LAUSR

Abstract In the present study, we have documented hitherto unreported Ag-Pb-S, Ag-Sb-S and Sb-Ag phases associated with galena, pyrrhotite, sphalerite, freibergite, argentite, gudmundite, nisbite and breithauptite from the remobilized ore at the Sindesar Khurd base metal sulfide deposit, Rajasthan, India. These Ag-Pb-Sb-(±Cu)-S phases display pronounced compositional variability and intimate reaction relationship with coexisting sulfides and probably signify crystallization from a sulfide partial melt. To examine the possibility and nature of such melts, we have conducted evacuated silica tube experiments at 500 °C in the system Cu2S-Sb2S3-PbS-Ag2S at 10 mol % Ag2S. The melts obtained in these experiments are S-deficient, with varying concentrations of Cu (14.65–21.01 atom %), Ag (7.03–20.32 atom %), Sb (9.32–19.92 atom %), Pb (6.35–11.32 atom %) and S (44.16–48.41 atom %). The solid phases obtained are galenass, Ag-tetrahedrite and famatinite. Non-stoichiometric S-enrichment is observed in the solid phases with a complementary S-deficiency in the melt produced, in which Ag and Sb are enriched. The results of this study indicate that significant amounts of Pb-, Cu-, Sb- and Ag-enriched sulfide melts can be produced even at 500 °C and fractionation of Ag and Sb into sulfide partial melt may concentrate Ag and Sb during metamorphism of base metal sulfide deposits. The various Ag-Pb-Sb-(±Cu)-S phases observed at Sindesar Khurd perhaps are the products of late-stage crystallization and testify to the presence of sulfide partial melt.