Mineral chemistry and associations of Bi-Te(S,Se) minerals from China

Microprobe analyses and observed phase associations have revealed the occur rences of a series of Bi-Te(S,Se) minerals from various ore deposits, genet ically related to the Yanshanian granite, in China. They include tetradymit e (Bi2Te2S), tsumoite (BiTe), sulphotsumoite (Bi3Te2S), pilsenite (Bi4Te3), joseite-A (Bi4TeS2), joseite-B (Bi4Te2S), hedleyite (Bi8Te3), and unnamed phases Bi2Te, Bi-6(Te,Se)(3) and Bi4Te2Se. The substitutions among Te, S an d Se in selenian joseite-B, Bi-4(Te,Se,S)(3), were recognized, suggesting t he presence of a complete solid solution between Bi4Te2S and Bi4Te2Se. The independent phases in the Bi-Te system seem to be composed of five limited solid solutions, corresponding to Bi2Te3, Bi2Te2, Bi4Te3, Bi2Te and Bi8Te3. The substitution between Te and S based on Te: S = 2: 1 and 1: 2 may yield ordered sulphotellurides with the compositions centered around the ideal f ormulae.