Noble metals in carbon-rich metamorphic rocks of the Khanka terrane, Primorie

Abstract

Carbon-rich metamorphic rocks of Riphean age in the northern part of the Khanka terrane were first analyzed for concentrations of noble metals (Au, Ag, Pt, Pd, Ir, Os, and Ru). According to the data of various physicochemical analytical techniques, the Au and Pt concentrations broadly vary: from 0.01 to 52 ppm for Pt and from 0.1 to 30 ppm for Au. Various techniques of sampling and analysis variably affect the losses of these metals because of difficulties in the decomposition of metal-carbon chemical bonds. The carbon isotopic composition (13C from −8.5 to −8.7‰) of the graphitized amphibolite-facies rocks widespread in the core of the Ruzhino paleodiapir suggest that their carbon is of mantle provenance. The Early Cambrian metaterrigenous rocks metamorphosed to the greenschist facies have 13C from −19.9 to −26.6‰, which testifies to its organic origin. The elevated concentrations of noble metals in these rocks suggest that the sources of carbon and metals were polygenetic and that the ore-forming system evolved over a long time span.