Abstract

A hitherto unnamed Bi–Pb tellurosulfide was discovered in the Wenyu quartz vein-type gold deposit within the Xiaoqinling gold province, in China. This is the first report of that rare mineral in China. This mineral is optically anisotropic and light gray, and it has a slightly higher reflectivity than galena. It occurs in close association with galena but not with any other tellurosulfide, Bi-bearing sulfide or telluride. Electron-microprobe analyses reveal an average composition of Pb0.85Bi4.09Te4.06S3.01 (stoichiometric: PbBi4Te4S3). The very small size of the mineral grains (usually 10–20 μm across) prevented structural analyses by X-ray diffraction. Tests by SEM revealed no heterogeneity on a micrometric scale, thus supporting the presence of a discrete phase rather than a mixture of submicrometric inclusions of PbS in tetradymite. By analogy with PbBi4Te7 and evaluating the compositional data available, we speculate that PbBi4Te4S3 has a layered structure, TeBiSPbSBiTe TeBiSBiTe, a seven-layer and a five-layer stacked together.

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