Platinum-group minerals from the Malaya Kamenushka River placer, Middle Urals, Russia

This work presents a detailed study of platinum-group mineral (PGM) assemblages from the Malaya Kamenushka River placer, whose formation is associated with the weathering of the Kamenushensky Uralian-Alaskan type massif, Middle Urals, Russian Federation. The deposit is characterised by the dominance of isoferroplatinum, together with significant numbers of inclusions of Os-Ir-Ru alloys and platinum-group element (PGE) sulfides. A study of the Os-Ir-Ru alloys permitted recognition of two types of iridium with different morphology and composition. The similarity of the PGM assemblages from the Malaya Kamenushka River placer and the lode mineralisation of the Kamenushensky massif is demonstrated. A comparison of PGM assemblages from the Malaya Kamenushka River placer with other placers and massifs of the Ural platinum belt demonstrates significant differences in the number of Os-Ir-Ru inclusions. Such differences for minerals of refractory elements cannot be explained by the vertical zoning of the lode mineralisation. Most probably this is associated with the enrichment of the primary substrate with Os, Ir and Ru and/or the degree of melting, depending on the chosen model of formation of the Uralian-Alaskan type massifs.