Mineral assemblages and the genesis of platinum metal mineralization of the Vuruchuayvench intrusion (Kola Peninsula, Russia)

The layered Vuruchuaivench intrusion is located in the eastern part of the Baltic Shield and is part of the Early Paleoproterozoic Monchegorsk Intrusive Complex. The platinum-metal mineralization of IW is localized within the stratiform platinum-bearing horizon of the reef type with a length of about 2 km and a thickness of 1-3 m, in some boreholes up to 15–20 m. The dissemination of Fe-Cu-Ni sulfides containing the platinum-group minerals, silver and gold is confined to areas of gabbronorites and anorthosites of massive and taxitic texture, with a wide development of fluid-bearing minerals in the intercumulus of cumulative phases. The uniform distribution of petrogenic, rare and rare earth elements in the rocks of the platinum-metal reef (PGE-reef) and its host rocks indicates the formation of gabbronorites during intra-chamber differentiation without additional portions of the melt. The composition and ratios of platinum group minerals (PGMs) with sulfides and silicates suggest a close genetic relationship between PGMs and igneous sulfides. As the temperature decreases, primary PGMs and sulfides are modified under the influence of high-temperature magmatic fluids and hydrothermal solutions, with the formation of a wide range of PGMs. The ores are dominated by palladium arsenides, stibioarsenides, and bismuth tellurides. A special role in the formation of platinum-metal mineralization in the Vuruchuaivench intrusion is played by the separation of an immiscible arsenide melt with the formation of numerous drop-shaped, globular intergrowths predominated by Pd-Ni-arsenides and Pd-stibioarsenides. In some sulfide scattered impregnations, instead of globules consisting of palladium and nickel arsenides, platinum diarsenide (sperrylite) occurs. The formation of specific platinum-metal associations is apparently due to the addition of As, Sb, and other incompatible elements to the magma during extensive assimilation of Archean crustal rocks.