University of California • Berkeley
Technical Paper 90
DEPARTMENT OF THE INTERIOR
BUREAU OF MINES
JOSEPH A. HOLMES, DIRECTOR
METALLURGICAL TREATMENT &*&•
OF THE LOW-GRADE AND COMPLEX ORES
OF UTAH
A PRELIMINARY REPORT
BY
D. A. LYON, R. H. BRADFORD, S. S. ARENTZ,
O. C. RALSTON, and C. L. LARSON
ISSUED JOINTLY BY THE BUREAU OF MINES AND THE DEPARTMENT OF METAL-
LURGICAL RESEARCH OF THE ENGINEERING STATION
OF THE UNIVERSITY OF UTAH
WASHINGTON
GOVERNMENT PRINTING OFFICE
1915
The Bureau of Mines, in carrying out one of the provisions of its organic
act — to disseminate information concerning investigations made — prints a lim-
ited free edition of each of its publications.
When this edition is exhausted, copies may be obtained at cost price only
through the Superintendent of Documents, Government Printing Office, Wash-
ington, D. C.
The Superintendent of Documents is not an official of the Bureau of Mines.
His is an entirely separate office, and he should be addressed :
SUPERINTENDENT OF DOCUMENTS,
Government Printing Office,
Washington, D. C.
The general law under which publications are distributed prohibits the giving
of more than one copy of a publication to one person. The cost of this publica-
tion is 5 cents.
First edition. March, 1915.
CROI 1 I IBKARY
CONTENTS.
Page.
Introduction, by D. A. LYON 5
The problem of Utah's low-grade ore, by ROBERT II. BRADFORD 7
Review of mining in Utah 7
Gold 7
Silver 7
Lead 8
Copper 8
Zinc 8
• Improvements in mining and methods of treatment 8
Porphyry mining at Binghain 9
Treating stope fillings at Park City 10
Low-grade ore in the Tintic district 10
Situation and extent of the low-grade ores, by S. S. ARENTZ 10
Examination of the mining districts • 11
Bingliam and Garfield 11
Park City district 11
The milling problem in the Park City district 13
The metallurgical problem in the Park City district 14
Tintic district 14
Stockton district 1C
Dry Canyon and Ophir district , 17
Deep Creek district 17
Milford district 17
Silver Reef district _• 19
Eastern Utah 20
Chemical characteristics of the Utah ores, by O. C. RALSTON 21
Results of analyses 21
Types of ores analyzed 22
Metallurgical treatment of the ores, by D. A. LYON, R. H. BRADFORD,
S. S. ARENTZ, O. C. RALSTON, and C. L. LARSON 24
Processes of treatment 24
Oxidized ores i 24
Complex sulphide ores 25
Removal of copper 26
Chief metallurgical problems 26
Treatment of oxide and carbonate ores 26
Treatment of zinc-bearing ores 26
Chloridizing processes 28
Holt-Dem process . 28
Principal features of process 29
Factors affecting the process '. 29
Summary 30
Knight-Christensen process 31
3
CONTENTS.
Metallurgical treatment of the ores — Continued. page.
Processes having a possible application to Utah ores 32
Lead carbonates carrying silver 32
Murex process 32
Sulphidizing and flotation 32
Electrostatic separation 32
Oxidized copper ores carrying gold and silver 33
Chloridizing and leaching 33
Sulphidizing and flotation 33
Mosher-Ludlow process 33
Slater process 33
Other processes 33
Oxidized zinc ores, occasionally carrying gold and silver 34
Igneous concentration 34
Leaching with ammonium carbonate solution 34
Bisulphite process 34
Leaching with acid solution and electrolytic precipitation of
zinc 34
Oxidized zinc-lead ores, carrying occasionally gold and silver 36
Bisulphite process 35
Leaching with ammonium carbonate solution 35
Sulphidizing and flotation 35
Oxidized ores of zinc and copper, carrying gold and silver 35
Leaching with ammonium carbonate solution 35
Bisulphite process 36
Leaching with acid solution and electrolytic precipitation 36
Igneous concentration 36
Oxidized ores carrying zinc, copper, lead, silver, and gold 36
Partly oxidized sulphide ores. 36
Raw materials for use as reagents 36
Iron for precipitation 37
Sodium sulphate (mirabilite) 38
Allied problems 38
Conclusion 39
Publications on treatment of minerals— 40
METALLURGICAL TREATMENT OF THE LOW-GRADE
AND COMPLEX ORES OF UTAH.
INTRODUCTION.
By D. A. LYON.
In the performance of its duty of conducting investigations to
increase safety, efficiency, and economic development in the mining
and treatment of ores and minerals the Bureau of Mines is cooperat-
ing with various State organizations in order that the necessary
work may be done to best advantage and without duplication of
effort.
At its tenth regular session in 1913 the Legislature of the State of
Utah provided for the establishment of a metallurgical research
department in connection with the State School of Mines of the
University of Utah. The act ° providing for this department stated :
The purposes of this research department shall be to conduct experiments
and researches, either alone or in cooperation with the National Bureau of
Mines and other agencies, with a view of finding ways and methods of profit-
ably treating low-grade ores, of obtaining other information that shall have for
its object the benefit of the mining industry and the utilization and conserva-
tion of the mineral resources of the State, and to publish and distribute bulle-
tins and articles relating to the department and its work.
The station has effected a working arrangement with the Federal
Bureau of Mines by which the bureau is furnishing the metallurgist,
who has charge of the research department, and an assistant metal-
lurgist. The University of Utah is providing the buildings and
equipment and also five metallurgical research fellowships of the
yearly value of $720 each. The fellowships are awarded to gradu-
ates of colleges, and preferably mining schools, who have shown
special aptitude for research investigations. Holders of the fellow-
ships are required to work on the bureau time schedule, except Sat-
urday, when they quit at noon. Their employment extends over the
entire 12 months.
The fellows selected by the university authorities for the fiscal
year 1913-14 were: L. F. Pattison, A. B., University of Utah; W. G.
« Laws of Utah, 1913, ch. 102, sec. 2, pp. 199-200.
6 TREATMENT OF LOW-GRADE ORES.
Woolf , A. B., University of Utah ; O. H. Pierce, A. B., University of
Nebraska ; A. E. Gartside, A. B., University of Oklahoma ; and C. Y.
Pfoutz, E. M., University of California.
Messrs. Pattison, Gartside, and Pfoutz resigned their fellowships
at the end of the fiscal year, and those selected, from a large number
of applicants, to take their places for the fiscal year 1914rl5 were:
R. M. Isham, Ph. D., Columbia University; C. L. Larson, E. M.,
University of Minnesota; and H. J. Morgan, A. B., Stanford Uni-
versity.
All of the men mentioned actively aided in obtaining the data used
in preparing this report.
Attention is called to the fact that this report is a preliminary
statement only. Much work must be done to determine the applica-
bility or the precise value of most of the different methods of ore
treatment that are mentioned.
THE PROBLEM OF UTAH'S LOW-GRADE ORE.
By ROBERT IT. BRADFORD.
REVIEW OF MINING IN UTAH.
When the ores from the head of Little Cottonwood Canyon were
shipped by wagon to San Francisco and by boat from there to
Swansea, Wales, their value per ton was necessarily high. These
were surface ores, and the value decreased with depth. However,
at the Emma and neighboring mines at Alta, the ores continued of
sufficient value to warrant shipping by team to Omaha and thence
by train to the smelters at Chicago. Early mines in other districts
added to the amounts shipped to the distant smelters, but none of
the mines of these districts yielded ores of enormous value, as have
many of the mines of the neighboring States. Utah's high standing
as a mining State has resulted from her enormous supply of medium
and low grade ores.
GOLD.
Utah has produced some free-gold ores, but these were seldom very
rich and were never found in any considerable quantity. The
gravels of Bingham Canyon yielded placer gold for a time, as did
also gravels near some other early mining camps. Mines near Rich-
field, in Sevier County, produced some " picture rock " and ore con-
taining enough finely disseminated free gold to pay handsomely
when cyanided. A few other districts have produced some gold,
but Mercur has given by far the greatest returns as a strictly gold
camp. The gold ore of Mercur was low grade and could not have
been treated profitably but for the advent of the cyanide process,
just when all old processes had failed. So even in the case of gold
ores the State of Utah has produced the lower grades.
SILVER.
Silver ore richer than that now mined was common at most of the
early camps. Later developments showed increased tonnage, but of
lower grade. From the first mining efforts in Utah the State has
ranked high in silver production. To-day much low-grade silver
ore awaits some cheap method of treatment.
8 TREATMENT OF LOW-GRADE ORES,
LEAD.
Lead ore mined for lead alone must carry a high percentage of the
metal to have much value per ton. In Utah the lead ores mined have
been rich in silver, and it was the combined lead and silver content
that made the ores valuable. Much low-grade lead ore and lead-
zinc-silver-gold ore is awaiting some cheaper method of treatment.
COPPER.
For the first 20 years of the State's mining history the red metal,
copper, was not considered valuable. In the last 20 years the copper
production has increased until now Utah ranks a close fourth
among the States of the Union in the production of that metal.
Low-grade copper ores are the source of the copper.
ZINC.
Up to date no zinc smelter has been built in Utah, but not because
the ores mined contained no zinc. To keep down the zinc content,
because of the penalty charged by the smelters, has been the im-
portant aim of the ore shipper. Now the proportion of zinc is in-
creasing and the zinc must be considered as a possible source of
profit in mixed sulphide ores and also in oxidized ores. Occasion-
ally the percentage of zinc is sufficient to make the ore worth ship-
ping direct to zinc smelters, but the amount of such ore found has
been small. Zinc ores, so long considered as of no value, now bid
fair to become a big source of income if methods of profitably treat-
ing the low-grade ores can be discovered.
IMPROVEMENTS IN MINING AND METHODS OF TREATMENT.
The first smelting furnace was erected at Bingham with the
hope that the cost of mining and smelting would be less than $100
per ton, which had been the cost of mining, shipment to Chicago,
and smelting there. Actually, the cost with this furnace was kept
down to $89 per ton, and as improvements in design and operation
were made the cost was still further reduced.
As the mining and treatment costs were lowered, ores of less value
were mined at a profit. During the seventies ores valued below $40
to $50 per ton were considered too low grade to save. In the early
nineties methods had been so improved that $20 ore was successfully
handled, and under favorable conditions $16 ore. Ten years later
$8 to $9 ore was worked and under certain conditions a profit was
made on $6 ore.
With the enormous deposits of low-grade ores the principal prob-
lem demanding attention is still, as before, the devising of cheaper
methods of mining and treatment.
THE PROBLEM OF UTAH'S LOW-GRADE ORE. 9
PORPHYRY MINING AT BINGHAM.
It is interesting to note the results of the improvements already
made. Compare, for instance, the costs for mining and smelting
high-grade ore at Bingham in 1872 ° — $89 per ton — with the costs for
ores at the same camp 41 years later, when the porphyry copper ores
were mined, milled, and smelted for $1.25 per ton.
In order to bring the costs down to this figure the Utah Copper
Co. is conducting work on a mammoth scale. The company is min-
ing an entire mountain, the largest developed ore body in the world,
and has an enormous equipment. Fifty-one locomotives and 22
steam shovels are day and night engaged in tearing down the ore.
Every 24 hours about 24,000 tons of ore and nearly double this
amount of overburden are moved, the pay ore to mill bins, the waste
to near-by gulches.
The feat of solving the problem of treating these ores was accom-
plished by careful and painstaking experimental research on the part
of the management of the company. Success was largely due to
its ability to anticipate the results of mining and milling on a scale
commensurate Avith the immensity of the low-grade ore body in the
monzonite-porphyry it had carefully prospected. The company has
expended $25,000,000 in improving its property, and produces yearly
8,000,000 tons of ore, from which it extracts over 150,000,000 pounds
of copper. These results illustrate the application on an enormous
scale of methods devised for one class of Utah's low-grade ores.
However, the Utah Copper Co. still has its problems. Enormous
quantities of monzonite are mined and treated at remarkably small
cost per ton, but the fact remains that the saving is low. For each
2 pounds of copper recovered by milling, a third pound goes to the
dump. To better this saving while keeping the cost of treatment at
a minimum is the company's constant effort.
Considerable of the ore shows a mixture of sulphides and oxides
of copper. To keep the oxides from going to the tailings and being
wasted requires a different treatment from that now employed
in the two mammoth mills. A method of leaching combined with
flotation is being worked out for this ore.
The oxidized capping as a rule carries considerable copper, in
many places as much as the porphyry ore, and the copper-bearing
capping is kept separate from the more barren waste rock that has
to be removed. The treatment of the enormous amount of low-
grade ore in this capping is a gigantic problem. More than 40,000,-
000 tons of such ore is awaiting treatment by a process that will
successfully and economically recover the contained metal. If such
0 Boutwell, J. M., Economic geology of the Bingham mining district, Utah : Prof. Paper
38, U. S. Geol. Survey, 1905, p. 90.
79474° — 15 2
10 TREATMENT OF LOW-GRADE ORES.
ores be leached, as they probably will be, it will be necessary to
employ a process that can be applied on a scale commensurate with
the size of the deposit.
TREATING STOPE FILLINGS AT PARK CITY.
In the Ontario mine at Park City, Utah, the material of too low
a grade to be treated at a profit was either not mined or was stored
in stopes, or rooms, underground. To-day, because of improved
methods of treatment, these old stope fillings and the low-grade ores
in place are being profitably mined and milled. The management
states that the new mill of the Mines Operating Co. treats 150 tons
of ore a day. Similar ores in the near-by mines are amenable to
the same process of treatment and will no doubt be economically
worked in mills now being designed.
LOW-GRADE ORE IN THE TINTIC DISTRICT.
In the Tintic district the better-grade ores have been shipped to
the smelters in the Salt Lake Valley, or else have been milled. Some
of the early methods of milling were quite crude. Ores high in
silica, and hence hard to smelt, that carried a metal content valued
at less than $10 per ton, were either left in the mine or stored on the
dumps. These low-grade deposits are known to be large. Of late
much research has been conducted with a view to devising some
method of treating these ores. A mill is now being tested in Silver
City which bears promise of giving desired results.
The three districts mentioned are the largest in Utah, and their
untreated ores have been measured in tons. Ores in smaller camps
promise much profit when cheap methods of handling and treating
are worked out. The " porphyry ores " of the mammoth deposits at
Bingham remained uninviting for years.
Ore, after all, is a relative term, one definition being as follows:
"A metalliferous mineral containing metals in sufficient proportions
to be profitably extracted." Hence minerals that once were dis-
carded as waste may later be classed as ore, and material that is con-
sidered valueless in one region may be deemed ore in a region more
favorably situated. The deciding factor in the classification is the
cost of treating the material to obtain its marketable product.
SITUATION AND EXTENT OP THE LOW-GRADE ORES.
By S. S. ARENTZ.
In considering what investigations would be most profitable to
take up in connection with the low-grade ore problem it at once
became evident that each low-grade ore presents its own problem and
that a survey of the State to determine the location and extent of the
developed low-grade ore deposits was necessary. Considerable time
SITUATION AND EXTENT OF THE LOW-GRADE ORES. 11
and attention have been given to the examination of reported large
low-grade ore deposits and tailings dumps. Some of them have
proved to be most inviting, whereas others have not. A report of the
results of the examinations made of the mining districts visited is
given here.
EXAMINATION OF THE MINING DISTRICTS.
BINGHAM AND GARFIELD.
The mammoth deposits of moiizonite porphyry0 at Bingham,
previously mentioned, carry small percentages of copper, silver, and
gold. The ore is low grade, but is mined in great quantity and is
treated by concentration and smelting. The tailings, which carry
0.6 per cent copper, make an enormous pile. Over 30,000,000 tons of
this material now collected may yet be re-treated.
The ore under the capping and above the sulphides, consisting of
oxides and sulphides intermixed, will need special treatment. A
combination of flotation and leaching is suggested.
The oxidized ore of the capping has been carefully saved and will
doubtless be leached.
The treatment of pyritiferous ores with a low copper content has
long been a problem of the mines in this district. When the zinc
content is below 8 per cent this material smelts well in blast furnaces
running " pyritically."
Ores high in silica and low in copper are sold to the smelters for
flux in the basic-lined copper converters. If these ores could be
leached to a better advantage, the district no doubt could supply a
large tonnage of such ore. Complex sulphide ores are also produced
in this district. Their treatment has long been a much-discussed
problem. At the Midvale mill of the United States Co. the ore is
concentrated, then the middlings are dried and treated electrostat-
ically. The company ships a zinc concentrate east to the " gas belt>"
but smelts the lead concentrates and also the pyrite. Much ore of
this class is demanding attention.
PARK CITY DISTRICT.
Mining has been conducted at Park City1 since 1869, and many
dividend-paying mines have been developed, so that operators in that
district are rather averse to admitting that anything like a low-grade
or complex ore problem exists there.
a For a discussion of the geology of the ore deposits, see Boutwell, J. M., Economic
geology of the Bingham mining district : Prof. Paper 38, U. S. Geol. Survey, 1905, 413 pp.
6 For a description of the geology of the ore deposits, see Boutwell, J. M., Geology and
ore deposits of the Park City district : Prof. Paper 77, U. S. Geol. Survey, 1912, 231 pp.
12 . TREATMENT OF LOW-GRADE ORES.
In this district there are three classes of ore, as follows :
1. Shipping ore.
Sulphide :
(a) Silver-lead ore.
(b) Silver-lead-zinc ore.
(<?) (Rarely) zinc ore.
Oxidized :
(a) Silver-lead ore.
(b) (Rarely) zinc ore.
2. Concentrating, or mill ore.
Sulphide :
(a) Silver-lead ore.
(b) Silver-lead-zinc ore.
(c) Zinc-iron-lead ore.
Oxidized :
(Rarely) silver-lead ore.
3. Low-grade oxidized ore.
(a) Oxidized silver-lead ores.
(b) Oxidized silver-lead-zinc ores.
(c) (Rarely) oxidized zinc ore.
There is a large amount of each of the above classes of ore in the
Park City and Alta districts. Owing to the nature of the deposits
the total available tonnage could not be determined even approxi-
mately. The production of Park City for 1913 was approximately
as follows: Shipping ore, 35,000 tons; concentrating ore sent to
mills, 188,814 tons; concentrates, 41,970 tons. This production will
be maintained for years, according to men who are familiar with
the district. To lessen the economic waste resulting from present
methods of treating these ores and mineral products will, in the
aggregate, add millions to the wealth of Utah.
The five ores given under " Shipping ore " in the classification are
resolvable into two classes as far as the smelters are concerned,
namely, lead ore and zinc ore. The zinc remaining in lead ore
brings no return to the shipper, and if it exceeds a certain percent-
age causes the ore to be penalized so that the shipper suffers a direct
loss as well. Lead remaining in zinc ore represents a loss — in most
cases a direct loss. The loss that occurs when treating ores such as
those above mentioned is illustrated by a published statement of a
Montana producer of zinc concentrate."
The recovery was high— 90 per cent— and the grade of the concentrate was
good — 50 per cent zinc — but it contained also small percentages of lead and
copper, with some silver and gold. The gross value of the merchantable metals,
0 Editorial ; The western metallurgical field ; the complex-ore problems : Met. and Chem.
Eng., vol. 12, September, 1914, p. 555.
SITUATION AND EXTENT OF THE LOW-GKADE ORES. 13
based on current quotations, was about $80 per ton of concentrate. The actual
market value at the smelter was about $24, leaving a difference of $56. A part
of this difference is accounted for in freight, smelting, and marketing charges,
but much of it probably represents a loss to the producer due to economic con-
ditions in the smelting industry. Such instances emphasize the limitations
of present methods of concentration and increase the demand for new processes
that are more efficient.
It is quite probable that the Park City district still has a long
life before it, during which time ore will be shipped direct to smelt-
ers. The loss of lead in zinc ore and of zinc in lead ore during this
period will amount to millions of dollars unless some process is de-
vised for the saving of these metals.
In the milling of the Park City ores it is doubtful if any consid-
erable part of the metals in oxidized ores sent to the concentrator is
saved. This is acknowledged by the operators, yet such ore con-
tinues to be sent to the mill. If this oxidized ore is low in silver and
gold content, and too low in lead and zinc to warrant shipping, it
could not be treated by any known (commercially economical) proc-
ess whereby a saving in lead and zinc could be made without a pro-
portional economic loss — that is, a loss in smelting as well as in
the tailings.
THE MILLING PROBLEM IN THE PARK CITY DISTRICT.
The problem constantly before the mill operators of Park City is
to keep low the zinc content of the lead concentrates and the iron
and lead content of the zinc concentrates. All the zinc in the lead
concentrate is a loss to the operator and an economic loss to the
Nation. The same is true of lead, copper, and other metals in the
zinc concentrate.
That a problem does exist in the treatment of the milling ores of
Park City is proven by the fact that for years the tailings carried
down Empire Canyon and Woodside Gulch have been re-treated in
a crude way by privately owned plants equipped with concentrating
machinery similar to that in the company mills.
The tailings carried down these waterways are retarded at in-
tervals by rough dams. From time to time the material caught above
a dam is shoveled into piles, gathered into wagons, and hauled to
a crude mill farther down the gulch, where the valuable minerals
are extracted by means of jigs and tables. Enough of these min-
erals is extracted to leave a fair profit after it has been shoveled at
least three times, hauled 1 to 3 miles, and treated.
A somewhat similar condition exists, perhaps, at any of the silver-
lead-zinc concentrating plants throughout the Western States. That
it does exist merely goes to prove that some losses occur even at such
successful plants as those of Park City.
Other than the above-mentioned ores, there is a variety of oxidized
ore containing 6 to 8 ounces, or more, of silver per ton and 0.5 to 1 per
14 TREATMENT OF LOW-GRADE ORES.
cent copper. This ore may be the filling of fissures, replacement
material at intersection of fissures, or a bedded deposit, and may be
material derived from high-grade ore or may be a distinct body of
low-grade ore.
THE METALLURGICAL PROBLEM IN THE PARK CITY DISTRICT.
Although it would not be commercially feasible to attempt a per-
fect extraction of all the valuable minerals from an ore, it would
seem that a better extraction should be had than 50 to 66 per cent of
the zinc content, as is stated to be obtained at the Park City mills.
It is not meant by this statement that the mills are not operated ac-
cording to good standards of mill practice, but rather that with even
the best of mill practice there is a loss of metals, which if possible
should be lessened. Such being the case, the problem is how to effect
a better saving of the valuable minerals than is now being made and
how to treat the low-grade oxidized ores, which are not at all amen-
able to concentration by the processes now being used.
A start in this direction has been made by the Mines Operating
Co., which is treating the stope fillings of the Ontario mine. This
oxidized material was considered as waste up to about two years ago.
The American Flag mill was constructed to treat ore similar to the
Ontario stope fillings, and the management contemplates the treating
of custom ore from a number of Park City and Alta mines.
The treatment of the oxidized ores will add much to the gold, silver,
and copper production of Park City, Alta, and similar districts.
What was waste yesterday is a valuable source of these metals to-day,
owing to the application in a new way of an old process — chloridiz-
ing, roasting, and leaching — to these ores. All the oxidized ores of
this district contain some lead and zinc, as previously stated. In
the present treatment of these ores no zinc is saved and only a very
small part of the lead. Ofttimes the value of these two metals is
greater than the gold, silver, and copper saved. As long as this con-
dition exists these ores will present a problem well worthy of all the
time and money given to its solution.
TINTIC DISTRICT.
The Tintic district0 includes all the mines adjacent to Eureka,
Knightsville, Mammoth, and Silver City. Shipments from this
district have continued since 1870.
The Tintic district is considered as being a silver-lead district,
although the ores mined can be divided into four classes: Highly
siliceous gold ore, gold-silver-lead-copper ores, gold-silver lead ores,
a For a description of the geology of the ore deposits, see Tower, G. W., Jr., and Smith,
G. O., Geology and mining industry in the Tintic district: 19th Ana. Rept., 1897-98,
U. 8. Geol. Survey, 1899. pp. 001-767.
SITUATION AND EXTENT OF THE LOW-GRADE ORES. 15
and oxidized zinc ores containing small amounts of silver and lead.
Primary sulphide ore in any quantity has not been encountered in
the district.
On account of the large proportion of sulphide ore and concen-
trates shipped to the Salt Lake smelters, siliceous ores are in de-
mand. Hence siliceous ores are shipped from the Tintic district in
large quantities. A few years ago such siliceous ore was not con-
sidered milling ore unless the value of the metal content was over $20
per ton.
The ores as mined in the district consist of highly siliceous gold
ore, high-grade silver-lead ore, siliceous silver-lead ore, oxidized zinc
ore, and, rarely, copper ore. In mining high-grade silver-lead ore,
generally the amount of lower grade oxidized material encountered
is much larger than the amount of high-grade ore extracted.
The oxidized ores now comprise the bulk of the ore shipments from
Tintic. The amount of sulphide ore mined is small, most of it
being high-grade lead ore varying in its silver content. The zinc
ore, for the greater part, is encountered in the development and
extraction of the two classes of silver-lead ore, generally as separate
stopes in the footwall of the silver-lead ore or as linings to silver-
lead stopes. In addition to the classes of ore mentioned, there is
encountered with them ores of low grade. If the valuable minerals
in this low-grade material are contained in scattered lumps of lead
sulphide, or oxidized lead, the mineral is sorted either by hand pick-
ing or by screening, depending on the fineness of the pay ore. The
rejected fines contain gold, silver, copper, and lead to the value of
$2 to $8 per ton, with general averages of $5 to $6 per ton. In addi-
tion to this class of material, large quantities of highly siliceous ore,
of an average value of $6 per ton, have been developed in the search
for higher grade ore. In some parts of the district the siliceous ore
carries chiefly lead and silver, and in others it carries gold, silver,
and lead, or gold, silver, copper, and lead. Nearly all the mines con-
tain some siliceous ore.
It is estimated that the Tintic district contains at least 2,000,000
tons of low-grade copper-lead-silver-gold ore, which assays approxi-
mately as follows: Gold, 0.10 ounce per ton; silver, 4 ounces; lead,
1 to 3 per cent ; copper, 0.5 per cent.
The Knight-Christensen mill, above Silver City, was constructed
to treat this class of ore. The mill has a capacity of approximately
100 tons a day, and the process used aims at effecting a large saving
of the gold, silver, and copper. The lead is brought into solution,
but at this writing little lead is saved, because a method of economi-
cally precipitating that metal has not yet been devised. In the
aggregate an appreciable quantity of lead is lost in this manner.
This problem is receiving considerable attention.
16 TREATMENT OF LOW-GRADE ORES.
Nearly all the mines in the Tintic district have more or less sine
ore, either in separate stopes adjoining the lead stopes or as shells
in the lead stopes. The zinc ores are all oxides and contain small
amounts of lead and silver.
The Yankee Consolidated, May Day, Uncle Sam, and Mammoth
mines report oxidized zinc ore in excess of 200,000 tons. The zinc
content ranges from 5 to 25 per cent. During the year 1913 a total
of 6,457 tons of zinc ore was shipped. The average zinc content was
33.06 per cent. Under present conditions it does not pay to ship
such oxidized ore containing less than 30 per cent zinc, if the price of
spelter is below 5.5 cents per pound. The problem presented here is
the devising of a method for the treatment of these low-grade zinc
ores; also for the extraction of the zinc contained in the lead-silver
ores shipped.
STOCKTON DISTRICT.
For some years past the only shippers from the Stockton district
have been the Bullion Coalition and the Ben Harrison mines. The
Ben Harrison ore is shipped to smelters and as far as can be deter-
mined at this time (February, 1915) no bodies of low-grade ore of
any moment have been encountered.
At the Bullion Coalition mine about 50 tons of silver-lead-zinc-iron
pyrite ore are treated daily. The mill is of the ordinary type of
lead-concentrating plant. The ore is very high in iron sulphide. No
zinc concentrate is made, the lead being separated from the iron
pyrite and zinc without much difficulty. The concentrates contain
about 9 per cent zinc ; the rest of the zinc goes into the tailings.
In the early operation of this plant oxidized ores formed the ma-
jor part of the material sent through the mill. It is estimated that
the tailings dump contains approximately 175,000 tons. About one-
half of this quantity is oxidized material. The balance, forming the
top layer of the dump, consists of lead-zinc tailings containing a high
proportion of iron, about 23 per cent, in the form of pyrite. These
tailings have a gross value, in gold, silver, lead, and zinc content of
about $10 per ton. The zinc is combined chemically with a high per-
centage of iron. The material in these tailings defies economical
separation of the contained lead and zinc minerals by ordinary meth-
ods, except through the application of one or more processes, such as
roasting, magnetic separation, or flotation, combined with hydro-
mechanical processes.
In the Stockton district a large supply of oxidized zinc ore is re-
reported. In the Old Honerine mine the oxidized ore extends to the
700-foot level; from the 700 to 1,300 foot level, the deepest work-
ings, the ore is a mixture of lead and zinc sulphides. The oxidized
zinc ore is of little value unless some means of concentrating it before
SITUATION AND EXTENT OF THE LOW-GRADE ORES. 17
shipment can be found. The zinc in the lead concentrates is an eco-
nomic loss. Some cheap and efficient means should be found for
treating the tailings and saving all the metallic contents.
DRY CANYON AND OPHIR DISTRICT.
Dry Canyon can be made a producer of low-grade zinc ore if a
method is devised for economically treating the mixed carbonate and
silicate of zinc. A considerable quantity of this ore is found in the
old workings. Much more could probably be developed if it were
profitable to mine low-grade zinc ores. In mining this low-grade
zinc ore much of the profit would undoubtedly be spent in the devel-
opment of new workings, particularly at depth, so that new mines
would actually be made from the profit derived from material con-
sidered waste at the present time.
Approximately 120 tons of tailings daily are being produced in
the Ophir Hill Consolidated mill. According to the management
750,000 tons of tailings accumulated on the dumps in Ophir Canyon
during the past 12 years.
These tailings are said to assay as follows : Copper, 0.65 per cent ;
lead, 0.74 per cent ; zinc, 4 to 5 per cent ; silver, 2.78 ounces per ton.
The concentrate produced from the crude ore contains approximately
7.5 per cent zinc, for which the shipper receives nothing.
DEEP CREEK DISTRICT.
With the exception of the Western Utah mine and several gold
mines, sufficient development work has not been done in -the Deep
Creek district to enable one to judge whether there will be a low-
grade or complex ore problem. Numerous fissures from 2 to 6 feet
wade have been partly developed throughout the granite area. Some
rich lead ore has been mined at a number of places. The material
on the dumps is highly siliceous and the sulphide ores are an inti-
mate mixture of lead-zinc and iron sulphides. More development
work will have to be done to prove the possibilities of this district.
The treatment of the gold, bismuth, copper, or silver-lead-zinc ores,
from the partly developed properties presents no especial difficulties,
except that water had to be brought long distances, and the district
is 50 miles from a railroad.
MILFORD DISTRICT.
The Milford district includes the Beaver, Frisco, Newhouse, and
other properties adjacent to Milford. There are marked differences
in the character of the different deposits. Ores are found in quartz-
monzonite which are similar to those mined by the Utah Copper Co.
79474°— 15 3
18 TREATMENT OF LOW-GRADE ORES.
at Bingham; ores are also found in the sedimentary rocks and in
volcanic rocks.
The quartz-monzonite type of deposit is represented by the Cactus
ore zone and by the O. K. mine. Both of these properties have pro-
duced high-grade ore, but their present value lies in the extremely low-
grade material making up the reserves of the mines. No tonnage is
reported from the O. K. propert}7. Various estimates have been made
on the amount of ore in the Newhouse or Cactus district. The ore is
a low-grade copper ore containing approximately 1.2 per cent of the
metal. In the tailings dump there is estimated to be over 500,000
tons of tailings containing more than 4,000,000 pounds of copper.
Deposits in the sedimentary rocks are numerous. For the most
part the ores mined from such deposits in this district have been
high grade and onty recently have low-grade primary ores been en-
countered. The operators report no considerable tonnage, and as
far as could be determined no metallurgical problem presents itself
except the economic loss represented by the zinc contained in the
lead-silver ore shipped, and the lead in the zinc ore shipped.
The same condition exists in the mining region adjacent to Miners-
ville and Beaver City. All the properties on which work is being
done are in the prospect stage; at least there are no mines in the
sense of having ore blocked out, except they be gold properties.
Undoubtedly deposits of commercial value will be developed in some
of the many old properties in the vicinity of Milford — ores that will
be similar to some of those found in the Park City and Tintic dis-
tricts.
Mineralization in the igneous or volcanic rocks has taken place at
numerous places. There are two commercially important mines of
this type in this section, namely, the Horn Silver and the Beaver
Carbonate.
It is reported that the Beaver Carbonate mine, developed to the
700-foot level, has blocked out a quantity of low-grade silver-lead
ore assaying 5 to 12 ounces of silver per ton and 6 to 10 per cent lead.
A considerable quantity of material is represented by the tailings
•dump, but its estimated value could not be ascertained.
According to the general manager of the Horn Silver property,
three ore problems are presented at that mine. These are :
1. The fillings of the old stopes, which consist of carbonate ore
high in silica and assaying approximately as follows :
Lead per cent— 12. 0
Copper do 0. 7
Silica do 52.0
Lime do 8. 0
Silver ounces__ 6. 0
About 200,000 tons of such material is in the stopes down to the
750-foot level.
SITUATION AND EXTENT OF THE LOW-GRADE ORES. 19'
2. Low-grade sulphide ore left in the mine below the oxidized
zone. This ore assays as follows:
Iron per cent— 5. 0-6.0
Zinc do 20. 0
Silica do 60.0
Lead do 10.0
Copper do 0.5
Silver ounces 5.0
3. The old concentrating-mill tailings, of which there are approxi-
mately 190,000 tons, reported to assay about as follows :
Lead per cent-, 8. 0
Zinc do 7.0
Copper do 0.4
Silica 1 do 61. O
Calcium oxide do 8. 0
Iron do 5. 0
Sulphur do 8. O
Silver , ounces— 6.0
111 1905 a " Peck centrifugal concentrator " mill was constructed to*
treat these tailings, but after a run of a few weeks it was found the
tailings could not be treated at a profit by this process. The mill
was closed down and nothing has been done, in a metallurgical way,
with these tailings since that time.
In order to treat successfully these ores and tailings some process
will have to be devised that will make an economical saving of prac-
tically all the valuable metals contained therein. The fact that the
tailings are finely ground adds to the difficulty of the problem. A
large part of the lead is in the sulphate form and tjie separation of
the lead and zinc is difficult. It seems necessary to devise a combi-
nation of processes for the treatment of these ores and tailings.
SILVER REEF DISTRICT.
Silver Reef district is the name given to an area containing a
series of silver and silver-copper bearing sandstones in the central
part of Washington County, Utah. The ore-bearing beds occur
west, north, and east of Leeds. The ores are confined to what are
locally called the Buckeye and White " reefs." North of Leeds the
ore-bearing beds dip north ; but to the east and west the strike and the
dip changes until, at points approximately a mile east and a mile west
of Leeds, the beds strike almost due south, are parallel, and dip away
from a common axis, forming the flanks of an anticline. As far
as exploratory work has been done, ore has been proven for dis-
tances of approximately 1£ miles on the west flank and about 2 miles
on the east flank. The outcrops can be seen for miles to the south.
The ores range from pure white sandstone, stained here and there
with iron and carrying a high silver content, to sandstone colored
20 TREATMENT OF LOW-GRADE ORES.
a deep blue from copper and carrying a high copper but a low silver
content.
Men who have mined in this district claim that the high-grade
silver ore seldom, if ever, contained copper, and that as the copper
content of an ore increased the silver content decreased.
There are other beds that are slightly mineralized, but the inner
or Buckeye Reef and outer or White Reef are the only productive
ones. These two reefs are separated by several hundred feet of
gypsum-bearing red beds. Both underlie the massive red sandstone
which outcrops about a mile west of Leeds as a bold, vertical cliff
400 or 500 feet in height.
No effort to extract copper was made in the treatment of the
Silver Reef ores. Neither was the treatment of silver ores contain-
ing less than 14 ounces per ton undertaken. Ores of this value con-
taining appreciable amounts of copper were not treated.
Thus, in the Silver Reef district there are low-grade silver ores
and also copper-silver ores. No work was done to determine the
depth to which the ore may extend; when water was encountered
work was stopped. The maximum dip of the "reefs" appears to
be about 35°, but the dip is generally less. The deepest workings
were in 650 feet from the outcrop.
There undoubtedly is a large amount of low-grade silver-copper
as well as low-grade silver ore in this district. There is consider-
able virgin ground, and dumps containing a considerable amount of
silver-copper ore that justifies attempts at treatment.
Silver Reef is 75 miles from a railroad; water is plentiful, but
fuel is costly. If this ore were treated by the Holt process — chlorid-
izing, roasting, and leaching — the costs would be too high, owing
to the long haul on the coal and the chemicals necessary. For treat-
ing these ores a method would have to be devised which would use
products to be had at low cost in the district. This would necessi-
tate a study of the local natural resources in order to determine the
presence of such necessary products.
Crude oil has been found near by in sufficient quantity, and filings
have been made on water-power sites on the Virgin River.
EASTERN UTAH.
Copper ores in sandstone are to be found in eastern Utah from
the Uintah Mountains to the Arizona boundary line. Few of these
copper showings are of any economic importance. The erratic oc-
currence in eastern Utah of these copper ores in sandstone is a feature
that tends to hinder their exploitation. The principal obstacles to
their development are as follows: Variable copper content, distance
from railroads, lack of water, and in most cases the smallness of the
CHEMICAL CHARACTERISTICS OF THE UTAH ORES.
21
deposit. If the copper content is high the deposit is small; if the
deposit is large the copper content is variable. A large supply of
ore of uniform grade is necessary if low-grade ore is to be mined at a
profit. Cheap mining calls for a large tonnage. A number of dis-
connected lenses of ore have to be considered as a whole, and the de-
velopment of one lens lends little or no value to an adjoining lens
as far as the blocking out of the ore is concerned. Such a condition
does not permit cheap mining, especially if the copper is scattered
irregularly through the mass.
CHEMICAL CHARACTERISTICS OF THE UTAH ORES.
liy O. C. RALSTON.
RESULTS OF ANALYSES.
The results of analyses of samples of complex and low-grade ores
collected in connection with this investigation that seem to present
distinct metallurgical problems are given in the table following.
Ordinary free-milling or cyaniding gold ore, for instance, has not
been investigated, as the treatment of such ore involves no special
difficulties. But an oxidized ore carrying copper, gold, and silver
in such amounts that there is too much copper to allow cyanidation
or amalgamation, and too little copper, gold, and silver to be worth
smelting, offers a distinct metallurgical problem. The follpwing
table of analyses represents samples of ores which so far have largely
defied economical treatment.
Results of awtliwx of low-grade and complex ores.
[Analysts: L. F. Pattison, W. G. Woolf, O. H. Pierce, A. E. Gartside, C. Y. Pfoutz, H. J. Morgan, R. M.
Isham, and O. C. Ralston.]
0
|l
SiOj.
CaO.
Fe.
Al,03.
MgO.
Mn.
As.
S.
C02.
Zn.
Pb.
Cu.
Ag.
Au.
Bi.
1
P.ct.
12.9
P.ct.
9.75
P.ct.
7.56
P. ct.
6.2
P.ct.
P.ct.
P. ct.
P.ct.
0.20
P.ct.
15.90
P.ct.
20.49
P.ct.
8.65
P.ct.
Oz.p.t.
0.45
o^.t.
P.ct.
2
10 6
8.20
33.00
3.3
13.19
8.6
.77
.28
Tr.
3
8 5
12 42
18 50
2 6
23 57
18 2
0 1
16
4
60 4
2.67
16.25
7.6
.40
1.81
.87
9.02
.1
1.32
Tr.
5
58 3
3 67
17 17
1 6
0 4
.74
4 77
.58
7
3 75
0 09
6
81.2
.74
10.12
.9
.17
.78
.4
5.53
.08
7
94 1
82
2 14
.6
37
.58
.1
5 30
.18
8
69.0
2.45
13.08
12.8
2.60
.58
.05
1.04
7.06
.25
9
69 5
2.56
8.38
2.7
6.18
.97
1.22
3 15
.23
10
52.7
2.30
11.75
5.8
6.50
2.12
7.80
1.1
Tr.
1.80
.03
11
80.8
.57
4.19
7
1.05
.50
5.5
7.90
.08
12
81 9
1 39
4 50
Tr.
22
52
50
4 3
2 80
03
13
31.4
10.25
4.19
Tr.
.65
19.84
15.7
.55
.30
.23
14
51 3
4.90
12.47
8.0
1.7
7.40
1.3
3.5
Tr.
9 55
.04
15
76.6
2.05
5.72
3.6
2.29
1.8
.3
.75
6.71
.13
16
17
59.6
.50
15.53
4.7
.07
.6
2.3
.2
1 02
4.42
10
.05
Tr
18
.87
Tr.
19
1.57
.10
20
2 47
20
21
.35
22
2 82
.1
23
15 0
2
?4
.6
25
95.0
1.00
.50
2.1
Tr.
10.48
22 TREATMENT OF LOW-GRADE ORES.
Results of analyses of law-grade ami complex ores — Continued.
®
¥
Si02.
CaO.
Fe.
A1203.
MgO.
Mn.
As.
S.
C02.
Zn.
Pb.
Cu.
Ag.
Au.
Bi.
26
P.ct.
P.ct.
P.ct.
P.ct.
P.ct.
P.ct.
P.ct.
P.ct.
P.ct.
P.ct.
P.ct.
P.ct.
0.1
Oz. p. t.
Oz. p. t.
P.ct.
?7
.00
2 1
12 18
Tr
7»
.50
7
6 2
29
60
g
7 68
30
1 .00
8
2 50
31
.00
8
6 40
33
.00
3.3
10 32
33
J.50
9
22
34
.80
1.6
92
35
.40
2 7
3 68
36
.60
4
2 68
37
1.3
1.1
2 00
0 03
38
1.9
4
14 24
39
13 8
1 4
2 76
01
40
41
21
19
0 94
4?
1 41
43
2 53
44
09
45
70
06
3 17
46
47
38.2
1.43
16.35
4.2
19.70
6.8
6.9
.(5
40 59
.07
48
49.2
21.45
6.70
2.2
18. 87
1.02
.20
.04
49
30.8
10.05
2.25
7.4
0.46
12.70
10.55
16.88
14.87
.72
29.56
.01
50
22.0
5.05
16.35
1.85
.20
24.75
6.48
12.0
15.39
.07
4.86
.04
51
43.3
3.20
5.30
21.6
.97
3.15
2.33
5.37
16.54
.62
17.90
.01
52
57.4
10.73
1.18
1.5
1.87
1.90
21.71
3.32
2.00
.07
4.66
.02
53
54
73.9
10.5
4.68
2.10
1.12
33.00
4.4
7.6
.37
i.13
.18
37.34
5.24
6.93
4.4
4.16
3.00
.11
.10
15.94
.78
.18
.01
55
9 3
3 40
28 8
15 8
2 33
35 86
8 5
10 47
07
2 43
.02
66
14.0
2.10
1.69
33.26
11.4
2.59
.06
1.06
.01
57
12.5
1.10
15.00
8.6
.92
19.04
29.9
.21
.13
.15
Tr.
58
18.0
1.10
22.2
14.6
2.42
30.32
13.1
10.56
.10
2.65
.02
59
3.00
60
53.6
2.20
4.4
8.5
.37
6.13
1.37
6.3
7.4
.25
6.7
.02
TYPES OF ORES ANALYZED.
The ores represented in the table of analyses may be considered as
a number of distinct types classifiable on the basis of chemical com-
position, mineralogical constituents, as shown by microscopic ex-
amination; on information in the geological reports on these ores;
on the action of dilute acids on the ores; and also on the history of
metallurgical failures in treating these ores. Eight types of com-
ple or low-grade ores may be distinguished, as follows :
1. Copper carbonate ores.
2. Oxidized ores carrying lead carbonate and silver. Samples 4,
11, 12, and 14 represent this class. In a number of places attempts
have been made to concentrate such ores, but much of the lead car-
bonate was lost in the tailings on account of the habit of that mineral
to divide into small flakes which tend to float off. Most of the ores
contain over 50 per cent of insoluble material, but the amount of
soluble iron and lime presents some difficulties to the application of
hydrometallurgical processes. Analyses indicate that these ores,
however, are markedly similar in composition (except for lack of
copper) to the ore from the old Ontario stopes now being treated
by the Mines Operating Co. at Park City, Utah.
CHEMICAL CHARACTERISTICS OF THE UTAH ORES. 23
3. Oxidized ores carrying small amounts of copper and lead as
carbonates and also gold and silver. Samples 5, 6, 7, 8, 9, and 15
are representative of this class. As stated, this type of ore has not
enough total value to make profitable at present its direct shipment
to the smelter, and the presence of oxidized copper minerals render
unprofitable the extraction of the gold and silver cyanide or amalga-
mate. Most of these ores are siliceous, but some of them show by
analysis high content of lime and iron and might be classed as basic
ores.
4. Oxidized ores with zinc as the chief constituent, and carrying
occasionally gold and silver. This type of ore is represented by
samples 2, 3, and 13. Most of these ores do not contain enough zinc
to be accepted by the zinc smelters, and the oxidized zinc minerals
present frustrate attempts to recover the gold and silver alone. The
zinc content is too high to allow smelting in a lead or copper blast
furnace. An oxidized ore in which zinc is the only valuable con-
stituent must contain at least 30 per cent of zinc to be accepted by
the zinc smelter, although some shipments of ore containing 22J per
cent were made with spelter at 7 cents a pound, but none of the sam-
ples showr even 22 per cent of zinc.
5. Oxidized ores with zinc and lead as the two chief valuable con-
stituents, and occasionally carrying some silver and gold. This type
of ore is represented by samples 1, 10, 52, and 53. In general, such
ores contain too much zinc to allow smelting in a lead furnace and
too much lead to allow smelting in a zinc retort. Moreover, the
oxidized condition of the ores does not permit clean mechanical
separation of the lead and the zinc minerals.
6. Oxidized ore containing zinc, lead, copper, gold, and silver.
There is some of this type of ore in nearly all of the Tintic district
mines, in the Horn Silver mine of the Milford district, and in the
Park City mines. It is both low grade and complex, and it might
be well to observe here that the " complexity " is generally due either
to the presence of zinc or to the oxidized condition of the ore. It is
practically impossible to separate mechanically the different mineral
constituents of oxidized ores.
7. Any of the above groups only partly oxidized. Examples of
such ores are samples 3, 51, and the copper ores of the Utah Copper
Co. Such ores call for two kinds of treatment, namely, one for
the sulphide minerals and one for the oxidized minerals, hence the
complexity of this group.
8. Complex sulphides of zinc, lead, copper, and iron carrying silver
and gold. These ores, which are represented by samples 47, 49, 50, 51,
54, 55, 56, and 58, are of common occurrence. As a rule the presence
of zinc is the complicating factor, as a penalty is exacted by the lead
and copper smelters if the zinc content is above a certain percentage.
24 TREATMENT OF LOW-GRADE ORES.
Improvements in the methods of treating complex sulphide ores of
this class are much to be desired in order that losses of zinc and lead
may be avoided or turned into profits.
It may be said that the main metallurgical problem in Utah is
to find processes which can successfuly and economically treat great
amounts of low-grade oxidized ores. Utah probably has more than
an average share of such ores. There are, for instance, few large
mining districts known in which the zone of oxidization extends so
deeply as it does in the Tintic district. The oxidized minerals are,
as a rule, soft and of lower specific gravity than the corresponding
sulphides, and often are so intermixed as almost to defy any known
kind of mechanical separation. On such ores as these, wet chemical
processes should be the first ones to be considered, with the possible
exception of the oxidized zinc ores. There seems to be a possibility
of successfully treating the latter with certain forms of "igneous
concentration.''
METALLURGICAL TREATMENT OF THE ORES.
By D. A. LYON, R. H. BRADFORD, S. S. ARENTZ, O. C. RALSTON, and C. L. LARSON.
PROCESSES OF TREATMENT.
OXIDIZED ORES.
The present practice in the State as regards ores of type 2 — those
carrying lead carbonate and silver — is to recover all that can be re-
covered by ordinary methods of gravity concentration and to allow
any flaky lead carbonate carried over to go into the tailings. The
recovered lead carbonate is shipped to the smelter.
The Holt-Dern process at Park City and the Knight- Christensen
process at Tintic were evolved for the treatment of ores of type 3.
In these processes the ore is roasted with salt and the metals leached
out with acid brine solution.
The ores of type 4. carrying oxidized zinc minerals as the chief
constituent and occasionally some gold and silver, are not concen-
trated in any manner whatever at present, except by hand sorting at
the mine. These ores must be of smelting grade to be of any value.
The zinc smelters require a zinc content of at least 25 per cent in the
ore shipped to them. Moreover, as the zinc smelters are all at some
distance, it is easily seen that in order to make an ore of this kind
yield the miner a profit at present it must run well over 30 per cent
in metallic zinc. On that account there is not a very great tonnage
of ores containing less than 30 per cent of zinc marketed. The greater
part goes to the dumps or is stored in the old stopes of the mines.
The ores of type 5, carrying both oxidized lead and zinc minerals,
with gold and silver are in some instances being concentrated.
Whatever heavy lead carbonate and silver can be concentrated out by
METALLURGICAL TREATMENT OP THE ORES. 25
gravity methods is saved, leaving the zinc and considerable lead and
silver in the tailings. These zinc tailings are sometimes shipped to
zinc smelters. When the zinc content is low enough (below 10 per
cent) they are sometimes shipped direct to a lead or copper smelter.
The ores of type 6, carrying oxidized zinc, lead, and copper min-
erals with silver and gold, also present a rather serious problem.
At present the object sought in milling these ores is to get rid of
the zinc entirely. Zinc is a detriment in the metallurgy of most other
metals, and ores of high gross value often lie useless on account of
the difficulty of separating the zinc from the other mineral constitu-
ents. Only those ores in which the zinc content is so low that it
will not interfere with smelting the other metals are shipped.
In the ores of type 7, which are partly oxidized, the heavy sul-
phides can be recovered by ordinary gravity concentration methods,
or by flotation. The only loss is in the oxidized minerals, with the
exception of the lead carbonate, part of which is also recovered. As
previously stated, the Utah Copper Co. in working its ores recovers
the sulphides, but not the oxides. However, the company is planning
to leach the tailings dumps later to recover the oxides.
COMPLEX SULPHIDE ORES.
The ores of type 8, complex sulphide ores, have been encountered
in those camps where the mines have reached the sulphide zone. At
Bingham this class of ores is being successfully treated in one in-
stance by wret concentration followed by drying and electrostatic sep-
aration, as practiced in the United States mill at Midvale.
At Park City mixed sulphides have been treated, at the Daly Judge
mill, by wet concentration, followed by drying, very close sizing, and
pneumatic separation. The mixed sulphides from another mine
were treated by wet concentration, followed by light roasting and
electromagnetic separation.
Smelting mixed sulphide ores in a lead or copper blast furnace is
practical only when the zinc content of the ore is less than 10 per
cent. When such ores are concentrated, the object is to obtain a rich
concentrate with less than 10 per cent of zinc. This concentrate
can then be sold to the local smelters, and the zinc middlings can be
treated as described above, or else sent to the " blowing up " furnace
to be made into paint pigment.
The application of dry chlorination processes to complex sulphide
ores is under experiment on a commercial scale at Kellogg, Idaho,
and at Helena, Mont. The sulphides are chloridized by heating in
contact with chlorine gas. The metals other than zinc are extracted
by leaching and deposition. The zinc chloride is concentrated, com-
pletely dried, and fused ready for the electrolytic cell. The results
of these tests are awaited with interest.
26 TREATMENT OF LOW-GRADE ORES.
Finally, the complex sulphide ores are also being treated by grav-
ity concentration as well as by the use of electrostatic and magnetic
concentrating machines.
REMOVAL OF COPPER.
In those ores in which copper is a cause of complications in the
metallurgical treatment there, seems now to be a fairly good assur-
ance that it can be removed economically. At many localities in the
United States the problem is being solved more or less successfully.
On that account the work of the present investigation is lightened to
some extent because only the most promising methods need be tried
on the Utah ores. As regards the treatment of zincky oxidized ores,
that is a more difficult problem. The investigation by the metallur-
gical research department of the State School of Mines has included
keeping in touch with the work of IT different concerns that are
trying to solve practically the same problem. Much pioneer work
remains to be done.
CHIEF METALLURGICAL, PROBLEMS.
Summing up, then, one may say that although many problems
present themselves to those who are attempting to devise processes
for economically treating the low-grade and complex ores of Utah,
the following seem to be the most difficult :
TREATMENT OF OXIDE AND CARBONATE ORES.
The waiters know of no commercially successful process whereby
the valuable minerals may be concentrated out of the low-grade
oxidized ores. As smelting processes are, for the most part, appli-
cable only to the treatment of materials in which the values are more
or less concentrated, it follows that, for the present at least, only
hydrometallurgical processes are suited to the treatment of low-
grade ores in which the metals are present as oxides or as carbonates.
The problem is, therefore, to devise, if possible, hydrometallurgical
processes that can successfully and economically treat low-grade oxi-
dized and carbonate ores.
TREATMENT OF ZINC-BEARING ORES.
At present none of the concentrating processes employed effect as
close a separation of the zinc and lead in complex sulphide ores as
is desirable, as is shown in the table following, taken from a paper a
•Lyon, D. A., and Arentz, S. S., Losses of zthe in mining, milling, and smelting:
Bull. 91, Am. Inst Min. Eng., July, 1914, pp. 1422-1423.
METALLURGICAL TREATMENT OP THE ORES.
27
by Lyon and Arentz, which was presented at the Salt Lake meeting
of the American Institute of Mining Engineers in August, 1914:
Recovery of zinc by various concentration processes.
Process.
Zinc in
zinc con-
centrate.
Zinc in
product
going to
blast
furnace.
Proportion of metal recovered.
Zinc.
Lead.
Silver.
Ordinary wet concentration:
1 'ark City, Utah
Per cent.
Per cent.
Per cent.
50.0
66.0
25.0
065.4
Per cent.
95.0
92.0
90.0
Per cent.
75-80.0
78.0
85.0
Do
Burke, Idaho
Joplin Mo
\Vetherill magnetic a
50.0
48.0-50.0
41.3
49.3
5. 0-7. 0
10.0
12.6
8.6
Huff, electrostatic: b
Mitl vale Utah
Eureka Colo
Potter Delprat c
66.2
38.5
50.9
De Bavay: d
1910
48.1
48.4
49.2
46.0
11.7
14.2
16.6
15.84
1911
1912
Mineral separation
85.4
74.8
80.1
48.7
10.2
Hyde process:
Butte /
88.1
86.4
83.4
80.0
Superior / ...
62.5
a Editorial, Magnetic separation of zinc blende at Denver, Colo.: Eng. and Min. Jour., vol. 74, August
16, 1902, p. 217.
& MacGregor, F. S., Progress in electrostatic ore dressing: Trans. Am. Electrochem. Soc., vol. 24, 1913,
p. 352.
c Hoover, T. J., Concentrating ores by flotation (London), 1912, p. 91,
d Hoover, T. J. , op. cit., p. 97.
« Hoover, T. J., op. cit., p. 105.
/ Results are for 1913.
g About.
The following extract is from the same paper :
In presenting these facts as regards the methods which are used for concen-
trating zinc ores, we do not wish to be understood as criticizing any of the
concentration processes mentioned, as they do the work for which they are
installed, namely, to separate gold-silver-lead-copper-zinc-bearing ores into two
products, one of which shall contain enough zinc to enable it to be profitably
treated by the zinc smelter, and the other no more than will permit of its being
satisfactorily treated in a copper or lead blast furnace. As is well known, in
such furnaces, if the zinc content of the ore constituting the charge is not
greater than 10 per cent, it can be gotten rid of in the slag and fumes. The
loss of this amount of zinc is, of course, a distinct waste. As to the amount
of zinc lost in this manner, the following example will serve to illustrate the
same.
If we treat ore containing, say, 28 per cent of zinc, we separate this into two
products, one of which will contain, say, 50 per cent zinc, whereas the other
will contain most of the gold, silver, copper, and lead and about 10 per cent
of zinc. In other words, of our original product of 50 tons we will have 28
tons (more or less, dependent upon the percentage of iron present) of product
containing 50 per cent zinc, and 22 tons containing 10 per cent, and, in addition,
most of the gold, silver, copper, and lead contained in the original product.
This latter product goes to the blast furnace and ordinarily the zinc content
is not saved, but is lost in the fume and slag. This amount of zinc therefore
28 TREATMENT OF LOW-GRADE ORES.
represents a loss of almost 1,500,000 pounds a year. Moreover, this zinc is lost
for all time, as it can not be recovered, and when we consider that this is lost
from the treatment of only 50 tons of concentrates per day, we can readily un-
derstand, as has been shown by those who have investigated this subject, that
the zinc lost in this wray amounts in the aggregate to thousands of tons annu-
ally, and, as has been pointed out by Clevenger ° and others, in the inability
to recover this zinc lies one of the greatest weaknesses of our present-day
metallurgical practice, in that the zinc so lost represents a distinct economic
waste, much of which will never be recovered, and that we must look to the
prevention of this waste as one of the sources from which we shall in the
future obtain a large part of our zinc supply.
The same thing is of course true to some extent of lead, for in copper smelt-
ing, if lead is present, it is volatilized and no attempt is made to recover it,
and so the lead is completely lost. As before stated, these facts are not pre-
sented with the idea of bringing an indictment against electromechanical
methods of concentration, or against modern methods of copper and lead
smelting, but rather to emphasize the fact that although mechanical methods
of concentration and modern methods of smelting have reached a very high stage
of development, their use nevertheless entails a very great loss of zinc, which
is not recoverable, and that therefore it is quite likely that in the future it will
be necessary to stop these wastes in order to add to the available supply of
zinc.
The problem therefore which presents itself is to derive processes which
will successfully treat low-grade and complex ores containing zinc.
CHLOBIDIZING PROCESSES.
The devising of practicable processes for treating the low-grade
and complex ores of Utah has already been given considerable time
and attention by various investigators and experimenters. As a
result of such work at least two chloridizing processes are being tried
out, one of which is known as the Holt-Dern process, and the other
the Knight-Christensen process.
HOLT-DERN PROCESS.
The Holt-Dern chloridizing process was discussed by Holt6 in a
paper before the August, 1914, meeting of the American Institute
of Mining Engineers at Salt Lake City. This discussion has been
reprinted in the mining journals and is doubtless available to those
who may desire to acquaint themselves with the details of the process
as applied at the plant of the Mines Operating Co., at Park City.
F. S. Schmidt c has also discussed this plant and personal tests
made at it, together with operating costs.
• Discussion by Clevenger, G. II., and others, Is there a complex-ore problem ? : Met.
and Chem. Eng., vol. 12, May, 1914, p. 299.
6 Holt, T. I'., Chloridizing leaching at Park City: Bull. 91, Am. Inst. Min. Eng., 1914,
pp. 1699-1708.
"Schmidt, F. S., Rejuvenating the chloridizing roast: Min. Sci. Press, Aug. 29, 19 M,
pp. 324-328.
METALLURGICAL TREATMENT OF THE ORES. 29
PRINCIPAL FEATURES OF PROCESS.
Following is a brief summary of the steps in the process. The ore
is ground to 8 to 10 mesh size, mixed with 7J per cent of salt, 2J per
cent of coal dust, and just enough water to ball up the mixture. This
pulp is then given a chloridizing roast in air-blast shaft furnaces.
The roasted material is leached with a brine solution containing up to
0.5 per cent of sulphuric acid. The leach solution is passed first over
scrap copper to precipitate the silver, and then through a long series
of iron boxes. The first of these boxes catches fine copper, the lower
ones produce a copper-lead product. From 90 to 95 per cent of the
silver and copper are reported to be recovered by the process out-
lined above, and also about 50 per cent of the gold. Should the gold
content be sufficient to warrant the addition of bleach to the pulp
over 90 per cent of the total gold content may be recovered.
FACTORS AFFECTING THE PROCESS.
The composition and the other pertinent characteristics of the ore
that must be considered in the application of this process to any
particular ore will now be discussed.
The results of tests at Park City, and also of many other tests
in various parts of the country strongly indicate successful extraction
of the gold, silver, and copper contents of low-grade ores, provided
that other factors, which are considered below, do not prohibit the
operation of the process.
A quartz or porphyry gangue is indifferent to the reactions that
take place in chloridizing, and therefore ores high in silica are espe-
cially desirable. A limestone gangue or one of dolomite or other mag-
nesium compounds takes such active part in the reactions that ores
with such gangues may or may not be amenable to chloridizing
methods.
Limestone is detrimental both in the roasting and in the leaching.
In the roasting, calcium oxide decomposes the metallic salts and also
silver chloride, thus preventing complete chloridization of the metal
contents. In the leaching, any undecomposed lime reacts with the
acid, thus weakening the solvent power of the leaching solution, for
the solvent action of the brine depends on the presence of a small
amount of free acid. However, should sulphur be present in the
ore or be added, in quantity sufficient to convert the lime, during
the roasting period, to chloride or sulphate, a good chloridization of
silver and copper may be obtained. In one test an ore containing
23 per cent lime was successfully treated by roasting with an addi-
tion of 12 per cent pyrite and 10 per cent salt. This might be taken
to indicate that the content of lime need be limited by economic
considerations only, the maximum allowable percentage of lime be-
30 TREATMENT OF LOW-GRADE ORES.
ing determined by the cost of the pyrite and salt necessary. The
consideration of lime content suggests another possible solution,
namely, the mixing of different ores in suitable combinations.
Magnesium compounds are similar in their action to calcium com-
pounds and the remarks on lime apply to magnesium equally well.
Arsenic and antimony do not seem to be of much importance in a
consideration of this process as applied to Utah ores. However, it
may be stated that arsenic and antimony compounds when present in
small amounts usually volatilize as chlorides.
Zinc sulphide is not affected by chloridizing shaft roasting, whereas
zinc oxide is converted to a chloride that is very volatile. Leaching
with an acidified brine after roasting recovers less zinc than may be
obtained by leaching the raw ore.
Lead sulphide becomes mostly converted to sulphate in the roast-
ing, owing to the oxidizing effect of the air blast. The sulphate does
not react with the sodium chloride in roasting. Lead oxide may be
formed, capable of being chloridized ; but both oxide and chloride are
volatile. Although at the Park City plant about 40 per cent of the
low lead content (0.72 per cent in original ore) goes into solution, the
extraction from solution by means of the iron-box precipitation is
stated to be inefficient. Electrolytic methods of precipitating lead
are under consideration at that plant.
Pyrite in the ore is advantageous in providing sulphur for the reac-
tions, for neutralizing lime and magnesium, and for combustion, thus
lowering the amount of fuel necessary. Sulphur in excess of that
necessary for the foregoing purposes lengthens the period of roast-
ing but the sulphur in the escaping fumes may be utilized in the
generation of sulphuric acid for the leaching.
Slimy ores that prohibit percolation would require a variation of
the Holt process — some method of agitation and vacuum filtration.
Water is required in the reaction, and also to ball up the slime so
as to make a product suitable for the furnace charge and a calcine
suitable for leaching.
SUMMARY.
The Holt process seems successful as regards extractions of copper,
silver, and gold in low-grade ores, and in addition recovers a small
part of the lead. The process is especially adaptable to siliceous ores
containing pyrite enough to provide the sulphur necessary for the
sulphatization that precedes the chloridization.
Limestone and magnesium are detrimental, but ores containing
these substances may be successfully treated if sulphur can be eco-
nomically added.
With the proper conditions as indicated, a recovery of 90 to 92
per cent of the total copper, silver, and gold content, seems usually
METALLURGICAL TREATMENT OF THE ORES. 31
possible. As regards copper, silver, and gold, the limit of applica-
tion of the process within the allowable limits as stated herein will
usually be the cost of treatment. Where salt and coal are available
at low costs, especially if ores of differing compositions are available
for mixing so that the important reactions can be naturally regulated,
the chloridizing process should be hard to equal in efficiency.
KNIGHT-CHRISTENSEN PROCESS.
The mines of Godiva Hill produce much siliceous ore carrying
silver. Although a market for such ore has been developed through
the operation of the basic-lined converter, the amount smelted is
comparatively small. The quantity of this ore has encouraged much
research on improved methods of treatment. A series of analyses of
these ores, accompanied by tests of methods of treatment, was made
by N. C. Christensen in the metallurgical laboratories of the Univer-
sity of Utah. As a result of these tests a new mill has been erected
just above Silver City for the treatment by the Knight- Christensen
process of 100 tons of these siliceous ores daily. At this mill the ore
is crushed to 20 mesh, mixed with salt and pyrites, and the mixture
roasted in a new type of furnace designed for the chloridizing roast-
ing of this ore. The furnace consists of an annular screen hearth 4
feet wide, 20 feet in outer diameter, and 12 feet in inner diameter.
On the hearth a thin layer of limestone is spread and the layer of ore
is built up to a depth of 4 inches. A crude-oil burner, which extends
across the hearth next to the feed hopper, gives a flame hot enough
to start the roasting of the admixed sulphides. The reactions be-
tween the salt and the roasting sulphides give a chloridizing atmos-
phere for the complete chloridization of the silver and copper in the
ore. Air is drawn through the roasting mixture by a suction fan
and the fumes are carried to the acid towers, where they are ab-
sorbed and collected in tower liquors. The acidified liquors are car-
ried to the storage tanks, where they are brought up to the required
strength, then being ready for the leaching tanks. The roasted ore is
transferred to the leaching tanks and the silver and copper are
leached out with the acidified salt solution. The metals are thrown
down by means of scrap iron in a series of tanks that extend length-
wise of the building. The spent liquors are used again for leaching
a new batch of ore, after being brought up to proper strength in the
towers, by the addition of the necessary salt.
The novel feature of the mill is the method of chloridizing the ore
and the use of salt acid tower liquors for leaching.
The successful operation of this mill is anxiously awaited by the
many mine owners near by who have an abundance of ore of similar
character.
32 TREATMENT OF LOW-GRADE ORES.
PROCESSES HAVING A POSSIBLE APPLICATION TO UTAH ORES.
One of the first things done by the department of metallurgical
research of the University of Utah, was to make a search, as
thorough as the facilities of the university library would permit, for
information on processes that might possibly be applied to the treat-
ment of the low-grade and complex ores of Utah. The literature
relating to patents on the subject was also studied. In the following
statement an attempt is made to outline concisely the possible appli-
cation to Utah ores of processes which are now in use, or have been
suggested.
LEAD CARBONATES CARRYING SILVER.
Analysis of the ores treated at the old Ontario mill in Park City
shows much lead and silver. Only a very small proportion of the
lead is being recovered and its recovery constitutes one of the
problems that now face the management. It is somewhat doubtful
if a chloridizing and leaching process can recover the lead in these
ores, as has been mentioned elsewhere in this report.
MUREX PROCESS.
A process of considerable interest known as the Murex process
has been described lately which, it is claimed, will recover lead car-
bonates. This process combines oil selection and magnetic separation.
SULPHIDIZING AND FLOTATION.
Preliminary tests have indicated the possibility of recovering lead
carbonate by " sulphidizing and flotation." The method involves a
conversion of the oxidized lead minerals into sulphides by means
of hydrogen sulphide gas, which is cheap, followed by ordinary
flotation of these artificial sulphides. Further work is to be done
along this line and the indications are that the method may be a
success.
ELECTROSTATIC SEPARATION.
Electrostatic separation of the lead carbonates carrying silver is
another method which has not been tested completely. As it is
possible to modify the outside coating on particles of lead carbonate
by the sulphidizing process mentioned above, they ought to act as
conductors and hence allow electrostatic separation from the gangue
minerals in case it is not possible to separate them by flotation, as
above mentioned.
METALLURGICAL TREATMENT OF THE ORES. 33
OXIDIZED COPPER ORES CARRYING GOLD AND SILVER.
CHLORIDIZING AND LEACHING.
As may be seen by reference to other parts of this report, the
chloridizing and leaching process is especially applicable to oxidized
copper ores carrying gold and silver, and high extractions of all three
metals can be obtained, provided the ore is not too basic.
SULPHIDIZING AND FLOTATION.
Sulphidizing and flotation of these oxidized copper minerals also
seems to be possible. Preliminary tests have resulted favorably, and
further tests are proposed. The presence of a basic gangue would
not affect this process in the least, as hydrogen sulphide does not
attack limestone. The process would hence be desirable because of
its applicability to ores of almost every kind of gangue.
MOSHER-LUDLOW PROCESS.
The Mosher-Ludlow process was worked out for those ores under
consideration which have a basic gangue, and involves leaching
with ammoniacal solution carrying cyanide. The ammonia dis-
solves copper and the cyanide dissolves gold and silver. Precipita-
tion of the copper is effected by boiling, the ammonia being recovered.
Tests indicate a high extraction of all three metals and a low con-
sumption of ammonia and cyanide. This process has not yet been
used on a commercial scale and there is some question as to the
difficulties of handling it in a large mill.
SLATER PROCESS.
Another process that may apply equally well to basic and acid ores
is the Slater process, as the leaching agent is hypochlorous acid, which
dissolves copper and gold but does not attack calcite. The process
is being developed by the Western Precipitation Co., which is to test
representative samples of Utah ores. Tests indicate a good extrac-
tion of the metals but difficulties still remain as regards the type of
cells to be used in generating the hypochlorous acid.
OTHER PROCESSES.
Other special processes are possible, such as the leaching of the
copper with dilute sulphuric acid and the cyaniding of the tailings.
As a rule those ores of copper, silver, and gold that present a prob-
lem to the metallurgist are the ones that are too low grade to smelt,
and, as a rule, the problem in cyaniding them is high recovery with-
34 TREATMENT OF LOW-GRADE ORES.
out a great consumption of cyanide through the action of copper
minerals. Preliminary leaching of the copper is hence one logical
solution, and will be tried out in a mill at Dayton, Nev., in the near
future.
OXIDIZED ZINC ORES, OCCASIONALLY CARRYING GOLD AND SILVER.
IGNEOUS CONCENTRATION.
Igneous concentration seems at present one of the most feasible
methods of concentrating earthy oxidized zinc ores, occasionally car-
rying gold and silver. It involves the use of blast grates, such as are
used in the manufacture of zinc-oxide pigment. Very few experi-
ments have been made with this method, but it is believed that the
cost of treatment can be reduced to a small figure, enabling the treat-
ment of low-grade ores of zinc. Any gold or silver remains, of
course, in the residue left after removal of the zinc, and can then be
recovered by smelting. In case the gold and silver contents were too
small to make smelting the residue profitable, special processes would
have to be devised to recover them.
LEACHING WITH AMMONIUM CARBONATE SOLUTION.
Leaching out the zinc with a solution of ammonium carbonate and
ammonia is easily accomplished when the oxidized zinc mineral con-
sists of smithsonite, the carbonate of zinc, but the silicates of zinc are
not attacked. Gold and silver can then be leached from the residue
or it can be smelted. Some rather extensive tests of this process have
been made at Ingot, Cal.a
BISULPHITE PROCESS.
At Swansea, Wales, a process has recently been brought to more or
less technical success whereby zinc is dissolved in a solution of sul-
phur-dioxide gas obtained by passing the gases from the roasting of
sulphide ores through a falling spray of water in a tower. The
zinc dissolves in this solution and is easily recovered. Where the
oxidized ores can be treated in conjunction with sulphide ores, this
process promises to have some value, if sufficiently low costs are indi-
cated by present experiments in Wales. No tests of Utah ores have
as yet been made.
LEACHING WITH ACID SOLUTION Atfb ELECTROLYTIC PRECIPITATION OF ZINC.
A great many processes are being tried out in which either sul-
phuric or hydrochloric acid is used as a solvent for zinc, the zinc
0 Bretherton, S. E., Tin- t K utim nt of complex ores by the ammonia-carbon dioxide
process : Bull. Am. Inst. Min. Eng., July, 1914, p. 1771.
METALLURGICAL TREATMENT OF THE ORES. 35
being later precipitated from solution by an electric current. Success
will depend on very careful engineering, as the amount of electric
energy necessary to precipitate zinc is large in comparison with the
value of the resulting metal. Large scale production and cheap elec-
tric energy and acid will have to be obtained to insure financial suc-
cess. Technically these processes work very well.
OXIDIZED ZINC-LEAD ORES, CARRYING OCCASIONALLY GOLD AND SILVER.
The main problem in treating oxidized zinc-lead ores, carrying
occasionally gold and silver, is to obtain the zinc and the lead as
separate products. On that account processes in which only one of
these metals is dissolved are preferable.
BISULPHITE PROCESS.
The bisulphite process previously mentioned dissolves only the
zinc and was, in fact, devised for the treatment of complex zinc-lead
sulphides. The zinc is dissolved out and precipitated. The residue
left contains all the lead, silver, and gold of the ore and can be smelted
in an ordinary lead blast furnace. The metallurgical research depart-
ment plans to try this process on the Utah ores later.
LEACHING WITH AMMONIUM CARBONATE SOLUTION.
In leaching with ammonium carbonate solution the zinc is sepa-
rated from the other metals as in the bisulphite process. As zinc
interferes with the metallurgy of almost all of the other metals, this
process would seem to be a desirable one for such ores.
SULPHIDIZING AND FLOTATION.
Sulphidizing and flotation, as previously mentioned, has been
found to remove lead minerals but not to affect zinc minerals, and
hence offers another method of separating lead and zinc. As the
silver and gold are quite likely to accompany the lead, the process
would seem to offer a most desirable type of mechanical concentra-
tion, provided the lead and zinc minerals can be separated from each
other by sufficiently fine grinding.
OXIDIZED ORES OF ZINC AND COPPER, CARRYING GOLD AND SILVER.
LEACHING WITH AMMONIUM CARBONATE SOLUTION.
In the ammonium carbonate process described both the zinc and
copper are dissolved, but they are easily separated by electrolysis as
the metallic 'copper will deposit on the zinc. The gold and silver
will remain in the residue, and can be recovered by leaching or
smelting. Tests of this process on the Utah ores have not been made
as yet by the metallurgical research department of the University
of Utah.
36 TREATMENT OF LOW-GRADE ORES.
BISULPHITE PROCESS.
The bisulphite process will also dissolve both the copper and the
zinc, and as they are easily separated, the remarks on the ammo-
nium carbonate process apply here as well.
LEACHING WITH ACID SOLUTION AND ELECTROLYTIC PRECIPITATION.
Leaching out the zinc and copper with acid solution, followed
by electric precipitation of the zinc and copper, separately, seems
feasible. Copper can be precipitated completely in the presence of
zinc without any zinc being precipitated, because the voltage required
to decompose the zinc salts is much higher than that required for
the copper salts.
IGNEOUS CONCENTRATION.
Igneous concentration of the zinc content is supposed to be per-
fectly feasible with these ores, the copper, gold, and silver being left
in the residue. As this residue is likely to be partly fused, nothing
but smelting can recover the copper, gold, and silver. Hence the
ore must be of high enough grade to stand the smelting costs ; other-
wise, one of the leaching processes should be better.
OXIDIZED ORES CARRYING ZINC, COPPER, LEAD, SILVER, AND GOLD.
In these ores, the presence of zinc is again the disturbing factor,
and its removal separate from the other metals eliminates most of
the difficulty. As mentioned above, both the bisulphite process and
the ammonium carbonate process under certain conditions remove
zinc and copper, and these two metals are easily separated from
each other. It would therefore seem feasible to apply these two
processes to this class of ores. Sulphidizing and flotation would
seem to be a very promising method of removing the lead, copper,
gold, and silver from the zincky residue.
PARTLY OXIDIZED SULPHIDE ORES.
Very few of the processes mentioned work well on both sulphide
and oxidized ores except igneous concentration, which should remove
zinc as a clean product from any ore that is not too high in lead.
All of the other processes discussed would doubtless require the
ore to be roasted before they could be applied. Also, most of the
sulphide minerals could be removed by ordinary methods of gravity
concentration before processes for the oxidized minerals were
applied.
RAW MATERIALS FOR USE AS REAGENTS.
The State of Utah has within its borders abundant supplies of
minerals that may be employed as reagents in processes for extract-
METALLURGICAL TREATMENT OF THE ORES. 37
ing metals from ores. The tremendous salt supply in the waters of
the Great Salt Lake and in the deposits near by was for many years
put to good use in the ore-reducing mills. New processes employ-
ing increased amounts of salt are coming into use. The salt and
associated mirabilite (NaSO4) will serve as the raw material from
which chemical works can make sodium carbonate, hydrochloric acid,
hypochlorous acid, iron chloride, and such chlorides, perchlorates,
chlorates, etc., as may be needed in leaching ores. A process for the
manufacture of hydrochloric acid from common salt, silica, and steam
has been evolved in the research laboratories of the university which
bids fair to provide for making this acid at a cost well below the
present cost of manufacture. The sulphur gases from smelter
smoke carry the constituents for the manufacture of sulphuric acid,
the acid most used in leaching plants. In localities near plants
smelting sulphide ore the price of sulphuric acid may possibly be
brought to a nominal figure. The removal of sulphur gases from
smelter fumes to make sulphuric acid will largely reduce the harmful
effects of smelter smoke on vegetation.
IRON FOR PRECIPITATION.
By a process of chemical replacement the gold, silver, and copper
of the leaching solutions may be deposited by metallic iron. Scrap
iron has been used extensively in regions where it is cheap. In the
mining districts of Utah the amount of scrap iron to be obtained
would be very small.
Within the State, accessible from Salt Lake City and vicinity, are
large amounts of ores suitable for the production of sponge iron, as
both sulphide and oxidized iron ore and copper-bearing sulphides
are suitable for this purpose. An economic saving is made if the
ores contain gold, silver, or copper, these metals being all saved, and
without added cost, if the iron, preferably sponge iron, made from
the ores is used as a precipitant in leaching processes.
In the July, 1914, number of the Bulletin of the American Institute
of Mining Engineers Frederick Laist and F. F. Frick present the
following description0 of a method they worked out for the manu-
facture of sponge iron:
The furnace, a Bruckner type, 4 feet 3 inches in diameter inside and 1 feet
long, is operated as follows:
One thousand four hundred pounds of calcine are charged and heated with
fuel-oil flame to about 1,300° F. This requires about one and one-fourth hours.
In a commercial plant the calcine would be drawn hot directly from the
MacDougall hoppers to the furnace. About 600 pounds of coal are then shov-
eled in through the front in small lots. The furnace continues to revolve, and
in about three-quarters of an hour after starting to charge the coal the hydro-
0 Precipitation of copper from solution at Anaconda, p. 1433.
38 TREATMENT OF LOW-GRADE ORES.
carbons are burned off. The oil flame is again started. In one and three-
fourths to two hours the charge is up to 1,680° to 1,700° F., and reduction is
complete. The discharging door is removed and the charge quenched.
SODIUM SULPHATE (MIRABILITE) .
Next to common salt, sodium sulphate suggests itself -as a profit-
able product of the water of Great Salt Lake.0 This substance
(known mineralogically as mirabilite) separates from the brine at a
certain low temperature. This critical temperature is probably
within a few degrees of the freezing point of fresh water.
As the crystallization of the mirabilite proceeds the water becomes
opalescent, and the substance deposits over the lake bed and is cast
up by the waves in such quantities as to cover the shore in places to a
depth of inches or even feet. It can be easily gathered by the use
of horse drags.
The easy preparation of sodium carbonate from mirabilite is self-
suggestive, and experience has demonstrated the success of the
undertaking at low cost. Limestone and coal necessary to trans-
form the sulphate into carbonate are of easy access.
ALLIED PROBLEMS.
In taking up an industrial problem one generally finds that
there are many allied problems awaiting solution, and this has
proved to be especially true of the investigation to ascertain the
feasibility of attempting to treat the low-grade and complex ores of
the State of Utah. To illustrate — certain electrometallurgical proc-
esses demand cheap power. Such being the case, information is
needed as to the availability of electric power either from the utili-
zation of flowing streams or from the coal resources of the State.
Again, with the question of hydroelectric power may be connected
the question of irrigation, as at The Dalles, Greg., and the working
up of this possibility alone may require considerable investigation.
If coal is to be utilized, the location of available coal beds, the nature
of the coal, and the possible utilization of the by-products from the
distillation of the coal become of interest.
Incidentally, the problem of utilizing such by-products of coal
as ammonia, tars, and tar oils is closely connected with metallurgical
processes, as ammonia can be used very well in the extraction of
metals from oxidized ores, both of copper and of zinc, and certain
coal-tar products are in demand for flotation work. A proper inves-
tigation might show that it would prove profitable to save these mate-
rials in the coking of the coals instead of letting all of the volatile
part of the coal be wasted, as it is at present in the preparation of
coke in Utah, Nevada, Idaho, and Montana.
"Talmage, .T. E., The Great Salt Lake, 1000, pp. 64-S5, 82-86.
METALLURGICAL TREATMENT OF THE ORES. 39
In the coking of coal it may be possible to find a solution of the
smoke problem in the city of Salt Lake, as coke and gas fuels are
smokeless, whereas the raw soft coals of the State, which are now
being used, make the city atmosphere very smoky under certain
conditions in wintertime. The department of metallurgical re-
search, in cooperation with the Federal Bureau of Mines, is at pres-
ent engaged in an investigation of this nature.
Again, as regards the use of electric energy in the preparation of
solvents from the waters of Great Salt Lake for the purpose of treat-
ing ores, there are likely to be by-products formed which can be
used in other industries in the State. As an instance, sodium hy-
drate, chlorine, or hydrochloric acid can be used in making phosphate
rock soluble and available for use as fertilizer, although this can also
be done with sulphuric acid, which can be cheaply made by treat-
ment of the smoke from furnaces for sulphide ores.
As is well known, in the eastern part of the State are extensive
deposits of hydrocarbons. In hydrometallurgical work it is gener-
ally necessary to use large vats. Concrete has proven satisfactory
for the construction of such vats, but if acid solutions be used, the
vats must, of course, have an acid-proof lining. It is stated that
the use of asphalt for this purpose has given excellent results.
Hence the hydrocarbons of Utah may become an important source
of acid-resistant lining.
A large number of such instances might be cited to show how in-
vestigations conducted for the purpose of solving the low-grade ore
problem may result in the discovery of unsuspected uses for other
natural resources of the State.
CONCLUSION.
As shown by its title, this paper is offered only as a preliminary
report. Its purpose is to give some idea of the size and extent of the
low-grade ore deposits of the State, and the necessity of conducting
investigations for the purpose of discovering processes that will be
commercially suited to the treatment of these ores and of developing
such other industries as may be brought about as the result of carry-
ing on the investigations.
PUBLICATIONS ON TREATMENT OF MINERALS.
A limited supply of the following publications of the Bureau of
Mines is temporarily available for free distribution. Bequests for
all publications can not be granted, and to insure equitable distribu-
tion applicants are requested to limit their selection to publications
that may be of especial interest to them. Requests for publications
should be addressed to the Director, Bureau of Mines.
BULLETIN 3. The coke industry of the United States as related to the foundry,
by Richard Moldenke. 1910. 32 pp.
BULLETIN 12. Apparatus and methods for the sampling and analysis of fur-
nace gases, by J. C. W. Frazer and E. J. Hoffman. 1911. 22 pp., 6 figs.
BULLETIN 47. Notes on mineral wastes, by C. L. Parsons. 1912. 44 pp.
BULLETIN 53. Mining and treatment of feldspar and kaolin in the southern
Appalachian region, by A. S. Watts. 1913. 170 pp., 16 pis., 12 figs.
BULLETIN 64. The titaniferous iron ores of the United States, their composi-
tion and economic value, by J. T. Singewald, jr. 1913. 145 pp., 16 pis., 3 figs.
BULLETIN 70. A preliminary report on uranium, radium, and vanadium, by
R. B. Moore and K. L. Kithil. 1913. 101 pp., 4 pis., 2 figs.
BULLETIN 71. Fuller's earth, by C. L. Parsons. 1913. 38 pp.
BULLETIN 77. The electric furnace in metallurgical work, by D. A. Lyon,
R. M. Keeney, and J. F. Cullen. 1914. 217 pp., 56 figs.
BULLETIN 81. The smelting of copper ores in the electric furnace, by D. A.
Lyon and R. M. Keeney. 1914. 80 pp., 6 figs.
BULLETIN 84. Metallurgical smoke, by C. H. Fulton. 1914. 90 pp., 5 pis.,
15 figs.
TECHNICAL PAPER 41. Mining and treatment of lead and zinc ores in the Joplin
district, Missouri, a preliminary report, by C. A. Wright. 1913. 43 pp., 5 figs.
TECHNICAL PAPER 50. Metallurgical coke, by A. W. Belden. 1913. 48 pp.,
1 pi., 23 figs.
TECHNICAL PAPER 60. The approximate melting points of some commercial
copper alloys, by H. W. Gillett and A. B. Norton. 1913. 10 pp., 1 fig.
TECHNICAL PAPER 81. The vapor pressure of arsenic trioxide, by H. V. Welch
and S. H. Duschak. 1915. 22 pp., 2 figs.
TECHNICAL PAPER 88. The radium-uranium ratio in carnotites, by S. C. Lind
and C. F. Whittemore. 1915.
TECHNICAL PAPER 95. Mining and milling of lead and zinc ores in the Wis-
consin district, by C. A. Wright. 1915. 39 pp., 1 pi., 5 figs.
40
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