UYTENBOGAARDTITE, Ag.Aus2, Ln the BULLFROG MINING
89 Canalian Mineralogist Vol. 31, pp. 89-98 (1993) UYTENBOGAARDTITE,Ag.AuS2, lN THEBULLFROG MINING DISTRICT, NEVADA STEPHENB.CASTOR NevadaBureau of Minesand Geology, University of Nevads.Rem, Nevada 89557, U.S.A. JAMES J: SJOBERG IJ.S.Bureau of Mines,Reno Research Center, 1605 Evans Avenue, Reno, Nevada 89507, U.S.A. ABSTRAc"I The rare mineral uyenbogaardtite,Ag3AuS2, has been identified in specimensfrom two mines in the Bultlrog district of southemNevada. The minesexploit gold-silver vein depositsof the low-sulfur type that arehosted by volcanicrocks of middle Mioceneage. At both mines,uytenbogaardtite occurs in local massesof high-gradeore within shallowly to moderatelydipping systemsof quartz-caxbonateveins emplacedduring late Miocene volcanismand extensionaltectonism. Uytenbogaardtite from the Bullfrog district is chemicallyand structurallyidentical to previouslydescribed synthetic and naturalAg3AuS2. It occursin associationwith two types ofelectrum: relatively coarse,early electrurn,with approximatelyequal molar amountsofgold and silver, andlate gold-rich electrum.It is also associatedwith acanthite,copper-bearing sulfides, and products of oxidationsuch as limonite and chrysocolla.Textural evidenceindicates that the uytenbogaardtitereplaced early electrum,formed contemporane- ously with late electrumand acanthite,and that its depositionmay have overlapped,in part, with that of mineralsformed in an oxidizing environment.Equilibrium relationshipsamong electrum, acanthite, and uytenbogaardtite in specimensfrom theBulllirog district
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