Mineralogy of Bi-sulfosalts and tellurides from the Yaoan gold deposit, southwest China: Metallogenic implications

Abstract

Bismuth-sulfosalts and -tellurides are commonly present in many hydrothermal gold deposits and can provide important genetic and physicochemical constraints on the metallogenesis. The abundant auriferous specular hematite veins in the Yaoan gold deposit of the Jinshajiang-Red River alkaline porphyry metallogenic belt (southwest China) contain an assemblage of Bi-sulfosalts and tellurides together with hematite, pyrite, and chalcopyrite. Bismuth-sulfosalts are characterized by replacement textures resulting from changes of fluid composition (e.g., Pb, Bi, Cu, and Ag) and mainly include bismuthinite derivatives (e.g., bismuthinite, paarite, krupkaite, lindströmite, and friedrichite-aikinite), paděraite, cuprobismutite homologues (probably submicroscopic intergrowths of hodrushite and cuprobismutite), and emplectite. Tellurides are tiny, comprising tsumoite, melonite, hessite, and calaverite, which coexist with bismuthinite derivatives. These Bi-sulfosalts and tellurides have direct contact with gold, indicating that the Yaoan gold metallogenesis was likely linked to the syenite porphyry magmatism that was originally sourced from a regional lithospheric mantle probably metasomatized by subduction of Te-rich sediments. The telluride assemblage also reveals that the gold was precipitated under oxidizing conditions that has a high tellurium fugacity at the beginning (fTe2 = ∼10−7.9 and fS2 = ∼10−8.5 at ∼300 °C).