Abstract

The 251 Ma Noril'sk magmatic sulfide ores, together with igneous rocks of trap association and underlying sequences, were affected by three stages of regional metamorphism under conditions of early zeolite, middle prehnite-pumpellyite, and late zeolite facies. The Rb-Sr age (apophyllite, calcite, metabasalts) of metamorphism varies from 232 Ma (onset) to 122 Ma (completion). The metamorphosed ores contain remobilized metamorphic-hydrothermal silver mineralization (Au-free silver, Hg-rich silver, Ag sulfides and selenides, chalcopyrite–lenaite solid solution, Ag-rich bornite, argentopentlandite), palladium (Sb-free paolovite, Ag-rich paolovite, vysotskite, palladoarsenide, vincentite, Pd-breithauptite, malyshevite, palladium, etc.), and platinum (kharaelakhite, cooperate, platinum). A metamorphic trend of dearsenization is outlined: initial majakite PdNiAs → palladoarsenide Pd2As → vincentite Pd3As → palladium Pd. The mineral assemblages and compositions of metamorphic-hydrothermal PGM and Ag minerals markedly differ from pneumatogenic PGM, Ag, and Au–Ag minerals. The low-grade metamorphism of the Noril'sk sulfide ores was accompanied by appreciable mobilization of Ag, however mobilization of Pd, and especially Pt, was less intense, and no Au mobilization was seen at all.

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