GEOLOGY, COMPOSITION, AND GENESIS OF THE SUKHOI LOG NOBLE METALS DEPOSIT, RUSSIA

Abstract

With resources estimated at 1100 t Au at an average grade of 2.45 g/t, the black shale-hosted Sukhoi Log noble metals deposit is the largest concentration of gold in Russia. The Au mineralization and associated platinum group element (PGE) mineralization of the Sukhoi Log deposit is controlled by a tectonic zone along the axis of an overturned anticline located in metamorphosed carbon-bearing Upper Proterozoic sedimentary rocks. Organic compounds have been carbonatized by hydrothermal fluids. The centro-symmetric zoning of the mineralization is typical of infiltration metasomatism whereas disseminated and veinlet gold deposits accompanied by a quartz, carbonate, and pyrite assemblage were superimposed on sedimentary rocks. Nearly 90 minerals occur at Sukhoi Log including native metals, intermetallic alloys, sulfosalts, phosphates, tungstates, and oxides. Native gold is the main one mineral, but calaverite, hessite, petzite, and krennerite also occur. PGE mineralization is located on the periphery of the gold mineralization in the form of native platinum, Pt–Cu–Fe metal alloys, sperrylite, and cooperite. The mineral assemblage also includes native Fe, Cr, Cu, Ni, Sn, W, Ti, and Te, as well as alloys of these metals. The ore-forming process involved fluid temperatures of 130–395 °C, pressures of 0.2–2.4 kbar, and salt concentrations of 3.7–9.5 wt.% NaCl equiv.Mineralogical, geochemical, and geophysical studies were used to develop a three-stage genetic model of the deposit involving deposition of terrigenous and carbon-bearing terrigenous-carbonate rocks in an intraplate rift about 800 Ma followed by regional metamorphism at 520 Ma culminating in the development of palingenetic granites and hydrothermal fluids transporting contrasting assemblages of elements—(Cr, Ni, Ti, Pt+Pd) and (Sn, W, Mo, Zr, Au, Ag, Zn+Pb)—at 320 Ma.