Sources and Typomorphism of Platinum in Carbonaceous Rocks in Far East Russia

Resumo

Results of the study of carbonaceous metasedimentary rocks in the northern part of the Khanka and eastern part of the Bureya massifs (Primorye and Khabarovsk territories, JAR) and associated platinum mineralization are presented. It is shown that platinum minerals are represented by microparticle dispersion in shales of the greenschist-facies metamorphism (Sutyr and Kimkan sequences, Mitrofanovo Formation) and by Pt and PtO₂ nanoparticles associated closely with graphite in shales of the amphibolite facies (Turgenev and Soyuznoe graphite deposits). The studied carbonaceous sequences were likely formed in the hemipelagic setting in a suprasubduction trench during the intense input of terrigenous material into basin. Carbon was derived from the marine biogenic material and superimposed graphitization related to a lower crustal material. Iron ores in the carbonaceous shales are hydrothermal formations. Platinum mineralization was likely related to two sources: (i) sedimentary-chemogenic source that made up the protolith of graphite–sericite–quartz shales of the Sutyr and Kimkan sequences (Mitrofanovo Formation); (ii) graphitizing fluid generated in deep magma chambers. Mineralization produced from these sources is transformed during the hydrothermal activity (coarsening of microparticles) and/or regional metamorphism (disintegration of microparticles and remobilization of Pt into graphite).