Phase equilibrium study in the system Cu2S-PbS-Sb2S3: non-stoichiometry in sulfosalts and isothermal variation in sulfur fugacity (original) (raw)

Abstract

Evacuated silica tube experiments (+halide flux) were conducted in portions of the system Cu2S-PbS-Sb2S3 at 440°C, using two-pyrrhotite indicator method to measure the sulfur fugacity. Product phases were identified by optical and X-ray powder diffraction methods supplemented with microprobe analyses. In addition to the previously reported mineral phases, famatinite (Cu3SbS4) appears to be a stable phase in the Sb2S3-rich portion of the system. Microprobe data indicate that almost all the sulfosalts depart from stoichiometry. Copper in Pb-Sb sulfosalts and Pb in chalcostibite and skinnerite are indicative of the coupled substitution 2Pb2+=Cu++Sb3+. Pb-solubility in skinnerite and Cu-solubility in zinkenite are dependent on the initial bulk composition of the charges. The compositions of meneghinite and boulangerite compare well with their natural analogues. The maximum isothermal variation of log_f_ s 2 falls in the range of-6.36 (1.06)≤log_f_ s 2≤11.12 (0.30). The experimentally derived log_f_ s 2 values for some two phase assemblages, compare reasonably well with the respective minimum log_f_ s 2 values calculated by the method of Craig and Barton (1973). The stable coexistence of famatinite with zinkenite plus stibnite instead of chalcostibite may be described by the sulfidation reaction: 3CuSbS2+1/2 S2=Cu3SbS4+Sb2S3.

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  1. Department of Geology and Geophysics, Indian Institute of Technology, 721 302, Kharagpur, India
    B. Mishra & K. L. Pruseth

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  1. B. Mishra
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  2. K. L. Pruseth
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Mishra, B., Pruseth, K.L. Phase equilibrium study in the system Cu2S-PbS-Sb2S3: non-stoichiometry in sulfosalts and isothermal variation in sulfur fugacity.Contr. Mineral. and Petrol. 118, 92–98 (1994). https://doi.org/10.1007/BF00310613

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