PLATINUM-GROUP MINERALS FROM THE OLKHOVAYA–1 PLACERS RELATED TO THE KARAGINSKY OPHIOLITE COMPLEX, KAMCHATSKIY MYS PENINSULA, RUSSIA

Mineral assemblages from the Olkhovaya–1 River placers, in Kamchatka, Far-Eastern Russia, provide genetic information on their evolution. The minerals are dominated by Os–Ir–Ru alloys (80%), consisting of all possible mineral species, and Pt–Fe alloys consisting of native platinum, Fe-rich platinum and isoferroplatinum. The following features of the mineral assemblage are characteristic of mineralization associated with an ophiolitic complex: (1) in the Os–Ru–Ir diagram, the compositions of the hexagonal alloy form a ruthenium trend; (2) there are two typical equilibrium magmatic parageneses of alloys: early osmium– iridium, and later isoferroplatinum–ruthenium, which both are associated with laurite and the solid solution laurite–irarsite (Ru,Ir) (S,As) 2 . The cooperite, sperrylite and Pd minerals formed at the postmagmatic stage. Tetraferroplatinum–tulameenite, replacing the Pt–Fe alloys, as well as the multicomponent compounds of Ru, Os, Ir, Rh, Pt with Fe replacing the Os–Ir–Ru alloys and PGE sulfides, result from serpentinization of PGM-bearing rocks. The PGM assemblage in the Ol’khovaya–1 River placers is related to the Karaginsky ophiolite complex of the Kamchatskiy Mys Peninsula.