises 150 feet in the
Richmond shaft, but remains at that point. From this it will be seen that
there is a difference in water-level of 250 feet between the two mines. The
surplus water from the twelfth level of the Eureka flows down a winze to
the Richmond ninth level, 70 feet below, and finally reaches a permanent
level in another winze 180 feet deeper. In the Richmond mine no ore has
been found below the ninth level, 900 feet from the surface, so that it can-
not be determined with certainty what its mineralogical character may be

below the water-level.
(51)

52 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

It will be noticed from a reference to the actual water-level line marked
on the elevation (Plate IIT.) that it is very irregular, showing that there is
not everywhere a free circulation of water between the extreme workings
on the mineral zone, as well as that the water-level at the northwest end is
very much below that at the southeast. The irregularity in the character
of the ore in the neighborhood of the present water-level is no doubt due
to the rise and fall of the water at different periods, and to the nature of
the ground, which in some places is more accessible to the action of the air.

Local differences in the Ruby Hill ore. —A]though there are some slight local differ-
ences in the ores produced by the mines of Ruby Hill, they are so incon-
siderable that it is not necessary to describe them by localities, and although
their variety is very great, yet the different oxidized ores do not seem to be
confined to any one level or any particular chute of ore, but occur indis-
criminately at all depths. Sulphurets, particularly galena, are found to
some extent intermingled with the oxidized ores, but those represent mere
remnants which have escaped oxidation and are usually insignificant in
quantity. Masses of sulphurets occur only below or near the water-line.

Minerals occurring in Ruby Hill— Before describing the different varieties of ore
found in the mines of Ruby Hill, it may be well to mention the minerals
of which they are composed. It is very possible that other minerals than
those which are given in the following list occur, but as their presence has
not been detected in the careful examinations which have been made of the
ores, it is not likely that they exist in any great quantity, or that they are
very numerous.

The galena is usually of a medium grain, and more or less mixed»
with sulphate of lead. It occurs in the form of nodules, which are
changed at the surface into sulphate and carbonate of lead, and in irregu-
lar masses distributed throughout the ore. It is often of a dull black color,
owing to the admixture of sulphate, and contains small quantities of arsenic
and antimony, and in some cases molybdenum, which is probably in the
state of sulphide. It usually carries from $100 to $150 per ton in silver and
from $1 to $10 in gold. It is richer in silver and poorer in gold than the
average ores. Pseudomorphs of galena after other minerals, although they
may exist, have not been noticed. This fact renders it improbable that any
sulphide of lead has been deposited since the period of oxidation.

THE ORES. 53

Anglesite (sulphate of lead) is an important mineral in the compo-
sition of the Eureka ores. It forms a large portion of the “yellow car-
bonate” of the miner, and is present to some extent in all the lead-bear-
ing ores of the hill. It is the product of the decomposition of the galena,
and occurs in three forms: as colorless crystals in geodes in the galena and
other ores in a manner that shows that it was deposited from a solution of
the sulphate; in compact masses of a dull black color, usually containing
undecomposed sulphide and a kernel of galena; and in finely divided par-
ticles disseminated throughout the ore. In the latter case it is not distin-
euishable by the eye, and its presence can only be detected by the usual
tests for sulphuric acid and lead.

Cerussite (carbonate of lead) almost always occurs crystallized, some-
times in acicular crystals mixed with other minerals throughout the ore;
sometimes in geodes and surrounding nodules of galena and anglesite,
and in massive aggregations of small crystals of a dark color. In this lat-
ter instance it is called ‘“‘sulphuret ore” by the miners, and probably con-
tains an admixture of mimetite, as arsenic acid can often be detected by
means of the blow-pipe. The dark color is due to the presence of manga-
nese. It is evidently the ultimate product resulting from the decomposition
of the galena after that mineral had been changed into sulphate. It seems
also to exist disseminated in a finely divided state throughout the so-called
“red carbonate,” a mixture of different lead minerals and hydrated oxide of
iron, for this ore gives a reaction for carbonic acid while it contains scarcely
any lime.

Mimetite* (chloro-arsenate of lead) is found in colorless crystals

2 Analysis of colorless mimetite from the Richmond mine, Eureka, Neyada, by F. A. Massie, of
the University of Virginia:

The specimen consisted of slender, almost acicular, hexagonal prisms, aggregated into a friable
mass, with a few small crystals of wulfenite scattered throughoutit. The individual crystals were color-
Jess and transparent, with adamantine luster and white streak, the general aspect of the mass very
much like that of cerussite. Hardness= about 3; sp. gr. =6.92; very easily fusible. Analysis gave:

As,O; 23.41
Pb,0; trace
PbO 68.21
PbCl, 8.69

100.31
In accordance with the well-known formula:
PbCly. 3 PhgAs20g.

54 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

and in yellow masses more or less mixed with sulphate. The occur-
rence of crystals is rare, but the ‘‘yellow carbonate” often contains consid-
erable quantities of this mineral. As the galena which has been found in
the mines of Ruby Hill rarely contains much arsenic, it is not likely that
mimetite was formed through the oxidation of galena alone, but that it re-
sulted from the simultaneous decomposition of that mineral and arseno-
pyrite. This is made probable by the fact that the ‘yellow carbonate,” a
widely distributed ore, although it is sometimes composed of sulphate of
lead and hydrated oxide of iron alone, is usually a mixture of sulphate of
lead, chloro-arsenate of lead, and hydrated oxide of iron. If the “yellow

’ resulted from the decomposition of arsenical galena alone it

carbonate’
would not contain the hydrated oxide of iron except as an admixture. ‘That
the iron is not always an ingredient resulting from a subsequent mixture of
the products of oxidation is shown by fragments here and there in the mass
which retain the original structure of the minerals which composed them.

This mimetite has been found in the form of stalactites, stalagmites,
and in columns in vuggs in some of the ore bodies. - It occurs as minute
hexagonal crystals surrounding a core of some brown mineral, which is
probably limonite. The vugg in which the specimen belonging to the
collection was found occurred in the upper part of an ore body, which
was distinctly stratified, indicating that the material composing it had
been re-arranged since it was oxidized. The minerals in the interior of the
vugg had evidently been crystallized from solutions since the rearrange-
ment of the ore. The manner of formation of these stalactites, etc., seems
to be plain. The arsenopyrite, pyrite, and galena, which formed the orig-
inal ore, were oxidized, sulphate of iron being first formed. This sulphate
of iron trickled down, forming numerous columns, upon which the later
product of decomposition, mimetite, was afterwards deposited. In time the
sulphate of iron lost its sulphuric acid and became limonite, which remained
as a core. |

Wulfenite (molybdate of lead) is of frequent occurrence in the ores
of Ruby Hill. It is found as aggregates of fine tabular crystals coating
nodules of galena changed into sulphate and carbonate, and frequently
mixed with crystals of the latter as well as in minute crystals disseminated

THE ORES. ys)

throughout the ore. Some of the galena contains considerable molybde-
num, but whether the quantity contained in it will account for the presence
of the considerable amount of wulfenite in some of the ore is a matter of
doubt. From the manner in which some of it is found surrounding nodules
of galena carrying molybdenam, and from its occurrence mixed with the
other products of decomposition of that mineral, it is evident that a portion
of it at least was formed by the decomposition of the molybdenum-bearing
galena. Thus far the existence of molybdenite (sulphide of molybdenum)
has not been detected in the oxidized or unoxidized ore. It exists, how-
ever, in the underlying quartzite. Several specimens of this mineral were
found in sinking the Richmond shaft from the 900 to the 1,200-foot level,
also in the cross-cut from the 1,200-foot station through the quartzite to the
limestone. As it is usually found in the quartzite, it is in a very finely
divided state, and were it not for the few exceptional specimens that have
been found, its presence would have been overlooked. It is probable that
its occurrence in the quartzite is due to secondary causes, and that, like the
pyrite, it was not an original constituent of that rock. It is not improba-
ble that it will be found in considerable quantity in the unoxidized ore below
the water level.

Pyrite and arsenopyrite both occur in the unoxidized ores, and the for-
mer is found in the quartzite and in some of the other rocks of Ruby Hill.
Arsenopyrite is not as plentiful in the unoxidized ores as the amount of
arsenic in combination with lead in the oxidized ores would lead one to
expect, if the theory that arsenopyrite was the original source of the arsenic
is correct; but the bodies of sulphurets hitherto discovered have been so
few and small that they cannot be taken as representing quantitatively the
minerals which originally composed the oxidized ore bodies. Marcasite has
been observed in the shale.

Limonite (hydrated sesquioxide of iron) is the principal component
‘of the Ruby Hill ores. It stains the ore from a light brown to a deep
reddish-brown according to the quantity present and the extent of its
hydration, and together with mimetite forms the coloring matter of the
“vellow carbonate.” It is sometimes found compact, but is usually un-
evenly distributed throughout the mass of the ore. Pseudomorphs of this

56 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

mineral after pyrite have occasionally been observed. Hematite (sesqui-
oxide of iron) is also present in the ore, but it is not as often met with as
the hydrate.

Blende (sulphide of zinc) is found to some extent in the upper portions
of the mines, and is of frequent occurrence in the lower workings in con-
nection with pyrite and galena. It is usually a dull black eryptocrystalline
substance, but is sometimes crystalline. In the latter form it is found in
the ‘ black” chamber between the eighth and ninth levels of the Eureka
mines.

Calamine (silicate of zinc) is often met with in fine characteristic crystals
in connection with earthy limonite. It usually occurs at the junction of ore
bodies with the limestone, and in many instances is pseudomorphous after
that rock.

Smithsonite (carbonate of zinc) is no doubt present in the ore and is
the product of the decomposition of blende, but no characteristic specimens
have been noticed. Zincite (oxide of zinc) is probably present, but its
detection is difficult on account of the admixture of iron in all the ores.

Calcite (carbonate of lime) is everywhere found in the Eureka mines.
It occurs transparent, but is usually of an opaque milky color, cement-
ing together the crushed mass of the rock and in clumps of crystals in vuggs
and other cavities. Calcite is of rare occurrence in the ore itself. The
calcite, as well as the limestone, carries more or less carbonate of magnesia,
but none has as yet been found which contains sufficient of that substance
to entitle it to the name dolomite.

Aragonite (orthorhombic carbonate of lime) is of frequent occurrence.
It is particularly plentiful in the caves and smaller cavities of the limestone,
where it often covers the entire roof and walls. In many places it is con-
stantly forming from the water which is oozing from the limestone. It
occurs in the form of radiating groups of acicular crystals and as fibrous
crusts and nodules covering the débris on the floors, as well as on the sides
and roofs of the caves.

Measurement of the growth of aragonite crystals —Ssome observations were made in a
large cave between the ninth and tenth levels of the Kureka mine in regard

to the growth of these crystals, which were measured as follows: A co-

THE ORES. DT

ordinate scale pasted on a board was hung directly behind the group of
crystals, the growth of which was to be measured, and a transit instrument
was placed at a convenient spot at from 10 to 15 feet in front of the scale.
It was found convenient to use a transit, as the construction of this instru-
ment permitted the removal of the telescope without the derangement of
the tripod, and as the moisture collected so fast on the lenses within the
telescope that it was impossible to observe the crystals if it was left under-
ground over night. When the telescope was replaced it could be put
exactly in its former position, thus preventing any inaccuracies which might
arise from the removal of the point of observation from the original line of
sight. The temperature in this case remained at nearly 544° F. (30.1 C.),
the variation not being 14° F. during the whole time (some six weeks) over
which the observations extended. The moisture in the atmosphere was very
near the dew-point, as was shown by a very slight decrease in the tempera-
ture upon moistening the bulb of the thermometer. The water was drip-
ping from many points in the roof of the cave, and the sides were wet
with it.

During the first period of observation the maximum growth of any of
the crystals observed was five-sixteenths of an inch in three weeks. This
particular crystal began its growth in a large drop of water, which gradu-
ally diminished in size until at the end of three weeks it had totally disap-
peared. During the first part of this time the crystal formed most rapidly,
and seemed to shoot out of the drop of water. Its increase was then per-
ceptible from day to day. The growth of this crystal, as well as others in
the group, was evidently dependent upon the size of the drop of water sur-
rounding it, for although the whole of the group of crystals was wet increase
was only perceptible in those crystals surrounded by a drop of water. No
definite growth within a given time could be fixed upon as normal.

The maximum growth in another aggregation of crystals observed for
a like period of three weeks was found to be three-eighths of an inch, and
the general conditions and results were similar to those noticed in the first
instance. It will be noticed that the evaporation of the drops of water was
comparatively rapid, notwithstanding the fact that the temperature was close
to the dew-point. This is explained by the character of the ventilation of

58 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

the cave, which at its lowest point was connected with the main incline and
at its highest by means of a winze with the ninth level above. Although
the atmosphere remained near the dew-point, it was constantly renewed.
The observations were conducted very near the center of the cave.

Roth" says that spathic and fibrous calcium carbonate (calcite or ara-
gonite, or both together) are common in the form of stalactites and stalag-
mites in the cavities and fissures of limestone, and in the tunnels, shafts,
and drifts ofthe mines. Dana’ mentions that it is forming in an old mine
in Monte Vasa, Italy, at a temperature below the boiling-point of water.
The conditions which govern the formation of aragonite and calcite, re-
spectively, are not understood. In Ruby Hill, however, aragonite is form-
ing under ordinary pressure at a low temperature.

Siderite (carbonate of iron and lime) has been frequently noticed.

Quartz is found in crystals in cavities and mixed through the ore at rare
intervals It is not an important mineral in the ore, except that it is neces-
sary to its reduction by smelting.

A silicate of iron has been noticed, but it is not of common occurrence.

Clays which are more or less mixtures of silicate of alumina, car-
bonate of lime, oxide of iron, and other substances, are to be found at
the contacts of the different formations, and at numerous places in the ore-
chambers. These clays are sometimes merely the products of attrition of
the two walls of a fissure, and again have been produced by the decompo-
sition of igneous rocks or an infiltration from above. Steatite and tale are
occasionally met with, but are unimportant

Rarer minerals —Molybdenite has been detected in the quartzite from the
bottom of the Richmond shaft, and both carbonates of copper (malachite
and azurite) have been met with in small quantities. As phosphorus has
been found in some of the ores it is highly probable that pyromorphite is
present. It isgalso likely that leadhillite (sulphate and carbonate of lead)
as a distinet mineral may occur here (if anywhere), as admixtures of sul-
phate and carbonate of lead are very common. Oxide of lead as a mineral

has not been found in the ores in the course ‘of the present examination,

*Roth: Algerneine Geologie. I., p. 534. Berlin, 1879,
>Dana: System of Mineralogy, p. 696. New York, 1874.

THE ORES. 59

though it may exist. It is not likely, however, that if it formed at any
time it could remain long in quantity uncombined with carbonic acid in the
presence of waters carrying so much of that compound. Wad has been
observed in the Pheenix mine and in some other localities; also other forms
of manganese in different places, and nickel is said to have been found,
though no specimens have been obtained.

Miners’ classification of ore —T he ores of the district are not accurately classi-
fied by the miners, but receive names indicative of their most striking char-
acteristics and the popular idea of the corresponding composition. It may
be well to describe some of the more important varieties. Most of the ore
has a reddish or yellowish color, due to the presence of oxide of iron, chloro-
arsenate, or molybdate of lead. The shades of color vary according to the
predominance of one or the other of these minerals and the quantity of
earthy material mixed with them. One of the principal kinds of ore is com-
posed of a hydrated oxide of iron mixed with some sulphate and carbonate
of lead and containing intermingled grains and lumps of undecomposed
galena. This ore is often called ‘‘red carbonate.” It usually carries about
equal values of gold and silver, from $25 to $50 of each per ton, though
sometimes the gold is considerably in excess. Another variety is the “yellow
carbonate.” ‘This term is applied in general by the miners to any ore of a
yellow color which contains lead. It belongs particularly, however, to a
very characteristic ore, which is a mixture of the hydrated oxide of iron
with the sulphate and chloro-arsenate of lead in varying proportions. ‘The
ratio of the silver to the gold in this ore is not at all uniform; sometimes
one metal, sometimes the other, being in excess. The value of both metals
does not usually exceed $100 per ton. Another variety of “yellow car-
bonate” is that which owes its color to the molybdate of lead mixed through
it. As the molybdate of lead usually carries but little silver and less gold,
this ore is not very rich unless it contains other minerals bearing the
precious metals. The so-called ‘‘sulphuret ore” of the miners is an almost
pure crystallized carbonate of lead. It is grayish in color, and consists of
aggregated crystals of cerussite. It is sometimes quite rich in silver, assay-
ing as high as $125, but like all the lead ores proper is poor in gold. There
are several varieties of red ore, consisting principally of the hydrated oxide

60 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

of iron, with a little lead and silver, which are tolerably rich in gold. There
is usually nothing in their appearance to indicate their value, and it is only
by constant assaying that it is possible to determine what they are worth.

Quartz ores, especially those carrying quartz in visible crystals, are
uncommon, except in the Eureka Tunnel and some parts of Prospect Mount-
ain, but when found they are usually rich in gold and poor in silver and
lead. There is a porous crystalline quartz ore found in some places in the
Richmond mine, from which assays of over $300 per ton (.04977 per cent.) in
gold, with but a few dollars in silver, have been obtained. The sulphuret
ores usually consist of a compact mass, composed of pyrite, arsenopyrite, ga-
lena, and blende, and vary very considerably in the amounts of silver and
gold that they contain. The miners do not as yet distinguish different va-
rieties by name.

Analysis of Richmond ore—The following analysis of ore from the Richmond
mine for the year 1878 will serve as an example of the ores from all the
mines of Ruby Hill, which greatly resemble each other both as regards
quality and the minerals which compose them. The sample analyzed was
an average of all the Richmond ore worked at the furnaces of that com-
pany during the previous year, and the analysis was made by Fred. Claudet,
of London.”

Per cent. f Per cent.
ead oxide) =... ese 35.65 Dead 3535 33.12
IBISMUtN Gene acces alee ———
Copper oxider=—-- 2-2. 15 Copper ...... 12
Tron protoxide® ......... 34.39 Tronie<--)--- -. 24.07
VANS (p-W0) & oaanao joadcs 2.37 VAN CoRR REG 1.89
Manganese oxide ..-..-. fo) FAS:
SATSENICACIG geese 6.34 Arsenic ...-.. 4.13
Am tiMOniyia-s c= enone 25 Antimony...- — .25
Sulphuric acid. .... Seabee > EH} Sul phir eee 1.67
Chlorine: Ss.ase eee cee ——
Silieats Sra eee ay. 2.95
AUMING = Stossel 64
MIME) oe aS acta 1.14

«Copied, by permission, from the records of the company.

>In this analysis the iron is represented in the form of protoxide, whereas it occurs as sesqui-
oxide. That it was intended to give it in the form of sesquioxide is shown by the percentage of iron
(24.07) given would correspond with 34.39 of sesquioxide.

THE ORES. 61

Magnesia ...... =o bedded Al

Water and carbonic acid. 10.90

Silver and gold......... 10 .
100.52

27.55 Troy ounces’ silver per ton.of 2,000 pounds.
1.59 Troy ounces’ gold per ton of 2,000 pounds.

Although this analysis does not show all the substances that are pres-
ent in the ores of the Richmond mine, yet it represents the most important
and principal ones. One of the remarkable features of this ore is its free-
dom from earthy material, the total amount of silica, alumina, lime, and
magnesia that it contains being but 5.14 per cent. That it should contain
but a small quantity of silica is but natural, as there are no highly silicious
rocks immediately connected with it, but that it should carry such a small
percentage of lime and magnesia, occurring as it does almost wholly in a
limestone formation, is a fact that it is somewhat difficult to account for.
Whatever the source of the ore may have been, it is evident that it was
deposited almost entirely free from earthy material. The hydrated oxide
of iron may be regarded as the gangue of this ore.

Discussion of the analysis —U pon examining this analysis it will be noticed that
the lead has been estimated in the form of oxide. The lead, however, is
present in the form of galena, carbonate, sulphate, molybdate, arsenate, and
chloride, the chloride being combined with the arsenate in the mineral
mimetite, which is of frequent occurrence.in the ore. The mineral pyro-
morphite may be present in the ore, but it has not been detected, although
there is a trace of phosphoric acid present. Lead is also present in other
forms, but as they represent in the aggregate but a small proportion of that
metal they may be regarded as merely accessory It is difficult to estimate
the proportion of the different lead minerals contained in this ore, but it is
probable that galena (sulphide), cerussite (carbonate), and anglesite (sul-
phate) are present in about equal quantities, and the next most important
combinations are mimetite (arsenate and chloride) and wulfenite (molybdate).

When copper has been detected in the ore it has been in the form of
carbonate. Zine has been estimated entirely in the state of oxide, but it

2$35.61. »$32.87.

62 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

occurs in the form of blende (sulphide), calamine® (silicate), and prob-
ably as smithsonite (carbonate). It is most common in the form of cala-
mine. Manganese occurs mostly as wad. Arsenic is almost entirely com-
bined with lead as arsenic acid, and the same is most likely the case with
the small percentage of antimony which the ore contains.

In the above analysis it will be seen that the sulphur has been esti-
mated almost entirely as sulphuric acid, although it is partly combined with
lead in the form of galena. Most of the sulphuric acid is combined with
lead, though to some extent it is no doubt combined with calcium. Silica
is present in the form of quartz principally and combined with iron and
aluminium. The calcium and magnesium are present, combined for the most
part with carbonic acid.

The silver is found in the form of chloride and sulphide, and the gold
exists in all probability in a finely divided metallic state. In this analysis
no account has been taken of the chlorine, and for some unaccountable
reason molybdic acid has been omitted. It must have been present in the
ore analyzed, as wulfenite is a common mineral in the Ruby Hill ores. The
footing of the different elements in this analysis amounts to 100.52, but it
would be considerably less if a portion of the sulphuric acid had been esti-
mated as sulphur, which would leave room for several substances which are
unquestionably present.

In a qualitative analysis of the Ruby Hill ores, Dr. Melville, of the
United States Geological Survey, detected the following elements:

Gold. Aluminium. Chlorine.
Silver. Calcium. Phosphorus.
Lead. Magnesium. Silicium.
Copper. Arsenic. Carbon.

Zine. Antimony. Molybdenum.
Tron. Sulphur. Manganese.

Relative value of the ores of Prospect Mountain and Ruby Hill.— The ores ot Prospect Moun-
tain are very similar to those of Ruby Hill, though perhaps there is a greater

«Jn this report the word calamine will be used to designate the silicate of zinc, and smithsonite
for carbonate of zinc, this being the nomenclature adopted by Dana. These terms have been used by
various writers in a promiscuous manner, some using smithsonite to designate the silicate, and calamine
the carbonate. Brogniart used calamine for silicate and smithsonite for carbonate. Brooks and Miller
in 1852 reversed these names. Quenstedt called the carbonate calamine and the silicate willemite.

THE ORES. 6

variety of them. As a rule they contain more silicious material, and as a.
class are probably richer than those of the hill. The difference in value is
in part owing to the fact that the deposits are smaller, and although it can-
not be said in reference to this district that small deposits in general are
richer than large ones, yet it is true that the ores brought to market from
Prospect Mountain are more valuable than those from Ruby Hill, inasmuch
as a body of ore of considerable size can be made to pay even when the ore
is of a low grade, whereas a small one containing the same grade of ore
would not yield sufficient metal to defray the expense of mining. A large
number of the mines of Prospect Mountain, however, actually contain
higher-grade ores than those of Ruby Hill.

Varieties of Prospect Mountain ores—The ores of the Ruby-Dunderburg mine
closely resemble those of Ruby Hill. The ores of the Eureka Tunnel, on
the other hand, which is at present the principal producing mine on Prospect
Mountain, differ in several respects from those of Ruby Hill. They are
more silicious, an ore occurring frequently which is composed in great part
of quartz; a great deal of the arsenic acid in the yellow carbonate is replaced
by antimonic acid; massive blocks of so-called ‘black metal,” a mixture of
sulphide and sulphate of lead carrying considerable silver (sometimes as high
as $1,000 to the ton), are often met with; carbonate of copper and oxide of
manganese are not uncommon, and quartz crystals are frequently found
scattered through the ore.

The ores of the mines on the west slope of the mountain are noted for
the relatively larger proportion of gold to silver that they contain. Among
the richest of these are the ores of the Silver Connor and Williams mines.
The ore from the former of these mines contains but little lead. The ore
of the Banner mine is noted for the large amount of silica it contains. It
can almost be called a quartz ore. The Dead Broke ore contains consid-
erable argentiferous galena and “black metal.”

CHAPTER Vil.

THE ORE DEPOSITS.

Classification of the ore deposits—T'he ore deposits of Eureka District, though
they contain gold, can be classed under the head of silver-lead deposits in
limestone The type of deposits to which those of Eureka belong is one
often met with in the older limestones of the Great Basin, and although
these particular deposits have been of more value, and are more widely
known than any of the others, and exhibit some very interesting structural
features, yet they cannot be said to form an isolated class. An extended
comparison of these deposits either with similar ones in the Great Basin or
with others of the same general character elsewhere, does not come within
the scope of this report, but it may be well to present some points, both of
resemblance and difference between them and the best known examples of
similar types in other mining regions. Although the gold and silver in the
Eureka ores are the metals which render their mining possible, yet the
quantity of them present in these ores, measured by weight, is so small, in
comparison with the lead, that a classification based upon these metals alone
would be misleading. As in many of their features they resemble other
lead deposits in limestone, it seems best to regard them simply as lead
deposits, in which the gold and silver are merely accessory, though very
important ingredients. All lead ores carry some silver, and with it some
gold, though in many of them it is only possible to obtain traces of these
metals.

Lead deposits in limestone of the Great Basin— Throughout the Great Basin there are
a large number of lead deposits, all of which exhibit many features of sim-
ilarity. They occur in limestones and dolomitic limestones of Palaeozoic

age, and are mostly of very irregular form. Their ores consist principally
(64)

THE ORE DEPOSITS. 65

of argentiferous galena with antimonial and arsenical combinations and
pyrite and the decomposition products derived from these minerals. Com-
pounds of copper, zine, and other metals occasionally accompany these
ores. In by far the greater number of instances the oxidation has been
carried to a great depth, sometimes reaching or exceeding 1,000 feet. The
extent of this oxidation is ina great measure due to the absence of any
large quantity of water until considerable depth is reached. The charac-
teristic gangue of these ores is the hydrated oxide of iron with more or less
calcite. Quartz is rarely found in any great quantity, except where the
deposits occur in the form of contact lodes between limestone and por-
phyry, the quartz being probably derived from the decomposition of the
porphyry. An example of such lodes is offered by the 2 G. mine in Tybo
District, Nye County, Nevada. It is found to be more profitable to reduce
all these ores by smelting than by any other process. Among the princi-
pal districts where such ores are found may be mentioned Eureka, White
Pine, and Bristol, in Nevada; Cerro Gordo, in California, and Ophir, Big
Cottonwood, and Little Cottonwood, in Utah—all of which occur in Pal-
eeozoic rocks, though in some cases, at all events, the deposition of ore is
referable to a much more recent era.

Deposits of the Upper Mississippi The lead deposits of the Upper Mississippi*
occur in dolomites of the Lower Silurian. The ore is found in caves, in
openings between the strata, and in so-called gash veins. ‘The stratification
of the country rock is flat, and it shows scarcely any signs of dynamic dis-
turbance or alteration through chemical causes even in the neighborhood of
the ore. The lead is found almost always in the form of galena, accompa-
nied by limonite and occasionally smithsonite (zine carbonate) and blende,
rarely by pyrite. Calcite and barite occur, but quartz and combinations of
lead with arsenic are not met with. The galena contains but traces of sil-
ver and gold. There are no signs of fissure veins and the ore is not found
at any great depth below the surface. From the occurrence of the galena
in the forms of stalactites and stalagmites in the caves, and the absence of
decomposition in the country rock near the deposits, it is evident that the
openings were first formed and the ore was deposited in them from solu-

2J,D. Whitney. Metallic wealth of the United States.

2654 L a)

66 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

tions or otherwise, and that substitution of minerals for country rock played _
no important part. With regard to the age of the country rock and the
occurrence of limonite with the galena, these deposits resemble those of
Eureka District, but in other respects, such as structure and manner of ore
deposition, they differ widely.

Deposits of Missouri The lead deposits of Missouri and Arkansas also occur
in the dolomites of the Lower Silurian. The ore is galena, with but traces
of silver and gold. It is often accompanied by calamine (zinc silicate) and
limonite. It is found in nests in clay, also in beds as fine impregnations in
the calciferous limestone, as well as in flat masses between the strata. In
the flat veins cerussite occurs. Galena is also found in impregnations in
dolomite and in cavities and caves mixed with gravel, zinc ore, clay, and
barite. Calamine and some blende, as well as barite, almost always accom-
pany the galena. Quartz crystals are also found. The occurrence of these
deposits is very similar to those of the Upper Mississippi, but very dissim-
ilar to those of Eureka.

Deposits of Leadville——The deposits of Leadville, Colorado, resemble those
of Eureka in a great many respects, as can be seen upon reference to an
“Abstract of a Report upon the Geology and Mining Industry of Lead-
ville, Colorado, by 8S. F. Emmons.”* Mr. Emmons states that the investiga-
tions made in Leadville have proved the following facts:

‘“‘As regards their origin—

“T. That they have been derived from aqueous solutions.

“TI. That these solutions came from above.

“JIT. That they derive their metallic contents from the neighboring
eruptive rocks.

“TV. That in their original form they were deposited not later than the
Cretaceous period.

“As regards their mode of formation—

“J. That the metals were deposited from their solutions mainly as sul-
phides.

“TI. That the process of deposition of the vein-material was a chemi-

7Second Annual Report of the Director of the U. S. Geological Survey, 1881.

THE ORE DEPOSITS. 67

cal interchange or an actual replacement of the rock-mass in which they
were deposited. \

“TIJ. That the mineral solutions or ore-currents concentrated along
natural water channels and followed by preference the bedding planes at a
certain geological horizon; but that they also penetrated the mass of the
adjoining rocks through cross-joints and cleavage planes.

“And with regard to distribution—

“J. That the main mass of argentiferous lead ores is found in caleareo-
magnesian rocks.

“TJ. That the silicious rocks, porphyries, and crystalline rocks contain
proportionately more gold and copper.”

As regards origin, the Eureka and Leadville deposits do not differ, ex-
cept that in Eureka District the metal-bearing solutions came from below,
and their connection with eruptive rocks is not as plain in Eureka as in
Leadville.

As regards their mode of formation, the deposits of the two regions
differ only in respect to the manner in which the solutions of minerals were
distributed. In Eureka, also, the lead is found only in the limestone, and
the most silicious rocks carry the most gold.

The varieties of minerals found in the two districts are similar, but the
galena in Eureka seems to have been more completely oxidized than that
in Leadville.

Deposits of Cumberland and Derbyshire——The lead deposits of Cumberland and
Derbyshire in England are found in the Carboniferous limestone, between
the strata of which there are masses of porphyry,’ which in that country
are called “‘toadstone.” The ore is found in fissures which cut the strata.
With these fissures pipes, caves, and other irregular openings containing
ore are more or less closely connected. Flat bodies or beds are also found
between the strata. The fissures are mostly occupied by true lodes, which,
however, do not contain ore where they traverse the porphyry, and are not

According to vy. Groddeck (Lagerstiitten der Erze, p. 245) it is doubtful whether this porphyry is
intrusive or whether the limestone overlying it was deposited after its eruption. Investigation made
by Mr. Emmons of the deposits in Leadville, which occur in limestones of the Carboniferous, seem to
prove that the porphyry, which in that region is also found between the strata, is intrusive. And
although this fact does not absolutely warrant the belief that such is the case with the deposits in
England, it heightens the probability of such a manner of occurrence.

68 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

productive in the overlying millstone grit and slate. With the exception
that the fissures themselves are not often ore-bearing and that almost all
signs of stratification have been obliterated in Eureka, there are strong
points of resemblance between the Nevada deposits and those of Cumber-
land and Derbyshire. The galena in the English ores* never contains over
$37.70 (0.1 per cent.) of silver to the ton of 2,000 pounds, and it is usually
poorer. It is not often accompanied by blende or pyrite. Fluorite and
barite, as well as calcite, are common; but quartz is seldom found.

Deposits of Westphalia — The ore deposits of Eureka resemble those of West-
phalia’ in a few respects. The ore in the latter locality is found in irregu-
lar masses, which are all more or less connected with fissures or breaks as-
sociated with slates and limestone. It occurs only in the limestone and
never in the slate, and it is evident that in both regions the nature of the
country rock has had an immediate effect upon the deposition of the ore.

Deposits of Upper Silesia —'he deposits of Upper Silesia,° in which calaminn
is the prevailing ore, although they have some points in common with those
of Eureka, are, on account of difference in structure and variety of mine-
rals, more widely removed from them than most of the lead deposits.

Deposits of Raibl—I‘he deposits of Raibl, in Carinthia, so fully described by
Posepny,* have considerable similarity to those of Eureka, and although
they are principally interesting on account of the bearing they have upon
the theory of substitution of ore for limestone, yet a general description of
them may be found useful here, as showing some physical characteristics
which they have in common with those of Eureka. According to this
author the deposits are found in a thick belt of ore-bearing limestone
(erzfiihrender Kalkstein), which overlies a caleareous tufa and underlies
slate on the southern slope of the Alps. The strata pitch gently to the
south. The upper portion of this ore-bearing limestone is more or less
magnesian, and contains here and there layers of dolomite slate. The
ore deposits are found concentrated on the hanging-wall side of these

«Henwood on Metalliferous Deposits and Subterranean Temperatures, Part I., pp. 108 and 109.

by, Cotta: Erzlagerstitten, II., p. 133.

¢ Pietch, Zeitschr. fiir Berg, Hiitten u. Salinenwesen, B. 21, 1873, p. 292.

4¥', Posepny : Die Blei- und Galmei-Erzlagerstitten von Raiblin Kirnten. Jahrb, derk, k. geolog.
Reichs-Anstalt, Wien, 1873, B. XXIII.

THE ORE DEPOSITS. 69

layers. They have sonietimes the form of lodes, sometimes of beds,
and are often very irregular. The galena deposits are found principally
in the dolomite and the calamine* deposits in the limestone. This for-
mation is cut up by numerous fault-fissures (Blitte) which have a north-
erly course. These correspond exactly with those found in the Eureka
mines, and are scarcely more than seams in the rock. The ore deposits
are found along them, sometimes on one side and sometimes on the other,
the enriching of the ore-bearing limestone seeming to depend upon the
presence of fissures and the dolomite slate. Occasionally the ore de-
posits take on the character-of lodes along these fissures, and sometimes
they are connected deposits of very irregular shape. The stratification of
the ore-bearing limestone is indistinct and in the neighborhood of the fissures
it is crushed and broken. The lead ores are poor in silver. Further refer-
ence to these deposits will be made when the theory of substitution is ex-
amined.

Age of the deposits in relation to the formation.— ‘he deposits of Eureka, as well as
all those which have been mentioned, are unquestionably of later formation
than the limestone or dolomite which contained them, and though but few
of them can be reckoned among the lodes in the narrower sense of the
word, yet they are all so intimately connected with fissures, crevices, and
seams that they unquestionably owe their existence to the presence of
fissures.

The discovery of a prototype for the deposits of any particular district
is hardly possible, as no two portions of the earth’s crust present exactly
the same geological features, and if any two such existed there is no prob-
ability that they would both be ore-bearing, or, if they were, that they
should have been supplied with ore by precisely the same agencies. The
occurrence of silver in paying quantities with lead ores is very common,
particularly west of the Rocky Mountains, but the presence of gold also in
paying quantities, which forms so marked a characteristic of the Eureka
ores, is exceptional.

Classification according to form.— A Classification of the ore deposits of Eureka
District as regards their form is a matter of considerable difficulty. There

*Posepny used the word calamine to include both calamine and smithsonite.

70 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

are some of them which can be termed fissure or contact veins, but in most
cases they are very irregular in form, and are better described by the Ger-
man word “Stock” than by any mining term used in English. The word
“pipe” can be applied to many of them, but in its ordinary use a “pipe”
implies a ‘‘rake,” while the ramified structure of the Cumberland deposits
is rarely well marked at Eureka. They are often lenticular. This term,
however, cannot always be used to describe their form, as they have off-
shoots in all directions. Any classification, however, which is dependent
on mere differences of form must be more or less imperfect.

Shape of the deposits —The deposits sometimes spread out into immense cham-
bers that measure more than fifty feet in each direction, and which are com-
pletely filled with ore, with the exception of an occasional cave or limestone
pillar. From the sides of these chambers, which scarcely ever present
smooth walls, there are branches, and auxiliary pipes lead up or down, or
in a horizontal direction, to other bodies. The ore bodies do not seem to
follow any particular direction, either as regards dip or strike, and at first
sight they appear to be distributed throughout the ore-bearing formation
without any regularity. This is not wholly the case, and although no well-
defined law can be found governing their occurrence, this is connected with
that of certain phenomena in the country rock, such as fissures, caves, and
broken limestone.

Relation of the deposits to the limestone —The distribution of the ore has been deter-
mined almost entirely by the physical character of the limestone in which
it is found, and not by any chemical or mineralogical differences in the rock.
In other words, whether the limestone was dolomitic or not, and whether it
was nearly pure or somewhat argillaceous, it was always a rock which would
fulfill the chemical conditions necessary to the deposition of ore. Even sup-
posing that dolomitic limestone is generally better adapted to induce deposi-
tion—and this is something which has never been proved—the greater facili-
ties offered by a crushed and broken limestone, no matter what its charac-
ter, to the percolation of the metal-bearing solutions, would more than
compensate for any chemical advantages which a particular kind of lime-
stone offered. Although the typical fissure vein is found in limestone
in many parts of the world, its occurrence in that rock in the Great Basin

THE ORE DEPOSITS. val

is rare. The rarity of this type of regular deposits at Eureka can be
accounted for in a great measure if the extremely crushed character of the
country surrounding them is taken into account. When the upheaval of
the mountain ranges began, the rock was cracked and fissured in many direc-
tions, the fissures no doubt extending to great depths and having consid-
erable lateral extent; but as the uplifting and grinding process was pro-
longed, these fissures themselves were in a great measure obliterated and
faulted, new ones of less magnitude taking their place. This operation
seems to have been carried on until the mountain was no longer a solid
mass penetrated by great cracks, but was composed of shattered zones of
limestone separated here and there by bodies of unbroken rock. The ore-
bearing solutions entered the rock through the channels of least resistance,
the crushed limestone offering less resistance in many places than the main
fissures themselves, and deposition followed in forms of a degree of irregu-
larity corresponding to the complexity of the preceding dynamical effects.

Disposition of the ore in the chambers—'I'he ore in the upper part of larger cham-
bers is mostly in a loose state, sometimes in layers, and is usually covered
by beds of sand, gravel, and bowlders of variable thickness. It is difficult
to believe that this mass owes its structure to any other cause than rearrange-
ment by subterranean water currents, though it is not likely that the original
position of the material was remote from that which it now occupies. There
is of course every reason to suppose that waters either from the surface or
from below have flowed through these rocks in notable quantities ever since
they were intersected by fissures, but the floods which have left the traces
just described in the upper portions of the chambers must be comparatively
recent, since the stratified ore has been rearranged since its oxidation. In
the lower part of the chambers, on the other hand, the ore is more compact
and usually appears as if it occupied its original position.

Connection of ore bodies with the quartzite——OQn Ruby Hill, in the mines lying south-
east of the “‘compromise line,” the ore is usually found in the limestone at
or near its contact with the quartzite, except close to the surface, where it
is generally at some distance from that formation. Although a complete
connection has not been established between all these ore bodies and the
quartzite, or between all the ore bodies themselves, yet their location and

(2 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

the relation that they bear to the secondary or contact fissure between
quartzite and limestone indicate that that fissure has often served as an ore
channel. This is more apparent as the ore is followed downward to the level
at which it takes up the whole of the space between the quartzite and the
main northeast fissure. (See cross-cut to Locan shaft, Plate VIII.) It has
been mentioned that most of the ore bodies in the Eureka lay along the
quartzite and limestone contact; but there has been one notable exception,
namely, the seventh and eighth level ore body. This, with its ramifica-
tions, reached to the northeast clay in places and extended from a short
distance below the fifth down to nearly the ninth level. It was the largest
single mass of ore ever found on the hill, and from it were extracted over
two million dollars. There have been several large bodies of ore near the
quartzite in the K. K. mine, but, with the exception of a mass near the sur-
face in the Jackson ground, the ore bodies in the portion of the mineral
zones lying southeast of the Eureka have not been very large.

Northwest of the ‘compromise line” the ore has been found on the
quartzite in only one place, viz., above the fourth level of the Richmond
mine near that line. A reference to the various horizontal sections (Plates
XIII. and XIV.) will also show that the mineral zone or the wedge of lime-
stone between the two fissures is small in this part of the hill. The surface ore
bodies at the Champion, Buckeye, and Richmond claims of the Eureka and
Richmond companies were of very considerable extent, but at the present
time it is difficult to say how much ore was extracted from them, as the
workings have caved in many places and are inaccessible. In fact, exact
data in regard to the quantity of ore extracted from any of the ore bodies,
except those of the Richmond, are wanting; but as they are not necessary
to a geological discussion of the Ruby Hill deposits, they can be dispensed
with. :

Occurrences of the ore bodies in Prospect Mountain.— ‘here is very little difference in
the manner of occurrence of ore bodies in Prospect Mountain and Ruby
Hill. On the mountain there are no workings in the neighborhood of the
quartzite, and thus far the metalliferous zones have been separated by belts
of undisturbed limestone and shale. The size of the ore bodies in the

THE ORE DEPOSITS. ie

mountain has been much less than those in the hill, and the caves have been
smaller and less numerous.

Fissures andfaults——Both Prospect Mountain and Ruby Hill are traversed
by numerous fissures or faults. The more important and persistent of these
follow the course of the axial plane of the anticlinal fold, which, in the case
ot Prospect Mountain, has a north and south course, and in the case of
Ruby Hill, a northwest by southeast course, and dip away from it. There
are, however, a great number of cross-fissures. The former seem to have
been faults accompanied by upward movements, while the latter show that
there has been lateral as well as vertical pressure exerted during their for-
mation. As a rule these fault-fissures are mere seams, although they may
extend several hundred feet in every direction. Sometimes, however, they
are of considerable width, and have been partially filled with bowlders
broken from the walls and débris washed in from above. They occasion-
ally contain ore and in several cases assume the appearance of fissure veins.
Where fissures containing lead ore occur in limestone in Cumberland, Der-
byshire, and in many parts of Europe, the country is very much less dis-
turbed than it is in Eureka, and the mountain folds are much less sharp.
Examples of fissure veins are not absolutely wanting at Eureka. There is
one in the Banner mine which crosses the axis of fold of Prospect Mount-
ain, and is remarkably regular for a lode in limestone. The east ore body
-of the Richmond mine begins in the Tip Top claim, one of the location
claims of the Richmond Company, and extends down to the Potts chamber
on the “compromise line.” A fissure seems to exist through the entire area
thus indicated, and though the ore does not always fill the fissure and though
the fissure itself often shrinks to a mere seam, the whole occurrence can
properly be regarded as a fissure vein. In the Ruby-Dunderburg there is
an instructive deposit which in some portions fills a clean-cut fissure a foot
or more in width, and in which at some points the ore penetrates the hang-
ing wall in large irregular outgrowths from the vein, which have supplied
most of the ore.

Caves in connection with ore bodies—Ciaves are found in many places in the lime-
stone and are of frequent occurrence in connection with ore bodies; in fact,
no large ore bodies have been found which had no caves over them; but

74 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

caves are by no means always accompanied by ore bodies. They resem-
ble all caves found in limestone, and have been~produced, in part at any
rate, by the solvent action of water carrying carbonic acid. These waters.
passed through fissures and cracks, enlarging them, and dissolved the lime-
stone, especially where it was crushed and broken. The finely crushed
limestone was dissolved first, and the large fragments and bowlders settled
down and were finally either completely dissolved or remained in the bot-
tom of the caves. This action was naturally most considerable at those
points where the best opportunity was afforded for the free circulation of
the water, and as the limestone was not uniformly shattered, and as the
different varieties of rock did not offer equal resistance, the openings formed
were of a very irregular character. The roof and sides of the caves are
sometimes entirely bare and only show the characteristic surface which re-
sults from the action of a solvent. Deposition of calcium carbonate, how-
ever, as well as its solution, has taken place on a large scale and is still
going on. The roof and sides of most of these caves are covered by arag-
onite crystals, and in some of them crystals of this mineral are still form-
ing.

Connection of ore bodies and fissures—In the neighborhood of seams the limestone
is often crushed to a powder or is broken into fragments, which are occa-
sionally cemented together by calcite, forming a breccia. This fissured and
crushed country gave ingress to waters both from above and below. The
surface waters, owing to the carbonic acid which they contained, had a
solvent action upon the limestone, and those from below carried ores in so-
lution, which were, at least in part, substituted for the limestone. The
waters from both these sources removed limestone, which was again depos-
ited when the solutions became supersaturated. The question whether
the caves were partially formed before the deposition of the ore, during
its deposition, or after it, will be discussed hereafter; but it may be stated
here that a great portion of the ore in these ore bodies was directly substi-
tuted for the limestone. The irregularity of the course of the dissolving
waters is everywhere perceptible in the ore bodies and caves. They have
every possible form and vary greatly in size, sometimes being but small
stringers and occasionally measuring upwards of a hundred feet in all di-

THE ORE DEPOSITS. 75

rections. They are sometimes round, and again tabular, and are found with
and without ramifications. There are pear-shaped deposits and pipes round
and flat, irregular and symmetrical. A common form is that of a bent sau-
sage somewhat flattened, and both ends downward. In fact, the form of the
deposit has been governed by the permeability of the rock. Although these
deposits are of all shapes and sizes, taken as a whole they have a down-
ward trend; that is to say, they extend farther in depth than they do lat-
erally. Some are found lying nearly flat, like bed veins, but this manner of
occurrence can usually be accounted for by the hardness and insolubility
of the underlying rock. The ore bodies at first sight often seem to have
no connection with any fissure or channel through which they could have
been filled, but such a connection has been demonstrated in so great a
number of cases that it may be presumed to have existed in all.

In by far the greater number of instances this fissure has led to the
discovery of the ore body, or its existence has been shown in the workings
subsequent to the discovery. In some it has been closed by pressure, in
others it has not been revealed by the explorations of the miner, who natu-
rally does not think it necessary to follow every small crevice or opening
which he may encounter. This connection of ore bodies with fissures is a
very important one, as it throws a great deal of light upon the nature of the
deposits, and although the fissure may apparently be very insignificant and
nothing more than a seam in the rock, the crushing and rending of the lime-
stone in its neighborhood attendant upon its formation have given the metal-
bearing solution an opportunity of penetrating the rock, and although the
fissure itself may not have been the ore channel, the formation of the ore
bodies has been dependent upon it.

Example of connections between ore bodies and fissures.—Numerous examples of an
evident connection between ore bodies and fissures are to be found in this
district. Besides the east and west ore bodies of the Richmond mine, which
will be more fully described hereafter, the Ruby-Dunderburg and Williams
mines, on Prospect Mountain, are among the best instances of this occur-
rence; but examples of fissures connected with ore bodies have been found
in almost all of the mines of the district. No doubt many of the deposits
in limestone which occur at numerous points in the Great Basin would

76 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

exhibit similar features as regards fissures and ore bodies if they were more
carefully examined.

The main fissures which follow the axial plane of the fold show that
there was a zone of crushed rock produced in the country parallel to them.
The dissolving waters followed this zone and often penetrated to a consid-
erable distance laterally. When there is more than one fissure in such a
zone it is a matter of great difficulty to decide which one ought to be con-
sidered the true ore carrier or decisive factor in determining the present
arrangement of the deposits. Several fissures may have been instrumental
in determining the ore channels.

Relative ages of fissures and ore bodies —A] though most of the fissures with which
ore bodies are connected were unquestionably formed before the deposition
of the ore, yet there are some few which may possibly have been made
since its deposition. It is a very difficult matter, where there are no signs
of stratification in the country rock, to tell whether a fissure has faulted an
ore body or not. When two ore bodies are found at some distance from
one another and on opposite sides of a fissure, it by no means follows that
they were originally portions of a mass which has been faulted by the
fissure. The two ore bodies may always have been distinct. There can-
not have been much faulting since the deposition of the ore, for fissures, the
existence of which prior to the deposition of ore cannot be disputed, show
very few signs of any displacement.

The partial falling in of caves and the mixing of bowlders of limestone
and ore near open fissures does not prove that there was any considerable
motion of the country. The roof of the big cave between the ninth and tenth
levels of the Eureka is falling in from time to time, but this is probably due
to the chemical action of water loosening blocks of limestone, and the mix-
ing up of ore and limestone in the northwestern portion of the Richmond
mine below the seventh level can be attributed to the mechanical action of
the same agent.

Sediment—In connection with fissures it may be well to describe the
transported material or sediment which is often an accompaniment of fis-
sures and ore bodies. It consists of loose bowlders of gravel more or less
connected together, of large and small brecciated fragments of limestone,

THE ORE DEPOSITS. 77

or of loose sand. Its nature, the position it occupies and its structure show
that it could only have been brought into its present place by the aid of
water. It is to be looked upon, therefore, as simply a wash from higher
points which has filled the cavities and interstices of the rock formed by
dynamic and chemical causes. This wash frequently accompanies large ore
bodies, and is usually found adjoining or overlying the ore, and although it is
not an infallible indication of its presence, it is one which is not to be over-
looked. The two-million-dollar ore chamber on the eighth level of the
Eureka mine was discovered by following such a wash. This body extended
up above the seventh level and down nearly to the ninth, and covered a great
deal of ground with its ramifications and pipes. On the other hand, there is
a very large mass of material of a similar origin, in the form of fine sand,
on the fifth level of the Pheenix, which, although pretty well prospected, has
not led to any discoveries. ‘These washes are more frequent at or near the
surface, but are found down almost to the water level.

Description of east ore body— It has already been remarked that the quartzite
and limestone contact in the Richmond ground bends to the west, and the
fissure that accompanies it continues with the narrow band of quartzite on
its normal northwest course. Parallel with this fissure there is a system of
fissures which extend from near the surface at the Tip Top incline down
to the tenth level of the Richmond mine. These were accompanied by
ore chambers which form an almost continuous body down to a point a
little below the seventh level of the Richmond. Below this point no ore
has been found in the Richmond in this part of the mine, although there
is a well-defined fissure extending to the tenth level. From the position
which this fissure occupies, however, it is almost certain that it is the Ruby
Hill fault, and it is very probable that the system of fissures mentioned
above joins the main one somewhere below the seventh level. From this
it will-be seen that the Tip Top fissure, or the ‘‘east ore body,” is an offshoot
of the main fissure which is shown at the winze on the ninth level on the
horizontal section, No. 6, Plate XIV. One of the most famous of this series
of ore bodies is the Potts chamber, most of- which in the Richmond mine
lies between the fifth and sixth levels. It is also connected with the series

78 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

of ore bodies which are found at the contact of quartzite and limestove-in
the Eureka ground.

Description of west ore body— The west ore body, as the second system of
chambers in the Richmond mine is called, begins near the surface in the
Eureka ground in the neighborhood of the ‘‘compromise line.” These
chambers are all connected with one another in some manner, and most of
them are connected with a system of fissures. It pitches nortli, and as
depth is obtained passes through the Richmond and enters the Albion
ground. It lies under and northwest of the east ore body, and does not in
any place connect with it or directly with the Potts chamber. Neverthe-
less, as the upper part of the west ore body lies on or near the quartzite in
the Eureka mine, and as in this mine ore is traceable along the quartzite
to the Potts chamber, the two ore bodies are indirectly connected. The
positions of these ore chutes can be seen in the vertical cross-sections,
Plates IX. to XII, and in the elevation, Plate III. From them has been
taken very nearly one-half of the ore extracted from Ruby Hill.

Connection of ore bodies with depressions in the quartzite. —As has been stated in Chapter
IV., many of the ore bodies in the Ruby Hill mines are intimately con-
nected with sags or depressions in the quartzite; and the manner of forma-
tion of these basins was there described. That large ore bodies should be
of frequent occurrence in these depressions is not strange when it is remem-
bered that the limestone in them was in a shattered and crushed condition,
and that the quartzite, with its casing of clay, served to a certain extent
to confine the metal-bearing solutions to this limestone mass, where large
quantities of those solutions were probably allowed to settle quietly and
deposit ore. It was in these basins that the conditions most favorable to
ore deposition were found.

In the Richmond ground, although such depressions in the quartzite
occurred in the upper as well as in the lower levels of the mine, they do
not seem to have been accompanied by ore bodies, in spite of the fact that
the character of the limestone was favorable to ore deposition. This can
be accounted for by several facts. The two main ore channels in the Rich-
mond mine, the east and west ore bodies, did not approach the quartzite,
owing to the fact that the fissures with which they were connected did not

THE ORE DEPOSITS. 79

lie near that rock in the portion of the mine above the water level. There
is, moreover, a large block of undisturbed ground, which has already been
described, page 32, and which in a measure separates the west ore body
from the crushed limestone near the quartzite. It is difficult to tell exactly
how this undisturbed ground deflected: the ore solutions, but it is likely that
it was one of the principal causes of the arrangement of the ore bodies.
There are large blocks of ground in the upper levels of the Richmond mine,
near the quartzite, which have been incompletely explored, and it is by no
means improbable that new ore channels may be revealed and important
ore bodies may be discovered by careful prospecting in that direction.

CHAPTER Vii:
THE SOURCE OF THE ORE.

Theories in regard to the formation of ore deposits —QOne of the most important inquiries
connected with the geology of the Eureka District relates to the source of
the ore, for a successful solution of this problem would afford information
valuable in the search for further deposits, besides possessing great scientific
interest. A discussion of the various theories which have been held in regard ©
to the formation of ore deposits in general, some of which might be found
applicable to the Eureka deposits, cannot find a place in this report, but it
may be well to mention the only solutions of this problem which are in any
way warranted by the facts which have been observed. These are: First, a
deposition of the ore in small particles simultaneously with the limestone,
the ore being afterward segregated into nearly isolated bodies, either by
chemical or mechanical action; second, a segregation of the ore in the
limestone from the country rock on either side of it; and, third, a deposition
from solutions which came from below.

Relative time at which the minerals were deposited — A]though the periods at which the
different minerals which compose the ore bodies were brought into their
present position may have been separate and distinct, it is highly improb-
able that such has been the case, and it is not likely that some of them
should have been segregated from the country rock, and others either have
been washed in from above or brought up in solutions from below. Evi-
dence against this last supposition is not plentiful in the oxidized ore masses,
where the original position of the ore has often been changed by the flow
of underground streams, although it can still be found in the least disturbed
portions of them. But in the undecomposed sulphuret ores there is clear |
proof that the various minerals were deposited simultaneously. They occur
irregularly, but in about the same relative proportions throughout the mass;
they show no signs of concentric structure or of successive deposition, and

although this is not positive evidence that their sources were the same, yet
(80)

SOURCE OF THE ORE. 81

it is difficult to conceive of a derivation from different sources without a
difference in the time of deposition, which would necessarily result in a
variation in the character of the ore.

Metals contained in the country rock.— ‘There is a sharp distinction between the com-
position of the ore and that of the inclosing rock. Iron oxide forms the
gangue of the ore bodies, aud about one-half of the ore is composed of
that mineral, the other portion being made up of lead, arsenic, sulphur,
zine, silver, carbonic acid, etc. The first four of these substances do not
seem to occur in the least metamorphosed limestone, and only appear in the
more altered limestone in small bunches and seams in the neighborhood of ore
bodies. There is a large block of stratified limestone on the sixth level of
the Richmond, which is very little altered, and it shows no evidence of ever
having contained any quantity of the metals enumerated above. It is hard,
compact, and erystalline-granular. It is distinctly stratified, and has been
comparatively little disturbed. ‘The highly-altered limestone, on the other
hand, contains notable quantities of some of these metals.

Ratio of the ore to the limestone —As close a calculation as possible has been made
of the relative proportion of ore to limestone, in order that some idea may
be formed of what percentage of the metals that rock must have originally
contained if the ore had been uniformly distributed in small particles
throughout its mass. The ratio of the limestone to the ore extracted from
that portion of the mineral zone situated between the main fissure (the
Ruby Hill fault) and the contact fissure, between the quartzite and lime-
stone in the ground southeast of the Richmond shaft, is about 100 to 1.
In the mineral zone northwest of this shaft the ratio of limestone to ore is
somewhat greater. If a reduction of one-half is made for large bodies of
low-grade ore which up to the present time would not warrant extraction,
and for yet undiscovered masses, of which it is but reasonable to suppose
there are some in existence in the portion of the mineral belt southeast of
the Richmond shaft, the ratio of the limestone to the ore would be 50 to 1.
Putting the assay value of the ore at $40 in gold and silver to the ton of 2,000
pounds, and the percentage of lead at 10 per cent., which cannot be regarded
as too high when all the ore which has been removed from the mines is
taken into account, then each ton of limestone must originally have con-
tained 80 cents in value of the precious metals and 0.2 per cent. lead.

2654 L——6

82 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Amount of silver in the country rock—A mong all the assays of country rock made
only one over 50 cents was obtained, and that was in the immediate vicinity
of a large ore body, near the sixth level of the Richmond mine. The far--
ther from an ore body a sample is taken the poorer as a rule is the lime-
stone, as will be shown hereafter when the assays are examined in detail.
Fifteen cents in silver is a remarkably high assay to be got from stratified
limestone. That rock lying near the shale outside of the main fissure con-
tains scarcely more than a trace of the precious metals. Suppose the

@ALEICN SHAFT

(SSURE Crug
ye AO

= — — = a See a)
Fic. 2.—Plan of main drift and cross-drift, 600-foot level, Richmond mine. Scale, 400 feet=1 inch.

calculation made above to be incorrect, and let the possible value of the
limestone be reduced to one-half, or 40 cents, this amount would still be
very considerably in excess of the average value of even the crushed and
most altered rock, and very much greater than the highest assays obtained
from unchanged limestone.

Assays of country rock— With a view to determining, if possible, whether the
ore was derived from the surrounding limestone, or whether the limestone
was impregnated with ore from the ore bodies or the solutions to which
they owe their origin, careful assays were made of the limestone on two
lines leading up to a large ore body, the lowest portion of which was about
30 feet above the sixth level of the Richmond mine. Since these assays

SOURCE OF THE ORE.

were made the continuity of this ore chute with but a few breaks has been
established nearly down to the ninth level.

The preceding diagram, Fig.

2, explains the positions of the ore bodies and their relations to the coun-

try rock.

First series of assays— I'he Arabic numerals on the main drift refer to the

numbers of the first series of samples which were taken for assay.

The

positions on the drift from which the samples were taken are marked by
black dots. The samples were taken every 25 feet, and the subjoined

list describes the character of the rock and its assay value in silver.

eas INTO le
No. Description. | Beeey, Averages. |
Cents.
TU THEE) EENG esp as Sono naneaee -oeoe co pseane eee tes | 6 6
BLACK STRATIFIED LIMESTONE.
2 | Yellowish broken limestone ..--...-------------- 9
Bh Mewes Gli) -Sas ao Sesesces shee cbeanc- so=adetooooberods a 184
Ce Qe seis ete se soa nea actor aunee eine ce’ mimm 13 |
¥ a 122
5 | Black, hard, compact, stained limestone -.-..----- 10)! <8
6 | SIU anne Rene eco gtouce Sew enercee cee oes | 18
7 | Same somewhat foliated -. --..-..--.-----.---...--- 14
fi} Genoese GW) a 5ee 388 eseee sc Sbee Spore De oseeie Sap oconics 16
CRUSHED BROKEN LIMESTONE.
9 | Broken friable white limestone .--..--.----.------ 12
10 | Broken friable sparry limestone - ....--..--.------ | 25
11 | Broken friable black limestone ~---...----.------ 15 >| 158
TP} Besa (CO Sanere erase me ie ceinsmneton i eeeaes 14
13 | Broken friable yellowish-black limestone .....--.- 13)
14 | Broken friable white limestone. .-..--...-.-...--. 10
15 Sane dankenes severe see see alae eee sesiea soma == |
16 | Broken friable brownish limestone. -.--....-...----- 14 /;| 153 |
17 | Broken friable blackish limestone .-----.--.------ 16!
18 | Broken friable highly crystalline limestone --..--. 26)
19 | Same more compact.-.. -.-.-.---..--------------- | 13)
20 Friable white limestone. .- | 18 |
Dit esod (iy se ASAE REE ae ee Se 11\| 143} 13.88
22 | Compact white limestone. -.-.-.-.-..--..--------- | |
23 Broken friable white limestone. .....-.-.---------- 15
24 jeceee Gt) acss Seedsceecedsosdeantssecoot sasesode 10) |
Doieerater Ow neere te erate en cenelacieenciciaciieaianis asaiee 12
26 | Same more CO i Seca sceocecdsoesscocosedacssd 9+) 102 |
OFM eee CO eres ecto ia aa |e an asa nnnmniecwersignaen ces ll
28 | Broken friable white limestone .-..-...--..--.---- 11 |
29 | Same compact --.---.-.-.---- -.--- 21
30 |----- - (ib) ose ce eee SenRe cee aneboe tees So esonco one 12
31 | White and black limestone with yellow spots. .--. 13 “A
Spy Shin @) eas ob asodecaca sbecos ont SrocherosSeA bosses 10
Bolleceae- OO) pases she ages sesek cast aac oS eee pce 10

aSee page 86.

84 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

List No. 1—Continued.

Second series of assays——The Roman numerals on the northeast side of the
main drift correspond to another set of samples which were taken in the
same drift at the designated spots. This second set of samples was taken
in order that a comparison might be made between the assay values of the
limestone and the electrical phenomena observed by Dr. Barus at the same
points. They are only given here that as many assays as possible may be
brought to bear on the question of the impregnation of the limestone, and
will be referred to in more detail when the results of Dr. Barus’s work are

examined.
1 ESE UNTO. ese

No. Description. ny Averages.
| Cents.
iT Blue ehial eee. saree ese eee ee eee | 6 6
II | Slightly stained black stratified limestone .....- | ie } =
III | Same less stained, with calcite...............-.- 12 a
IV | Broken friable white limestone iff
Mf [eecore (Olt) Sa-Seescn sation enticed sex 10
Wau leecacs (rasa mopeccnerseaas sackman sssetene Seebece 12
VII | Same slightly stained .......-..-..----- 10 |
VIII | Same MOLVAWOCO sees ee eee eee ae 9|> 105
Tbe | baeee: Ree ee ere kee oh ee 10 |
X | Same brecciated and slightly stained --- - 12
XI | Broken friable white limestone ..-......-....-.. | 12 |
x | Broken brecciated limestone stained black...-.. 15 |
XIII | Reddish stratified limestone | 10 | 10
XIV | Black broken stained limestone 65
XV | White broken stained limestone ..-.-. 20
Vil lSonne CORR astee est atec cea snes aces teas em 27 274
XVII | Samoe;slightly stained'.=-=-.-2----- -<2----<. cst 10 |
XVIII | Black stained limestone ...... .........-....---- 17

SOURCE OF THE ORE. 85

Third series of assays.— A third set of samples marked with dots and numbers
on the diagram was taken from the cross-drift, and the result of the assays
with a description of the samples is annexed.

Lee SEN Gon.

No. | Description. Asaay. Averages.
|
Cents.
1 | Rina shaleten sce snseee ee reer Gn tennessee eae eet 5 | 5
STRATIFIED LIMESTONE. |
2 Grayish limestone ...-......--. crore sc ceeeseseeeees
3 | Hard black limestone, with calcite and red spots. - - -| 15 9
Ab Saee Oar mann ces Sats mc niscie aes cee wa acei sees as
oi) \Grayvinh lim 6etone- = 225 -2--202-Gs-cccn-e secre sees.
BROKEN AND CRUSHED LIMESTONE.
6 | Crushed black limestone, with calcite .........-.--- 15
7 | Same more broken and stained.......-..-....--.---- | 30 163
8 | White brecciated limestone slightly stained .-...--. 10
9} Hames but Soller ses eee ee casce aces <neee ee | 12
POW MName as INOS smc ae asses eas coos sel onc a= oe | 15 |
11 | Compact calcite slightly stained ----......-.. .----- 20}. 173
12 | White crushed limestone .........-..---.---------- | 22 |
IBY 5406 DO rear fee eet ee ae we nen epee neee meas 13
14 | Bluish broken limestone, with calcite .-....-........ 15
15 | Same more broken .--..--.-- Tehseeseeneeeee sees 11 133
NG Saeces Oona eye sesamiae seen eect seat ate ae 16
17 | Grayish, very much broken limestone ...-.-.-...--. | 12 |
ISH iSimvargbut pulverizedna-qseasen aves nee en shane 51 | )
190i)! Similar; but bluishee pass so-- 24s eee sete ee | 32: ( 323
20 Yellow and reddish soft broken limestone -..---.--. | 23 | |
21 | Bluish, somewhat broken 24 |J
22 | Same more broken .---...---..------.- 15 | |
Son | eemne CO ae Cone reer cer Boars 15 | \ 16
24 | Eluish stained limestone .........-...--.-.---------- 6
25 | Same more broken and stained a8 |)
26 | Hard white sparry stained limestone........--.-.... 6 | |
27 | Soft yellowish broken limestone ..-..---.-..-..----- 20 | > 195 |
| 28 | Soft, taken near No. 14 of List No.2.-............... 32 J

Discussion of assays—None of the specimens of limestone assayed contained
any ore, at least none that was perceptible to the eye, and they had the
appearance of the ordinary limestone found in the mineral belt. The
assays, which were made with great care in the manner described in Chap-
ter XI., prove: First, that the country rock near the ore bodies is richer in
silver than that at some distance from them; second, that the least changed
and metamorphosed limestone is the poorest; and, last, that the most
crushed and broken limestone, and that which is somewhat stained with

86 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

ferric oxide, is usually the richest. There are several exceptions to be
noticed in these specimens, but they do not seem to be sufficient to affect
these general results. Although it has not been possible to fix with cer-
tainty on any particular variety of limestone which is to be regarded as
the poorest, or richest, its contents in the precious metals bearing no very
definite relations to its physical properties, yet it is usually possible to form
some idea of the value of a piece of rock from its appearance, the crushed
and stained varieties being usually the richest. It will be noticed that the
specimens taken on either of the lines leading up to their junction below
the large ore bodies do not show a gradual increase in value as the ore is
approached. The want of regularity in this increase is owing to the facts
that there is no uniformity in the character of the limestone, and that there
appear to be zonés of rich and poor rock crossing the course of the main
drift and cross-drift. The existence of such zones cannot be fully estab-
lished by the number of assays that were made, as the limestone is con-
stantly changing, and a rich piece and a poor piece are often found side by
side; still the variations of certain groups of assays from the general aver-
age indicate that such zones exist.

Sample No. 3, in the first list of assays on the main drift, shows 34
cents in silver. This is an extraordinary amount to be obtained from lime-
stone within the stratified zone, but although other samples were taken
from the same spot no second such assay was obtained. It is abnormal,
and it would have been struck from the list had it not been deemed proper
to give the assays exactly as they were taken, although in reckoning the
average assay value of the stratified limestone (Nos. 2, 4, 5, 6, 7, and 8) it
has been omitted, as the other samples which were taken afterwards in the
same spot were less than the average (12% cents).

The average of the next five samples, from 9 to 138 inclusive, which
were taken from the crushed limestone, is 153 cents. The stratified and
crushed limestones are separated by a fissure which may have been the
source of impregnation of the zones on each side of it. At any rate the
averages of five samples decrease down to the fourth lot assaying 105, when
they begin to increase again up to No. 34, which is in the next zone of
stratified limestone. The average value of this zone of stratified limestone

SOURCE OF THE ORE. 87

is only 95 cents. The four samples, 39 to 42, inclusive, are in the broken
limestone just below a large ore body, and their average is 192 cents. The
samples which are marked on the map with Roman numerals do not show
any remarkable changes until No. 13 is reached, which was taken from
near No. 42 of the other list. It assayed 65 cents, and an average of nine
other samples taken in the drift southeast of this point showed 17% cents.
These samples were not far removed from ore bodies. Although the
samples in list No. 3, taken in the cross-drift, do not show a uniform increase
in metallic contents as the ore is approached, yet they indicate that the
rock in the neighborhood of the ore is the richest on the average. The
stratified limestone which lies outside the main fissure in this drift averages
but 9 cents. The shale is invariably of low grade, the highest assay ob-
tained being only 6 cents.

Results—From the foregoing facts it will be seen that it is scarcely
possible that the ore bodies could have been formed by segregation from
the surrounding limestone. Had such been the case all the metals compos-
ing the ore bodies would have been found in appreciable quantities in the
least changed limestone. The assays prove moreover that the silver in this
rock was in all probability an impregnation accompanying the deposition
of the ore bodies and was not an original constituent of the limestone.

Segregation from the limestone —If the ore had been collected in its present
position by segregation of any kind, there would have been innumerable
places in which minute clusters and bunches would have been formed, and
the limestone, instead of being perfectly barren or practically so for great
distances in all directions, would have exhibited here and there at least
signs of ore. The large caves and pipes are not the only openings to be
found in the mass of limestone. There are openings of every size and
shape; vuggs, small holes, drusal cavities, open cracks, and fissures are of
frequent occurrence throughout the ore-bearing zone as well as in the lime-
stone which has not been found to be productive, though the last has not
been sufficiently explored to prove that these openings are as common as
in the above-mentioned zone. That some of the cavities referred to may
have been formed since the deposition of the ore is very possible, but it has
been shown already that most of the fissures and cracks were produced

88 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

before the formation of the ore bodies. Had segregation taken place at all,
it must have taken place throughout the mass of limestone; and it is very
difficult to conceive of metal-bearing solutions or ore in any other form
traversing hundreds of feet of limestone, offering every opportunity for the
deposition of ore, and passing across fissures in such a manner as to leave
no trace of their passage in many of the openings which must necessarily
have been in their course, if they were derived from the country rock; yet
this is what must have occurred, if the theory of segregation were applicable.
Had the ore been segregated, it is probable, too, that there would have been
no well-defined boundary between the country rock and the ore. Such is
not the case, however. The ore is as definitely cut off when it comes in
contact with the limestone as if it had been shoveled or rammed into the
caves and openings. The limestone is often impregnated with ferric oxide
in the neighborhood of ore chambers, but the dividing-line between the fer-
ruginous limestone and the ore is very plain. The limestone at a distance
of 6 inches from very rich ore often shows no signs of iron or of anything
else that would indicate the proximity of ore.

Segregation from the shale——'Ihe shale nowhere carries more than a trace of
silver and gold, and what has been said in regard to a segregation from the
limestone applies also to the shale. Indeed, it is still more improbable that
metal-bearing solutions should have been uninterrupted in their passage
through the clay of the Ruby Hill fault and should not have been concen-
trated on its hanging-wall side. A derivation of the ore from the shale is,
therefore, inadmissible.

Segregation from the quartzite —Silver, gold, lead, and some other minerals have
been found in small quantities in the quartzite, but ores were never obtained
from the latter rock in paying quantities, and occurred chiefly in small
seams and fissures. It has been explained that there has been considerable
motion of the quartzite upward against the limestone along a fissure, and
that this fissure contains a great deal of clay and was of prior origin to the
ore bodies. What has been said in regard to mineral solutions traversing
the clay of the main fissure is equally true in this case. A segregation of
ore from the quartzite is, therefore, hardly among the possibilities. Neither
is it possible to suppose that the ore was introduced from above, for none

SOURCE OF THE ORE. 89

of the rocks which may have covered the present surface contain any
heavy metals.

The manner in which the ore entered the limestone —T he evidence in regard to theactual
source of the ore is rather of a negative than of a positive character. The
theory of segregation is untenable; and other theories, such as that of a
deposition in beds simultaneously with the country rock or of an infiltra-
tion from above, are not to be thought of. The only reasonable explana-
tion which can be given of the source of the ore, and the only one which
is not contradicted by the observed facts, is that the ore bodies were formed
by infiltration from below. It has already been shown that the ore cham-
bers are intimately connected with fissures. Some of these—for instance,
the main fissure, as exposed on the twelfth level of the Eureka, in the cross-
cut to the Locan shaft—evidently served as channels for ore-bearing solu-
tions, and it is extremely probable that most of them at one time or other
have carried mineral solutions to the ore bodies. All fissures are more or
less connected with the two principal ones, and many of the ore bodies
are also connected together, and they have in general a downward trend.
All the facts point to an ascension of the solutions, and these solutions were
in all likelihood a result of the solfataric action consequent upon the erup-
tion of rhyolite.

Cause of the solfataric action —It, has already been stated that there is a strong
probability, if it is not absolutely certain, that the eruption of rhyolite pre-
ceded the deposition of ore. Extensive eruptions of this rock took place at no
great distance from the mines, and, as has been described, a dike of it follows
one of the chief fissures of the mineral zone. The decomposition of this ~
dike and of other rocks accompanying it, especially the quartz-porphyry, is
such as is characteristic of volcanic regions, and its occurrence must almost
inevitably be ascribed either to the rhyolite eruption or to the still more
recent outburst of basalt. There is no basalt, however, either in or near
the mines, and therefore nothing to indicate a connection between its ejec-
tion and the deposition of ore. The solfataric action traceable in the mines
is therefore most naturally referred to the rhyolite eruption. It is of course
no objection to this hypothesis that the rhyolite is itself decomposed, since
the decomposition of lavas within a few days of their ejection, by the gases
and solutions of the same eruption, has frequently been observed; while

90 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

the period of the rhyolite eruptions near Eureka may have covered cen-
turies. The character of the decomposition of the rhyolite is familiar, and
consists largely in the extraction of the heavy bases and alkalies, leaving
siliceous clay as a residue. * Sulphureted hydrogen is almost invariably an
accompaniment of volcanic action, and the alkalies in solution were in part
converted thereby into sulphides. As most of the sulphides of the metals
are soluble in solutions of the alkaline sulphides, a vehicle was thus formed
for the transportation of any of those metallic sulphides which might be
present. Those sulphides, or compounds which would yield them, might
have formed constituents of the rhyolite.

Rhyolite as a source of the ore— As a matter of fact there is no rhyolite in the
immediate vicinity of the ore which contains sufficient gold, silver, or lead
to admit of its being regarded as the source of these minerals in the ore.
It is barely possible, though not likely, that the rhyolite body of which the
dikes in the mines are the upward continuation, may have carried a notably
larger percentage of heavy metals than that now to be found in a fresh
state on the surface. In fact, near the mines, it is almost completely decom-
posed, and it cannot be obtained in a tolerably fresh state above ground at
considerable distances from the workings.

Quartz-porphyry as a source of the ore—The rhyolite is not the only eruptive rock
met with in the mines. Quartz-porphyry also occurs, but only in the neigh-
borhood of Adams Hill. This rock, however, contains considerable quantities,
relatively speaking, of gold and silver, particularly of the former. The
explorations in the mines in which it is found are not sufficient to give any
definite idea of its extent, but it is possible that it is much more extensive
than its croppings suggest. The result of the assays made of this por-
phyry, which are described in the chapter on assays, indicates that this
rock contained silver and gold, and perhaps lead, after it solidified and before
any solfataric action could have affected it. Though the age of the quartz-
porphyry cannot be proved from this district, there can be no doubt, from
its lithological character and its mode of occurrence in innumerable other
localities, that it is pre-Tertiary and far older than the rhyolite. That the
solfataric action incident to this eruption had an effect upon this porphyry
is extremely probable; at any rate, changes of a solfatarie character were

SOURCE OF THE ORE. 9]

brought about in it, such as the formation of iron pyrite and the concen-
tration of gold and silver in that mineral from the porpiyritic mass.
Moreover, although it is not certain that the gold, silver, and lead in the
mines in its immediate neighborhood were derived from this rock, yet the
amount of gold, silver, and lead it contains, and the transformation it has
undergone, render it a possible source of these metals in the ore of the mines
of Adams Hill. The mines of Adams Hill, which are mentioned in another
portion of this memoir, are many of them noted for the large proportion of
gold to silver found in their ores. As regards the mines of Ruby Hill,
which are separated from those of Adams Hill by an intervening belt of
shale, it cannot be stated as anything more than a possibility that their ore
was derived from the decomposition of the quartz-porphyry.

Granite as a possible source of the ore—It_ has already been mentioned (page 12)
that granite probably underlies the sedimentary rocks of Ruby Hill, and
perhaps those of the whole district. This rock has but one small outcrop.
It has been carefully assayed, but only a trace of silver and no gold has
been discovered in it. The only place where specimens could be obtained
was on Mineral Hill, and they were all much decomposed. It is nowhere
exposed in the underground workings, although bowlders resembling granite
have been found in the quartzite near the bottom of the Richmond shaft.
It is only natural to expect that this decomposed granite should show very
little of the precious metals even if the undecomposed rock originally con-
tained perceptible quantities. Investigations which have been made of mas-
sive rocks carrying gold and silver have always shown that the decom-
posed varieties were invariably poorer in these metals than the unaltered
rock, except where enriched by infiltration.

Source of the ore in Prospect Mountain. — With reference to the deposits of Prospect
Mountain, which are almost identical with those of Ruby Hill, it can be
stated that although there is no quartz-porphyry or any other massive
rock carrying perceptible quantities of gold and silver in its imme-
diate vicinity, yet there is no proof that such rocks do not exist in depth
in or near the ore-bearing formation, and that, as such rocks have been
found on Adams Hill in connection with ore deposits, it is possible that
they may have been the source of the ore in that region as well.

92 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Conclusions —'T'he results of the chemical and physical examinations which
have been made of the rocks of Eureka have been rather negative than
positive as regards the source of the silver. They have shown what rocks
have not been the source of the ore more conclusively than they have
proved its origin. They seem, however, to point in but one direction,
namely, to some massive rock which has been decomposed by the solfa-
_taric action attending the eruption of rhyolite. Through the decomposi-
tion of this rock metal-bearing solutions were formed which afterward pene-
trated the limestone and deposited the ore

Cia PVE RY VLE EF:

MANNER OF THE DEPOSITION OF THE ORE.

Derivation and circulation of the metalliferous solutions—In the foregoing chapter it has
been stated that the ore was probably derived from some massive rock by
solfataric action. The solutions containing the ore penetrated the limestone,
passing through fissures and interstices in the broken rock, and deposited
the ore where conditions of temperature, pressure, and chemical activity
were favorable to its precipitation. The irregularity of the deposits and
their connection with fissures and other phenomena have already been
described and accounted for, but as yet no attempt has been made to
explain the causes which led to the release of the minerals from the solu-
tions which contained them and their aggregation in immense chambers.
It is impossible to determine what may have been the chemical composition
of these solutions, but it is not improbable that they consisted in great part
of sulphides of the heavy metals dissolved in alkaline sulphides. These
solutions were necessarily formed under the influence of heat and pressure.
Rising into the shattered limestone at a diminishing pressure and tempera-
ture, the liquids lost much of their solvent power and many of the metals
that they contained were precipitated.

Manner in which the ore was deposited —As to the manner of this precipitation, two
theories only are admissible, either that the ore was precipitated from the
solutions in pre-existing large openings, or that it was substituted directly
for the limestone, that rock being dissolved and metallic minerals being left
in its place. In other words, the ore was either deposited in caves and
other openings, or the caves found above the ore bodies were caused by a
shrinkage of the ore and the action of dissolving waters.

Importance of the manner of deposition.— At first sight this question does not seem

of great practical importance, for if the mineral-bearing solutions came
(93)

94 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

from a considerable distance below, and it is highly probable that they did,
it would be reasonable to suppose that the deposition would continue as far
as it would be possible to follow it. An investigation of the phenomena
attending the formation of these deposits will show, however, that the man-
ner in which the ore was deposited has a very important bearing upon the
probabilities of finding ore at any considerable distance below the water
level.

Theory of the formation of caves— he formation of caves in limestone is usually
attributable to the action of waters percolating from the surface and carry-
ing carbonic acid in solution. As is well known, even rain-water contains
carbonic acid in solution, though in small quantities corresponding to the
traces of carbonic anhydride always present in the atmosphere. The air
occupying the pores of the soil for a considerable distance from the surface
ismuch more highly charged with carbonic anhydride than the free atmos-
phere, a fact no doubt due to the oxidation of organic matter, and the per-
colating waters are correspondingly charged with carbonic acid. Below the
permanent water-level of a limestone country the water is nearly saturated
with calcium carbonate, and though there is a slow circulation of subter-
ranean currents beneath this level no strong local action can be expected.
To form a cave at a given spot, water containing free carbonic acid must
be supplied in sufficient quantities, and an escape must be provided for the
more or less saturated solution of calcium carbonate which results from the
corrosion of the rock. Caves cannot, therefore, form at an indefinite depth
from the surface of the limestone under any circumstances, for, after pass-
ing a certain distance through limestone, the percolating waters would be
nearly or quite saturated. Caves, too, can only be found in a country with
deep drainage, since otherwise the saturated solvent could not be removed.

The rate of cave formation is dependent upon the quantity of water,
the amount of carbonic acid that it contains, and the velocity with which
it fows. Climatic changes and changes in the formation from dynamic
causes accelerate or retard the action of these waters as the case may be,
but a tendency to the formation of caves exists wherever water percolates
through limestone. The solution of limestone ordinarily appears to be
accompanied by the deposition of more or less calcium carbonate in the

MANNER OF DEPOSITION. 95

same neighborhood. When the processes of solution and deposition go on
simultaneously their coexistence is no doubt due to local differences of
temperature and pressure. Changes in the amount of percolating water
and other circumstances may also bring about deposition where solvent
action once prevailed, or vice versd. As before stated, the dissolving of the
limestone in particular directions has been owing in great measure to the
antecedent crushing of the limestone.

Connection of caves with fissures, ore bodies, and each other in Eureka.— | ‘he caves in Kureka
District are of more frequent occurrence near the surface than they are in
depth, no caves of any importance having been found below 1,000 feet.
They are almost invariably connected with some fissure, and are also often
connected with one another by fissures and open pipes. No oxidized ore
body of any great magnitude is found without a cave above it, which is
usually proportionate in size to the ore body, but all caves are by no means
accompanied by masses of ore. Though the caves are very irregular,
having ramifications in all directions, they form a system or systems which
have a downward trend approaching the foot wall of the formation in which
they are found. As the ore bodies are associated with caves their deposi-
tion is, of course, similar.

Action of water in the caves.—'T'he roof and sides of the caves sometimes pre-
sent the appearance of a chamber blasted out of the solid rock, and do not
show any signs of the action of water. This, however, is rarely the case,
and is a result of the falling in of the roof and sides as they were originally
formed. The action of the. water can often be observed upon some of the
sides of the bowlders, which in such instances always cover the bottom of
the caves. Usually the surfaces of the caves show the effect of the cor-
roding action to which they have been subjected; the rock is hollowed out
in cup-like forms, which are roughened and indented with lines caused by
the difference in solubility of the various parts of the rock. These surfaces
have a light-grayish color streaked with white, and in the neighborhood of
ore are more or less stained with ferric oxide.

Formation of aragonite and cal ite in the caves.—(C]usters of aragonite and calcite
crystals are frequently found covering large areas on the roof and sides.
Although water is found dripping from the roof of some of these caves it

96 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

never accumulates in any considerable quantity on the floors, but the
atmosphere is always damp. The growth of aragonite crystals is not con-
fined to the roofs and sides of the caves, bowlders which have fallen from
the roof often being covered with them. Whether these crystals are of
stalagmitic origin or whether they owe their formation to exuddations from
the floor is uncertain, but the latter supposition seems the more likely, for
although drops of water were seen falling from clusters of aragonite crys-
tals in the roof no corresponding aggregations were noticed where the drops
struck below. The caves above ore bodies do not differ in any resyect from
those in which no ore is found, and although they may have been formed
at a different period there is no reason to suppose that they owe their origin
to a different cause.

Connection of caves with the outer air— That some of these caves are connected
together by openings, and that they have connection with the outer air, is
proved by the fact that in many of them there is a very decided draught
of air, although they may be several hundred feet below the surface. In
some instances this draught is so strong that a lighted candle held near
contracted openings leading to the caves is extinguished.

Depth to which the cave formation extends—F yom the foregoing, it appears that
the cave formation in general does not extend to any very considerable
depth and that its limit in Eureka is probably reached within a thousand
feet. If the theory of a simple crystallization of minerals from solutions
in pre-existing caves were correct, it is evident that the practical limit of
ore deposition would be reached at the point where cave formation was no
longer possible. This would naturally be the point where the carbonic
acid solution, being saturated, ceased to dissolve limestone. In Eureka,
the limit of the cave formation is probably reached in less than a thousand
feet, or before the water level” is attained, as in the Richmond ground
between the 7th and 9th levels there are several partially open fissures.
which, although they show that considerable water has passed through
them, nevertheless do not exhibit anything like the same amount of corro-
sive action which is everywhere apparent in the upper caves. ‘The struct-

« In speaking of the water level, reference is had to the mines of Ruby Hill, those of Prospect
Mountain not yet having reached that depth.

MANNER OF DEPOSITION. 97

ure of the fissures is plainly visible, and the bowlders in these are angular,
showing that they have not been much attacked by water.

Arrangement of the ore in the chambers. —During the investigation of the Eureka
deposits, upon which this report is based, several favorable opportunities
were offered for examining freshly-discovered ore bodies of considerable
size. In two of these cases the ore was discovered by following seams
stained with ferric oxide. The two places mentioned were above the ninth
level of the Eureka and below the sixth level of the Richmond. The ore
was struck in both instances considerably below the caves which formed
the apices of the chambers. The ore in the lower part of the chambers, if
not in what could be called a solid state, was at least in a much more com-
pact form than it was in their upper portions. It had the appearance of
being in place, that is to say, that of being in the position which it originally
occupied when deposited from solutions. With the ore composing the
upper portion of these ore bodies it was otherwise; this was in a loose state
and often distinctly stratified, the strata being composed of different varieties
of ore. There was frequently a layer of gray carbonate of lead, followed
by a yellow one composed of a mixture of ferric oxide and plumbic sul-
phate, with here and there, through the whole, bunches of galena surrounded
by its products of decomposition.

In the Richmond ore body a small cavity in the ore-mass was observed
containing stalactitic columns of minerals, which were evidently formed by
crystallization from solutions. The layers of ore were covered by layers of
sand and gravel and bowlders which formed the bottom of the caves. The
whole upper portion of this mass showed clearly that it was brought into
its present position by water, and the stratification of the ore proved that
it was deposited in its present position since oxidation took place. There
were layers of the miners’ yellow carbonate, composed of every shade of
yellow and brown, which, although some of them were not a sixteenth of
an inch thick, were as distinctly defined and as clearly visible to the eye
as any layers would be in a piece of shale of unquestioned sedimentary
origin. The planes of stratification were rarely horizontal, and this was
not remarkable, as a large mass of loose ore in a cave of irregular shape

and with inclined sides would not settle in a uniform manner, and the strata
2654 L——7

98 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

would be more or less bent. Moreover, water carrying fine particles of
ore in suspension, trickling slowly down over an irregularly-inclined sur-
face, would not deposit the particles in horizontal layers, but in layers con-
forming more or less to the inclination of the bed in which it flowed. This
stratification is common enough in the upper part of ore bodies, and is occa-
sionally met with in the lower portion, though it is, of course, most apparent
when the strata have been least disturbed by pressure. It is not meant
that the ore throughout these chambers had a stratified appearance; on the
contrary, the different ore-minerals seemed to be mixed throughout the
mass without reference to any law of distribution. It sometimes appears
as if there were more unaltered galena in the lower portions of ore bodies
than in the upper, but the difference, if any exists, is so slight that it is not
of much importance. In large ore bodies the ore is much more compact
at the bottom than at the top, which may be accounted for by the difference
of pressure. The limestone surrounding ore chambers is frequently stained
with iron. This seems to be less common in the upper part of the caves
than it is lower down. The staining of the limestone is often observed
where seams are found leading to ore bodies or where separate masses are
connected together, as is often the case, by small pipes.

Evidences in the ore of pseudomorphism after limestone. —In many of the ore bodies which
have been discovered strong evidence has been found that a portion of the
ore is pseudomorphous after limestone, or, in other words, that it has been
substituted for that rock. A mass of ore sometimes contains a rounded
bowlder of limestone as a nucleus; a great deal of the ore, when it has not
been stratified or pressed into a compact mass, exhibits the form of crushed
and brecciated limestone. Small masses of ore sometimes completely fill
the spaces between the limestone walls; are perfectly solid, and show clearly
that they have not been disturbed since they were deposited. If these
deposits had been formed by the crystallization of minerals from solution
they would have exhibited, notwithstanding their oxidation, the banded
structure which is everywhere supposed to be an accompaniment of this
manner of deposition. Although the deposits first described are oxidized
to a great extent, the change in their chemical nature would not have been
sufficient to obliterate all traces of structure from their mass. Pseudo-

MANNER OF DEPOSITION. 99

morphs of galena after calcite have been observed at Andreasberg and in
other mines. Had they been found at Eureka, it is scarcely probable that
they would have remained recognizable, in view of the subsequent oxida-
tion of the ore. It is probable, however, that calcite crystals were not
formed until after the period of ore deposition, and it is, therefore, in no
way remarkable that the search for pseudomorphs after calcite was unsuc-
cessful.

Relation of the rhyolite eruption and the caves to the formation of or.— The disturbance inci-
dent to the rhyolite eruption caused the faulting and crushing which pre-
pared the limestone for the circulation of the metal-bearing fluids. It is
not likely that the waters carrying carbonic acid had effected any material
dissolution of the limestone before an opportunity was given for their free
circulation by the shattered condition of the country. If the deposition of
ore is correctly referred to solfataric action consequent upon the rhyolite
eruption, the precipitation of the sulphurets may have begun immediately
after the outburst of voleanic rock and before a sufficient period had elapsed
to allow of the formation of caves. Besides the caves above ore bodies,
there are many cavernous openings in the limestone in which no ore occurs;
but some of these empty caves, as has been mentioned, are connected by
open fissures or pipes with ore bodies. Had these caves existed at the time
of the deposition of ore, it is difficult to see why they failed to receive a
share of the deposits. Although this is not absolute proof that these caves
were made after the ore was deposited, it is entirely consistent with such a
theory.

If the caves had been formed first, they certainly would have contained
gravel, bowlders, etc., washed in by water or representing insoluble residues,
and this material would have been found underlying the ore. This, how-
ever, is not the case; the ore is very free from admixtures of foreign sub-
stances, and wherever this detritus is found, it either overlies the ore or
occupies a position adjacent to it, consistent with the hypothesis of subse-
quent placement. If the caves were not formed after the deposition of the
ore, they must necessarily have been enlarged during the oxidation of the sul-
phurets, for this can have been sustained only by supplies of oxygen carried
by water from the surface. This water must have held carbonic acid in

100 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

solution and must have attacked the limestone. It is true that in many caves
the ore has the appearance of having been placed in the cup-shaped cavities
which are so common and which were evidently formed before the ore came
into them; but it must be remembered that much of the ore, especially in
the upper part of the caves, has been brought into its present position by
water.

Partially formed caves and ore chambers——In a portion of the ground already de-
scribed, between the seventh and ninth levels of the Richmond mine, there
is a great deal of open country; there are no caves, however, and it does
not often show signs of the action of surface waters. The ground is shattered
and there are large fissures which are filled for the most part with bowlders
and fragments which have fallen into them. Around some of these bowlders
ferric oxide and ore are found, but these masses are not of any great
size. Some of the fragments are rounded off as if ore had been substituted
for their exterior parts, and the whole mass presents the appearance of an
ore chamber, the formation of which had been interrupted. From the
seventh level a distinct ore channel can be traced up to the west ore body
as well as downward to the ninth level.

Effects of oxidation on the bulk of the ore bodies —T he chemical reactions which took
place when the ore was substituted for the limestone are unknown, but from
observations made in small masses of oxidized ore resulting from the decom-
position of sulphurets, that were evidently formed by substitution, it would
seem that the ore replaced the limestone very nearly bulk for bulk; that is
to say, very nearly though not quite filled the space originally occupied by
the limestone. In the masses referred to there were no signs of the vigorous
action of water carrying carbonic acid, and the walls were compact; there-
fore it is not likely that these bodies had been disturbed since the ore was
deposited as sulphurets, and it is probable the slight shrinkage of the masses
was due to oxidation. In the large chambers, where there is a cave directly
over the ore body, the size of this cave has usually, but not invariably,
borne a direct relation to the size of the ore body, a large cave being fol-
lowed by a large mass of ore. This would indicate that the cave owed its
origin in a measure to the shrinkage of the ore. Whether the ore shrinks
or expands in oxidizing is a point which depends upon its composition.

MANNER OF DEPOSITION. 101

Were the ore composed entirely of pyrite it would shrink on oxidizing.
Although the hydrated oxide of iron occupies molecule for molecule more
space than the pyrite, yet the quantity of iron left in place after the oxida-
tion of a mass of pyrite is not equal to the amount of that metal that the
pyrite originally contained, owing to the fact that in the process of oxidation
soluble salts are formed which are carried off. To the action of such soluble
salts is no doubt due the staining of the limestone with ferric oxide in the
neighborhood of ore bodies. On the other hand, if the ore were composed
entirely of galena it would increase in bulk when changed into carbonate,
though the carbonate of lead is to some extent soluble in waters carrying
carbonic acid.

Observations made in a mass of pyrite——F'rom what has been observed of a mass of
pyrite containing’ but a little blende and galena on the eleventh level of the
Eureka mine, it would appear that oxidation is followed by a slight shrink-
age of the ore body. This body of mineral is a compact mass which seems,
as far as explorations have developed it, to touch the limestone everywhere
throughout its surface. The pyrite, however, is separated from the lime-
stone by a coating of ferric oxide nearly a foot thick. The ferric oxide
contains grains and rounded fragments of limestone, and by its structure
shows that the pyrite from which it was derived was brought into place by
substitution. Pseudomorphs of pyrite after calcite are well known, although
no specimens have been observed in Eureka; pseudomorphs of pyrite after
fragments of limestone, however, are often found on Ruby Hill. The ferric
oxide is also much more porous and less compact than the pyrite. A shrink-
age of the mass took place upon the leaching which followed oxidation.

Evidences of the contraction of ore bodies since oxidation —As pyrite originally composed
more than half the volume of the ore bodies, it is highly probable that a
considerable contraction has taken place in their mass since oxidation began.
Supposing such a decrease of volume to have been brought about by oxid-
ation, an opening would be produced above the ore body proportioned to its
size, as the ore becoming porous would naturally settle by its own weight.
Add to this the action of surface waters carrying carbonic acid, which
would enlarge these cavities and to some extent redistribute the ore, and a
condition of things is brought about precisely similar to that which at

102 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

present exists in the large ore chambers. In the unchanged ore bodies,
which are encountered occasionally near the water, there is nowhere any
evidence of the banded structure characteristic of the simple crystallization
of minerals from solution. The galena, blende, and pyrite of which these
ore masses are principally composed are distributed in bunches and compact
masses, and nowhere is there any evidence of paragenetic order. It is true
that a paragenesis of minerals is traceable in many places in the oxidized
ore, but this is due to successive stages of decomposition.

Description of the Raibl deposits —Attention has been already called (Chapter
VI.) to Raibl, in Carinthia, where galena and zinc deposits occur in a
limestone formation. PoSepny,* who very fully describes these deposits,
mentions the following facts: The galena deposits occur principally in the
dolomite, and the zine deposits in the underlying limestone. They are to
be classed neither as beds nor as lodes. As to the genesis of the ore, they
differ very widely; the galena deposits were made in pre-existing cavities
in the dolomite, while the zine ore is pseudomorphous after limestone, or, in
other words, was brought into its present position by substitution for coun-
try rock. The proofs this author gives of the manner of formation of the
lead deposits are very conclusive. The ore, which consists principally of
galena, blende, pyrite, and dolomite (cerussite, smithsonite, calcite, and
barite being comparatively uncommon), is deposited in concentric layers,
the cavities being sometimes completely filled, though often an empty space
is found at the center, and hardly admit of a doubt in regard to their being
formed by crystallization from solutions. The occurrence of a peculiar
tubular galena ore (Réhrenerz), which was formed around pre-existing
stalactites of dolomite, effectually establishes the fact that the cavities existed
before the ore-bearing solutions made their appearance. As regards the
manner of their formation, the zinc deposits are widely different from those
of lead. The ores composing them are zinc bloom, smithsonite, calamine,
and mixtures of these minerals with manganese and iron oxides, different

kinds of iron ores, and peculiar clays. The calamine is seldom found

2F. Posepny. Die Blei- und Galmei-Erzlagerstiitten von Raibl in Kiirnten. Jahrb. der k. k.
geologischen, Reichsanstalt. Wien, 1873, B. xxiii.

MANNER OF DEPOSITION. 103

except in the dolomite, and the smithsonite is the principal zinc ore in the
limestone.

Posepny's conclusions.— It is not necessary to give a detailed description of
the specimens of zine ore from which Posepny concludes that these de-
posits are pseudormorphs after limestone. Suffice it to say that the zine
minerals have very often precisely the same structure as the original lime-
stone, and that many pieces have been found in which the thin veins of
calcite in that rock are continued in the form of smithsonite in the adjoin-
ing zinc ore. In some few places in the mineral zone the galena-blende
deposits have undergone decomposition, and galena, blende, and calamine
are found together. Posepny gives the priority of formation to the
galena-blende deposits, as at some points where decomposition has taken
place and a portion of the ore has been removed part of the space has
been filled with calamine. He further says that the calamine is probably
the product of the decomposition of the blende, and that the zine deposits
themselves were formed by the substitution of zine carbonate for calcium
carbonate. From the fact that the galena-blende and the zine deposits in
Raibl are formed each in a different manner, this author regards it as prob-
able that in the regions of Upper Silesia, Belgium, and Sardinia, where
these two kinds of ore occur in the same deposits, they owe their origin to
the same different causes which brought about their deposition in Raibl.

Comparison of Raibl and Eureka —A]though the Hureka ores do not contain a
very large amount of zinc, either as blende, calamine, or smithsonite, yet
numerous specimens of calamine have been found in the oxidized ores which
exactly correspond with the pseudomorphs after limestone which Posepny
describes, and which were evidently formed directly or indirectly by sub-
stitution for limestone. Whether the zinc was originally substituted for
the limestone as blende, and afterwards oxidized to calamine, or whether it
was oxidized first and in the form of a solution attacked the limestone, is
uncertain, but it is probable that it was deposited as silicate from a solution,
as examples of other secondary minerals in the form of stalactites and sta-
lagmites are not uncommon in druses in the oxidized ore bodies. The infer-
ences which Posepny draws regarding the deposits of Upper Silesia, ete.,
from those of Raibl, are certainly not applicable to the Eureka ores.

104 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

The internal structure of the ore masses in no way resembles those of Raibl.
Where the ore is not oxidized there are no signs of a banded or concentric
structure, and the phenomena observed point entirely to substitution of the
sulphurets for country rock.

Some of the ore bodies formed by substitution — The unoxidized ore haties have not
yet been sufficiently explored to establish the fact that they were formed in
toto by substitution, but sufficient evidence has been obtained to prove that
a considerable portion of the ore at least was deposited in this manner.
In the cases of the Upper Mississippi, and those of Missouri, the galena is
found in the form of stalactites and stalagmites, which proves the pre-
existence of the openings, but in Eureka no such case has been noted. _

Evidence against the substitution theory— here is one argument to be advanced
against the theory that the ore bodies were formed exclusively by substitu-
tion, namely, that some of the ore chambers are far removed from what
seems to have been their most natural course. It has been remarked that
in the mines southeast of the ‘‘compromise line” the ore bodies are of rare
occurrence near the Ruby Hill fault-fissure, except when the two fissures
approach in the deeper workings. The ground in the neighborhood of this
fault presents all the conditions necessary to the fulfillment of the phe-
nomena of substitution; it is crushed, shattered, and broken in various
ways, and is traversed by cross-fissures. The lines on which ore is found
gradually approach the quartzite foot wall, and correspond almost exactly
with what would have been the natural channels of surface-waters descend-
ing through fissures. If the caves were not formed before the ore, why did
the ore solutions not follow other channels apparently offering equal facili-
ties for the substitution of ore? No satisfactory answer has been found for
this question, but it is manifest that mine-workings, however extensive,
never fully expose the system of underground fissures, and it is entirely
possible that a barrier to the passage of solutions in this direction existed
which has not been brought to light. Even had ore been deposited only in
pre-existing openings, traces of lead minerals should have been precipitated
in the interstices of this broken ground if it was accessible to metalliferous
solutions, but none such could be discovered.

MANNER OF DEPOSITION. 105

Preponderance of evidence in favor of the substitution theory— Weighing the evidence on
both sides of the question, it appears that a large part of the ore was
brought into its present position by substitution, while it seems impossible
to demonstrate that any part of it was deposited in pre-existing caves. It
is highly probable that all the ore was deposited by substitution, and that
future developments will effectually establish the fact. There is no reason
for believing that, if the physical conditions favorable to the deposition
continue below the water level, deposits of ore will cease to be found below
that point.

Age of the ore—In the Ruby-Dunderburg mine, on Prospect Mountain,
there is a rhyolite dike similar to that of the Jackson and Phenix. In all
of these mines ore has been found in contact with and below the rhyolite
in the limestone, but has never been found on the opposite side of it. This
fact alone would not necessarily prove that the dike is older than the ore
bodies, for these might occupy their present relation to it in consequence
of a fault; but the manner in which the ore is deposited on the rhyolite,
showing no signs of having been disturbed, and the fact that the rhyolite
does not in any place contain inclosed fragments of ore, though it often
contains country rock, go to prove that the eruption occurred before the
deposition of the ore and that it did not fault the ore bodies. Another
fact tending to prove the subsequent formation of the ore is the extreme
decomposition of the rhyolite through the ore-bearing region, which was
no doubt brought about by chemical action attending the deposition of ore.

Although it has not been established beyond doubt that the rhyolite
eruption caused the upheaval which made the main fault on Ruby Hill, yet
it is extremely probable that such was the case. It has been shown that
this fault was the last dynamic disturbance of any importance that occurred
in this region, and nothing is more natural than to connect it with the latest
volcanic outburst in its neighborhood. If the Ruby Hill fault was formed
by the rhyolite eruption it is likely that the rhyolite was injected into it at
the time of its occurrence. The ore solutions seem to have entered the
limestone through the main fissure after its formation and not simultaneously
with it. And it may be inferred that the ore solutions owe their genesis to
the solfataric action following the ejection of that eruptive rock. As the

106 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

‘rhyolite eruption covered a considerable period it is not improbable that
there have been overflows of that rock since the beginning of the ore
deposition at some point in the district. As the rhyolite eruption occurred
in the Tertiary it follows that the ore formation was not of an earlier date.
The solfatarie action to which this region was once subjected has long
since spent itself, and there is nothing to indicate that the increment of heat

is abnormal.

Ci Ag PAT i RS TX:
WATER.

Water in Prospect Mountain —T'he deepest shaft on Prospect Mountain, the
Atlas, the working shaft of the Ruby-Dunderburg Company, has attained
a depth of over 800 feet, and up to that depth but little water has been
encountered. In the other mines in this part of the district no water of
any consequence has been met with, and from the great altitude of many
of them above the valley no trouble on account of water need be expected
for some time to come.

Water in Ruby Hill—QOn Ruby Hill, the water question is becoming a very
important one, and in the future the difficulty of draining the mines may
prove a serious impediment to exploration. The water now stands just
below the 1,050-foot level in the Richmond shaft, but in the old workings
of the Eureka it rose to the twelfth level, 220 feet above this point, before
the cross-cut from the 1,200-foot level of the Locan shaft cut the Ruby
Hill fissure. The surplus water from the twelfth level of the Eureka flowed
down a winze to the Richmond ninth, and finally reached a permanent level
at. about 1,050 feet. A reference to the water line on Plate III. shows that
the water level in the mines on Ruby Hillis highest at the southeast end
or where the limestone wedge is the smallest, and that it gradually declines
until, in the Richmond ground, where the limestone is the widest, it stands
in the Richmond shaft at a point 650 feet below the water level in the
incline of the Pheenix. It will thus be seen that the water from the south-
east end of the mineral belt gradually finds its way into the Richmond;
that is to say, that it has a tendency to flow in that direction, though owing
to the fact that the workings of the mines are not everywhere connected

in the lower levels the water does not follow an uninterrupted course.
; (107)

108 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

This is not surprising when the nature of the ground is taken into account.
The two fissures, which are everywhere accompanied by a thick casing
of clay, meet at a point much nearer the surface in the Pheenix, the line
of junction gradually descending as the Albion is approached. This line
of junction corresponds very nearly with the water level, showing that the
closing in of the two fissures forms a sort of flat funnel which debouches
in the Richmond mine. The water level in this mine is something below
the level of Diamond Valley, where the Eureka Canon enters it. It has
already been mentioned that there is a considerable zone of fissured ground
in the lower levels of the Richmond. This broken ground naturally per-
mits a tolerably free circulation of the water, and as the water level in this
mine is about what it would be in the upper part of Diamond Valley it is
reasonable to suppose that a permanent water level has been reached in
the Richmond. Irregularities in the distribution of water are often brought
about by the intervention of blocks of unfissured ground, or by the pres-
ence of clay seams. An illustration of this was given by the occurrences
observed in a drift from the 1,200-foot level of the Richmond shaft. This
shaft was comparatively dry down to a depth of 1,230 feet. The last 500
feet were sunk in quartzite. At 1,200 feet a cross-cut was started through
this rock to the north. No water that could not be easily handled with
bailing tanks was encountered, and when the limestone was penetrated it
was found to be nearly dry, the water from the quartzite being excluded
by the clay. In driving a short drift to the northeast from the main cross-
cut, however, a stream of water was struck which became unmanageable
without the aid of pumps, and it rose to near the 1,050-foot level, and at
this point it has remained, notwithstanding the large flow of water that
there has been from the Eureka mine. This Eureka water, however, did
not flow down the shaft, but into a winze which was sunk on what appears
to be the fissure of the Ruby Hill fault. The ground near this fissure is
much shattered, and the disappearance of the water goes to prove that this
condition continues to some depth.

Water in the Locan shaft—-In the Locan shaft, which has now attained a
depth of over 1,200 feet, it had always been possible to control the water,
which was first encountered at a depth of 700 feet, with the hoisting

WATER. 109

machinery with which the shaft was equipped even while sinking to the
84(-foot level. When this level was reached a cross-cut was driven to the
old workings with which connection was made just above the twelfth level,
a little over 1,000 feet below the top of the Lawton shaft. The water from
the Locan shaft was allowed to flow along this cross-cut and enter the
twelfth level, where, joining with the other water on that level, it was con-
ducted to the ‘‘water winze” on the Richmond ninth.

Shortly before this report was finished, pumping machinery having a
capacity of 600 gallons per minute was completed at the Locan shaft and
sinking was continued. Stratified limestone and shale were struck at a
depth of 1,020 feet. The stratification of this bed was nearly horizontal,
and at a depth of over 1,200 feet the shaft had not penetrated it. A south-
west cross-cut was run from the 1,200-foot station to the main fissure, a
distance of 300 feet. The first 60 feet were in shale and the rest in a mass
of limestone mixed with clay, which is the product of the Ruby Hill fault.
The fault fissure contained ore, and when it was cut by the drift a body
of water was developed which soon filled the cross-cut in spite of the pump.
The flow of water was so sudden that the men had barely time to escape
from the drift. It rose to a height of 1,035 feet in the shaft (about 50 feet
above the water level in the Richmond), and up to the present time (Decem-
ber, 1883) it has not been possible to materially lower it.

The flow of water from the shale was not as great as from the lime-
stone above it, the shale acting as a barrier. It will be observed that
before the large body of water was struck in the end of the cross-cut from
the 1,200-foot level of the Locan shaft, the water rose in the shaft to the
840-foot level, and ran into the twelfth level of the old workings, but after
the fissure was cut it only rose to 1,035 feet, or about the upper surface of
the shale. The fact that the tapping of the main fissure partially drained the
twelfth and thirteenth levels, shows that there was a water channel between
these levels and the point at which the vein was cut on the 1,200-foot level
of the Locan shaft, and as this water, as well as that which drained into the
shaft from the limestone overlying the shale, would not rise higher than
1,035 feet, a level which is but a few feet higher than the water level in
the Richmond, it would appear that there was a water channel also along

110 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

the main fissure between the place where the vein was struck in the 1,200-
foot Locan cross-cut and the Richmond ground. This is made all the more
probable by the fact that although the Richmond received the water of the
Eureka in the manner mentioned on page 51, yet the water level in the
‘water winze” of the former mine was not materially altered.

Prospects of water in the future——A though this flow of water has not been con-
trolled by the present pumping machinery, it is unlikely that it is of such
an extent that more powerful pumps would not exhaust it. It must be
borne in mind that the lower belt of shale cannot but act, partially at any
rate, as a barrier to the flow of water from the upper limestone, and, there-
fore, it is but reasonable to expect that the flow of water in the lower lime-
stone will not be uncontrollable. This has been indicated in a measure by
the fact that the limestone encountered in the cross-cut on the 1,200-foot.
level of the Richmond was at first nearly dry, and the water that was after-
wards struck on the same level was not present in such quantity that a pump
like the one at the Locan shaft would not easily have managed it. It is
very likely that the contact of the quartzite and limestone will be the
principal source of the water, and for that reason it is to be avoided as
much as possible.

CebiAOP Tab xX.

DO THE RUBY HILL DEPOSITS FORM A LODE?

Difference of scientific opinions on this subject——Qn this subject there appears to have
been a great difference of opinion. In the celebrated lawsuit between the
Eureka and Richmond mining companies, which was argued before Justice

Field, of the United States Supreme Court, Judge Sawyer, of the ninth

United States circuit, and Judge Hillyer, for the district of Nevada, in
July, 1877, a large amount of expert testimony was offered by both parties.
Messrs. T. Sterry Hunt, W.S. Keyes, R. W. Raymond, T. J. Reid, and I. E.
James testified in favor of the Eureka that in their opinion the zone of
limestone included between the quartzite and the shale® was a lode in the
miner’s sense of the term; whereas Messrs. Clarence King, J. D. Hague,
J. D. Whitney, William Ashburner, and N. Wescoatt declared it as their
opinion that neither from a practical nor a scientific point of view could the
above mentioned belt of limestone be regarded as a lode, and denied the
existence of a stratum of shale in the position mentioned by the other ex-
perts.

Causes leading to the suit—The Richmond company had been following down
a body of ore which had been developed in the Richmond and Tip-Top
inclines and terminated in the Potts chamber, which lay partly in the ground
claimed by both companies. The so-called ‘compromise line” had been
established, after a former trial, as a boundary between the properties of
the two companies, and it was the prolongation of this line, or rather of a

«This shale was variously referred to by the Eureka experts as clay and shale. In the Eureka
ground the clay was supposed to be a thin belt of shale which had been flattened out by pressure and
decomposed. By some it was believed to be a continuation of the same body of shale which existed
on the surface and below in the Richmond mine. It is, in reality, a rhyolite dike in the Jackson and
Phenix.

(111)

112 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

perpendicular plane passing through this line, that the Eureka company
claimed as the limit of their ground. In order to establish their claim it
was necessary that the Eureka should prove that they possessed a lode, or,
at any rate, a mineralized zone within the meaning of the United States
mining laws. The Richmond company, on the other hand, claimed the
whole of the Potts chamber, inasmuch as they had a sight to follow their
body of ore, as developed in the Richmond, as it passed into the Eureka
claim beyond the extreme northeasterly point of the compromise line as it
was originally established. This body of ore, which was continuous, or
very nearly so, from the surface down to the deepest workings of the mine
(at that time about the ninth level), followed a fissure or system of fissures
for nearly the whole distance. Sometimes the ore was found on the lower
side of the fissure planes, sometimes on the upper, the fissures frequently
expanding into an ore body. The course of the fissures was about N. 45° W.
On the other hand, the Eureka company followed an ore body lying on the
quartzite from some distance above the end of the fifth level down to below
the seventh. From this point ore was traced to the body at the end of the
ninth level which connected with the Potts chamber.

There was considerable difference of testimony in regard to the con-
tinuity of the ore-connection between the Eureka seventh and ninth levels.
In some places it consisted of iron,oxide carrying but a small amount of
gold and silver, which was found along the quartzite.

In view of the existence of a secondary fissure between the quartzite
and limestone, which the investigations forming the subject of this report
have proved, this ore-connection was a valid one. The Eureka and Rich-
mond, therefore, each established the existence of a lode leading into the
Potts chamber from their respective claims. The former claimed that their
lode extended from the quartzite to what they called the shale (the clay of
the Ruby Hill fault or main fissure), and the latter that their lode was
wholly in limestone and had noonnection with either quartzite or shale.

Decision of Judge Field. —The court decided that the belt of limestone between
the quartzite and shale (as understood by the Eureka people) constituted a
lode in the sense of the law of 1872 and the usage of miners, and that,
therefore, the portion of the Potts chamber situated southeast of the exten-

THE LODE QUESTION. 1315;

sion of the compromise line belonged to the Eureka company, as a vertical
plane passing through the compromise line, and its extension was, by virtue
of the agreement between the two parties, the boundary of their individual
rights; moreover, that the Richmond company could not follow the ore
outside of a vertical plane passing through their end line.

Decision of the United States Supreme Court—T'he case was carried to the United
States Supreme Court, on appeal, and the decision of the lower court was
sustained by Chief Justice Waite, upon the ground that the agreement
effected between the two parties in 1873 gave all ground situated on the
northwest side of a vertical plane passing through the compromise line to
the Richmond company and all that lying to the southeast of this plane to
the Eureka company, and that the conditions under which this compromise
was made necessitated the prolongation of this plane across the mineral
zone. Chief Justice Waite did not state whether, in his opinion, this min-
eral zone between the quartzite and shale or clay constituted a lode or not.
Summary of the physical characteristics of the mineral zone.— Beginning at the extreme
southeastern corner of the plan of contacts (Plate III.), a belt of limestone
is visible which Mr. Arnold Hague has determined as Cambrian, and to
which he has given the name of Prospect Mountain limestone. ‘This lime-
-stone extends in a northwesterly direction nearly to the Albion shaft; is
bounded on the southwest by a mass of quartzite, also Cambrian, and on
the northeast by a belt of stratified limestone and shale belonging to the
same period. These three formations, which all dip to the northeast, were
originally laid down one upon the other at the bottom of the sea and
afterwards raised above water at the close of the Carboniferous. At some
period subsequent to their upheaval and prior to the deposition of ore, a
deep and extensive fissure and fault cut through these formations. Its
course was about northwest and its dip about 70° to the northeast. For
the present purpose, it can be taken as extending from one end of the plan
of contacts to the other. It can be seen near the surface southwest of
the American shaft, in the Jackson, Bell-shaft and Utah tunnels, and in
a short incline beyond the Richmond mine office, and may be visible in
other places. It no doubt could be traced for the whole distance exposed
on the map if trouble were taken to remove the débris from the rock in

place. This fissure is exposed in numerous places underground and its inter-
2654 L——8

114 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

section with the quartzite is laid bare in the deeper workings of all the
mines except the Richmond and Albion. It is accompanied by an auxiliary
fissure between quartzite and limestone which joins it below.

Conditions below the junction of the two fissures. — Where the two fissures come to-
gether in all the mines southeast of the compromise line the ore has been
found filling the fissure between the quartzite and the limestone, or between
the quartzite and the lower belt of shale. Whether this will continue to be
the case as the fissure is followed downward is a matter of speculation. It
is likely, however, that when the lower wedge of limestone widens out the
ore bodies will take on their usual irregular character, although they will
be no doubt in some way connected with the fissure to which they owe
their origin.

Conditions northwest of the compromise line he change which takes place in the
Richmond ground soon after the compromise line is passed has been fully
explained. The two ore chutes, called, respectively, the west ore body
and the east ore body, have the complexion of two distinct lodes in lime-
stone. Whether the Potts chamber, which forms a part of the east ore
body, actually touched the quartzite or not is uncertain, but, at any rate,
it was within a few feet of it. This ore body, however, does not approach
the quartzite in any other place. The west ore body touches the quartzite
in the Eureka ground near the compromise line, but in all other parts of
the mine occupies a position about midway between the secondary fissure
on the quartzite, and the main Ruby Hill fault to the northeast. As these
two fissures are gradually coming together, and, no doubt, meet at greater
depth, it is evident that if these two ore chutes continue down they will
eventually form the filling between the two fissures. From the present
appearance of the ground it would seem as if the ore-channel which fed
the east ore body was near the compromise line, and that it was on the
main fissure which is exposed in the winzes from the seventh, eighth, and
ninth levels of the Richmond near that line; and that the source of the ore
of the west ore body was the system of fissures which branch out from
small ore bodies, extending from the sixth to the ninth levels near the A C
line. ‘The fact must not be overlooked that there is a connection between
these two ore chutes along the quartzite in the Eureka ground; that is to

say, there is a fissure with ore in it here and there. It is, however, impos-

THE LODE QUESTION. PES

sible to state with certainty what the original ore channels may have been.
No doubt many cracks, fissures, and vents through which the ore-bearing
solutions passed have been completely closed since the ore was deposited,
and it is likely that in many such openings the ore has left very little trace of
its passage. When the openings were small, these solutions would naturally
pass with considerable velocity, and little or no ore would be precipitated.

The immense pressure of the surrounding rock would be sufficient to
completely close many ore channels. The ore that has been exposed in the
Albion mine is a continuation of the Richmond west ore body, and nearly
the same conditions prevail in this part of the hill as in the Richmond.

Discussion of the meaning of the words “lode,” “horse,” ete.—In a word, the main fissure
and the secondary fissure branching from it inclose between them amass
of limestone which is penetrated in many places by crevices. The ore
bodies occur within the limestone mass and are all connected with the fissure
system just described. The ore bodies are usually lenticular or irregular in
form, but sometimes follow the fissures as tabular masses. What name is
to be given to this occurrence, though no doubt important from a legal
point of view, is a verbal rather than a scientific question. There are por-
tions of it to which no one has hesitated to apply the name of lode or vein.

In the usage of English-speaking miners the terms vein and lode are
nearly but not quite synonymous. <A vein may or may not carry ore, for it
is perfectly correct and entirely usual to speak of a vein of calcite or other
barren mineral, a connection in which the word lode could not be applied.
In reference to ore deposits, lode is not used to denote the filling of very
small fissures, for a stringer might be called a vein of small size, but scarcely
alode. It is most often used to indicate the contents of more complex fis-
sures, or as synonymous with composite vein, system of veins, etc., while
the term vein, with qualification, usually refers to the filling of fissures
of a simpler character. Thus in the early days of the Comstock the two
main branches of the deposit were known as the ‘‘east vein” and the ‘west
vein,” while the whole system was called the Comstogk lode. So, too,
Henwood says:* ‘The wider parts of lodes rarely consist of veinstone only,
but inclose also blocks of the adjoining (country), and thus assume a brec-
ciated structure. Their widest portions often (take horse) split, but such
separate veins are seldom rich.”

*Metalliferous Deposits, p. 84.

116 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

As there is an unquestionable connection in depth between the various
ore-bearing regions of the Ruby Hill deposits, if this nomenclature is cor-
rect the ore bodies are to be regarded as branches of a single lode. Never-
theless, the fact is that these deposits differ essentially from those which
yielded the usually accepted definition of the words vein and lode, and the
analogies between the two varieties are so distant that an attempt to apply the
terminology of typical veins to the Ruby Hill deposits as a whole leads
immediately to misunderstandings. In ordinary veins ore is deposited in
pre-existing openings, while the bodies of Ruby Hill were mainly deposited
by substitution. In ordinary veins nearly all the space not occupied by
fragments of rock is filled with ore and other minerals. In the Eureka
occurrence many of the fissures have served merely as channels for the
solutions, and space for deposition has been provided mainly by chemical
means. The bearing of those differences is readily made apparent. In
typical lodes a fragment of country rock entirely inclosed within the fissure,
and hence completely and substantially surrounded by ore and gangue
minerals, is called a “horse,” but a mass of rock divided from the surround-
ing country by mere cracks not filled with vein matter is not called a horse.

The term ‘“‘horse” is usually unequivocal and signifies a mass of country
rock of considerable size entirely inclosed in ore or vein matter. One can
always conceive, however, of the croppings of a vein being eroded to the level
of the center of a horse, one surface of which would then be exposed to the
air, and the horse would not be entirely inclosed by ore and gangue.
Masses of rock in the croppings of a lode when they resemble horses in
other respects are therefore known by the same name. No definite limits
can be assigned to the size of a true horse, which certainly depends upon
the size of the lode as well as upon individual opinion. Nevertheless,
although there are horses in the Comstock lode a few hundred feet wide, it
would be a most extraordinary lode that would contain a horse exceeding
1,000 feet in width, and the limestone wedge of Ruby Hill is much wider
than that on the surface. All miners will probably agree that a horse must
be a portion of the contents of a vein or lode.

In the mineral zone of Ruby Hill many masses of rock are surrounded
by fissures, most of which are mere fault seams, though some of them have

THE LODE QUESTION. o17

been no doubt the channels of ore-bearing solutions. These masses in
ordinary veins might have been surrounded by vein matter, but, owing to
the peculiar manner in which ore was deposited in this locality, the sur-
rounding fissures do not often show ore. These masses of rock then take
the place of horses from a structural point of view, but do not answer the
current definition of the term, and a misunderstanding or an error is involved
either in calling them horses or in denying their structural analogy to horses.
If it were once admitted, however, that a mass of rock not substantially
inclosed in ore or secreted gangue minerals may be called a horse whenever
the fissures by which it is divided from the solid country belong to an ore-
bearing system the consequences would be serious, for a horse is always
regarded as a part of the fissure filling, as a portion of the vein or lode, and
the lode would then necessarily be coéxtensive with the fissure system. In
that case the term lode would be synonymous with mining region. The
quicksilver belt of California would be a single lode, as, too, the California
gold belt, and the great Arizona and Utah mineral zones would each repre-
sent a single complex vein.

Classification of ore deposits according to different authors———Such an extended significa-
tion of the words lode and horse would also be wholly at variance with any
system of the classification of ore deposits which has hitherto been adopted,
for these depend to a very great extent upon the external form of ore bodies.
Von Cotta says:* “I divide all ore deposits primarily according to their
form into regular and irregular. The former fall into two groups, beds and
veins; the latter into stocks and impregnations.” In the next paragraph he
says: “A single aggregation of ore may consist of several separate deposits
of different forms.” These passages make it as clear as possible that von
Cotta regarded a substantially regular tabular form as essential to a vein,
and when ore masses of different shapes are so associated as to imply a
simultaneous and common origin he would relegate them to different classes
without regard to the community of origin. Since von Cotta, two eminent
mining geologists, Grimm and von Groddeck, have written important mono-
graphs dealing with the classification of ore deposits. Each has endeavored
to give greater weight to genesis in classification than von Cotta did. The
following table explains the classification of each of these authors:

«Erzlagerstiatten, I., p. 2.

118

SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

VARIOUS CLASSIFICATIONS OF ORE DEPOSITS.

* Von Cotta (1859).

I.—Deposits of regular
form:

1. Beds.
a. Metalliferous strata
and coal.
b. Placers.
2. Veins (giinge?).
a. Ordinary veins (Quer-
gange?>).
b. Bed veins
gangec).
c. Contact veins.
d. Lenticular veins (Len-
ticulargiinge@).

(Lager-

Il.—Deposits of irregular
form:

1. Sharply defined bodies
(stocks ®).
a. Reticulated veins
(Stockwerke/s).
. Contact stocks (Con-
tactstécke).
ce. Cave fillings (Héhlen-

ausfiillungen).
. Butzen. 9
- Racheln.9
f. Rinner.g
. Tascheng (pockets).

aso

. Nester, Niereng (nests,
kidneys), ete.

Grimm (1869).

I.—Ore-bearing strata [de-

posits in which the ore
is an essential constit-
uent of the country
rock]:
1. Original dissemina-
tions.
2. Secondary dissemina-
tions.

a. Placers.
b. Ore-bearing bowlders.

Il.—Separate deposits of
ore [deposits in which
the ore is distinct from
the country rock]:

1. Tabular masses.
a, Beds.
b. Veins.
ce. Segregated zones.
2. Deposits of irregular
form.
a. Bedded masses.
b. Masses independent
of stratification. e
c. Reticulated veins.

Von Groddeck (1879).

I.—Primary deposits:
1. Stratified deposits.

a. Compact ore seams.
b. Seams with dissemi-
nated ore.
e. Ore beds.
| 2. Deposits forming orig-
inal portionsof mas-
sive rocks.
3. Deposits forming the
filling of cavities.

a. Veins: In massive
rocks; in stratified
rocks.

b. Cave fillings.

’ 4. Deposits formed by
metamorphism or
substitution.

| 1I].—Secondary or detrital
deposits.

«The German word Gang comprises the English words lode, vein, and dike.

»Veins which cut the stratification of formations if the country rock is stratified.

¢Veins between the strata of a formation which have been formed since the rock was deposited.
7Similar to gash veins, only not coming to the surface.
«Von Cotta makes a sharp division between ore and country rock a part of the definition of

stock.

are sharply defined, stocks (Sticke).

form to the stratification of the country rock and those that do not.

/Von Cotta remarks that, strictly speaking, reticulated veins should not be classified as de-
posits of irregular form, but as the union of a great number of small veins; in other words, the
included angular fragments are so large, compared with the width of the fissures, that they cannot be

cousidered as horses.

Grimm calls bodies which pass over gradually into the country rock, as well as those which
Von Cotta also divides stocks into two classes—those that con-

Von Cotta uses these terms to describe the local occurrence of various irregular ore bodies.

An examination of this table will show that the term lode as under-
stood by these authors cannot be applied to the wedge of limestone between

THE LODE QUESTION. 119

the quartzite and the Ruby Hill fault. Prof. R. Pumpelly also has pub-
lished, in Johnson’s Encyclopedia, a classification of ore deposits according
to which, however, the ore deposits of Ruby Hill as a whole would be as
far removed from typical veins as in the other systems. Some of the ore
bodies in the limestone wedge are well-defined veins, and when they con-
nect with each other they can be considered as parts of the same lode.

Miners’ definition of lode—Nevertheless, it will be conceded that the miners’
definition of the word lode, however indefinite it may be, has a much more
comprehensive meaning. Dr. Raymond, in his testimony in the Richmond
and Eureka lawsuit,* says: ‘The whole subject of the classification of min-
eral deposits is one in which the interests of the miner have entirely over-
ridden the reasonings of the chemists and geologists. The miners made
the definition first. As used by miners before being defined by any au-
thority it [lode] simply meant that formation by which the miner could be
led or guided. It is an alteration of the word lead; and whatever the
miner could follow, expecting to find ore, was his lode. Some formation,
within which he could find ore and out of which he could not expect to
find ore, was his lode.” The mining law of the United States as interpreted
by the courts also gives a broader signification to the word lode

Necessity of a better classification of ore deposits.— ‘he different definitions of the word
lode have given rise to a great deal of discussion in the courts, and a classifi-
cation of ore deposits which would reconcile the adverse views would tend
to simplify the question for the miner, the lawyer, and the geologist. Mr.
S. F. Emmons,’ while introducing the classifications of Messrs. von Cotta,
Grimm, von Groddeck, and Pumpelly, in his abstract of a report upon
Leadville, Colorado, recognizes the necessity of a more satisfactory classifi-
cation. He says: ‘That the difference of origin and manner of formation
should be a more important factor in the classification of ore deposits than
has been the case hitherto is generally admitted, but, owing to the fact that
the definite determination of such origin requires more laborious and ex-
pensive investigations, especially from a chemical point of view, than geolo-
gists are in general able or willing to make, trustworthy data are as yet too
meager to form a basis for a general classification from this standpoint.”

*Supreme Court of the United States, Nos. 1058 and 1059, p. 210.
>Second Annual Report of the Director of the United States Geological Survey, p. 233.

OH APE P2G:
ASSAYING.

Object of assaying country rock——With a view to discovering, if possible, the
source of the ore in the mines of Eureka District, numerous and careful
assays of all the different kinds of country rock in the neighborhood of the
ore bodies were made by the author. As the quantity of the precious
metals contained in any of these rocks is extremely small, it was necessary
to take unusual precautions in order to determine with any. degree of exact-
itude the amounts of gold and silver present. Assayers do not ordinarily
attempt to estimate with accuracy any values of either gold or silver less. _
than one dollar to the ton (0.0001659 gold or 0.0026518 per cent. silver),
and as the country rock of this district never contains so much as this,
particularly delicate methods were required in the determination of the
actual quantities of these metals.

Difficulty of obtaining pure lead—Qne of the principal obstacles to be overcome
in obtaining satisfactory results in the assaying of all rocks containing very
small percentages of the precious metals, is the difficulty of obtaining a
lead flux which does not contain very appreciable amounts of gold and sil-
ver. The purest litharge which it was possible to obtain from dealers con-
tained from 10 to 50 cents of silver to the ton of 2,000 pounds (0.0002652
to 0.0013259 per cent.), and as it was necessary to use from twice to three
times as much litharge as the weight of the material assayed almost all the
silver obtained from assays of country rock made with such litharge came
from the litharge itself.

Approximately pure litharge required —At first sight it might seem possible to ob-
tain correct results by assaying the litharge separately and deducting its
value in silver from the value of the assayed rock. This is not practicable,

however, for the litharge of commerce is not only argentiferous but of very
(120)

ASSAYING. 121

variable composition, and no mechanical method of mixing is sufficient to
bring about the degree of homogeneity required. The smaller the relation
of the silver in the rock under assay to the silver in the litharge the greater
is the uncertainty arising from the argentiferous character of the flux, and
unless the litharge is nearly pure it is impossible to discriminate between
errors arising from this cause and those due to insufficiency in the time of
melting, imperfect fluidity of the slag, and the like.

Quantity of reducing material necessary— The weight of the lead button is depend-
ent upon the amount of reducing material used in the flux and the amount
of sesquioxides present in the rock, which it is necessary to reduce to pro-
toxides, provided reducing gases be excluded. As there were no other
sesquioxides than that of iron present, and this only in very small quanti-
ties, the weight of the lead button was not materially altered in that way.
For reasons which will be given hereafter, it was found advisable not to
use sufficient reducing matter to exclude all the oxide of lead from the slag.

Relation of the silver to the amount of lead reduced —xperiments made with different
quantities of reducing material upon the same flux showed that part of the
silver in the litharge went into the button of metallic lead, while a part of
it remained in the unreduced litharge in the slag. As might naturally be
supposed, the proportion of silver to lead in the reduced button was always
greater than in the litharge employed. T he proportion of silver to lead
also increased with the time during which the flux was kept melted and
varied with the temperature and perhaps with other circumstances in such
a manner that no law governing the proportions in which the two metals
were reduced could be detected. When rich litharge, or litharge contain-
ing very appreciable amounts of silver, was used, it was therefore impossi-
ple to estimate with any sufficient degree of accuracy the amount of silver
from the litharge which is united with that of the rock in the lead button.
Even when the whole of the litharge is reduced, or as nearly as possible
reduced, it is not likely that all the silver it contained is concentrated in the
lead button, and it is only by using litharge (or any suitable form of lead)
which contains little or no silver that it is possible to render the resulting
error small enough to permit of estimating the probable amount of silver
which the litharge gives up to the lead button.

122 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Different kinds of lead — White lead (carbonate of lead), sugar of lead (acetate
of lead), and the best granulated lead ordinarily contain upwards of ten
cents to the ton (0.000265 per cent.), and although any of them may be
used in assaying rocks containing less than 50 cents to the ton (0.001325
per cent.), yet the results obtained are more or less uncertain, and are not
at all to be relied upon in very poor rocks, such, for instance, as carry
below 10 cents to the ton (0.000265 per cent.). Moreover, the carbonate
- of lead, owing to the carbonic acid it contains, is liable to boil over in the
crucible, though this can be obviated by a previous calcining. A like ob-
jection can be made to the acetate, the acetic acid of which contains more
carbon than is needed to reduce the oxide of lead. If it is used in its
natural state it swells up, and after the acetic acid is decomposed the resid-
ual carbon thickens the slag and prevents the proper settling of the globules
of lead which everywhere permeate the mass. This difficulty, however,
can also be remedied by a previous calcining. Granulated metallic lead,
though otherwise unobjectionable, melts too quickly and unites at once in
a mass at the bottom of the crucible, thereby preventing every particle of
the powdered rock from coming in direct contact with it; and although
such an intimate contact is unnecessary in assaying ordinary ores, it is
found indispensable where the material to be assayed contains such ex-
tremely small quantities of the precious metals as do the ordinary country
rocks of a mining region.

Oxide of lead required in the slag—It. has been remarked that the slag is the better
for the presence of oxide of lead. This is notably the case when the rock
treated is silicious, as in combination with other bases it renders the silicate
formed more fusible and liquid. Litharge seems also to attack quartz more
energetically than even soda or potash. Even in those rocks which con-
tain scarcely anything but carbonate of lime it is found to assist in the
formation of a proper slag.

The process adopted for making litharge—T he litharge used in assaying all the Eu-
reka rocks, as well as those of the Comstock, was made at the refining
works of the Richmond Company in Eureka. The following process was
adopted in manufacturing this litharge. One thousand pounds of market lead
the refined lead obtained from the parting of silver and lead by the Luce &

ASSAYING. 123

Rozan method, containing about $1 to the ton (0.00265 per cent.), was
cupelled on a fresh bone-ash test in an English refining furnace. The
first 300 pounds of litharge resulting from this cupellation ran very poor,
containing scarcely 2 cents to the ton (0.000053 per cent). The litharge
which followed gradually increased in value until toward the last it con-
tained nearly as much as the original lead. This last litharge was reduced by
charcoal in a black-lead crucible, and the resulting lead was again cupelled,
yielding an excellent quality of litharge. Upon reducing and recupelling
the best litharge it was found that the percentage of silver was but little
reduced, showing that a point can be reached in the process of desilveriza-
tion at which it is not practicable to separate the silver from the lead by
cupellation. The refined litharge also contained a trace of gold, but the
quantity was so exceedingly small that it was neglected in the estimation
of gold values in assays of single samples., .

Assaying the litharge—In assaying the litharge itself an interesting phenome-
non was observed. If the litharge was mixed with sufficient charcoal to
effect its reduction and the resulting lead was cupelled, it was found that a
very much smaller quantity of silver was obtained than if the usual flux,
consisting of bicarbonate of soda and bitartrate of potash, was used. ‘To
what imperfection in the process this is due is not clear. The proportional
loss with ordinary litharge is much smaller than with that which contains
extraordinarily little silver.

Experiments—The following experiments illustrating the fact were made
_ in duplicate, in order that the results might be conclusive: (a) 800 grains
litharge were reduced with 600 grains bicarbonate of soda, 200 grains bitar-
trate of potash, and 200 grains borax. Silver resulting from cupellation, 6
cents per ton (0.0U0159 per cent.). (b) 800 grains litharge were reduced with
600 grains bicarbonate of soda and 200 grains, tartrate of potash. Silver
resulting from cupellation, 5 cents (0.0001325 per cent.). (¢) 800 grains
litharge were reduced with 30 grains powdered charcoal and 200 grains
borax. Silver resulting from cupellation, trace. (d) 800 grains litharge
were reduced with 30 grains powdered charcoal. Silver resulting from
cupellation, trace.

124 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Results——F'rom these experiments it will be seen that the largest amount
of silver was obtained from the method employed in (a), and that the addi-
tion of borax increased the quantity of silver where charcoal was not used
as the reducing agent. It is probable that the effect of the borax was
merely a mechanical one, facilitating the settling of the minute particles of
lead by rendering the slag more liquid, and that it had no reducing power
on the silver in whatever form that metal may have been. In all these
assays two hours.were occupied in melting, and the lead buttons were
cupelled at the lowest possible temperature.

Experiments in reducing agents — Several experiments were made to determine the
best reducing agents, and bitartrate of potash was found to give better
results than any other. Upon the application of heat this substance is
decomposed into carbonate of potash and carbon, both of which act ener-
eetically upon the substances to be reduced. Borax in the presence of
strong reducing agents never takes up silver, even when it is used in con-
siderable quantity.

Composition of fux——The following is the composition of the flux used with
377.09 grains of the limestones of Eureka District:

Grains
IDMINEVERS Co ee cnsSzess soaoGh cebens dopensc00dudseece 770
Bicarbonate OL SOda: s.cnsiecec eo cciee sees eso elect ee 580
Bitartrate of potash ... ...-. SOeHAD FIDE A ROCA SBS: 165
ROTA save cicero oe OR ee ee ee ee ee eee 400

With but slight modifications this flux answers for-almost any coun-
try rock.

Weights usea—The weight adopted for the assays of the Eureka rocks, as
well as those of the Comstock made for Mr. G. F. Becker, was 377.09 grains.
Grains were employed instead of grams, as they correspond with the
Oertling assay weights used with the latest improved Becker balance, and
377.09 of them were taken, as the .U2-grain rider then represented 10 cents
to the ton (0.000265) for every division of the balance beam. The values
were calculated in cents to the ton of 2,000 pounds, as is usually the case
on the Pacific slope, but they are also given in percentages.

Time and manner of melting —In order to obtain the maximum results it was.
necessary to melt the assays for nearly two hours. This was accomplished

ASSAYING. 125

in a charcoal draft furnace, which would admit four No. 10 French eruci-
bles at once. The fuel employed was charcoal made from the pinon pine,
and it was scarcely inferior in heating power to coke. The heat was kept
as nearly as possible at a point a little below the melting point of cast iron,
and experience showed that after two hours the silver obtained no longer
increased nor yet perceptibly diminished. With a higher temperature it
may be that the time might be shortened, but taking into consideration the
volatility of silver at high temperatures this expedient cannot be considered
advisable. When the melting was less prolonged the maximum amount of
silver was never obtained; indeed, in a series of careful experiments made
to determine the best time of melting, it was found that some assays which
had been kept at a melting heat too short a time, though thoroughly melted,
yielded less silver than the litharge alone was known to contain.

Cupellation and cupels——The lead buttons were cupelled in a small mufile
furnace, the heat of which could be easily regulated, the fuel employed
being also charcoal. Usually but two cupellations were carried on at one
time and great care was taken to reduce the loss by cupellation to a mini-
mum by keeping the heat at the lowest temperature consistent with the
oxidation of the lead. In order that the heat should be maintained at the
lowest possible point, the cupels used were made from one part of fine
leached wood ashes and two parts of bone ashes. The ashes were those
resulting from the burning of cedar wood, the most available wood con-
taining little silica. The cupels were prepared in the following manner:
The mold was filled with the requisite amount of the moistened mixture
of the two ashes and the mass was pressed into shape by the punch. Then
a coating of dry elutriated bone ash was spread over the top of the cupel,
the punch again inserted and driven home. In this way a cupel was ob-
tained which had great absorbing power, allowed the lead to be cupelled
at an exceedingly low temperature, and because of its smooth surface pre-
vented the small silver button from being engulfed in the coarse material
of which the cupel was composed. ~The button, too, could easily be re-
moved by the point of a knife without retaining any of the bone ashes.

Loss by cupellation— Many experiments with a view to determining the loss
by cupellation have been made by Hambly, Klasek, Plattner, and others;

126 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

but as the conditions attending this loss are dependent upon the quality of
the cupel and the character of the furnace and fire, it is not possible to ac-
cept the results obtained by them as applicable in all cases. Some exper-
iments upon the loss by cupellation were made for this investigation, as
nearly as possible under the same conditions as those existing in the assays
for the determination of small amounts of silver. It was found that when
the temperature was not too high for feather litharge to form and when the
draught was not too great, there was no perceptible loss of silver under .01
grain, which represents $1 to the ton of 2,000 pounds, notwithstanding
that this .01 grain was cupelled with 400 grains of lead. In fact, in most
instances, the button resulting from the cupellation of .01 grain or less of
silver with 400 grains of lead weighed from 0.5 to 10 per cent. more than the
actual amount of chemically pure silver cupelled with the lead. This ex-
cess is owing to the fact that the silver button obtained by cupellation is
never absolutely pure, but always contains from 0.2 to 5 per cent. lead, as
well as fine particles of the cupel. There is always a loss of silver in cu-
pellation, but as this loss rarely exceeds 1 per cent. of the amount of silver
present it can be entirely neglected in rocks containing less than $1 to the
ton (0.00265 per cent.). This loss does not begin to be important until a
value of over $10 to the ton (0 0265 per cent.) is reached. When the con-
tents in silver is less than .01 grain, or less than $1 to the ton of 2,000
pounds, and the amount of lead alloyed with it 400 grains or less, the but-
ton resulting from the cupellation is invariably slightly in excess of the
actual quantity of silver contained in the alloy. With amounts of silver
exceeding .01 grain and lead exceeding 400 grains, up to a point where the
quantity of silver does not exceed .1 grain, the weight of the button does
not vary perceptibly, no matter what may be the quantity of lead (within
reasonable limits) used. At first sight it would appear to be inexplicable
that the quantity of lead did not to a greater extent affect the quantity of
silver obtained, but it must be remembered that the greater part of the loss
by cupellation takes place at the moment of “brightening,” and that this
loss is directly proportional to the quantity of silver present. It is also
true that the greater the quantity of lead to be oxidized the greater is the
loss of silver. But this latter loss is so small in comparison with the former

ASSAYING. 127

that it makes no perceptible difference whether 100 or 1,000 grains of lead
are used with .1 grain of silver. It has been pointed out that the loss of
silver is compensated for in small buttons by the lead retained and it would
seem that this ought to be equally true of large ones, but as a matter of
fact it is not, probably because large buttons remain for a longer time
melted, thereby being more completely cupelled. As the silver contained
in any of the country rocks of Eureka District scarcely ever reached 50
cents to the ton (0.001325 per cent.) the assays can be regarded as unaffected
by any loss in cupellation. An experiment was made to test this inference,
and it was found that there was no perceptible loss in cupelling 50 cents
(.005 grain) of silver with 400 grains of lead at a temperature considerably
above that required for proper cupellation.

Experiments —In regard to the loss by cupellation in general the following
experiments may be of interest as showing the differences in loss at various
points in the muffle.

Nine assays, each containing 5 grains silver and 30 grains lead, were
cupelled and the losses expressed in thousandths of the unit of 5 grains
attending each, with the number of the assay, are shown in the diagram of
the muffle in the position occupied by the corresponding cupel:

Back of muffle.

Fig. 3.—Position of cupels in muffle.

The order 9, 6, 3, 2, 8, 5, 7, 4, 1 represents the order in which the
cupels were withdrawn from the muffle, and therefore the speed at which
the cupellation took place. Nos. 7, 8, and 9 were cupelled at the proper
temperature, but those in the back part of the muffle were too hot. It will

128 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

be observed that Nos. 9, 6, and 3 were finished first, showing that the draft
on that side of the muffle was the strongest. The assay which showed the
least loss was No. 7, which was in a position where the draft was the least
and the temperature the lowest and where the cupellation occupied nearly
the maximum time. The quantity of lead used with these assays was con-
siderably more than was necessary for a proper cupellation. It was used
in order to render the differences in loss as palpable as possible.

Six assays of 5 grains silver with 25 grains lead gave the following
result:

Back of mufile.

Fic. 4.—Position of eupels in mufile,

The order in which they were removed was 6—3-2-5-1-4; 5-1-4 being
finished at about the same moment. Here, also, the draft was greatest on
the right side of the mufile, and No. 4, which occupied the position of No. 7
in the former experiment, exhibited the least loss. The quantity of lead
was still too great for perfect cupellation.

Two assays of 5 grains silver with 15 grains lead, cupelled side by side,
gave a loss of 3.5 and 3.8 thousandths of the unit of 5 grains. This loss
corresponds very nearly with that which Kerl* gives, and it is about as
small as it is possible to render it.

Manner of removing buttons from cupels—As many of the silver buttons obtained
from the assays made of the Eureka rocks were so small that they could
scarcely be discovered by the naked eye, it was found next to impossible to
remove them from the cupel by raising them in pincers. Another method

a Bruno Kerl, Hiittenkunde, IV., p. 35. Leipzig, 1865.

ASSAYING. 129

was therefore resorted to. After they were loosened from the bone ash, the
cupel was tipped up and the buttons were allowed to fall upon a polished
steel anvil. When struck by a polished steel hammer any adhering impuri-
ties were removed and the flattened button was found sticking to the face of
the hammer, from which it could be easily brushed into the scale-pan.

Manner of weighing —In the Becker balance, used in weighing the silver but-
tons, the right arm of the beam is divided into twenty parts. If a rider
weighing .005 grain is used each one of these spaces will represent .001
grain, and if a weight of rock equal to 377.09 grains is used in making the
assays each one of these parts will represent 10 cents to the ton, or 0.0002652
per cent. By placing a card-board scale, on which each one of these parts
is divided into ten, behind the beam and using a magnifying glass in front
of it the position of the rider between any two of the points marked on
the beam can be determined with accuracy up to one-tenth of the space,
which would represent a value of one cent to the ton (0.0000265 per cent.).
When new and in good order the Becker balance is sensitive up to .0001
grain, which represents a value of one cent to the ton. Allowing a differ-
ence of one cent (0.0000265 per cent.) one way or the other, it is safe to say
that buttons can be weighed with almost absolute accuracy up to within
two cents to the ton, or plus or minus one cent. As is well known, Harkort
and afterward Plattner,’ instead of attempting to weigh extremely small but-
tons, measured their diameters between two fine lines converging at a small
angle, which were engraved on an ivory scale. Very small silver buttons are
almost exactly spherical, and the method is therefore not only rational but cal-
culated to give more exact results than weighing, but it requires very delicate
manipulation to place the button so that both lines are exactly tangent to it.
A common microscope with a micrometer eye-piece may be used instead of
Plattner’s scale, and the measurement made both more rapidly and more
accurately. This method also obviates the necessity of removing the but-
tons from the cupel.

Inaccuracies of the results—Admitting that the loss by cupellation is so small
that it can be neglected, and that the method of weighing is correct within
two cents, the other sources of inaccuracy attending the assaying of rock
containing but minute quantities of silver are reduced to two, the imperfect

2Plattner’s Probrikunst. Theodor Richter, p. 35; Leipzig, 1865.
2654 L——9

130 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

reduction of the “pulp” and imperfect determination of the contents of
the litharge. If proper care is taken in melting, most of the silver contained
in the rock can be collected in the lead button. It cannot be expected that
all the silver will be obtained, but what remains in the slag can be reduced
to an almost constant quantity by reproducing in all assays nearly the
same conditions, such as fineness of ‘‘pulp,” length of time of melting,
quantity of flux, etc. Assays of the same rock have been repeated several
times with identically the same results. The quantity of silver produced
after a certain point does not seem to vary perceptibly with the time during
which the assay is kept melted. The second source of inaccuracy is the
more difficult to control, namely, the impossibility of obtaining a flux abso-
lutely free from silver, or of correctly determining the amount of silver in
the button which is derived from that source.

Action of bitartrate of potash on litharge— The quantity of litharge used in assay-
ing Eureka rocks was about 770 grains. To reduce this litharge 165 grains
of bitartrate of potash were added, and the resulting button of lead, when
reducing gases from the fire had been excluded as far as possible, usually
weighed in the neighborhood of 425 grains. Almost all the limestones in
Eureka district carry more or less free carbon.* The quantity of sesquioxide
of iron present was so slight that only a very small portion of the carbon
was absorbed in reducing it to the protoxide (FeO.). Where there was
any quantity of that mineral present in the rock it was necessary to increase
the amount of bitartrate used in order to obtain a lead button of about 425
grains in weight.

Bearing of the silver in the litharge on the results — he silver contained in the 425
grains of lead reduced from the 770 grains of litharge was 6 cents per ton
(0.0001591 per cent.) when the flux itself was assayed. This amount scarcely
ever varied, but frequent check assays were made. When peroxide of iron
or other substances requiring reduction were present the weight of the lead
button was less and the amount of silver it contained was also less. When
other reducing substances were present, such as organic matter in the lime-
stone, the weight of the lead was greater as well as the amount of the silver
resulting from cupellation. This increase or decrease in the amount of silver-

«This is particalarly the case with the so-called ‘‘ back limestone.”

ASSAYING. 151

was, however, not proportional to the weight of the lead, as has been explained
before. The difference, however, between buttons weighing 300 grains and
those weighing 500 grains never exceeded 2 cents (0.000053 per cent.), and
it is therefore safe to say that when the lead button did not vary more than
25 grains either way from 425 grains the possible difference could not ex-
ceed one cent (0.0000265 per cent.). Allowing 2 cents (0.000053 per cent.),
or plus or minus one cent for inaccuracies in weighing, the total amount of
all the possible inaccuracies can be reckoned at 3 cents (0.0000795 per
cent.), or plus or minus 14 cents.

Resumé of errors—'[he possible errors in the silver assay as it has been
described are the following: Inaccuracies in weighing the ‘“‘pulp”; imper-
fect fluxing; insufficiency of the time of melting; impurity of the litharge;
loss by cupellation; mechanical losses; and inaccuracies in weighing the
silver button. All these errors, with the exception of those caused by silver
in the litharge and the inaccuracies in weighing the silver button, are so
infinitesimal, when the assay has been properly conducted, that they may be
neglected altogether. The other two sources of error, the litharge and the
balance together, cannot change the results more than three cents, and the
influence of the latter of these can be very much reduced by the substitution
of a microscope with a micrometer eye-piece for the balance.

Estimation of gold—The determination of the amount of gold in any country
rock where it is present in extremely small quantities is attended with great
difficulties. It is scarcely ever as much in value as the silver and is always
very much less in quantity. It is only by the concentration of a large
number of assays that it can be determined at all, and the results even of
this method are not always reliable. It is impossible to obtain litharge free
from gold as well as silver, and it is much more difficult to determine its
quantity or the effect that it has upon the assay. As nearly as could be
determined, the amount of gold in the litharge used was about one cent to
the ton of 2,000 pounds (0.0000016 per cent.). This result was obtained in
the following manner: Twenty assays of the ordinary flux were reduced in
the usual way, and the resulting lead buttons were separately cupelled until
the lead remaining would weigh about twenty grains. The cupels were then
removed from the fire and allowed to cool. The twenty lead buttons, which

132 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

collectively would weigh about 400 grains, were removed from the cupels
and placed in a scorifier in the muffle with 5 grains of borax glass. When
the mass was thoroughly melted it was poured into a mold and the lead
was again cupelled. The gold in the rock was all determined by concen-
trated assays in this manner, except when a series of assays were made
from samples taken near together. In this latter case the average value in
gold was determined by dissolving the whole number of the silver buttons.

Use of assays— While various purposes may be subserved by assays of
country rocks the main objects of those here described were first to ascer-
tain in which of the rocks the precious metals could be detected, and second
to trace the variations of tenor in different occurrences of the same rock.
As a qualitative method exception can scarcely be taken to the dry assay,
while even if the degree of accuracy reached in determining the absolute
contents in precious metals of the Eureka rocks has been overestimated,
the value of the results would scarcely be impaired; for it will hardly be
denied that the results form a sufficient basis for a comparison of different
samples of the same rock all containing very small quantities of silver and
gold. For the purposes of this report it makes very little difference whether
a certain mass of limestone really contains 10 cents or 20 cents, if it can
be proved that a second body of limestone contains twice as much, or it
may be half as much. In other words the main purpose was to ascertain
the relative contents, not the absolute contents, of the samples assayed.
Even if the methods employed were ideally exact it would be impossible
to calculate the metallic contents of any large blocks of ground with pre-
cision, since it would be impossible to obtain samples which should correctly
represent the average of the mass. The following pages contain all the
assays of Eureka rocks, except those which were given in the chapter on
the source of the ore, as well as some special determinations which were
made of several minerals.

ASSAYING. 133

SAMPLES TAKEN EVERY EIGHT FEET IN THE SECOND CROSS-CUT ON THE FOURTH
LEVEL OF THE EUREKA MINE, BEGINNING AT THE JUNCTION.

Assay value

No. Description. rae

Cents.
Brownish crushed limestone. ..--------------------- 31

Yellowish crushed limestone..-..-.----------------- 19
Bluish, slightly stained, hard limestone .------------
Grayish limestone, much crushed? ......-.-.-------|----0-+-+-----
Grayish limestone, harder .........--..---------+---
Grayish limestone ..-... .----. --------22--2s-0-s00--
Grayish limestone, more broken....-..-------------
White limestone, not very hard.....-..-.--.--...--.

i
>

Same, but more compact.........
Bluish limestone, medium hard... -

Pee ee
ooaonau

no
i}

Medium hard, stained limestone.........--..-....-.
Crushed, stained limestone ...-....--...-...--..----
Crushed, bluish limestone ------ Becerc eecedoeeeore4
Same, more compact.......--.-----.--.--------+----
Crushed, broken limestone ........-....------------

REBRER

ie)
&
a
°
;

=
°
:

:
‘
:
‘
:

‘
.

a The average value in gold was 3 cents to the ton.
> Button lost in removing from cupel.
SAMPLES TAKEN EVERY FIVE FEET IN SINKING THE RICHMOND SHAFT FROM THE
1,100 TO THE 1,200-FOOT LEVEL.

Cents.

a Button lost in removing from cupel.

134 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

This quartzite contained iron pyrites and some molybdenite. All the
silver buttons were dissolved together, and the resulting gold gave an
average of 4 cents to each sample. The usual flux was employed in assay-
ing this rock, except that 150 grains bitartrate of potash and 350 grains of
borax were used.

Chlorination test of Richmond “red” and “yellow” ore—The finely pulverized sample
was leached for one week with hyposulphite of soda, and the difference be-
tween the assay value of the unleached samples and that of the leached
sample showed that 36.1 per cent. of the silver contained in the ore was in

the form of chloride.

ASSAYS OF VARIOUS ROCKS.

Description.

Granite from Mineral Hill much decomposed...-.-.------
Red porous quartzite from Mineral Hill carrying much
ferwleOXi0G posse eee eee ee eee
Weathered limestone from top of Ruby Hill, near U.S.
Geological Survey monument............-...--..-------
Eureka quartzite from Caribou Hill, average of four sam-

Quartzite from near Membres shaft on Adams Hill..-.....
Quartzite from end of cross-cut on third level of the Al-

Dion Mine seem eeesee cee eee ae ee ee eee eee
Rhyolite tufa from quarry back of Nob Hill, Eureka ...-.

‘‘Back” limestone from end of cross-cut on seventh level |

Oh iS ACH MION ose. em onen eames eee eas seer ie
Limestone from junction of first cross-cut and 1,050-foot
level/otthe Richmond ass --s eas seeteeeeneee asco
Limestone from the contact with quartzite from first

north cross-cut on the Richmond ninth level....-........ ee

Reddish ‘‘ back’’ limestone from end of first southwest
drift opposite second north cross-cut ninth level of the
SRICHMNIONG feeeee tence me ese a eee

Decomposed rhyolite from “rhyolite winze,” fifth level
ofthe nents. coon cassette eee eee eee
“Front” limestone from same place...........-.--....--.

“Front” limestone from the second cross-cut on the |
sixth level of the K. K., 30 feet from main drift ........ |

Assay value.

Gold. | Silver.

Centa.
ecccenc- 2
Trace.| a95
Neemincee Trace.
Trace. 10

a These two samples came from near low-grade ore.

ASSAYING. 135

SAMPLES TAKEN 30 FEET APART, BEGINNING AT THE END OF THE FIRST CROSS-CUT IN
THE “FRONT” LIMESTONE ON THE SIXTH LEVEL OF THE K. K.
i es SS

Assay value
No. Description. in silver.

This limestone was of a grayish-white color, sometimes
friable and sometimes compact. It did not differ from
the ordinary limestone.

re
RP Semranreaone

From contact with main flasure -...------+-+-+----+++7-27777"

Determination of carbon in various limestones. — [he determinations were made in the
following manner: One hundred grains of finely pulverized rock were dis-
solved in hot chlorhydrie acid, filtered, and the residue was dried at above
100° and weighed. This insoluble part was ignited and the carbon deter-
mined by difference.

SSS |

No. Description. Pec.ort of
eee
1 | Black limestone at contact with quartzite on the cross-
cut from shaft 1,200-foot level of the Richmond. In-
soluble matter 6.5 per cent... Se to Ee eee 1.50
2 | ““Back’’ limestone at end of cross-cut on the seventh level
of the Richmond. Insoluble matter 7.24 per cent .-.--.- 0.84

A great deal of the limestone between the main and secondary fissures
carries free carbon, the amount sometimes reaching 1 per cent.

An examination was made of the clay from the main fissure from all
the points where it is exposed in the Eureka mine, for the purpose of deter-
mining the quantity of the carbonates of lime, ete. which it contained.
The largest percentage of carbonates obtained was 85 per cent. and the
lowest 15 per cent. As a rule the clay was most calcareous near the sur-
face and the most silicious below, though there were local exceptions. As
it was in part the product of attrition and decomposition of walls of quartz-
ite, limestone, and shale, and no doubt in part also a product of the decom-
position of rhyolite, its variable composition is accounted for.

136 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Examination of quartz-porphyry from the Bullwhacker mine—'| his porphyry occurs in the
form of a dike in the above-mentioned mine. It contains numerous cubes
of pyrite distributed throughout its mass, which sometimes measure as much
as one-eighth of aninch. The pyrite is bright, and shows no signs of weath-
ering except where it has been exposed for some time to the action of the
air. Clean crystals of this pyrite were picked from the matrix and were
assayed for gold and silver, 377.09 grains being pulverized and roasted
sweet in the muffle. The roasted mass was mixed with 770 grains litharge,
580 grains bicarbonate of soda, 270 grains bitartrate of potash, and 700
grains borax. The whole mass was melted two and one-half hours and the
resulting lead button cupelled.

Per cent.
Valueinisivers6b) contsr a. saneeee wae eeee eee 0.0017236
Value in gold, 80 cents -.......... Poe anoea .--- 0.0001327

The amount of silver and gold contained in this porphyry when it was
assayed without separating the pyrite was:

Per cent.
Silver, Gicents in. sa. 0s-2es ecco eee anes 0.0001591
Goldl2icents: 3.5. -sceer eee eer Sone oeee - 0.0000199

From this it will be seen that the ratio of the gold to the silver was
greater in the porphyry than it was in the pyrite itself, and that either the
coarse crystals of pyrite (those that were selected for assay) were purer
than the fine crystals, which is highly improbable, or that the porphyry
carried gold and silver independently of the pyrite. Usually pyrite is
found to be the matrix of gold and not of silver, but in this instance these
relations seem to have been reversed.

A sample of porphyry from the surface, in which the pyrite had been
completely decomposed by the continued action of the atmosphere, gave
very nearly the same amounts of gold and silver as that which contained
undecomposed pyrite. The results were:

Per cent.
Silvers Ticents: i. Vas as ose eh eee ee ee 0.0001856
Gold, "TS cents 22. staat sa. eee ene eee 0.0000215

The amount of pyrite contained in the porphyry was 1.89 per cent.
This was determined by Dr. Melville, assistant chemist of the Geolog-
ical Survey, by calculation from the amount of sulphur in the rock.

ASSAYING. 137

That the iron pyrite did not carry all the gold and silver in this porphyry
is shown by the fact that it contained when assayed separately only 80
cents (0.0001327 per cent.) gold and 65 cents (0.0017236 per cent.) silver,
whereas it should have assayed $6.34 (0.0010518 per cent.) gold and
$3.17 (0.0085062 per cent.) silver, there being 1.89 per cent. of it in the
porphyry, had it contained all the precious metals present in that rock.
There seems to be no doubt that the iron pyrite present in this porphyry
is a secondary product; that is to say, that it was not crystallized out of the
melted mass when it cooled, but that it was formed later either through the
action of sulphureted hydrogen or sulphur in some other form upon the
iron contained in the rock. It is difficult to conceive of the formation of
pyrite from a melted mass under conditions which would permit of the iron
retaining the extra atom of sulphur necessary to its composition. As it is
evident that this porphyry contains silver and gold independent of that in
the pyrite, it is highly probable that these metals were present in that rock
before the formation of the pyrite, and that the same causes, probably those
of solfataric action, which brought about the formation of the pyrite, effected
a partial concentration of the silver and gold in this mineral.

This porphyry was also examined for lead. The ordinary methods of
analysis failed to reveal its presence, although it was thought highly prob-
able that it entered into combination with the rock in very minute quanti-
ties. I adopted the following method, founded on the well-known tendency
of gold to retain small quantities of lead even when in a melted state and
exposed to the air. Forty grammes of the finely-pulverized porphyry were
mixed with 150 grammes of carbonate of potash in a porcelain dish, and
the whole was moistened with an acid solution of terchloride of gold which
contained 10 grammes of gold. The mass was dried and fused for four
hours in a French clay crucible in a coke fire. The resulting gold button
was then analyzed by Dr. Melville in the following manner: The gold was
dissolved in aqua regia and filtered hot to remove traces of slag. The gold
was precipitated with oxalic acid, the solution filtered, and the filter washed
with hot water to remove chloride of lead. The filtrate was evaporated to
dryness and ignited at the lowest practicable temperature to decompose the
oxalate, and also to remove the excess of oxalic acid used in precipitating

138 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

gold. The residue was dissolved in nitric acid and filtered. The gold pre-
cipitated was treated with hot nitric acid to remove any oxalate of lead
present; filtered, and this nitric acid solution was added to the first nitric
acid solution obtained, and the whole evaporated to a small bulk, about 1
c.c. This was divided into two portions. One was tested with diluted
sulphuric acid and the insoluble sulphate of lead was obtained ; the second
portion was tested with potassic chromate, when chromate of lead was pre-
cipitated_and crystallized by boiling. The whole of the lead was then con-
verted into sulphate and weighed. The weight was 0.0033 grammes. That
there might be no question as to the character of the compound, the sul-
phate was finally reduced to metallic lead. The 0.0033 grammes (0.00825
per cent.) do not represent all the lead that was probably contained in the
porphyry, as there was no doubt some loss, but the result is sufficiently accu-
rate to establish the fact that this rock, although considerably metamor-
phosed, contained appreciable amounts of lead as well as gold and silver.
As the assay value of the porphyry in silver was 6 cents (0.0001591 per
cent.), there was about 52 times as much lead present as silver.

(CITLA PER 2.b1:
PROSPECTING.

Methods of prospecting in mines southeast of the compromise lin—T he method of prospect-
ing adopted by the superintendents of the mines on Ruby Hill has been
somewhat different in the two regions which are separated by the compro-
mise line. This line, which was adopted by the Richmond and Eureka
companies as a boundary line between’their respective claims, seems also to
have been a natural division, as the ground on either side of it in the belt
of mineral limestone exhibits somewhat different structural features. This
difference has been fully explained in the chapter on the structure of Ruby
Hill. The fact that most of the bodies of ore found during the earlier
workings lay near the quartzite in the mines southeast of the compromise
line, caused the adoption of a method of prospecting which consisted in
sinking perpendicular shafts in the limestone, driving cross-cuts to the
quartzite, which was called the foot wall, and running levels along the con-

_tact of that rock and the limestone. When this contact was not so irregu-
lar that the drifts became longer and more expensive than the advantages
of a clay seam warranted, the levels were kept close along the quartzite,
and cross drifts were run off into the limestone where indications were
favorable for finding ore. Where the course of the quartzite face was too
irregular the levels were driven near it parallel to its general direction. To
define exactly what the Eureka miner considers to be ‘‘indications” is a
difficult task. Fissures and. seams, crushed, broken, and brecciated lime-
stone, limestone stained with ferric oxide, and caves are considered to be
good indications for ore—though drifts in which the country rock has shown
all these phenomena have often developed nothing. On the other hand, no
ore bodies have been found which, on one side or another, do not exhibit

(139)

140 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

some of these “indications.” Ore bodies have sometimes been found after
drifting hundreds of feet through the hardest and most unfavorable looking
ground. This was the case on the seventh level of the Richmond (see
Plate XIV.), where a drift had been run to make a connection. Where the
ore was first found there was no indication whatever of its proximity until
the ore body itself was encountered. The limestone was of a hard, com-
pact nature and grayish color, and was not considered particularly favora-
ble for ore. On the eighth and ninth levels some notice of the near ap-
proach to ore was given by stained limestone through which the drifts
passed before it was reached, and by a fissure. Since the discovery these
ore bodies on the different levels have been connected by upraises and
winzes, and a well-defined ore channel has been established from the seventh
to the ninth levels, even connecting with the west ore body above the sixth.
True, the ore was not entirely continuous, but fissures, seams, and stained
limestone extended over the whole distance, forming a connection between
the ore bodies such that all of the latter would have been discovered if the
indications had been followed downward from the large ore body on the
fifth level.

Method of prospecting in the Richmond—OQwing to the nature of the Richmond
ground it is doubtful if the method of following the quartzite and limestone
contact adopted in the Eureka and other southeastern mines would have
been productive of good results. The ore bodies in the Richmond, with one
exception near the compromise line, do not touch the quartzite, but are inva-
riably connected with some fissure. In the deeper workings of this mine it
has been customary to drive straight levels in the limestone, independently of
the quartzite, and to follow the fissures which may be encountered in all direc-
tions. Drifts are also run where other indications point to a possible ore body,
or where it is necessary to cut up a large block of ground, which, though
it may not be thought particularly favorable for ore, must not remain un-
prospected. This last method is made necessary in this mine by the fact
that the ground which lies between the quartzite and the Ruby Hill fault is
very extensive and ore bodies might easily exist in it without indicating
their presence in any manner. Although ore has not been found near the

quartzite in this mine, except in one instance, there is a possibility that it

PROSPECTING. 141

may exist in that neighborhood in the upper levels, as there are no drifts
for any distance along the quartzite except on the fourth and sixth levels.
The company is now prosecuting a search in this direction with reason-
able hopes of success. In fact there is a great deal of ground in all the
upper levels of the Richmond mine which warrants systematic prospecting.
In the mines southeast of it, however, the limestone has been very thor-
oughly prospected down to the point where the two fissures come together,
and it is not likely that any very extensive ore bodies will ever be discov-
ered in it, although it will probably be worked for a long time to come, for
the sake of the small masses of ore that have been overlooked or neglected.

The structure of the country in these mines has been fully explained
and the existence of a second limestone wedge, below the lower belt of
shale, has been pointed out. The obvious method of prospecting this ground
is to sink shafts through the lower belt of shale northeast of the present
workings and to drift in the underlying limestone. Such a system of pros-
pecting is at present being carried on in the Eureka, and if successful the
example of this company no doubt will be followed by the others. A cross-
section of the old and new workings of the Eureka is given in Plate VIII.
As the two fissures in the Richmond mine are still very far apart, the
same methods of prospecting which were followed in the upper levels are
continued below.

Methods of prospecting on Prospect Mountain—'T?he methods of prospecting followed
“in the large mines of Prospect Mountain do not differ much from those in
vogue on Ruby Hii. In the small mines the ore is usually followed from
the surface down, either by vertical or inclined shafts, and the ore is ex-
tracted as the conditions of the ground permit. The Ruby-Dunderburg
and Hamburg mines, as well as several others, are worked systematically
with perpendicular shafts and levels run at stated intervals.

A portion of Prospect Mountain is being prospected by driving tunnels
from both sides of the mountain at those points where the nature of the
ground permits of obtaining a great depth with a comparatively small
length of adit. As a means of opening mines tunnels are in general expen-
sive and unsatisfactory. Usually the distance to be driven im order to attain
any considerable depth is very great; the tunnel is nearly useless in explor-

142 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

ing the ground below its level, and is only advantageous as a means of
ventilation and as an exit for the water. Ground below the tunnel level
can be worked and drained to advantage only by the help of a vertical
shaft from the surface, and such a shaft costs as much as if there was no
tunnel. The advantages of the tunnel system in Prospect Mountain, how-
ever, as a means of prospecting are numerous. In the first place, owing to
the topography of the country, it is possible in many places to gain a foot or
more in depth with every two feet of tunnel. Again, the deposits are found
throughout a belt of limestone over a mile in width, and are as likely to be
discovered by a tunnel as a shaft. Moreover, many of the claims on the
surface are owned by small companies, which cannot afford expensive hoist-
ing machinery, but which could pay their proportion of the outlay neces-
sary for the part of the tunnel developing their ground.

The presence of ore cannot be predicted with certainty, but this much
at least can be said, that all the indications, and the results so far obtained,
point to the existence of numerous ore bodies in the heart of Prospect
Mountain, and although mining for the precious metals has not been
reduced to anything like as great a certainty as is the case with coal and
iron mining, a skillful use of the knowledge already obtainable will in
some measure reduce risks which invariably attend mining operations. The
air and ventilation are good in all the mines of the district where proper con-
nections have been made, even in the lower levels.

Electrical observation and assays—In describing the second list of assays, page
84, reference was made to some observations by Dr. Barus in the Rich-
mond mine in regard to the electrical activity of ore bodies. Mr. Becker,
in summarizing this investigation,* says: “Of the different surveys made,
the one on the 600-foot level of the Richmond mine, west drift, presents
the greatest interest, because it was here that all the precautions neces-
sary could be satisfactorily applied. The line of survey, moreover, lay
completely outside of the ore body, and all the points tapped were in rock,
essentially of the same kind. The measurements were made in various
galvanometric ways, and the results were subsequently checked by a ‘zero’

*The methods employed and the results obtained are fully explained by Dr. Carl Barus in the.
Geology of the Comstock Lode, Chap. X.

PROSPECTING. 143

method. It was found that the distribution of potential along the length of
the drift, even after an interval of four months, has not materially changed,
and that on passing from barren rock toward and across the ore body,
small, though decided, variations of potential were encountered in its
vicinity.

“ Results—The electrical effects observed were too distinctly pro-
nounced to be referable to an aggregate of incidental errors, and they
were of the character which must have been produced had the ore bodies
been the seat of an electromotive force. The experiments made cannot be
said to have settled the question as to whether lode currents will or will not
be of practical assistance to the prospector. Indeed, as yet it cannot even
be asserted with full assurance that the currents obtained are due to the ore
bodies. What bas been observed is simply a local electrical effect suffi-
ciently coincident with the ore body to afford in itself fair grounds for the
assumption that these contained the cause. Giving the investigations of
Fox and Reich proper weight, however, the supposition that the currents in
the Richmond mine were not due to the ore bodies is exceedingly improb-
able. But unfortunately they are so weak as to require an almost imprac-
ticable delicacy in the researches designed to detect and estimate them. It is
highly probable that under certain circumstances more powerful currents
are generated than those found in Eureka. It is not unlikely, for example,
that galena, cinnabar, and the copper sulphosalts produce electrical effects
of far greater magnitude, and that the method might be readily available
for the discovery of such ores. The results thus give much encouragement
to further investigations in this direction.”

Fig. 5, page 144, represents the plotted curve resulting from Dr. Barus’s
determination of potentials, and Fig. 6, same page, represents the curve
resulting from the plotting of the assay values of the samples taken from
the points I, IL, up toXVIN. In plotting the electric as well as the assay
curve, the linear distances between the points I. and IL. I. and III, ete.
are taken as the abscissas, the values of the potentials being the ordi-
nates in the electric curve, and the assay values being the ordinates in
the assay curve. Beyond the point XVIII. no samples were taken, as it
was not possible to find Dr. Barus’s points. The assays were made some

144 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

time after Dr. Barus’s electrical experiments, but before his results were
known to me. Fig. 2, page 82, represents the position of the points L, IL,
IIL, ete., as well as the relations of the ore bodies to the formations. Mr.
Becker, in his summary, states that the question of the practical value of
lode currents to the prospector has not yet been settled.

The same may be said to be true of the value of the assays of country
rock as a means of determining the positions of ore bodies. Nevertheless
the coincidence of the two curves just mentioned, although by no means com-
plete, is yet too remarkable to be overlooked. The assays taken at points

Fic. 6.—Assay curve.

XIII. and XIV. are abnormal. Although other assays were taken after-
wards at these two points, no assays as low as XIII. nor anything as high
as XIV. were obtained. If, therefore, the assays XIII. and XIV. were left
out, and the points XII. and XV. joined by a straight line, a curve almost
identical with that of Dr. Barus would result.

Practical use of assaying in prospecting for ore—T here are many things that render it
a very difficult matter to make practical use of the assay value of the
country rock in prospecting for ore bodies. The maximum differences be-

tween the various specimens-are in any case small; ordinarily the country

PROSPECTING. 145

rock is not of a sufficiently homogeneous character to exhibit a uniform
increase in value as an ore body is approached. Usually when there is a
marked increase in this value there are other indications of the presence of
ore bodies, such as stained and broken rock, fissures, and like phenomena,
which lead the miner in the proper direction; and the determination of the
direction in which an ore body lies from a point in a drift where good assays
have been obtained is a very difficult matter, while prospecting in a wrong
direction is always a very expensive affair. At a remote point, where data
indicating the direction of an ore body would be of exceeding utility, the
relative differences in the assays are so small that no marked advantage can
be obtained from them and they would be very liable to mislead the pros-
pector. Notwithstanding these drawbacks, it is possible to render the
assaying of country rock of practical advantage, especially when the
diamond drill is used as a means of prospecting. Subsequent to the elec-
trical experiments and to the determination of the values of the country
rock on the 600-foot level of the Richmond, a considerable body of ore was
discovered just a few feet below this level near the point XV., where the
electrical phenomena and the assays indicated the presence of ore. The
discovery was made, however, by following a stratum of ferric oxide in a
cross-drift a short distance from the main level, and was not due either to
Dr. Barus’s experiments or the assays of country rock, as before the discovery
of this ore body it was supposed that the phenomena observed were referable
to the large body of ore which existed above this level. This body of ore,
however, was further removed from point XV. than the ore subsequently
discovered.

The correspondence between the assay values of the rock and the
values of electrical potentials found by Dr. Barus is clearly not accidental.
If it is possible that the phenomena are connected as cause and effect, or
that the differences of potential are due to the traces of ore in the rock,
then both methods only lead to the detection of local differences in compo-
sition, which may indeed be referred with some probability to the presence
of ore bodies in the neighborhood, but which might also be due to an acci-
dental dissemination of metallic compounds and be independent of the
existence of ore in considerable quantities. On the other hand, if the two

2654 L——10

146 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

series of phenomena are to be regarded as two effects of one cause, and are
not immediately dependent upon one another, each affords a remarkable
confirmation of the inferences which would be most naturally drawn from
the other. The facts were submitted to Dr. Barus for his opinion, which is.
as follows:

“Tt is entirely impossible that there should be any direct connection be-
tween the assay value of the rock at a given point and the value of earth poten-
tial for the same point. The nature of the distribution of electrical potential
can be made clear to those unfamiliar with the subject by the aid of an anal-
ogy. Instead of drawing inferences with reference to an ore body considered
as a source of electrical activity, I will suppose that we have to do with a hot
body, that is, one whose temperature is decidedly above that of the surround-

SS Parana Dae
SS eee nt foo ae 7
~ a

eae a os
ne fe:
gee
—! nee

Fic. 7.—Illustration of electrical activity.

ing rock. Let ¢ b, Fig. 7, represent the surface of the earth. Let A be an
area (in section) of constant high temperature beneath it. Suppose the
body has been in place for an indefinite length of time, so that the thermal
distribution has become stationary. Let the problem be that of finding the
body A from observations made on the surface of the earth. The first
step would be to take earth temperatures at convenient number of points.
intermediate between ¢ and some remote point, b. If the distances were
then plotted as abscissas and the earth temperatures as ordinates, a curve
would be obtained which in the simplest case would be characterized for
an abscissa corresponding to a point nearest the hot body 4 by a maximum.

PROSPECTING. 147

“By an extension of the same reasoning, it is clear that if the surface
were level and horizontal, and if a complete thermal survey of the surface
were to be made, the result might be expressed by a series of isothermal
contours analogous to those by which topographical features are ordinarily
presented, and that the summit of an elevation on the thermal map would
lie vertically above the hot body.

“Similar methods of procedure and expression are applicable to a center
of electrical excitation. If the body were electrically active, an electrical
survey would result in the determination of a series of equi-potential con-
tours separated by a fixed difference of potential, and these would culminate
above the ore body. In short, replace temperature by potential, isothermal
by equi-potential, and the consideration made in reference to the hot body
will apply to an ore body, only that in the case of electrical excitation we
have to do with circumstances vastly more complex, with a body, as it were,
in part hot, in part cold, or one over which heat is irregularly distributed.

“The remarks made on the surface manifestations of a subterranean hot
body apply readily to any imaginary line or any imaginary plane lying be-
neath the surface and sufficiently near the hot body. To make the case per-
fectly general, however, we should have to consider the isothermal surfaces
themselves in their actual position and contour. ‘The first of these would
completely envelop the hot body; whereas, subsequent ones intersect the sur-
face of the earth until finally they would become indistinguishable from the
normal terrestrial isothermal, as shown by the dotted lines in the figure.
Similarly, in the case of a detailed electrical investigation, it would be nec-
essary to trace the equi-potentials as surfaces surrounding and intersecting
the electrically active ore body. The presence of an ore body is evidently
manifested throughout the whole superficial and subterranean region in
which the equi-potential surfaces are traceable or in which an electrical
disturbance due to the presence of an ore body exists, and the applicability
of the electrical method of prospecting consists in the fact that the indica-
tions of the existence of an ore body occupy a space greatly in excess of
the size of the body itself, namely, the whole region of sensible electrical
excitation.

148 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

“The analogy between the electrical method and the method of assays
is clear, for in the latter advantage is also taken of the fact that the indica-
tions of ore occupy a greater space than the ore body itself. The differ-
ences are also clear, for while the assay method depends upon the solubility
of the ore, the permeability of the rock, the distribution of fissures, and the
like, the electrical method depends upon the distribution of electrical
activity in the body producing the effect, and upon the electrical conduc-
tivity of the surrounding rock. The two methods are, therefore, entirely
independent, and it is a particularly interesting fact that the results obtained
in the Richmond mine were accordant. Mr. Curtis and I have met with a
coincidence of two independent effects of the same cause, both of which
indicate in different ways the presence of ore in the vicinity of point XV.
of the 600-foot level of the Richmond mine. It is gratifying to find that
an ore body was actually discovered, subsequently to our experiments and
independently of them, precisely where we had most reason to look for it.
I greatly regret not to have been able to be present to study the distribu-
tion of potential relative to the new body in detail.

“There is one more remark with a bearing on these inferences which
I desire to make. The relation of the earth-potential encountered along
any line of electrical survey to distance, when expressed graphically, appears
as a broken line possessing certain distinct characteristics. I proved, how-
ever, that the progress in the values of earth-potential, observed on passing
from one point of a drift to another, is continuous, and that therefore the
potential line in our diagram, however sinuous, never suffers a break of
continuity; whence it follows that we may regard the curves obtained as
containing unknown disturbing effects superimposed on the decidedly larger
electrical effect attributable to the ore bodies. I infer that in any extended
line of electrical survey, besides the large field of electrical excitation due
to the ore bodies, very many smaller fields, distributed throughout the
mine, are constantly encountered and intersected.”

Use of the method of prospecting by assays— The method of prospecting by assays
has one important advantage over the electrical method; it can be carried
eut with comparatively little expense and with little loss of time. It must
be remembered, however, that the assays will be useless unless made with

PROSPECTING. 149

the greatest care. And as many assays as convenient should be made in
order that local differences in the rock should be rendered as small as
possible. In running a drift, it would be well to take four assays per day,
which might be used separately or averaged. Care should be taken to
exclude all seams containing traces of ore, which can be assayed separately
if desired, as it is the enriching of the country rock itself that it is necessary
to observe.”

Great caution should be employed in making use of these assays and
the results should be carefully compared with other indications in the
country rock and the general structure of the ground. With proper pre-
cautions the assaying of the country rock will in many instances become
an important aid to the miner. The method is better adapted to the dis-
covery of large and irregular bodies of ore in a formation similar to that
in Eureka than it is to the search for small, though rich veins. -

2 The methods used in assaying the Eureka ores are fully explained in Chapter XI.

CHAPTER XIII.

TRIBUTE SYSTEM.

Wages—The wages paid to miners in Eureka District, as well as in most
mining camps of Nevada, are $4% per shift of ten hours. In most of the
mines on Ruby Hill the shafts are sunk and levels opened by contract, as
are likewise drifts, cross-cuts, winzes, and upraises when driven in the
country rock. The companies furnish timber, lumber, and tools, and the
contractors candles, powder, fuse, ete. The waste is usually removed by
men paid by the company. The contract price varies with the kind and
size of the excavation and the hardness of the rock. For drifts run by the
Burleigh drill, the minimum price paid the miner is $5 per running foot,
and the maximum $12. The latter price is only paid in extraordinarily
compact and ‘‘short-breaking” ground; $9 per foot would be about the
average for hard ground. The cost per foot for blasting material is from
$1.25 to $1.80. For drifts run by hand-drills the cost is from $6 to $14,
but the cost of blasting material is only about one-fifth of what it is when
Burleigh drills are used. In sinking shafts and winzes the cost is somewhat
greater. Where blasting is not necessary drifts are run for less than $3
per foot. At these rates it is supposed that the miner will earn something
over $4 per shift, as contractors usually work harder than miners paid by
the day. Asa matter of fact, however, contractors often make less than
$4, as work by the shift at those wages is usually scarce, and they prefer
earning less to remaining idle, while the rules of the Miners’ Union prohibit
them from taking smaller wages.

Ore is generally extracted from the chambers by miners on day’s pay,
except where it is removed under “‘tribute”—a pro rata method of paying

2In some places where the work is particularly hard or dangerous, as is the case in some mines
on the Comstock, the length of shift is reduced to eight hours, and even less.

(150)

TRIBUTE SYSTEM. 15%

miners which has been in use for many years in Cornwall and elsewhere.
A general description of this system as it has been applied in the mines of
Eureka District will perhaps be of interest.

the tribute system —In the year 1878, in the older workings of the Eureka
mine, there was a very considerable amount of ore which had not been ex-
tracted from the ore chambers, either through oversight or improper mining.
Many small ore bodies also had been passed over as too poor or insignifi-
cant to be worth removing, and there was reason to believe that undiscov-
ered ore bodies of small size existed, as turned out to be the case.

In the year mentioned, Mr. T. J. Read, superintendent of the mine,
introduced the method of taking out ore on tribute, in order to utilize the
large quantities of it known to exist in the earlier workings. The ground
which was to be worked in this manner was divided up into blocks or
“pitches,” as they are called by the Cornish miner. These pitches were
allotted to individuals or companies (which usually consisted of two men),
and 10 per cent. of the assay value in gold and silver of all ore above $40
was paid to tributers. This rate was paid for about one year when it was
increased to 15 per cent. Then a new schedule of prices was arranged,
based upon the assay value of the ore: $6 per ton of 2,000 pounds was
paid for $40 ore and $3() for $100 ore, with proportional prices for the inter-
vening grades. Finally, in 1881, still another schedule of prices was adopted:
$2.50 was paid for ore assaying $30 per ton, and 50 per cent. of all that it
assayed above $30. Thus $65 ore brought the tributer $2.50 plus $17.50,
or $20. The company furnishes tools, hoists the ore, and transports it to
the smelting works. The tributer supplies his own candles, fuse, powder,
etc., as well as timber, buying them from the company at or near cost, handles
his own waste, and delivers his ore at the shaft. When a tributer runs a
prospecting drift and does not succeed in finding ore, it is not customary to
charge him with powder, ete. In those cases where a tributer strikes a
very large body of ore requiring timbering in square sets, the ground is
taken away from him after he has been allowed to make remunerative
wages. Such a fortunate strike both for the tributer and the company has
only occurred in one instance since the tribute system was introduced.

152 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Extracting ore under the tribute system has also been introduced in
the Richmond as well as in many other mines of the district, and it has
been found to work very well.

Advantages and disadvantages of the tribute system. he tributers sometimes fill up
drifts and other workings which ought to be kept open, and injure the mine
generally, but this is the case only when they are not properly restricted
and the foreman of the mine does not attend to his duty. Ground worked
under the tribute system soon acquires an ill-kept, disorderly appearance
not calculated to impress visitors favorably. The approbation which orderly
galleries excites in the mind of a mining man is not founded on love of
neatness, however, but on the fact that it facilitates the operation of the
mine. It must be remembered that the ground is not given over to tributers
until it has been practically abandoned by the company, and that the ore
which is obtained in this manner is nearly clear gain; and since the ground
left by the tributers is entirely valueless, there is no object in maintaining
it in working order. In fact, extraction under the tribute system is analo-
gous to cutting away the pillars of a coal seam rather than to more regular
mining operations.

Although some tributers are fortunate and discover valuable deposits
of ore, by far the greater number do not make miners’ wages; but men gen-
erally, and miners in particular, prefer to run the risk of making nothing if
at the same time they have the chance of getting extraordinary remunera-
tion for their labor. The difficulty of obtaining continuous employment at
day’s pay also acts as an inducement. to tributers. As the large ore bodies
are worked out, the demand for such labor decreases and many miners are
thrown out of employment who prefer to work on tribute to seeking their
fortunes in new camps. As adopted in Eureka District the tribute system
has been very successful.

CHAPTER XIV.
TIMBERING IN THE EUREKA MINES.

The method of timbering——The methods employed in timbering shafts and
drifts in the mines of the Eureka District do not differ in any material re-
spect from those employed in other regions of the Pacific slope, while the
system adopted for preventing the caving of excavated ore chambers origi-
nated on the Comstock, and has been described by Mr. J. D. Hague." It is
now in use in all districts of the West where the size of the ore bodies has
made it necessary to depart from the methods usually employed in small
lodes. The framing of the timbers at Eureka, however, presents some par-
ticularities to which it is desirable to call attention.

Physical nature of the different formation. —As a rule, the limestone composing the
ore-bearing zone requires but little timbering where it is penetrated by
drifts and winzes, and it is only where it has been crushed to a powder that
workings of this character need to be kept open by timbers. Where drifts
have been run along the line of the quartzite and limestone contact, tim-
bering is almost always necessary, as the quartzite and accompanying clay
scale off and in the course of time fill up the drift. Drifts in the quartzite
itself stand better, but, nevertheless, often require timbers, especially where
there is much water. There are but few workings in the shale, but if there
were, much timbering would no doubt be required to keep the ground open
for any considerable length of time, as is shown by the cross-cut through
the lower belt of shale on the 1,200-foot level of the Locan shaft. The
“crawling” of the shale in this instance is much increased by the water
present in it at this level, and it has been necessary to retimber the cross-
cut several times within a few months. Shafts and winzes in the limestone

«Exploration of the Fortieth Parallel. Vol. III.
(153)

154 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

of course require some timbers, but usually no more than are necessary
for the support of ladder-ways, ete. The Richmond shaft, over 1,200 feet
deep, which passes through shale, limestone, and quartzite, is only “‘cribbed”
for the entire distance with two-inch plank, except at the stations, where
timbers are used. 'Timbering, however, will eventually be necessary in this
shaft, not only below the water level but above as well. Below the water
level the limestone stands very well, owing partly to its nature and partly

_ to the more compact character of the rock as depth is attained. The quartz-
ite ought always to be timbered below the water level, and it would be
found more economical in the long run to timber all working shafts care-
fully.

Fic. 8.—Set of timbers.

Method of timbering — Fig, 8 represents a complete set of rectangular tim-
bers, as they are used in carrying up a stope in an ore body. These tim-

TIMBERING. 155

bers are similar in their general features to those in use on the Comstock.
It is only as regards the manner in which they are framed that they differ,
and eyen in this respect the differences are but slight.

When an ore body is encountered in driving a drift, it is usual to place
the first sill across the drift, laying the ties parallel to the drift. This is
done to retain as wide a space as possible for the passage of the car, the
sills being longer than the ties. In carrying up the timbering the timber
which forms the cap of a lower set becomes the sill of the set above it.
The same is the case with the ties. In beginning a stope the sills often
consist of a long piece of timber in which the posts are mortised at their
usual distance apart. As each set is raised the caps are covered with two-
inch plank, and in this way floors are constructed. The spaces between
the floors and timbers are filled with waste, and thus a compact mass is
formed from one side of the ore chamber to the other and from the bottom
to the top, which takes the place of the ore removed, and which is capable
of sustaining the enormous pressure exerted by the surrounding rock. The
timbers are wedged and braced against the limestone walls of the cham-

Fic. 9.—Richmond framing.

bers, so that the whole stands solid. It is customary to fill in with waste,
as opportunity offers, the absence of that peculiar “crawling” ground so
common on the Comstock obviating the necessity for immediate filling.

156 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Sometimes the flooring is removed before the spaces between the timbers
are filled.

Method of framing in the Richmond— Fig, 9 represents the posts, caps, and ties as
framed in the Richmond mine. The tenon of the post is 9 by 6 by 1# inches;
that of the tie, 92 by 6 by 1s inches. The tenon proper of the cap is 9
by 7% by 3 inches, but there are several shoulders on the cap made to fit
the spaces left between the post and tie. The dimensions of all these differ-
ent parts can be seen in Fig. 9, and the manner in which they come together
in Fig. 8.

This method of framing is complicated, and therefore expensive, but it
is claimed that it gives great strength to the joint. Upon an examination
of Fig. 9 it will be observed that the tenons of the posts, and also some of the
shoulders of the caps, are cut somewhat short of what would be their proper
length if they were framed to meet exactly. This is to allow the timbers
to come together easily, as any irregularities in the joints caused either by
imperfect cutting or subsequent warping would interfere with their proper
fitting were not some space allowed. This is the more necessary on account
of the complicated system of joining. Pressure soon causes any imperfect
parts to meet. ,

Method of framing inthe Eureka —F'ig, 10 represents the timbers as they are
framed at the Kureka mine. The tenon of the post is 8 by 8 by 2 inches,
that of the cap 6 by 8 by 4 inches, and that of the tie 12 by 8 by 2 inches.
The tenons of all these are also cut somewhat scant, but as there are not
so many shoulders as in the Richmond timbers they do not need as much
play and are easily fitted together. Timber men usually prefer the Eureka
to the Richmond method, contending that the timbers are equally strong
and more easily framed. The Eureka timbers seem best calculated to resist
pressure from all sides, while those of the Richmond offer the greatest resist-
ance parallel with the caps. This would be what was required in timber-
ing an ore body the greatest dimension of which was along the course of
the lode, as is the case with Comstock bonanzas. In this case the ties would
be placed parallel to the walls and the caps at right angles. In Eureka,
however, the ore bodies are very irregular and the pressure is usually about
the same from all sides. On the first discovery of an ore chamber, too, it

TIMBERING. 157

is impossible to determine with any certainty what may be its ultimate
course, and consequently how the timbers should be placed. It is, there-
fore, well to have a system of timbering which will be equally effective in

Fig. 10.—Eureka framing.

all directions. When all the pressure comes from above, which, however,
is rarely the case, it would be well to have the ends of the posts rest
directly on each other, not allowing the tenon of the caps to intervene.

Material and size of the timbers —T he usual length of the posts is 6 feet between
shoulders; that of the caps and ties 5 and 4 feet, respectively. The timber
used is pine from the Sierra Nevada. It is hewn 12 by 12, 10 by 12, or
10 by 10 inches square, and is of excellent material. The ties used in the
Richmond are 10 by 10 or 10 by 12 inches, as the case may require. In
the Eureka they are usually 12 by 12, though occasionally they are but
10 by 12 inches. Sets of timbers 10 by 10 inches are sometimes used
when the ground will permit of it and the ore bodies are small, but 12 by
12 inches for the posts and caps at least is the rule.

The timbers are cut into the required lengths by circular saws, and
framed by hand. Split lagging and sometimes poles are used in the
drifts and small ore bodies where the heaviest timber and planking are not
required.

CHA. PTE R Poy:
METALLURGY OF THE EUREKA ORES.

Reduction of ores—A]most all the ores of Eureka District are reduced either
at the Richmond or Eureka smelting works, which are situated, respectively,
at the south and north ends of the town of Eureka. At different periods
other companies have smelted their own and custom ores, but it has usually
been found most advantageous to have ores reduced at one or the other of
the above-mentioned works, as the large scale on which their operations are
conducted enables them to smelt at a less cost.

No exhaustive investigation of the metallurgical processes carried on
in Eureka is intended in this report, and only such a general description
will be given as will enable the reader to compare the general methods and
apparatus with those employed in other districts. The ores have already
been described in a separate chapter, and an analysis of those of the Rich-
mond mine, which closely resemble all others in Ruby Hill, has been
added, so that a further description of them will be unnecessary here.

Description of Richmond works—The works of the Richmond company, which
are the largest and in some respects the most complete, are situated in the
southern part of the town of Eureka, and are connected with the company’s
mine on Ruby Hill by a narrow-gauge railroad, about three miles in length.
The distance to the mine by wagon road is somewhat shorter, as, on account
of the difference in elevation between the town and the hill, the railroad
could not be built in a straight line. These works have a capacity of from
250 to 300 tons per day, according to the nature of the ore to be reduced.
A refinery is connected with these smelting works, in which the furnace
lead is calcined and the silver and gold are separated from it.

Description of furnaces—In the smelting department there are four shaft fur-

naces with an individual capacity of from 50 to 100 tons of raw ore per day.
(158)

METALLURGY. 159

These furnaces, although they differ slightly in size, are all constructed in
nearly the same manner. The portion of the stack above the smelting
zone is constructed of ordinary brick and is cylindrical in form. It is sup-
ported by cast-iron pillars, which rest on a solid foundation. The smelting
zone itself is composed of a water jacket, or rather several water jackets,
called “‘baches,” and is oblong in shape. The “baches” are hollow boxes
of boiler plate 30 inches high, 20 inches broad, and 6 inches deep at the
top and 4 inches at the bottom. In the center of each is an opening for a
tuyere, which may be a water tuyere or merely a pipe to convey the blast.
The water tuyeres are long, and are used at-those points where it is neces-
sary to convey the blast for some distance into the charge. The baches.
are inclined a little outward at the top on the upper edge of the crucible or
lead well. They are joined to the stack above by a course or two of fire-
brick luted with clay. They are fastened to each other on the sides by
key-bolts, which can be easily removed in case of an accident, such as the
burning through of the iron of the bache. This arrangement allows the
removal of one of these water jackets and of its replacement by a new one
without interference with the working of the furnace. The baches are open
at the top and continually receive a stream of cold water which keeps them
cool. The iron comes in direct contact with the charge as in all water-
jacket furnaces. The furnace has an open hearth at one end with a slag
spout as well as one for speiss. The latter is placed one and one-half inches
below the former. The lead is allowed to run out of an opening on the
side of the lead well, which is a very short distance below the speiss spout.
When one of the large furnaces is working properly there is a continuous
flow of all the three smelting products, slag, speiss, and lead, from the cru-
cible. The furnaces are barred out regularly once every twelve hours, the
front bache being removed for that purpose. It is said to have been
proved by repeated experiments that the nature of the Eureka ores renders.
their advantageous smelting in a furnace with a closed hearth impossible,
as the large quantity of iron in the ore makes a continual barring out nec-
essary in order to prevent the formation of ‘‘sows.” The separation of the
different smelting products, slag, speiss, and lead, is tolerably complete.

160 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Composition of charge and analyses of slag and speiss — | he analysis of the Richmond
ore shows less than 3 per cent. of silica and about 30 per cent. of iron sesqui-
oxide. In order to make a slag with sufficient silica for good smelting,
quartzose ores are added, or quartzite when such ores are not to be obtained.
The slag and speiss, analyses of which by Mr. F. Claudet are annexed, re-
sulted from smelting the ore, an analysis of which by the same chemist is
given on page 60. The material furnished Mr. Claudet is stated to have
been the regular daily samples taken throughout an entire year.

SPEISS.

Per cent.
ATSONIG Mee Aan eacacee eee ae wis edicts cic ela stoma sats wetste 32.95
PAM SINGIN Yas aee ee Ado0Sy BHORbn SAaaoS SROCOOBOOD Heat 13
Molybdenum: 255.25. sone cis seco emcees oe ceeine seers 2.81
Sulphur's 22 ssccestne hotonline ee Mae 3.34
1b US RnSon GeRobp CSSnos GanDed Esasc0.46 la sielers aimemdelstoete 2.18
ONS) So Gop Socacn and ono sco ose esa ccosEstecoanoseasec 1.06
ft) SOU A See OE AAG ACORS MSO Ae area Soe See See 57.02
DANG: ci sayeed sis See cia a mals enue eis ei citar Rieter mateo pee lees 07
DING) a tojedionre Sere ees ysets ee ee ate ee eee eR 4
SiiCa «5 <siocce see cies ae ade clas como oe ete eee 23
Silver’and golds so. -cccccinese acces Coe eee oer 5 APR!

Silver, per ton of 2,000 pounds, 8.01 ozs.; gold, 0.43 oz.
SLAG.

Per cent
Pilies oo Scie to slec asin wetelae tecie hicks Crm Cleese aie Seer eee 23.67
Tronsprotoxide ac =e sissies ieee eee eicie eee 58.32
I NUP DE isos toe poco ep DOUG Obs Oconee COON AE SSOO CHESS oor 1.64
Lead oxide ..... yensast neaandonsdanobESoULsedsos5o0aee 3.51
MotallicIeadie cca cictencececsica cee enema micoesee eee 3.26
Bismuth ..... w/sialejai sre filaioe ess este mings ic memstrat erent aravewdtaterajerceisiets
Copper'oxide cea. ck caseee see ee ec ta RE eee eeee 1.08
ZINCVOXIG Osean SSDS RL ORES ADnOSrck GAOSAGaSoae 4.44
Manganese:0xide) « j.45 sone aie n/o.t=b se oes ee ele eee 23
Molybdenum ............ aislnieiawwinaelsteish = aetcisteiciaieiaiaie ners 52
ATHONIO; eee eicaelaa Belaleln iota /aranitleriete ete stereo atest etoe 25
Antimony...... sivjolsjoe aiwin=\sioiai=ialovntsje\aininiciaielatmintelelseiaie sicieteeeteiets
Sulphur ...... POpOGS COO RON dusddbodaso5an SAb6eS SSO CIOS 2.19
11112 ine SSO MER CAC HOOOSOCE Cad sot cas arose anscaOTss odac 4.78
IMA SNESIG a's o omintai vin wlelniri sist winnie sisioselsisie see eC See ee 1.27

Silver, 0.58 oz. ta the ton of 2,000 pounds; gold, trace.

METALLURGY. 161

This speiss contains an unusually small atomic proportion of arsenic,
for if the sulphur is supposed to be combined with the metals and arsenic
an arsenide of iron corresponding to the formula Fe;As, remains, whereas
in many speisses the arsenide of iron is either Fe,As, or Fe,As,.

The analysis of slag shows that it is very basic and the formula deduced
from it is that of asubsilicate Although this slag is very much more basic
than is ordinarily the case where lead ores are profitably smelted, yet the
Eureka smelters claim that they obtain better results than they would if the
percentage of silica was much increased. The amount of arsenic in the
ore, which causes the formation of speiss, without doubt renders the smelt-
ing of such a basic mixture possible. The flue dust, which is collected in
long canals connected with a high stack on the hillside, is mixed to a thick
paste with clay and water in the proportion of one part clay and two parts
of dust, is somewhat dried, and added to the charge.

Example of a charge—The following is an example of a charge of one of the
furnaces:

OlMIGNA a cewaseo tea Hee docceceseuse Ge sSeses scoops.--- 40
HATCH MTOM OLN ese a sales ainie eels ee ose te = a shovels.... 50
Ruby-Dunderburg (silicious ore).-..---.---..----d0.-..-.- 10
Hoosac slag (silicious and rich)...--------------. doeaeea= 50
Silver Lick (silicious ore) -...-----. ------------- A@ -Sonec 6
Adobe flue dust ...... ighe SAAe BR OoSUnSCeDSaOoOS dOkee ae 4
SHOES ed bee beon Ggudoe cdc aisSuy odessa doEDoor doses 52 i
(ATOMIC) shonge sageencoter oes cs0ede sande be Bt! eerie 2

The Richmond ore contained three to four per cent. silica. The rest of
the silica required for smelting is supplied by the Ruby-Dunderburg, Silver
Lick, and other more or less quartzose ores, and by the Hoosac slag. The
Hoosac slag was a rich slag from the imperfect smelting of lead ore with a
quartz gangue. The charge is supposed to contain about the following per-
centages:

Per cent.
INTO Ga) de GdeGuBkOOBCEH ue bab bocood OooRcEnsorhmrpad 40
Sidi caeeery tetera ecto reciers cre rettie elec wren ceiaeiscuicic do me 2 ule 20
Binns Oh.¢0) 4G os 666 Soo00 peodos copper ccaee Pee See)
Ofer mineral Nye eee steele) oetelemisieiate sialals'olea1~ yoerseeesiee 18
100

2654 L——11

162 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Fuel—The fuel used in smelting is charcoal made from the pinon pine.
The coal produced from this wood is usually very good, and in this district
it is of an exceptionally fine quality, the method by which it is manufact-
ured having been brought nearly to perfection. Nearly all the coal-burners
are Italians who have been attracted to this country by the opportunities
offered for this particular class of labor. About 30 bushels of coal are
required per ton of ore smelted, and the present cost is 30 cents per bushel.

Refining—'The lead from the smelting of Richmond ore does not usually
require calcining. Hard lead is refined in large rectangular cast-iron pans,
which will hold about 14 tons. The time required for softening is from two
to four days, according to the quality of the lead.

Pattinsonizing. —The process used in concentrating the silver in the lead is
the Luce & Rozan process, a modification of the Pattinson method, and is
carried on as follows: The principal portions of the apparatus employed are
two melting pots, one comparatively large crystallizing pot on a lower level,
two receivers or molds below the crystallizing pot, and a crane to handle
the cakes of lead after they have solidified in the molds. The upper pots
are provided with covers and the lower one with a hood and pipe to
carry off the steam and fumes. There is a pipe by which water is let into
the crystallizer above, and one for admitting steam into it below. The
steam valve consists of a horizontal pipe which penetrates to the center
of the pot, and within this pipe there is a rod with a button on the end
which enters the pot. On screwing the rod in, the button is. removed
from the end of the pipe and steam is forced into the melted lead through
which it is distributed, by means of a perforated false bottom, through-
out the whole mass. The receiver or molds on each side of the crys-
tallizer hold 7,400 pounds of lead. When the lead is drawn off into
these molds an “eye” is introduced into the melted mass before it cools.
In removing these cakes the hook of the crane chain is inserted in the eye,
and by means of the steam hoist attached to the crane they are removed
from the molds. When either market or rich lead is drawn from the erystal-
lizer, molds on two wheels and a peg are placed in a semi-circle around the
discharge pipe and filled by a movable spout. The cakes are hoisted and
placed in the melting pots by the crane. It is unnecessary to enter into a

METALLURGY. 163

further description of the mechanical details of the apparatus and process,
which have been repeatedly described in the technical journals.

The first operation consists in melting down 50 tons of lead in one of
the pots. This is then drawn off into the crystallizer, and water is turned
on to chill the lead, because much time would be required to cool it by radia-
tion. Then steam is admitted, which thoroughly stirs and at the same time
completely refines the melted mass. When the crystallization is completed,
which takes place in about one hour from the time the lead is drawn off
from the melting pot, about two-thirds of the mass is in the form of crystals
assaying 100 ounces to the ton and one-third is still melted, containing
about 460 ounces. This rich lead is drawn off into molds and taken to the
cupel furnaces. In the mean time enough lead of the value of 100 ounces
to the ton has been melted in the second pot, and is allowed to flow into the
erystallizer, where it immediately dissolves the crystals of 100-ounce lead.
This is now crystallized, giving 75-ounce poor lead and 150-ounce rich lead,
which is drawn off as before. The lead is thus crystallized until market
lead of about the value of one ounce to the ton is obtained. This requires
nine crystallizations, which give lead of approximately the subjoined values:

LEAD FROM THE CRYSTALLIZATION OF 220 OUNCES LEAD.

Ounces to the ton.

First crystallization.........------ Ae speticreetine see 100
Second crystallization....-..-..--.-----..-.---.------ 75
Ehind (crystallize glOMe ees ipe ae cea re sl arate so. = 2l=raf 50
Fourth crystallization .......-.--.------------+--- = BO
Bifthverystallizations. 2. -2--.-.25-20-+6--+--00+ 8-2 2~= 18
Sixth crystallization ........-..-..-------------+----- 9
Seventh crystallization ........-.-.-----5---+------++-- 5
Eighth erystallization ....-...---.-- Bee eee eater 2.5
Ninth crystallization ......------. HS GRECO FBCAEE ee Fay

It is found that there is no sensible enrichment of the lead after it has
reached 550 ounces (less than 2 per cent.). The ratio of the gold to the silver
in the lead from the smelting furnaces is about 1 to 32 by weight, or in value
about $1 gold to $2 silver.

The use of steam in this process appears highly advantageous. The
stirring produced is probably more thorough than that accomplished by

164 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

machinery, which as hitherto designed is somewhat complex and subject to
frequent stoppages for repairs. The steam is also in part decomposed at the
temperature maintained, and thus accomplishes a very considerable refine-
ment of the lead during the process of concentration, producing an excel-
lent market lead from comparatively hard bullion.

Cupetiation—The rich lead is cupelled in furnaces of the English model
with bone-ash tests. The test holds from a ton upwards. It is filled with
lead which is brought to .a cupelling heat and an air-blast is turned on.
This blast is preferred to steam, as the-latter becomes moist and also in-
creases the loss in silver, although the loss in any case is slight. The test
is kept full of lead by adding bars one by one at the back of the furnace
and allowing them to gradually melt down. It is tapped every twenty-
four hours, when from six to eight bars containing two-thirds silver are ob-
tained, Sixty such bars, on a second cupellation, give in about sixteen
hours 16,000 ounces of doré silver, .965 fine in silver and .030 fine in gold.
A test lasts about ten days. In refining, concentrating, and cupelling
mountain mahogany wood is used. It is a very superior fuel, and costs
from $10 to $12 per cord.

The poor litharge, containing about an ounce to the ton, is reduced to
market lead in reverberatory furnaces, with refuse charcoal from the bins.
The rich litharge, containing as high as 75 ounces, is resmelted with a fur-
nace charge, as there is almost always a dearth of lead in the ores.

Advantages and disadvantages of refining —It is a question whether Eureka is an
advantageous locality for refining bullion, fuel being high and labor $4 per
day. Refining on the spot obviates the necessity of paying interest upon
the money required to freight the unparted lead to a refinery in San Fran-
cisco or the East, and the market is frequently so overstocked with lead
that it is better to wait for a rise before shipping. On the other hand, high
charges are incurred in expressing the doré silver, which would be avoided
if the bullion were transported by freight as it comes from the furnaces.

CHAPTER XVI.
ADAMS HILL.

Topography and formations —The summit of Adams Hill is situated about 3,400
feet nearly due north from the top of Ruby Hill. The hill is a gentle ele-
vation which rises to a height of 6,940 feet above sea-level and slopes with
a gradual descent toward the valleys on the west and north. It is divided
from Ruby Hill by a moderately deep ravine which enters Spring Valley.

The principal part of the hill is composed of Hamburg limestone, the
Secret Cafion shale forming a band running east and west along its south-
ern flank, and the Hamburg shale making its appearance in a like manner
on the northern slope. ‘To the north of the Hamburg shale and to the east
of the Hamburg limestone the Pogonip limestone is exposed. ‘The non-
appearance of the Hamburg shale between the Hamburg and Pogonip
limestones at the latter place is due to the continuation of the Jackson fault
described by Mr. Hague. North of the Hamburg shale, in the Pogonip
limestone, there is a large outcrop of quartz-porphyry, and still further on
in the same rock a smaller overflow which is visible underground in the
workings of the Bullwhacker mine. The dip of all the formations of
Adams Hill, including the Secret Cation shale, is apparently to the north.

structure —Although the mining explorations which have been made on
Adams Hill are not sufficient to give a complete idea of its internal struc-
ture, they are, nevertheless, extensive enough to show that it is composed
of a bed of limestone underlain and overlain by distinct beds of shale, all
of which have a variable dip to the north. There is much less evidence of '
faulting and crushing in Adams Hill than there is in either Ruby Hill or
Prospect Mountain. The rock does not seem to have been subjected to the

enormous pressure that has caused the erinding up of the limestone in
(165)

166 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

those last-mentioned localities. On Adams Hill that rock is harder, more
compact, and less subject to sudden changes in its physical characteristics.
In many places the Hamburg limestone is capped by a conglomerate con-
sisting of bowlders of limestone cemented together by a tough calcareous
material. In this conglomerate fragments and even bowlders of ore are
often found. This ore does not resemble in any respect the ores of Ruby
Hill, and it is likely that it, as well as the accompanying limestone, are the
products of the erosion of the immediate neighborhood, which have been
cemented together by calcareous waters.

Ore deposits —The deposits of this portion of Eureka District are as varied
in regard to form as those of Ruby Hill, but in many other respects they
differ from them. There is very little resemblance between them and true
lodes, though they are all more or less connected with fissures and slips,
and some of them which occur in the limestone near the shale seem to have
a general course parallel to the contact of those formations. An instance
of this occurrence can be observed in the Bowman mine, which lies near the
Secret Cation shale. Caves, which are so characteristic of Prospect Mount-
ain and Ruby Hill, are rare; and although it is possible that such openings
may exist in numbers, the explorations have not yet revealed them. It is true
that the deepest mine workings have as yet attained but a moderate depth,
not much exceeding 200 feet, although the explorations have been quite
numerous. Nevertheless it is probable that if caves were numerous they
would have been revealed before now, for it can besafely said they are of more
frequent occurrence and usually of greater extent near the surface than at
great depth. This is easily explained by the fact that the waters carrying
carbonic acid, to which they owe their origin, becomes saturated with cal-
cium carbonate as it descends, thereby losing its solvent power. The
absence of caves, which in other portions of the district are so intimately
connected with ore bodies, would seem to indicate that the genesis of these
deposits was somewhat different from that of the ordinary class. This
theory is also sustained by the fact that the ores are of a different character
from those of Ruby Hill. The most noticeable difference is the prevalence
of quartz ores. This can be said to be the distinguishing feature of the
ores of Adams Hill, as well as those occurring in the Pogonip limestone on

ADAMS HILL. ~ 167

the flat to the north, which is designated on the map as Mineral Point. The
ores do not occur in compact form as the filling of chambers, but are found
in bunches in cracks and seams in the limestone, and although masses of
ore of considerable size are not unknown, they exist in the form of silicified
limestone more or less impregnated with silver and lead minerals.

Theores—The Kureka quartzite, which Mr. Hague has placed just above
the Pogonip limestone, at one time covered the whole of Adams Hill, and
there is still a small area of this rock to be seen on the northwestern slope
of the hill near the road to the Wide West mine. It is not impossible that
the quartz in the ore was derived from this quartzite. Still it is not likely,
however, as it would be necessary for the silicious solutions, which were
formed from this quartzite, to traverse the underlying Hamburg shale
as well as the Pogonip limestone. Also, if the quartz in the ore was
derived from the quartzite, it is likely that the ore was as well, as the two
seem to have been deposited simultaneously, though this might possibly
have occurred where the components of the ore were derived from different
sources. The Eureka quartzite also carries small amounts of the precious
metals; but the same objection to the secretion of the ore from this rock
can be advanced that was offered in regard to the secretion of the ore in
Ruby Hill from the outside country rock. It could hardly have passed
through the Hamburg shale: It is possible, however, that the ore in the
Pogonip limestone was derived from this source, though, as has been
explained in Chapter VII., it is more justly referable to another source.

Another noteworthy fact in regard to the ores of Adams Hill is that
they carry as a rule a high percentage of gold, although there are some
that carry no gold whatever. The contents in gold is a distinctive feature
of this region. Lead in the form of carbonate and sulphide is common, and
both the Bullwhacker and Williamsburg mines have produced large quan-
tities of this metal.

Quartz-porphyry as a source of the ore—The quartz-porphyry which occurs in the
Bullwhacker mine has already been mentioned (Chapter VII.) as the prob-
able source of the ore in its immediate neighborhood. This porphyry still
contains considerable quantities, relatively speaking, of gold, silver, and
lead (see Chapter XI.), and although it does not cover a very extensive

168 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

area on the surface it is very likely that it may extend underground into
Adams Hill. If this is the case, it has very likely been the source of the
ore in the mines of that region. If it has been the source of the ore it is
probable that the quartz has also been derived from it through the decompo-
sition of its silicates.

Mining —The ore of this region is usually of very good quality, but the
rock is frequently hard and it is extracted with some difficulty. The mines
have been opened by individuals and small companies, and they have not
been sufficiently explored to determine either their permanency or their
future value. Just at present there is not very much mining going on in
this part of the district, but there seems to be no reason for believing that
the deposits do not extend to considerable depth, and it is to be hoped that
the decreased cost of mining and of reduction which inevitably follows the
increasing age of a mining camp will cause the revival of this industry.

CHAPTER XVII.
FUTURE OF EUREKA DISTRICT.

extent of the Prospect Mountain deposit The mining region of Prospect Mountain,
comprised between Spring Valley on the west and the Secret Cafon road on
the east, will no doubt produce large quantities of ore for years to come.
As yet a beginning only has been made in the development of the deposits
in this portion of the district. It is true that there are several mines, the
Hamburg, Ruby-Dunderburg, and one or two others, which have been
pretty well opened, though in all of these there is a great deal of ground
which remains as yet in a virgin state, but in by far the majority of instances
the claims of Prospect Mountain and vicinity have not been explored to any
great extent. If the surface geological map is examined it will be seen that
the two belts of limestone, which Mr. Hague has named, respectively, the
Prospect Mountain and Hamburg limestone, are very wide; and although
they cannot be regarded as ore-bearing throughout their whole extent, yet
surface explorations have shown that the deposits contained in them are very
numerous. Underground developments, as far as they have extended, have
also proved that these deposits are continuous to a considerable depth. It
is therefore very probable that numerous unexpected ore bodies will be dis-
covered throughout this region in the course of future deep-prospecting
operations.

Relative size of the Prospect Mountain and Ruby Hill deposits.— At first sight no reason
appears why as extensive ore bodies should not be encountered in Prospect
Mountain as have been found hitherto in Ruby Hill, but a careful exami-
nation of the structural features of the two regions leads to the belief that
the ore bodies of the former locality will never reach the size of those of

the latter.
(169)

170 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

It has been stated before that the opportunities for the deposition of ore
have depended in a great measure upon the extent to which the limestone
has been crushed and thus prepared for its reception and deposition. It
cannot be said that such a shattering of formations has not taken place to a
great extent on Prospect Mountain. It has, and its results are shown by
the numerous fissures and zones of pulverized rock which are encountered
in this region; nevertheless, the upheaval and faulting did not take place
under conditions that were in every way as favorable as those which resulted
in the present structure of Ruby Hill. The faults which brought about the
present arrangement of the formations in the latter locality were accom-
panied by the formation of a fault-fissure which acted as a channel through
which the metalliferous solutions entered the wedge-shaped mass of lime-
stone lying between this main fissure and the quartzite. Whatever other
part this quartzite may have played in the formation of the mineral zone of
Ruby Hill, it certainly had the effect of confining the ore-bearing solutions
to the crushed limestone bounded by the clay of the Ruby Hill fault. Had
these solutions entered a mass of limestone of unlimited extent, although
the amount of ore deposits might have been as great in the aggregate, it is
not likely that ore bodies of a size equal to that for which this mineral belt |
has been noted would have been deposited. It cannot be denied that cer-
tain ore channels exist in Prospect Mountain, and that they are also con-
fined in some instances between belts of shale, or between walls of lime-
stone; yet, as far as present developments have shown, there has been no
such limitation of the ore to a well-defined region.

Resources of Prospect Mountain. — These facts, however, need not prove a draw-
back to a careful exploration of the resources of Prospect Mountain. The
Ruby Hill deposits were worked to a large extent when the cost of mining
and reducing ores was far greater than it is at present, in spite of which
they paid large profits; and a reduction in the cost of working-ores, coupled
with the increased facilities offered by the tunnels aad more systematic
methods of mining, will compensate in a very great degree for any dif-
ference in the size of the ore bodies which may exist in the two regions.

Relative richness of the deposits of Prospect Mountain and Ruby Hill—It is said that the

ore of Prospect Mountain, as a rule, is richer than that of Ruby Hill. This

FUTURE OF THE DISTRICT. a Eyal

may or may not be the case. The only present means of determining the
facts are by judging of the ore that is brought to the smelting works for
reduction. The returns show that the ore of Prospect Mountain averages
richer than that of Ruby Hill, but this is very likely owing to the fact that
only ore of a high grade will pay for mining when the deposits are small,
and cannot be taken, therefore, as a criterion of the value of all the ore in
these mines.

Difficulty of making predictions. — What will be the future of the mines of Ruby
Hill is very uncertain, and any predictions in regard to it must necessa-
rily be inferences from the results of the explorations which have been
made in the present lower workings. These explorations have not been
carried sufficiently far to give indisputable indications as to the changes
which may be expected in regard to the ore below the water-level. More-
over, the structural features in the lower levels of these mines have under-
gone a change, and it is impossible to tell with any certainty what effect
they may have upon the general worth of these ore deposits.

Probabilities of finding ore in the lower workings—'I‘he structure of the ore-bearing
zone and the relation of the ore bodies to it have been fully described in
the preceding pages of this report,-down to a level, in the mines southeast
of the compromise line, where the two fissures come together, and in the
Richmond and Albion mines to a depth at which it is clear that they are
approaching and will probably meet below. It has been stated that the
bodies of ore in the Richmond mine have decreased in size as well as num-
ber below the sixth level. The ground, however, below this level, although
it has been prospected to some extent, has not been sufficiently cut up to
prove the absence of large ore bodies, and it is possible that the failure of
ore is only apparent, and that future developments may expose large bodies.
There is nothing in the nature of the limestone inconsistent with such a
belief. The same may be said of that portion of the Albion ground which
lies immediately northwest of the ‘“‘A C” line. The ground in which the
Albion shaft is sunk and that which lies west of it is unfavorable for ore, the
limestone not resembling that which contains ore in other parts of Ruby Hill,
while the faulting motion has not been great, and the limestone is therefore
less disturbed. Even if ore should not be found in any quantities in these

172 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

two mines in the lower levels before the two fissures came together, this will
not prove that no-ore bodies are to be expected in the limestone which un-
derlies the lower belt of shale. It will only prove that the limestone or the
fissure system in this part of the hill was for some unknown reason unfavor-
able to the deposition of ore. It will be a very discouraging circumstance
to the companies interested, but it may be expected. Large zones of barren
ground have been known in the upper levels as well.

Conditions of ore deposition in the lower wedge of limestone—I f Plate VIII. is referred to,
it will be seen that the lower mass of limestone is gradually widening out, as
would inevitably be the case if the ideal section of Ruby Hill (Plate IV.) be
true. The main fissure below the great limestone wedge has a hanging wall
of crushed limestone which is overlain by a belt of shale. If the theory of
the source of the ore stated in Chapter VII. is correct, the ore solutions
passed upward through this fissure along the contact with the limestone,
which offered all the conditions necessary to a deposition of the ore, pro-
vided the ore substituted itself for limestone. If such was not the case, and
the ore was deposited in caves previously formed, there is little likelihood
that this cave formation could have taken place in the lower bed of limestone,
for the following reasons: It is certain that the caves in the upper lime-.
stone were formed after the faulting occurred which broke up this mass of
rock and formed the main fissure. This main fissure with its wall of clay
and the lower belt of shale effectually excluded any great flow of surface
water into the lower belt of limestone, nor does the cave formation even in
the upper limestone seem to have extended to the lowest points of this
wedge of rock, probably because percolating surface waters became satu-
rated with calcium carbonate upon reaching this depth. It is therefore
improbable that caves of any great extent could have been formed at the
depth at which this limestone lies. It will be seen, therefore, that the
chances of finding any considerable bodies of ore in the lower limestone,
if the ore deposition was dependent upon the prior formation of caves, are
very few. But the evidence that the ore bodies were formed, at least in
part, by substitution is very conclusive. There seems to be no probability
that such a manner of deposition should be limited to a few hundred feet
or to the upper mass of limestone.

FUTURE OF THE DISTRICT. 13

The lower bed of limestone lying between the fissure on the quartzite
and the lower stratum of shale affords almost equal structural facilities to
the upper. It has been rent and crushed by the upward movement of the
quartzite in a similar manner for a considerable distance, at least below the
region where the lower stratum of shale was cut off by the fault. It would,
therefore, offer every possible opportunity for the circulation of metalliferous
fluids. Ore has also been found in the Ruby Hill fault-fissure at the place
where it was cut by the drift from the 1,200-foot station of the Locan shaft.
The flow of water was unfortunately so great, however, that it was not
possible to determine the extent of this body. There thus seems to be no
well-founded reason for believing that. masses of ore do not exist in the
lower stratum of limestone.

Whether the ore bodies will prove as large and as numerous as they
have been above is a matter which cannot be decided from the limited
number of facts which have been observed in the lower workings. Whether
the extraction of this ore will be profitable will depend upon the flow of
water, size of ore bodies, value of ore, and facilities with which it can be
reduced. As to the size of the ore bodies, no satisfactory predictions can
be made. No very great change in the value of the ore as regards silver
need be feared. There will be poor ore bodies as well as rich ones, no
doubt, but the ore is more likely to be somewhat richer in silver than the
reverse, if there is any analogy between the ores of this district and those
of a similar character in others where oxidation has taken place. With
regard to the value in gold it is otherwise. .The contents of the Eureka
ores in gold has on the average been gradually decreasing as depth was
attained, and it is but reasonable to suppose that this will be the case below
the water-level. No entirely satisfactory reason can be given for this de-
crease in gold, but it is of very frequent occurrence in auriferous silver ores
in many parts of the Great Basin. It was, however, not the case on the
Comstock, and the change noticed in the ores of Eureka may be only a
local one.

This fact need not necessarily be a cause of uneasiness, as there is no
likelihood that the gold will give out altogether, and a slight reduction in
the quantity of this metal present would not materially reduce the value of

174 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

the ores. While many geologists and many engineers believe that ore
deposition is not limited to any depth within human reach, others are of the
opinion that ore in considerable quantity usually occurs only within a mod-
erate distance of the surface. This question, however, cannot be satisfac-
torily discussed from a theoretical point of view until much more is known
of the chemical and physical conditions of ore deposition, nor as a matter
of observation until far more thorough explorations have been carried on
at great depths in mining regions. Some deposits have been followed to
an immense depth (over 3,000 feet) without any diminution in yield; and
if it were possible to gauge the erosion to which their croppings have been
subjected since their formation, these and others would very likely yield
more striking data. On the other hand, in many cases the search for ore
below a certain depth has proved futile, but such cases afford purely nega-
tive evidence. Explorations at considerable depths are extremely expens-
ive, and are rarely made on a large scale. It is consequently as yet im-
possible to say even of any single district that ore in paying quantities does
not exist below a certain level, though it is certainly true of some that no.
indications of its existence have been found which would warrant the con-
tinuance of the search for it.

That the various companies owning these mines are fully justified in
view of the former enormous production and the probabilities of finding
ore in prosecuting a diligent though expensive search below the levels as.
yet reached seems to be beyond question.

As regards the future of Adams Hill and adjacent country, not much
can be said; the mines have not been worked to any great depth or extent,
and but few predictions can therefore be made in regard to them.

CHAP Tan ONLI,
SUMMARY.

The following summary states in a condensed form the nature of the
investigations described in the foregoing chapters and the conclusions to
which they have led.

Description of Eureka District—Hureka Mining District is situated on the west-
ern side of the Diamond Range, in the eastern part of the State of Nevada
and south of the Central Pacific Railroad.

The district was discovered in 1864, but it was afterwards abandoned
until the latter part of 1868, when mining operations were again begun.

The most important town in the district is Eureka, situated about 2
miles distant from the principal mines which are on Ruby Hill.

This hill forms the northern spur of Prospect Mountain, a ridge several
miles long, which reaches an altitude of over 9,000 feet, and itself forms a
spur of the Diamond Range. North of Ruby Hill lies Adams Hill, a low
elevation distant something less than a mile. On these hills and on the
mountain and its spurs are situated all the mines of any importance in the
district.

As nearly as can be estimated the production of the precious metals
up to the end of 1882 has been about sixty millions of dollars. It is difh-
cult to ascertain the quantity of lead produced, but this is approximately
225,000 tons.

SURFACE GEOLOGY.
Mr. Arnold Hague has described the general geology of this district,”

“Abstract of Report on the Geology of the Eureka District, Nevada, by Arnold Hague. Third

Annual Report of the Director of the U.S. Geological Survey. 1882. 8)
(

176 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

. but a reference to his results is necessary to a clear conception of the rela-
tions of the mines to the different formations.

The Cambrian, Silurian, Devonian, and Carboniferous are all repre-
sented in this district, though it is only in the rocks of the first two that
metalliferous deposits of any kind have been found.

Formations —Mr. Hague distinguishes the following beds in the Cee
beginning with the oldest: Prospect Mountain quartzite, Prospect Mount-
ain limestone, Secret Cafion shale, Hamburg limestone, Hamburg shale.
Those five formations have all been laid down conformably. The rocks of
the Silurian in the order of succession are Pogonip limestone, Eureka quartz-
ite, and Lone Mountain limestone. The rocks of the Devonian in_ this
neighborhood are the White Pine shale and Nevada limestone.

Relations of the mines to the formations —With the exception of the Hoosac mine
in the Eureka quartzite, and the Bullwhacker and other mines in the Pogo-
nip limestone on the slope north of Adams Hill, all the mines which have
been discussed in this memoir are found in the Prospect Mountain and
Hamburg limestones. No deposits whatever have been found in the Secret
Canon shale which separates these two beds, and although it is true that
pyrite, both as impregnations and in masses, as well as distinctly-defined
veins of quartz accompanied by calcite, have been found in the Prospect.
Mountain quartzite, the lowest of the sedimentary beds ‘of the district, it
has had no economic value. These occurrences, moreover, do not seem to
be in any way connected with the deposits in limestone, and, as far as is
known, there is no ore in the Hamburg shale.

Massive rocks—The only massive rocks which make their appearance in
the metalliferous zone which is occupied by Prospect Mountain and its off-
shoots are granite, quartz-porphyry, and rhyolite, but hornblende-andesite
is found in its neighborhood. Quartz-porphyry, probably Mesozoic, ap-
pears in two places north of Adams Hill, and seems to be of earlier origin
than the ore. Rhyolite is abundant in the neighborhood of the mines, as
well as in immediate proximity to the ore. In some portions of the district
it covers large areas, but in the mines it is only found in the form of dikes.
Hornblende-andesite occurs near Hoosac Mountain, where it covers con-
siderable territory, and basalt is found within three miles.

SUMMARY. ea

THE STRUCTURE OF PROSPECT MOUNTAIN.

Manner of upheaval— Prospect Mountain and its adjacent spurs form an anti-
clinal fold, of which the axial plane is somewhat west of the crest of the
principal ridge. The course of this plane is nearly due north and south
“except at Ruby Hill, where it turns towards the west. Evidences of bed-
ding are so rare that it is often impossible to form an accurate idea of the
prevailing angle of dip. When the formations which at present compose
the mountain were folded and uplifted, an enormous crushing and grinding
force was exerted upon the different members of the series. Those rocks,
such as the shales, which were flexible were much twisted and distorted,
but retained their original character. The limestones, on the other hand,
were much crushed and fissured, and faulted in many directions. Most of
the fissures were found parallel to the axis of fold, and as the uplifting and
crushing continued great zones of limestone were ground almost to powder.

Influence of eruptive rocks— Subsequently to the primal folding the various
eruptions, especially that of rhyolite, had a further disturbing effect upon
the structure of the country. Many fissures and faults have unquestionably
been caused by the eruption of the rhyolite, and, as will appear later, it
had a direct influence upon the deposition of ore.

The only known occurrence of granite in the district is on Mineral
Hill at the north end of Prospect Mountain. It is probable that this mass
formed a submarine hill upon which the quartzite, limestone, etc., were laid
down, and that its exposure in its present position is due to erosion after
upheaval had taken place.

Bowlders resembling this granite have been taken from the quartzite
in the Richmond shaft. The strata of the formations which compose Pres-
pect Mountain usually dip away from the axial plane of the fold, though
there are notable exceptions to this rule.

Section of Prospect Mountain through Eureka tunnel— The best opportunity for studying
the formations on the eastern slope of Prospect Mountain is given by the
Eureka tunnel, which has been driven from a point near the head of the
west branch of Goodwin Cafon in a nearly due west direction into the

heart of the mountain.
2654 L——12

178 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

The following are the different formations encountered, in the order of
their succession from the mouth of the tunnel:

85 feet mineral limestone® .-.-.-. Hamburg limestone.

290; feet shale: 2... -sis520ahes: soe Secret Cafion shale.

935 feet mineral limestone......-. Prospect Mountain limestone.
3d0 feet shale? 0... cts. jeeceer Prospect Mountain limestone.
51 feet mineral limestone......-- Prospect Mountain limestone.

460 feet shale ...... ete eNO Ere ohne Prospect Mountain limestone.
90 feet stratified limestone ...--. Prospect Mountain limestone.
50 feet mineral limestone. ....--. Prospect Mountain limestone.

At various points along its course the tunnel cuts through seams and
fissures, which generally cross it at right angles. Their usual pitch is east-
erly, though there are many exceptions to the rule. The msot prominent
one of these fissures is at a point 840 feet from the mouth of the tunnel.
It dips nearly vertically, perhaps a little inclined to the east. It is open in
places and filled with sediment, bowlders, etc., which have been washed in
from above. At the point where it is encountered it is about 350 feet below
the surface, and it is a characteristic example of numerous occurrences of
the same kind both in the mountain and in Ruby Hill. Like many others,
it has been accompanied by ore which was formed on the west side of the
tunnel. Faulting has occurred on most of these fissures, and it is safe to
say that the portions of country which lie west of the fissures or upon the
foot-wall side have as a rule been relatively raised, and the strata have
reached their greatest relative elevation just over the axis of fold.

The stratified limestone in the end of the tunnel pitches west at a
steep angle where first encountered, but gradually becomes flatter until a
little distance west of the summit its stratification is nearly horizontal.

Section of Prospect Mountain through Prospect Mountain tunnel. — [he Prospect Mountain
tunnel, starting at a point about 2,700 feet west of the summit, nearly op-
posite the Eureka tunnel and several hundred feet below it, has been driven
over 2,350 feet into the mountain. For the first 1,400 feet it passes through
a hard, compact, white limestone, which in places resembles marble. This

2‘‘Mineral limestone” is the term employed in the district to designate the broken and meta-
morphosed rock almost invariably connected with ore.

>The term ‘‘ Prospect Mountain limestone,” of course, refers to a group of beds characterized by
the presence of certain fossils. Though limestones predominate, the intercalated shales are necessarily
classified as members of the same group of beds.

SUMMARY. 179

limestone is not often fissured, but contains some cavities excavated by
water. There is nothing about it to indicate that it is mineral limestone.
At a distance of 1,400 feet from the entrance a fissure is encountered nearly
‘at right angles, which dips 80° to the west. From this point the character
of the limestone changes; it is much more broken, and many of the ordi-
nary varieties of mineral limestone are found, as well as seams, crossing
the course of the tunnel. At 1,835 feet ore was discovered, but as yet
the deposit has not proved valuable. At about 2,100 feet stratified lime-
stone was encountered along a fault-seam which dips to the west, and at
2,250 feet shale makes its appearance along a similar seam (see Plate IT.).
It is probable that this shale is the same body as that encountered toward
the end of the Kureka tunnel. All of the rock encountered in this tunnel
belongs to the Prospect Mountain limestone.

General internal structure of Prospect Mountain—IJt will be noticed (Plate II.) that
the west side of the mountain differs greatly from the eastern. This in
some measure is owing to the fact that a larger portion of the overlying
rocks have been eroded, and that the axis of fold lies somewhat west of the
ridge. ‘

Distribution of ore in Prospect Mountain —The larger portion of the mountain and
its adjacent spurs is composed of mineral limestone, and evidence of the
number of metalliferous deposits contained in it is offered by the numerous
outcrops of gossan which occur along its whole extent, but which are
particularly numerous from Ruby Hill to the Secret Canon divide. With
the exception of some few mines, the properties of Prospect Mountain have
been but slightly developed. Those, however, that have been opened to
any great extent show that there are numerous masses of ore contained in
the Hamburg as well as the Prospect Mountain limestones, although no
bodies of such a size as those discovered in Ruby Hill have been found.

THE STRUCTURE OF RUBY HILL.

The formations of Ruby Hill——The position of the different formations on the
surface of Ruby Hill, and the relations that they bear to the granite of
Mineral Hill, can be observed by a reference to the geological map of the
district. The limestone of these two hills formed one and the same body

180 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

before erosion, and it is merely the continuation of the long belt of lime-
stone of which the greater part of Prospect Mountain is composed.

The main beds of Ruby Hill are a mass of quartzite, which is probably
underlain by the granite of Mineral Hill; a broad zone of mineral limestone
and an overlying belt of shale. All of these beds have been tilted so that
they stand at an angle of about 40°, though nowhere on Ruby Hill does
the dip of the stratification of any of the beds conform to the dip of their
planes of contact. This lack of parallelism is characteristic of the region
of Ruby Hill, and is due to a succession of faulting movements. There
are two systems of fault-fissures on Ruby Hill. The first consists of those
which are approximately parallel to the strike of the formations, and which
were produced entirely by the main folding and upheaval, and the second
made up of those which were caused by the same forces supplemented by
strong lateral pressure.

That there has been lateral pressure exerted from a northeasterly direc-
tion at some time is shown by the direction of the striation marks observ-
able on these latter faults, which have been called cross-faults. Beginning
at the Jackson mine at the southeast, the strike of the formations is to the
north, but it is soon deflected to the west until in the Albion mine it is .
nearly due west.

The quartzite and limestone contact——The line of the contact of the quartzite and
limestone on the surface of Ruby Hill represents very nearly the crest of
the anticlinal fold. Underground, this contact is extremely irregular.
Besides smaller irregularities in the quartzite there are three large protru-
sions along the course of this contact, which occur respectively in the
Pheenix, K. K., and Richmond mines. Along the line of dip of the quartzite
and limestone contact there is a great depression several hundred feet in
vertical extent, which occurs at about the same depth in all the mines, and
which combined with undulations along the line of strike forms large basins.
These basins are intimately connected with the ore bodies and will be re-
ferred to later.

The main fault—The most important structural feature of Ruby Hill is a
fault which at the southeastern end of the mineral zone is first to be seen
at the American shaft. (See Plate III.) From this point, this fault, which

SUMMARY. 181

has been called the Ruby Hill fault, though not perceptible in many places
on the surface, passes west of the Jackson hoisting works, its course veering
toward the west, and is visible in a tunnel near the Pheenix line. It passes
northeast of the Pheenix, Lawton, and K. K. shafts, but must be very close
to the latter. It can next be seen near the mouth of a tunnel run to con-
nect with the Bell shaft. The last place where it can be observed on the
surface is near the Richmond office. Although this fault is not continuously
traceable above ground owing to the d¢bris, its existence is fully established
by the fact that it is encountered at numerous points in the underground
workings of all the mines of Ruby Hill. The average dip of the plane of
this fault is about 70° northeasterly, and it is of remarkable uniformity,
scarcely ever varying 5° one way or the other. Its course, also, is ex-
‘tremely direct, with the exception of the bend between the Phoenix and
Jackson. This Ruby Will fault is marked by the presence of a fissure filled
with rhyolite and clay which is widest in the Jackson and Phoenix, where
in places it measures as much as 15 feet. In these two mines it is filled
with rhyolite, which, although much decomposed, is still easily recogniz-
able. In following the fissure west the clay is found to be more calcareous,
and in the K. K. and Eureka positive proofs of rhyolitic character are lost.
In the Richmond mine the fissure is narrow, and although a distinct and well-
defined seam is only a few inches wide.

The main fissure— This fault fissure has been called the main fissure, as to
its formation are due the most important features of the present structure
of Ruby Hill. A proof of its comparative recent formation is the fact that
it faults all the formations with which it comes in contact, but is itself
nowhere faulted. It is evident that the country southwest or on the foot-
wall side of this fault has been raised many hundred feet above its hanging
wall. The distance has apparently been greatest in the Eureka, where it
has certainly exceeded 1,400 feet. (See Plate VIII.)

The dip of the quartzite and limestone contact does not greatly exceed
40°, while the dip of the main fissure is about 70°. The two surfaces of
motion therefore approach each other, and the line of junction is exposed
at various depths in the lower workings of all the mines except the Rich-
mondand Albion. In these mines the lowest workings have not yet reached

182 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

the junction. The face of the quartzite when in contact with the fissure
is no longer the original contact of quartzite and limestone, but is the fault
face of the southwestern uplifted country. (See Plate IV.) It is evident
that if the fissure continues downward with its present dip, at some depth
it must enter the quartzite.

The secondary fissure——At the time of the disturbance which produced the
Ruby Hill fault, another and secondary fissure was formed along the con-
tact of the quartzite and limestone, and the quartzite was raised higher
than the limestone, giving rise to the formation of a wedge of limestone
between the quartzite and the main fissure. Up to the present time all the
ore of any importance taken from Ruby Hill has been extracted from this
wedge of limestone, the crushed condition of which is due to the upward
movement of the southwestern country against the hanging wall of the
main fissure. Section 7, Plate VIIL., is typical of the relations of the
two fissures to each other and to the quartzite, limestone, and shale in the
mines southeast of the ‘“‘compromise line.”

The two belts of shale—T'wo belts of shale, only one of which appears on the
surface, are known to exist in Ruby Hill. The upper or surface shale can be
observed on the map, Plate I. Taking into account the general dip of the
surface shale and that of the shale where it is encountered below, it is
at once apparent that the two must be distinct masses in all the mines south-
east of the compromise line. In the Richmond mine, however, it is dif-
ferent. The shale on the surface in which the shaft is sunk is the same
body of shale that is encountered below. The manner in which the Rich-
mond shale and the lower belt of shale have been brought together in the
lower workings of the Richmond and Eureka, and the manner in which
this lower shale has been faulted, have been fully explained in the body of
this report.

Influence of the main fissure on the ore formation— The time and manner of the forma-
tion of the Ruby Hill fault and its subsequent filling either with rhyolite
or clay are matters of very great importance as regards the mineralization
of the limestone between the quartzite and this fissure, and the prospects
of finding ore either at a greater depth or by prosecuting developments in
the so-called “front limestone.” This body of rock lies northeast of the

SUMMARY. 183

main fissure, and although it has in many places the appearance of ore-
bearing ground has hitherto been found unproductive, all the ore having
been obtained from the wedge of limestone between the main fissure and
the quartzite. It is true that the prospecting done in the front limestone
has not been sufficient to prove that it contains no ore bodies, but it has
been sufficient to discourage search in that direction.

As far as prospected, the front limestone does not exhibit the crushed
condition that is so apparent in the wedge of limestone between the quartz-
ite and the main fissure.

The quartzite in the Richmond— | he quartzite southeast of the Richmond shaft
appears to be a solid mass many hundred feet thick. Its contact with the
limestone is very irregular, and the rock near the surface is often displaced
to a greater or less extent by faults, but it is comparatively easy to explain
these irregularities and to account for the phenomena exhibited. Not so,
however, with the quartzite in the Richmond and Albion ground northwest
of the working shaft of the former mine. The quartzite in these two mines
consists of a narrow band from a few inches to 90 feet wide, which bends
and twists in many directions. It accompanies the secondary fissure which
leaves the face of the main body of quartzite somewhere near the Rich-
mond shaft.

Formation of the narrow quartzite——The manner in which the narrow band of
quartzite found its way into its present position seems to admit of but one solu-
tion, namely, that its occurrence is due to a fault or a succession of faulting
movements which followed the line of the accompanying fissure, and that
it originally formed part of the main body of quartzite, which must here
underlie the limestone. It is altogether improbable that it constituted a
distinct bed of quartzite laid down upon the back limestone. In this case
some indications of its existence would have been noticed in other parts of
Ruby Hill. It is not possible that it is quartz, and was deposited after the
formation of the fissure, as under the microscope it exhibits the structure of
quartzite.

Back limestone — The term ‘‘back limestone” is given to the limestone which
is found on the foot-wall side of the narrow band of quartzite. This rock
differs in many respects from the limestone which is encountered between

184 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

the quartzite and shale. As yet no ore of any kind has been found in it.
Its peculiarities are very characteristic, and it is easily recognizable wher-
ever found,

The Jackson fault—The main fissure joins a fault which Mr. Hague has
called the Jackson fault, somewhere near the American shaft.

ORES OF EUREKA DISTRICT.

Minerais—The following minerals have been noticed in the ores of
Eureka District: Galena, anglesite, cerussite, mimetite, wulfenite, limonite,
calamine, smithsonite, calcite, siderite, aragonite, quartz, steatite, blende,
pyrite, arsenopyrite, molybdenite, malachite, azurite, and wad. The lead
minerals are well represented, and it is highly probable that most of the
known varieties exist in greater or less quantities in the ores, although the
presence of all of them has not been detected. Antimony is present in
many ores, but in what form has not been determined. Silver and gold
are present; silver in the form of chloride and sulphide, and gold prob-
ably in the metallic state. Down to the somewhat irregular water-line the
ores are substantially oxidized, and consist mainly of lead carbonate and
sulphate carrying precious metals, and accompanied by ferric hydrate. The
average tenor is 15 per cent. lead, 0.079 per cent. silver, 0.00248 per cent.
gold. Quartzose ores are rare, but when found are important as a flux for
the ordinary basic variety. The various classes of ores recognized by the
miners are described in Chapter V., but may be omitted here.

Classification of the ore deposits —T'he ore deposits of Eureka District, though
they contain gold, can be classed under the head of silver-lead deposits in
limestone. The type of deposits to which those of Eureka belong is one
often met with in the older limestones of the Great Basin, and although
these particular deposits have been of more value and are more widely
known than any of the others, and exhibit some very interesting structural
features, they cannot be said to form an isolated class.

The lead deposits of the Great Basin in general, and those of Eureka
in particular, have some points in common with all the known varieties of
lead deposits in the world, but the resemblance is not sufficient to allow
any one of these to be taken as a prototype of those of Eureka. As re-

SUMMARY. 185

gards the ores and their manner of formation, the Leadville deposits of Col-
erado, described by Mr. Emmons,* resemble those of Eureka most, but the
two regions differ widely in respect to the structure of the country and the
relations of the deposits to the different formations. A classification of the
ore deposits of this district, as regards their form, is a matter of considera-
ble difficulty. Some of them may be termed fissure or contact veins, but
in most cases they are very irregular in form and are better described by
the German word “Stock” than by any mining term used in English.
They are often lenticular, but this word cannot always be used to describe
them, as they often have offshoots in all directions. Any classification,
however, that is dependent on mere differences of form must be more or
less unsatisfactory.

pistribution of the ore bodies. —The ore bodies do not seem to follow any partic-
ular direction either as regards dip or strike, and at first sight they appear
to be distributed throughout the ore-bearing formation without any regu-
larity. This is not wholly the case; and although no well-defined law can
be found governing their occurrence, this is connected with that of certain
phenomena in the country rock, such as fissures, caves, and broken lime-
stone.

Formation ofthe ore bodies —T'he distribution of the ore has been determined
almost entirely by the physical character of the limestone in which it is
found, and not by any chemical or mineralogical differences in the rock.
The greater facilities offered by a crushed and broken limestone, no matter
what its character, to the percolation of metal-bearing solutions would
more than compensate for any chemical advantages which a particular
kind of limestone might offer. During the process of upheaval to which
Prospect Mountain and Ruby Hill were subjected, the limestone was fis-
sured and crushed, great zones of shattered rock being formed, which are
separated here and there by unbroken belts. The ore-bearing solutions
entered the rock through the channels of least resistance, the crushed lime-
stone offering fewer obstructions than the fissures themselves, and deposition
followed in forms of a degree of irregularity corresponding to the complex-

ity of the preceding dynamical effects.

aSecond Annual Report of the Director of the U. S. Geological Survey, 1881.

186 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

Rearrangement of the ore by water—F rom the disposition of the ore ina stratified
form in the upper part of many of the large ore chambers it is evident that
it owes its present position to rearrangement by subterranean water cur-
rents. This occurrence has been of comparatively recent date, as the ore
has been thus deposited since its oxidation.

Connection of ore bodies with fissures, etc —Ore bodies are intimately connected with
the occurrence of fissures, caves, sediment, and on Ruby Hill with depres-
sions in the quartzite. The ore bodies at first sight often seem to have
no connection with any fissure or channel through which they could have
been filled, but such a connection has been demonstrated in so great a
number of cases that it may be presumed to have existed in all. In by
far the greater number of instances the fissure has led to the discovery of
the body, or the existence of the fissure has been shown in the workings
subsequent to the discovery of ore. Sometimes it has been almost oblit-
erated by pressure, and in others it has not been revealed by the explora-
tions of the miner.

caves——Caves are found in many places in the limestone, and no large
ore body has been found which had no cave over it, but caves are by no
means always accompanied by ore bodies.

Depressions in the quartzite and ore —he manner in which the depressions in the
quartzite on Ruby Hill occur has been already explained. That large ore
bodies should be of frequent occurrence in these depressions is not strange,
when it is remembered that the limestone in them was in a shattered and
crushed condition, and that the quartzite with its casing of clay served to
a certain extent to confine the metal-bearing solutions to the limestone
mass, where large quantities of these solutions were probably allowed to
settle quietly and deposit ore.

Relations of the ore bodies to the formations —Q)n Prospect Mountain there are no
workings in the neighborhood of the quartzite, and thus far the metallifer-
ous zones have been separated by belts of undisturbed limestone and
shale. The size of the ore bodies in the mountain has been much smaller
than those on Ruby Hill, and the caves have been smaller and less numer-
ous.

SUMMARY. 187

In the mines on Ruby Hill, southeast of the ‘compromise line,” the ore
bodies usually occur connected with the quartzite, but in the Richmond
and Albion they are almost always far removed from it.

SOURCE OF THE ORE.

Possible sources of the ore —The possible sources of the ore are a deposition in
small particles with the limestone, the ore being afterwards segregated into
nearly isolated bodies either by chemical or mechanical action; a segrega-
tion of the ore in the limestone from the country rock on either side of it;
and a deposition from solutions which came from below.

Precious metals in the different rocks —Several series of assays made with extraor-
dinary precautions show that the stratified limestone contains only the mi-
nutest traces of silver, while the mineral limestone, especially where it is
iron-stained, contains a number of cents per ton. The silver contents, how-
ever, on the whole, diminishes as the distance from the ore bodies increases,
and nowhere answers to the composition which the rock must have pos-
sessed had the ore bodies been derived from it. The trace of silver in
the limestone is an impregnation from the ore bodies. The shale never
carries more than a trace of silver and gold, and the quartzite could not
have furnished the material of the ore bodies. There are also good struct-
ural reasons for believing that the ore cannot have been formed by segre-
gation from the surrounding rocks. Neither do the examinations furnish
any reasons for believing that either the granite or the rhyolite yielded the
metallic compounds of the ore bodies.

Quartz-porphyry as a source of the ore——OQn the other hand, the quartz-porphyry
proves to contain silver, gold, and lead in no inconsiderable quantities, and
has manifestly been subjected to chemical action involving the solution of
a portion of its metallic contents. Of this the decomposition of the rock,
combined with a notable concentration of silver and gold in the pyrite
(which is of secondary origin), are evidences. While the quartz-porphyry
appears on the surface only in a small area, it is entirely possible that the
mass underlies a great part of the district, and that it may have yielded the
core which was deposited in the limestone. This, however, is uncertain,

while it is tolerably safe to say that of all the rocks which appear at the

188 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

surface the quartz-porphyry is the only one which can have furnished the
metals of the ore bodies.

The solfataric action and the ore formation The manner of occurrence of the ore
and its connection with the fissure system are consistent only with the sup-
position that whatever the source of the ore may have been, it reached its
present position in ascending solutions. The formation of the ore-bearing
solutions is almost certainly due to the solfataric action arising from the erup-
tion of the rhyolite. The intrusion of this rock was the last dynamical dis- °
turbance on Ruby Hill, for the main fissure with the rhyolite dike faults all
formations with which it comes in contact, except the ore bodies, and is
itself nowhere faulted. The rhyolite dike also shows every evidence of
solfataric decomposition. There is no evidence of two «distinct periods of
solfatarism, and unless the ore formation and the alteration of the lava are
due to comparatively late volcanic agencies, which have left no other trace
of their existence, the ore deposition and the eruption of rhyolite must have
been related phenomena.

MANNER OF THE DEPOSITION OF THE ORE.

The deposition of the ores—The solutions containing the ore penetrated the
limestone, passing through fissures and interstices in the broken rock, and
deposited the ore where conditions of temperature and chemical activity were
favorable to its precipitation. It is impossible to determine what may have
been the chemical composition of the solutions which carried the ore, but it
is not improbable that they consisted in great part of metallic sulphides dis-
solved in alkaline sulphides. These solutions were necessarily formed under
the influence of heat and pressure. Rising into the shattered limestone at a
diminishing pressure and temperature, the liquids lost much of their solvent
power and many of the metals that they contained were precipitated. This
precipitation could have occurred in only two ways: either through deposi-
tion in pre-existing large cavities or through a substitution of ore for country
rock. The manner in which the deposition took place has a very important
bearing upon the probabilities of finding ore at any considerable distance
below the water level.

SUMMARY. 189

The formation of caves —The formation of caves in limestone is usually attrib-
utable to the action of waters percolating from the surface and carrying car-
ponie acid in solution. To form a cave at a given spot, water containing
free carbonic acid must be supplied in sufficient quantities, and an escape -
must be provided for the more or less saturated solution of calcium carbonate.
Caves cannot, therefore, form at an indefinite depth from the surface, and
their practical limit is reached at the water level. The caves in Eureka are
of more frequent occurrence near the surface than in depth, and they are
not found at all below the water level. If the theory of a simple deposition
of minerals from solutions in pre-existing caves were correct, it is evident
that the limit of the ore would be reached at the point where cave formation
was no longer possible.

the substitation theory.—In the Eureka deposits nothing has been observed
which would indicate that the ore had been crystallized from solutions in
pre-existing cavities. The banded and concentric structure, characteristic
of that manner of deposition, is nowhere visible, and although it is conceiv-
able that it might have been obliterated in the oxidized ore bodies, it is im-
possible that such should have been the case in the unchanged masses of
sulphurets. The masses of sulphurets on the other hand offer strong evidence
in favor of the theory of substitution. The minerals have replaced the lime-
stone in such a manner that they have often retained the structural form of
that rock. Rounded bowlders of limestone have also been found as the nu-
cleus of masses of ore.

The sulphuret ore shrinks to some extent owing to the leaching which
follows oxidation, and this accounts for the apparent relative size of many of
the caves over ore bodies. These caves were no doubt subsequently con-
siderably enlarged by the waters bearing carbonic acid. If the deposition
of ore is correctly referred to the solfataric action consequent upon the
rhyolite eruption, it is likely that the precipitation of the sulphurets began
soon after the outburst of volcanic rock, and before there could have been
much cave formation. ”

That the lead deposits of Raibl (see Chapter VIII.) and of other
places should not have been formed by substitution is not an argument which
would prove that the same was the case in Eureka. In the Leadville de-

190 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

posits, which in many respects resemble those of Eureka, the ore has been
substituted for limestone, according to Mr. Emmons.”

Preponderance of evidence in favor of the substitution theory.— Weighing the evidence on
both sides of the question, it appears that a large part of the ore was brought
into its present position by substitution, while it seems impossible to demon-
strate that any part of it was deposited in pre-existing cavities. It is highly
probable that all the ore was deposited by substitution, and that future
developments will effectually establish the fact.

ASSAYING.

Object of assaying country rock—With a view to discovering, if possible, the
source of the ore in the mines of Eureka District, numerous and careful
assays of all the different kinds of country rock in the neighborhood of the
ore bodies were made. As the quantity of the precious metals contained
in any of these rocks is extremely small, it was necessary to take unusual
precautions in order to determine with any degree of exactitude the amounts
of gold and silver present. Assayers do not ordinarily attempt to estimate
with accuracy any value of either gold or silver less than one dollar to the
ton (0.0026518 per cent.), and as the country rock of this district never
contains so much as this, particularly delicate methods were required in the
determination of the actual quantities of these metals.

Accuracy of the process of assaying —T'he process by which the results given in
this report were obtained have been fully explained in the chapter on
assaying, and it is only necessary to state that it was found possible to de-
termine the value of silver in any country rock within a cent and a half.
It was not possible, however, to determine the gold value with equal accu-
racy, as the quantity of it was extremely small; and it was neglected in most
cases.

Use of assays——While various purposes may be subserved by assays of
country rocks, the main objects of those described in this report were, first,
to ascertain in which of the rocks the precious metals could be detected,
and, second, to trace the variations of tenor in different occurrences of the
same rock. As a qualitative method, exception can scarcely be taken to the

“Second Annual Report of the Director of the U. S. Geological Survey.

SUMMARY. 191

dry assay, while even if the degree of accuracy reached in determining the
absolute contents in precious metals of the Eureka rocks has been over-
estimated, the value of the results would scarcely be impaired, for it will
hardly be denied that the results form a sufficient basis for a comparison of
different samples of the same rock, all containing very small quantities of
silver and gold. For the purposes of this report it makes little difference
whether a certain mass of limestone really contains 10 cents or 20 cents, if
it can be proved that a second body of limestone contains twice as much,
or, it may be, half as much. In other words, the main purpose was to
ascertain the relative contents, not the absolute contents, of the samples
assayed. Even if the methods employed were ideally exact, it would be
impossible to calculate the metallic contents of large blocks of ground with
precision, since it would be impossible to obtain samples which should cor-
rectly represent the average of the mass.

PROSPECTING.

Methods of prospecting— ‘There is nothing remarkable about the methods of
prospecting in the Eureka District. On Prospect Mountain it consists in
following seams or fissures in the limestone which show indications of ore,
or in sinking shafts and driving levels in different directions in that rock.
At present Prospect Mountain is being explored by a system of tunnels,
which method, owing to the nature of the ground and the relation of the
claims to each other, offers some advantages. On Ruby Hill the shafts are
sunk in the zone of mineral limestone between the quartzite and shale, and
prospecting is carried on by cross-cutting between the two last formations,
particular attention being paid to the following of fissures and broken
ground. Caves, as well as stained limestone, are usually considered an
indication of ore.

Earth currents and assays in relation to prospecting —It cannot be said that the electri-
cal experiments made by Dr. Barus in the Eureka mines have as yet led to
any decisive results as regards the indication of the presence of ore bodies.
There is, however, a remarkable coincidence in the results obtained by Dr.
Barus with those obtained from assays of country rock along a line leading
up to an ore body. In both cases the presence of the same body was indi--

192 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.

cated as it was approached, although the indications were not so pronounced
that they might not have been caused by qualities of the rock independent
of the ore body itself.

As yet no practical benefit has been derived either from the electrical
experiments or from the assays of country rock. This is partially due to
the fact that neither of those methods of search have been sufficiently de-
veloped to give definite results. As regards assaying, it may be said that
although the indications are often indefinite, this method can be carried out
with comparatively little expense and with little loss of time, though great
care must always be used in making the assays and in employing the re-
sulting values.

FUTURE OF EUREKA DISTRICT.

Future of Prospect Mountain.— The mining region of Prospect Mountain com-
prised between Spring Valley on the west and the Secret Cafion road on
the east will no doubt produce large quantities of ore for years to come.
Though several of the mines of this portion of the district have been de-
veloped to a considerable extent, there remain a great many claims which
are still in a virgin state. Underground explorations have proved that
many of the deposits are continuous to a considerable depth. It is there-
fore very probable that numerous unexpected ore bodies will be discovered
throughout this region in the course of future deep prospecting operations.
The ore bodies of Prospect Mountain, however, are not likely to be as
large as those of Ruby Hill, owing to the structure of the country. Taking
into consideration the height of the mountain and the fact that no quantity
of water has been encountered even at a depth of over 800 feet, no trouble
need be anticipated from that source for some time to come.

Future of the mines of Ruby Hit. What will be the future of the mines of Ruby
Hill is very uncertain, and any predictions in regard to it must necessarily
be inferred from the results of the explorations which have been made in
the present lower workings. These workings have not as yet given any
certain indications of the future. The probability of finding ore in the
lower wedge of limestone depends in a great measure upon the validity of
the theory of substitution. If this theory is the true one—and the proofs

SUMMARY. 193

favoring of it are strong—there seems to be no reason for doubting the
presence of ore below, provided that the limestone was in a fit state to ad-
mit the ore-bearing solutions during the period of deposition. That this
was the case is indicated by what has been thus far observed in the lower
limestone and by the fact that ore was found in the Ruby Hill fault-fissure
when it was laid bare by the cross-cut from the 1,200-foot level of the
Locan shaft. On the other hand, if the ore bodies were dependent upon
the prior formation of caves they will not be found below the water-level,
as cave formation could not take place much below that plane.

Whether the extraction of the ore in the deeper workings will prove
profitable will depend upon the flow of water, size of ore bodies, value of
ore, and facilities with which it can be reduced. Water may prove aserious
impediment, but it is not necessarily one which should be fatal to the ex-
ploration of these mines. As to the size of the ore bodies no satisfactory
predictions can be made. No great change in the value of the ore as re-
gards silver need be feared, though it is possible that the contents in gold

may decrease.
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A. C. line, Description of the......--------------------- 40
, Stratified limestone near the --.-...-.--..---- 32

Acid, Carbonic; influence in cave formation..........-. 94
Adams Hill, Altitude of. .-....---------------.----++++-- 3

, Condition of mining in
, Position of ...-...---

Age of ore
, Relative, of ore bodies and fissures .....-..--.----- 76
Alps, Erzfiihrender Kalkstein in the

IN ini) aoe onscesacbescsneetc eC OsSaeeOaseeoS SeReee Hes
American shaft, Ruby Hill fault at the...-.... -24, 28, 113
, Main fissure at the ..-.... -. 24, 28, 113
Anglesite ...----.--2---2-- 29-22-22 nn -eenn see enesencesnne
Aragonite, Formation of; Roth and Dana...........---

, Measurement of crystals of ....

Arizona mineral zones .-..

Arkansas, Deposits of ..-...
Arsenic, Source of, in the ore.......---.----------+-++--
Assays, Discussion of. ........--.--------------02+eeeeee

in connection with electrical experiments - .... 142

of Comstock rocks for G. I’. Becker

, ord list ---

WER OE lseagoocarecoacseeoe 183, 134, 135
of quartzite ......--:--....- -..--.-- --133, 134
of quartz-porphyry ..--.----.--.---- --136, 137
Gf TLVOltelesrce ase etae seen -- 134
= WIRE pancE aca onbe Sone Get Serer aa ro nee ce oecra 132
Ashburner, W. T.; Testimony of.......-. --------..... lil
Assaying; action of bitartrate of potash on litharge..-. 130
country rock as a means of prospecting..... 144
, Object of

Bac elt en) apne ccm eres ancnose sen IOebosSaSen=
o (CRIES EGS SannsseaneAcoering seeneciecseoce 125
; estimation of gold. Bib
ppdolkre recite esos aasmomscae 124
, Mmaccuracies of results in -. 129
IN Pema ty eo ea ades ons p gore srinos nedoccncsos 123
, Loss by cupellation in................ 126, 127, 128
, Measuring buttons in.-.-..-..... ---. 129
6 WERIG te Se deeeoe ores == 132
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6 MGS Wetter Res Soc eeneoseencecces-bo 124
WAVES OOa. COSE Reno eu See sen Bea FR DSR ROR CEE OAC OSC eR Se 58

Back limestone, Description of.
Banner mine, Fissure in the
, Ores of the Se LOD,

Barus, Dr. Carl; electrical experiments in the Rich-
ONG Gree eee sealers eee ee ae 142, 191

Page.

Barus, Dr. Carl; on the electrical activity of ore
(DOGies tances ees es eae 146, 147, 148
Basalt, near the mines, Absence of .........-.....--.--- 89
Becker, G. F.; Assays of Comstock rocks for .......-.-. 124

; on tho electrical experiments of Dr. Bar-
ME) Sooo sh Ses cts 4G aceses sce Saesaz3 142
Bell shaft tunnel, Main fissure in the .........-....-.. 30, 113
Big cave, Dew point in the .-.....-.. 57
, Experiments in the 56, 57, 58
y oof of the. -~.--.-~. <= 76
, Lemperature in the 57
Big Cottonwood District........-...........eeses.ssse-- 65
Bitartrate of potash, Action of, on litharge ............. 130
Blitte in the deposits of Raibl.-. 68
DGG Wsssoe a oaccancogesccrecces 56
Bristol DisMac teenies eceeeeenseer aaa seers 65
Buckeye claim. ......-----------------------eene- cenens 3
Orajsbodicesiof, (here. -.nees- oe. aaa 72
Buel & Bateman organize Eureka Con. Co ............. 3
Bullwhacker mine in the Pogonip limestone ............ 5
, Lead in the 167

, Quartz-porphyry in the -.136, 137, 138, 165

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Cambrian, Ore deposits almost exclusively in the....... 5
represented at Eureka .......--..--.-------- 5
Carbon in rocks, Determination of...-............ poenae 135
Carbonate of copper 58
lead 53
lime 56
zine = 56
Carbonic acid in cave formation, Influence of -.......... 94
Carboniferous, Ore deposits in the ..-...-.....-....-... 67
represented at Eureka ............-.----- 5
Caves, Action of water im .-......0--. 2.0.00. 220ce- cence 95
ASN CieAtONSiOMOLG ese se sae «oe misaainces eee eise 139
, Climatic changes in regard to formation of ...... 94
, Connection of, with fissures and ore bodies ...... 95
, Connection of, with outer air ............----.... 96
, Depth of formation of. .... DCC R ane SasOsee 96
oe TNO! ecconnan spbaconcgesosncsaa-cenasnese 189
SICA ANSE eee weet sales annie ate areata aes 166
in connection with ore ......-....--.-.....----- 74, 186
, Partially formed, and ore chambers ...:..-....-. 100
, Relation of, to the formation of ore .........-..-- 99
, Theory of the formation of. 94
Cerro;GordotDisttict=---24-eec- scents eee coneean as
Cerussite ...--- ----- Saeco oneesiS EDO CE GESE DASE eS aces
Chamberve Outs pea eo see ae nes eeerate

Chambers, Arrangement of ore in

196 SILVER-LEAD
Page
Chambers, Stratification of ore in...-..------.--------- 97, 98
i@hampion claiitesseeae see es eeee cee eee ee eer ee 3
, Ore bodies of the 72

Charcoal; how burned...
Charge for a furnace. ----
Chioro-arsenate oflead -.-.<...-.-+-+----<-------------
Claudet, F.; analysis of Richmond ore by --------------
; analysis of Richmond slag by - -
; analysis of Richmond speiss by.

COP Fi oe oe te pea me ree teenie same Sone
Climatic changes affecting formation of caves -.-------- 94
Compromise line as a natural boundary-..--------- ----- 139
, Description of the..-..-.----.-------- 23
fault, Effect of the, on the two shale
belts io-cse cee ase eee sea nee
Comstock Lode --..-----.---.--

Contact of limestone and shale
Contact of quartzite and limestone
Country rock, Assays of..-.-.--. 82, 83, 84, 85, 133, 134, 135, 136

, Metals contained in
Crane used in Richmond works.-..-.-----
Cumberland, Ore deposits of
Cupellation; description of the process at the Richmond. 164

, LOSS DY. ------ 222-2 e ene nee een eens 126

, Temperature used in.--...--.-.------------- 125

Cupels, Preparation of ...---.-------------------+------ 125
Dana, J. D.; on formation of aragonite-.---...---------- 58
Dead Broke mine, Ores of the -.-.---------------------- 63
Deposition of minerals, Relative time of the.-..-------- 80
Derbyshire, Ore deposits of.... --..-----------+-------- 67
Devonian represented at Eureka..--.------------------- 5
Drifts, Cost of running ..--...--..---------------------- 150
, Timbering of. -......--------------------+---- 153, 154
Earth currents in relation to prospecting .---..--.------ 191
East ore body, Connection of the, with fissures .-....-.- 75
, Description of the .....-.---------------- 77

in Richmond mine ..-.-.----------------- 73

, Ore channel of the.-----.---------------- 114

East vein on the Comstock :

Electrical activity of ore bodies in connection with assays. 142

Emmons, S. F.; description of Leadville deposits. -66, 67, 185
; on necessity for the classification of ore

deposits........------------------------
; on porphyry at Leadville
Eruptive rocks, Description of. .-...-..----------
, Influencei0f 2. --c-.= + eaee= en
Erzfiibrender Kalkstein in Raibl..--...-.-.----.--------
Eureka, Altitude of the town of.----.------------------- 1
Eureka District compared with Raibl..--........------. 103
, Description of.......------------ 1, 2,3, 4,175
, Fires at > 4
, General geology of.------.------------- 5
7) History Of =< seceeene-=- neem ene nn n= sl 3
, Massive rocks 'of.--... -----._.---.2-_.- 8,9

, Minerals in....- 52, 53, 54, 55, 56, 57, 58, 59, 184

, Population of - . 4

, Position of - - - =u

. »kroduction of ---..---.----== 4

, Sedimentary formations of.....--..--. 6,7,8

, Lopography of...--...-..--<0.e--ncnnne 1

Eureka mine; law suit with the Richmond... 111
, Main fissure in the -----.---...- Ss 1)

, Method of prospecting in the. -189, 140

, Method of timbering in the..-..--..----- 156

, Order of the formations in the. ....-.---- 26

, Organization of the......-..-.---.---.--+ 3

DEPOSITS OF EUREKA, NEVADA.

Eureka mine, Tribute system in the ..-........----.----

Tunnel, Formations in the . 178

, Ores of the .....- - 63

Experiments, Dlectrical’- 27 j2-.--—-- .--20. --ae5-eneeaees 142
Experiments on loss by cupellation -..-....-..--. 126, 127, 128
Haut, The: JReksOn 2 os. ocean oe ice sonata cele eee 21, 184
op AUT ae oS ies te het an reece 24

Faulting in Prospect Mountain. ---

, Manner of, near Compromise line 39
movements in Adams Hill ........-..--------- 165

Faults in the Eureka Tunnel ...--..-----.-------------< 178
in'therquentziter cee eey aaa ae 44, 45, 47

in Ruby Hill..... Monger eccecascocstass --20, 26

, Manner of occurrence of.. .-...-----.---
Field, Justice, Decision of .............--- --.--
; tries Richmond and Eureka suit

Hissure|in| Bannerming 2---cse--2 ss ceee ens enna ee eae
in the Ruby-Dunderburg

, Rhyolite filling of .........----.. ....

Fissure, The secondary, between quartzite and lime-
stone 112, 182
139
between the 7th and 9th levels of the Richmond 96
, Connection of, with ore bodies and caves _74,75,95, 186

injA dams PLU eae. 2 eke ee semen ee eee 166
in Cumberland and Derbyshire 73
in Prospect Mountain ..-.-----......-.2....... 16
, Junction of the two principal...-.....---.----- 114
, Manner of occurrence of
Flux, Composition of... --. -
Formations of Adams Hill. --
of Eureka District......-..----
, Relations of, to ore bodies
Front limestone, Barrenness of, accounted for.....-..--- 41
pC haractenigniCa 0 tess=es ene aee aca se ete ste 42
, Description of . 41
in the Eureka. - 41

in the K. K.
Riel for Amel tin Peewee eee late eee
Furnaces, Description of the Richmond. .........-...-.. 159
Future of Eureka, The probable
of Prospect Mountain. .- ss
OfRuDy Holl. eseaseaeeaea ease
Galena in Cumberland and Derbyshire, Value of ----.--- 68
in the Eureka ores. --
Gang, Definition of ............-----

Geddes & Bertrand mine .........--
Gold as a reagent
, Decrease of amount in the Ruby Hill ore......... 170
MStiMAtLOM Ofiseny a5 -ee ec eoer asee~ ene ae 120, 131
in the different rocks .......--..----- pecoriseatose 187
in the ores of Adams Hill.-....---- mLeoconadsace 167
, Ratio of, to silver in Richmond lead

Granite as a source of the ore....-..---

, Assay value of .......---

dnt Raby sea See eae toe teal we eee eee

, Occurrences’Of, « «.< c.0c--csiesteeweccc==sc-caeene

Great Basin, Occurrence of fissure veins in-.

Grimm, J.; on classification of ore deposits..-.....-----
Hague, Arnold ; description of formations. ...--......

; determination of formations by..-...---

, Direction of Jackson fault according

$0 os 25cm cs apna een <a eas eaen eee 50

Page.
Hagne Arnold, Stratigraphical classification by-....--- 5
Hague, J. D., Testimony of ......-.---.-..-- shcecesases 111
; timbering on the Comstock described by.- 153
Taf rae deN Ue) aoe se Set omcer aaa Bee OE MOE Sor a oCeAeDcoSer 169
Harkort; on measurement of buttons .-.--.-.-.-------- 129
VCC ame Sao a Eee ee oe SEE eae ee eT 55
Ilenwood, Description of lodes by--...--.-. Re aceeese a 115
; on value of galenain English ores... oa Ais)
Hillyer, Judge; in Richmond and Eureka lawsuit 111
EN OSROMMING same eee oe ae ace ee clne 5
Hoosac Mountain, Position of .............--....-.----- 3
BLD en ole ree an tenancies acca accesso lsccces ee 161
Hornblende-andesite, Occurrences of ...-.
Tlorse, Definition of...............- naebees
Hunt, T. Sterry; Testimony of . oS
Tilastrations Waistiofes- = 25. 2-f2sss-nct le clekac ees sacese
Indications OMOLe es an-- = clown anemone eens sateen eee

Industry mine
T-andula shaft
Jackson fault in Adams Hill..-...........-.
named by Mr. Hague

, Relation of the, to Ruby Hill fault.....-.

Jackson Company, organization of the.-........-...----
Jackson mine, Main fissure in the.......-.---------.---
Jackson tunnel, Main fault in the..-.-..-.--
James, I. E.; Testimony of -
Kentuck mine
Kerl, B.; on loss by cupellation
Keyes) W-.iS:, Lestimony of: 2-22 - eee seac cee cscssas ces
King, Clarence, Testimony of.
K. K. mine, Main fissure in the. --..--.--.--.--
owned by the Eureka Co ...-.

Lawsnit between the Richmond and Enreka com-

TPES screen Siac Sa oso ese cose cence ce ae Seeeeas 111, 112
Lead deposits of Missouri 66
of the Upper Mississippi. --.---.- --. 65
Lead, Determination of, in quartz-porphyry ---. -137, 138
, Different kinds of, as flux ...-....--.----...--..-.. 122
, Difficulty of obtaining pure .---.---..--..--------- 120
in ores of Adams Hill..-.....-.-- Onecorehasésa Bee 167
oxide required in the slag. .....-...-..--..-------- 122
ROUUG hear eae = ae
mefinin pee nese
Leadhillite.-...........-....-..
Leadville, Ore deposits of ...--..
-Letter of transmittal ...........20-.0.2-20ee-ee0- 22s -=e
Limestone, Amount of silver in the...-..-.-- SSS OSS 82
TPASSSYS\OL~. ~ << scenaee se
, back, Assays of
SEDeReriphON Ofp. an oeriae< ete em see 134, 183

, Broken and stained, as an indication of ore...

, Dolomitic, whether favorable for ore........ 70
from 4th level of the Eureka, Assays of . 133
from Richmond mine, Value of - 134
from top of Ruby Hill, Value of ....-........ 134

PONG ASSAY S| Obaee seen eee nee alee aia ae 134

; barrenness accounted for 41
, Characteristics of . 42
, Description of -.- 41
SAT Ge TOOK alent tee anise see sal 41
Rute Wey Keen. teteeiecisnn ee io cesanie/ =< 42

, Impregnations of, with ore...............--- 82

, Manner in which the ore entered the.. .. 89

co en ee ee ees sOnnee

, Physical nature of the .....-...-..--....

» Pseudomorphs of ore after

INDEX.

/ Page.
Limestone, Pseudomorphs of pyrite after............--- 101
yy eatiO. Of £0 OFO.5-- cee ele alee coco eee. 81
, Segregation of ore from the.........-....--. 87
wedge, Ore taken from the........----...---- 34
LETTUCE hes eat ne Oe es Ae ee een oe oe a 55
Litharge, Action of bitartrate of potash on-.........-.- 130
, Approximately pure, required..............-. 121
: bearing of silver in it on results .............. 130
, Best reducing agent for....................--. 124
Heontenta in SUVOr = .cacs.--n sevens c alesce ese 123
, Poor, how reduced at the Richmond mine .... 164
; process by which made .........-.........-... 122
WERUNLOy Obie eee ene a era NEC awe: 120
Little Cottonwood District...........-....-.-..--..----- 65
Lode; applied to the Ruby Hill deposits..............-. 119
webtiners}definitioniones <2 seen ee aces eee 115, 119
question, Differences of opinion in regard to....-.. 111
Linde &JRozaniprocesss)-= sans 2 55 -Sasvecencc-eecee see 162
Main fissure (Ruby Hill fault)...... _... -180, 181
at the American shaft .-..-............--- 28
, Detailed description of the ......:........ 27
, Filling of the, in the Richmond ........... 26
, Influence of the, on the formations ....... 182
in the Eureka 30
in the Jackson 27
ATMO NGS Pennasa sce eno een epeee cates 29
in the Phenix....-.....-- 29
in the Richmond .-....... 31
McCoy, Major; early mining operations by . 3
Melting, Time and manner of, in assaying .............. 124
Malachite 58
Manganese 59
Marcasite ssn seats meee can ata as tsea5 55
Melville, Dr., Analysis of Ruby Hill ores by -.......-.. 62

, Determination of pyrite in quartz-por-

phiyryDyeceme aes coe ates eet

, Separation of lead from gold by.

Method of prospecting in Prospect Mountain -.
in the mines southeast of the

compromise line

in the Richmond

Mimetite, Analysis of

, Manner of formation of ....................-.
Mineral Hill, First workings at.-.....................-:
Minerals in Ruby Hill; aragonite

; Cerussite
; galena
; gold

; leadhillite .......... Be
; limonite ae
siMAalaChitOsssssanc~ os ose e Son
; Manganese
; marcasite . .-
; mimetite...
; molybdenite -.
; nickel
; oxide of lead

198 SILVER-LEAD

Minerals in Ruby Hill; pyrite. .-.... caec
; pyromorphite ....
§ QUUBTED. — <6 0 ne cenen as eceeenee=- on
5 NGM eins stisecabasserceceoccdcoe
; smithsonite
; Steatite
; talc .-
; wad .
in the ore deposits of the Upper Mississippi -. 65
‘* Mineral” limestone .....-----.--------20----seeeeee=e=
Maneral POimntsss-e=<-c~ eens en cap ee wana n= v= sien
Mineral zone, Characteristics of the -.-.
Mine workings in Adams Hill.--...-....
Missouri, Formation of ore in
, Lead deposits of
Molybdate of lead ........-..------00+- 02-22 e seen ee eee
Molybdenite . ..--.-..----..-.-.-..----
Molybdenum, Source of, in the ore -.-
Mountain Boy claim .-.-.---.

Mountain mahogany as fuel .........--.-------+----+----
Ophir District ----.-- .--.-.--.------.. --.
Ore, Age of the ..--.--..-.-----6+ -.--ces-0--2--cesns- 2 =
, Analysis of Richmond.........-...----------+-+--
, Arrangement of the, in the chambers
channel of the east ore body...........
channel of the west ore body .-.....-
connectiOn . --. =~. -. .---.----.- 5.0 2- ene ewe nes ----
deposition, Conditions of, in lower limestone..-..-- 172
, Deposition of, in the chambers..--..--------.---- 71, 188
, Distribution of, in Prospect Mountain .-....-.--- 18,179
, Evidences if, of pseudomorphism after limestone. 98
, Extraction of, on tribute ..-.-.--..-.. ------ 150, 151, 152
, Granite as a source of the.--...-------------------- 91
, Importance of manner of deposition Ofjeeee weed 93
in the lower workings of Ruby Hill.-.....--------- 171
in the Ruby Hill fault .......-...--
, Manner of deposition of the
in which it entered the limestone.........- 89
, Possible sources of the ........-.----------.-++---- 187
, Quartz. .---.--2------ 02. nee n eon ene wane ey ennn n= 60
, Quartz-porphyry as a source of the.--..--..----- 90, 187
, Ratio of the, to the limestone.....--.-------------- 81
, Red carbonate .-....--.----- ----- + eee een ee renee 59
, Relation of caves to the formation of .....---.----- 99
rhyolite to the formation of.....-...... 99
, Rhyolite as a source of the. .......--------.--------
, Richmond, chlorination test of......-..-..---------

, Segregation of, from the limestone. .
, from the quartzite -
, from the shale...

, Shrinkage of the 101
, Source of the, in Prospect Mountain. ...-.......--- 91
, Stratification of, in the chambers .....--.-.--..--- 97, 98
pSUlphuret..-- 5. .-.--- cane nncnnecccc--- scence cease= 59, 60
, Yellow carbonate 59
Ore bodies; connected with fissuresin the Ruby-Dunder-
DOU eee mie ae ieee 75
, Connection of, with fissures and caves ..74, 75, 95
of the Richmond claim. ....--...-----.-----.

, Relations of, to the formations...

, Size of, in Prospect Mountain .-..

, Stalactites in the ............-.

, Timbering of the ....-......-----cecces----- e

, Connection of, with the quartzite...:......-. 72
secondary fissure. - 72

, Continuity of, in the Eureka.......... eet 112

DEPOSITS OF EUREKA,

NEVADA.
Page.
Ore bodies, Continuity of, in the Richmond ........---.- 112
, Contraction of ......---......- i 101
, Effects of oxidation on.........-...-.---.---- 100
, Electrical activity of ......---..----- 146, 147, 148
PRODI ALON Oboe se ete eee ieee eer 185

in connection with depressionsin the quartzite. 78
fissures in the Williams

TN igen 5s nassoc 75
in Prospect Mountain..............-.....---- 72
of the Buckeye and Champion .......-------- 72
Ore deposits, Age of the....... toseaeiees doccnaseeeesaeen 69
, Classification of, according to different au-
Llane Aadoeesasiortcs 118, 184
the Eureka.-.....-....-.. 64
, Comparison of richness of Prospect Moun-
tain, with Ruby Hill..........--..-...-. 170
; depth to which they extend .......-....-- 174
, Necessity of classification of.........-.--- 119
Of A damigh Hill on eeeeeee aes - 166
of Cumberland and Derbyshire. ... co. CY
of Eureka compared with others. --.- 64, 65, 66,
67, 68, 69
of Leadville, Description of ....-.-....-- 66, 67
OP MMIBBD ON yess ae ese te sce ae ieee ee
of Prospect Mountain........-..---.------
Ota D Ue ase eee a eane

of the Great Basin .....-
of the Upper Mississippi. ---

of Upper Silesiawes---sessee oes ence eee
Of Westpiahiae- =) sa. oencen eas ae eae = eee
, Relation of the limestone to the
SISO pepe sonsethacrrocecccecusscace
, Theories in regard to the formation of.... 80
, Lhe shape of the.................02.------ 70
Ores, Classification of ...-...---.-..---- 2-25.25. ------- 51
, Composition of, in the Great Basin - =- 65
, Miners’ classification of....-...----. = Et!)
of Adams Hill........- i 166, 167
of Prospect Mountain .....--.-..----------------. 63
of Ruby Hill, Local differences in ......... prcasees 52
;PRBOUCHION Of eaerea= ae ee eee 158
, Value of, in Raibl - 69
Oxidation, Influence of the water level upon. - - 51
of ores in the Great Basin .......-....-..--.- 65

Palzozoic rocks, Ore deposits in

Pattinsou process te. see seen = =a = een ene
Phenix Co., Organization of the ...... pocwsesesunenas aco
mine, Main fissure in the. .--...... - 29

, Peculiar formation in the -.

Phosphorus, Presence of, in the ores..-. - 58

Pietsch, on deposits of Upper Silesia.....-..--..--- Aasan) GE

Plattner, on measurement of assay buttons ....--.--- «-- 129

Pogonip limestone ..-..-...---.--------+-------2+-++--+- 8

Porphyry in Cumberland and Derbyshire. ...--.-------- 67
(ead ville <= 2 -2-2—e~ eee

Posepny, F., Conclusions of
; on deposits of Raibl...

Pots, Cryastallizing -.... 2.500 .ccecn ese e mee nmessnne=n ==

Potts chamber. .--..-...-.2---.ccee------ceece-==-

IPPOLACO eww eee) s i esi =ietel min ems

Production of the District

Prospecting by assays, Use of the method Ofeesakes 148, 149
, Methods of .........--.----- 139 140, 141, 142, 191

: INDEX.

Page
Prospect Mountain, Altitude of .........--..- Lasstencx'ss 2
, Dip of the formation in ......-..... 12
, Distribution of the ore in .-...----- 11
rlroptive rockaiin - 2. ..-5-.----<-.-s 11
, Extent of the ore deposition in..... 169
SUMAN In ose ee eeepc tale couens 170
PPMIBBUPES Moe sa5 <2 cows e'eG Sas sees 16
PPRIRGMO Obes tee a owe sate ie ee -2- 192
PGMA LGAN: feces ea ckeg east ale cee s 12
limestone, Description of.....-....- 14
, Occurrences of . o
, Manner of upheaval of.-...-....-..- 177

, Occurrence of ore bodies in ...-....

ore deposits, Extent of the -.
, Section of. --
, Shale belts of

' , Size of ore bodies in............---- 72
; source of the orein'--..------.-- << 91
MELUCLUEG OLssa ceo cseetacteaesos soe 11
5 tunnel, Formations in the-..--..-.. 179
, Water in the .......... 107
Pseudomorphs of galena after calcite............... 99
ore after limestone ...-. ee
pyrite after calcite ...........-...--.. 101
limestone ......-....----- 101
Pumpelly, Prot. R. ; on classification of ore deposits.... 119
Pyrite as a matrix of gold and silver. .-...........-..... 136
MUINOLAl ios ae colnet oneiaee ato ce ena secon case 55
, Keffect of, oxidation on ..:...---.--2--.-4-.--<<-- 101
, Gold and silver in the ........... -- 137
, Observations ofa massof .. -....-...--.-...-. 101
TEV ROTO Goo oc oeesaees eo snotee Seog cenecstece esos 58
Quartzite and limestone contact in Ruby Hill... ---- 180
| SSBB IG See em eset Anes ae HB sees -133-134

, Connection of ore bodies with depressions in

WG) Sc ReCeSh i Cone Se SaCe Cesc Ree CoSU Scene
MMAnIta OM Uhes so. csoscdtacan meted eae seas

in the Richmond aud Albion
, Minerals in the

, Occurrences. --...-.
, Physical nature of the....-..-..........-....
, Relation of secondary fissure to the .......... 48
, Segregation of ore from the .--........ 5
southeast of the compromise line. -
, The narrow; description of.....
; dip and strike of .-.........-...
; manner of formation of......._. 48
, Upward motion of the..-.-.......-...-.....-. 47
Quartz-porphyry, Age of the -..-.--.---........-....... 90
as a source of the ore - ---90, 167, 187
, Decomposition of the ....--.........-- 89
, Determination of lead in the........ 37, 138
invA\damsiHall 6 seo ao Seco e acc oesee 165
mear/ Raby Hill. 522. cs ccesscac. ene 20
; Occurrences of......-. cic iel)
Raibl compared with Eureka .....-....-..-...-. == 103
POLE nOSIts) Ofse—= ate eee earn asec -- 68, 102
, Theory of substitution applied to 103, 189
RakerUse ofthe words. -20- Seems aeeine see coon 70
Raymond, R. W.; on miners’ definition of lode... 119
: PLGAUMNONY OF oc. . cope eames
Read, T.J., Testimony of .-..........--....-.-.
Reducing agents, Experiments on. .-....................
litharge, Experiments on .--..--..-.....-..--.
material; quantity required......

Refining, Advantages and disadvantages of

, Inaccuracies of, in assaying. 129
Rhyolite as a source of the ore............-..--..--- 90
PA SBAY A) Obereien oe aoe aire cane sNomecices cnceee 134
sPUecOMNOsibiomOfersssseese essen ss eee BO
dike in the Ruby-Dunderburg, Jackson, and
PROB ee fea ena Roe es 105
eruption in the Tertiary -- -- 106
filling of the main fissure. 25
ELOMY QUALITY et cte sian eiceis yatabis sae ae canoes 134
Occurrence ofenee sear neo aes eee 9
ofpEorple! Mountains esss eee cease eee 21
Relation of, to the formation of ore.-.....-.--- 99
Richmond claim, Ore bodies of the 72
UOCaOn OL tha ttasteene eee aoe 3
Company, Organization of the...........-..- 4
; lawsuit with the Eureka Con. Co.. 111
furnaces, Description of the ........_....-..-
IUGLNG Raat Pee ae ae
mine, Chlorination test of ore of the..
, Cross fissures in the............
, Main fissure in the ....................

, Method of timbering in the
of prospecting in the...

, Potts chamber of the...-............
, Prospecting by assays in the .-.
» Quartzite in the .............2..
shaft, Granite in the........-.....--....
USD UN ON the seae oasee enone 12
slag and speiss, Analyses of..........-..-.... 160
smelting works, Description of the.......... 158
Robbins, G. Collier, Early smelting operations by .....- 3
Rocks) Massive: «a2 5-26. boctee ce ecect cele tczctee shaw.

Roth; on formation of aragonite -
Ruby-Dunderburg mine, Dip in the
in the Hamburg limestone. . ..8, 169

, Ore deposits in the............ 73

HOLOS(OL+tNG) oa scecce neces 63

Re bry eA Gd @ Olen sen eeeee a hee ee eee ne nee 2
NORM Dilan Ane pe en tse es see saeco tele

, Granite in ....-. =e

mines, List of the
ORION Ob eam alana mee eee ee a yl
, Quartz-porphyry eruption near
, Relations of the formations of ............... 22
, Rhyolite near
, Rocks of

, Cause of the.........-..-

, Deseription of the 113, 180, 181

, Extent of the, in Eureka mines........ 26

Oren the y-nao-c essen eee ee ee 173

, Relation of the, to the Jackson fault .. 50
Sawyer, Judge; in the Richmond-Eureka suit . Se abh!
Seams as indications of ore ...........2..-2...0.--00-00e 139

200 SILVER-LEAD DEPOSITS OF EUREKA, NEVADA.
Page. Page.
Secondary fissure, Connection of ore bodies with the.-.. 72 | Supreme Court of the United States, Decision of the.... 11
, Dip and formation of the............ 33 | Table of Contents vii
, Relations of the, to the quartzite .... 48 | ‘Tertiary, Rhyolite eruption in the -- --- 106
Sediment in connection with ore .-.-....-...-..--.------ Theory ofsubstitotions. <= --L~s2ce ssoce occas basecerear 189
Seventy-six mine ....... Timbering, General method of..-.......--.--..-2------- 153
Shafts, Timbering of Timbers, Material and size of. ..........-..-....----.--- 157

Shale, Connection of the two belts of
; Dip of the; in the Wureka 2.2. -... 2. -csccesest-ena=
PACKSON oa-- seule ease eee

AMS ALD ONenact.< tense cone ee ereereeeeeeeT

in the Richmond and Eureka
Lower belt of, in the American and Jackson...-. B4
Eureka

PhOnIKe seenc ere sa eee 35
, Physical nature of the -..-..--
, Two belts of
Silicate of iron..........
WANG) Ae ene ace a ee ena eee
Silurian represented at Eureka ..-...-.-..---..---------
, Lower, Lead deposits in the
Silver, Estimation of, in country rock......
in ores of Adams Hill ..........-- ce
in ‘the/different:rocks:222s-cs0cs-soenss -e==-s5-55 187
, Ratio of, to gold in Richmond lead. .-...-.--.--- 163
, Relation of the, to the amount of lead reduced.. 121
Silver Connor mine, Ores of the
Silverado District................-.--.-
Slag, Analysis of Richmond ..-.---.:.-.--.-----.
Smelting, First attempts at....-... .......-...
Solfataric action and ore formation
, Causes Of 22 fees so ecewcinee ec nences
Solutions, Derivation of....-..........-....

, Formation of metal-bearing
Specimens from the Eureka tunnel....-..... <i
SPEIRS PAN ALY AIS Of eee eren canna nace tee eee se ee ee ene
Stalactitesin ore Odes. ---e~eoew woeew nee eee
Steam, Use of, in the Luce & Rozan process ......-....-.- 163
Stock, Use of the word

MD OURIION. Olsossaacece soos eee cen eee
Substitution, Eureka ore bodies formed by 2
theory, Evidence against the 104

in favor of the ...105, 189, 190
Sulphatowteleadenesseeensneeerceee ee ese ee ae eee
Sulphide of molybdenum -

Sulphuret ore, Evidences of manner of deposition of the 60

co)

Tip Pop aim Sek «2c ewes <oJnse cos aawe toes caneenee anes 3

INCHNG =i 2s2 Sees esees wees eset esceceneecee sn 111
Toadstone in Cumberland and Derbyshire. -.-.....-..--. 67
Tribute system, Description of the........-........-. 150, 151
Tunnels as a means of prospecting ...........----..- 141, 142

Mybo;'2'Gimine aire. ee en eee eee aeeane ee aes 65

Upper Mississippi region, Formation of ore in the-.-.--.- 104
Lead deposits of the ..-... «s- 65

Upper Silesia, Ore deposits of........-.-...--------.----

Utah mineral zone .-----..-...---.

tunnel, Main fault in the. - --.
Vein, Miners’ use of the word........-
von Cotta; onclassification of ore deposits

; on deposits of Westphalia -...............-..
von Groddeck; on classification of ore deposits .-...-.--. 118
; on porphyry in Cumberland............ 67
AR as SS Sos S ao ecc aon A Sods sacar Sceee nae - 59
Wages of miners . - + Srooesasoen Sobscecdo secs 150
Waite, Chief Justice, Decision of ................-..---. 113
Water, Extent of flow 0f.-22-—- «s-sc~ neces ca tea senses 109
in Prospect Mountain -............-.-...-.----- 107
the Atlas shat oo oe noses een tee 107
Ruby Mill workings sccse<s--s=e2s2==~oo=e 107
level in Diamond Valley -.-........-....--..---- 108
, Prospects of, in the future ........--..-----.---- 110
, Rearrangement of ore by .--....-----..-.. mas aene) 150
winze in the Richmond ..........-.-.--...--.---
Weighing assay buttons ..............-..-...--.--.-----
Weights used in assaying. -..--..-
Wescoatt, N., Testimony of .-...-
West ore body, Description of the .---
, Connection of the, with fissures.-....... 75
JOreichannelotthe..-=-- 52. -sescceaccesen 114
Westphalia, Ore deposits of...-. ead canscetenecees veanee 68
West vein on the Comstock. --..-- Saepceco ti
White Pine District 222-222 -.on- ces sanc ene oetesecen eens 65
Wihitney,J. D., Lestimony/of ~~~ -- <--.- mons sem aceanee ee 111
Wide West mine on Adams Hill ...... BROssceossebsssce 167
Williams mine, Ores of the...-..... S esbseno 63
Williamsburg mine .- - : Swiss Uy!
Wulfenite ...-.-........--... Scereseescostaccostsccrece (tt

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