Using isotope-geochemical criteria for Olympiadinskoye gold deposit gas system genesis diagnosis

Abstract

   The authors studied modern gas manifestations spatially associated with the ore deposits in the Kaitbinskaya lithological-facies zone of the Yenisei Ridge.   The purpose of the research is to obtain scientifically based data on the genesis of gaseous and vaporous fluids in various sampling environments of the Vostochny open-pit mine of the Olympiadinskoye gold deposit: rocks, natural waters, free-flowing gases from blastholes and air of the surface atmosphere.   It has been conducted a complex of field and analytical works including degassing, gas chromatography, pyrolysis of the organic substance of lithified and metamorphosed deposits, analysis of carbon isotopic composition in carbon dioxide and methane in fluidal systems. In order to study normal gas-geochemical field (natural background) of the work area an atmospheric geochemical survey was carried out at the reference site – an “environmentally friendly” site with the minimal influence of technogenic factors. It has been determined that the surface atmosphere of the site had been formed due to the landscape and geomorphological conditions of the Kaitbinskaya lithological-facies zone as well as fluidal systems of deep horizons. The latter, due to the presence of an extensive network of disruptive disturbances and diffusion-filtration processes of mass transfer reached the zone of exploratory geochemical sounding. The conducted pyrolytic studies of rocks have proved that within the open section of the Vostochny open-pit mine the organic substance of the Kordinskaya series of the lower Riphean deposits has implemented its oil and gas generation potential and cannot serve the formation source of abnormal gas fields of the Olympiadinskoye gold deposit. The studied gas systems are polygenic in nature and, being allochthonous to the host sediments, are formed without the participation of gases from the upper generating (bio) zone. According to isotope-geochemical criteria, these are mainly endogenous and naphthidogenic fluids identical to the gas condensate accumulations of the Yurubcheno-Tokhomskaya oil and gas accumulation zone.