Ore minerals in the telluride-bearing gold-silver ores of Salida, Indonesia, with special reference to the distribution of selenium

Abstract

Te-Se-bearing gold-silver ores from Salida in Sumatra, Indonesia, show carbonate and sulfidic diffusion bands in quartz incrustations. The sulfidic diffusion bands show a fine diffusion zoning with: 1. an earliest or inner zone with concentrations of Zn, Cu, Fe, S (sphalerite, chalcopyrite, pyrite); 2. an intermediate zone with concentrations of Pb, Au, Ag, S, Te, Se (galena and Au-Ag-tellurides in Te-bearing parageneses; galena, electrum and acanthite in Te-free parageneses); and 3. a zone of As-bearing minerals (tennantite, enargite or luzonite, arsenpolybasite) superimposed on the first two zones. In the telluride-bearing ores paragenetic relations suggest that galena, altaite, hessite, and γ-phase and “x”-phase solid solutions originally crystallized above about 120 °C; on cooling this assemblage equilibrated into one stable below 50 °C and consisting of galena, altaite, hessite, hessite-sylvanite intergrowths, and hessite-petzite aggregates. Se is concentrated in sulfides of the intermediate diffusion zones; microprobe analyses indicate up to 4.0 weight percent Se in some acanthites and up to 0.45 weight percent Se in some galenas; arsenpolybasite also contains up to 4.0 weight percent Se but only when replacing seleniferous acanthite. The concentration of Se with Pb, Au, Ag, S, Te in intermediate diffusion zones is ascribed to solution differentiation during solute diffusion. Microprobe analyses are given of hessite, sylvanite, petzite, minerals of the pearceite-polybasite group, mckinstryite, and the Fe-, Mn- and Cd-contents in sphalerites.