Genesis of gold and silver sulfides at the Ulakhan deposit ( northeastern Russia )
N.E. Savva a , G.A. Pal'yanova b
a Northeastern Research Institute, Far East Branch of the RAS, 16 ul. Portovaya, Magadan, 685000, Russia
b Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090
Keywords: Uytenbogaardtite; oxidation zone; thermodynamic modeling; Au(Ag)-containing pyrite
Pages: 799-810
Abstract
Geology and mineralogy of the Ulakhan Au-Ag epithermal deposit (northeastern Russia, Magadan Region) are considered. A four-stage scheme of mineral formation sequence is proposed. Concentrations of Au and Ag in minerals of early and late parageneses were determined. It has been established that uytenbogaardtite is associated with native gold and hypergenesis stage minerals - goethite, hydrogoethite, or limonite replacing pyrite. The compositions of uytenbogaardtite (Ag3AuS2), acanthite (Ag2S), and native gold were studied. The composition of the Ulakhan uytenbogaardtite is compared with those of Au and Ag sulfides from other deposits. Thermodynamic calculations in the system H2O-Fe-Au-Ag-S-C-Na-Cl were carried out, which simulate the interaction of native gold and silver with O2 and CO2-saturated surface waters (carbonaceous, sulfide-carbonaceous, and chloride-sodium-carbonaceous) in the presence and absence of acanthite and pyrite at 25
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