Geochemistry of the Platiniferous Ultrabasites of the Feklistov Massif

The mean contents of the petrogenetic and trace elements, including the platinoids, have been established in the main ultramafite varieties in the Feklistov intrusion, which serve to refine its metallogenic specialization and to compare it with zoned ultrabasites in the Urals and Alaska. The geochemical characteristics are compared with those of zoned clinopyroxenite-dunite intrusions in the Siberian platform (Konder, Guli, and others). The types of platinum-group element fractionation, established for the first time for the rocks of the Feklistov intrusion and various other clinopyroxenite-dunite intrusions, are different from those previously known and are readily explained from the viewpoint of the differentiation of the platinoids during fractional melting of the mantle substrate, presumed a pyrolite, with the formation of complementary ultramafite-mafite melt and ultramafic restite. Further redistribution of the platinoids is related to the duration of mantle diapir formation and emplacement. The low ¹⁸⁷Os/¹⁸⁶Os in these platinum-group minerals confirm a mantle origin for clinopyroxenite-dunite intrusions.