Bismuth–Tellurium Mineralization of the Namovskoe Gold Deposit (Southern Sikhote-Alin, Far East of Russia)

Detailed mineralogical studies on ores of the Namovskoe deposit revealed their different mineral compositions. Two stages of ore formation were identified at the Namovskoe deposit, which are characterized by different composition of bismuth and tellurium minerals. In total, eight groups of bismuth and tellurium minerals were identified and studied. Native bismuth, gold intermetallic compound (maldonite Au2Bi), compositionally different bismuth tellurides and sulfotellurides (hedleyite Bi2Te, pilsenite Bi4Te3, tetradymite Bi2Te2S, joseite-A Bi4TeS2, joseite-B Bi4Te2S) were detected at the first stage of ore formation. Pb–Bi sulfosalts of variable composition (ashamalmite Pb6Bi2S9, vikingite Ag5Pb8Bi13S30, galenobismuthite PbBi2S4, cannizzarite Pb8Bi10S23, cosalite Pb2Bi2S5, lillianite Pb3Bi2S6, nuffieldite Pb2Cu(Pb, Bi)Bi2S7), bismuth sulfides (bismuthinite Bi2S3, ikunolite Bi4S3), sulfobismuthite Ag (matildite AgBiS2), and silver telluride–hessite Ag2Te crystallized at the second stage. Constant impurity elemental Pb, Ag, and Se have been established in bismuth sulfotellurides, and Ag is a typomorphic impurity in Pb–Bi sulfosalts. The first ore-forming stage occurred at high temperatures of 530–270°C with low sulfur fugacity fS2 and high fTe. The second-stage ore formation occurred within a temperature range of 350–150°C.