PLATINUM-GROUP MINERALS FROM THE DEEP COPPER ZONE OF THE STRATHCONA DEPOSIT, SUDBURY, ONTARIO

Among the different ore zones of the Strathcona deposit, in the Sudbury district, Ontario, the Deep Copper Zone has the highest concentrations of platinum and palladium. Most of the Pt and Pd is not present in solid solution in base-metal sulfides and magnetite: rather, they occur as platinum-group minerals (PGM). These include niggliite, froodite, insizwaite, paolovite, sperrylite, michenerite, sobolevskite and a palladium chloride. The PGM, up to 50 mum across, are intergrown with tellurides (hessite and altaite), native bismuth and bismutite. They occur mainly along grain boundaries and in microfractures in sulfide minerals, magnetite. and silicates. Mass-balance calculations indicate that sperrylite and niggliite are the most abundant platinum-bearing minerals, and froodite and michenerite are the most abundant palladium-bearing minerals. Textural relationships suggest that the deposition of the PGM occurred mostly tater than that of base-metal sulfides and magnetite. The occurrence of Pd chloride associated with other PGM suggests that Cl may have been an important agent for the transport and deposition of Pd. Other important elements involved in the precipitation of the PGM include Bi, Te, As and Sn.