Carbonization and geochemical characteristics of graphite-bearing rocks in the northern Khanka terrane, primorie, Russian Far East

Abstract

Regional carbonization was examined in Riphean metamorphic complexes in the northern part of the Khanka terrane. The results obtained by various techniques of physicochemical analysis indicate that all petrographic rock varieties of this complex bear elevated concentrations (from 10−4 to 10−6 wt %) of Au and PGE. XRF data were used to describe a wide spectrum of trace elements: Ti, V, Ni, Cr, Pt, Pd, Re, Rh, Os, Ir, Cu, Hg, Au, Ag, Ta, Nb, Sr, Rb, Zr, La, W, Sn, Pb, and Zn. The Rb/Sr-Ba diagram shows the fields of anatectic granite-gneisses, biotite granites, lamprophyres, graphitized crystalline schists, black shales, skarns, and quartz-graphite metasomatic rocks. The C isotopic composition in graphite from the metaigneous rocks (lamprophyres and crystalline schists of the amphibolite facies) corresponds to δ13C from −8.5 to −8.7‰, which suggests that the carbon could be of endogenic provenance. The carbon isotopic composition of the greenschist-facies black shales corresponds to δ13C from −19.9 to −26.6‰, as is typical of organogenic carbon. The concentrations of precious metals in the rocks are, on average, one order of magnitude lower than in the graphitized crystalline schists. The origin of the precious-metal ore mineralization was likely genetically related to the regional carbonization process.