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PHYSICAL SCIENCES LIBRARY - / UC DAVIS i GEOLOGY AND ORE DEPu^i i S OF THE BODIE MINING DISTRICT MONO COUNTY, CALIFORNIA .... JUi ^5 !^B' \ CAl-!F, 0€?»©S BULLETIN 206 THE RESOURCES AGENCY GORDON K VAN VLECK SECRETARY FOR RESOURCES STATE OF CALIFORNIA GEORGE OEUKMEJIAN GOVERNOR DEPARTMENT OF CONSERVATION RANDALL M. WARD DIRECTOR DIVISION OF MINES AND GEOLOGY JAMES F DAVIS STATE GEOLOGIST ■-^v GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT MONO COUNTY, CALIFORNIA By Charles W. Chesterman Rodger H. Chapman and Cliffton H. Gray, Jr. DIVISION OF MINES AND GEOLOGY 1986 Jy ^-'^^JM^ UNIVERSITY OF CAUFORNIA DAVIS Jl'L 1 5 1SB7 CALIF. DEPOS. GOVT. DOCS. -LIBRARY BULLETIN 206 California Department of Conservation Division of Mines and Geology 1416 Ninth Street, Room 1341 Sacramento, CA 95814 To Francis H. Frederick 1907-1968 CONTENTS Page ABSTRACT yH INTRODUCTION 1 Location 1 Field Work end Acknowledgments 1 Previous Work ■\ REGIONAL GEOLOGIC SETTING 2 Pre-Tertiory Basement 2 Tertiary Rocks 3 GEOLOGY OF THE BODIE MINING DISTRICT 3 Silver Hill Volcanic Series 3 Tuff Breccia 4 Docite Flov^s 5 Intrusive Dacite 5 Chemical Composition 7 Age of Silver Hill Volcanic Series 7 Murphy Spring Tuff Breccia 7 Pyroclastic Deposits 7 Dacite Flows and Plugs 7 Chemical Composition ]0 Age of Murphy Spring Tuff Breccia 10 Potato Peak Formation }q Dacite Flows 10 Tuff Breccia 1 1 Age of Potato Peak Formation 1 1 STRUCTURE H Faults 12 Jointing and Sheeting 14 P'ugs 14 GEOLOGIC HISTORY 16 Structure Interpretation 1^ Tertiary Rocks 1^ ALTERED AND MINERALIZED ROCKS 17 GEOPHYSICAL INVESTIGATIONS !"."!."'I.'".."."!""..! 19 Regional Gravity and Mognetic Dato 19 Detailed Gravity and Magnetic Data 20 Results of the Gravity Survey 21 Results of the Ground Magnetic Survey 22 Summary 24 ECONOMIC GEOLOGY ."..... 24 Standard Hill areo 25 Fortuno Series 25 Incline Vein Series 26 Burgess Vein Series 27 Middle and Southern Mines Area 27 Concordia Vein 27 Red Cloud Vein 27 Oro Vein 28 Base Metal Vein 28 Booker Vein 29 Distribution of Metals in the Veins 29 Depth of Mineralization 3I HISTORY OF MINING AND PRODUCTION 3I SUGGESTIONS FOR PROSPECTING !"!1."!."".""".""."!!"1 33 REFERENCES CITED !!!!!!!!!!!!!!!"!H!!!!!!!!!"I"" 34 APPENDIX: KAR SAMPLE DESCRIPTIONS AND LOCATIONS 35 III ILLUSTRATIONS Plates (PLATES 1-5 IN POCKET) Plate 1. Generalized geologic map of the Bodie mining district and surrounding region. Mono County, California, showing gravity and mognetic profiles Plate 2. Geologic mop of the Bodie mining district. Mono County, California, showing rock alteration zones, residuol gravity, and vertical intensity magnetics Plate 3. Claim mop of the Bodie mining district Plate 4. Mine workings of the Bodie Bluff-Standard Hill area Plate 5. Mine workings of the Southern Mines area Figures Figure 1. Index mop of east-centrol California showing location of Bodie mining district 2 Figure 2. Index to Plates 3, 4, and 5 2 Figure 3. Normative compositions of rocks of the Silver Hill Volcanic Series in the Bodie mining district 9 Figure 4. Normative compositions of lovos from the Murphy Spring Tuff Breccia of the Bodie mining district 11 Figure 5. Normative compositions of dacite lavas of the Potato Peok Formation of the Pototo Peak-Bodie Mountoin areo 13 Figure 6. Polar plot of the faults in the Red Cloud mine 15 Figure 7. Cross section of the vein system of the Standard mine 17 Figure 8. Vertical section through the Fortuna stopes, Bodie mine 18 Figure 9. Face in o stope on the Fortuna vein, Bodie mine 19 Figure 10. East-west section through the Fortuna stope in the north drift no. 1 of the 432-foot level of the Bodie mine showing the cross-cutting age relationships of the Fortuna and Gildeo veins 19 Figure 11. Cross section of the veins of the Incline vein series showing their relationships to the Moyle Footwall fault, Standord mine 27 Tables Table 1. Chemical anolyses and normative compositions of dacite flows and intrusives of the Silver Hill Volcanic Series, Bodie mining district 8 Table 2. Chemical analyses and normative compositions, in percent, of docite flows from the Murphy Spring Tuff Breccia, Bodie mining district ond odjocent area 10 Table 3. Chemicol analyses and normotive compositions, in percent, of dacite flows of the Potato Peak Formation, Potato Peak- Bodie Mountain area 12 Table 4. Magnetic susceptibility measurements of rocks of the Bodie mining district and surrounding orea 20 Table 5. Rock density measurements of rocks of the Bodie mining district and surrounding area 22 Table 6. Production of gold and silver of the Bodie mining district. Mono County, California, from 1860 to 1941 32 Table 7. Production, dividends, and operations of the Standard Consoli- dated Mining Company, Bodie mining district. Mono County, California 33 Photographs Photo 1. View of Bodie in 1932 from Standord Hill 1 Photo 2. View looking southeastward with the White Mountains in left distance. Glass Mountain in middle distance, and the Sierra Nevada in right distance 3 Photo 3. View westward toward Sugarloaf 4 Photo 4. Intrusive dacite of the Silver Hill Volcanic Series as exposed in the face of the Roseklip cut f, Photo 5. View to the southwest of the Bodie mining district 14 Photo 6. View to northwest of central and northern sections of Bodie mining district 1^ Photo 7. Veined ond propylitically altered tuff breccio of the Silver Hill Volcanic Series, as exposed underground in the Bulwer tunnel 20 Photo 8. Fractured ond propylitically altered intrusive docite of the Silver Hill Volcanic Series, as exposed underground in the Bulwer tunnel 21 Photo 9. Ribbon quartz, containing fine-grained gold. Typical of the veins mined in the Bodie Bluff area 23 Photo 10. Ribbon quartz veins in the intrusive dacite near the summit of Bodie Bluff 24 Photo 11. Quartz-breccia zone, containing free gold, 436-foot level of the Bodie mine 25 Photo 12. Fortuna vein, 400-foot level of the Bodie mine 26 Photo 13. Ralston vein, just south of the Bulwer tunnel 28 Photo 14. Argillicolly oltered tuff breccia of the Stiver Hill Volcanic Series, cemented by dork-gray, pyrile-rich chalcedony. 700-foot level of the Red Cloud mine 29 Photo 15. Lent shaft hoist house and office, as they appeared in 1895 30 Photo 16. View of Bodie looking southwest from Stondard Hill. Excavation in foreground in port of large-scale sampling conducted by Yukon-Treodwell Company, Inc. in the spring of 1931 31 Photo 17. View north toward Standord Hill 34 ABSTRACT The Bodie mining district, located in the northeastern part of Mono County, California, was the source of gold and silver valued at more than $34,000,000 between 1860 and 1942. The district is underlain by volcanic rocks, including flows, plugs, ond pyroclostic deposits, principolly of dacitic composition. The oldest rocks ore those of the Silver Hill Volcanic Series, which consists of lovo flows, plugs, ond tuff breccio with minor layers of welded tuff. This sequence is overloin unconformably by lava flows and pyroclostic deposits of the Murphy Spring Tuff Breccia, which, in the southern part of the district, ore intruded by several plugs of porphyritic dacite. Flows and pyroclostic deposits of the Potato Peak Formation unconformobly lie upon units of the Silver Hill Volcanic Series in the northern port of the district. Investigotions of the geochronology of the rocks of the Bodie mining district, using the K-Ar method, indicate that the several units of the Silver Hill Volcanic Series were emplaced 8.6 to 9.4 m.y. ago and, furthermore, that they ore o locol phase of on extensive suite of colc-olkaline volcanic rocks (including bosalt, ondesite, docite, and rhyolite) that were erupted 7.8 to 9.5 my. ago in the region surrounding the Bodie mining district. Volconism ceased in the district and in the region surrounding it, following ore deposition in the district, and did not resume until 5 m.y. ago, when rhyolite plugs intruded rocks of docitic composition west of the district. Four plugs in the district were emplaced into vents from which the lava flows and pyroclostic deposits of the Silver Hill Volconic Series evolved. The largest plug, comprising Bodie Bluff ond Stondord Hill, is the host rock for the quartz veins from which more than 90 percent of the total production of gold and silver wos obtained. The other plugs at the Red Cloud mine. Queen Bee Hill, and Sugarloaf ore smoller in size and contain fewer quartz veins. The two major faults, the Moyle Footwoll ond the Standard Vein, along which movement was both pre- and post-mineral, were responsible for the formation of the grobcn in the Bodie Bluff-Standard Hill plug. Other pre-mineral foults ore the sites of vein deposition. The post-mineral foults, especially the Mono ond the Tioga, did much to offset the veins. Hydrofhermal alteration of the rocks was widespread in the district. Propylitic alteration, which is characteristic of the morgins of the district, occurred first; orgillic and potassic olterotion sequences occurred later and were more pervasive. Propylitically altered rocks ore greenish in color and contain chlorite, epidote, various cloy minerals, albite, pyrite, and minor quortz. The orgillicolly altered rocks ore usually light colored and contain montmorillonite, illite, sericite, quartz, and pyrite. They weather easily and form sparse croppings. The potossically altered rocks ore only locally light colored, and tend to resemble the original rock in color and texture. They show extensive development of odulorio, quartz, sericite, and pervasive, irregular veins of quortz-oduloria, with or without colcite. The silicic olterotion generolly occurred lost. Silica -altered rock is light colored, hard, and forms o capping on argillicolly altered rocks. K-Ar dating of odulorio in the gold-bearing quartz veins and in the hydrothermolly altered rocks indicotes that the alteration-mineralization occurred between 7.2 ond 8.6 m.y. ago and that the hydrofhermal system responsible for the mineralization lasted for about 1.4 m.y. Principol gold-silver production in the Bodie mining district came from severol systems of quartz veins in the intrusive docite plug of the Bodie Bluff-Stondord Hill area. Farther south, in the Silver Hill area, the mineralization wos pervosive, and the gold and silver were recovered from quortz veins ond irregular silicified zones in dacite flows and tuff breccia. The ore minerols include native gold, pyrorgyrite, tetrohedrite, stephonite, ond pyrite. The ratio of gold to silver by weight in the northern port of the district wos obout 1:12, whereas in the southern port of the district the ratio was obouf 1:40. Mining activities ceased in the district in 1942, but interest in the mineral deposits in the district hos not reloxed. The intensely mineralized and mined bononzo zone of the Bodie Bluff Standard Hill area contains numerous narrow, gold-bearing quartz veins that, collectively, may constitute o lorge, low-grade deposit thot would be o fair target for further exploration and development. VII Photo 1. View of Bodie in 1932 from Standard Hill. Photograph by Fronds H. Frederick. INTRODUCTION Location The Bodie mining district (Figures 1 and 2), in which the mines and the now famous ghost town of Bodie are situated, is in the southern part of the Bodie Hills in northeastern Mono County. The two routes leading to the Bodie mining district from State Highway 31 and US Highway 395 are graded dirt roads that are usually closed durmg the winter. The B(xiic mming district, as originally defined in 1860, "shall extend in each direction from the Bodie claim, north, south, east and west, five miles" (Hakes, 1902). For many years, however, the Bodie mining district (Plate 1 ) has been confined to a nar- row tract of mountainous land which measures about 3 miles long and one mile wide, roughly encompassing a north-trending, ridge-hke feature. At the northern end, Bodie Bluff, the highest peak in the district at 9,(XX) feet in elevation, stands some 600 feet above the Bodie townsite. The southern end of the district is about one mile south of Sugarloaf, a conical shaped peak which is a prominent landmark of the area. Bodie Creek drains the area and flows throughout the year down Bodie Canyon. Field Work and Acknowledgments Most of the 1968 field season was spent by Chcsterman and Gray making a detailed geologic study of the Bodie mining district. R.H. Chapman made detailed magnetic and gravity surveys. Fortunately, several of the long-inaccessible mine tun- nels had been reopened in 1968 for prospecting, making it possi- ble for the writers to make limited observations underground and to collect samples of rock and ore for laboratory study. All geologic field work was plotted upon enlarged aerial photo- graphs and transferred to a topographic base, scale 1:4,800, which had been compiled in 1931 from a survey made by D.W. Ormsbee. M.L. Silberman of the U.S. Geological Survey assisted in the collection of rock and mineral samples for age dating and geo- chemical studies, and to him are tendered special thanks for making readily available all analytical data from the laboratories of the U.S. Geological Survey. The writers are especially grateful to the late E.W. Billeb of the J.S. Cain Company for making available unpublished notes and maps and for his many helpful suggestions and discussions. The late F.H. Frederick permitted the use of his maps as part of his long-continued interest in the district. Previous Work The Bodie mining district was organi/ed in I860, and several reports about il have appeared in various technical journals since that time The earliest, perhaps, of the published rep<irts is by Joseph Wasson (1879), who obtained much of his information from visits to the district and from early investigations made by Blake (1863, p 17), Silliman (1864, p 13-15). and Browne ( 1 864, p. 17-18) Wasson's report was made for members of the New York Bullion Club and received limited circulation Mel- ville At wood ( 1879, p. 169) examined wall nxks from the mines CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 Figure 1. Index map of east-central Californio showing location of tfie Bodie mining district. at Bodie and reported his Findings before the California State Geological Society. Toward the middle of the 1880s, H.A. Whiting, superintend- ent of the Bodie Consolidated Mining Company, made an exten- sive study of the mines at Bodie and published his report in 1888 (Whiting. 1888, p. 382-401). In the early 1900s, several investi- gations were made of the district; notable among these are stud- ies by R.P. McLaughlin (1907, p. 795), R. Gilman Brown (1907, p. 343-357), and AS. Eakleand R.P. McLaughlin ( 1917, p. 143-160). Much later still, Al-Rawi, then a graduate student at the University of California, reported upon the age of mineral- ization at Bodie (1968, p. 30). REGIONAL GEOLOGIC SETTING The Bodie Hills (Plate 1) comprise a complex mass of late Tertiary volcanic rocks (KleinhampI and others, 1975) which consists of lava flows, tuff breccia, and intrusive dikes, plugs and domes that were erupted from well-defined vent areas. The rcx'ks range in composition from rhyolite to basalt, and those of dacitic and andesitic compositions are most widespread and volumi- nous. The oldest volcanic rocks in the Bodie Hills, range in age from II to 29 m.y., consist of andesite, dacite, and rhyolite. and occur principally in the northeastern part of the area. These older volcanic rocks are overlain unconformably by ash tlow luff units that are mildly to intensely welded, but lixally non-welded, and include conspicuous black to dark brown vitric zones. They are trachyandesitic in composition and have an average age of 9.4 my. Pre-Tertiary Basement R(Kks older than Tertiary are not exposed in the immediate area surrounding the Bodie mining district, but in adjacent areas Figure 2. Index mop showing locotion of plates 3, 4, and 5. to the west and northwest, the Tertiary volcanic rocks rest un- conformably upon pre-Tertiary metamorphic and granitic rocks that crop out usually as islands in the lava flows and pyroclaslic deposits (Chesterman and Gray. 1966; Chestcrman, 1968; and Chesterman and Gray. 1975) The metamorphic rivks include gneiss and schist of pre-Cretaceous age (Koonig. 1963) at Ma- sonic Mountain. 12 miles northwest of Bodie. and quarizofeld- spathic hornfels and greenstones of Paleozoic(?) and Mcsozoic(?) age (Chesterman. 1968) cast and northeast of Con- way Summit, 12 miles southwest of B<')dic. Granitic bodies iKCur in the Bixiie Hills and are generally found intrusive into the pre-Cretaccx)us metamorphic rocks. East of Conway Summit, there is a body consisting principally of biotile granite which has a Cretaceous age of 93.4 my (Chester- man, 1968). Masonic Mountain, that is at the northern end of 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT Photo 2. View looking southeastward, with the White Mountains in left distance. Glass Mountain in middle distance, and the Sierra Nevodo on the right distance. In the middle-ground ore Bodie Townsite (B) , Bodie Bluff (BBj , Stondord Hill (St. H| , Silver Hill (SH) , lookout Peak (LP), Queen Bee Hill (QH) ond Sugorloof (S). Photograph by Norman F. Prine, U.S. Geological Survey. the Bodie Hills, is underlain by a body of granitic rock whose composition ranges from granodiorite to quartz monzonite. This body is presumed to be pre-Cretaceous in age (Koenig, 1963). A sample, referred to as black chert possibly altered from some underlying sedimentary formation, is said to have been collected at a depth of about 500 feet in mine workings near the Lent shaft (McLaughIm, 1907, p. 795) (Plate 2). Specimens of a fine-gramed, dense, dark gray to black rock were collected from the waste dump of the Dudley shaft. Presumably this is the underground workings to which McLaughlin referred. A micro- scopic examination of specimens of this material collected by the writers indicates that the rock is a well-indurated, fine-grained phase of welded tuff There are several outcrops of the welded- tuff phase of the Silver Hill Volcanic Series in the district, and It seems most likely that the malenal from the Dudley shaft is from a layer of this welded tuff that was encountered under- ground in the Dudley mine. Tertiary Rocks The most widespread volcanic rocks of the Bodie Hills consist largely of lava flows, tufT breccia, and intrusive plugs of dacitic composition, although lava flows, lufTbreccia, and intrusive bod- ies of rhyolilic, andesitic, and basaltic compositions arc present. Several small plugs of rhyodacilic composition iKcur near the mining district These rcK-ks form a blankcl-likc deposit and include the Mount Biedcman and Potato Peak Formations, the Murphy Spring TufT Breccia, and the Silver Hill Volcanic Series (Chesterman and Gray, 1966). Their range in age is approxi- mately 8.6 to 9.4 m.y. Lying unconformably upon the late Miocene volcanic rocks are lava flows of andesitic and ba.saltic composition of the Cedar Hill-Trench Canyon complex (Al-Rawi, l<}69). Their range in age is 2.2 to 3.6 m.y. GEOLOGY OF THE BODIE MINING DISTRICT Rocks of the Bodie mining district (Plate 2) include extrusive and intrusive lavas and pyrtKlastic deposits of the Potato Peak Formation and Murphy Spring Tuff Breccia (Chesterman, 1968, p. 51-60) and of a unit referred to as the Silver Hill Volcanic Series (Chesterman and Gray, l'>66, p 14), all of which appear to range in age from 8.6 to 9.4 my. (Silbcrman and others, 1972, p. 601). Silver Hill Volcanic Series The riKks of the Sihcr Hill Volcanic Series (Chesterman and Gray, 1966, p. 14) crop out extensively in the liodie mining district. They consist of inlerlayered lava flows and lufTbreccia, and intrusive plugs, and are named after Silver Hill, a small hill near the center of the district (Plate 2) Outcrops of thi-sc rcKks that show contacts are nol common, but their relationships arc well exposed in underground mine workings. It appears (hat luff CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 i .ji» -(> ^ r* '^^''iWf _^ •-»^» ^^M^ •>^/. ,-J*^%^ Photo 3. View westward toword Sugorloof, o plug of docite of the Silver Hill Volconic Series ot the southern end of the district. Snowcapped Sierra Nevada in distance. breccia layers were deposited and are overlain by lava flows and more layers of tuff breccia. The principal tufT breccia layer, which underlies a large portion of the district, is about 400 feet thick. Remnants of a thinner tuff breccia layer caps Silver Hill and occupies the small graben near Standard Hill; it has been extensively altered and probably is no more than 150 feet thick. Several flows are exposed on the surface, and some are ex- posed in mine workings, especially the deeper ones. One compos- ite flow in particular, which underlies much of the district, is between 500 and 700 feet thick and appears to be composed of two units. The upper unit is biotite-nch dacilc and the lower unit is hornblende-rich dacite. The contact between the two was not observed. Four plugs of dacite intrude the tuff breccia layers and flows of the Sliver Hill Volcanic Series. The largest plug (xcurs at the northern end of the district and makes up the bulk of the rocks that form Bixlie Bluff and Standard Hill (Plate 2) The other plugs are near the Red Cloud mine, al Queen Bee Hill and at Sugarloaf (Plate 2) These plugs are composed of hornblende dacite and are probably connected at depth. In general, the sequence of pyriKlastic deposits and inlerlay- ered lava flows dips from 5 to 15 degrees in a southerly direction except near the plugs where they dip outward al steefwr angles. TVff BRECCIA Throughout much of the Bodie mining district the rocks of the Silver Hill Volcanic Scries are difficult to discern because Ihcv have undergone alteration. The tuff breccia is best exposed in scattered exposures at the north end of the district, where a stratigraphic section consisting of about 200 feet of pyroclastic rocks was studied and measured The basal unit is gray luff breccia which is massive and sufTiciently indurated to form low cliffs. It has indistinct layering and consists of angular and subangular blocks of dark- and light-colored dacite from a few inches to several feet across enclosed in a matrix of volcanic ash and mineral grains. At least 125 feet of this basal unit is exposed. The basal, gray tufT breccia is overlain unconformably by a layer, from one to 60 feet thick, of well-induraicd, buff-colored tufT breccia which is massive, ptwrly layered, and consists of angular fragments of tan-colored tuff breccia. Grading into it is a layer of black welded lutT. which ranges in thickness from 4 to 6 feet. The welded tuff has been referred to by various people as obsid- ian, and in color, texture, structure, and nuxle of ivcurrence it resembles other layers of welded tufflhat (Kcur in several of the volcanic formations in the Btxiie Hills (Chesterman, I'JbS, p. 49-5.'') At Us contact with the underlying luffbrcccia the welded luff IS dark brown, and the color transition from dark welded tuff to buff-colored tuff breccia is gradual. The welded tuff is dense, has a well-developed vitroclaslic texture, and consists of angular and rounded fragments of light to dark gray and dark brown porphynlic dacite enclosed in a dark gray, fine-grained groundmass streaked with black glass. The lithic fragments rarely cxcecxi several inches in diameter, and Ihe average size is less than one-half an inch The dacite clasls contain euhedral phenocrysts of glassy while plagiocla.se 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT (An ivio). black hornblende, and deep-brown biotite. A small mass of dark gray to black welded tufT crops out in the eastern part of the district, about 700 feel southeast of the Defiance shaft (Plate 2). It is completely enclosed in I utT breccia overlain by hornblende-rich dacile, all in a triangularly shaped fault block. Still larger and more prominent outcrops of the welded tuff are exposed in the walls of Milk Ranch Canyon in the northwestern part of the study area. Although outcrops of the black welded luff are neither very large nor abundant, it is apparent from their distribution that the rock cmered nuich of the Bodie mining district. Much of the pyroclastic riK-k of the district probably was derived from vents in the district, which are now sites of plugs, and because of the lack of sorting and layering, they suggest a lahar mode of deposition. Lying above the black welded tuff in what appears to be a conformable relationship is a sequence of weakly indurated tuff breccia layers. Because of scarce and inadequate exposures of this sequence of tuff breccia layers, it was not possible to ascer- tain its thickness or structural characteristics. It is composed of angular and subangular blocks and fragments of medium-gray dacite, ranging in diameter from a few inches to one foot and enclosed in a matrix of fine-grained volcanic ash and mineral grains. The sequence of upper tuff breccia layers is unconforma- bly overlain by mtxderately indurated and layered tuff breccia of the Potato Peak Formation. The clasts in all of the tuff breccia layers, except the black welded tuff, range in color from light and medium gray to brown and tan. The rock is principally hornblende dacite in composi- tion and contains phenocrysts of black hornblende and glassy white plagioclase enclosed in a fine-grained, light gray ground- mass of plagioclase, hornblende, minor biotite, and devitrified volcanic glass. DACITE FLOWS Based on sparse information from records of extensive mining operations in the district, several fiows of dacite, separated by relatively thin interlayers of luff breccia, were encountered in shafts. In the Lent shaft (Plate 2), which extended to a depth of 1,200 feet below its collar elevation of 8,422 feet, a layer of dacite about 8 feet thick was encountered at a depth of 650 feet. Composite Flow A composite flow covers much of the district and is exposed in many of the mine workings. The composite flow is made up of two rather distinct units: The upper unit is biotile-rich dacite and the lower unit is hornblende-rich dacite. Because of the lack of adequate exposures, it was not possible to ascertain the thick- ness of the composite How or to delineate its individual units and their contact relationships, but it is estimated that the thickness of the flow is between 5(X) and 700 feet. The interrelationship of the two units is constant throughout the district. Exposures of unaltered units of the composite flow are uncom- mon, primanly because of extensive hydrothermal alteration of the rocks, but relatively unaltered samples were obtained on the south side of Queen Bee Hill and in the underground workings of the Red Cloud mine (Plate 2). The lower hornblende-rich unit has well-developed platy jointing and conspicuous necdie-like. black crystals of horn- blende. The upper biotite-rich unit lacks the platy structure but shows blix'ky jointing, conspicuous black crystals of biotite, and an equigranular appearance of the plagioclase phenocrysts. LOWER UNIT. The hornblende-rich dacite is light gray, por- phyritic, and contains phenocrysts of plagioclase and hornblende enclosed in a fine-grained groundmass of mineral grams, niicro- phencKrysIs of biotite, and partly dcMtrified volcanic glass. The plagiiK'lase, with phenocrysts of euhedral and subhedral grains, ranges in composition between intermediate and calcic andesine (An„,^), and shows multiple twinning and oscillatory zoning. It is remarkably fresh in spile of the generally slightly altered con- dition of the rock, and it constilulcs about 60 percent of the phenocrysts. The hornblende is light brown and greenish-brown, is weakly pleochroic, and occurs in euhedral and subhedral grains, of which the larger are partly resorbed and the smaller are com- pletely resorbed, leaving residues of tiny grains of black iron oxide. The hornblende constitutes about .^0 percent of the pheno- crysts. Biotite is dark brown in color and strongly pleochroic from Ian to dark brown. It is in euhedral and subhedral grains, all of which are resorbed to varying degrees. The biotite consti- tutes about 10 percent of the phenocrysts. The groundmass constitutes about 30 percent of the rock It consists of plagioclase microlites which show simple polysyn- thelic twinning and are probably sodic andesine in composition. They are unaltered and (K'cur with microphenocrysts of horn- blende and biotite in partly devitrified volcanic glass Samples of altered hornblende-rich dacite from the under- ground workings of the Red Cloud mine (Plate 2) and from outcrops elsewhere in the district illustrate very well the types and degrees of hydrothermal alteration to which the rock has been subjected. UPPER UNIT. The biotite-rich dacite of the upper unit ranges in color from pale gray to pinkish gray. It is porphyritic and contains phenocrysts of dark brown biotite, scarce black horn- blende, and glassy-white plagioclase enclosed in a fine-grained groundmass. Phenocrysts make up about 60 to 65 percent of the rock. The plagioclase phenocrysts are in euhedral and subhedral grains, which occur singly or in clusters. They show multiple twinning, oscillatory zoning, and range in composition between sodic and intermediate andesine (An^M,,). Alteration is present in the large phenocrysts and manifests itself as a narrow zone immediately beneath a clear glassy rim on the grain. The plagio- clase phenocrysts constitute from 40 to 50 percent of the pheno- crysts. The groundmass plagioclase is in small microlites that show simple polysynthetic twinning, and has a composition of sodic andesine. Sanidine occurs as small rectangular-shaped euhedral grains which show simple carlsbad twinning. The grains are skeletal and have dark shadowy interiors. They are not altered and con- stitute about 5 percent of the rock. The femic minerals are generally resorbed. Relatively fresh biotite occurs in dark brown, strongly pleochroic euhedral grains which constitute ab<iul .10 to 40 percent of the phenocrysts. Hornblende is subordinate to the biotite, and where it is incom- pletely resorbed it (xcurs as deep-green euhedral and subhedral grains which are weakly ple(x;hroic. The groundmass gla.ss is usually pinkish-Ian in color and somewhat devitrified. It constitutes aboul .15 to 40 percent of the rock. INTRUSIVE DACITE Aside from dikes, which crop out rarely but were cncounlcrcd in mines, the bulk of the intrusive dacite occurs in plugs. The dacile shows well developed fiow banding, especially near con- tacts with wall rocks, and shows a range in color from pale gray CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull 206 li^ Photo 4. Intrusive doclte of the Sliver Hill Volcanic Series as exposed in the face of the Rosekllp cut, on the south side of Standard Hi! Photograph by M.L. Silberman, U.S. Geological Survey. to medium gray, rarely pinkish (Photo 4). The dacite is porphy- ritic with phenocrysts of hornblende occasionally up to 10 mm in length and plagioclase as much as 5 mm across; biotite. when abundant, tends to form cuhedral plates as much as 3 mm across. The phenocrysts range in amount from 40 to 80 percent of the rock. The groundmass is fine grained and generally contains from 10 to 15 percent volcanic glass that is more or less devitri- fied. The plagioclase, which constitutes 40 to 60 percent of the phenocrysts, occurs as euhedral to subhedral grains which show multiple twinning and complex oscillatory zoning. Their compo- sition range is from sodic to intermediate andesine (Anl^„). Many of the larger euhedral-shapcd grains show considerable alteration, generally as a narrow zone of calcite and scricite surrounding an unaltered core and rimmed by a narrow zone of clear, glassy feldspar which lacks twmning and has an extinction position different from the interior feldspar. Inclusions of vol- canic glass commonly form a narrow zone immediately beneath the clear glassy rim of the grain. Other inclusions include femic minerals and magnetite. Sanidinc phenocrysts. as much as 3 mm across, are common in the dacite that forms the eastern part of the plug at Btxlie Bluff, and constitute about 40 percent of the phenocrysts. They are euhedral. gla.vsy where unaltered, and show carlsbad twins. Altered sanidine phenocrysts contain carbonate and sericite. Feldspar in the groundmass. which constitutes about 20 per- cent of the rock, is sodic andesine and sanidme. The sodic ande- sine occurs as small lath-shaped grains and as microlites which show simple polysynthetie twinning and are generally unaltered. The sanidine is in rectangular-shaped crystals which are com- monly uniwinned and generally unaltered. Phenocrysts and microphenocrysts of bioiite and hornblende are largely resorbed and altered, but unaltered phenocrysts are dark brown in color and strongly pleochroic. The strongly re- sorbed femic phenocrysts arc represented by residual accumula- tions of small black grains of iron oxide. Partly rcs<irbed grains contain the residual iron oxide grains, calcitc, and the unaltered mineral. Apatite and magnetite occur as inclusions in the unal- tered biotite The femic minerals comprise generally 10 to 40 percent of the total phenocrysts. Apatite and sphene are accesso- ry minerals. The volcanic glass is usually completely devitnfied to crypto- crystalline and microcrystalline aggregates. Tridymite occurs as small, wedge-shaped, twinned crystals, but it is rare. The intrusive dacite of the Bodie Rluff-Slandard Hill plug (Plate 2) has undergone p«itas.sic alteration as well as livally intense argillic alteration (sec section on hydrolhcrmal altera- tion). 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT CHEMICAL COMPOSITION The lava flows of the Silver Hill Volcanic Series in ihe Bodie mining dislnct have a range in composition from iatite-andcsitc through latite and dacite to rhyodacite. Fourteen chemical anal- yses, available through the U.S. Geological Survey, are given in Table I. Norms were calculated for these rocks and plotted on a Streckeisen diagram (Figure }). The spread of points on the diagram reflects the alteration effects on the rix;ks. RiKks of the plug at Bodie Bluff-Standard Hill, in spile of iheir apparent freshness, have undergone considerable potassic alteration; the added potassium shows up principally in the groundmass. The comp<isite flow, of which analysis 12 is from the upper biotite- rich unit and analysis 13 is from the lower hornblende-rich unit, appears to be fairly constant in chemical comptisition. regardless of its two-phase division on a basis of mineralogical composition. AGE OF THE SILVER HILL VOLCANIC SERIES Biotite and hornblende separated from plugs and flows of the Silver Hill Volcanic Series have been dated by the K-Ar method. The flows have ages ranging from 8.8 i .2 m.y. to 9.1 ± .5 m.y., and the plugs have a range of 8.3 ± .4 my. to 9,2 ± .5 m.y. (Silberman and others. 1972. p. 601). Murphy Spring Tuff Breccia Lava flows and pyroclastic deposits of the Murphy Springs Tuff Breccia (Chesterman. 1966. p. 51-52) crop out extensively in the southern part of the Bodie mining district. The formation consists of flows and plugs of dacite and tufT breccia of dacitic composition. The pyroclastic member of the Murphy Springs TufT Breccia in the district consists pnncipally of tuff breccia and minor luff layers. The tuff breccia in the vicinity of Sugarloaf (Plate 2) has a maximum thickness of about 750 feet. The source vents for much of the pyroclastic deposits in the district are at the south- ern end of the district, where the tuff breccia dips steeply away from central plugs of dacite. The dip of the layenng in the tuff breccia flattens greatly and is generally in a westerly direction. Individual lava flows cannot be traced for more than a few hundred feet because of poor exposures, but they tend to range in thickness from a few feet to several tens of feet. Several flows in the low hill west of Sugarloaf. which contain very little inter- layered fragmenlal or pyroclastic material, have an aggregate thickness of about 375 feet; on the northwest slope of Lookout Peak, just within the distnct. the dacite lava flows have an aggregate thickness of at least 450 feel. Flow banding within the flows locally dips in many directions, but in general the flows tend to have a low to moderate dip to the west and southwest. PYROCLASTIC DEPOSITS The luff breccia is a ma.ssivc rock in which layering is most distinct near the source vents. Exposures of luff breccia arc scarce, principally because of removal by erosion, but the pres- ence of the rock can easily be ascertained by the large number of small rock fragments and angular boulders up to 5 feel across lying on the surface Tuff breccia exposed west of Sugarloaf can he divided into a gray luff breccia unit and an underlying brown luff breccia. The color of the clasts contained in the two units is the ba,sis for Ihe division. The gray tuff breccia appears to be restricted lo this small area, whereas the brown luff breccia is widely distributed Tlie gray tuff breccia lies unconformably upon the brown luff breccia, and is estimated lo be approximately 170 feet thick Layering is indistinct in the rock, but indications are that the general dip of the unit is toward the southwest at a low angle. The clasts are pale lo medium gray in color and occur as angular lo subangular btiulders and fragments that range in size from a few inches to several feet across, enclosed in a matnx of pale gray rock, mineral fragments, and volcanic ash. The clasls are com- prised of porphyritic hornblende dacite. in which phenocrysis of black hornblende, glassy feldspar, and scarce black biotite are enclosed in a fine-grained matrix of plagioclase and partly devi- trified volcanic glass. Hornblende compnses about 40 percent of the phencKrysts. It occurs in euhedral grains which are pleo- chroic from dark brown to greenish brown. A few of the grains are partly resorbcd and contain granules of iron oxide concen- trated at the central part of the host grain Plagioclase (Ann,,) constitutes about 40 percent of the phenocrysis. It occurs as euhedral to subhedral grains which show multiple zoning, inclu- sions of volcanic gla.ss, and evidence of re-solution during a complex cooling history. The interior part of some of the larger plagioclase phenocrysis are altered to carbonate and kaolin, which are surrounded by a rim of glassy feldspar. Black biotite is in euhedral phenocrysis that are strongly pleochroic and part- ly resorbed. The groundmass plagioclase is in the form of small euhedral and subhedral lath-shaped grains which are more sodic in com- position than the plagiocla.se phenocrysis. Excepi for the groundmass plagioclase and microphenocrysts of hornblende and minor biotite, the remainder of the groundmass is cloudy, partly devitnfied volcanic glass. The clasts in the brown tuff breccia unit are hornblende dacite, angular and subangular, and range in size and shape from sharp angular fragments several inches across to large angular blocks as much as 5 feet in diameter. The average clast size is ab<iut one fool. Near Ihe source vents, this tuff breccia unit has distinct, massive layering with individual layers that range in thickness from several feet to several lens of feel. The clasts range in color from dark reddish-brown to pale pinkish-brown The rock, similar petrographically lo the dacite in the gray tuff breccia, is porphyritic and contains phenocrysis of basaltic hornblende and plagitKlase enclosed in a fine-grained, microcryslalline and glassy groundma.ss. The basaltic horn- blende IS strongly pleochroic, from pale yellowish- to deep golden-brown, and is the principal contributor lo Ihe color dis- tinction between the clasts in the two tufT breccia units. The groundmass has a pale pinkish-yellow color due to the secondary limonite which contributes to Ihe overall color of the rock. The color of the scarce biotite is deep golden brown, identical to that of Ihe basaltic hornblende. Because Ihe clasts in Ihe two luff breccia unils arc hornblende dacite and differ only in the type of hornblende, one can assume that the brown dacite was extruded at a higher temperature than was ihc gray dacite. and that Ihe color differences are due princi- pally lo the presence of brown basaltic hornblende and brown colored glass in Ihe brown dacite. The pyrix-lastic deptisits of the Murphy Spring TufT Breccia lie unconformably upon unils of the Silver Hill Volcanic Series. DACITE FLOWS AND PLUGS I^va flows of the Murphy Spring Tuff Breccia arc dacitic in composition and crop out principally in the s<Hilhern and s<iuth- caslcrn parts of the Hodic mining dislnct The thickness of indi- vidual flows within the district could not be measured, but several flows outside the dislnct on the south flank of Ltxikoul Peak (name applied by Icxral residents), the west fiank of which lies within the district, range in thickness from 10 to 20 feel CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 Table 1. Chemical analyses and normative compositions, in percent, of the docite flows and intrusives from the Silver Hill Volcanic Series in the Bodie mining district. CHEMICAL ANALYSES 10 11 12 13 14 SiO, A 1,0, feA, FeO MgO CaO Na,0 K,0 T-0, PA MnO ZrO, CO, Total 63 67 6866 6211 6383 6266 62 14 6152 60 30 62 44 6115 66.23 64 15 64 20 6407 1602 1453 1710 1621 1692 1721 1659 1678 1744 1733 16.31 1649 1738 1662 260 361 4 70 280 300 360 233 342 331 332 280 4.00 422 350 ISO 032 020 140 150 1.60 2.33 161 120 171 100 052 036 068 220 052 130 220 240 2.00 263 2.81 190 222 160 190 0.95 120 3.30 076 19 250 4 10 430 476 5.33 321 463 340 380 342 400 3.00 231 031 3.50 360 450 364 3.22 401 403 350 360 392 400 511 7.32 10.91 4.60 310 230 2 73 251 261 272 340 300 3.21 340 135 120 240 201 1.42 1 11 129 281 281 1 71 085 150 1.21 1.40 062 053 056 056 071 080 070 073 067 074 050 062 071 069 026 023 019 025 029 035 030 034 031 033 025 026 038 032 006 004 009 009 004 007 13 009 10 O10 010 004 004 000 0.00 000 005 004 1 11 006 008 006 0000 100.00 10000 10000 100.00 100.00 100.00 100 00 100 00 10000 10000 10000 10000 10000 NORMATIVE COMPOSITIONS Ouanz Corundum Onhociase Albile Anorlhile Wollaslonile Enslalile Ferrosilile Magnetite Hematile llmenile Rulile Apatite Calcite Total Salic Femic 16923 25.492 0167 1989 30170 43 421 25413 19 508 14689 2273 5485 1298 0245 3.774 3609 1 179 0677 0175 0616 546 98662 98808 87 363 92 504 11.299 6305 18.051 17104 16034 19056 17390 20316 15.007 24039 21739 21438 18.465 1633 0534 0421 2304 2936 0.125 1419 1229 2159 27 193 18335 13599 16144 14847 15400 16.074 20.100 17714 18997 20114 29 628 32183 38101 30 823 27214 33 925 34 099 29.628 30438 33153 33 884 10.457 18462 18804 14574 23 940 106 13882 20.819 14861 16634 14 451 17317 0.032 5 481 5983 4984 6552 1330 7008 4 743 5520 3986 4 728 2377 2992 3 184 3073 2070 3374 0605 0883 1.554 3483 2.225 3717 2101 0^05 0323 1.064 1.350 1520 1326 1.015 1773 0.761 1352 3.855 4.219 3.281 1.393 1275 1397 O950 1 177 0850 1312 0592 0688 0830 0719 0809 0736 787 0592 615 0266 759 0114 0091 2531 0137 0182 0904 137 98 003 98 595 98 908 98 731 97 205 97 211 98 306 99.164 98516 98815 98615 86936 86619 86959 82.899 83.391 86459 86124 90045 87 753 90198 89 781 11040 11.976 11949 15832 13815 10752 12 192 9118 10 762 8616 8835 (BH-27I*) Homb)endc-bioiited«aierrcpfT) theinirusiveda' cue of lh« Silver Hill Vokanic Senes of ihe Bodie BlufT- Sundard Hill plug^ colkcled from Ihe dump of (he New Standard thaft in ihe ioulh central p«n of Sec 9. T4N. R27t (BH-272) Hornblende btolite dacitc Trom the intrusive da- cite of the Silver Hill Volcanic Senes of the Bodie BlufT Standard Hill plu^ collected Trom a thallow prospect pit at Ihe lummil of Bodie Bluff in the central pan of Sec. 9, T4N. R27E (II4G-1) Biolile-hornbtende dacile from the intrusive da- cile of Ihe Silver Hill V<ilcanic Ser»e» of the B<xlie BlufT Standard Hill pluf. cotleclcd from ■ tunnel near the vtuth- ern margin of Sec 10. T4N. R27K, abtml one -quarter mik Mnilhwetl of the Gray Mill (ll^Wi B) Hornblende dacile frimt Ihe inlruiive dacile of Ihe Silver Hill Volcanic Senc* of the Bodie BlufT-Slandard Htll plug, collected from the M)-called Rineklip cut in vKilh tenlral part of Sec 9. T4N. R27K (III I 17) Hotnhlende ila«.iir from the iniru\ue d»i lie of ihr Silver Hill Vokanic Sene% of the Quern Bee Hill plug, col Iccled near the tummit of Queen Bee Hill m (he «ve%ucntral pan of Sec 21. T4N. R27E (8H J0> Hofnbkttdebiolile dacite from the homblcfMle- rxh unit of the compoulc tUrm of the Silver Hill VokanK Senea. collected near (he eutcm bour»dary of Sec 20. T4N. R27E 7 (BH-273) Homblende-biolite dacile from the intrusive da- ate of (he Silver Hill Volcanic Senes of the Queen Bee Hill plug, collected on the nonh ude of Queen Bee Hill in (he we»t central pan of Sec 21. T4N. R27E 8 (BH-I$) Biot lie- hornblende dacite from a lava fV>w of Ihe Silver Hill Volcanic Senes. collected in (he nonh ccnlral pan of Sec 21. T4N. R27E. about 300 feci u>uthe»tcrly from the Red Cloud ihaD ** (S# 1 ) Homblende-btotitc dacitc from the intrxuive Silver Hill Volcanic Senes of the Sugartoaf plug, collecled at the summit of Sugafloaf in the touthwcst quaner of Scc- 21, T4N. R27E. 10. (BH-26) Homblende-biolilc daate from the intrusive Silver Hill Volcanic Senes of ihe Sugarloaf plug, collecled from the nonh slope of Sugarloaf in the loulhwcst quaner of Sec 2 1 . T4N. R27E- 11 (S36I0) Btotitc-honiblende dacitc of the Silver Hill Vol- canic Senes from a small intrusive plug, collecled jusi out> tide (he Bodie mining disinci in the wcsi central pan of Sec 1 7. T4N. R27E. On the basu of cbcnucal compositton and abundance of biotKc. (he rock might be considered as rhyodaate. 12 (Lilac) Honiblende daalc from the homblende-rKh unit of (he composite flow of dacite of (he Stiver Kill Volcvuc Senea. collected from a small hill m (he ikortbeast quarter of Sec 16. T4N. R27E. about 1.000 feel eastcrt) from the Dudley shaft . (BH-16) Btoute-bomblendc dMste from the bwute-nck unit of the oompoaile daate flow of (he Silver Hill Vokamc Scnct, coUected from a prominent cropping in the iou(hcut quarter of Sec. 16. T4N. R27E (BH-32) Biodte-homblcDde daale from the bMtitc-nch unit of (he compoaitc daate flow of the Silver Hill Vokanic Senes, collected near (be top of a small hill tn the center at Sec 21. T4N. R27E For samples 6 af>d 1 4. method of analysts used is the ungle •olulKin procedure docnbed in US Geological Survey Pro- fessional Paper 5758. p 187-141 ( |Q67) Ana)>-stv P D- more. S Botts. L Artts, J Kdaey. H Smith and t Gknn For samples 1. 2. 3. 4. 5. 7. g. 9. la II. 12. and U. methods of analysu used are descnbed m US Geokipcal Survey Bulletin 1 144- A. suppiemenied by atomic abaorpliOB Ana- lys(s. P Elmore. S Bo((v G Chloc. H Smith. J Kehey. L- Ann and J Glenn ' liMbcatrt fieM nuinbrt 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 60, '■ I I J- \ Rhyohte / , . Rhyodacite.v. \ Dacite / .g/ / / '. '4« '«.'«8.' Latite - andesite \ .1 * PC'_ : - F«ld«por Latife Latite - basalt \. y^ .-■ugiutloii Ftldtpor Figure 3. Nonnative compositions of rocks of (he Silver Hill Volcanic Series in the Bodie mining district plotted on o Streckeisen diogrom. (lumbers refer to analyses in Table 1. Diagram adapted from Streckeisen (1967, p. }61J. Individual flows wedge out laterally, and the thickesi section of them (about 450 feet) is in the vicinity of Lookout Peak — one of the local vents for much of the matenal for the Murphy Spring Tuff Breccia. The plug at Liwkout Peak is somewhat circular in plan and is about half a mile in diameter. Another plug lies about one mile south of Sugarloaf It has a circular plan and is about one quarter of a mile in diameter (Plate 2). TTie dacite in the plugs and flows is dense, shows flow banding, and ranges in color from pale to dark gray and medium brown. Brown is the predominant color, especially in the plugs. The dacite is porphyrilic, and 30 to 40 percent of the rock is made up of phenocrysis enclosed in a fine-grained groundmass com- posed of mineral grains and volcanic glass. About 50 to 60 percent of the phenocrysts are plagioclase They occur in cuhedral and subhcdral grains which show multi- ple twinning and oscillatory zoning. The interiors <if a few larger phenocrysts arc altered to calcite and kaolin and have glassy clear nms of more sodic plagioclase The unaltered plagioclase phenocrysts range in composition from sodic andesine to calcic andesinc (Ann«). and the average composition is intermediate andesine (An,,). Inclusions of volcanic glass are common, espe- cially in the rims of the larger phenocrysts. About 30 to 35 percent of the phencKrysts arc hornblende and biotite. The biotite. usually less abundant than the hornblende, is pleochroic and ranges from pale yellow to dark brown, but where ass(Kiatcd with basaltic hornblende, it is reddish- to golden-brown and strongly pleiKhroic, Many of the biotite grains have undergone resorption, which leaves a residue of black iron oxide grains at their nms Hornblende in the gray dacite occurs in euhcdral and subhcdral grains that are mtxler- ately pleochroic and range from pale yellowish-grccn to deep yellowish-brown. Many of the grains are partly to completely resorbed and leave dark nms around unaltered hornblende or residues of dark iron oxide grains. The amphib«ile in the brown dacite IS basaltic hornblende It is strongly pictxhroic and ranges in color from pale yellowish- to deep reddish-golden brown. Those grains that are strongly resurbcd show subhcdral form, whereas those that arc weakly resorbed show cuhedral form The groundmass of the dacite, regardless of the color of the rock, appears lo consist of an aggregate of microlites of plagio- 10 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull 206 clase, microphenocr>'sts of short prismatic plagioclase, euhedral hornblende and biolKc, and partly devitrified volcanic glass. The plagioclase is probably sodic andesine or calcic oligoclase in composition The mafic minerals in the groundmass are general- ly partly to completely resorbed. The groundmass of the brown dacite has a pale bufT color due to secondary limonite. The partly devitrined glass is cloudy and contains minor carbonate and kaolin. CHEMICAL COMPOSITION Four new chemical analyses, all by the U.S. Geological Sur- vey, are given in Table 2 for the dacite of the Murphy Spring TufT Breccia. Three of these analyses are of samples collected in the Bodie mining district, and the fourth is from a prominent out- crop of dacite near Murphy Spring, about 2.5 miles west of the district (Plate 1). Norms for these analyses are plotted in Figure 4. The spread of the points on the diagram indicates a change of composition due to different source vents for the samples. Points 2, 3, and 4 represent samples from the flows near the large plug at Lookout Peak and Point 1 represents the sample from a flow whose source is near Murphy Spring (Plate 1). Table 2. Chemical analyses end normative composition, !n percent, of the dacite flows from the Murphy Spring Tuff Breccia of the Bodie mining district and adjacent areo. CHEMICAL ANALYSES 1 2 3 4 SO, 60.34 6154 63 56 64 36 A1A teao 1771 1752 1694 FeA 332 450 420 3 19 FeO 161 068 0.36 130 MgO 181 200 1.30 liO CaO 493 510 3.S0 398 Na,0 3.82 3.90 3.70 428 K,0 2.92 2.40 300 279 H,0 1.79 084 1.80 100 TO, 0.70 082 058 061 P,Os 0.37 033 0.30 032 MnO 0.08 008 007 004 ZfO, 000 000 000 000 CO, ooo 006 009 001 Total 10000 100 00 10000 10000 ACE OF THE MURPHY SPRING TUFF BRECCIA Biotites separated from dacite samples from the plug at Look- out Peak give identical K-Ar age dates of 8.7 ± 0.2 m.y. Potato Peak Formation Several hundred feet of Potato Peak Formation, consisting of interlayered dacite flows and layers of tuff breccia of dacitic composition, are exposed in the northwestern comer of the Bo- die mining district (Plate 2). DACITE FLOWS NORMATIVE COMPOSITIONS Quartz 14 744 16883 22175 19370 Corundum 0791 O390 2732 0411 Orthoclase 17 235 14 192 17 746 16483 Albile 32 339 33 024 31340 36248 Wollaslonile Enslatile 4509 4985 3^41 2977 Ferrosilile Magnetite 3408 0076 2543 Hemalile 0968 4451 4^04 1434 llmenite 1337 15580911 1.154 Rulile O101 Apatite 0881 782 0711 0755 Calcite 182 0205 0023 Total 98.230 99177 98214 99021 Salic 87 126 87 143 88 841 90135 Femic 11 104 12 034 9373 8886 Individual flows of dacite are not well defined in the district, but their aggregate thickness is estimated to be appro.ximately 350 feet. The dacite lies unconformably upon tuff breccia. The dacite is medium- to coarse-grained, is medium gray col- ored, and shows well-developed flow banding. It is porphyritic and contains phentxrysis of andesine, black bioiiie, and dark greenish-brown hornblende enclosed in a fine-grained crystalline to semi-crystalline groundmass composed of andesine, biotite, hornblende, deep-green diopsidic augite, and devitrified glass. The feldspar phenocrysis are generally euhedral, show well-de- veloped twinning and oscillatory zoning, and are in the composi- tion range of intermediate to calcic andesine (An,,,,). The groundmass feldspar is in small lath-shaped crystals whose com- position ranges from sodic to intermediate andesine (An,,,,). Biotilc IS generally more common than the hornblende. It (Kcurs in dark brown to golden brown euhedral plates; the hornblende is in dark brownish-green euhedral grains Both, when altered, show black borders consisting of dust-like magnetite. Diopsidic-augite is not common, but usually occurs in deep- green, weakly ploKhroic euhedral grains in those dacite flows with hornblende content exceeding that of the biotUe Quarts •'< rare and generally (x:curs in anhedral grains. Pctrographic examinations of the lava flows in the Potato Peak Formation indicate that the flow rocks arc andesilic in composition Chemical analyses, on the other hand, indicate a dacitic composition (Table 3, Figure 5). (BH-14*) Biotite-homblende dacite from near the top of one of the latest lava flows in the Murphy Spnng Tuff Brec- cia, collected from the west edge of Sec. 24, T4N, R26E, MDM, about three-quarters mile westerly of Murphy Spring. (BH-18) Biotite-homblende dacite from a lava flow in the Murphy Spring Tuff Breccia, collected in the northeast comer of Sec. 21, T4N, R27E, MDM, about one and one- quarter miles northeasterly of Sugarloaf (854G-1) Biotite dacite from lava flow in Murphy Spring Tuff Breccia, collected in the central part of Sec. 28, T4N. R27E, MDM, about 300 feet southeast of Sugarloaf. (BH-20) Biotile-homblend dacite from a lava flow in an easternmost exposure of Murphy Spnng Tuff Breccia, col- lected at an abandoned railroad cut in the northca.st quarter of Sec. 23. T4N, R27E, MDM. For samples I, 2 and 4, mcthixls of analysis used arc de- scnbed in U.S. Geological Survey Bulletin 1 144-A. supple- mented by atomic absorption. Analysts: P. Elmore, S. Bolts. G Chloc, H Smith, J Kelscy, L. Artis and J Glenn For sample 3, method of analysis used is the single solution prcKcdure described in US Geological Survey Professional Paper 575-B, p 187-I<J1 Analysis: P Elmore. S. Bolts. L. Anis, J. Kelscy, H. Smith and J Glenn. * Indinln ftcld numtM-r 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 11 i ..u \ Rhyolite / ' Rhyodacite ' Loi.te \ \ \ •-.■■..■:•. VA \ i LGtite Pototlium IQ FtldtpOf ! 'Lafite - dndesite"^) \ Lotife - basalt -.vX'.! 65 90 Plo9iocio»« ^•Idipar Figure 4. Normative compositions of docite lavas from tfie Murphy Spring Tuff Breccio of tfie Bodie mining district and adjocent area plotted on a Streckeisen diagram. Numbers refer to onalyses in Table 2. Diagram adopted from Streckeisen (1967. p. IAD- TUFF BRECCIA TufT breccia of the Potato Peak Formation is a massive rock unit whose actual thickness in the Bodie mining district is not known, but whose exposed thickness is estimated to be about 1 50 feet. ExfKJSures of the tuff breccia are scarce; but, where ob- served, it is medium gray in color and firmly indurated, and contains minor interbcds of luffaceous sandstone and conglom- erate The tuff breccia is po<irly bedded and consists of angular fragments and blocks of light gray biolite dacitc, as much as 6 feet across, enclosed in a matrix of small rock fragments and volcanic ash The average size of blocks in the tu(T breccia is approximately one foot. The luffaceous sandstone and conglomerate layers are lens- like and generally range in thickness from 6 inches to 2 feet The tuffaceous sandstone is well bedded, medium to fine grained, light gray in color, and firmly indurated The tuffaceous con- glomerate, too, IS hght colored, and firmly indurated, and con- sists of subangular and well-rounded clasts that range in size from pea-size fragments to boulders ten inches acros<i. Volcanic ash makes up at least 40 percent of the matrix material, and the clasts consist largely of light gray biotitc dacite and minor brown-colored hornblende andesite. The tuff breccia unit rests unconformably uptm tuff breccia of the Silver Hill Volcanic Series and is unconformably overlain by dacite flows of the Potato Peak Formation. AGE OF THE POTATO PEAK FORMATION Based upon K-Ar age determinations of biotite from flows of dacite, the age of the Potato Peak Formation ranges between 9 I and 8.4 my. STRUCTURE Whiting (1888. p. 383) favored a siruclurat picture for the B<xlie mining district consisting of inter-laycrcd \a\a flows and tuff breccia layers dipping gently toward the south The irregular outcrop pattern of the hydrothennally altered rocks and their 12 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 disturbed condition, due principally to faulting, may have con- tnbuted much to this thesis. F.H. Frederick (wntten communi- cation, l*)60) earned on a systematic geologic investigation of the district m the early l93C)s, and many of his thoughts and maps were the basis of some of the conclusions expressed by Wisser (I960, p. 70), who considered the structure to be an irregular northeastward-trending anticline, upon which are su- penmptised several domes. Table 3. Chemical analyses and normative composition. In percent, of the dacite flows of the Potato Peak Formation of the Potato Peak-Bodie Mountain area. CHEMICAL ANALYSES 1 2 3 4 5 SiO, 61.70 6181 6147 62 53 6140 AlA 17.63 16.93 17 49 17 74 17 53 Fe,Oj 401 3.81 4.30 3.31 4.21 FeO 130 1.20 0.72 150 096 MgO 1.30 240 190 130 2.20 CaO 5.01 4.81 4.90 431 4.91 Na,0 391 3.61 4.00 3.91 391 KjO 2.50 2.60 2.60 301 230 H,0 1.50 160 1.50 130 083 TO, 0.73 0.62 064 068 088 PA 0.34 0.40 047 034 73 MnO 0.07 0.21 0.02 008 014 ZrO, 0.00 0.00 0.00 000 000 CO, 0.00 0.00 0.00 000 000 Total 100 00 10000 100.00 100.00 100 00 NORMATIVE COMPOSITIONS Quartz 17.684 18107 16 270 18078 18123 Corundum 0202 0395 0322 1035 1436 Orihoclase 14797 15 390 15356 17763 13613 Albile 33 054 30514 33 830 33 067 33 054 Anorlhile 22 620 21236 21228 19149 19571 Wollasloniie Enslalile 3.243 5987 4730 3.244 5488 Ferrosilile Ivlagnelile 2.306 2761 0531 3131 1002 Hematite 2.416 1902 3932 1 147 3516 ilmenite 1389 1 180 1215 1294 1674 Rulile Apatite 0807 0949 1 113 0807 1732 Calciie Total 98516 98 421 98 525 98716 99 208 Salic 88 356 85 641 87 005 89 093 85 797 Femic 10160 12779 11520 9623 13.411 (48101*) Biotite-homglende dacite from a lava flow in the Potato Peak Formation, collected from a peak in the western part of Sec. 4, T4N, R26E, MDM, about two miles west of Potato Peak. (48102) Biotite-hornblende dacite from a lava flow in the Potato Peak Formation, collected from the southeast flank of Potato Peak in the eastern part of Sec. 3, T4N, R26E, MDM (48103) Biotite-hornblende dacite from a lava flow in ihc Potato Peak Formation, collected from the southeast corner of Sec. 3, T4N, R26E, MDM (BH-13) Biotite-hornblende dacite from a lava flow in the Potato Peak Formation, collected from a small hill in Sec. 23, T4N, R26E, MDM, about three-quarters mile northwest of Murphy Spring. (BM-2) Biotilc dacite flow of the Potato Peak Formation, collected from the center of Sec 12, T4N. R26E, MDM, about two and one-half miles northwest of Bodie townsitc. For analyses I, 2, 3 and 5. methixl of analysis used is Ihc single solution procedure described in U.S. Geological Sur- vey Professional Paper 575-B. p. 187-191 (1967). Analysts; P Elmore, S. Bolts, L. Artis, J. Kelsey, H. Smith and J. Glenn. For sample 4, methods of analysis used are described in U.S. Geological Survey Bulletin 1 144-A, supplemented by atomic absorption. Analysis: P. Elmore, S. Bolts, G. Chloe, H. Smith, J. Kelsey, L. Artis and J. Glenn. * Field numbrr) Uktmh on plalc 2. Faults The main faults, the Moyle Footwall fault and the Standard Vein fault, are parallel in general to the axial plane of the anticli- nal upfold (Plate 2) mentioned by Wisser. Both faults are nor- mal with very little stnke-slip movement. The Moyle Footwall fault has a fairly constant stnke of N 38° E and dips eastward from 60 to 70 degrees. It can be traced intermittently along its strike for a distance of about 4,000 feet It was encountered underground in the Bodie and Standard mines and supposedly in the Syndicate mine at the north, but no evidence could be found to indicate whether it was cut by the later Mono fault (Plate 2). Where seen in the Roseklipcut, underground near the Standard New shaft, the Moyle Footwall fault has a well-defined breccia zone about 2 feet wide that contains quartz fragments. It appears from the character of the gouge and the off-setting of veins formed later that activity on the Moyle Footwall fault extended from pre-mineral into post-mineral time. The Standard Vein fault, so called because it contains the Main Standard vein, has about the same magnitude a.s the Moyle Footwall fault. It slnkes N 18-20° E, has a 60 to 70 degree westerly dip, and can be traced intermittently along its strike for a distance of about 3,500 feet. The fault was encountered in the Standard and Syndicate mines and in small intervening mine workings, but apparently not in the workings from the Lent shaft. It is pre-mineral in age, but with sustained post-mineral movement which produced a saccharoidal or granular condition in large sections of the Main Standard vein. As the direct result of extensive sloping in the Standard mine, a relatively large block of rock pnncipally altered tuff breccia of the Silver Hill Volcanic Series, dropped. At the surface, this produced an eastward-facing escarpment 3 to 5 feet high and 800 feet long at the Moyle Footwall fault and a westward-facing escarpment from one to 4 feet high and 150 feet in length along a segment of the Standard Vein fault. A third major fault, which also is roughly parallel to the axial plane of the anticlinal upfold (Plate 2), is in the valley occupied by the Bodie townsite, where it is overlain by alluvium. The position of the northern trace of the fault is indicated by several springs. The fault slnkes N 18° E for much of its studied length, but strikes N 30° E at its northern end. It is a stcx-p. normal fault whose dip could not be measured, and it appears to have down- dropped the block on the east by at least several hundred feet. There are several cross faults in the district; the Tioga, the Mono, and the Jupiter. The Tioga and Mono help define what has been referred to as the Bonanza zone Brown ( 1907. p. 356) ptiinted out that the riKks underground between thc-se faults are highly altered but contain no ore. The Tioga fault, which forms the northern boundary of the Bonanza zone, strikes N 62° E. It crosses the canyon west of Bodic Bluff and follows Milk Ranch Canyon in a westerly direc- tion (Plate 2) The fault is clearly marked on the surface by depressions and gulches, c-spccially on the west slope of Bodie Bluff. It is a normal fault in which the bUxk on the south has dropped, probably in a near-vertical direction, by perhaps as much as 5(X) feet. It is a pre-mincral fault, as veins pa.v. through altered, brecciated rock in its fault zone and reappear on the 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT iQtz 13 • * 90 Plogioclot* Ftldipor Figure 5. Normative compositions of docite lovos of the Pototo Peak Formation of tfie Bodie Mountain-Potato Peak area plotted on a Streckeisen diagram. Numbers refer to onolyses given in Table 3. Diagram adopted from Streckei%er} (1967, p. 1611. Other side. Post-mineral movement along the Tioga fault was relatively small, probably no more than several tens of feet at the most. The Mono fault forms the southern boundary of the Bonanza zone. This fault strikes N 66° W and, like the Tioga fault, is marked at the surface by topographic expression as well as by displacement of rock units. It, too. is a normal fault with a horizontal right lateral displacement of about 500 feet; the extent of vertical displacement, down on the south, is not known. The Mono fault zone, about 100 feet wide, is visible on the surface and in mine workings. The water storage tank for the Bodie State Historic Park is situated in the Mono fault zone, and during the excavation for the tank's foundation, relatively pure montmoril- lonitc and altered dacite were encountered. Major movement on the Mono fault was pre-mineral, as no quartz veins were offset in the fault zone The Fortuna vein fracture was traced into the Mono fault zone and its presence was indicated by vein material consisting essentially of coarsely crystalline gypsum Faulting in the Middle mines and Southern mines areas of the district has done much toward dislcxaling various units of the Silver Hill Volcanic Scries and opening them to mineraliz.ation and alteration. The principal fault in the Southern mines area extends in a northwesterly direction through the Queen Bee shaft, across the northern flank of Queen Bee Mill, and through the University and Spaulding shafts (Plate 2) Beyond the latter shaft, it dies out at or along the contact between tulT breccia and dacite lava flows of the Silver Hill Volcanic Series. This is a normal fault which dips eastward 60° in the Boiiker workings, and whose principal movement was pre-mineral. The amount of downward movement is not known, but an andcsile dike on Queen Bee Hill was cut and its segments were displaced by as much as 200 feet by sirikc-slip movemenl Quart/ veins along the fault have been crushed as the result of post-mineral movement, which apparently was not great. A fault whose strike rangi-s from N 75° W to S 60' W trends across the district just north of Sugarloaf( Plate 2) It is a normal fault whose upward movement on the south side brings the lower hornblende-rich dacite unit of the composite flow into contact with the upper biolile-rich unit of the flow. This fault is cut off on the east by what appears to be one of the youngest faults in the district, which trends approximately north, dips steeply to- ward the west, and forms for some distance the contact between units of the Murphy Spring Tuff Breccia and rocks of the Silver Hill Volcanic Scries. Numerous small faults occur in the district Although Mime of them can be found at the surface, others are identified only in mine workings where they have displaced veins or are fracture zones along which veins were der>osiled and were avenues for the migration of hydrolhcrnial fluids A polar plot (Figure 6) of the 14 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 Photo 5. View to southwest of the Bodie mining district, showing the Syndicate mine (Sd), Whitney tunnel (W), Davis tunnel (D), Tiogo tunnel (Tt), Bodie Bluff (BB), Standard Hill (St.H), Tailings pond (Tp) ond Sugorloof (S), Sierro Nevada on skyline. Photograph by Bennie W. Troxel. principal faults encountered underground in the Red Cloud mine indicates that the faults here essentially trend north and are parallel in large measure to the trend of the shear zones and vein system. Jointing and Sheeting Studies of the outcrops of the intrusive dacite and flows in the Bodie mining district failed to reveal any joint patterns or sys- tems that might help to decipher the structural history of the rocks. In the mines, especially those in the Standard Hill area, early investigators found closely spaced parallel fractures called "sheeting" in the wall rocks, generally parallel to the so-called fissures which contained the quartz veins in the Standard and Bodie mines. Whiting (1888, p. 387) states: "Even in the minut- er structure of the rock this effect of compression is no less stnkingly evidenced by a schistose foliation along now one, now the other, wall of a fissure; and, as a peculiar feature of these ore bodies such foliated portions have invariably been found to be very rich in gold and silver; as though this structure, originally due to compression, had affected in the innumerable, though minute, fault fissures thus formed, such retardation to the flow of the mineral bearing solutions and such virtual increase of deposition surface as to have caused a more abundant minerali- zation of the veins at such l<x;alities." The development of sheeting and tension fissures in the intru- sive dacitc of the B<xlic Bluff-Standard Hill plug has been at- tributed to up-arching of the rocks to form the Ikxiie aniiclinc (Wisser, 1960, p. 73). Certain sheeting planes became the Moyle Footwall and the Standard Vein faults, which produced the graben in the Standard Hill mines area. The fan pattern of longi- tudinal sheeting, which is said to show up so well in cross section in the vicinity of the Syndicate mine (Whiting, 1888, p. 387), is related to the same dynamics that produced the longitudinal sheeting in the Bodie and Standard mines. This same fan pattern is said to occur in the mines near Silver Hill and Red Cloud mine, where the tension fractures and sheeting are in lava flows of the Silver Hill Volcanic Senes and are related directly to the forma- tion of the anticlinal upfold. Farther south at Queen Bee Hill and at Sugarloaf, evidence of sheeting is scarce, although the flows and intmsive bodies are highly jointed. Plugs The largest plug in the district underlies Bodic Bluff and Standard Hill. In plan, it is elongate in an easterly direction, with its greatest development at Btxlic Bluffand Standard Hill, where it is approximately 3,500 feet across. At the surface, the plug is divided into two sections by a narrow septum of brcccialcd. propylili/cd luff breccia of the Silver Hill Volcanic Scries, the eastern mass is p<itassically altered dacite. but the main btxiy of the plug has undergone strong propylilic alteration and mild p<ilassic alteration. Internal structures in the plug are not abundantly evident, but flow-banding, where observed, is generally sleep. Contacts 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 15 N East Dipping / ° ^^ / o / ° \ / * ctoO o\ o o o \ o (P o \ ° I \ ° ^ West Dipping Figure 6. Polar plot of faults in the Red Cloud mine. Plotted on upper hemisphere. between the plug and the wall rock are steep and generally accompanied by intense argiliization of both the plug r<Kk and the wall rock and by local shearing in the walls of the plug. Based upon exposures of the plug in the field and the sequence in which the several types of hydrothermal alteration occurred, it is reasonable to assume that the plug was emplaced m two separate yet overlappmg pulses of volcanic activity. The main body of the plug at Bodie Bluff was formed first, as the dacite of which It IS composed was subjected to early propylitic altera- tion, and later the plug dacite east of the septum in the plug was emplaced at a time when p<ilassic alteration was taking place. The plug at Queen Bee Hill, which was emplaced at about the same time as was the Bodie Bluff-Standard Hill plug, is small and elongated in a northwesterly direction, and has a maximum dimension of about 1,000 feet. Flow-banding is vertical or dips steeply, generally inward toward the central part of the plug. Lack of accevs to mine workings al Oucen Bee Hill made it impossible to observe the contact between the plug dacite and the wall rock, but the nature of the flow-banding in the plug indi- cates that the contact is steep. The dacile of the plug has under- gone argillic alteration, which extends outward from the plug into the wall rock for only a few lens of feet Ihc wall rock consists principally of units of the composite flow thai have undergone propylitic alteration. The plugs at Sugarloaf and near the Red Cloud mine were emplaced between 8.3 and 8.9 my. ago, and are later than the other plugs in the district (Silbcrman and others, 1972, p 601 ) The plug al Sugarloaf forms a symmetrical cone when viewed from ground level and has an ellipsoidal shape whose north- trending axis measures approximately 1,300 feet. Flow-banding and ihe principal joint pattern in the plug dip very steeply to vertically. The Gorman tunnel (Plate 2), on the west side of Sugarloaf, passes first through the lower hornblendc-rich dacite unit of the composite flow, then penetrates the intrusive dacite of the plug at a point about 100 feet from the portal, which is now caved (Frederick, I960, written communication) The con- tact between the plug and the wall rock is sleep and marked by a zone about 4 feet wide, of clay and sheared rock. Inward from the contact, a zoneof propylili/ed inlrusive dacite ab<iul 1 50 feel wide is uniformly developed around the circumference of the plug. The interior of Ihe plug is relatively unaltered hornblende dacite. The smallest plug in the distnct lies a few hundred feel south of the Red Cloud mine It is roughly circular in plan and has a diameter of approximately 5f)0 feel I'niikc Ihc olhcr inlrusive bodies, this plug has no dislinclivc topographic expression The contact between the plug and the wall riKk is concealed by soil Flow-banding is scarce, but where found it is steeply inclined 16 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 Photo 6. View to northwest of the central and northern sections of the Bodie mining district, showing Red Cloud mine (RC), Silver Hill (SH), Standard Hill |St.H| and Bodie Bluff (BB|. inward. The plug is composed of hornblende-biotite dacite, which is relatively unaltered at the interior but argillically al- tered near the margins. The biotite-rich dacite unit of the com- posite flow, which forms the wall rock of the plug at the surface, also has been argillically altered. Silver Hill is considered by Wisser ( 1960, p. 70) to be under- 1am by an anticline at whose core is a dome, but no evidence could be found to support this hypothesis. Instead, the topo- graphic high at Silver Hill is capped by a mass of intensely silicified tuff breccia of the Silver Hill Volcanic Series that lies upon the biotite-rich dacite unit of the composite flow. GEOLOGIC HISTORY Structure Interpretation The interpretation of the structure of the Hodie mining district by the present writers is based on detailed geological mapping of the district and of the area immediately surrounding it. a great deal of which lies in the Hodie quadrangle (Chestcrman and Gray, \^15) The writers concur in general with the anticlinal suggestion of Wisser, but the structure of the district is complex and can be perhaps best understood through a discussion of its history. Tertiary Rocks The extrusive rocks of the Silver Hill Volcanic Series are considered to be the oldest exposed volcanic rocks in the Bodie mining district. The distribution of thepyroclastic deposits of the Silver Hill Volcanic Series indicates that the pnncipal eruptive vents for the materials were what are known as Bodie Bluff, Queen Bee Hill, and Sugarloaf (Plate 2). The pyroclasiic depos- its in the \icinity of Bodie Bluff are thickest north of the peak of Bodic BlutT Because of the lack of adequate exposures, the thickness of the series in the district can only be estimated at between 800 and 1,000 feet. That there were several explosive periods in the volcanoes of the district is indicated by the occur- rence of several thin tuffbreccia layers among dacite flows in the vicinity of Silver Hill The deposition of the main (lowermost) layer of tuffbreccia was followed by flows of dacite, the first of which, from the vent near Silver Hill, was interrupted by brief pcncxls of explosive activity The emplacement of the comp<isile flow at B«xlic Bluff some 'i A to S.8 my. ago was near the closing phase of \olcanic activity in the district The emplacement of the plugs at Bodie Bluff, near the Red Cloud mine, at Queen Bee Hill, and at Sugarloaf represents the intrusion of dacite into the several vents following the last outptmnng of lavas as flows. It seems most likely that these plugs were connected with the same magma chamber; the activity at each vent, however, was not neces.sanly contemporaneous with that of the others, although their overall 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 17 range in age from 8.3 ± .4 m.y. to 9.2 ± 0.5 m.y. indicates a relatively brief time interval within vshich these plugs could have been emplaced. The chemical analyses and pctrographic studies indicate that no appreciable difTerentiation has taken place with- in the magma chamber. The emplacement of the plugs was accompanied by a general anticlinal upfolding of the earlier dep<isited interlayered lava flows and pyroclastic layers. Bedding in the tuff breccia and flow banding in the lava flows in the immediate vicinity of the plugs is steeply dipping, especially around the plug at Btxlie Bluff and Standard Hill, where contacts were observed in the mines The evidence suppcirts the assumption that the plugs are apophyses of a larger intrusive body of volcanic rock, probably dacitc. at depth, and that the shape of this body is elongated in a generally north-south dirtx-tion. Both magnetic and gravity data support this concept The axis of the anticlinal upfold is parallel to the general alignment of the plugs. The major fractures, faults (other than the cross faults), and veins arc parallel to the axis of this upfold and dip generally toward its axial plane. The fracture systems which opened the rocks to alteration and mineralization were developed in the intrusive btxlies following their emplacement and the formation of the anticlinal upfold The Fortuna vein fracture is perhaps the oldest in the district. It strikes approximately N 10° E. In the upper levels of the Bodie and Standard mines, the fracture dips 30° toward the east and, in the lower levels of these mines, steepens to as much as 45° E. Where it steepens, the fracture contains very little vein material and appears pnncipally as a zone of thinly sheeted and highly altered dacite and gouge showing slickensides and striations (Whiting, 1888, p. 392). The Fortuna fracture (Figures 7, 8, 9. and 10) is cut by later veins and fractures, and its origin may be related more to the emplacement of the plug at Bodie Bluff than to the general anticlinal upfolding in the dislnct. Wisser ( I960, p. 73) related the Fortuna fracture to a period of uplift which was supposed to have occurred east of the Bodie anticline and developed before the extrusion of lava from the vents at Bodie Mountain. Lava flows of the Potato Peak Formation overlap the pyro- clastic deposits and flows of the Silver Hill Volcanic Series at the northern and northwestern parts of the Bodie mining district, but nowhere could any evidence be found to support Wisser"s thesis that units of the Potato Peak Formation covered the entire area now encompassing the Bodie anticline. Tension fractures would have been developed in the flows and pyroclastic layers in the development of the anticlinal upfold, but what dynamics are required to produce linear fractures and sheeting in the intrusive dacite plugs themselves, which should have been marked by radial and concentric fracture systems? Although the K-Ar age data indicate a continuous process of emplacement of the intrusive bodies in the district, specific age dating indicates that the plugs at Bodie Bluff-Standard Hill and Queen Bee Hill were emplaced ab<iut 9.2 i 0.5 my. ago (Silber- man and others, 1972, p. 602) — older than those at Sugarloaf Peak and near the Red Cloud mine, which were emplaced at 8.3 and 8.9 my. ago, respectively. Partial withdrawal of the magma from the plug at Bodie Bluff to form the plugs at Sugarloaf and near the Red Cloud mine resulted in the development of the faults and graben stnicture in the Bodie Bluff-Standard Hill area. Mineralization in the Bodie mining district seems to have commenced shortly after the emplacement of the plugs K-Ar age determinations made on adularia obtained from a vein in the Moyle Footwall fault zone gave an age of 7 t 2 my to 7.0 ± 0.1 my. Adulana from the waste dump of the McClinlon shafi, either from the Burgess or Incline vein series, gave an age of 8.0 ± 0.2 my. (Silbcrman and Chcstcrman, 1972. p 17). w*- Incline Series — E 1 v™^ ^ 1 • 1 1 FhT^-'^^II^ low>i«. -n k s 11 It " r o \ a 11 I o o 1 1 II II — :d it U II 11 • // // // ' • o^ 1 1 // / "" r-" •^ II 1 II 1 — • a. \k /// '' \ //I \ s s // ^Lo^ 1 ^ / r^ Burgais \ / /I "\ Senas ( i • Figure 7. Crojs section of the »ein tyslem of the Standard mine. Modified from Brown, 1907 Adularia from the vein specimen, of coarse-grained calcite and intergrown fine-grained quartz and adularia from the Red Cloud mine, gave an age of 7.7 ± 0.1 m.y. (Silberman and Chesterman, 1972, p. 17). ALTERED AND MINERALIZED ROCKS Hydrothermal alteration (Plate 2) has been widespread in the Bodie mining district. The type of hydrothermal alteration has determined to a considerable degree the color of the altered rock. Propylitic alteration has given a greenish color to lava flows and tuff breccia: argillic and silicic alteration generally results in white and pale gray rocks, with fracture surfaces thinly coated by reddish, reddish-brown, and yellow hydrous iron oxide stains. Rocks that have been alTected principally by potas,sic alteration do not appear to have suffered significant color changes; where these rocks have not been affected by additional argillic altera- tion, they are dense and firm and have the general appearance of unaltered rock. Hydrothermal alteration in the district commenced during or soon after the closing stages of volcanism (Silberman and others, 1972. p. 602). Detailed field mapping in the district indicates that there were four stages of hydrothermal activity, commenc- ing with propylitic and followed in succession by argillic. pcitas- sic, and silicic. The propylitic alteration was widespread and seems to have afTected all rock types regardless of composition and structure. The resulting mineral a,sscmblage includes chlontc. scricitc, epi- dotc. quartz, pyrile. and hematite, in addition to the feldspar and other minerals characteristic of the original rock (Photos 7 and 8). Argillic alteration resulted in formation of rocks characten/ed by quartz, chalcedonic and opaline silica, montmonllonilc. kao- lin, limited sencite, carbonate, and pyritc (see Photo 14) The altered rock is usually soft and friable, and forms smimth slopes The pyritc is irregularly distributed in the argillically altered rocks and appears to be more concentrated along joints and fractures and occasionally sparsely disscininatcd throughout lo- 18 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull 206 Bodle New Shaft 1 Ml" III III III III III III III III III -^ III ^ g U «, t»z-- ;iU206' Lev Burges LEGEND ^^5?l - r.-^^ptii yfifi^ Fortuno Slopes i:XI308' Lev. ^ a ;,'i«; Faulting Veint 1 ■to -■I'-f. Wall Rock ~iir"" 432' nCi III * ^^i 1 460' Le/'v 1 ■1 k k 462 " Lev^ll^^^'. -;•.. S «> 2 ^ t) (5 ^3 536' Lev,- AT^ ^^■:.."t * v-^ 554' Lev^ 641' Levl;^;'' 1 '^^^j;i!:3;.r. 50 SCALE M"^^^^ 100 200 ft ^Op "•'-<"•'' ^..;---5%A'^- Lent Shaft 707' Lev.'@i"£ ~Z~ZZ ZI.ZZt^S'3i'Wrnze No 3 ^» ^^ ^— ^H ^H ^B ^m 4_ ^B ^^ ^M ^"^BK- Jj »**. 4^ 1 ■\V^cS«r!P.^ ~-7Sf<' Figure 8. Vertical section through Fortuna slopes, cal areas. Oxidation of the pyrite has given outcrops of the rock a blotchy brown and reddish-brown color. Potassic alteration appears to be confined to the rocks in and surrounding the Bodie BlufT-Slandard Hill plug, where it is obvi- ously later than the propyliiic alteration. The relationship of potassic to argillic alteration is not well known, but exposures in the Bulwer tunnel suggest that the potassic alteration is later. Dacite thai has undergone potassic alteration is firm, appears unaltered in hand specimens, and forms bold outcrops, especially on and near crests of ridges and hilK. It is porphyrilic; a micro- scopic examination revealed small rectangular microphenocrysts of sanidinc and fine-grained adularia in the groundmass. Analyses 1, 2, 3, and 4 (Table I) on rocks from the Bodie Bluff-Standard Hill plug show abnormally high K.O content in comparison to the analyses (nos. 5, 7, 9, 10, and II) of dacite from the plugs al Queen Bee Hill and Sugarloaf Pota.ssic alteration undoubtedly (Xcurred over a considerable span of lime, even into the formation of quart/ veins in rixks which had potassic alteration superimposed upon earlier propy- liiic and argillic alteration processes. Adularia is a common constituent in some of the quart/, veins, especially those of the Bodie mine. Modified from Whifing, 1888. Burgess series, which are clearly later than those of the early Fortuna series, and which have been dated as being between 7.1 and 8.0 my. old. Silicic alteration, the last stage of hydroihermal activity and perhaps a factor in the formation of the quartz veins, is evident on the surface at several areas but is kvalized in the central part of the district on Silver Hill (Plate 2), in an area surrounding the Noonday mine and near the portal of the Aurora tunnel Two rock types arc involved in silicic alteration, the biotite-nch dacite unit of the composite flow and a tuff breccia layer that lies ab*ive the composite flow. The silicically altered rock is pale gray to white in color and dense, and appears to consist largely of quart/ and chalcedonic silica. A sample of silicified tuff breccia, which forms the cap on Silver Hill, contains 91 14 percent SiO... 0.11 percent CaO. 006 percent Na..O. and 0.72 [XTcenl K.O; the remainder consists pnn- Lipally of iron and sulfur and minor amounts of aluminum (Maj- inundar, written communication. 197.1) Where the alteration has affected the dacilc la\a flows, icxiurc-s and structures of the original rcxk are Msible but not common However, the original clastic structure is plainly visible in silicified tuff breccia. A 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 19 structural control for selective siliciflcation can be deduced from the fact that the pyrivlastic materials, because of their lower bulk density and high porosity, are more readily and completely silicified and pervasively mineralized than are the denser flow rocks. M Sillclfi«d (Andesl»«) doelfe «'tm^(P ill (Andesite) Oacitt ^ S^ ^ f' Ui +ttJ m\ -r (^ c — c Crossing illl ''^'- t^vfflt' w Figure 9. Foce in stope on th« Fortune vein, Bodie mine. Modified from Brown, 1907. '/ ' I '' / -'' !^^^i * v/ • li^r' >7 y J \^^ ^\^ V-"'^'* Wi' 4M tl li.al W^/ \ ^^m EAST , :0% • lEST Figure 10 Eail well icdion through the Fortuno ilope m the north drift No. 1 of the 432 foot level of the Bodie mine, showing the cross-cutting oge relationships of the Fortuno ond Gildeo veins. Modified from Whitifig, J838 GEOPHYSICAL INVESTIGATIONS Regional Gravity and Magnetic Data The results of regional aeromagnctic and gravity studies in the Bodie Hills area of California and Nevada by the L' S Geological Survey and the California Division of Mlnc^ and (icology have been discussed by Kleinhampl and others (1975). The aeromag- nctic and gravity data presented by Kleinhampl and others (Plate 1 and Figure 4) include anomalies thai have a significant bearing on the interpretation of the geology of the Bodie mining district. The features of greatest importance shown by these may be two nearly coincident, north-trending anomalies: a negative aeromagnctic anomaly and a positive gravity anomaly, both of which are centered near the mining district. Plate 1 shows a comparison of the regional aeromagnctic and gravity data along Profile RS across the Bodie mining district near Queen Bee Hill (location shown on Plate 2) This profile illustrates the close association of the aeromagnctic and gravity anomalies here and suggests the possibility thai bi>ih anomalies may reflect the same source or closely related sources. The local gravity anomaly is a part of a more extensive positive anomaly trend that extends through the Bodie Hills area This major feature trends northeastward from near Lundy Canyon, north of Mono Lake, to Cottonwcxxl Canyon, where it turns almost directly north and passes through the Bodie mining dis- trict (Kleinhampl and others, 1975, Figure 4; Plate 1 of this report). Near Bixlie the anomaly turns northeastward again and continues to the vicinity of Aurora Peak in Nevada. The anom- aly is essentially continuous except for a possible interruption near the change in trend east of Cottonwood Canyon. Pre-Tertiary ba.semeni rocks are closely associated with the gravity anomaly in the northeastern and southwestern parts of the Bodie Hills, but in the intervening area, which includes the Bodie mining district, only younger extrusive and intrusive rocks are exposed. Thus, a possible explanation for ihis anomaly may be relief on the basement rock surface. An alternative explana- tion for the gravity high, which would be reasonable at least in the Btxlie mining district, is suggested by the series of dacite plugs that have been mapped in ihe area (Plate 1). These plugs are believed to be apophyses of a larger intrusive mass at depth (this report, page 17). Either of these possible explanations, basement relief or intrusive rixrks, assumes a higher average density for the anomaly source than for the surrounding rocks. The cause of the local aeromagnctic anomaly in the vicinity of the Bodie mining district might be either the extensive hydro- thermal alteration, which has resulted in destruction of magnet- ite in some of the extrusive and intrusive rocks underlying the district (this report, page 17), or simply a contrast in magnetic properties between two or more rock types. The results of meas- urements of the magnetic susceptibility of a number of samples (Table 4) suggests that the average value (0.0012 emu/cm) for extrusive daciie from the Bodie mining district is only slightly less that that (0.(X)14-0(X)17 emu/cm) for similar rtx-ks (dacite and andesite) from the surrounding areas in the Bodie Hills. Nevertheless, it is possible thai Ihe sampling did not give proper weight to the relatively altered extrusive riKks in the mining district. The average value (0(XX)« emu/cm'; Table 4) of magnetic susceptibility obtained for intrusive dacilc from the Bodic min- ing district is distinctly lower than ihal (0.0012-0.0017 emu/ cm') for the extrusive rocks given above. Although this apparent difference may be large enough to cause the observed anomaly — considering ihe p<issible si/e of Ihe intrusive mass at depth — ii is not known whether these results are truly representative of the mass of the rock The relatively low magnetic susceplibililies of the intrusive rocks sampled may. however, be Ihe result of the intense hydrolhermal alteration which characlcri/es these rtKks in surface exposures throughout most of ihe B<xlic mining dis- incl. The loss of magnetite during alteration of the nvks in ihc mining district also would reduce the effect on the magnetic field caused by remanent magnetism. This, or the presence of reverse- 20 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull 206 Photo 7. Veined ond propyiiticaiiy oitered tuff breccia of the Silver Hill Volcanic Series, as exposed underground in the Bulwer tunnel, about 150 feet west of the contact with the intrusive dacite. Scale is 6 inches long ond rests against o pyroclost of orgillicotly altered dacite. ly magnetized rocks, might also help account for the negative aeromagnetic anomaly, but no measurements of the intensity of remanent magnetism of samples were made during this study. The direction of remanent magnetism was determined in the field for a number of intrusive and extrusive rock samples from the Bodie Hills (see Chesterman and Gray, 1975). In the Bodie mming district, these measurements showed normal and re- versed directions of remanent magnetism for appro,\imaIely equal numbers of both intrusive and extrusive rocks. Thus, it was not determined whether the direction of remanent magnetism contributes significantly to the observed anomalies in the Bodie area. A more detailed and extensive study would be required to resolve this question. Detailed Gravity and Magnetic Data While the regional geophysical work for this report was in progress, relatively detailed gravity and ground niagnelic sur- veys were also undertaken in the Uodic mining district Approxi- mately 180 gravity and magnetic stations were (Kcupied at points of known IcKution aiid elevation in the district. A Worden gravity meter and a Jalander fluxgate magnetometer were used. These p<>inls include a few bench marks established by the U.S. Coast and Geodetic Survey and the LIS. Geological Survey and spot elevations from U.S. Geological Survey topographic maps, but most are spot elevations that had been established by survey- ing in the district. In addition to these stations, a few lines of closely spaced magnetic values were added in parts of the area. Table 4. Magnetic susceptibility measurements of rocks of the Bodie mining district and surrounding oreo. (i>c> rn» No ol lim, am'l Intrusive rock* of »*• BodaHM VM dKlM niy<*w 0001 • 0Q?O 0011 OO0& Inwutnw tockM ol Om DKM 16 000O4 OKI aoH ExtrutfV* rodisolVi* BodNHMHM •ndmlt (Mew bftuN mKMOIuII 4 s 1 1 0O06 . OQ?S 0006 - 0Q?1 0017 OOK 0Q?1 001 r EalruWv* rodi* ol tf« or*, IMCM MltncoK • 1 000O1 ooos 0017 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 21 Photo 8. Ffoctured ond propyiiticolly altered intrusive dacite of the Stiver Hill Volcanic Series, os exposed underground in the Bulwer tunnel, about 50 feet from the contact between the intrusive dacite ond tuff breccio. Scale is 6 inches long and lies across a quortz vein that dips steeply to the right. Values of observed gravity were tied to a local station in Bodie which was referenced to a California Division of Mines and Geology base station in Bridgeport (Chapman, 1966, p. 46). Terrain corrections were calculated for all stations; these include inner zone corrections out to 2.29 km, estimated from topo- graphic maps by using Hayford zones A-F and subzones (Oliver and others, 1969, p. 20-21). The remaining terrain corrections, out to a distance of 166.7 km, were obtained by the use of a U.S. Geological Survey computer program (Plouff, 1966). The ter- rain corrections calculated for stations in the Bodie mining dis- trict range from about 3 mgal in the flat area south of the townsite of Bodie to more than 9 mgal for a station on top of Bodie Bluff. Gravity values were reduced to complete Bouguer anomalies for densities of 2.67 g/cm' and 2.50 g/cm' usinga U.S. Geological Survey reduction program. Values of the vertical intensity of the magnetic field were determined at each of the gravity stations and on a few separate profiles, as mentioned above. These values are on an arbitrary datum but were tied to a base in the Bodie townsite. Repeated readings at this base were used to remove drift and diurnal effects. RESULTS OF THE GRAVITY SURVEY The Bodie Hills, including the Bodic mining distnct, arc locat- ed near the axis of a large regional gravity minimum (Woollard and Jocsting, 1964). Although the Bodie mining district is on the eastern side of this minimum, there is apparently only a relative- ly gentle regional gradient in this area. Therefore, a flat regional anomaly surface was assumed for purposes of constructing a residual gravity map of the Bodie mining district area Gravity values calculated for a density of 2.50 g/cm' were used because the density measurements given in Table 5 indicate that this should be close to the average for the Tertiary intrusive and extrusive rocks of the Bcxiic Hills. The value of density used is important, because local elevation changes, which are as much as 600 feet in this area, will greatly influence the results if an incorrect density is assumed. After subtracting the estimated regional gravity gradient from the values at indiMdiiai stations, the resulting residual values were plotted and contoured using a 1 mgal interval. The result- ing gravity map, I'late 2, shows a north-trending gravity high with an amplitude of 7 mgal in the south part of the district near Queen Bee Hill which decreases to an amplitude of about 5 mgal near the north end of the mining district In the southern end of the district, the axis of the anomaly passes close to Sugarloaf Queen Bee Hill, and Silver Hill, but to the north this axis turns northeast and passes east of Bodie Bluff. The southern end of the anomaly in Plate 2 appears to consist of two parts: a relatively broad high with an amplitude of a few mgal. up«in which is superimposed a second anomaly of short-wavelength with an amplitude of 2 <ir .1 mgal. Although the positive residual gravity anomaly in the Bodie mining district is larger in areal extent than the district, the anomaly appears to be spatially related to the mining district, particularly in the southern part. This can also be seen in the 22 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 regional gravity map (Plate I). Furthermore, the steepness of the gravity gradients, especially in the southern part of the dis- trict, suggests that at least part of the source of the anomaly should be close to the ground surface. As mentioned above, the Bodie gravity anomaly could be caused by relief on the basement rock surface if these rcx'ks have a sufTicienlly high density and if they are at a relatively shallow depth beneath the mining district. Measured values of densities for pre-Tertiary rix;ks from the Bodie Hills area, given in Table 5, show a range from an average of 2.60 g/cm' for plutonic (granitic) rocks to an average of 2.82 g/cm' for a sample of greenstone (altered basic volcanic rock). For comparison, the most common Tertiary extrusive and intrusive rcK'ks range from averages of 2.39 g/cm' for samples of dacite to 2.60 g/cm' for samples of andesite. Samples of basalt (2.79 g/cm') and Quater- nary tuff and pumice ( 1.36 and 1.14 g/cm', respectively) repre- sent extreme values for rocks which are not quantitatively significant in the Bodie mining district. Thus, density measure- ments confirm the possibility that the anomaly could be related to the underlying basement rock surface, considering the fact that dacitic intrusive and extrusive rocks are probably the most common of the Tertiary rock units in the area. However, this would require that a basement topographic high coincide in position with the mining district. The fact that no basement rocks crop out in this area and that mining operations to a maximum depth of about 1,000 feet apparently have not encoun- tered any such rocks does not tend to support this explanation. The other possibility is that the gravity anomaly in the Bodie mining distnct might be caused by an intrusive mass, which is believed to underlie and extend beyond the district. The average density of a suite of samples of the dacitic intrusive rocks from the mining district is 2.41 g/cm' (Table 5). This value is not significantly different than those for the extrusive dacite and tuff breccia measured (2.39 and 2.41 g/cm', respectively) and is decidely low for intrusive igneous rocks of this composition. Both the extrusive and intrusive rocks in the Bodie mining dis- trict are commonly affected by argillic, potassic, or prophylitic alteration, however, which may account for these lower than normal density values. The intrusive rocks exposed near the Red Cloud shaft. Queen Bee Hill, and Sugarloaf appear to be less affected by alteration than those in most of the rest of the mining district. Density values obtained from samples of these rocks average approximately 2.59 g/cm', in sharp contrast to the over- all average. Thus, the density contrast between these intrusive rocks and the surrounding extrusive rocks is nearly 0.20 g/cm' in this part of the area. This may explain at least the local, short-wavelength part of the anomaly which is closely associated with the exposures of intrusive rocks in the south end of the distnct. The remaining part of the gravity anomaly might be caused by a large mass of intrusive rocks at depth. These deeper rocks might be less affected by alteration and thus have a higher average value of density than those measured at the surface. The intrusive mass at depth may also have a different, p<5ssibly more basic, composition, which could also result in a higher average density. In the north end of the B(xlie mining distnct, the axis of the gravity anomaly turns northeastward, away from the surface exposures of intrusive rocks at Bodie Bluff and also eastward from the location of the apparent northern extension of the acromagnetic low. This fact is pu/.zling if the p<isitive gravity anomaly is caused by the exposed intrusive rcKks of the area. It may suggest, however, that the pnncipal intrusive mass dix-s not underlie Bcxlie Bluff, but instead is located ab<iut ' .. mile to the east An incorrect density used for reduction of the data or failure to obtain complete terrain corrections in the area of high local relief near Bodic Bluff may affect the gravity map, but errors of the magnitude required to shift the location of the anomaly appear unlikely. Table 5. Rock density measurements of rocks of the Bodie mining district and surrounding area. te€k tn» No of D«*t%dtf tango At Scvno o/ Onto iomptot Ig'cm') o*>on 1)964. r Ml OoMurf l» cm' I Docil* of )h« %oa^ maM,g diitnci oiif Eamnir* rock* of l*M »0<ft« Dociw >OK>lt WoldMJ tiM CitivtJv* racit of Iho Bodfo Mining Dtttrxt enfy I»ff brOCCM* TKii f l.U 1.M 1.19 ^f»- Tortioo' M«fo«ic racki M«iotuff Tliit lopert T),ii ropen T>wi report TM npofl Ow rot«n PokiM*. ond oihon n«6' r^knm.ona oltMn < 196, f> 131 TK(( npvft TImi roporl 2J4^1.M }ao 2J0.3J< 349 - UT _ Ul J2i.2J9 3J9 J1HJ9 341 3 4}}«9 760 3 63-7 94 37» _ U> _ 3AS RESULTS OF THE GROUND MAGNETIC SURVEY Possible causes for the aeromagnetic low associated with the Bodie mining district are discussed earlier in this report. Meas- urements of values of the magnetic susceptibility of samples from the Bodie mining district (Table 4) did not provide a conclusive answer to the question of the cause of the magnetic anomaly, but did suggest that the cause might be related to rock alteration, particularly of the intrusive rocks. Plate 2 is a vertical intensity magnetic map of the Btxlic min- ing district with a contour interval of 200 gammas, based on an arbitrary datum. Magnetic values shown for most stations arc the average of approximately 3 or 4 separate observations taken around each station site. The resulting map of the magnetic field vanes in magnitude from a low cast of Queen Bee Hill (zero contour), to a high exceeding 1200 gammas southeast of the Red Cloud shaft Because of the irregular station interval and possi- ble rapid liKal variations in the magnetic field, this magnetic contour map may not shov* many of the lival features that would be detected in a more detailed survey. In contrast to the relationships shown by the regional anomal- ies, there is little apparent correlation between the gravity and 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 23 Photo 9. Ribbon quartz, containing fine-grained free gold. Typical of tfie veins mined in tfie Bodie Bluff Oreo. Photograph by Francis H. Frederick. ground magnetic maps of the Bodie mining district (Plate 2). Furthermore, the negative aeromagnctic anomaly which charae- lenzes this area is difficult to identify in Plate 2, but this is probably because of the relatively small area studied on the ground (a part of this negative anomaly can be seen in profile X-Y, Plate 1). The observed variations in the magnetic field shown in Plate 2 arc relatively minor features which probably are all within the major regional magnetic low. It would be expected, however, that these minor features might show some general correlation on the map with local geology within the area of the mining district. The highest magnetic values observed in the ground survey are generally, but not exclusively, a.ssociatcd with the intrusive da- cites and tuff breccias of the Silver Hill Volcanic Series TTie intermediate and low values are a.vsociated with the dacitc flows of the Silver Hill Volcanic Series. This is contrary to what might be expected, in general, from values of magnetic susceptibility given in Table 4. which suggest that the intrusive daciles and the tuff breccias might even cause magnetic lows If is probable that liKal magnetic values actually arc more related to the degree of rock alteration than to specific r(xk type. However, no consist- ent relationships between the magnetic map and mineralization or a map showing r<K-k alteration ( Plate 2 ) could be determined Of interest in this regard is profile X-Y which traverses the mining district just south of the Red Cloud shaft, where il crosses the northern edge of a small dacite intrusive plug, shown on the geologic map (Plate 2) This profile shows a sharp, local, posi- tive anomaly, with an amplitude of about 5(X) gammas, which is closely ass(K"iatcd with the intrusive rocks In contrast with many of the other intrusive rixrks in the Btxiie mining district, the Red Cloud intrusive is believed to be relatively unaffected by alteration The results of magnetic susceptibility measurements of samples of these rixks yielded a relatively high average value of 0.0021 emu/cc. Thus, the susceptibility measurements tend to confirm the apparent asMKialion of the intrusive plug and the magnetic anomaly in this area Therefore, il appears that rcia- 24 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 Photo 10. Ribbon quartz veins in intrusive docite near summit of Bodie Bluff. Photograph by Francis H. Frederick. lively unaltered intrusive rcx;ks in the Bodie mining district might be more Hkely to cause magnetic highs, or normal back- ground values, than magnetic lows. Summary Evidence from the regional and local geophysical data in the Bodie mining district and measurements of some of the rock properties suggests the following: ( I ) the negative aeromagnetic anomaly is probably caused by extensive hydro! hernial altera- tion of the intrusive and extrusive rocks in this area, which has removed a large part of the normal magnetic content of these rocks; (2) the positive gravity anomaly is most likely caused by an intrusive mass underlying the Bodie mining district; (3) hy- drothermal solutions responsible for the rock alteration were probably closely related to the emplacement of the intrusive body, thus explaining the close spatial relationship of the major gravity and magnetic anomalies; (4) some of the minor magnetic and gravity anomalies are associated with the relatively unal- tered intrusive rcKks of the Bodie mining district — otherwise there is little apparent relationship on a local scale between these anomalies and riKk types, types of alteration, or mineralization; and (5) iheextensionsof the gravity anomaly beyond the mining district suggest additional areas as possible targets for mineral exploration. ECONOMIC GEOLOGY The mines of the Bixlie mining district have been divided, principally upon the basis of their geographic distribution, into three groups (Plate 3): (1) Standard Hill area, centering essen- tially around Standard Hill and Bodie Blufl"; (2) Middle mines area, occupying the low saddle-like area between Standard Hill and Silver Hill; and (3) the Southern mines area, which lies between Silver Hill and Sugarloaf More than 90 percent of the ore from lixle deposits has come from mines in the Standard Hill area, where the ore occurs in quartz veins, principally in the intrusive dacite of the Standard Hill-Bodie Bluff plug, and to a lesser extent in tuff breccia of the Silver Hill Volcanic Series (Photos 9, 10. and IDA substantial lode production came from several mines in the Southern mines area, where veins occur in flows and tuff breccia units of the Silver Hill Volcanic Series. Lode production in the Middle mines area was small and is not known, but it, too, was from veins in the riK-ks of the Silver Hill Volcanic Series. Placer operations were conducted at sites centered principially in a small area in the eastern part of the Middle mines area, where gold was first discovered in the district. The prixluction of gold from the Placer area is not known but was not great. Because accessibility of many of the mines in the distncl was limited during these investigations, it was necessary to make extensive use of published reports and pnvate reptirts for subsur- face information on the mines and ore deposits. Brown (1907), McLaughlin ( 1907). and Whiting (1888) have been the sources of published data, and the extensnc personal files of Francis H I-rederick (deceased in 19b8) provided much valuable data that were obtained in the district between 1929 and |9,M These published and unpublished data, plus our detailed field investigations, provide an outline of the general features of the mines and ore deposits. 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 25 Pholo 11. Quartibreccio zone, containing free gold, 436 level Bodie mine. Pencil is 5 inches in length. Photograph by Froncii H. Frederick. Standard Hill Area Brown (1907) called altenlion to the Fortuna, Incline, and Burgess series of veins, all of which appear to occur only in the Standard and Bodie mines of Standard Hill Before the mines had become inaccessible, the relationships of these three vein senes had been mapped and clearly deciphered. The Fortuna is the oldest and the Burgess the youngest. In order of decreasing productivity, the Incline is followed by the Fortuna and the Burgess. Several prominent faults, of which only the Moyle Foolwall fault and the Standard Vein fault arc observable at the surface, have cut the veins into segments The Incline senes occurs in the hanging wall segment of the Moyle F-'oiUwall fault and the Bur- gess series is in the footwall segment of this fault The Fortuna scries is cut and displaced by all other veins and fractures it meets (Figures 7. 8, 9, and 10) In spitcof theclosejuxtaposition of the three vein scries and the fact that they intercscct one another, each series has distinguishable features. FORTUNA SERIES The F'ortuna vein scries yielded the richest ore in the Bodie mine. The senes consists pnncipally of the Fortuna and the Beehive veins, which are fissure veins. The Fortuna vein did not crop out at the surface and was first encountered in 1878 in the Bodie new shaft about 340 feet below the collar. Early in 1879, the vein was again cut in a crosscut on the 4?0-foot level of the Bodie mine, about 125 feet east of the Bixiie new shaft, and its apparent richness was quickly determined. The Fortuna vein had a strike around N 10° W and a variable dip. ranging from 30 degrees toward the east, where first encountered in the Bodic new shaft, to 45 degrees in the workings below the 600-fixit incline level of the B<xiie mine. The average width of the vein was no more than 2 feet (Figure 9. Photo 12). and in many places it was only a few inches The strike length of the Fortuna vein is not known, but it was encountered in the east crosscut of the 1,000-fixit level and at points above in the Standard mine, fol- lowed for several hundred feet southward into the Mono claim, and encountered in the lower levels of the Lent shaft workings The Fortuna bonan/a. the /one from which the greatest value was produced, extended down the dip of the vein in the Bodie mine for some 1.000 feet It had Us maximum horizontal deve- lopment of .350 feet on the 600-f(X)t level of that mine and an average length of 200 feet. The quartz in the Fortuna vein is hard, flint-like. white, and adhered tightly to the walls Drusy cavities and comb structures are common The ore minerals include native gold and silver, argenlitc. pyritc, and sphalcntc The sphalentc content increased 26 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 Photo 12. Fortune vein, 400 level Bodie mine looking south. Vein is approximately one foot maximum width at this ploce. Photograph by Francis H. Frederick. with depth as the gold content decreased. Minor amounts of pyragyrite were encountered in drusy cavities in the vein below the 670-foot incline level of the Bodie mine. At the bottom of the Forluna bonanza, near the 600-foot level in the Bodie mine where the dip of the Fortuna vein starts to steepen, a very narrow vein, referred to as the Beehive, left the footwall of the fortuna vein at a high angle (Figures 7 and 8). The Beehive vein ranged in thickness from one inch to one foot and extended downward from its junction with the Fortuna vein to the 707-foot level of the Lent shaft, a distance of about 180 feet; below there it disappears as narrow seams and thin veinlets of weakly mineralized quartz. The Beehive vein was rich in silver and was mined extensively throughout its length and depth. The Fortuna vein was observed on the 1,200-foot level of the Lent shaft, where it appears to occupy a fissure whose dip steep- ens to an angle greater than that observed at higher levels in the Standard mine. The vein had dwindled down to small isolated bunches of quartz veinlets which were occasionally rich in gold and silver. The Fortuna vein was not prospected below the 1,200- foot level of the Lent shaft workings. INCLINE VEIN SERIES The veins of the Incline series (Figure 1 1 ) were said to be gash veins by Brown (l'K)7, p. .150), although the evidence does not always support this designation. All of the veins of this series, except the Gildca in the Bodic mine, terminate at or above the Moylc Footwall fault in the Standard mine. Important veins of the Incline series include the Main Standard vein, the Gildea vein, the Bullion vein, the Incline vein, and the Bruce vein. Most of the veins of the Incline senes dip to the west at high angles, from near vertical to 65 degrees; the main Standard vein, however, had a dip of only 40 degrees. At their contact with the Moyle Footwall fault, which is a normal fault, the dip of the veins flattens and many of the veins seem to curl up into masses of broken quartz ( Figures 7 and II). Most of the veins range in width from 14 inches to 6 feet, but on the 380-foot level of the Standard mine, the Main Standard vein, the largest in the dis- trict, was 90 feet wide and averaged about 20 feet. The general strike of the veins of the Incline scries is from north to N 20* E. The Main Standard vein follows closely to the strike trend of the Standard vein fault, which is generally N 15' E. The Incline vein series can be subdivided (Brown. 1907. p. 351) into two distinct groups of veins of difTcrcnt ages. The older group, which includes the Main Standard and Incline veins, is characterized by massive, well-banded, flint-like quariz. which is usually firm, but in places highly fractured, and is associated with red ferruginous clay that was donvcd through attntion and alteration of the wall rtxrk. The walls of the older group of veins are well defined. The veins of the Incline scries that were fonned later, includ- ing the Bullion vein, are charactenzed by well-handed, ptirous quart/ which is crumbly and contains scarce black manganese oxide and minor amounts of clay. Post-mineral movement in the oldest group of veins accounts for the fractured condition of the quariz and the development of the clay, whereas simple crushing action is said to account for 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 27 the crumbly condition of the quartz and small clay content of the later group of vems (Brown, IW?, p. 351). II \Vi Figure 11. Cross section of the veins of ftte Incline series showing their relationships to the Moyle Footwoll fault. Standard mine. From Brown, 1907. The precious metal content of the Incline veins, which were mined profitably along a strike length of 3,000 feet, seems to have dropped off greatly at about the 500-foot level in the Standard mine. Gold content was uneven in the veins of the younger group of this series, and it was soon discovered that small veins (called "ennchers" by the miners), which branch off generally into the footwall, earned fabulously rich gold ore, assaying several hun- dreds of dollars per ton. These enricher veins, the latest of the series, were thought to be related to the Burgess vein series, but the character of the quartz and the coarseness of the gold indi- cate that the enricher veins are more likely a third group of the Incline series (Brown, 1<J07, p. 352-353). Although the walls of the Incline series of veins are well defined, the dacite adjacent to the veins is highly altered and contains considerable limonite, derived from pynte. Adularia occurs in the veins of this series, especially on the 260-foot level of the Standard mine, and the entire width of the Bullion vein was composed of coarse quartz. BURGESS VEIN SERIES The Burgess scries makes up the youngest veins in this part of the distncl, and includes the Ralston vein in the Standard mine (Photo 13). These veins arc rep<irted to lie in the f(Xitwall below the Moyle Footwall fault, and very few of ihcm reached the surface Their strike trend is from north to N 20" E and their dip IS at high angles toward the east They arc rarely a foot in thickness and arc charactenzcd by weakly banded, while quartz with a comb-like structure, generally at the center of the vein. It was common to find a thin layer of high-grade, gold-bcanng quartz, referred to as "scale", adhering to one of the vein walls. An unfailing indication of nch ore was a layer, up to '/,K-inch thick, called "shale," composed of ground wall-rock and quartz particles in clay. Brown ( IWT, p. 354) suggested thai the "shale" indicates movement along the vein. The dacite adjacent to the veins is altered, but limonite is not abundant. Some of the veins were rich in gold, so much so that veins no more than ' ..-inch thick were sloped. Not only were the veins rich, but the wall rock on both sides of the vein for as much as several feet contained sufficient gold to make the vein zones worth mining. The so-called Burgess bonanza, which was some 12 feet in width on (he 300-foot level of the Bodie mine, consisted of mineralized wall rock and numerous, rich, narrow quartz veins. The length of the Burgess vein series is not known, but the Ralston vein was prospected and mined for a distance of more than 500 feet. Middle and Southern Mines Areas Many of the mines in the Middle mines and Southern mines areas have been under water since 1882 and hence were not accessible to the early investigators who provided so much of the useful data on the veins in the Standard Hill area. Work done in the early 1930s by Treadwell-Yukon Company, Ltd., especial- ly in the Red Cloud mine, provides a limited amount of informa- tion on the Concordia, Red Cloud, and Booker veins, all of which appear to have provided the principal lode production in the Southern mines area. CONCORDIA VEIN The Concordia vein was the principal producer of silver and gold in the Noonday mine and was encountered on several levels in the western part of the Red Cloud mine. On the 402-foot level of the Red Cloud mine west of the Red Cloud shaft, the Con- cordia vein dips 60° E and has a strike of about N 5° W. Farther south, this ■. ..n changed to a south strike and a dip of 65° E. The vein ranged in width from a few inches to as much as 12 feel. It consists of vuggy white quartz, coarse-grained calcite. pseudo- morphs of quartz after calcite, and clayey gouge. The ore miner- als are tetrahedrite, pyrargyrite, and pyrile. Several ore shoots were encountered and sloped in the Con- cordia vein in the Noonday mine. The largest and most imp<ir- tant of these shoots was encountered between the 450-foot level and the 700-foot level. It raked to the south, measured 400 feet in length on the upper levels, and b<illomed on the 7C)0-f(Xit level. The best ore mined from this shtwt in the Concordia vein was more than 3 feet wide and had an average per-lon content of about 6 ounces of gold at the 1931 price of S20.6718 per ounce) and 53 ounces of silver. It was presumably from this ore shcxit that most of the total production of SI, 200,000 was realized for the Noonday mine. RED CLOUD VEIN In most places where the Red Cloud vein was encountered and developed, it was accompanied by gouge and crushed quartz Its strike is generally to the north and its dip to the east ranges from near vertical lo 45 degrees The vein ranges in width from a few inches lo 4 feel On the 256-fiHM level of the Red Cloud nunc north of the shaft, the vein consists of a zone of numerous narrow, parallel, and anastonuzing quartz veins and gouge Far- ther south on the same level, the vein became a definite band of yellowish ribbon quartz and calcite. One ore shoot, stopcd between the 256-foot level and the 592-f«it level, was 120 feet in length, 4 feel in width, and raked to the south The total Nalue of the ore, in gold and silver, was S10.05 per ion at 1931 prices 28 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 Photo 13. Ralston vein, just off Bulwer tunnel, looking soutfi. Photograph by Francis H. Frederick. At deeper levels in the Red Cloud mine (Photo 14), the Red Cloud vein was consistently better defined and contained, in addition to quartz and pseudomorphs o( quartz after calcite, coarse-grained calcite and fine-grained adularia. Ore minerals included tetrahedrile, pyritc, galena, chalcopyrite. and minor sphalerite. Pyrargyrite was reported to be present in the Red Cloud vein by OH Hershey (written communication, 1^29). ORO VEIN The Oro vein, the pnncipal vein developed and mined m the Oro mine, has a general strike from N 10* E to north and a dip of 50* E (locally steeper) The length of the vein is not known, but mine maps show at least 400 feet It ranges in thickness from 2 to 6 feel Must of the ore was obtained from a north-raking shoot which assayed as high as S.140 per Ion at 1*1 .M values for gold and silver Ore minerals included letrahednte, stephenile, pyrargyrite, pyrile, and galena. BASE METAL VEIN Hershey, in his study of the mines of the Btxlie mining district (written communication to Treadwell-Yukon Co., Inc., I''2<'), applied the name of "Base Metal \ein" to a minerali/ed /one which he maintained extended discontinuously from the Bulwer tunnel in the Standard Hill area to the King Bee shaft on Queen Bee Hill (Plate 2). a distance of about 8.000 feet. According to OH. Hershey (written communication to Treadwell-'^'ukon Co., Inc., 1''2'') this vein's maximum development in grade and width in the Silver Hill area ranged from 12 to 250 feet in the Red Cloud mine No zone corresponding to the Base Metal vein could be found on the surface. In the Red Cloud mine, a zone was encountered This /erne consisted principally of intensely brecciated wall rtx'k that had been bleached and replaced in part by veins of comb quart/ and irregular bixlies composed of quart/, calcite. and adulana The quartz is generally fine grained but developed into glassy, needle-like crystals lining vugs and as 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 29 Photo 14. ArgiUicotly altered lu(f brcccio of the Silver Hill Volcanic Series, cemented by dark groy, pyrite-rich chalcedony. 700 level of the Red Cloud mine. Photograph by Francis H. Frederick. pseudomorphs after calcite. Calcite commonly occurs as fine- grained intergrowlhs with quartz, and lamallar plates up to one inch across arc not uncommon. The adularia is fine grained and occurs largely m the fine-grained, quartz-calcitc intergrowlhs. Pyrite is abundant and occurs as small crystals, usually less than Vi inch across, disseminated throughout the bleached and altered dacite fragments. The largest pyrite crystals occur in vugs in quart/ masses and veins. Other ore minerals include letrahednle, pyrargynte, galena, chalcopyrilc, and sphalerite; a/urite and malachite are rare and pnncipally represent alteration of chalco- pynlc. According to E.W. Billeb (oral communication to the au- thors, 1965), a small ore shoot in the Base Metal vein was developed and sloped in the 622-A raise of the Red Cloud mine. This shoot was about 50 feet long and 3 feet wide; it had an average pcr-ton content of about one ounce of gold ($20.55 at the 1931 pnce of $20.6718 per ounce) and 32.27 ounces of silver. BOOKER VEIN Several prominent veins were prospected in the area between the Noonday mine and Queen Bee Hill The Booker vein ( Plates 2 and 5) seems to have been the largest and most promising of these and the one that was developed the most. In the vicinity of the Noonday mine, the Booker vein stnkcs north, but farther south It bends to the east, stnkcs S 30* E and dips 40' E The thickness of the vein is not known, but near the Booker shaft it is less than one f(wt The vein appears lo consist of quart/ and calcite, and much of the quart/ is pscudomorphous after calcite Pyrite is present, usually as small crystals in the quart/ Distribution of Metals in the Veins A characteristic feature of the veins in the Southern mines area is the direct relationships between their silver and gold 30 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 Photo 15. Lent shaft hoist house and office, as it appeared in 1895. Photographer unkown (Frederick, 1960, private communication). content and the amount of quartz present. Those veins that had the highest quartz content had the highest content in silver and gold, both contained in minerals such as tetrahedrite, pyrargy- rite, and pyrite. Because of the inaccessibihty of the underground workings of the mines (Plate 4) in the Standard Hill area, it was not possible for the writers to obtain first-hand information regarding the distribution of metals and the grade of ore. Whiting (1888, p. 389), from whom much of the data about the vcms in the Standard Hill area was obtained, made the following comment regarding the metal distribution in the In- cline and Burgess vein systems: "In all of these younger series of hxles the gold content largely exceeds in value that of the silver, though in the relative proportions of the two metals by weight, the silver is somewhat in excess of the gold tenor. In the average assay value of the Standard ore, as given in its Superin- tendent's rep<irt for the fiscal year ending February 1, 1883, the gold content was stated at $34.28 per Ion, the silver at $4.07, in a total of $38.35 per ton of two thousand pounds. Its silver value was calculated at $1.2929 per troy ounce, the gold at $20.6718 per ounce In weights, therefore, the average gold contents of the ore for the year were 1.65 troy ounces per ton; while the silver tenure amounted to 3.14 ounces per ton, furnishing 65.6 percent by weight of the precious metals in the ore of these so-called gold mines. The native gold of these Bodic veins, moreover, is itself an alloy with silver in the proportion of about six hundred and ninty-five thousandths gold and three hundred and five thou- sandths silver. Apart from this occurrence of the silver, however, these veins also carry that metal in flakes and wires, and mineral- ized as argentite and kerargyrite..." Further along in his report. Whiting (p. 392) slates, "As is the case along all of the Bodie fault fissures the andesite on either wall of the nch vein is more or less thinly sheeted, and along such structural planes, to the depth of a fixit or more from this narrow quartz vein, nalise silver was often found in the wall-rock, in small fronds and wires; so that where the quartz of the vein did not exceed six inches in width, from eighteen inches to two fc"et could be profitably mined." Brown ( 1907, p. 347), in his analysis of the veins in the B<xlic mining district, stated, "The Fortuna is the only \ein with marked easterly dip. It is also the only one presenting the charac- teristics of a strong, deep-reaching zone of fissunng Unfortu- nately, this permanency is of structure alone, and does not extend to Ihe contents; for in the lower portions the vein rapidly becomes imp<nerished; sphalerite, from being almost absent, increases to a large percentage; gold values weaken and almost die out; and silver diminished to a few sparse patches of wire in ma.s.scs of impure, bluish kaolin." Wisser (I960, p 76) summed up Ihe relation of structure to nictalli/.;ition at the B<x)ie mining district as follows; "All Bodie 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 31 Photo 16. View of Bodie looking southwest from Standard Hill. Excavation in foreground is port of lorge scale sampling conducted by Yukon-Treodwell Compony, Inc. in the Spring of 1931. Photograph by Francis H. Frederick. veins earned both silver and gold, but some were relatively high in silver, some in gold. Where earlier vein matter was fractured and later vein minerals deposited in the openings created, the later vein matter was invanably richer in gold than the earlier. Solutions, therefore, changed in time from relatively silver-rich to relatively gold-nch " Depth of Mineralization As was brought out in the discussion of the veins, mineraliza- tion in the district appears to be shallow , and the precious metals values rarely e.xtended much lower than the 500-foot level in any mine. This is especially true in the Standard Hill area for the Incline and Burgess vein series. The Fortuna vein, an exception to the general depth rule, was mined down dip for 1,000 feet, or to a depth of about 600 feet below the surface. Mineralization in the Southern mines area appears to have extended at least 800 feet below the surface. Below this depth, veins continue but consist almost wholly of calcile with an occa- sional small irregular body of quartz pscudomorphous after cal- cite. The depth to which precious metal mineralization extends in the Middle mines area is not known, although the Dudley shaft (Plate 2) IS said to have been sunk 500 feet below its collar (O.H. Hcrshey. written communication to Treadwell-Yukon Co., Inc., 1929), and no veins of any significance were encountered in cither of the long crosscuts extending east and west from the bottom of the shaft. A study (ONcil and others, 1973, p. 780) of the stable iso- topes of hydrogen, oxygen, potassium, rubidium, and strontium in the quartz veins and their unaltered and altered host rcKks, and alteration clay, fluid inclusions, and mcxicrn spring waters in the district indicates that alteration and ore deposition oc- curred over the approximate temperature interval of 2 1 S-240* C. The study also indicates that the source of the ore constituents is probably magmatic and perhaps from the same source as was postulated for the dacite plugs of the district. HISTORY OF MINING AND PRODUCTION The discovery and early development of the mines in the BtxJie mining district have been described by Cain (1956. 196 p ). Billeb (1968, 229 p.), and Wedertz (1969. 211 p ). all former residents of Bodie. The account by Wedertz goes into considera- ble detail on the mines of the district. Early accounts on the mines of the district are by Browne (1865. p. 274-284) and Wasson ( 1879, 46p. ). Other accounts have been published in the past 10 years, but they deal primarily with events that took place in the town of Bodie and only incidentally with the mines of the district (Johnson, 1967, 119 p; Calhoun, 1967, 172 p.). These reports and information obtained from discussions with Emil W Billeb and others who have been closely associated with the mining activities of the district were the source's for preparation of this historical sketch. Gold was discovered in the Bodie mining district in mid- summer of 1859 in shallow placer deposits situated in the east- central part of the district. Later that summer, gold-bearing quartz veins were discovered on a claim, then known as the Montauk (Plate 3) but now called the Gixxlshaw. In I860, the mining district was organized and named B<xley; in 1862 the spelling was changed to Bodie The first mining company was formed in 1863 when owners of several adjacent mines con- solidated their claims and holdings to form the litnlic Bluff Consolidated Mining Company with Governor I.cland Stanford as president and Judge F' T Hechtel as secretary Between 1859 and 1876. spxiradic development was earned on in the district with moderate production, no statistics on this 32 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 development are available. Rich ore found on the Bullion loca- tion in 1872 was milled in arra-siras on Rough Creek, about 5 miles northwestward from the district. In April 1877 the Stand- ard Mining Company was incorporated, and the first ore mined by the new company was milled in the Syndicate mill, which was situated on Bodie Creek at the north end of the district. Soon thereafter, however, the Standard Mining Company constructed Its own mill. Rich ore found in the Standard mine in 1878 sparked a boom which lasted for about 10 years, during which period as many as 50 companies were operating simultaneously in the district. Costs of mining and milling of the ores were very high in the district, owing principally to the high cost of firewood for the generation of steam. In the early 1890s, the Standard Mining Company brought in electrical power for mining and milling purposes from its hydroelectric power plant on Green Creek, some 13 miles to the west of the district. The introduction of electrical power into the district dramatically reduced mining and milling costs, and this, in turn, stimulated new interest in developing the mines. The bonanza in the Standard mine was exhausted in the late 1 880s and the district was faced once more with drastic decline in production, activity, and interest. In 1915, the Standard Con- solidated Mining Company was dissolved and its properties were acquired by the J.S. Cain Company, which still retains title to them. Small-scale lease operations continued for about 15 years on high-grade ore in place and on tailings and mine dumps. The first systematic development of the Bodie mining district was undertaken between 1928 and 1931 by theTreadwell-Yukon Company, Ltd. Extensive, deep exploration were conducted in the Noonday and Red Cloud mines of the Southern Consolidat- ed Company. A total of 18,000 feet of drifting and crosscutting resulted from these exploration attempts to locate a southern extension of the Fortuna vein. Although the results were en- couraging, the search was eventually abandoned. Treadwell-Yu- kon also examined the Standard Hill mines area, by systematically sampling underground and surface exposures (Photo 15) and by a large-scale pilot plant investigation of treat- ment of mine dumps and surface ore in place. Treadwell-Yukon discontinued its investigations in 1931. In 1935, the Roseklip Mines Company, organized by John Rosek- ranz and Henry Klipstein, obtained a lease from the J.S. Cain Company and constructed a mill and cyanide plant of 500-ton- per-day capacity. It was operated continuously until 1942, at which time most gold mining ceased in the United States. Dunng this period, the mill treated 346,000 tons of material from dumps and 55,000 tons of ore mined by mechanical shovel from surface cuts. In 1945 the J.S. Cain Company leased the mines to Sierra Mines Incorporated. This company proposed to continue opera- lions to confirm the existence of a large quantity of marginal ore in the Standard Hill mines area. This operation, however, was short-lived, for on April 3, 1946, a fire of accidental origin de- stroyed the mill and cyanide plant, which at the time were being enlarged to a capacity of 20.000 tons per month. Since 1946. sporadic interest has been shown in the district. The American Smelting and Refining Company acquired most of the properties in ihe district in 1967 through lease and option, and in the summer and fall of 1968 carried on a brief extensive program of sampling both underground and on the surface, and the testing of ores. In 1970. the Phelps D<xige Corporation ac- quired a lease on the properties in the dislncl and immediately commenced a detailed, systematic sampling of veins exposed at the surface and in mine workings that could be made easily accessible. By 1972. prospecting by core dniling was started, particularly in areas where previous mining activities had not been extensive. Table 6. Year 1860- 1876' 1877 1878 1879 1880 1881 1882 1883 1884 1885 1886 1887 1888 1889" 1890 1891 1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 1910 1911 1912 1913 1914(2) 1915 1916 1917 1918 1919 1920 1921 1922 1923 1924 1925 1926 1927 1928 1929 1930 1931 1932 1933 1934 1935 1936'" 1937 1938 1939 1940 1941 Totals (1) Go\d Silver Value Value 731.06302 67.86728 1.890.531 18 239.66914 2.371.964 36 298.137 13 2.333.59086 636.66386 2.743.39177 416.675 74 1.751.152 07 466.62817 Production of gold and silver of the Bodie mining district. Mono County, Californio, from 1860 fo 1941. Total Value 4.000.000 00 798.950 30 2.130.200 32 2.670.12149 2.970.253 87 3.160.067 51 2^17.780 24 1.582.667 08 1.123.583 96 449,765 95 526.455 15 341.782 03 126294 91 193.264 00 144.18000 302.514 00 396296 00 293.637 00 358.824 00 552.690 00 451.552 00 520.10100 446.107 00 697.069 00 670200 00 493.355 00 510.596 00 334,713 00 268.930 00 311.959 00 338.698 00 383.971 00 413.946 00 3S4.90900 435.724 00 261232 00 377,518 00 141.772 00 6,82100 107,302 00 237.064 00 209.040 00 31252 00 29,42800 144.746 00 37.754 00 65,74700 34.66100 49.65100 5.50300 20204 00 3.68600 6.X7 00 9077134 26.773 00 16.30000 95.48100 72.888 00 100.94200 78,335 00 150278 78 76.669 133.965 37 89.65886 223.55163 59,43865 12.643.496 38 2.518.93083 90.771 34 43.07300 168.36900 179277 00 226,94863 223.624 23 282,99028 33554,91929 ' (islimale based upon sparse reporting ol annual production value ' ' Between 1889 and 1928. total value includes $2,960,000 00 in goU and $4,815. 869 00 in silver reported from oilier districts m Mono County • • • GokJ calculated at S35 00 per line ounce and silver at $0 70 per line ounce lor period Irom 1936-1941 ( 1 1 Between 1860 and 1935 gold was calculated at $206718 per fine ounce and silver at $1 2929 per line ounce (?) Standard Mill closed down 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 33 Table 7. Production, dividends and operations of the Standard Consolidated Mining Company, Bodie mining district. County, Californio (Eakle & McLoughlin, 1917, p. 151). Mono 1177- ino ini im na MM IMS mo itii ifij »i] '•.437710 1.033 3*3 35 1.441.134 47 I.39V.U4 67 I.937.t43 33 7.049.331 33 »,t73.73«0t t.0»4.914 46 347.093 74 nt.nioo M3.707IO 137440 94 1 34.900 17 Ua.73 36 33 79937I 7]9.]«l 70 17135139 193.907 30 >3«17 9« J94J7»97 M1.73aO 443.179 91 4U.*I>7I U1J04.0S M0.77S.40 3n.ayst nijTon 373.04&9I mow 03 1»U>47J« 3J3.3U03 n«.4040l J47.9JJJ9 n3.47&<l in.9D3)4 133.943 69 tU.304.79»U Vokf p*> r<ni o/ Coil mtning P*rc«Al Tolol p«r ion U»«d pvnwit tn mtl tC*Ml •90.000 00 330.000 00 930.000 00 973.000 W •73.00000 373.000 00 30.00000 x.ooooo 40.000 00 I •903 to 3«S34 30 ia.903(0 37.ao3.ta I •.903 10 UiTtao M.tft.ao S3.511JO 7U)7«a 71.357 40 71J57 40 S3J1t.30 17.(39 40 44 39*30 33.t7«a0 33.i7«^KI 17.t39 40 17.nt40 tt 44.39*30 3.364 407 SO r.430 6.930 10.111 10.160 13.967 13J3« I7.M3 30.473 ia.047 14.734 17,734 10.310 1^.340 16.031 14.339 11J33 13.13* •.79* •.130 6J43 360.901 3*44 1663 30 40 33 37 3«71 3&06 19.14 l>4a 30 70 l>36 19 77 17 13 14.34 14.14 14.M 14^14 1171 130* I I I 7.017 7J4J 11.037 9.337 10.603 13.93* 14.773 11433 14.t61 30.934 9.147 *179 14.7*4 13.433 13.077 14.749 319,903 1143 <U4 Ml] 4407 4034 33*3 4741 7M1 7304 6106 6049 3437 1634 »*} 60*7 4440 «»4 4214 3*46 37a 6.03 493 9(3 143 731 113 *90 393 734 333 *ll IK) *oa 3 17 74a 19« 793 339 905 3 34 • 13 169 397 160 436 143 493 113 733 163 a79 1.2a 755 303 1367 193 10 71 164 10 50 — AtMtuMMi «l |33.00a00 — AtM*iM*Af ol 373.000 00 ^ fWotK pew*, wttTodwcd — SAnM. crOM,d« pion< b«90>< flp«i 90 MJ ond Umm plant ckM*d. Ociofe** i« end tt ftrnt •frvm wKrw^ laaa. p 19* tCa>6w hgum i^woJohh tTOvy III iii| | i tnm 1911. »«t Thi.s apparently was the first core drilling in the Bodie mining district. Mine records fail to indicate whether any long-hole percussion drilling had been done in the mme workings. Because many of the veins thai were profitably mined underground have not been found at the surface, especially in the bonanza zone, core drilling from underground mine workings may disclose new veins or extensions of veins that had been dislocated by faulting but not found by crosscutting and drifting. Dunng the productive life of the Standard Consolidated mines from 1877 to 1915, the group accounted for more than 90 per- cent of the bullion produced in the district, which exceeded $18,000,000 in value at pnces prevailing at that lime (see Tables 6 and 7). In the course of mining and milling ore from the bonanza zone, an estimated 527,000 tons of waste material was hoisted to the surface and placed as waste dumps. An estimated 150,000 tons of waste material remains underground as slope filling. The Bodie Histonc State Park was created in 1956 to preserve a ghost town of a colorful past It encompa.sses the townsite of Bodie but docs not include the mining properties in the Bodie mining district Milling The first ore mined in the Bodie mining district was milled in arrastras on Rough Creek, about 5 miles northwestward from the district, and some ore was hauled 1.1 miles to Aurora. Ne- vada, and processed in stamp mills Ab<iut 186.1 a mill was established low at the western base of Bodic Bluff (Wcdertz, 1969, p 178) By 1882, eight mills were operating in the district; they contained 140 stamps, all powered by steam engines. The Bodie ores were characterized as "free-milling." A large percentage of the gold was recoverable in the free and relatively pure stale by amalgamation or strakc (shaking table) concentra- tion. The silver occurs in the gold and as sulfides or as the chloride-cerargyrite. In the early 1900s, it was found that the Bodie ores were amenable to simple cyanidation; the process yielded high extraction with relatively low costs and low con- sumption of reagents. SUGGESTIONS FOR PROSPECTING On the basis of sampling by Treadwell-Yukon Company, Inc., during the early 1930s, the bonanza zone (a highly prtxluctive block bound by the Mono, Tioga, Moyle Footwall, and Standard Vein faults) offers the best possibilities for new exploration and development This conclusion is ba.sed up<in several factors: ( I ) the character and widespread distribution of innumerable veins in the bonanza zone, of which many yielded high-grade ore; (2) productive history of the mines in this zone; and (.1) detailed sampling of some of the underground workings in the margins of the bonanza zone. The bonanza zone yielded more than 6.1.1.000 ounces of gold and as many as 800.000 ounces of silver from approximately .180.000 tons of ore (SB. McCluskey, written communication. Rcp<irt to Sierra Mines, Inc.. 1947). It has been estimated that the bonan/ji zone still contains as much as 25,000,000 tons of ore whose average value in 1947 was reported to be $1 86 per ton. rurthcrmorc, this value might be increased substantially (to perhaps $2 10 per Ion) from enrichment due to fills, pillars, and veinlets of high-grade ore that were undiscovered or rejected because of the high costs of operating the mines 34 CALIFORNIA DIVISION OF MINES AND GEOLOGY Bull. 206 im^f^ ■i-.'i.iri Jt^ ■IX Photo 17. View north toward Standord Mill. High peck is standard Mill Zones of marginal ore lie in the footwalls of the Moyle Foot- wall and Standard Vein faults adjacent to and on the west and east sides of the bonanza zone and on Bodie Bluff on the north side of the Tioga fault. The marginal ore zones contain many quartz veins, barren and ore-bearing, and an intervening lattice of veinlets, stnngers. and seams which form a stockwork in the firm intrusive dacite. Underground workings in these zones are, in a majority of cases, accessible, and from them drilling can be done in many directions, even into the bonanza zone, where mine workings have been inaccessible for many years. Only a few of the veins south of the Mono fault were produc- tive, but those that were apparently barren or too low in grade to be considered at the time were not explored along their length or to any significant depth. These veins occur in highly altered tuff breccia and dacite flows, and, as most of them are also highly mineralized, none should be overlooked. Because of extensive surficial debris at the southern end of the B<xlie mining district, especially in the areas surrounding Sugar- loaf and underlain by units of the Silver Hill Volcanic Scnes. very few quartz veins and zones of mineralized rock were found at the surface Samples of mineralized rock containing significant amounts of pyrargyrite and pyrite were collected from the waste dump of a shaft that is located about 2.000 feet south of Sugarloaf and were found to contain 18 ounces in silver and 0.2 ounces in gold. Pyrargyrite and pyritc were found on the waste dumps of other prospects in this particular area, thus indicating widespread min- eralization worthy of consideration and/or testing. REFERENCES Al-Rowi, Y.T., 1968, Age and structure of mineralization ot Bodie District, California: Geological Society of America (abstroctj, 64th Annual Meet- ing, Cordilleran Section, Tucson, Arizona, p. 30. Al-Rowi, Y.T., 1969, Cenozoic history of the northern port of Mono Basin. California and Nevada, Ph.D. thesis. University of Califomio. Berieley. 163 p. Anderson, C.L., 1880, Mop of the Bodie mining district. Mono County, Cali- fornia: Published and illustrated by Edward Eysen, San Froncisco, Califor- nia. Atwood, M.. 1879, Wall Rocks of the Bodie auriferous lodes: Mining and Scientific Press, Son Francisco, California, v. 38, r>o. 11 (Mofch 15, 1879), p. 169. Billeb, E.W., 1968. Mining camp days: Howell-North Books. Berkeley, Coli- fornio, 229 p. Bloke, W P., 1862, in Complete guide to Mono County mines, by Joseph Wosson: Joseph Wosson (1880), p 17 Browne, J.R., 1864, in Complete guide to Mono County mines, by Joseph Wosson: Joseph Wosson (1880), p. 17 18. Browne, JR., 1865, A trip to Bodie Bluff and the Dead Sea of the west: Harpers New Monthly Magazine, v. 31 (June to November, 18651, p. 274 284. Brown. R.G.. 1907. The vein system of the Stondard mine. Bodie. Colifomio: Trans. AIME. v. 38. p. 343 357. Cain. EM., 1956, The story of Bodie: Fearon Publishers. Son Francisco. 196 P Colhoun, M., 1967, Pioneers of Mono Basin: Robert C. Calhoun, 172 p Chopmon, R.H., 1966, The Colifomio Division of Mines and Geology gravity bose station network: California Division of Mines and Geology Speciol Report 90, 39 p. 1986 GEOLOGY AND ORE DEPOSITS OF THE BODIE MINING DISTRICT 35 Chestermon, C.W., and Groy, C.H., Jr., 1966, Geology and itructure of the Mono Bosin, Mono Counfy, Colifornio: Guidebook olong the enstcentrcl front of the Sierra Nevodo: Geologicol Society Socromento Annual Field Trip )966, p. 11 18. Chestermon, C.W., 1968, Volconic geology of the Bodie Hillj, Mono County, Colifornio: in Studies m volconology, Geological Society America Mem- oir 116, p. 45-68. Chestermon. C W , and Groy. C.H., Jr., 1975, Geology of the Bodie 15 minute quodrongle. Mono Courity. Colifomio: Colifornio Division of Mines ond Geology Map Sheet 21. Eokle, AS. and McLoughlin, R.P , 1917, Mono County, 15th Annuol Report State Mineralogist, p. 143-160 Gilbert, C.M., Chnstensen. M.N., AlRowi, Y T . ond Lojoie, K.R , 1968, Struc turol and volcanic history of Mono Bosin, Colifornio-Nevodo, in Studies in volconology. Geologicol Society of America Memoir 116, p. 275-329. Hakes, OF,, 1902, Mining lowi of Bodie mining district: Bodie Miner Index. Bodie, Californio. 48 p. Johnson, Russ and Anne, 1 967, The ghost town of Bodie: Cholfant Press, Inc., Bishop, California. 119 p. Kleinhompl, F.J., Davis, W.E., Silbermon, M.L., Chestermon, C.W., Chopmon, R.H., and Groy. C.H , Jr., 1975, Aeromognetic ond limited gravity studies ond generalized geology of the Bodie Hills Region, Nevada ond Colifor- nio: U.S. Geological Survey Bulletin 1384, 38 p. Koenig, J.B., 1963, Geologic Mop of California, Olaf P. Jenkins edition. Walker Lake Sheet: California Division of Mines ond Geology, scole 1:250,000. Loose, W., 1971, Bodie Bonanza: Exposition Press, Jericho. New York, 246 P Mojmundar, H.H., 1973, privote communicotion. McLaughlin, R P., 1907. Geology of the Bodie district: Mining ond Scientific Press, Son Francisco. Colifornio, v, 110. p. 795. Oliver, H.W., Griscom, A., Robbins, S.L.. and Honno, W.F., 1969, U.S. Geologicol Survey grovity doto in California, port IV: U.S. Geological Survey Interogency Report. 53 p. O'Neil, J R , Silbermon, ML., Fobbi, B.P., ond Chestermon, C.W., 1973, Stoble isotope ond chemical relations during mineralization in the Bodie mining district. Mono County, Colifornio: Economic Geology, v. 68, p. 765-784. Pakiser, L.C., Kone, M,F., ond Jackson, W.H., 1964, Structurol geology and volconism of Owens Volley region. Colifornia — o geophysical study: U.S. Geological Survey Professionol Paper 438, 68 p Plouff, D., 1966, Digitol terrain corrections based on geographic coordinotes [abstract): Geophysics, v. 31, no. 6, p. 1208. Silbermon, ML., ond Chestermon, C.W., 1972, K Ar age of volconism and minerolizotion. Bodie mining district and Bodie Hills volcanic field. Mono County, Colifornia: Isochron West, no. 3, p. 13-22. Silbermon, ML., Chestermon, C.W., Kleinhompl, F J . ond Groy, CM., Jr.. 1972, K-Ar ages of volconic rocks and gold-beoring quartz odulono veins in the Bodie mining district. Mono County, Colifornio: Economic Geology, V. 67, p 597 604. Sillimon, B., 1864, in Complete guide to Mono County mines, by Joseph Wosion: Joseph Wosson (1880), p 13- 15 Streckeisen, A.L., 1967, Clossificotion ond nomencloture of igeneous rocks: Neues Jahrbuch fur Mineralogie Abhandlungen, v. 107, p. 144-240. Wosson, J., 1879, The mines of Bodie, o complete and occurote occount of the mining properties in and odjocent to the town of Bodie. Mono County, Colifornio: The Mining Record Office, New York, 46 p Wedertz, F.S., 1969, Bodie, 1859-1900: Cholfant Press, Inc , Bishop, Colifor- nia, 21 1 p. Whiting, H.A., 1888, Mono County: 8th Report State Mineralogist, p 382- 401, Wisser, E., 1960, Relation of ore deposition to doming in the Americon Cordillera: Geological Society of America Memoir 77, p. 70-77. Woollord, G.P., ond Joesting, H.R., 1964. Bouguer grovity mop of the United States (exclusive of Alaska ond Howoiil: American Geophyncol Union, Special Committee on the Geophysicol and Geological Study of Conti- nents, and U.S. Geologicol Survey, scale 1:2,500,000. APPENDIX: K-Ar Sample Description and Locations* 1. Adulona-quortz vein (S-centrol Sec. 9, T4N, R27E, on south tide of Standard Mill. Mono County. California) USGSIM) -7346-1. 2. Adulorio-cokite-quartz vein (S-centrol Sec. 16, T4N, R27E, watte dump of Red Cloud mine. Mono County. Colifornio) USGS|M| RCD1B 3. Adulorio-quortz vein (S-centrol Sec. 9. T4N, R27E. wotte dump of McClinton thofl. Mono County. Colifornro) USGS (M) -B270. 4. Porphyritic biolile fiomblendc docile mtruiive |NW '/^, Sec. 21, T4N, R27E, about 500 feet loutti of Red Cloud thofl. Mono County, Colifor- nio) USGS(M) BH15. 5. Porphyrilic hornblende docite intrutive (SW '/, Sec. 21. T4N, R27E, on lop of SugoHoof, Mono County, Colifornia) USGS (M) -SI 6. Altered porphyntic hornblende docite intrutive of Bodie Bluff |S central Sec 9. T4N. R27E. cut »rett of Siondord thoft. Mono County. Colifor nio) USGS(M) B271 7. Porphyritic hornblende docite intrutive ol Queen Bee Hill (NW '/i S«c. 21. T4N. R27E, Mono County. Colifornio) USGSIM) BH17. 8. Pofphyritic hornblende pyronene ondetite flow, "Wall Andciite" (SE '/« Sec. 10, T4N, R27E, Mono County. Colifornio). USGS (M) -7346-3. lo- cality off mop. 9 Porphyritic biotitehornblende docite (NE Vi Sec. 21, T4N, R27E. Mono County. Colifornia) USGSIM) BH32. locolity off mop. 10. Porphyritic biotitehornblende docite IE centrol Sec 16. T4N, R27E. old quarry near ditmontled railroad. Mono County, California) . USGS(M) - 85632. 11. Porphyritic biotite-hornblende-rhyodocite intrutive (W-centrol Sec. 16, T4N, R27E, 1 mile touthwetl of Bodie. Mono County. California) . USGS(M) 856 10 locolity off mop 12. Porphyritic biotile hornblende docite flow, lower unit of compotiie flow |NE '/. Sec 16. T4N, R27E. about 2000 feet eoit of Red Cloud mine. Mono County. Colifornia) USGS(M) BM16. 13 Porphyritic bioliie docite flow (N centrol Sec. 28. T4N. R27E. Mono County. Colifornio) USGSIM) 854-1 14. Porphyritic biotite docite flow (center Sec 12. T4N. R26E. Mono Coun ty, Colifornia) USGS(M) BM2 locohty off mop 15 Porphyritic biotite hornblende docite intrutive (NE \ Sec 23. T4N, R27E. near ditmontled roilrood. Mono County. California). USGS|M|- BH29 locality off mop 16 Porphyritic rhyolite ( SW >/, Sec 7. T3N. R26E. Mono County. Colifor mo) USGS(M) BH27 locolity off mop. *Fke4d numbm ihown on pUir 1 THIS BOOK IS DUE ON THE LAST DATE . ^, ^ STAMPED BELOW BOOKS REQUESTED BY ANOTHER BORROWER ARE SUBJECT TO IMMEDIATE RECALL I FEB 2 1 ^993 RECEIVED ■."• V 4 LIBRARY. UNIVERSITY OF CALIFORNIA. DAVIS D4613(7'92)M m THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW /*f K 05^5 BOOKS REQUESTED BY ANOTHER BORROWER ARE SUBJECT TO IMMEDIATE RECALL FEB 2 1 ^993 RECEIVED LIBRARY. UNIVERSITY OF CALIFORNIA, DAVIS 04613 (7.92IM en — to o ir > < UJ CD < o O -I UJ o (D tij < o Z UI < I- X O tr a. >- cr. a z < < 3 O SWWWV9 Nl A±ISN3iNI TViOi snvomiw ni AiiAVdo i33J Nl N0li\/A313 STVDmiW Nl AilAVaO SVWWV9 Nl A1ISN3±NI 0li3N9VW HVOIiaBA 1333 N0liVA3T3 < o o o SI PS z s C8 E Urn H U c« ^ c NN • P4 w 0^ o E C/5 (4-1 KTi U NN hm a> Q rt SB E O u x: OX) Z >^ .a o ^N -^^ Q£ ►^»- c ■o ^ s oi >-, *^ o Q. ^ S U E o u u o a a. >1 HH n a. Q o S © O u O n OX) o O o < Z < a. X UI tc (9 /7 o o O 03 3 s 'a* S.g w 1 c// — " .•r c T3 o CD — o C O V Q. 3 O Eif UJ t. ** a: O o (- < z < a. X «3 O _l o UJ IS "oO^ a. ^ O 3 O ^ — O £, , O ® O > O O <IU CM em = 6 U 0* Q O II, 0. e Q. < CD s « O T o o o 01 o o UJ >! ■o 3 o a c o 3 o O u: H 1- C -^ V F F X « D o UJ M a ft> J. z U ^ < Wo o =* C 3 OS >.-o o o _ a) — H5 c c Co X — a SO O * pi M 3 - - . (C o c ° O-f _ >>0 4) ^:^- 2"° O O (D —^S St 2 ." e o^ S s« e " = ? So- I -.5 j3 41 — -O I. CT — a) W I- E o < » N o: £ DIVISION OF MINES AND GEOLOGY JAMES F, DAVIS, STATE GEOLOGIST STATE OF CALIFORNIA - GEORGE DEUKMEJIAN, GOVERNOR THE RESOURCES AGENCY - GORDON K VAN VLECK, SECRETARY FOR RESOURCES DEPARTMENT OF CONSERVATION - RANDALL M. WARD, DIRECTOR ^^7^"^ XT'* "" Tsd Sd "^ H^^ B) y^^ k ^ BULLETIN 206 PLATE 2 / f -1- LOAFPCAK *\.n ^•'^ ^^ B600 j^' y^ „ \a405 ^^ ^837 7 Ov-.,,^^^ .^ ^ <^ ''^ .:^ AMM^ \\ ' \""V< / ^^■''"^^ \ 1 ^ \ Tsd /- / r V (A) y GEOLOGIC MAP SHOWING MAGNETICS, GRAVITY, AND ROCK ALTERATIONS BODIE MINING DISTRICT Mono County, California Geology by Charles W. Chesterman & Cliffton H. Gray Geophysics by Rodger H. Chapman PHrSICAl SCIENCES lIBMRr UC DAVIS CONTOUR INTERVAL 50' SCALE 500 lOOOft. Note: Refer to Plate I for gravity and ground magnetic profile X-Y and aeromagnetic and gravity profile R-S. 7900 >— Btxiis ..... Mono Fault Queen Bee Hill I Sugorloaf Tsdi Tst Tsd (A) Tmd 9000 8600 8400 8200 8000 7800 8000 Bodie Moyle 8800 — 8400 — 8200 — 8000 — 7800 I— ^^ 9000 8800 8600 IJ 8400 8200 m 8000 -■ 7800 8800 I- 8600 - 8200 — 8000 7800 Moyle Footwall Fault Standard Hill Standard New Shaft 7400 F .■7 projected H 8800 8600 8400 8200 8000 7800 7600 — ' 7400 8000 7800 7600 LEGEND GEOLOGIC EXPLANATION E^ Qal Os Tpd Tp» Tsdi Tsf i/ ye Mill tailings Plocered area Alluvium Slope Wosh Dactte flows Tuff breccio Doctte flows and plugs Tuff breccio; (G) groy, (B) brown Docile plugs Docile composite flow; (A) hornblende-rich, (B) biotrte-rich Tuff breccio, Includes vltric zones (WT) Silicic alteration Potossic alteration Argillic alteration Propylitic alteration Incline vein series, various veins Incline vein series, main Standard Burgess vein series Fortune vem GEOLOGIC SYMBOLS Contoct; dashed wh«re probable, queried where uncertain. Fauiti dashed where uncertain, dotted where concealed. Bor and bell on downthrown block. Vein; showing strike and dip, dashed where uncertain. strike and dip of bedding. Strike and dip of flow bonding. Strike of vertical flow bonding. Strike and dip of ioints. General direction of dip. Specimen locality of rock sampled for K-Ar age dating. GRAVITY EXPLANATION Gravity Station Contour Intervol: I.Omilllgals Reduction density : 2 50g/cm' Axis of positive onomaly trend MAGNETIC EXPLANATION Magnetometer station Contour Intervol: 200 gammas Arbitrary datum DRAFTING AND LAYOUT BY CA ALLEN DIVISION OF MINES AND GEOLOGY JAMES F DAVIS, STATE GEOLOGIST »^»»-, 4. Tioga Mine 5. Con Pacific Mine STATE OF CALIFORNIA - GEORGE DEUKMEJIAN, GOVERNOR THE RESOURCES AGENCY - CORDON K, VAN VLECK, SECRETARY FOR RESOURCES DEPARTMENT OF CONSERVATION - RANDALL M- WARD, DIRECTOR Belvedere Mine -.vr^^-jjir-r^- v^: 7. South Bulwer Hoisting Works 8. Jupiter Hoisting Works 5S0C jwrfv. ng Works 9. Dudley Hoisting Works .0^ <b 830t ^tjGAf ^0RN£ IN. ^ .^£IN en BULLETIN 206 PLATE 3 -■*f»fv. fHYSIMl SCIENCES new ( UC OAVIS ^^. L' I !i !S!! S! 10. Defiance Hoisting Works » 11. Booker Mine ■jo^j: I j*^«*f<*-^ nDli-^^ 1. Syndicate Mine REFERENCES. 1 STANDAQD-BUUNER MILL. 2 MOUTH Of BULWER TUNNEL. 3 OeiBINiL SUMMIT MINE. il BODIE BLUFF MINE 5 BECHTEL MINE. 6 STANDARD MINE 7 CON. PACIFIC MINE a BELVIDERE MINE 9 eODIE MINE . 10 STANDARD MILL . II SOUTH BULWER MINE 12 MONO MINE 13 CHAMPION MINE 14 GOODSHAW MINE. ie4^&^^ GENERAL VIEW OF BODIE MINING DISTRICT Showing the Western Slope of the Maim Range from North to South 1880 cas- NO.'t SCALE 500 1000 ft. CLAIM MAP BODIE MINING DISTRICT Mono County, California Surveyed and compiled by D.W. ORMSBEE - G.E. January, 1931 Contour Interval: 50ft. rlK^*- -i^'-se :*Si. 12. University and Maryland Mines 13. Queen Bee Mine ;>^^2.V 26 'tJS^i^.tL^ _iSi«i» ^f-'swiMStosii^afei-- FROM ORIGINAL ILLUSTRATION BY EDWARD EYS£N REFERENCES, 15 GIPSV QUEEN MINE 16 SOUTH BODIE MINE. 17 ADDENDA MINE 18 SOUTH STAND Ago MINE 19 OHO MINE 20 SILVEH HILL TUNMEL. 2i NOONDAY MINE 22 NOONDAY MILL. . 23 S PAUL DINS MILL . 24 SPAULDING MINE 25 BOOHEH MINE 26 UNIVERSITY MINE Zl MARYLAND MINE 28 BOSTON CON_ MINE. 29 HING BEE MINE Drafting and layout by C.A Allen DIVISION OF MINES AND GEOLOGY JAMES F. DAVIS, STATE GEOLOGIST STATE OF CALIFORNIA - GEORGE DEUKMEJIAN, GOVERNOR THE RESOURCES AGENCY - GORDON K. VAN VLECK, SECRETARY FOR RESOURCES DEPARTMENT OF CONSERVATION - RANDALL M. WARD, DIRECTOR to 20C= BULLETIN 206 PLATE 4 i ^'MiillMiimiiiiu^s ^"^D'CATOR NEW STANDARD TUNNEL BULWER TUNNEL PORTAL ^^LVIOER^ C^ A/r k ic/ ^/c ffA L C/p Ic I I I I ! BODIE B^LUFF - Mine Workings of the STANDARD HILL AREA / BODIE MINING DISTRICT Mono Countj, California Revised by Charles W. Chesterman Scale 50 100 200 300 400 500 600 FEET 55! GRAPHICS BY ROBERT A, SWITZER, 1979 DIVISION OF MINES AND GEOLOGY JAMES F DAVIS, STATE GEOLOGfST STATE OF CALIFORNIA - GEORG THE RESOURCES AGENCY - GORDON K VAN DEPARTMENT OF CONSERVATION - Pa Pa %0 cka pd ^LOuc Mopt ^^£7 TO/^ M 0/?r /^^. ^4 ^^/= 0/\,, T) <J O^r Mine Workings of the SOUTHERN MINES AREA BODIE MINING DISTRICT Mono County, California Compiled by Charles W. Chesterman Scale ° ^° '?° 200 300 400 500 600 TOO 800 900 1000 FEET fL ^^^/, I I I I I I I - GEORGE DEUKMEJIAN, GOVERNOR N K VAN VLECK, SECRETARY FOR RESOURCES VATION - RANDALL M WARD, PmECTOR^ ^__ BULLETIN 206 PLATE 5 PHVSICAL SCIENCES IIBRIRV UC DAVIS I A/ H' L K U T IV £ N ^R P H E N > ■a' C^ Off GRAPHICS BY WOBERT A SWITZER, 1979 o m O r- O Q -< > Z o o m o m Tl O O) H C/) O -n H I m O g m z o g H o H I c I m o