Platinum-bearing of chromitites in the Kharcheruz ultramafic massif(the Polar Urals): new data

Yurichev А. N., Chernyshov A. I., Karbovyak E. V.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2020. V. 149. N 3. P. 38-53

https://doi.org/10.31857/S0869605520030107

Language: Russian

Abstract

In chromitites of the Kharcheruz ultramafic massif, which is part of the Khadatinsky ophiolite belt that closes ophiolite complexes of the Polar Urals in north, small inclusions of minerals of rare platinum-group elements (PGE) (ruthenium, osmium, and iridium): sulfides and sulfoarsenides were first discovered. The complete absence of Os–Ir–Ru metalic solid solutions (typical for chromite ores) in composition of analyzed samples, indicates an increased fugacity of sulfur with low fugacity of oxygen at time of formation of chromite ores and syngenetic minerals of rare PGE. The evolutionary direction of rare PGE fractionation in chromitites of the Kharcheruz massif is noted: ruthenium and osmium fractionation dominates in disulpfides, in complex sulphides of rare PGE with non-ferrous metals (MeS, MeS₂, and Me₂S₃) iridium and rhodium increase along with ruthenium and osmium, in sulfoarsenides – iridium and rhodium take leading role in composition of compound with minimal (or complete absence) osmium and ruthenium. The process of forming associations of identified rare PGE minerals occurred in several stages. Earliest are disulfides of laurite-erlichmanite series (mainly fractionation of ruthenium). The remaining sulfides and sulfoarsenides of rare PGE belong to later formations and associated with processes of mantle metasomatism, when under influence of reduced fluids, enriched S and As and bearing such elements as Ni, Cu, Rh, and Pd, processes of remobilization and redeposition of PGE are occurred.

Keywords: Polar Urals, ophiolites, Kharcheruz massif, chromitites, PGE minerals, chemical composition, genesis