Phase relations in the systems Cu2S-PbS-Bi2S3 and Ag2S-PbS-Bi2S3 and their mineral assemblages

The phase diagrams of the systems Cu₂S-PbS-Bi₂S₃ and Ag₂S-PbS-Bi₂S₃ have been investigated in the present study. The paper is concerned with the complete solid solution between bismuthtite and aikinite above 300°C in the system Cu₂S-PbS-Bi₂S₃. The synthetic phases CuBi₃S₅ and Cu₃Bi₅S₉ have their solid solution ranges in the ternary system with 9 and 26 mole% PbS at maximum, respectively. A complete solid solution between PbS and AgBiS₂ divides the phase diagram of the system Ag₂S-PbS-Bi₂S₃ into two parts: Bi-rich and Ag-rich. All sulfosalt minerals and solid solutions, including pavonite ss, lillianite ss, heyovskyite and benjaminite are on the Bi-rich side. And divarant relations were found between pavonite ss -lillianite ss, benjaminite and bismuthtite as well as between lillianite ss -bismuthtite and galenobismutite. Synthetic experiments using LiCl-KCl flux technique show that when a minor amount of copper (less lwt.%) is added in, many of Ag-and Pb-bismuth sulfosalt minerals, for example, vikingite (Ag₅Pb₈Bi₁₃S₃₀), are synthesized successively, particularly at 400°C. So is heyrovskyite, which has a solid solution range with 3.7 mole% Cu₂S at maximum in the system Cu₂S-PbS-Bi₂S₃.