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Rocks and ores of the PGE-bearing Vuruchuaivench massif (Kola Peninsula, Russia).

Aleksey Pakhalko

Vol. 41, no. 1 (2015), s. 118-119

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The early Palaeoproterozoic mafic-ultramafic layered Monchegorsk pluton is located in the north-eastern Fennoscandian (Baltic) Shield, on the Kola Peninsula. The Monchegorsk pluton is the second largest layered pluton in Europe (ca. 60 km2), and consists of two branches: one N-E trending (the Nittis, Kumuzh’ya, and Travyanaya (NKT) massifs), and sublatitude trending (the Sopcha, Nud, and Poaz massifs). The Vuruchuaivench massif occurs at the marginal part of the Nyud-Poaz intrusions (Smolkin et al. 2003). The Vuruchuaivench massif entirely consists of hydrothermally altered gabbronorite that is exposed in separated outcrops (ranging from meters to tens meters) northeast-wards for a distance of 7–8 km, and disappears in Lake Imandra (Ivanchenko 2008). The width of the exposure is 1.5–2.0 km. The intrusive is known for its PGE mineralization (prognostic resources 100 tof PGE). Reef ore body is similar with Platinova (Skaergaard) and Sonju Lake (Duluth Complex) PGE reefs. Rock ores are presented by metasomatised taxitic leucogabbronorites and anortosites (Knauf et al. 2008; Smolkin et al. 2003). The reef ore body hosts low-sulphide Ni-Cu and PGE mineralization. Average content of PGE in rocks is 2.0–2.5 ppm, samples containing 19 ppm are also found (Knauf et al. 2008). The ratio of Pd/Pt varies from 2–8:1.The samples (13 samples) were selected from the detailed study area (0.03 km2). Petrographic features were studied using optical microscope and X-ray analysis. The trace elements and precious metals analysis was performed with ICP-MS. Isotopic research was provided with SHRIMP-II. All analyses were carried out in A.P. Karpinsky Russian Geological Research Institute (VSEGEI) in Saint-Petersburg. The presence of a propylite rock was established for the first time in the territory of massif. Two propylite groups that differ mineralogically were identified. PGE mineralization is associated with the quartz-chlorite-albite group, whereas mineralization is unrelated with another, the albite group. There is a difference in total REE content in gabbronorites and propylites. Propylites of first group differ from second group and gabbronorites by a noticeable spread of values in REE content. The similarities of REE patterns in all rocks may indicate a genetic relationship. Arsenides and sulphoarsenides are predominant among the platinum group minerals in the Vuruchuaivench massif. The age of the propylites (based on Rb-Sr isotopic system) is 2,470 ± 130 Ma. The Initial 87Sr/86Sr ratio (ISr= 0.703537) and δ34S = 1.4‰ (Grokhovskaya et al. 2009) indicate a slight part of a crustal component in formation of rocks and ores of the Vuruchuaivench massif.