The superlarge Malmyzh porphyry Cu-Au deposit, Sikhote-Alin, eastern Russia: Igneous geochemistry, hydrothermal alteration, mineralization, and fluid inclusion characteristics

摘要

The Malmyzh porphyry Cu-Au deposit cluster ( > 10 Mt Cu-eq.) is the largest in eastern Russia. It is located in the turbidite terrane and was formed in a transform continental margin setting. The deposit is related to a magnetite-series, dominantly low-K calc-alkaline diorite-tonalite igneous suite, with a higher potassium content in the younger (quartz monzonite to granodiorite) intrusive phases. These metaluminous to peraluminous I-type igneous rocks exhibit slightly elevated Sr/Y and have combined subduction-related to post-subduction geochemical signatures. The magma was emplaced in a series of separated local magmatic "porphyry centres" that vary in petrologic features and relative abundance of different igneous rocks as well as in the dominant development of different hydrothermal alteration and mineralization types. The deposit comprises quartz-K-feldspar +/- biotite +/- chalcopyrite stockworks in zones of potassic alteration, followed by quartz-magnetite +/- chlorite and then by quartz-sulfide-magnetite (with chalcopyrite and bornite) stock-works in zones of propylitic alteration. The latter is partially overprinted by quartz-sericite-chalcopyrite and quartz-sericite-pyrite stock-works formed during phyllic alteration stage. The most productive Cu mineralization is related to a later (quartz-sulfide-magnetite) hydrothermal event during the propylitic alteration stage, and to an early (quartz-sericite-chalcopyrite) event during the phyllic alteration stage. Further development of phyllic alteration caused a dilution of Cu grades. Minor Au, Bi and Te mineralization accompanied Cu mineralization.