Platinum-group minerals were distinguished and studied in mining of alluvial-deluvial gold placers in Salair. These minerals are Os-Ir-Ru alloys (all modifications), isoferroplatinum, native platinum with elevated contents of Ir (up to 8.19 wt.%), and multicomponent solid solutions mainly of Pt-Ru-Ir composition. Solid metal solutions occur in association with PGE sulfides and sulfoarsenides of younger paragenesis. Laurite RuS2 forms rims and replacement structures in cleavage planes in the grains of Os-Ir-Ru alloys. Cooperite PtS is present in multiphase microparageneses (MPG) filling voids in isoferroplatinum. Optically homogeneous phase (Ir,Ru) (As,S)2 of variable composition intermediate between laurite RuS2 and irarsite IrAsS was found as inclusions and rims in Os-Ir-Ru alloys. Hollingworthite RhAsS contains 15% RuS2 end-member. Sperrylite PtAs2 has elevated concentrations of Fe and S. Based on the composition of platinum-group minerals and their ratios, it is suggested that the paragenesis under study resulted from ophiolitic ultramafic rocks which formed under high-temperature and high-pressure conditions. At the early stage, mineral formation proceeded at low sulfur fugacity. At the late stage, sulfur fugacity increased, and PGE sulfides and sulfoarsenides formed.

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First page of PLATINUM-GROUP MINERALS IN GOLD PLACERS IN NORTHWESTERN SALAIR
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