A New Type of Noble Metal Mineralization in Fluidolites of the Poperechny Deposit, Lesser Khingan, Russia

摘要

The fluid-explosive breccias of the Poperechny iron-manganese deposit, Lesser Khingan, Russia, contain high concentrations of platinum group elements (PGE), gold, and silver. Noble metals are represented by isoferroplatinum crystals, Os-Ir alloys, PGE sulfoarsenides, and gold grains with a size of tenths of a millimeter and micron-sized segregations of native silver. The mineral composition of the PGE of the Poperechny deposit is consistent with that of the ore and placer objects of the Ural-Alaskan type and corresponds to the isoferroplatinum-osmium magmatic assemblage. The euhedral morphology of the isoferroplatinum and PGE sulfoarsenides indicates that they were formed in a stable environment at the crust-mantle boundary owing to partial melting of slab rocks. The appearance of PGE minerals in the magmatic-hydrothermal system under subsurface conditions is related to a highly mobile gas-saturated fluid flux capable of transferring deep mineral phases. The high content of PGE (up to 11.3 g/t), gold (up to 2.58 g/t), and silver (up to 256 g/t) in the fluidolites of the Poperechny deposit makes it possible to revise the criteria for searching for the bedrocks and placer sources of noble metals in the Lesser Khingan.