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

Abstract

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.