An experimental study of some solid solutions in the system Ag2S-PbS-Bi2S3 at low temperatures

The gustavite-lillianite s.s. series (KARUP-MOLLER 1970) in the Cu-free Ag2S-PbS-Bi2S3 system was experimentally confirmed at 350-450 degrees C up to the composition Gu(7)Li(1) but fell still short of the postulated gustavite endmember PbAgBi3S6 A new solid solution series in the same system has been identified from the marginal phase near Ag2Bi4S7 to a composition containing 23 mole % PbS at 450 degrees C. This benjaminite-type series extends strictly parallel to the PbS-bearing pavonite series and to the gustavite-Ag3Bi7S12 join. Its correlation with the natural Cu-bearing benjaminite remains to be confirmed. Long period dry experiments revealed further interesting features of the hitherto unexplored low temperature region across the PbS -AgBiS2 s.s. series. The intermediate range of this PbS-type series persists from 200 degrees C downward with extensive miscibility gaps flanked on both sides. Formation of some discrete members of this intermediate range was observed at temperatures down to 144 degrees C which dictates their final exsolutions to galena/matildite at still lower temperatures.