Vein formation of the Monchepluton and the Monchetundra intrusion contact zone

Abstract

The Monchegorsk region (Kola Peninsula) is distinguished by its platinum metal specialization and is a promising target for prospecting and exploration of valuable, strategically important platinum group metals. In the course of the study, the petrographic, petrochemical, and geochemical features of the vein bodies in the junction zone of large Early Proterozoic layered intrusions (the Monchegorsk pluton and the Monchetundra intrusion) have been characterized. Vein bodies are observed within the South Sopchinsky massif and the Moroshkovoe Lake massif. The veins are located near the contact of fine-medium-grained metapyroxenites (metanorites) and coarse-grained gabbronorites. Two main types of veins are identified: 1) veins of plagioclase-pyroxene and plagioclase-amphibole composition and 2) veins of quartz-feldspar and amphibole-plagioclase composition. Analysis of the content of chalcophilic elements in this area rocks has shown that the increased content of platinum group elements is associated with the first type of vein formations. Vein rocks of plagioclase-pyroxene and plagioclase-amphibole composition (type 1) contain on average Cu - 0.22 %, Ni - 0.11 %, ΣPGE - 1 g/t, Au - 0.042 ppm. Vein rocks of quartz-feldspar and amphibole-plagioclase composition (type 2) contain on average Cu - 0.04 %, Ni - 0.01 %, ΣPGE - 0.05 ppm, Au - 0.012 ppm. The distribution spectra of rare-earth and rare elements in the vein rocks of the South Sopchinsky massif and the Moroshkovoe Lake massif show both the commonality of all types of veins and the regular nature of differences in the composition of the veins.