Mineral Assemblages and the Genesis of Platinum Metal Mineralization of the Vuruchuaivench Intrusion (Kola Peninsula, Russia)

The layered Vuruchuaivench Intrusion (VI) is located in the eastern part of the Fennoscandian Shield and is part of the Early Paleoproterozoic Monchegorsk Intrusive Complex (MIC). The platinum metal mineralization of this intrusion is localized within a stratiform reef-type platinum-bearing horizon that is about 2 km long and 1–3 m thick; in some boreholes, up to 15–20 m. The dissemination of Fe–Cu–Ni sulfides containing platinum-group minerals (PGMs), silver, and gold is confined to areas of gabbronorites and anorthosites with a massive and very-textured structure, with a wide development of fluid-bearing minerals in the intercumulus of cumulative phases. The uniform distribution of rock-forming, trace, and rare-earth elements in the rocks of the platinum-metal reef (platinum-group element reef) and its host rocks suggests the formation of gabbronorites during intrachamber differentiation without supplying additional portions of the melt. The composition and ratios between platinum group minerals and sulfides and silicates indicate a close genetic relationship between PGMs and magmatic sulfides. As the temperature decreases, primary PGMs and sulfides are altered under the influence of high-T magmatic fluids and hydrothermal solutions, with the formation of a wide range of PGMs. Ores are dominated by palladium arsenides, stibioarsenides, and bismuth tellurides. The separation of an immiscible arsenide melt, with the formation of numerous drop-shaped and globular intergrowths dominated by Pd–Ni-arsenides and Pd-stibioarsenides, plays a significant role in the formation of platinum-metal mineralization within the Vuruchuaivench intrusion. In some sulfide impregnations, platinum diarsenide (sperrylite) occurs instead of globules composed of palladium and nickel arsenides. The formation of specific platinum-metal associations appears to be due to the addition of As, Sb, and other incompatible elements to the magma through extensive assimilation of Archean crustal rocks.