Low-Sulfide PGE-Copper-Nickel Mineralization From Five Prospects Within The Footwall Of The Sudbury Igneous Complex, Ontario, Canada.

摘要

North Range low-sulfide mineralization is dominantly hosted by Sudbury breccia, with amphibole-plagioclase equilibrium metamorphic temperatures of 440 to 533 ± 75°C, produced by the SICs thermal aureole. Mineralization led to increases in the bulk halogen content of the host Sudbury breccia and the formation of Ni-enriched ferromagnesian silicates. South Range low-sulfide mineralization is typically hosted by metabasalts of the Huronian Supergroup. Garnet-biotite-plagioclase-quartz geothermobarometry produced equilibrium metamorphic conditions of 513 to 645 ± 50°C and 2.0 to 7.7 ± 1.0 kbar, probably corresponding to a late-Penokean overprint of peak Blezardian/Penokean metamorphism. Silicates associated with South Range mineralization are compositionally similar to the host rock equivalents and no alteration selvage is commonly observed due to subsequent recrystallization.;Platinum-group minerals (PGM) from the North Range comprise platinum and palladium tellurides and bismuth-tellurides, with Sb-bearing palladium bismuth-tellurides and sperrylite from the South Range. Kotulskite-sobolevskite from the North Range shows a previously unreported Ag-Pd substitution, with michenerite from irregular veinlet style mineralization showing the substitution of Se and Sb for Bi. Two unknown PGMs were identified from the South Range, along with kotulskite-sobolevskite-sudburyite crystals displaying extensive Te-Bi-Sb solid-solution not noted before at Sudbury. A new Se-bearing variant of pilsenite was identified at McKim. Polyphase aggregates from both Ranges indicate that Bi-Te melts may have been widespread at some stage postdating the emplacement of the main magmatic sulfides.;Normalized plots for low-sulfide mineralization show enrichments in the precious and semimetals relative to contact and sharp-walled vein mineralization. This enrichment has resulted in elevated concentrations of Ag and Se in chalcopyrite and Pd+Ag and Se in pentlandite from the North Range. The mass balance for North Range samples found that a significant fraction of Ag and Se occurs in sulfides with all other elements preferring discrete phases. A substantial fraction of Pd is hosted by pentlandite on the South Range, with gersdorffite also a major host despite its low abundance. The enrichments observed reflect the formation of low-sulfide mineralization from a fractionated sulfide liquid and hydrothermal fluids that have interacted with a fractionated sulfide source, and suggest that the precious and semimetals behave incompatibly with crystallizing sulfide.