Geochemistry of mafic rocks of the PGE-bearing Vurechuaivench Massif (Monchegorsk Complex, Kola region)

Abstract

The platinum-bearing Paleoproterozoic Vurechuaivench Massif in the Monchegorsk Pluton is made up of amphibolized and saussuritized gabbronorites, anorthosites, and norites. The geochemical features of the massif rocks are considered at four detailed areas. It was confirmed that the Vurechuaivench and Nyud-Poaz massifs are geochemically similar. The rare-earth element (REE) distribution in the rocks of the Vurechuaivench Massif is peculiar in the low total REE content (9.4–27.6 ppm), negative REE slope, significant LREE enrichment [La/Yb] n = 3.7–8.7), and distinctly expressed positive Eu anomaly ([Eu/Eu*] n = 1.2–2.2). The REE distribution pattern remains unchangeable throughout the entire section, including the rocks of the Pt reef, with a gradual upsection REE increase. It is suggested that the PGE reef of the Vurechuaivench Massif, as the Platinova Reef (Skaergaard massif) and Sonju-Lake Intrusion (Duluth complex), was formed during fractional crystallization in a large magma chamber without new magma influx. It is conceivable that the Vurechuaivench Massif is the allochthonous fragment of a large loppolith-like body, the lower portions of which compose the Nyud-Poaz Massif, while the middle part was almost completely eroded.