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Silver-Rich Central Idaho Silver-rich Disseminated Sulfides From a Tungsten-bearing Quartz Lode Big Creek District Central Idaho GEOLOGICAL SURVEY PROFESSIONAL PAPER 594-C Silver-rich Disseminated Sulfides From a Tungsten-bearing Quartz Lode Big Creek District Central Idaho By B. F. LEONARD, CYNTHIA W. MEAD, and NANCY CONKLIN SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY GEOLOGICAL SURVEY PROFESSIONAL PAPER 594-C Study of a low-grade tungsten deposit whose associated suljide minerals, extracted as waste, are rich in silver and contain some gold UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY William T. Pecora, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 - Price 35 cents (paper cover) CONTENTS Page Page Abstract __________________________________________ _ C1 Mineralogy and paragenetic sequence-Continued Introduction ______________________________________ _ 1 Alteration products ____________________________ _ C15 Location and operation _____________________________ _ 4 Paragenetic sequence ___________________________ _ 16 Geology __________________________________________ _ 4 Geologic thermometry __________________________ _ 18 Ore deposit _______________________________________ _ 5 Classification and origin of hypogene mineralization ____ _ 19 Mineralogy and paragenetic sequence ________________ _ 6 Oxidation and enrichment ___ ------------------------ 20 Typical ore ___________________________________ _ 6 Economic considerations ____________________________ _ 21 Gangue indicated by mill products _______________ _ 7 Acknowledgments ___________________ .:. ______________ _ 23 Tungsten minerals _______ ,______________________ _ 8 References ________________________________________ _ 23 Sulfides and related minerals ____________________ _ 8 ILLUSTRATIONS [Plates follow page C24f - PLATE 1. Drawing and X-ray micrographs of acanthite and copper sulfides on galena. 2. Drawing and X-ray micrographs of electrum in pyrite. 3. Photomicrograph of electrum in pyrite. 4. Photomicrographs of native silver and inverted Ag-Fe-S mineral in pyrite. Page F~GURE 1. Index map of parts of Big Creek and Yellow Pine districts, Idaho_________________________________________ C4 TABLES Page TABLE 1. Assays of concentrates and tailings, McRae Tungsten Corp. milL___________________________________________ C2 2. Semiquantitative spectrographic analyses of concentrates and tailings, McRae Tungsten Corp. milL___________ 3 3. Semiquantitative spectrograptic analyses of handpicked mineral fractions of sulfide concentrates, McRae Tung- sten Corp. milL_________________________________________________________________________________ 3 4. Approximate mineralogic composition of sulfide fraction of sulfide concentrates, McRae Tungsten Corp. milL___ 4 5. Minerals of the New Snowbird deposit _____________ --------------··------------------- ----------------- 7 6. Chemical analysis of tailings, McRae Tungsten Corp. milL__________________________________________ _ _ _ _ _ 8 7. -D1str16ution -of ore-mineral inclusions in discrete grains of the sulfide-sulfosalt-native-element suite____________ 17 8. Metal concentration (recoverable basis) in crude ore, New Snowbird tungsten deposit and San Manuel copper deposit_______________________________________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 22 III SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY SILVER-RICH DISSEMINATED SULFIDES FROM A TUNGSTEN-BEARING QUARTZ LODE, BIG CREEK DISTRICT, CENTRAL IDAHO By B. F. LEONARD, CYNTHIA W. MEAD, and NANCY CoNKLIN ABSTRACT gold, and a few percent each of copper, lead, and zinc. Sulfide colliCentratels :removed as wa1ste :from the milling of The sulfides were very sparsely disseminated in the l<mr-~grade tun~ten ore at the New Snowbird deposit rontain tungsten ore, and the accumulation of "pyrite concen­ roughly 100-300 troy ounces of ,silver per ton, 2-4 ounces <Yf gold, trate" known to contain base metals and silver was and a few percent each of copper, leald, and zinc . .S'parsely di,s­ roughly 1 ton per year, an amount regarded by the oper­ seminated sullfides make up only about 0.1 weight if*"rcent of the tunglsten ore, and not more tJhan 1 ton oif sulfide concentrates ator as too small to be worth marketing. Nevertheless, wrus accumulated annually during the :short Ufe of the mine. milling of the tungsten ore carried out an experiment The total metal eontent per ton of ore is eompa:rable to tlhat of in concentration that nature apparently failed to per­ 'some 'PO!rrfuyry 'Copper deposits. At the New Snowbird, tungsten form on a large scale in this district, where bonanzas proxies for 'copper, and the precious metals and base metaLs a•re have not been found. Sulfide concentrates from the New potential coproductJs. The isize o:f the disseminated sulfide­ Snowbird mill thus provide the first large sample of a tungtsten depoisit is unknown, 'but itls o~urren!ce a!s a xenotihermaiJ. replacement witlhin a very ·la·rge 'Sili'cified zone coextensive wi:th disseminated sulfide deposit from the district, revealing a!major Tertiary dike swarm 'su~gestJs tlhat the New Snowbi1rd its mineralogy and 1netal content in a way that conven­ abd similiar deposits are potentially valuable, though extr,emely tional sampling and a~ssaying could not have done and low grade, sources of precious meta'ls. suggesting that the extensive, sparsely sulfide-bearing This report defineis the mineralogy orf one deposit by micro­ silicified zones of the district may merit attention as scopic, electron prdbe, X~ray, spectrochemi•cal, and ·C'hemical analyse'S. Huelbnerite, sC'heeUte, and a little stolzite a'r,e the main potential sources of disseminated metals in bodies rem­ tllllglsten minerals. Pyrite, chalcopyrite, 'Sphalerite, ,galena, iniscent of the porphyry copper deposits of the Western d~genite, and acanthite are the principal sulfides. Elemental States. g~ld is present as gold-rich electrum included in pyrite. Ele­ This report deals mainly with the mineralogy of the m~ntal silver is present in native silver, electrum, argentopy­ sulfide concentrates. The deposit from which they came rite ( ?) , acanthite, argentian tetrahedrite, silver sulfosalts, hes­ site, argentian digenite, cera:f!gyrite, anld perhaps otiher minerals. was, economically, a tungsten ore body in which the Deposition oif the complex mineral assemiblage within the quartz value of the other metals probably did not exceed 30-80 'lode :began witJh huebnerite and ·scheelite. Pyrite with abundant cents per ton of crude ore. The sulfide-bearing 1naterial heterogenoous ore-mineral inclusions was then dumped. IncLu­ itself was not ore ; the sulfides were remo-ved merely 'sion~rich base-metal sulfides and tetJrahedrite followed in weakly because a price penalty is imposed for sulfur in tungsten ordered sequence, telescoped upon miaTgyrite( ?) , acantJhite, and late rim~forming copper sulfides. '.Dhe inferred tempertature range concentrates. Other tungsten deposits of similar type for hypogene sulfide mineralization extends from 491°0 or less occur in the neighborhood, but this deposit alone has (pyrite-pyrrhotite-arsenopyrite assemblage) to 177°C or less been worked, and no low-grade sulfide deposits have ( acantJhite formed 'below ~he argentite-acantJhite inversion been exploited except. the Yellow Pine and Meadow t~mperature) . Olay mineral's and oxidation products a~re sparse. Creek (fig. 1) .1 The intensity of sulfide mineralization The extent Olf 1supergene sulfide enrichment i1s indeterminate hut proba'blly 1sligtht, tJhough an unknown quantity of supergene 1 The Yellow Pine mine became the Nation's leading producer of tungsten in 1942-44, when it yielded more than 800,000 units of WOa. a'lteration 1products may have 'been eroded. Though the ratios of the dollar value of tungsten, antimony, and gold in the ore were approximately 2: 2: 1 during the productive life of the INTRODUCTION mine (1938-52), the ore came from a low-grade pyrlte-arsenopyrlte­ stibnlte-quartz lode that contained a large shoot of scheelite ore. Thus, Sulfide concentrates accmnulated as a waste product sulfides predominated over scheelite in the ore body as a whole. The Meadow Creek mine produced antimony and gold only, but some scheelite during the beneficiation of low-grade huebnerite­ was present in the deposit. Silver was recovered from both deposits, the scheelite ore from the New Snowbird deposit contain weight ratio of Ag: Au being 8.2: 1 at the Yellow Pine mine and 3.4: 1 at Meadow Creek. For details, see Cooper (1951) and U.S. Bureau of 110'---316 troy ounces of silver per ton, 2.7-4.1 ounces of Mines (1938-52). C1 C2 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY at the latter deposits was at least one order of magnitude TABLE 1.-Assays of concentrates and tailings, McRae Tungsten Corp. mill greater than that inferred for the New Snowbird. Thus [Parts per million, ppm; parts per billion, ppb] there is no local standard against which to compare the New Snowbird sulfide assemblage. 2 3 4 5 Fine grain size and sparse dissemination of 'the New Field No ______________________ SN/56/7b SN/64/1 SN/64/2 SN/56/7a SN/64/3 Snowbird sulfides hamper one's study of the deposit in ---------------------------- Lab. No _______________________ D113983 D115110 D115111 D113982 Dl00632 the field and limit the usefulness of any collection of -------------------------------- ore samples
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