THE LIBRARY THE UNIVERSITY OF BRITISH COLUMBIA Digitized by the Internet Archive in 2010 with funding from University of British Columbia Library http://www.archive.org/details/preliminaryreporOOcraw COLORADO STATE GEOLOGICAL SURVEY BOULDER R. D GEORGE. State Geologist BULLETIN 1 A PRELIMINARY REPORT ON THE GEOLOGY OF THE MONARCH MINING DISTRICT CHAFFEE COUNTY COLORADO BY R. D. CRAWFORD QS c^ ^ 0 CONTENTS I Page Introduction 7 Field work and acknowledgments 7 Situation of the district 7 Water-supply and timber S History ^ Production 9 Literature 10 Outline of geology 11- General geology li! Topography 12 Pre-Cambrian rocks 12 Granitic gneiss 12 Gi'anite 12 Diorite, syenite, and hornblendite 13 Paleozoic sediments 14 Pre-Devonian limestone and quartzites 14 Ouray limestone 15 Post-Devonian igneous rocks 17 Quartz monzonite (adamellite) 17 Petrography 17 Texture and structure 18 The name 19 Apophyses 19 Quartz monzonite (banatite) 19 Porphyries 20 Quartz monzonite porphyry 20 Latite and latite porphyry 21 Breccia 22 Quaternary deposits 22 Moraines 22 Rockslides and landslides 22 Structure 23 Folding 23 Faulting 26 Jointing 28 Caves and underground channels 28 Igneous intrusion 29 Contact metamorphism 29 Economic geology 31 Character of the ores 31 Tenor of the ores 32 Mineralogy of the ores 32 Copper minerals 32 Azurite 32 Page Chalcocite 32 Chalcopyrite 33 Chi-ysocolla 33 Copper, native 33 Copper-bearing pyrite 33 Cuprite 33 Malachite 33 Tenorite, melaconite 33 Gold 33 Iron minerals 34 Hematite 34 Limonite 34 Magnetite 34 Pyrite 34 Turgite 34 Lead minerals 34 Anglesite 34 Cerussite 34 Galena 34 Mimetite 35 Wulfenite 35 Manganese minerals 35 Psilomelane 35 Pyrolusite 35 Silver minerals 35 Zinc minerals 35 Calamine 35 Smithsonite 35 Sphalerite 36 Gangue minerals 36 Calcite, "spar" 36 Dolomite 36 Quartz 36 Types of ore deposits 36 Replacement deposits in limestone 36 Filling in fault-fissures 3S Contact deposits in the sedimentary rocks 38 Syenite-granite contact deposits 3-S Fissure veins in quartz monzonite 39 Terms used to describe ore shoots 39 Age of the ores 40 Genesis of the ores 41 Practical inferences and suggestions 42 Description of mines 44 Mines of Monarch Hill 44 Madonna mine 44 Silent Friend and Fairview mines 49 Hawkeye mine 50 Eclipse mine 50 Fairi)lay mine 54 Grent .Monarch mine 54 Page Little Charm mine 55 Little Wonder mine 55 Wilson mine 55 Evening Star mine 55 Delaware mine 56 Black Tiger mine 56 Other mines 56 Mines of Taylor Gulch 56 Lilly mine 56 Rainbow-Eagle Bird mine 60 Mountain Chief and Pinyon mines 61 Last Chance mine 62 Bonnie Belle, Ben Hill, Fraction, and Desdemona mines. . 62 Shamrock mine 63 Major mine 63 Garfield mine 64 Alaska mine 64 Missouri Boy mine 64 Other mines 65 Prospects and Developments in Taylor Gulch 65 Mines of Cree Camp , 66 Song Bird mine 66 Clinton mine 66 Mines of Columbus Gulch and vicinity 66 Golden Age mine 66 Darling mine 66 Limestone Marble . . Brighton mine 67 Columbus mine 67 Alpha and Beta ^^ 68 6S 68 69 Uncle Sam mine. Prospects in Hoffman Park. Index '^^ ILLUSTRATIONS Page Plate I Topographic map of the Monarch district 8 II Geologic map of the Monarch district 12 III Geologic sections of the Monarch district 25 IV Mining claims of Monarch Hill 45 V Horizontal plan of Madonna mine 46 VI Vertical plan of Madonna mine above third level 48 VII Cross-sections of Madonna ore bodies 48 VIII Horizontal plan of Eclipse mine 52 IX Vertical plan of Eclipse mine 53 X Mining claims of Taylor Gulch 57 XI Horizontal and vertical plans of the Lilly mine 59 Fig. 1 Diagram to show probable trend of limestone-granite con- tact east of Cree Camp 26 2 Diagram to illustrate faulting on Monarch Hill 27 3 Diagram to illustrate terms used in describing ore shoots 39 INTRODUCTION FIELD WORK AND ACKNOWLEDGMENTS The field work on which the present report is based was done in the summer of 190!). Considerable mapping still remains to be done in the Monarch district, but it seems desirable to publish at this time the more important results of examinations already made. During the summer of 1910 the survey will be extended over a wider area, including that part of Gunnison County con- tiguous to the Monarch district. The topographic mapping was done by P. G. Worcester, R. C. Coffin, and R. M. Butters, who also assisted in the geologic work. Traverse plane-tables were used in both triangulation and tra- verse. Elevations were determined b}' means of aneroid barom- eters, and hence the contours as shown on the map should not be taken as quantitatively accurate. It is believed, however, that but few of them are in error more than two contour inter- vals. The topographic map was prepared for the engraver by Mr. Worcester. Mr. Butters has made many assays and chemical analyses for use in the report. Professor Junius Henderson, of the University of Colorado, has determined the fossils collected, and correlated the formations with those in other parts of Colo- rado. The mine owners, managers, superintendents, miners, leasers, and prospectors in the district have done much to facilitate the work of the field party. They have not only shown payable ore bodies, but have pointed out their unprofitable undertakings and have not attempted to conceal unfavorable conditions. Many non-resident mine owners have given valuable assistance. Mr. F. P. Black, who has made many mine and patent surveys in the district, has generously responded to frequent requests for maps and other data. The plans and vertical sections of mines are reductions of drawings furnished by the mining companies. SITUATION OF THE DISTRICT The Monarch mining district is in the southwestern part of Chaflfee County, Colorado, on the east slope of the Sawatch Range, which forms a part of the Continental Divide. The district may be reached by rail or by triweekly stage from Salida, about b A PRELIM IX ARY REPORT OX THE twenty miles distant. There are two villages in the region, Gar- field and Monarch, about a mile and a half apart. Beside the productive area shown on the map (PI. I) ore has been found on Pass Creek several miles southeast of Monarch, and on the North Fork of the South Arkansas Kiver, north of Mount Aetna and Taylor Mountain. The White Pine mining district lies just over the range toward the west. WATER SUPPLY AND TIMBER Precipitation during the winter is heavy, and the snow that accumulates on the highest slopes may remain until nearly the end of summer. The melting snow and frequent showers furnish abundant water within the district for every purpose during the summer. In the winter the streams are continually fed by numerous springs. (See p. 28.) Formerly pine, spruce, and fir covered most of the slopes below timberline, but much of the timber is now removed. Al- though a few restricted areas are still densely forested, the re- newal of a demand, such as existed in the ei^ghties. would soon ■exhaust the supply in the immediate vicinity of the mines. Even now a large part of the timber used comes from near Leadville. HISTORY In 1878 ore was discovered on the Great Monarch claim by the Boone brothers. This was followed in 1878 or 1879 by discoveries of ore, by the four Boones, on the Fairplay, Pay Mas- ter, Ben Bolt, and Eclipse. Creede (?) located the Oshkosh in 1878 or 1879. At about the same time Smith and Gray discov- ered ore in the Madonna and Silent Friend. Early in 1879 Mr. Daih^ found ore at Cree Camp on the Song Bird claim, w^hich he afterward sold to Alex Cree. The Mountain Chief, Missouri Boy. Eagle Bird, and others in Taylor Gulch, w-ere soon located. The first ore shipped from the district came from the Great Monarch, and was hauled by wagon to Canon City. It ran about 200 ounces silver per ton. A small amount of ore from other mines was freighted by wagon to Canon City before the railroad was built to Maysville in 1881. The ore from most of the mines was of too low grade to ship after hauling by wagon even to Maysville. The ownei's of the Madonna, to whom the discoverers sold that claim, built a small smelter at the foot of the hill to treat the ^Madonna ores, but this was not a success. In 1883 Mr. A. Eilcrs saw the possibilities of the Madonna, secured the x;-^ N\-^^ -A^ % J A \ ^y A A DI Tnile 2 kiloai BULLETIN NO. I PLATE I LEGEND EH Mine I'mnpect MINES 7 Madonna No. o 8 Madonna No. i 9 Madonna No. i No. ) 3 Madonna No. 5 3 Madonna No. 6 4 Hawk«ye 6 Eclipse No, 3 8 Eclipse No, 1 o Os 3, Evening Star mcL, 39 Evening Startunm 33 Black Tiger 35 Thirty-S 11 -Thirty 36 Ohio & Colorado Co qi v-Eagle Bird V. Eagle Bird n Chief tun ain Chief shi Topography by P G. Worcester R C. Coffin and R. M. Butters TOPOGRAPHIC MAP OF THE MONARCH MINING DISTRICT, COLORADO Scale 2 5000 or ttpprosiina-lely 2 _ inches to J nule GEOLOGY OF THE MONARCH MIXING DISTRICT 9 exteusiou of the railroad from Maysville to Monai'ch — nine miles — and organized the Colorado Smelting Company, which took over the Madonna mine and erected a smelter at Pueblo. Since an abundance of basic ore was supplied by the Madonna for fluxing siliceous ores purchased from other Colorado districts, this enter- prise was a success from the first. For about ten years, beginning with 1883, the production of the district was large. In 1893 Monarch shared the common experience of Colorado silver-producing camps, and for some time the district was nearly deserted. Within the past few years, however, with a home market for zinc and an increasing demand for basic fluxing ores, there has been a revival of interest in the district. The recent discovery of ore on the lowest level of the Madonna, and in the Mason and Moose mines, the increasing output of the Lilly, the reopening of the Eclipse, and the devel- opment work in Taylor Gulch, will probably stimulate the great- est activity that has been known in the district since the early nineties. That the production of the region has not been greater is due in part to the methods of a number of mine owners, who have been satisfied to acquire modest fortunes with the least possible risk. Very little development work was carried on in some of the good mines while ore was being taken out, and they were closed when the known ore bodies began to fail. To the credit of the district it should be stated that there has been a minimum of expensive litigation among the mine owners. Probably not more than two mines have ever been shut down pending court decisions. PRODUCTION Since there have been so many estimates, guesses, and ex- aggerated statements as to the output of the district a special effort has been made by the Surv-ey to secure data which would be reasonably accurate. Many of the mine owners have co- operated, and the result is fairly satisfactory. The tonnage and value, by years, have been obtained for the Eclipse, Fairplay, Lilly, and ^fadonna mines, but in most instances only the total production could be learned. Conservative estimates have been accepted for a few mines of which the exact output was not known. The gross value of the ore shipped appears to be between 17,000,000 and |8,000,000. Of this amount the Madonna has pro- duced |4..^35,543.94. (See p. 47.) The production of several others is noted in the description of mines. 10 A PRELIMINARY REPORT OX THE LITERATURE Aside from a three-page article in tlie Keport of the State Geologist for 1883-84\ treating chiefly of the Columbus mine, I have seen no description of the region in geological or mining publications. Brief reference to the district is made in several volumes of Mineral Resources of the United States by the United States Geological Survey, and in the reports of the State Geolo- gist, and of the Bureau of Mines of Colorado, Ore was not dis- covered at Monarch until after the work of the Hayden survey was completed in Colorado, and it appears that the geologists of that organization passed over the region somewhat hurriedly. In 1885 the late George H. Eldridge, of the United States Geologi- cal Survey, examined the Madonna mine and surroundings, but his report was not published. •Report of E. LeNeve Foster, State Geologist, 1884, pp. 30-33. GEOLOGY or THR MONARCH MINING DISTRICT 11 OUTLINE OF GEOLOGY The area mapped is a small part of a large metamorphic area which was intruded by granite probably in pre-Cambrian time. The granite itself underwent a moderate degree of meta- morphism. Probably in Cambrian time marine sediments of unknown thickness were laid down on the granite. Later, elevation ex- posed these sediments to erosion until they were nearly all removed. The surface was again submerged in Ordovician time. The presence of Silurian and Lower Devonian strata has not been proved. Upper Devonian and Lower Carboniferous times are represented by sediments more than a mile in thickness. At an unknown time subsequent to the period of sedimenta- tion the entire region was left high above sea-level and subjected to folding and faulting. After the folding, a large mass of quartz monzonite was in- truded into the sedimentary rocks, and this was followed by the intrusion of many porphyry dikes. Subsequent to the folding and probably after the intrusion of quartz monzonite, metallic minerals were deposited in the tilted sedimentary rocks. Some mineralization immediately suc- ceeded the intrusion of porphyry. Erosion has removed a large amount of rock and exposed the porphyry dikes and ore bodies. Whether or not the quartz monzonite originally reached the surface is not known, but ero- sion has made the outcrop of this rock prominent. Probably in Pleistocene and Recent times, local glaciers, heading on the divides, moved down the valleys where they de- j)0sited moraines. 12 A PRELIMINARY REPORT OX THE GENERAL GEOLOGY TOPOGRAPHY The area covered bv the map is one of high relief, having a vertical range of approximately 4,500 feet. High sharp peaks and valleys with steep sides are characteristic features. Most of the valleys are V-shaped, but U-shaped valleys heading in glacial cirques near the top of the Continental Divide are not uncommon in this area and farther south. The region is drained by the North, Middle, and South forks of the South Arkansas River and numerous smaller tributary streams. North Fork, which does not appear on the map, flows eastward a short dis- tance north of Taylor Mountain. Glaciation has been an important agent in the development of minor features of the topography. It has been effective ia three ways: (1) In planing down and reducing the irregularities of surface, (2) in gouging out rock basins, (3) in forming rough- and-tumble morainal topography. Good examples of the first may be seen in the roches mou- tonees east of Garfield, west of Boss Lake, and in the valley of North Fork. Strife are present only where the abraded surface has been protected by a covering of soil. Boss Lake presents the best example of gouging. Glaciation was unusually effective here perhaps because of mineralization of the faulted sediment- ary rocks at the contact with the eruptive quartz monzonite. This is indicated by the large amount of magnetite and iron sul- phide just east and north of the lake. Rough-and-tumble topog- raphy occurs in several places, but is perhaps best seen in the valley a short distance southeast of Cree Camp. PRE-CAMBRIAN ROCKS GRANITIC GNEISS Although no highh- metamorphosed pre-Cambrian rocks are piesent in the area covered by the map, granitic gneiss occurs over wide areas not far east and southeast. GRANITE One of the most imi»<>r(anl rocks of the district in areal extent is biotite granite which was intruded into the gneiss prob- iTct; color z miles BULLETIN NO. 1 PLATE X (X Dip Overturn Strike ' « Mine Quarrj Prospect GEOLOUIC MAP Qp THE MONARCH MININ(i DISTRICT. C(^L()I{AD() ScaJe f&o55 or Hpproxiuialelv 2'^2inrlies to 1 mile dss.sied ov R M Suttsrt, ; C Cotf.fl apd P G, WorcMti m GEOLOGY OF THE MONAIU'll MINING DISTRICT 13 ably ill pi'o-Caiiibriiiii tiiiH\ TIh' reasons for fonsi- it |)re- Canibriaii are its structural similarity to granite in other ])arts of Colorado, whose age has been fairly well established, and the stratigraphic evidence of overlying rocks noted below. The granite ranges from light gray to darker gray and to red. It is medium to coarse in texture. Much of the granite is even-grained but a porphyritic facies is present over considerable areas, particularly in the east part of the field where feldspar phenocrysts from half an inch to an inch and a half long form a large portion of the rock. Very commonly these phenocrysts show a parallelism in arrangement, probably due in large part to their assuming a similar position in the moving rock magma before it had solidified. In general the even-grained granite is massive or only slightly gneissoid, but locally granite-gneiss has been developed through shearing stresses. In the southern and southwestern part of the field the gran- ite is predominantly pink or red and even-grained. The color of the rock is due in part to the color of the feldspar but is also in large measure a result of the weathering of the biotite. The essential constituents of the granite are potash feldspar, quartz, biotite, and plagioclase. Although the proportions of the minerals vary from place to place the order given is in gen- eral the order of importance. I DIORITE, SYENITE^ AND HORNBLENDITE In the granite area east of Garfield are several intermediate to basic dikes, trending in a general northerly direction. These dikes are probably intrusive into the granite since they extend long distances and in most cases are sharply differentiated from the granite walls, apparently forming an eruptive contact. They have, however, shared the regional inetamorphisni with the gran- ite, and are hence probably but little younger. The dike seen at the railway about 800 feet east of the base of the limestone is a heavy, dark, fine-grained rock composed of hornblende and subordinate feldspar with considerable titanite and a small quantity of magnetite. The microscope shows the feldspar to be microcline and plagioclase in about equal quan- tities. The Bay State and Independence tunnels about a mile north of the railroad, cut a similar or probably the same dike. The rock in the specimens examined differs from that at the railroad chiefly in that the feldspar is all oithoclas(». This dike, or one 14 A PRELIMINARY REPORT OX THE parallel to it, can be traced northward nearly half a mile to a point where it passes under the glacial drift. A few feet east of the first dike mentioned is one of horn- blendite composed chiefly of hornblende but carrying some pyrite. A strong dike of diorite, about a mile and a half east of Garfield, runs nearly parallel to those described. It is por- phyritic in appearance and shows evidence of having been squeezed and folded through shearing stresses. While the dike appears to be intrusive into the granite it does not show walls as well defined as do some of the others, and is itself cut by veins of pegmatite from a fraction of an inch to several inches wide. PALEOZOIC SEDIMENTS A series of sedimentary rocks more than a mile in thickness is present between the east side of Taylor Gulch and the west side of Columbus Gulch. North of Clover Mountain eruptive rocks enclose large masses of sediments which differ lithologic- ally from any toward the east and are probably younger. The entire section is nowhere exposed, but the general character can be determined and the lower part of the series can be examined in detail. Within the lower 4.000 feet Ordovician, Devonian, and Carboniferous fossils have been found, but the upper part of the series has thus far yielded no fossils. PRE-DEVOXIAX LIMESTONE AND QUARTZITES Throughout the district wherever the contact of the sedi- ments with the underlying granite is exposed at the surface the limestone described below lies immediately on the granite. But in several mines quartzite varying in thickness from a few inches to several feet lies between the granite and overlying lime- stone. This quartzite may be seen in the Clinton and Lilly mines north of Garfield and in the Evening Star tunnel on Mon- arch Hill. Since no fossils have been found in this quartzite it cannot be referred with certainty to any age. The fact that it is a remnant left at the close of a pci-iod of erosion before the Ordo- vician sediments were deposited, indicates that it may l)e of Cambrian age. Bluish-gray limestone. Imviiig a thickness of '2:^') lo LTjO feet, overlies the quartzite where the lattcM- is pi-esent, and rests on the granite where the quartzite is absent. The limestone is mag- nesian througliout, is for the most part thick-bedded and con- GEOLOGY OF THE MONARCH MINING DISTRICT 15 tains several cherty strata. Most of the chert is in nodules but there are more or less continuous beds up to three inches thick. Above the liiiiostone described is a persistent bed of quartz- ite. locally called the "parting quartzite". No attempt is here made to correlate this formation with the Parting Quartzite of Leadville and Aspen, although it is not impossible that the two may occupy the same stratigraphic position. The quartzite varies in thickness from 37 feet, east of Garfield, to less than 20 feet, southwest of Monarch. It is bluish to white and for the most part rather fine in texture. Locally it carries a thin bed of car- bonaceous shale near the upper part. The quartzite is conform- ably overlain by magnesian limestone in which chert is less common than in the limestone below the quartzite. Fossils from this limestone, 40 feet above the quartzite, were identified as Receptaculites oiucni by Professor Henderson and by Dr. E. O. Ulrich who consider them to represent an Ordovician horizon. The late George H. Eldridge collected a number of specimens from Monarch Hill in 1885. Doctor Girty, who has very kindly looked up Mr. Eldridge's notes and collection, states that several years ago he provisionally identified Ordovician fossils from this collection. He has also found lists, which he thinks were made by Doctor Walcott, giving the following species obtained by Mr. Eldridge : Halijsites catenulatus Ealy sites agglomeratus Diphyphyllum sp. Zaphrentis sp. Heliolites sp. Stromatopora sp. Orthoceras of the type of Multituhulatu}n The present writer does not have at hand Mr. Eldridge's notes but the description of stations as given by Doctor Girty indicates that at least part of the fossils were found below the quartzite. Hence it appears that neither the upper nor the lower limits of the Ordovician have been specifically determined. OURAY LIMESTONE About 900 feet of limestone conformably overlies the "part- ing quartzite" and is overlain by a thick series of quartzites, shales, and limestone. The limestone is for the most part blue or gray but a stratum of black limestone occurs in the upper part. Beginning at about 100 feet above the quartzite is a stratum 16 A PRELIMINARY REPORT OX THE about 80 feet thick which ranges from siliceous limestone to a structureless hard mottled shale which breaks with a conchoidal fracture and weathers to reddish or chocolate brown. Most of the limestone is magnesian or dolomitic, fine-grained, and breaks with sub-conchoidal fracture. However, about GOO feet above the quartzite is a bed approximately 100 feet thick composed of almost pure calcium carbonate; it is blue in color and crystalline. This is the rock that is quarried at Garfield for flux. Girty^ has recorded the following Devonian fossils collected by Eldridge from the Ouray limestone of Monarch Hill : Athyris colorodoensis Girty Caijiarotorchia contract a (Hall) Hall and Clarke Camarotcechia endlichi (Meek) Schuchert Monotrypella sp, Orthoceras sp. OrtJiothetes chemnngensis (Conrad) Hall and Clarke= Schuchertella chemungensis (Conrad) Kindle- OHhothetes chemungensis var. Productella semiglohosa Nettleroth? = P. coloradocn.sis Kindle^ Productella suhlata Hall? Productella suhlata var. SchizopJioria striatula (Schlotheim) Schuchert=*S'. striafula var. australis Kindle* Spirifer disjunctus animasensis Girty Straparolhis clymenioides Hall? Specimens of all the fossils named above, excepting Pro- ductella and Straparolhis, were found by our party. The lowest horizon in which we found Devonian fossils is about 240 feet above the bed which carries an Ordovician fauna. Since there is no ai)parent strudnral unconforniity it is possible that during the Sihii-ian period and porhajjs })art of the Devonian, sedimenta- tion was very slow and that the time mentioned is represented by scarcely 200 feet of limoslone. Further search may extend the vertical range of Ordovician and Devonian forms. 'Girty, G. H., Devonian Fossils I'nim Sdiithwfslcrn Colorado: tho Fauna of the Ouray Umcstonc. IT. S. Geol. Surv.. 20th Ann. Rcpt. Pt. 2, pp. S4-S0. =Kindle, E. M., The Devonian Fauna of the Ouray Limestone. U. S. Geol. Surv., Bull. 391. p. IG. 'Idem, p. 17. *Tdem, p. 21. CJKOIAXn' OF THE MONARCH MINING DISTRICT 17 The Carboniferous fossils collected by Eldridge on Monarch Hill and described by Girty^ are: Spirifcr centronatus Winchell Syringopora aculeata Girty Syringopora surcularia Girty In course of the present survey the following were collected : Fenestella sp. Productus sp. Spiriferina solidirostris White Syringopora aculeata Girty Syringopora surcularia Girty These fossils were found in two horizons: (1) in the black limestone mentioned above; (2) in a shale stratum on the south slope of Syncline Hill and about 3,000 feet higher stratigraphic- ally than the black limestone. It should be added that no Devon- ian fossils were found in the black limestone or above, and it is possible that this limestone may be at the base of the Carboni- ferous. A more detailed study will be made later. POST-DEVONIAN IGNEOUS ROCKS QUARTZ MONZONITE (ADAMELLITE) This rock, which is provisionally called quartz monzonite, occurs in a stock, or body of irregular form, in the northwestern part of the district. It extends northeastward beyond the North Fork of the South Arkansas; its southwestern extent has not been determined, but the stock probably forms an irregular con- tact with the pre-Cambrian granite southwest of Boss Lake and distant one to three miles. Its greatest width within the area mapped is about one mile. Petrography. — In the field this rock would be readily taken for a quartz-poor granite. In fact, west of Boss Lake where it is much weathered and quartz is prominent, it is impossible to dis- tinguish between the older granite and the later eruptive. The absence of microcline and the presence of much plagioclase and abundant accessory titanite seen in thin sections are characteris- tic features of the younger rock. It is medium to coarse in tex- ture and composed of pink and white feldspars, quartz, biotite, hornblende, and accessory titanite, apatite, zircon, and magnetite. On Taylor Mountain, where it can best be studied, the rock is generally even-grained, but occasionally a pink feldspar pheno- 'Girty, G. H., Carboniferous Formations and Faunas of Colorado, U. 8. Geol. Surv., Professional Paper 16, pp. 273, 286, 531. 18 A PRELIMINARY REPORT OX THE cryst with a maximum diameter of one inch (25 mm.) may be seen. Ordinarily tlie feldspars are less than 5 or 6 mm. in di- ameter. The biotite and hornblende crystals are 1 to 3 mm. in diameter. Although quartz is nearly always present it is fre- quently subordinate in quantity and in some cases almost dis- appears. Titanite is a constant and conspicuous accessory in yellow crystals 1 to 3 mm. long. Nearly everywhere the dark minerals are subordinate in amount. The fresh rock is pinkish- gray but in some weathered exposures is nearly white. The miscroscope shows plagioclase in excess of orthoclase in many specimens, but the proportion is not constant. In some cases orthoclase is almost wanting; in others it equals or exceeds the plagioclase in amount. Although labradorite is present extinction angles indicate that the plagioclase is principally andesine with perhaps some oligoclase. Carlsbad twinning in a few instances accompanies the universal albite twinning, and twinning after the pericline law is common. The plagioclase shows a strong tendency toward automorphism, and zonal structure is not infrequently seen. Occasional crystals enclose many flakes of biotite. Excepting quartz, orthoclase was the last mineral to crystallize. Its crystallization was in part synchronous with that of ctuartz. This feldspar presents no crystal outline and poikilitically en- closes all the earlier formed minerals. It is occasionally perthitically intergrown with the plagioclase. Carlsbad twins are only occasionally seen. Hornblende and biotite are present in nearly equal amounts, and are intergrown in many cases. On the whole they appear to have crystallized a little later than the plagioclase, but are automorphic toward the ortho- clase. The hornblende is the common green pleochroic variety and not infrequently twinned. Small magnetite crystals are commonly associated with, or enclosed by, both hornblende and biotite. While small apatite crystals are included in all the essential constituents they seem to have a special affinity for the biotite. Titanite, the most abundant accessory, is present in irregular grains and wedge-shaped crystals. IVIinute zircons are enclosed by quartz and the feldspars. Texture and structure. — In general the quartz monzonite is medium to coarse in texture as above stated. However, along the west border of the mass on the slope of Mount Aetna the rock is extremely coarse with the dark minerals segregated in hjrge patclies, and feldspar crystals up to an inch in diameter. Here also the rock is distinctly gneissoid in slrncture, which may possibly be a fluxional arrangement. Except near the border at this and other points the quartz monzonite is massive and presents no evidence of ni('t!iiii(ii|)liisin. The rock is irregularly jointed in blocks wliich may I'cacli l.") IVet oi- nuire in diameter. GEOLOGY OF THE MONARCH MINING DISTRICT 19 The name. — On the sti-engtli of mineral detennination alone ii is voi-y (lifticnlt to })la('e lliis rock, and as slated above the Iciiii (|iiartz iiioiizonite is used i)rovisionally. Some specimens iiii.ulit 1)0 inilH'silalinjily called granodioi-ite. In places, by increase in quartz and orthoclase the rock approaches the diorites or quartz diorites. In addition to the granite dikes mentioned below there are within the main body granitic facies with a large proportion of quartz and orthoclase and subordinate plagio- clase. In the main, however, the mineral composition seems to be essentially that of quartz monzonite, that is, a rock between syenite and diorite with the addition of considerable quartz. Apophyses. — Along the east border of the stock, apophyses extend into the sedimentary rocks usually in the form of dikes. In most cases these dikes are roughly parallel to the border of the stock, and in several instances there is no observed connec- tion with the main body at the surface. The rock of most of these dikes is finer in texture and more acidic than the main mass. It ranges from a biotite granite to alaskite, which is a granite composed essentially of quartz and alkali feldspar. In- clusions of the sedimentary rocks are common. Some of these dikes, even though but a few feet wide carry parallel dikes or veins of pegmatite. Pegmatite veins extend also into the con- tact-metamorphosed sedimentary rocks, where they may be from a fraction of an inch to a foot or more in width. Examples of this may be seen on the south wall of the spillway of Boss Lake where the largest vein varies from three to ten inches wide. This vein shows feldspar with a little quartz at the sides, and at the center quartz with a little feldspar together with black tourma- line, biotite and muscovite. QUARTZ MONZONITE (BANATITB) There is an outcrop of monzonite carrying a small amount of quartz about three-fourths of a mile westward from Monarch, and the same rock may be in contact with the limestone a short distance northAvest of the village. This is indicated by the large number of boulders on this slo])e and the coarse marble formed by the metamorphism of the limestone. The boulders, however, may have been brought to their present position by glaciers. This monzonite does not resemble the more acid monzonite of Taylor Mountain. It carries much less quartz, is finer in texture, contains a larger pr(>]»orti()n of the dark minerals, and 20 A PRELIMINARY REPORT ON THE closely resembles diorite. It is omitted from the map because the boundaries have not vet been traced. PORPHYRIES Dikes of porphyry are common in and near the quartz mon- zonite. They range from a few inches to 50 feet in width and to perhaps half a mile on Mount Aetna. Most of the dikes are less than 30 feet wide. Many are very irregular in their course in the sedimentary rocks and not infrequently follow the bed- ding planes for some distance as sheets. As a rule outcrops are easily followed on the ridges and upper parts of the slopes, but in the valleys talus and soil cover the dikes too deeply to permit them to be readily traced. There is no doubt that many of the dikes seen on the ridges and higher slopes are continuous through the valleys. Mineralization is common in many places. Pyrite may be present in considerable quantity in cubes or more usually as irregular grains or masses. Quartz monzonite porphyry. — Coarse porphyries are common and range in composition from diorite porphyry to soda-granite porphyry-. In some instances quartz-bearing porphyry can be traced from the interior of the dike to a fine-grained diorite or diorite porphyry near the walls. The latter rock carries a very small amount of quartz. In a few cases highly quartzose por- phyry and quartzless porphyry have been intruded into the same fissure at different times. No satisfactory evidence as to the relative age of the two has been noted. A very common phase of the quartz monzonite porphyry in the wider dikes is one which carries pink feldspars from 5 to 50 mm. in diameter, smaller white plagioclase phenocrysts, quartz, and hornblende phenocrysts as the megascopic constituents in a crystalline groundmass. In a few instances biotite is present in amount equal to that of the hornblende. The rock bears a striking resemblance to the Lincoln porphyry of Leadville but carries hornblende as the dominant ferromagnesian mineral in- stead of biotite, and has a coarser groundmass than the Leadville rock. Many of the pink orthoclase phenocrysts are twinned after the Carlsbad law, and some enclose other minerals of the rock poikilitically. Not infrequently by the aid of a lens twinning striae can be seen on cleavage faces of the plagioclase. The quartz phenocrysts varj- from a few millinioters to a centimeter GKOr.OGY OF TIIK MOXARCH MININ(; DISTRICT 21 in dianietei- aud are generally rounded by re-solution. The (juartz is very irregularly distributed. Locally it is an abundant con- stituent, but it is absent from the rock in many places. Horn- blende occurs in crystals up to one centimeter in length. This mineral is alwaj's present in considerable quantity but is fre- quently chloritized. In thin section the hornblende is brownish-green, and many crystals show orthopinacoidal twinning. The plagioclase is in part labradorite, but probably more sodic varieties predominate. The groundmass is holo- crystalline and commonly even-granular. When plagioclase exceeds ortho- clase in amount in the groundmass it occurs in small rectangular forms while the orthoclase is packed in the interstices. The ratio of orthoclase to plagioclase varies greatly in groundmass as well as phenocrysts. In addition to the megascopic constituents the microscope shows ac- cessory magnetite, titanite, zircon, and apatite. There are several variations from the rock described both in texture and mineral composition. On Clover Mountain and in Hoffman Park the coarse acidic porphyry appears to grade toward the dike walls into a very fine-grained diorite, or micro- diorite, carrying great numbers of long, slender hornblende crys- tals, hypautomorphic plagioclase crystals, and a small amount of interstitial orthoclase and quartz. On the southeast slope of Taylor Mountain is a dike of what might be termed micro-mon- zonite. It is very fine in texture, even-grained and composed of hornblende, orthoclase and plagioclase with no quartz. In a few dikes, at least part of the rock has a coarser ground- mass and smaller phenocrysts than the first variety described. It is composed essentially of white orthoclase and hornblende. Taken alone it would properly be called syenite porphyr}-. Latite and latite porphyry. — The dikes mapped as latite and latite porphyry range in composition from andesite to rhyolite, and in texture from felsitic to moderately porphyritic. The greater part of the rock carries orthoclase and plagioclase in approximately equal amounts. Free quartz occurs sparingly but is absent from the greater part of the rock. Hornblende is pres- ent in most of the rock, but is accompanied in some cases by much biotite. Rarely biotite occurs to the exclusion of horn- blende. Titanite, magnetite, and apatite occur as accessories. The groundmass is composed mainly of poorly individualized feldspar microlites with a variable amount of interstitial feld- spar. Secondary quartz is present in some cases. The ratio of groundmass to phenocrysts is large, and in several dikes pheno- crysts are all but absent from the rock. The rock in a few dikes closely resembles the T^eadville "white porphyry". In many 22 A PRELIMINARY REPORT ON THE specinieiis the advanced stage of alteration prevents the accurate determination of the constituent minerals. BRECCIA On the ridge north of Clover Mountain in the vicinity of the Mason mine, the greater part of the rock is breccia which carries angular fragments ranging from microscopic dimensions to masses many feet across. The fragments are mainly shale, sand- stone, and arkose. but considerable gneissoid granite or quartz monzonite like that on the east slope of Mount Aetna, is present. The matrix is greenish and much weathered. The few specimens examined are too badly altered for specific identification but appear to be andesitic or latitic in composition. QUATERNARY DEPOSITS MORAINES Glacial deposits are widely distributed within the area cov- ered b}- the map and are found in greater quantity several miles east. The moraines are composed of glacial clay with a large proportion of sub-angular boulders which show but little, if any, facetting. Boulders high on the slopes were probably deposited by ice masses of considerable size. The glaciers were local and moved from the west and north. One of the largest had its source near Mount Aetna and moved down Middle Fork. Another moved down Lake Fork. One, and perhaps two, reached Monarch from the west. The large amount of morainal material southeast of Cree Camp shows that a gla- cier had its source either on Taylor Mountain or at the head of the gulch toward the northeast. Much of the glacial deposits has been removed by erosion, and it is probable that the moraines within the district are no- where very deep. Near the old Columbus mill-site on Middle Fork a tunnel driven about 85 feet into the steep north wall of the canyon does not go through the glacial covering, but in many places the streams have cut down to bed-rock. Many of the smaller patches of ice-deposited debris are not represented on the geologic map. ROCKSLIDRS AND LANDSLIDES Large masses of sliderock occur on several of the steeper slopes particularly west of Ross Lake, on Mount Aetna and the north slope of Taylor Mountain. The longest of these extends GEOLOGY OF 'J'HK MOXAUCII MINING DISTRICT 23 from the top of Aetna to Middle Fork where it may be seen from a long distance as a light-colored streak in contrast with the darker weathered rock on both sides. Near the top of the Continental Divide are accninnlations of loose rock which have api)arontly been deposited at the front of large banks of snow or ice which may or may not have been in motion. Subseqnent melting of the snow or ice left depressions v.hich now contain small bodies of water up to 50 feet or more wide. It is assumed that these rock masses are the accumula- tions of many years. Typical landslides are not common. On Monarch Hill a short distance south of the entrance to the Madonna No. 6 tunnel is a mass of the siliceous shaly stratum of the Ouraj' limestone men- tioned on page 15. This stratum carries a layer of quartzite and strangel}' enough has lodged almost directly above the "part- ing quartzite" cut by the tunnel. The thinness of the quartzite bed at the surface and difference in dip and strike from that underground, together with the presence of the chocolate-colored shale at the surface, prove that the exposed rock has come from a higher position. STRUCTURE Owing to the scarcity of extensive underground workings and the abundance of talus and drift the details of structure have not been worked out as fully as desirable, but the general features have been determined. In addition to the processes of sedimentation and the changes in conditions which accompanied those processes the principal factors to be considered in the structural geology of the region are folding, faulting, jointing, solution, and igneous intrusion. A phenomenon less important for the purpose of this paper is the moderate regional inetamor- ])hism of the pre-Cambrian granite. FOLDING Next to the mountain-making movements which have left marine sediments more than two miles above sea level, tangential movements have perhaps been the most prominent. Tliese hori- zontal movements were accompanied by vertical movements. Un- til studies are carried westward and northward it is impossible to say to what extent the folds of the ^[onarch district are part of a larger structural unit. It appears from the evidence at hand 24 A PRELIM IX ARY REPORT ON THE that there were two directions in which strong forces acted, namely, east-west and north-south. The result of these stresses was a synclinal fold having a general north-south axis, with minor echelon folds. The sedimentary beds have been tilted through an angle which ranges from 15° to 90° and even more in a number of instances. On Monarch Hill the dip is moderate, ranging from 30° to 45° for the most part. East and north of Garfield the strata are nearly vertical. In the Lilly mine the granite floor on which the sediments were laid down now stands vertical or but slightly inclined from vertical toward the west. In the Garfield tunnel driven northward along the limestone-granite contact from the creek below Garfield the dip is tow^ard the west near the tunnel entrance, but near the breast the granite forms the hanging wall with an eastward dip of 73°. Similar overturns are not uncom- mon in a number of places. The most extreme case occurs on IMonarch Hill where it can be well seen in the Hawkeye mine. The Hawkeye tunnel was driven several hundred feet to the granite contact and thence along the contact where the granite forms the hanging wall with a westward dip of 40° to 60°. In the upper part of an upraise from the end of the main tunnel the granite hanging wall can be seen dipping westward 25°. A crosscut to the east limb of the fold found the granite footwall dipping westward 28°. In the Madonna No. 6 tunnel the quartzite of the northwest limb of the fold dips 60° N. 53° W. From this point northward the boundary between the granite and limestone cannot be accurately determined at present. Al- luvium in the creek and drift toward the north, conceal the bed- rock, while no serious prospecting has been done along the con- tact. It is probable that in this vicinity there is a sharp fold which passes into the fault toward the north. The broken lines in CC, Plate III, indicate the possible attitude of the beds if ihey are not indeed faulted along this line. East of Cree Camp the limestone-granite contact offsets more than a quarter of a mile while holding its northward trend. Faulting first suggests itself to the observer. However, a short distance northeast of the cabins of Cree Camp an opening ex- poses the contact which dips toward the northeast swinging grad- ually but sliari)ly from north toward oast. Alluvium and mo- rainal material conceal the contact between this outcrop and the Clinton mine, but it is inferred that an echelon fold connects GEOLOGY OF THK ^lONARCH MINING DISTRICT 25 26 A PKELIMIXAKY REPORT OX THE Fig. 1. Diagram to show probable trend of lime- stone — granite contact east of Cree Camp. the limestone of the Clinton mine with that at Cree Camp (Fig. 1). The j)OSsi- bility that this sharj) fold may have cul- minated in a fault is conceded. FAULTING Loral faults of small throw are nu- merous in mines in all parts of the sedi- mentary area. Movement has been in practically all directions as can be deter- mined by slickensided surfaces. A few of the larger faults are represented on the map. The one which has the greatest throw passes southward from Boss Lake an undetermined distance. From the divide southward its exact position cannot be determined because of the surficial material, and hence its position on the map is only provisional. On the north slope the granite is exposed very near the upended sedimentary rocks, and the ])Osition of the fault here can be determined with reasonable accuracy. As it is represented in section BB. Plate III, the hade toward the west is only tenta- tive. It is probably even greater than the figure indicates. It will be seen from the section that the sedimentary beds of Syn- cline Hill are about 4.800 feet thick. Even if no allowance be made for the erosion of sedimentary rocks which formerly over- lay the granite west of the fault the throw and stratigraphic throw must be nearly or quite a mile. The faults of Monarch Hill have been mapped largely from surface indications. L^nfortunately the plans of the mines do not show the positions of the faults underground and the acces- sible workings do not disclose the relationships of the most im- portant ones. While of comparatively small throw, these faults are important in that they accompany fissures which formed channels for the circulation of mineral solutions. The crushing of the rock which accompanied the faulting furnished open ground favorable to ore deposition. The Madonna fault appears to be a thrust fault hading to- ward the southwest, that is, with the upthrow on the southwest side. The Mayflower fault is probably a gravity fault with the downthrow on the southwest. It can be most easily seen where the quart/.ite offsets from tlie I^-lijtsc discovery sliaft almost to the enframe of Eclipse No. 1 niiuicl. It is |>roli;il»I(' iliat a GEOLOGY OF THE MONARCH MINING DISTRICT 27 shorter fnult shikiiig noitliwest, crosses the saddle between these two and meets the Madonna fault at Zero level. According to Mr. A. Eilers the block between the Madonna and Mayflower faults has dropped downward through a vertical distance of 200 to 250 feet and is badly broken. There is no regularitj' in dip and strike and the bedding planes are not con- tinuous, Mr. Eilers also states that the Madonna fault con- tinues into the underlying granite as shown in a number of levels, and that the granite on the southwest side of the fault extends some 200 feet farther northwest than it does on the north- east side. Figure 2 is a graphic attempt to show the possible history of these faults. As stated above, the stresses which developed the folds were principally north-south and east-west. The re- sultant would be a compres- sive force in a northeast- southwest direction. Such a stress would naturally pro- duce a system of thrust faults at right angles to the force, as shown in Figure 2, a. After this stress was re- lieved through folding, fault- ing, and probably other causes, there would naturally be a sub- sidence of the fault blocks and 1 and 2 of Figure 2 could very easily drop together to the position shown in &, There may also have been differential movement between 1 and 2 which would only necessitate a greater thrust along the Madonna fault than that indicated in a. It is possible that another considerable fault extends from a point a short distance east of Garfield and near the creek to a point not far from the Columbus mill-site. The abrupt change in dip of the few outcrops along this line indicates either a sharp fold or a fault. Southeast of Garfield near the extremity of the synclinal fold there has been much local faulting. The sud- den disappearance of the "parting quartzite" which, where ex- [losed, can usually be readily seen with the underlying limestone, suggests bedding faults. At the head of Taylor Gulch and in the vicinitj' of the Last Chance mine there has been much local faulting which cannot be represented on a small scale map. Fig. 2. Diagram to illustrate faulting on Monarch Hill, a, probable position of blocks when first faulted; 6, present posi- tion. 28 A PRELIMINARY REPORT OX THE The major part of the faulting probably accompanied or closely followed the folding, but there have been some slight dis- placements since the ore was deposited. JOINTING In some parts of the quartz monzonite the blocks are of large dimensions, up to 15 or 20 feet across, but all the other rocks are much jointed. Locally the jointing of the limestone presents considerable regularity, but in the main the joint-planes intersect at irregular angles. In those parts of the sedimentary rocks least affected by folding and faulting the joints are usually tight, and here also the mineralization is least. CAVES AND UNDERGROUND CHANNELS The formation of caves and development of subterranean drainage are genetically connected with jointing, folding, and faulting which formed fractures and thus facilitated the circula- tion of ground waters. Limestone is taken into solution and re- moved by these waters with comparative ease. The caves thus formed are small in this district. The largest noted was cut in the Shamrock mine at the limestone-granite contact and is about six or eight feet wide by 50 feet high. Another, perhaps somewhat smaller, was found in the same mine. Others may be seen at the creek level in Garfield. Just below the stone quarry west of Garfield a large stream issues from beneath the limestone south of the creek. This may or may not have direct connection with the creek higher up. A short distance south of Garfield a stream emerges from beneath a mass of granite talus and doubtless has flowed some distance through the limestone. At Monarch a short branch of the creek has its visible source in an excellent spring which furnishes the village with water for domestic use and could adequately supply a town many times larger. A somewhat smaller stream issues from the limestone half a mile east of Garfield. This is probably the exit of the underground channel which drains the bench-like area three-fourths of a mile south of the spring. This area is nearly flat for a considerable extent as may be seen from the topographic map (PI. I). Morainal material forms a barrier along the north side except at the northeast corner where there is a small ravine presumably an ontlot for storm waters only. GEOLOGY OF THE MONAUCII MINING DISTIUCT 29 During the field season no water was running through this outlet although there was an abundance of melting snow above. Underground streams, perhaps in fault-planes, are indicated in the upper part of Taylor Gulch and below a depression head- ing toward Taylor Mountain where there is little or no surface drainage during the season of melting snow. IGNEOUS INTRUSION The occurrence of diorite and syenite dikes in the pre-Cam- brian granite has been mentioned. Subsequent to the principal folding of the region and at an undetermined geological time the large mass of quartz monzonite described above was forced up- ward through the sedimentary rocks now exposed, and extended into the granite on each side of the synclinal fold. The longer axis of this stock extends diagonally across the syncline. Whether magma from this mass reached the surface above the once overlying sediments as an effusive rock or whether it was intruded as a plutonic rock and has since been uncovered by erosion, is not known. Nor has the form of the mass been de- termined. Indications on the east slope of Mount Aetna point to a westward dip of the west contact. The existence of the several dikes of granite on the east slope of Taylor Mountain suggests the extension of the stock at depths to a considerable distance east of its boundary at the surface. That the stock divided the syncline is clearly shown by the occurrence of meta- morphosed sediments on the east slope of Mount Aetna and north of Clover Mountain. Later, both the sedimentary rocks and existent igneous rocks were cut by porphyry dikes which trend, for the most part, in a general northeast direction. The focus of this activity appears to have been about where Aetna now stands. Near the east border of the quartz monzonite the dikes dip westward or are nearly vertical. On the east slope of Aetna and on Clover Mountain and northward, the quartz monzonite porphyry, near its border, en- closes portions of pegmatite and sedimentary' rocks, Avhich range from microscopic fragments to masses scores of feet across. The breccia in the vicinity of the Mason mine perhaps represents one phase of this vulcanism. Contact metamorphism. — The effects of metamorphic agen- cies are shown in the sedimentary rocks to a distance of perhaps a quarter of a mile from the quartz monzonite stock. Shales have 30 A PRELIMINARY REPORT OX THE been baked almost to porcellanite, sandstone bas been changed to quartzite. and it is probable that some marble was formed through the agency of heat from the quartz monzonite. But the fact that the best marble and largest quantity occurs near the porphyry dikes, indicates that the porphyry has been more effect- ive in transforming the limestone than has the quartz monzonite. Epidote, garnet, magnetite, and feldspar have been developed in considerable quantity and asbestos, wollastonite, diopside, titanite, and zircon in less amount. Perhaps all the ores on the west side of Taylor Gulch and a small amount of others are con- tact-metamorphic deposits. The subject of contact metamorphism in this field will be taken up more fully in a later report. GEOLOGY OF TllK MONAUCII MINING DISTRICT 31 ECONOMIC (j EULOGY CHARACTER OF THE ORES Nearly all the ores of Hie region are basic ores, and all that are now being mined are shipped directly to the smelters. More or less silica from the alteration of chert is present in the ores which occur in limestone, and quartz in small amount is present in some of the contact deposits. Zinc silicate occurs in small quantity. Aside from the lime which is intimately associated with some of the ores in variable amount, there is generally more than enough iron to satisfy the silica present. The "excess iron" commands a price dependent on the demand for basic ores. By excess iron is meant the quantity present after deducting suf- ficient, as shown by assays, to satisfy the silica content. Man- ganese in oxide form in the Clinton and Rainbow-Eagle Bird mines increases the value of the ore by lessening the treatment charges. There are no mills in the district. Formerly the ore of the Columbus mine Avas concentrated in the company's mill which was sold and removed after the mine Avas shut down. Hitherto the greater part of the product of the district has been oxidized ore, chiefly silver-bearing lead carbonate, in which bunches of sulphide have been found at any depth. In some cases solid galena occurs within a few feet of the surface. On Monarch Hill galena is the only sulphide in considerable quan- tity present in the ore bodies now being mined. In Taylor and Columbus gulches sulphides of iron, copper, lead, and zinc occur. Monarch Hill produces mainly ores of lead, silver, gold, and zinc, with some copper in the Madonna and Eclipse mines. The ores of Taylor Gulch are of copper, silver, gold, and lead. A promising discover^^ of zinc ore has been made on the New York claim but no shipments have been made at the time of writing. Columbus Gulch has produced silver, gold, copper, and lead. During the period of greatest activity there were no zinc smelters in Colorado, and much zinc ore was left in the mines. Part of this is now being taken out. The silver of much of the silver-zinc and silver-lead-zinc ores was recovered by mixing these ores with lead and silver-lead ores and at the same time keeping the zinc content below the limit fixed bv the smelters. 32 A PRELIMINARY REPORT ON THE TENOR OF THE ORES Since so few records of tonnage and values have been kept, it is impossible to determine accurately the average value of the ores. An estimate of the average value based on data in hand from a number of mines would be about |20 to |25 per ton for the ores of Monarch Hill and considerably higher for those of Taylor Gulch. Most of the shipping ores carry a value between $8.00 and |30.00 a ton. The Madonna ores have averaged $24.20 per ton. (See p. 47.) The copper ores of the Lilly mine average about 10 i)er cent in copper. Ore worth $7.00 a ton can be mined at a profit under present conditions. The range in value is very great. One carload from the Fairplay mine carried 130.75 oz. silver per ton, 39.95 per cent zinc and 10.05 per cent lead, b}' smelter returns. The best car from the Little Charm mine returned from the smelter .48 oz. gold and 226.2 oz. silver per ton, 24.5 per cent lead, 7.65 per cent zinc and .15 per cent copper. A sample from a narrow streak below the fifth level of the Madonna, assayed in the Survey lab- oratory, yielded 16 per cent lead, .50 oz. gold and 816.25 oz, silver per ton. The moisture content ranges from 5 to 20 per cent. The greater part of the ores carries between 10 and 14 per cent mois- ture. MINERALOGY OF THE ORES In describing the minerals it is intended to mention only those characters which the minerals of this region possess. The iron and manganese minerals are included in this list because they add to the value of the ore. For the convenience of miners and prospectors in the district who may not have at hand a text- book of mineralogy, the metallic content of the pure mineral is given for each variety. COPPER MINERALS Azurite, basic cupric carbonate 2CuC03.Cu(OH)o, copper 55.3 per cent. This mineral occurs as a blue coating on surfaces of jointed limestone and disseminated in the mineralized lime- stone near the copper ore bodies. It is also present in massive form associated with malachite. Chalcocite, cuprous sulphide, Cu^S, copper 79.8 iier cent. Good chalcocite was seen by the writer only in the Hercules tunnel where it fills a narrow fissure in the quartz monzonite. It is nearly black, and friable. GEOLOGY OF THE MONARCH MINING DISTRICT 33 Ghalcopyrite, copper-iron sulphide, CuFeSo, copper 34.5 per cent. It occurs in the lower Avorkings of the Lilly and probably in the Columbus. It is brass-yellow and massive. ChrijsocoUa, copper silicate with water, CuSiO.}.2H20, copper 36.1 per cent. This is found as a sky-blue mineral coating the walls of small cavities in the Lilly mine and filling narrow fis- sures in the other copper ores. Chrysocolla of good quality is sometimes used as a gem. Copper, native, Cu. Native copper has been reported from the Columbus mine. Copper-hearing pyrite^ sulphide of iron with a variable amount of copper, FeS,- It is found in the Lilly mine in bunches surrounded by oxide of iron derived from it. It is massive and brass-yellow, sometimes shows purple tarnish. Cuprite, cuprous oxide, CUoO, copper 88.8 per cent. This is present in the Lilly mine both as a soft red mineral intimately associated with iron oxide, and as purer harder mineral in the upper workings. Malachite, basic cupric carbonate, CuC03.Cu(0H)o, copper 57.54 per cent. This green carbonate is present in nearly all the mines which have produced copper, particularly the Lilly and the Madonna. It is found in considerable quantity asso- ciated with other oxidized copper minerals and disseminated through the limestone as a replacement, in sufficient quantity to make payable ore. Tenorite, melaconite, cupric oxide CuO, copper 79.8 per cent. Black earthy melaconite occurs in the Lilly and Shamrock mines associated with other copper minerals. It is very impure from the admixture of other substances. GOLD No gold minerals liave been reported from the district, but the smelter returns from most of the ores now being shipped show .02 to .50 oz. gold per ton and in some of the contact deposits the gold content is many times greater. Since the ores are largely oxidized and no tellurium has been reported\ it is in- ferred that the gold is present in the native state. 'Since this paper was written, telluriiim has been reported from Madonna, No. 6, but no special tests have been made. 34 A PRELIMINARY REPORT ON THE IRON MINERALS Hematite, ferric oxide, FeoOg, irou 70 per cent. Hematite was not seen associated with the ores, but much black specular hematite is present on a dump a few yards south of the Ingersoll. A large part of the mineral is practically pure. Limonite, ferric oxide with water, 2Feo03.3HoO, iron 59.8 per cent. Brown limonite and, to a less extent, the yellow ocherous variety occur in nearly every ore-body discovered. ^luch of it carries a small quantity of silver. Very large bodies of limonite are present in the Madonna mine. Magnetite, a compound of ferrous oxide and ferric oxide FeO.FCoOg, iron 72.4 per cent. This mineral was not seen by the writer in any of the ore deposits, but it is present as a contact mineral on the southeast slope of Taylor Mountain, and forms a vein two or three feet wide just east of Boss Lake. Pyrite, iron disulphide FeSg, iron 46.6 per cent. Both as crj-stals and in the massive form pyrite is found in the Lilly and Garfield, in smaller quantity in the Madonna, and perhajis in other mines. Its rarity on Monarch Hill is explained by the fact that nearly all the ore mined comes from the zone where the pyrite has been oxidized to limonite. Turgite, hydrous ferric oxide, 2Fe203.HoO, iron 66.2 per cent. Bed, earthy turgite occurs with limonite in the Madonna mine below No. 5 level. LEAD MINERALS Anglesite, lead sulphate, PbSO^, lead 68.3 per cent. In the summer of 1909 Mr. Thomas Penrose found in the Little Wonder mine a small group of anglesite crystals near the center of a mass of galena weighing several hundred pounds. These had a dull surface due perhaps to the formation of carbonate, but with- in, the mineral Avas pure water-clear anglesite. The largest crystal was nearly two inches long. Cerussite, lead carbonate, PbCOo, lead 77.5 per cent. This mineral, in the form of soft carbonate with an admixture of limonite and carrying silver, has been produced in far greater quantity than any other in the district. Hard carbonate occurs in but few mines. Crystallized cerussite Avas noted by the writer only in small amount on a few specimens of galena from which it is derived. Galena, lead sulphide, PbS, lead 86.6 \)vv cent. Coarsely crystallized galena is present in practically all the mines which GEOLOGY OF THE MONARCH MINING DISTRICT 35 produce lead. In nearly every case it is surrounded by lead car- bonate. Most of the galena is silver-bearing. Mimctitc, a double salt of lead arsenate and lead chloride, SPb^As^Os-PbCl., lead 69.5 per cent. Mimetite occurs in small quantity in the Lilly mine and on one of the Jewell claims, as a yellow to green earthy mineral intimately associated with limon- ite and insoluble material. Wulfcnite, lead molybdate, PbMoO^, lead 56.4 per cent. This mineral was not seen in any of the mines, but a specimen found on the Hawkeye dump contained many yellow tabular crystals of wulfenite coating galena. It has also been found in the Ma- donna mine. MANGANESE MINERALS Psilomelane, perhaps H^MnO^, manganese nearly 40 per cent, occurs as a black massive mineral carrying considerable lime carbonate and iron in the Rainbow-Eagle Bird, and possibly other mines. Pyrolnsite, manganese dioxide, MnOo, manganese about 79 per cent. Pyrolusite in earthy form is found with psilomelane in the Rainbow-Eagle Bird and possibly without psilomelane in the Delaware mine. SILVER MINERALS The best silver ores of the district were mined many years ago and good specimens are now^ very scarce. Although native silver probably occurs in the oxidized ores, halogen salts of silver were common in those of highest grade. Chlorides and bromides appear to have been present in considerable amount. A few small pieces of green silver mineral picked from the dump of the Little Charm closely resembled silver iodide, but the specimens were lost before an analysis could be made. Silver sulphide has been reported from the Song Bird mine, and stephanite from the Little Wonder. ZINC MINERALS Calamine, hydrous zinc silicate, HaZn^SiOs, zinc 54.2 per cent. Calamine in small tabular crystals occurs in narrow veins in the smithsonite. A part of the massive zinc mineral with which the crystals are associated may also be calamine. Smithsonite, zinc carbonate, ZnCO^, zinc 52.2 per cent. This is the most common zinc mineral which the district is now pro- ducing. It occurs as a hard, massive, dark gray mineral, as a 36 A PRELIMINARY REPORT OX THE softer yellowish to brownish ininera], and as small crystals in vugs and narrow veins. Sphalerite, or zinc hlende. zinc sulphide, ZnS, zinc 07 per cent. Crystals of sphalerite Avith galena occur in the Columbus mine and the massive mineral is found on the Kew York claim, associated with garnet. GANGUE MINERALS Calcite. '^spar\ calcium carbonate, CaCOg. Coarsely crystal- lized calcite is common at the border of ore bodies, and is con- sidered a favorable indication when encountered in prospecting. It is in some cases slightly mineralized, carrying small amounts of galena, pyrite, or silver mineral. Calcite is also present in considerable amount in many of the prospects in which no ore has been found. Z)o7omife^ carbonate of calcium and magnesium, (Ca,Mg)C03. Brown, coarsely crystallized dolomite is associated with the ore in the Kainbow-Eagie Bird. Quartz, silica, SiO,. Quartz in large amount is associated with the ores in the fissure veins in the quartz monzonite. It also occurs in small amount with some of the contact deposits. TYPES OF ORE DEPOSITS Since there are intergradations no attempt is made here to name the types in the order of importance. Those which have come under obsenation are : 1. Replacement deposits in limestone. 2. Filling in fault-fissures in limestone and quartzite with more or less replacement of the wall rock. 3. Contact deposits in the sedimentary rocks not far from the intrusive rocks. 4. Deposits at the contact between basic syenite dikes and granite. This type has yielded but little ore. 5. Fissure veins in the quartz monzonite and at the erup- tive contact Avith the sedimentary rocks. REPLACEMENT DEPOSITS IN LIMESTONE Excepting those ore bodies in the fault-fissures on Monarch Hill and jiossibly the Lilly ores in part, all the known dei)Osits in the lowest limestone near the contact with the pre-Cambrian granite, are of the replacement iype. Also most of those above GEOLOGY OV THE MONARCH MINING DISTRICT 37 the ''parting quartzite" on Monarch Hill are replacement de- posits. In the largest bodies the ore lies in practically continuous shoots which follow the dip of the sedimentary rocks downward, but in most cases bear either to the right or left of the dip. This divergence from direction of dip is but few degrees in every in- stance noted except in the Lilly mine. Here where the contact is nearly vertical the longest shoot pitches north about 20°. As a rule, the ore bodies near the granite either lie on the granite or are separated from it by but a few feet of limestone, departing from the contact perhaps 20 or 30 feet in rare instances. Cross-sections of the shoots are sometimes circular but much oftener are elliptical with the longer axis parallel to the strike of the strata. Most of the shoots do not have a constant width and thickness, but pinch and swell. The swells may be lenticu- lar or irregular in form, and connected by a workable body of pay ore or by an iron-stained joint- or bedding-plane in the lime- stone. Nearly all the shoots show smaller dimensions in the lower workings than nearer the surface, but it is not known that any have completely failed at the greatest depth reached. Other replacement deposits occur in bunches or pockets which may be roughly tabular, lenticular, or wholly irregular in form, but the longest diameter is generally parallel to the bed- ding of the limestone. Some of these in their relation to the en- closing rock closely resemble the flats of the zinc and lead ores of the Upper Mississippi Valley, but are highly inclined or nearly vertical conformable to the beds in which they lie. As in the longer and generally larger shoots, a series of these bunches may be connected by an iron-stained joint- or bedding-plane. In some cases a seam of gouge connects two or more ore bodies, and here it is difficult to distinguish between the replacement type and those deposits along faults and shear zones. In all cases of these replacement deposits it is assumed that there has been a metasomatic interchange betw^een the calcium carbonate of the limestone and the metallic salt in solution in the circulating ground water. In most cases the ore gradually grows leaner toward the periphery with increasing limestone con- tent, and not infrequently passes into disseminated ore near the outer limit of mineralization. The wall is merely the boundary of the ore which can be profitably mined. 38 A PRELIMINARY REPORT ON THE FILLING IN FAULT-FISSURES The largest ore bodies whicli have yet been opened in the district are of this type, as for example those of the Madonna and the Eclipse. While there has been much local faulting in the vicinity of the Lilly mine it is not definitely known that the Lilly ore bodies lie in fault-fissures. If they do the fault must be parallel to the bedding of the limestone. There is also in this type much replacement of the wall rock, and the ore is in shoots as in the replacement type described. The essential difference between the two types lies in the prob- ably greater size of the ore bodies deposited in the fissures, be- cause of more favorable conditions for the circulation of mineral solutions. CONTACT DEPOSITS IN THE SEDIMENTARY ROCKS Although the ore of this type occurs largeh' in bunches in SO far as it has been mined, it has yielded some of the highest values of the district. Silver, as chloride and sulphide, is the most important metal thus far produced by these deposits which have also contributed the best gold ore of the region, in addition to some lead and copper. Good zinc ore — sphalerite and smith- sonite with a little calamine — has been discovered on the New York claim, but no shipments have been made. This type in most cases replaces limestone, dolomite or shale not far from the porphyry dikes. It is probable that much of the ore on the west side of Taylor Gulch owes its origin to the quartz monzonite toward the west. The sphalerite on the New York is associated with garnet, practically proving its contact- metamorphic origin although perhaps several hundred feet from any known intrusion. In some cases these ores are in immediate contact with the porphyry, but replacing the sedimentary rocks rather than the porphyry. Like the replacement ores described above, they grade into the enclosing rock; there are no well defined walls. Examples of contact deposits in addition to those mentioned above are found in the Mountain Chief, Rainbow-Eagle Bird, Major, Shamrock and probably part of the Lilly ores. SYENITE-GRANITE CONTACT DEPOSITS Examples of this type are found in the Missouri Boy and perhaps on the Bay State and Independence claims. The under- ground workings of these claims were inaccessible in lOOH. GEOLOGY OF THE jMOXAUCII MINING DISTRICT 39 FISSURE VEINS IN QUARTZ MONZONITE At least tln('(> Hssnic veins outcrop on the slopes of Taylor Mountain and Mount Aetna, and the ores of the Columbus and Brighton mines have been furnished by these veins. Several shallow prospect pits have been sunk on fissure veins in Iloffman Park and on the east slope of Aetna. These veins can be readily followed on the surface because of the depressions which they occupy. Moreover, gossan is common. In a shallow prospect on the east slope of Aetna the limonite in a westward dipping vein ranges from a thin seam up to a foot in width. A specimen taken here yielded on assay |7.20 per ton in gold, but no thorough sampling of the vein was undertaken. At the surface the vein dips west 35°, Neither the Brighton nor the Columbus ore bodies could be examined in 1909 but a brief description of the Columbus mine is quoted on page 67 of this report, TERMS USED TO DESCRIBE ORE SHOOTS Although ore is found in bunches or pockets in a number of mines, the typical occurrence of the largest bodies is in shoots which dip at a fairly uniform angle to- ward the north and northwest. The terms used in the descriptions of these shoots will be those employed by Lindgren and Ran- mmfi in their de- iSci'*iptions of the Cripple Creek ore shoots^, Avith but one ichange. The terms width, thickness, stope length, pitch length, and pitch Avill be used, ''The stope length is the distance along the drifts over which payable ore extends; the pitch length, or axial ■Geolog-y and Gold Deposits of the Cripple Creek District, Colorado. Pro- fessional Paper 54, U. S. Geol. Surv.. pp. 205-206. Fig. 3. Diagram to illustrate terms used in de- scribing ore shoots. (After Lindgren and Ransome, modified to suit conditions at Monarch.) 40 A PRELIMINARY REPORT ON THE length, as it might also be termed, is the distance between the two extreme ends of the shoot; the pitch is the angle which the pitch length makes with the horizontal". Width will be under- stood as the horizontal distance from wall to wall at right angles to the pitch length just as it is used by the authors quoted. The distance across the shoot at right angles to the pitch length and width will be called the thickness. In the Lilly mine and in a few other instances the width is less than the thickness, but ordinarily the width is the greater; in some cases the two are equal. In many mines the stope length is identical with the width. Figure 3 will make clear the relations of the terms used. AGE OF THE ORES The contact deposits may have been formed at two different periods. Ore was certainly deposited after the intrusion of the porphyry and probably represents the last stage of this period of vulcanism. Some contact deposits were probably formed im- mediately after the intrusion of the quartz monzonite and pre- vious to the porphyry intrusions. Until mining developments are carried deeper all that can be said of the age of the ores of Monarch Hill, the Lilly mine, and a few others, is that they were deposited after the folding and principal faulting of the sedimentary rocks in which they lie. The few fractures and faults seen in the ore bodies are too slight to have been caused by the folding and faulting noted on pages 23-28. Knowing that Mr. Eilers had had opportunities, which do not now exist, to observe the relation of the largest deposits to the faulting, the writer asked him several questions, and re- ceived the following definite statements: "The ore in the Madonna was all deposited, without the slightest doubt, subsequent to the faulting and folding, "The ore showed no crushing or breaking in any part of the mine. "There was never found any evidence of more than one period of ore deposition, which was subsequent to the faulting and prior to oxidation. "The principal ore body in the Madonna down to the fourth level, was in the big fault itself, but small branches went out for some distance to the southwest and northeast into the lime- stone strata, generally following the planes of stratification to the southwest, and being very irregular in the broken ground to the northeast of the fault. GEOLOGY OF THE MONARCH MINING DISTRICT 41 "The ore bodies themselves were never faulted ;inywhere in the mine.'' GENESIS OF THE ORES There is little doubt that the ores of the known contact de- posits in the sedimentary rocks were deposited from solutions emanating largely from the porphyry, but probably in part from the quartz monzonite. This conclusion is based primarily on the relation of the ores to the intruded porphyry, and their associa- tion with minerals of contact-metamorphic origin, such as garnet. By far the greater part of the known ores of the district are replacements and fault-fissure-fillings, removed a considerable distance from an eruptive contact. Conclusive evidence of their origin is lacking. However, facts mentioned below lead to the inference that the ores have been deposited from ascending solu- tions which may have had their source in the quartz monzonite toward the northwest. Meteoric waters, highly heated by the intrusive rock, may have had a part in dissolving the metals and carrying them upward. Although sulphides of copper, iron, lead, and zinc are pres- ent in other deposits, they are common minerals in ores which have been deposited from ascending hot solutions. The presence of gold and considerable silver in the Monarch ores indicates a deep-seated source. The ore minerals of Monarch Hill are very similar to the minerals of the contact deposits, a fact which sug- gests a similar or common source. While the general northward to northwestward pitch of the ore shoots is in large part due to the structure, it also indicates that the mineral-bearing solutions flowed in a common .direction. This direction might possibly have been toward the northwest on Monarch Hill, but there is no conclusive evidence that under- ground waters would take this course at the time of ore deposi- tion, and previous to erosion. Any considerable downward move- ment of ground water toward the north in the Lilly and Clinton mines, at a time when the intrusive rocks were probably still at a high temperature, v»-ould be anomalous. Hence the inference is that the mineral-bearing solutions moved upward and south- eastward. The solutions which reached Monarch Hill may have followed bedding planes in the rocks, but it is more probable that they passed along the fault-plane which extends southward from Boss Lake. 42 A I'UELmiXARY REPORT OX THE So far as is known, the base metals were almost entirelj' deposited as sulphides. Probable exceptions are the mimetite and wulfenite both of which occur in small quantity. Some dis- tance above the "parting quartzite" is a stratum of fossiliferous limestone which emits a bitumenous odor when broken. This stratum and other fossiliferous strata may have furnished suf- ficient hydrogen sulphide to precipitate all the base metals as sulphides from solutions made alkaline by the dissolved lime- stone. Or, ascending solutions may have carried the metals in the sulphide form, while a combination of causes may have brought about their precipitation. Among these, supersaturation due to decrease in temperature and pressure, and increased alka- linity due to the limestone, would be important factors. What- ever ma}' have been the primary cause of precipitation the lime- stone has certainly exerted an important influence. PRACTICAL INFERENCES AND SUGGESTIONS There is a limit to the depth at which metallic minerals are likely to be precipitated from solution, and the thickness of rock that has been removed by erosion since the Monarch ores were deposited, cannot be determined from observed facts. Neverthe- less, a number of features noted in connection with the ore bodies, when considered with reference to the general structure, justify the statement that, in the faulted ground in the south- western part of the field, ore shoots may be expected to extend considerably below the level of ground water and possibly to the bottom of the synclinal fold. While the gold and silver values may grow less with increasing depth, recent developments in the Madonna point to a possible increase in the value for a short distance at least. It is also probable that a greater or less degree of minerali- zation extends along the axis of the fold from the southAvest down to the point at which mineral-bearing solutions entered the syncline. Uncertainty as to the precipitating agents pre- vents an unqualified prediction, but along this line the lime- stone may be expected to be considerably broken and hence fa- vorable to ore deposition. It is jjrobable that comparatively deep prospecting will be required to determine the presence or absence of ore along the fault-plane toward Boss Lake. Should ore be found at the bottom of the svnclino it might be confidentlv GEOLOGY OF THE MONARCH MINING DISTRICT 43 looked for toward the north where the fault-plane passes through the limestone. Other ore shoots between the granite and '^parting quartzile" on Monarch Hill and in Taylor Gulch will probably continue to a depth dependent on the degree of fracturing of the limestone. Although large contact deposits have been mined in a num- ber of districts, in general this type tends to be bunchy. In re- gard to the persistence of the contact deposits of the Monarch district, only one thing is known, namely, that the contact itself goes down. Of contact deposits Lindgren^ says: Although cases may be easily conceived in which the deposits would continue in depth and length for several thousand feet it is far more common to find them irregular and spotted in their mineralization, so that while there is no genetic reason why they should not be continuous to the greatest depth attainable by mining they will as a matter of fact often give out when least expected. Owing to the irregular surface of contact the finding of the continuation of lost ore bodies is often very difficult. Slight changes of composition and texture of the rocks in- fluence their susceptibility to contact metamorphism to a very surprising degree. Few mines on contact deposits have been worked at a greater depth than a few hundred feet. Oxidizing surface waters may greatly enrich contact deposits of poor grade by the development of oxidized ores; this especially refers to copper deposits although such oxidized ores rarely extend downward more than a few hundred feet at most and this only in very dry climates. Nevertheless, indications at the surface and in the shallow workings of the mines of the Monarch district in which contact deposits are found, fully justify a moderate outlay in develop- ment work. Aside from known ore bodies, the possibilities of discovery fn the district are not exhausted. Although blind leads have not been encountered, and may never be found in the region, there are a number of places, where talus or glacial material overlies the bed-rock, that should be prospected. Wherever fault- ing or extreme folding may be present in the limestone below and immediately above the quartzite or in the vicinity of por- phyry dikes, there is a possibility of finding ore. The fold (or possible fault) southwestward from the Clinton mine would ap- pear to be a favorable location. (See Fig. 1.) A shaft through the glacial debris into the limestone, and a few crosscuts in addi- tion, would cost a comparatively small amount. Although there 'Lindgren, Waldemar, Ore Deposits and Deep Mining, Economic Geology, Vol. I, p. 37. 44 A PRELIMINARY REPORT ON THE may be do ore here, the structural features aud the position be- tween the Lilly and Clinton ore bodies offer encouragement. DESCRIPTION OF MINES Many of the mines which formerly were producers have been idle for a number of years. The ore bodies and stopes of these were inaccessible during the summer of 1909 because of their caved condition or bad air, or both. This statement also applies to the earlier workings of all the large mines operating at the present time. Because of the heavy rains which shortened the field season the mines of Middle Fork were not visited, and hence must be omitted from the present description. A few mines have been worked through vertical shafts, a number through inclines, but by far the greatest part of the ore mined has been hauled out through tunnels. The ground water level has probably not yet been reached in any of the mines, except on Taylor Mountain, and it is said that there has never been a pump in the district. Surface water from the melting snow which continues late into the summer is in many cases a detriment in that it gives to the ore of the more open ground a high moisture content. No timbering is required in many cases where the tunnels pass through barren rock, but the walls are not self-supporting adjacent to the ore bodies. • Here square sets are generally used both in the drifts and in the larger stopes. A few of the smaller stopes are stulled but many of the larger ones are several sets high and many sets wide. For convenience the mines will be considered in groups of the following localities : Monarch Hill, Taylor Gulch, Cree Camp, and Columbus and Kangaroo gulches with Hoffman Park. MINES OF MONARCH HILL The mines on Monarch Hill which were producing ore in the summer of 1909 are the Madonna, Silent Friend-Fairview, Wilson, Little Wonder and Great Monarch. Of these only the Madonna was shipping daily. Late in the year the Eclipse was leased by the Giant-Eclipse Mining Company, and shipping from this mine began in December. Madonna wme.— Soon after the discovery of the Madonna mine by Smith and Gray it was sold to a company of New York and Iowa men who erected a small smelter at the foot of the hill for the purpose of smelting the ores from their mine. Be- GEOLOGY OF THE MOXARCH MIXING DISTUICT 45 COLORADO GEOLOGICAL SURVEY BULLETIN 1 PLATE IV R.6 E ^33 A^^: ^^< / , \%\ / r. / \^ ^ / --\ / ^/ Q / ^ 1-^ / > ^o^^^ 2 Cha ^^-r °°On s f, '-" 0 . fc o u o m ^S 1^ c c c Cf^H u ^ c « o8 N o ^ O '^ -r t re r; -M ^ »o c^i o> Oi "M «« ^ -„^C-Ji-i-«iJ« CO i-^ CD C^ CO CO CD W CO CO CO CO 8 ^ '— ' CO t^ ^O CO CO >— < CD CO "M COC^iOOi'Tp^-it^OOOOOOOCCOOOOQOOOOqj'^ o i-HCOOSCDiOOOCDOCO'CCCOCDt^CC^DCl-rfO-^COt^OCliOiO CD 0'-<0'^'cr Tf' c^ i-T i-T i-T ,-r .»O'^"^'Tt< O »-* lO O »0 CW r^ h^ ■^' C^' CO Co' CD O cd' CD 00 Ol 1^ QO O CD r-- »o »— t r^'*'0;icc^h-0':>ocot^oi"rto o'csT-t-'cD'o'^' cocoi-i" oi'i-Tofio co'cooo'cc ^f o o ■* ^ ;<:■ X' -rf oi oi CO i-H '-• '-' O CD CO Ot-t-COcDCOC»-'5 0C:OQOOOOOOcD010:3'-^*-**0 »-J 3* j;^ 010iOI>-GCO»CC:01'— coo5i;;^jt;ooco -^^ 2Ci-iT-^C0OO)O'*"*-t'CDOIC3SC0i0OOO'— 'COT-iCiCOrtiO r^oioci-^Olodr^OOOJcO-rt^'-t'— •--HTjild'-tcDQOOCDCOCOO »£? -^lOOJlOCOCO'— 'Tt*T-.aioO'^c^cocoi-< i-iOl 1-lM O Ol Ci CO — »ft -H t- oco -rt- r^ i-^ o r- 1-* o lO oo oi o 00 OS'^CO'— lO*— tt"-»-t *^ CO CO CO CD •-< CO >— ' :0 CO CO Di Oi »-< CD t^ c; CO CO ^*" CO o oi CO o GO -^ T-t 05 CO O CO CO lO CDiMt^OOIC^ffO lO 1—1 000'-<00'-« o o JO*-" CO O CO ■^CO CO CO CO o 3 CO CD Ol ^ OS OCQOOOOOO-f»J^OOI^CO«OOOOOOOCO r^LO-occooi'^Cidsoioit^«cooix^--cDrrt--oicDco^^ococo3COc;-t'-*' McO'-^^id'^c^oioioi'-^oi-^-t'^s-^-^'— 'oi-t'-rco»0"^30ibooioscococD.-< O Ol O Ci CO -D - ■ :r^ o ^ (^cD c: a: c coi^cocDcociOQ*ocoO'Or^cooir COCCDlOiCC'^'^iOCOC-lOOOiJrSr-'t-^C i^^COCO^COOlCOCDCCr^^^oicO »S^^ ^ i55 ?3 O ^ lO^ X!_ o o5^ c: »o oo_ o o_ <3^oi_ 00 00* •^" o' co' ift h-' Oi' o' cd' cd' »o oi" of t-T ITS ^ oi" CO* -^ ^ *-»' co" ^ rt CO M 0 1 ^ — ( »OcDt^GCClC^OICO'^»CCDr-300S<: "^ C: O Oi CI C5 Oi Cj C co__;oo-^»ocDt^oooic^oi CO t^- 00 00 czj 00 CO 5b c: OS Oi X c coooococoxxxxci!: cocwccxcocoooc 8-HOJC oo< 1 Oi C Oi Oi Oi "as 48 A PRELIMINARY REPORT OX THE tween this and the Mayflower fault. Many branches extend from the main shoot into the limestone on each side. These branches are said to follow the stratification planes on the southwest, but they are more irregular in the broken ground on the northeast side. Plate VI shows the broken character of the rock by the position of detached masses of quartzite surrounded by ore, and also the size and position of the largest ore bod^'. The main shoot kept its course in the fault-fissure down to No. 4 leyel at a nearly constant distance aboye the granite, but on No. 5 leyel it was nearer the granite. Below this point it ex- tends out into the limestone toward the northeast and diyides into seyeral branches. The stope on the 150-foot level (below Xo. 5) was 45 feet high and 40 feet wide Avhen yisited. This is not far below the quartzite. Onlj' one branch of the ore body had been opened on the leyel at the bottom of the winze, and was about 6 feet thick by 25 feet wide. The ore grades into the lime- stone without well defined walls, and is limonite and lead car- bonate with some galena, all of which carry yalues in gold and silver. At the loAvest point reached a small amount of pvrite was enclosed bv limonite. The zinc produced in 1909 came largely from No. 4. No zinc ore has been found below No. 5. The ore, which runs 30 to 42 per cent in carload lots, is in the form of carbonate and silicate. It is comparatively soft, and most of it can be broken with picks. The zinc ore which is on the foot-wall of the main shoot, extends upw'ard several hundred feet. Zinc minerals on the highest dumps indicate that the ore may extend nearly to the surface. The largest stope in this ore is 11 sets (61 feet) wide by 13 sets long. It holds this size upward four or five sets, but grows smaller above. In addition to the zinc the main shoot carries lead and silver, but not much gold on No. 4 level. The stope is 20 to 60 feet wide by 170 feet long. A lens nearly parallel to the largest shoot, which may be a branch, carries .04 to .25 oz. gold and 5 to 6 oz. silver x>er ton, and 2 per cent lead on No. 4. The ore increases in value downward. Ore on the level at the bottom of the winze below No. 5, averages .43 oz. gold and 31 oz. silver i)er ton, and 30 per cent lead. The quantit}' of iron decreases with depth. Some distance northeast of the largest ore body on No. 5, near the Mayflower fault, a copper ore shoot was encountered. The ore is immediately above the granite in the limestone which m COLORADO GEOLOGICAL SURVEY BULLETIN 1 PLATE VI I L PLAN oTtHE madonna MINE ABOVE THE THIRD LEVEL BULLETIN 1 PLATE VII 50 100 150 200 feet _._1 . 1 ■ 1 1 1 COLORADO GEOLOGICAL SURVEY BULLETIN 1 PLATE VII CROSS SECTIONS OF THE MADONNA ORE BODIES (;i:olO(;y of tiik aio.naucii mim.m; uisikict 49 has an uinisually liijili (li|) al lliis point. Tlio shoot is :> to ('• tVct thick by (JO to 70 feet wide and about 150 foot ion*;. The oi'e bodies on Iho hijiiiosi Icvols are now inaccessible, bnt plates \l and VII show their siy.e and relationships. In August, 1909, No. G tunnel had been driven to a point a few feet below the quartzite where a eonsiderable body of coarsely crystallized calcite was encountered. This calcite showed con- siderable pyrite and carried a small amount of silver, but no pay- able ore had then been found. Recently an ore shoot 12 feet thick was cut on this level a short distance southwest of the breast of the tunnel. The width has not been determined but a drift GO feet long is in ore all the way. The ore lies on the granite at the contact which has a very high dip. Six carloads have been shipped at the time of writing. The first four averaged .51 oz. gold and 28.40 oz. silver per ton. Since the hade of the Madonna fault is unknown it is im- possible to state its exact position at this level. But it is prob- able that this ore body is not far from the fault, and is hence nearly in line with the main shoot. If this ore body proves to be continuous with the main shoot, by taking a vertical depth of 1,520 feet and a pitch of 85° a pitch length of 2,650 feet is ob- tained from the surface above Zero to No. G. ^Siloit Friend and Fitirvicw mines. — Next to the ^ladonna the Silent Friend has had a greater production than any other mine in the district with the i)ossible exception of the Eclipse. The Silent Friend and the Fairview have not been worked on a large scale for several years and we were unable to sop the largest stopes. Mr. J. F. Sundbye, who is leasing these mines, has shipped a few carloads of ore within the past year. In August, 1909, he was driving an upraise from the Fairview tunnel in a vertical vein about two feet thick. Over half the ore in this u]»raiso was galena, the remainder was load carbonate and iron oxide. I am indebted to Mr. D. F. Hamilton, former superintendent of these mines, for the brief notes which follow. The Silent Friend ore shoot dips about 45° N. .34° W. and was worked continuously through a vertical range of nearly 700 feet. This gives a pitch length of nearly 1,000 feet. The shoot was 15 to 50 feet thick and was square set throughout the entire distance through which it was worked. The shoot, following a somewhat spiral course, was in part close to the granite but ran out into the limestone 40 to GO foot in places. It was thinnest when dipping toward the granite. The best ore was galena which 50 A PRELIMINARY REPORT ON THE carried 20 oz. silver per ton and about 70 per cent lead. When the ore was near the granite it carried a small quantit}' of gold. Hawkeyc mine. — This mine is a recent producer and although idle at present all the Avorkiugs except the winzes may be readily examined. The main tunnel was driven about S. 45° E. 550 feet in granite to the limestone-granite contact and thence along the contact 300 feet, bearing S. 20° to 25° W. the greater part of the distance. Along the contact the granite forms the hanging wall, the plane of contact dipping northwestward 40° to 60°. Near the breast of the tunnel an ore shoot Avas encountered which has been worked upward nearly 200 feet along the pitch and also some distance below the tunnel level. The ore body removed would average perhaps G to 8 feet each way in cross-section. Granite forms the hanging wall which dips northwesterly 25° to 40°. Five hundred seventy feet from the tunnel entrance a cross- cut was driven through the limestone to the east limb of the synclinal fold where it cut an ore shoot lying on the granite foot- wall which dips northwestward 28° to 40°. A winze has been sunk a short distance and the ore has been stoped out above the tunnel level for 166 feet along the pitch. The ore body was largest a short distance above the tunnel level with a maximum width of 66 feet. The stulls here are 4 to 9 feet long Avith an average of perhaps 6 feet. Through the last 70 feet of the stope the stulls will average about 7 feet in length, while the stope is about 10 feet wide. The ore pinches to 4 or 5 feet in Avidth at the extreme upper end. When considered with reference to the ore bodies of the dis- trict as a whole, this increase in size with increasing depth is encouraging even though it may be local. Had this shoot been worked from higher levels by underneath stoping and by timid operators, in all probability it would haA'G been abandoned at about 160 feet or more above the level of the Hawkeye tunnel. In this connection it is significant that previous to the discoA'ery of ore in Madonna No. 6 tunnel, the greatest depth reached on any ore shoot immediately overlying the granite was in the Hawkeye. The mine is equip]>ed with electric lights and electric hoist and fan. Eclipse mine. — Although but a small ]»art of the hnvor Avork- ings of the Eclipse Avas accessible in 1909 a good idea of the geo- logical conditions may be had from examination of the hori- GEOLOGY OF THE MONARCH MINING DISTRICT 51 zontal and vertical plans (IMates VIII and IX). The ore is found in two distinct shoots — one lying on the granite, the other just below the quartzite. The granite shoot extends below the fourth level while the quartzite shoot was lost several hundred feet above. At this point a thrust fault hading S. 58° W. brings the ore up against the end of the quartzite stratum which forms the footwall on the northeast. In this fault-tissure the ore was galena with lead carbonate. Several pieces of solid galena four to five inches in diameter may still be seen. A few feet below in the same stratigraphic position is a large body of limonite re- ported to carry a small amount of silver and gold but of too low grade for shipping. No eJBfort has been made to determine whether or not the ore body continues below the quartzite northeast of the fault. It is not clear whether the faulting at this point occurred before or after the ore deposition. Indications point to the former, but the evidence noted was insufficient to justify a con- clusion. A short distance southeastward higher up in the stope, grooves on the hanging wall indicate that the faulting has been at least in part comparatively recent. Mr. J. L. Farrell, former superintendent for the Company, gives the following information concerning the mine. The quartz- ite shoot, discovered at the surface, was cut successively by Nos. 1, 2, and 3 levels. On No. 2 level there were 110 square sets (4x5 ft.) on the sill floor in the quartzite shoot, and the size of the ore body remained practically the same up to No. 1. The shoot grew narrower below No. 2 where it formed a stull stope 5 to 12 feet thick from No. 2 to No. 2 intermediate. Below this the ore was somewhat bunchy. The granite shoot was cut suc- cessively by levels Nos. 2, 3, and 4. The thickest part of this shoot was encountered on No. 3 level where it was about 25 feet thick by 80 feet wide. Both shoots bear slightly to the right of the dip as they descend. The bulk of the ores shipped carried their chief values in lead and silver. Before 1893 the shipments carried 25 to 50 per cent lead, but later, ore was shipped which carried only 5 per cent lead. About half the lead content was in the carbonate form, the remainder was sulphide. In general, the higher the lead content, the greater were the silver values. The highest silver returns in a carload lot were 28 oz. per ton. The silver averaged about 8 oz. per ton. The ore shipped since 1893 has carried a small amount of gold. 52 A PRELIMINARY REPORT ON THE 1^ (0 " (V4 OEOLOGY OF Till': MONARCH MIXING TjISTRICT 53 54 A PRELIMINARY REPORT OX THE A considerable body of zinc carbonate and zinc silicate was fonud above the silver-lead ores in the granite shoot from No. 2 intermediate to No. 4 level. This ore carried silver values and was sometimes mixed with the lead ores in such proportion that the zinc content was kept below the 10 per cent limit fixed by the smelter. Excepting a few cars shipped recently the zinc ore was never sold as such by the company, but in 1905-6 the I*aul brothers, who were working the mine under lease, shipped con- siderable zinc ore. A small amount of copper ore occurs in the granite shoot also, but no zinc or copper was found in the quartzite shoot, Kecently this mine has been leased by the Giant-Eclipse Mining Company, the old levels and stopes are being cleaned out and several carloads of ore have been shipped. There is a large amount of low grade zinc ore in sight. No record of tonnage or gross values has been preserved by the Eclipse Company. But Mr, W. K. Spinney has kindly given the figures for the net receipts (gross value less freight and treat- ment charges) by years from 1887 to 1907, and Mr. Clyde H. Jay of the leasing Company, has furnished the smelter settlement sheets from December, 1909 to February 7, 1910. Some ore is reported to have been shipped before the mine was purchased by the company but no records are available. The net receipts since the purchase in 1887 have been $581,811.79. Fairplay mine. — This mine was located in 1878 by the Boone brothers and is reported to have shipped a considerable tonnage in the eighties. No figures are available for that period. Since the present owners have operated it the production has been 728 tons with a gross value of $14,974.00. It has been closed since 1908 and hence was not examined in the present survey. Great Monarch mine. — The Great ^Monarch vein outcropped in a conspicuous fissure in a limestone cliff, and has been devel- oped through a shaft and adit to a depth of ]>erhaps 200 feet. Mr. Thomas Penrose states that the shoot was 8 to 10 feet wide for the first 30 feet, but narrowed to 2 inches for tlie next 60 feet. Below the adit level a winze was sunk 60 feet on the shoot which remained rather narrow but did nof i)inch out. The ore was galena and lead cai-bonate carrying about 200 oz. silver ])er ton. Within the past few years several caildiuls of /.iiic ore have been shipjicd from near the surface. GEOLOGY OF THK MONARCH MINING DISTRICT 55 A tunnel has been driven some 1.200 feet just above the creek level on this property, but has not yet cut any payable ore bodies. Little Charm mine. — This mine is on the same lead as the Great Monarch and has been worked partly through the dis- covery shaft and partly through the Great Monarch adit. The ores of this mine were similar to those of the Great Monarch but ran somewhat higher in silver. According to Mr. Penrose both silver chloride and stephanite were present. The Little Charm claims the record for high grade ore in a carload lot (10 tons). Mr. J. Scott Boyd, General Manager of the Monarch Pool Mining Co., gives the following as the smelter returns from this car : 0.48 oz. gold and 226.2 oz. silver per ton, 2.45 per cent lead, 7.65 per cent zinc and 0.15 per cent copper. Little Wonder mine. — This mine has produced several car- loads of ore from near the surface but the ores are pockety like those of other mines which have not yet been developed below the quartzite. In 1909 several tons of galena were taken from a pocket within 20 feet of the surface. Wilson mine. — This mine has been developed through two tunnels on the Wilson and Kuter claims. In the summer of 1909 leasers were shipping from the lower tunnel a few carloads of zinc-lead ore which had been left on the hanging wall when the mine was formerly producing. The total thickness of the vein, where seen, was five to six feet. All but about two feet from the upper part had been removed several years ago. Evening Star mine. — The Evening Star ore shoot was dis- covered on the Little Chief claim from which it was worked through an inclined shaft sunk on the ore body. The Evening Star tunnel, driven later, along the contact, crossed the old work- ings about 70 feet above the end of the incline, but no ore has been taken from the tunnel. At the tunnel level the ore body was nearly two feet thick with a stope length of 12 or 13 feet. A little galena, in rotten granite, can be seen on the foot wall. Below this point the shoot is reported to narrow north and south and thicken at right angles to this direction. It is possible to descend 120 feet or more from the collar of the incline at the present time. As a rule the ore lay close to the granite, but in the limestone. Some galena and limonite can still be seen in the limestone Avails as a replacement. At 120 feet below the surface the stope length is 50 feet or more. The thickness is much greater than that at the tunnel level below. 56 A PRELIMINARY REPORT OX THE Mr. William Miller, one of the owners, states that low grade zinc ores extended from 40 to 130 feet below the surface but not at greater depth. He reports a total output of 600 tons which averaged |i20.00 a ton. The principal values were in silver and lead ; two cars yielded 90 cents a ton in gold. Dcliticare mine. — This mine was also worked through an in- clined shaft which is now caved. Mr. Miller reports output and values approximately the same as those of the Evening Star. At the bottom of the shaft oxide of manganese was encountered, but carried no values. Black Tiger mine. — This mine is reported to have produced S or 10 carloads of lead-silver ore in 1881. Judging from the workings, which were in jiart accessible in 1909, the main shoot was 3 or 4 feet thick at the tunnel level and had a slope length of 9 feet. The ore lay in limestone about 3 feet from the granite. The croppings show quartz and a little iron stain and galena. Other mines. — The April Fool, Ben Bolt, Elkington. Pay- master, and Oshkosh have produced more or less ore, but all were idle in August, 1909, and the ore bodies were inaccessible. Sev- eral of these have had an output greater than a few that have been briefly described. The Ingersoll mine south of Garfield is reported to have pro- duced a carload of ore. Several tons of ore, galena with some iron oxide, lay in the shaft house in 1909. The Thirty-Six-Thirty mine southeast of the Ingersoll is re- ported to have produced considerable ore many years ago. Much prospecting has been done in the vicinity, but no other pay ore has been found. MINES OP TAYLOR GULCH The Lilly is the only mine in Taylor Gulch which has been producing steadily for a number of years. In the summer of 1909 a few small shipments of high grade ore were made from the Rainbow-Eagle Bird. At the time of our visit to the Last Chance mine several tons of ore were sacked and shipments have since been reported. The Jewell Tunnel & Mining Company in August, 1909, resumed work in the Jewell tunnel which is being driven to develop that part of the field Avest of the gulch. Lilly mine. — This mine, which is owned by the Taylor Moun- tain Mining Company, is now worked through a tunnel, 2,530 feet long. A few hundred feet from the breast a winze has been sunk 200 feet or more. The tunnel begins just west of the "part- ing quartzite", crosscuts llie sedimentary beds to the granite (jKOLOGY of TIIK MONAUCH iMIMXG DISTRICT 57 COLORADO GEOLOGICAL SURVEY BULLETIN 1 PLATE X 0 ioo 600 900 1200 isoo feet. MINING CLAIMS OF TAYLOR GULCH Patented claims from map by F. P. Black. Data for unpatented claims furnished by M. R. Jewell. 58 A PRELIMINARY REPORT ON THE contact, and continues north in the limestone but a few feet from the granite. For nearly the entire distance along the contact the tunnel follows a streak of limonite connecting several bunches and shoots of ore which have a maximum width of 8 or 10 feet on the tunnel level. The thickness is much greater. The best ore bodies on this level are of copper, but workable silver- lead and silver-iron ores have been encountered (PI. XI). The largest stope on the tunnel level is 35 feet high by 100 feet long. Several stringers lead out into the limestone but have never been followed. A few bunches of ore have been stoped out on the first and second levels below the main tunnel. Foreman Frank Hunter reports the ore on the first level to have carried about 10 per cent copper and 3 to 6 oz. silver per ton. In a letter dated Feb. 24th, Superintendent Geo. H. Purmort states that develop- ments between the 100- and 200-foot levels show that the shoot dips farther out into the limestone and that sulphides are pres- ent carrying about 15 per cent copper, 6 to 40 oz. silver and fl.OO to 13.50 gold. From the surface down to the 230-foot level most of the ore taken from the mine was hoisted through the discovery shaft. At present considerable ore is being taken from this level which is now connected with the main tunnel 138 feet below. Large bodies of ore are reported in the old upper workings but cannot be recovered because of bad ground and rotten timbers. The ores are chiefly carbonates and oxides with some chrys- ocolla and considerable sulphide. The sulphides, which are chal- copyrite and copper-bearing pyrite have been found beloAv the tunnel level and in smaller quantity nearer the surface. They are found associated with oxidized ores. Much of the chrysocolla is very pure but is usually in thin seams. In at least one in- stance it occurs as a coating an inch thick or more on the walls of a small cave or fissure in the limestone. The copper ores are partly in limonite gangue, partly disseminated through limonite which also carries silver. About half tlie ore carries a small amount of gold. Through the courtesy of President W. F. Norway we are able to give the following figures from the smelter settlement sheets shoAving the outi>ut of the mine from ^Nlarch 17, 1900, to Janu- ary 18, 1910: Output, 4,991.G5 tons. Copper, 757,163 lbs. wet assay. Silver, 17,743.13 oz. GEOLOGY OF THE ISIONARCH MINING DISTRICT 59 GO A PRELOIIXARY REPORT ON THE Lead, 4,037 lbs. Gold, 67.44 oz. Gross value, $103,111.20. Average value per ton, |20.66. Output from 1888 to Jan. 18, 1910 : Total tons produced. 8,827.15. Gross value, |173,898.71. Average value per ton, |]9.70. About two-thirds of the oie has carried an average of 10 per cent copper. The remaining one-third was silver ore which car- ried very little copper. Until the end of 1907 the ore carried 30. to 40 per cent excess iron. In 1909 the mine produced 1,832 tons with a gross value of |26, 121.34. This is the largest output for any one year in the history of the mine. As a rule quartzite lies against the granite wall wherever ore occurs and varies in thickness from a few inches to perhaps six feet. It may be continuous but there are no crosscuts to it from the tunnel where ore is not found. A narrow porphyry dike follows the contact more or less continuously, sometimes in the limestone, sometimes in the granite. The limestone is consider- ably broken, movement having taken jtlace in practically every direction as shown by the slickensiding. The mine is equipped with motor, compressor to operate the machine drills, an electric fan for ventilation, electric lights, and at the shaft an electric hoist. The ore is carried by gravity over an aerial tramAvay 7,174 feet long to the railroad at Garfield. RainJ)otu-Eagle Bird mine. — Although very little work has been done on this property it is reported to have produced about 115,000-worth of ore. It is worked through two short tunnels near the surface. The ore occurs in a brown, ferriferous, crystal- line dolomite overlying the "parting quartzite" and within 8 to 30 feet of an overlying porphyry dike or sheet which dips west- ward. It is a contact deposit replacing the dolomite. The best ore body seen by the writer was 18 inches to 2 feet thick in a vein parallel to the bedding of the sedimentary rocks, ^lineralization has extended a foot or more into the enclosing rock on each side of the good ore. Two samples of the dolomite taken from the dunq) and assayed in the laboratory of the State Survey carried 4.2.5 oz. silver and a trace. Although lead is present in considerable (piantity the chief values of the ore are in gold and silver. The lead occurs largely as galena. Sonic of Ihe best silver valnes are carried by a slreak GKOLOGY OF TIIK .MO.NAUCII .MINING DISTRICT Gl of iiiiuifianese oxides which oxtonds thronp;hout the lenp;tli of the tunnel, 8 to 30 feet below the ]K)i'i»hyrv dike. The i»iinci[)al manj>anese mineral is psilonielane. Some (luaitz is present as a ganone mineral. ^'ery high values are repitrted from this mine and a few samples assayed by Mr. Butters, gave the following results: 1. ITighly iiianganifcrons ore. silver 161). 7.") oz. per ton. 2. Galena with a little carbonate; lead 61 per cent, gold 0.21) oz., silver 3.50 oz. per ton. •>. Quartz with galena and lead carbonate: gold 1.81 oz., silver 16.7.") oz. per ton. It is probable that these results are con- siderably below the average. The ore is somewhat pockety, and the mine was visited at an unfortunate time for the examination of the largest bodies. Two shafts on the Eagle Bird claim north of the breast of the tunnels have opened a body of silver-manganese ore which has not proved sufficiently valuable to mine under present condi- tions. A sample taken from the dumps yielded on assay 7.50 oz. silver, 24.70 per cent manganese and 5.71 per cent iron; some silica and much lime carbonate were present. Two other samples which were not run for manganese assayed 1.75 oz. and 2.60 oz. silver. Mountain Chief and Pin yon mines. — The Mountain Chief was one of the earliest producers, and is reported to have yielded some of the highest grade ore of the district. It is stated that the first lot was packed on burros to Garfield, thence hauled 73 miles by wagon to Canon City, and shipped by rail from Canon City to the smelter at Omaha. Notwithstanding this heavy ex- pense it netted a large profit. Mr. E. Gimlet states that Mr. J. L. Emerson later shipped 20 tons from this property, which re- turned a gross value of |10,600. When visited last summer the shaft was half filled with ice, but the tunnel below could be entered. At about 60 feet from the entrance, the tunnel was filled with waste from a crosscut in a porphyry dike which overlay the ore. Mr. Gimlet, a former sujK'rintendent at this mine, states that the ore was in a pocket and mostly within 70 feet of the surface. Its thickness at the u])per part was about two inches and at greater depth was tlu-ee feet. This mine and the IMnyon are re])orted to have ])rodu(ed together $150,000-worth of ore. The Pinyon. which joins the Mountain Chief, is said to have produced |22,000-worlli of ore from one pocket which i>inched 62 A PRELIMINARY REPORT OX THE out. No further work has been done. This pocket was but a few feet thick, having its greatest diameter parallel to the strike of the enclosing brown limestone. This limestone is a coarsely crystalline ferriferous rock similar in appearance to the dolomite of the Eainbow-Eagle Bird but carries little or no magnesia. Last Chance mine. — But little work has been done on this claim. When examined a tunnel had been driven about 100 feet and several tons of ore had been taken out. The large body of limonite (gossan) at the surface, the fracturing of the sedimen- tary rocks and evidence of faulting, all indicate the possible presence of a workable ore body. It is reported that a tunnel to develop this property, has been started lower down on one of the Jewell claims. Bonnie Belle. Ben Hill, Fraction, Desclemona mines. — These mines, which are on one lead, produced some ore in the 80"s and but little since. Only the Fraction, the least important of the group, could be examined in 1909. This was worked through a short tunnel and a winze about 50 feet deep. A vein three feet thick was found in a short drift toward the north. This vein is parallel to the bedding of the enclosing sedimentary rocks which dip 56° N. 75° W. A bedding fault is indicated by the slicken- sided hanging wall. This movement probably occurred after the ore was deposited. I am indebted to Mr. Everett Anderson for the following notes on the other mines of this group. The Ben Hill shaft is 275 feet deep. Drifts were run north and south at 125, 175, and 225 feet from the surface. At the 175-foot level a drift running northward 125 feet is the longest in the mine. At 30 feet from the shaft on this level 3 feet of galena was cut, which carried an average of 85 oz. silver per ton and 73 per cent lead. Tliis ore Avas in the form of a shoot pitch- ing northward and extending upward practically to the 125-foot level. Carbonate ore occurred on the border and in some places graded into the galena. The average tenor of the carbonate was 22 to 28 oz. silver per ton and 30 per cent lead. Between the 175- and 225-foot levels the ore was spotted. In the bottom of the shaft 7 feet of ore was struck Avliich assayed 90 oz. silver per ton and 60 per cent lead. Water stopped the work here and a tunnel was driven to cut this lead about 400 feet below the bottom of the shaft, but at the time of writing this report no ore in payable quantity has been found in the tunnel. The Bonnie Belle shaft is down 140 feet. At 60 feet. 6 feet of galena similnr to that in the Ben Hill was discovered. With GEOLOGY OF THE MONARCH MINING DISTRICT 63 this was associated oxide of iron which enclosed masses of galena. In places some carbonate of lead occurred with the galena. This ore was in the form of a northward pitching shoot having a stope length of 60 feet. Tlie vertical distance covered by the ore in the shaft was 40 to 50 feet. The Desdemona shaft is 118 feet deep. Drifts extend north and south at 60 and 100 feet from the surface. The ore was largely galena in streaks and bunches with occasional large pockets of carbonate ore. The total output of these claims is not known, but the Ben Hill shaft has produced $12,000-worth of ore. Ore seen on the dumps and platforms at these mines was galena with both hard and soft lead carbonate. At the Bonnie Belle there is considerable breccia having sedimentary fragments in a granite matrix, indicating the proximity of the ore to the granite. Granite dikes occur a short distance west. SJianirock mine. — This mine has been worked through a tun- nel about 900 feet long from which extend several drifts, a few upraises and winzes. Considerable ore was hoisted through a shaft before the tunnel was driven. The limestone is much broken and apparently faulted. A porphyry dike having an easterly trend passes through the mine, and shows very abrupt changes in dip and strike. Mr. F. C. Watson, who is leasing this mine, states that he took a carload of ore, carrying 1.58 oz. gold and a few^ ounces of silver per ton, from a pocket just above the porphyry. The greater part of the ore which has been found in the mine was in pockets. The tunnel follows a lead several hundred feet, but the vein exposed in the roof is less than three feet wide. The best ore found, lay near the porphyry and quartzite, and in the quartzite. Prospecting near the granite has not been profitable here. No ore was found in the caves mentioned on page 28. Major mine. — The Major mine is operated through two shafts, one of which is about 40 feet deep. The ore is a contact deposit replacing the limestone not far from a porphyry dike which is probably the same as the dike in the Shamrock. Tlie ore seen by the writer lay below the dike in the lime- stone in a body about 5 feet thick, consisting of limonite, lead carbonate, and copper oxides and carbonate. This pocket had produced at. least one carload of ore that carried 8 per cent 64 A PRELIM IXARY REPORT ON THE copper. Two carloads of co])per ore are reported from the mine in addition to the copper of the lead-silver ores. Most of the ore from the Major and Shamrock carries values in gold, silver, lead, copper, and iron. The total ontput of the two mines is about 1,000 tons averaging flS.OO a ton net. Garfield mine. — This mine w'as closed during the summer of 1909 and the ore bodies were inaccessible. It has i)roduced a small quantity of sulphide ore. Considerable pyrite and a little galena were seen on the dump. From the creek east of Garfield village a tunnel, through which it is proposed to work this prop- erty, has been driven over 2,200 feet along the limestone-granite contact, but the breast of the tunnel is still a considerable dis- tance from the known ore bodies. No w^orkable ore was found in the tunnel along the contact. Plowever, a small amount of galena and zinc blende was discovered out in the limestone by cross- cutting. The tunnel is equipped with electric lights, fan and ma- chine drills. Alaska mine. — The Alaska was worked principally from 1886 to 1888. In 1898 Harrington and Anderson shipped a little more than a carload from this mine. Mr. Anderson gives the following information : Forty-five feet west of the granite a shaft was sunk 110 feet on an east-west streak of ore. In all, there are about 1.000 feet of drifts at 30, 60, and 100 feet below the surface. The ore was galena, hard carbonate, and oxidized iron. The carbonate ore occurred in a shoot about 10 to 18 inches thick, extending along the north-south drift 30 feet. The shoot pitched north about 3 feet for each foot of vertical descent. A few tons shipped by Harrington and Anderson ran |37.00 in gold, 14 oz. silver, 18 per cent lead and 32 per cent iron. The west wall was limestone; the east wall was gouge material which extended to the granite. The galena, which carried 20 to 2.") oz. silver, 60 per cent lead and no gold, was found in ])Ockets of oxidized iron above and below the carbonate shoot. The iron ore carried S7.00 to .fll.OO in gold and about 10 oz. in silver per ton. Missouri Boy mine. — It is reported Hinl about .*;3,ono.O(i worth of oi-e was shipped from this ])ro]»erty from shallow work- ings which arc now caved. The dcei»esi shaft, which is on the contact between a ha^^ic syenite dilvc Mn('(Mi ill ji,()ld, silvoi', and lead. A few specimens on tlie diiiiip show a little copper. In 1 !)()!) Mr. T. X. Iliilihai-d was ])rospecling this cont«act on llie Mockinji' liird claim soiilli of the Missouri Roy. At the time of onr visit he had found a little jjaleiia and cerussite with some pyi'ite. hut no ]»ay ore. Still farther south the Bay State and Independence tunnels have cut a dike similar to, and perhaps the same as that men- tioned ahove. Two or three tons of ore were lying on the jilat- form at the u]»]»er tunnel which was caved when visited. The ore is galena and ju'oliably silver chloride in vein quartz. Other mines. — Several claims in Taylor Gulch jiroduced small amounts of ore in the early days. The Denver-Rainbow, fiidianapolis, and Stem Winder have each produced a carload or more. The ore in these claims was found near the surface in jiockets or narrow veins, and but little work has been done to determine the extent of mineralization. Prospects and developments in Taylor Gulch. — A shaft was sunk on the Exchequer claim to a considerable depth in mineral- ized limestone in what would appear to be favorable ground, but no jiayable ore was found. Material on the dump indicates that a considerable body of limonite is present. A porphyry dike was cut in the shaft, and is probably the same dike as that with v.iiich the ores of the ]\Iajor and Shamrock are associated. The Jewell Tunnel & Alining Company holds a group of twenty-tive claims on the west side of Taylor Gulch where sev- eral leads have been opened. For the most part the ore replaces beds of the sedimentary rocks which dip at a high angle toward the west. Xo shipments have yet been made by the company, but the grouj) of claims includes several of the old small producers men- tioned above and also the INIountain Chief. A tunnel is being driven from near the head of Taylor Gulch to develop these hold- ings. Recause of the high inclination of the strata and the dci»th of the tunnel level below the surface, these developments will do much tOAvard disclosing the extent of the ore bodies. An electric machine drill has been purchased and will be installed when the tunnel is sufficiently advanced to allow the shooting of machine drilled holes without damage to the plant. 66 A PRELIMINARY REPORT ON THE MINES OF CREE CAMP Song Bird mine. — Attention was first drawn to this part of the district by the discovery of rich silver ore in the Song Bird in 1878. The deposit was in the limestone above the "parting quartzite" in a zone of local faulting. Although the mine was a producer of good ore for a short time no figures are available as to output. Considerable prospecting was done in the vicinity but results were generally unsatisfactory. Clinton mine. — The Clinton mine on the northwest slope of Missouri Hill was first opened in the early 80's, but lay idle for a. number of years. During 1901 to 1904 it was operated, when, according to Mr. A. B. Brewington, it produced about $12,000- worth of ore. The values were in silver, gold, copper, and lead. The manganese content was sufficiently high to secure a reduc- tion in treatment charges. The ore occurs in northward dipping shoots in the limestone 6 or 8 feet from the granite. One shoot carried ore practically from the surface to a depth of 300 feet, below which it was not worked. The greatest width of this shoot was 8 or 9 feet but at this point it did not carry values high enough to pay for the necessarily long haul. Were the mine nearer the railroad it is probable that further work would have been done before now. MINES OF COLUMBUS GULCH AND VICINITY In the summer of 1909 there were six men employed in de- velopment, and a few doing assessment work in this part of the district. No payable ore bodies were exposed at the time of our visit. Golden Age uvinc. — A tunnel about 550 feet long in the quartz monzonite and a drift about 40 feet long constitute the developments of this property. The drift is on a shear zone which shows gouge and pyrite in the roof. Mineralization ex- tends through a Avidth of about three feet. A small amount of galena was found in the breast of the tunnel in the country rock. Pyritization was frequently seen in the tunnel. This })roperty has produced two carloads of ore. Accord- ing to Mr. Henry L. Acker, the better car netted $30.00 a ton after paying freight and treatment charges. harJiiKj mine. — One carload of ore is reported from this property, from a shaft 26 feet deep which is now filled with ice. GEOLOGY OF THE MONARCH MINING DISTRICT 67 Good galena was seen on the platform. A tunnel is now being driven below to cut the ore body. Bnghton mine. — This mine, which was once a producer, was worked through a shaft which is now nearly filled with water. The dump is nearly all vein quartz stained with limonite. A small amount of galena and pyrite may be seen. Columbus mine. — This mine was worked through tunnels on several levels all of which are now caved except the lowest. Bad air in this one prevented an examination by the field party. The workings are, in the main, just east of the eruptive contact be- tween the quartz monzonite and metamorphosed sedimentary rocks. Much vein quartz and a considerable quantity of sul- phides of iron, copper, lead, and zinc were seen. Water issuing from the tunnels carries in solution an appreciable amount of copper salts. The following is taken from the Report of E. Le Neve Foster, State Geologist •} The Columbus mine is situated about 12,000 feet above sea level on the southern slope of Taylor Mountain. Its workings consist of shafts and tunnels and develop a true fissure vein to a depth of 300 feet, and horizontally 1,100 feet. The outcroppings of the vein may be clearly traced upon the surface for this entire distance, with almost unbroken continuity, commencing at its southern extremity in a deep depression in the side of the mountain, and following very crookedly a mean north- easterly course up an ascent of 30°, where it is finally hidden under sur- face debris. * * * The matrix of the vein is quartz from wall to wall. The clay selvage usually accompanying the walls of fissure veins is in this instance more often lacking, though occasionally present, with a thickness of one- fourth to two inches. For the first 200 feet of depth the quartz is irregu- larly banded, composed in a great measure of agglomerations of coarse amorphous [xenomorphic ?] crystals, or spongy from the decomposition of pyrite, and deep brown in color from the presence of much iron oxide. The whole width of the vein, from 6 to 20 feet, is productive of good value in silver, which occurs as a sulphuret and contains' also varying quantities of gold. At the depth of 200 feet the vein material changes abruptly to a pure white quartz, containing large quantities of pyrite and sphalerite intimately associated, in very perfectly shaped crystals of one-twentieth to one-half inch in diameter. Copper is also found; native, in spongy masses and as a thin coating of blue or green car- bonate, while silver is less widely distributed through the thickness of the vein, being confined to certain localities rich in iron and zinc sulphurets. These conditions remain constant in the lowest depths of exploration. A spur or branch of the vein has its apex in the granite [quartz mon- zonite] to the west and joins the main vein at a depth of 200 feet. Its strike is due north, and its dip about 70° to the east. The vein material •Report of E. Le Neve Foster, S'tate Geologist, 1S84, pp. 30-32. Mr. Foster credits the account to Mr. F. G. Bulkley. 08 A PRELIM IXAKY lUn'ORT OX THE here is productive of small quantities of silver, and consists of a com- pact brownish quartz. No influence seems to be exerted upon the pro- ductiveness of the vein by the junction of this spur, either in quantity or quality of the ore. The mine was operated for several years, the ores being con- centrated in a mill on Middle Fork. The mill has since been sold and removed, and the aerial tramway which connected it with the mine is no longer standing. The men who owned the mine when it was operating are now dead, and no record of the output is known to exist. Mr. W. K. Jewett, the present owner, writes : ''Tradition says that its gross production during the period of its operation was approximately |300,000. the values being mainly silver and copper.'' Alpha and Beta. — An output of 20 tons of silver-lead ore is reported from these two claims in Kangaroo Gulch. The ^Nlav- erick tunnel below, through which it is proposed to work these leads, has been driven 650 feet. Uncle ^Saiu mine. — The Uncle Sam in Hoffman Park is re- ported to have been operated while ^laysville was the terminus of the railroad. The workings are now inaccessible but it is probable that the ore was either in the quartz monzonite porphyry or at the contact between the porphyry and the quartz monzonite on the east. Prospects in Hoffman Park. — There are here a number of shallow shafts and several tunnels, but at the time of our visit only the Hercules tunnel was being driven. This tunnel is in over 600 feet in the quartz monzonite. A narrow vein in a drift near the breast carries galena and chalcocite with a small amount of chalcopyrite, LIMESTONE The Ohio & Colorado Smelting & Eetining Company owns a quarr3^ at Garfield from which limestone is shipped daily to the compan3''s smelter at Salida. The shipments for the twelve months closing July 31, 1909. were 978 cars of about 25 tons each. Seventeen men were employed almost continuously through the year, and tlie nnnibei' was increased in Ihe summer. The Garfield (|uarry under lease to ^Ir. L. W. Hubbard was operated during ])art of the year, 1909. Ten men are emjdoyed when the (piarry is working regularl\. Tlu* limestone is shipi)ed to the smellers at Leadville and Salida, and io the sugar factory at Tvocky Ford. The limestone of Ihese two quarries is crystal- line and is alniosl piii-c cii I'iiini r;irl)()nate. GEOLOGY OF THE :\K).\AUC1I MIXING DISTRICT G9 MARBLE There is a large aniouiit of marble in Taylor Gulch and in the vicinity of Cree Camp, but it is not likely that it can be quar- ried under present conditions in competition with the large quar- ries of Colorado. A small quantity at the head of Taylor Gulch is blue, but most of the marble is pure white and very coarse in texture. In general the rock near the surface contains too many joints to make a satisfactory building stone. A quarry near tlie Exchequer shaft is reported to have fur- nished a small quantity of marble for the Colorado capitol. A number of tons have been quarried. The largest pieces seen on the dump were about six feet long. The marble is pure Avhite and practically free from chert. INDEX A Acker, H. L., quoted 66 Adamellite 17 Aetna ( see Mount Aetna) Alaska mine, described 64 Alaskite 19 Alpha mine 68 Anderson, E., quoted 62, 64 Anglesite 34 April Fool mine 56 Asbestos 30 Athyris 16 B Banatite 19 Bay State tunnel, dike in 13, 65 ores of 38, 65 Ben Bolt claim 8,56 Ben Hill mine, described 62 Beta mine 68 Black, F. P., acknowledgments to 7 Black Tiger mine, described 56 Bonnie Bell mine, described 62 Boone Brothers, work of 8 Boss Lake, faulting near 26 glaciation in and near 12 mineralization near 12' origin of 12 sliderock near 22 Breccia 22^ Brewington, A. B., quoted 66 Brighton mine 39 described 67 Bulkley, F. G., quoted 67 Burton, K. E 46 Butters, R. M., work of 7, 61 c Calamine 35, 38 Calcite 36 Camarotcechia 16 Cambrian 11, 14 Carboniferous 11, 14, 15 Caves 28 Cerussite 34 Chalcocite 32 Chalcopyrite 33 Chert 15 Chrysocolla 33 Clinton mine 14 described 66 folding near 24, 43 ore deposits in 41 i_ IXDEX Clover Mountain 14. 21, 22, 29 Coffin, R. C, work of 7 Colorado Smelting Company 9, 46 Columbus Gulch, mines of GG ores of 31 sedimentary rocks of 14 Columbus mill 31, G8 Columbus mine, described 67 ores of 33, 36, 39 Contact deposits 38, 41, 43 Continental divide 7, 12, 23 Copper minerals 32 Copper, native 33 Cree. Alex 8 Cree Camp, discovery of ore at 8 folding near 24 marble near 69 mines of 66 moraines near 12,22 Creede, work of 8 Cuprite 33 D Daily, work of 8 Darling mine, described 66 Delaware mine, described 56 ores in 35 Denver-Rainbow mine 65 Desdemona mine, described 62 Devonian 11, 14, 15 Dikes 29 Diopside 30 Diorite 13 Diphyphyllum 15 Dolomite 36, 60 E Eaglebird claim, discoA'ery of ore on 8 Eclipse claim, discovery of ore on 8 Eclipse mine 44 copper in 31 described 50 faulting in 26, 51 ores of 38 production of 9, 54 reopening of 9 Eilers, A., acknowledgments to 4G quoted 27, 40 Eldridge, G. H., work of 10, 15, 16, 17 Elkington mine 56 Emerson, J. L Gl Epidote 30 Erosion 11 Evening Star mine, described 55 Evening Star tunnel 14 Exchequer claim 65 F Fairplay claim, discovery of ore on s Fairplay mine, described 54 production of 9. 54 INDEX t6 Fairview mine 44 described 49 Farrell, J. L., quoted 51 Fault-fissures, filling in 38, 41 Faulting 2G, 38 relation to ore deposits 26, 40, 42 Faults, ore deposits in 41, 43 F'eldspar 30 Fenestella 17 Fissure veins 39 Folding 23 relation to ore deposits 42, 43 Folds, echelon 24 Fossils 14, 15, 10, 17 Foster. E. LeNeve, cited 10, G7 Fraction mine, described 02 G Galena 34 Gangue minerals 36 Garfield 8 faults near 27 glaciation near 12 quarries 68 underground streams near 28 Garfield mine, described 64 pyrite in 34 Garfield quarry 68 Garnet 30, 36, 38, 41 Geology, economic 31 general 12 outline of 11 Giant-Eclipse Mining Company 44, 54 Gimlet, E., quoted 61 Girty, G. H., acknowledgments to 15 cited 16, 17 Glaciation 11, 12, 22 Gneiss, granitic 12 Gold 33 Golden Age mine, described 66 Gossan 39, 62 Granite 12,19 Gray, work of 8 Great Monarch claim, discovery of ore on 8 Great Monarch mine 44 described 54 Ground water level, ores below 42 reached - 44 H Halysites 15 Hamilton, D. F., acknowledgments to 49 Harrington 64 Hawkeye mine, described 50 overturn in 24 wulfenite in 35 Hayden survey, work of 10 Heliolites 15 Hematite > 34 Henderson, Junius, work of 7, 15 Hercules tunnel 68 chalcocite in 32 74 INDEX History 8 Hoffman Park 21 mines of 66, 68 Hornblendite 13, 14 Hubbard, L. W 68 Hubbard, T. N 65 I Igneous intrusion 29 Igneous rocks 17 Independence tunnel, dike in 13, 65 ores of 38, 65 Indianapolis mine 65 Ingersoll mine 56 hematite near 34 J Jay, C. H., acknowledgments to 54 Jewell claims, mimetite on 35 Jewell Tunnel & Mining Company 5G, 65 Jewett, W. K., quoted 68 Jointing 28 K Kangaroo Gulch, mines of 68 Kindle, E. M., cited 16 Kuter claim 55 L Lake Fork 22 Landslides 22 Last Chance mine 56 described 62 faulting in 27 Latite 21 Latite porphyry 21 Lead minerals 34 Lilly mine 40 described 56 faulting in 38 fold near 44 increasing output of 9 mimetite in 35 ore deposits 41 ores of 32, 33, 36, 38 ore shoots of 37, 40 Limestone, carboniferous 15 Devonian 15 for flux and sugar refining 68 pre-Devonian 14 Limonite 34, 39 Lindgren, W., quoted 39, 43 Literature 10 Litigation 9 Little Charm mine, described 55 ores of 32, 35 Little Chief claim 55 Little Wonder mine 44 anglesite in 34, 35 described 55 INDEX 75 M Madonna claim, discovery of ore on 8 Madonna fault 27 Madonna mine 10 copper in 31, 33 described 44 No. 6 Tunnel, landslide near 23 ores of 32, 34, 38, 40, 41, 42 overturns in 24 production of 9, 47 recent discoveries in 9 Magnetite 30 occurrence of 12, 34 Major mine, described 63 ores of 38 Malachite 33 Manganese minerals 35, 61 Marble 69 origin of 30 Mason mine, country rock of 22 recent discoveries in 9 Maverick tunnel 68 Mayflower fault 27 Melaconite 33 Metamorphism 11, 13, 14, 29, 30, 38, 41 Middle Fork 12, 22, 23 Miller, Wm., quoted 56 Mills 31 Mimetite 35,42 Mineralogy of the ores 32 Mines, description of 44 Missouri Boy claim, discovery of ore on 8 Missouri Boy mine, described 64 ores of 38 Mockingbird claim 65 Monarch 8 glaciation near 22 spring at 28 Monarch Hill, dip of sedimentary rocks on 24 faults of 26, 27 landslides on 23 mines of 44 mining claims 45 ore deposition on 26, 41, 42 ores of 31, 32, 36, 40, 43 pyrite of 34 Monarch-Madonna Mining Company 46 Monotrypella 16 iMoose mine, recent discoveries in 9 Mount Aetna 8, 22, 23, 29 fissure veins of 39 Mountain Chief claim, discovery of ore on 8 Mountain Chief mine 65 described 61 ores 38 N New York claim, ores of 36 zinc ore on 31, 38 North Fork, glaciation in 12 ore on 8 Norway, W. F., acknowledgments to 58 7