Sidorovite, PtFe3, A NEW MINERAL FROM THE SNEGOVAYA RIVER PLACER, KORYAK HIGHLANDS, RUSSIA

Abstract

Abstract Sidorovite, ideally PtFe3, is a new mineral from the Epilchik ultramafic complex and nearby Snegovaya River placer, Koryak Highlands, Russia. It was found in isoferroplatinum grains extracted from a heavy-mineral concentrate obtained from crushed lode chromitites and alluvial material. Sidorovite occurs either as a part of complex grains comprising tetraferroplatinum, native iron, hollingworthite, magnetite, serpentine, and chromite or as part of secondary rims which formed together with tetraferroplatinum after isoferroplatinum. According to the Laue pattern obtained by synchrotron microdiffraction, sidorovite is cubic, crystallizing in space group Pm3¯m and adopting an Au3Cu-type crystal structure. Its unit-cell parameters are a = 3.725(4) Å, V = 51.687(4) Å3, Z = 1. The calculated density is 11.815 g/cm3. The strongest X-ray diffraction lines are [d (Å) (I, %) (hkl)] 2.161 (100) (111), 3.711 (48) (100), 1.871 (36) (200), 1.673 (27) (210). No cleavage was observed and hardness could not be determined owing to the small size of the grains. The empirical formula of sidorovite calculated based on four atoms is: Pt1.04(Fe2.89Cu0.05Ni0.02)Σ2.96. The mineral is posited to form through the incorporation of Fe0 by tetraferroplatinum, which arises through the reduction of Fe via H2-bearing fluids produced through the serpentinization of olivine at T < 450 °C. The name of the new mineral honors the Russian geologist and mineralogist Evgeniy Gennadievich Sidorov (1955–2021).