PGE mineralization in andesite explosive breccias associated with the poperechny iron-manganese deposit (Lesser Khingan, Far East Russia): Whole-rock geochemical, 190Pt-4He isotopic, and mineralogical evidence

Abstract

We report in this paper an unusual occurrence of platinum-group minerals in evolved explosive breccia associated with the Poperechny iron-manganese deposit (Lesser Khingan Range, Far East Russia). PGMs in andesite breccia are represented by Fe-Pt solid solutions (85%) and PGM (mostly Os-Ir-Ru) solid solutions, sulfides and sulfarsenides (15%). Textural and compositional variations in PGM assemblages suggest that Pt-Fe and Os-Ir-Ru solid solutions, as well as erlichmanite-laurite series sulfides were formed during high-temperature fractionation of mantle-derived mafic parental melt (similar to Alaskan-type complexes) and were entrained in the evolved andesitic melt during its emplacement in the crust. Pd-Pt plumbostannide and copper-gold solid solutions reflect late magmatic re-crystallization and metasomatism. Early Cretaceous (~125 Ma) age of ferroplatinum in the explosive breccia suggests that PGM-bearing ultramafic material could have been sampled during regional slab-window tectonics related to the Late Mesozoic subduction of Izanagi plate along southern margin of the North Asian continent.