Geological and geochemical characteristics of escaped hydrocarbon epigenetic alteration in the Dongsheng mineral deposit and its significance

Abstract：This paper presents the following distinctive characteristics of the Dengsheng sandstone-type uranium deposit in the Ordos basin: (1) there exist a pronounced ore-controlling green alteration zone and the bleaching phenomenon in the deposit; and (2) discontinuous, lenticular, carbonated, calcareous-cemented sandstone is widespread in the ore horizon. X-ray diffraction analysis, SEM identification and analysis of the inclusion chemical composition of clay minerals indicate that the green alteration and bleaching phenomenon formed in an extensive reducing environment, and that the reducing fluids are mainly related to hydrocarbon escape. Carbon isotope analysis of fill-up gas and carbonates and analysis of part of organic geochemical parameters in the ore horizon indicate that the above-mentioned alteration is mainly related to NE-directed escaped hydrocarbon alteration of coal gases containing components such as CH4, H2S, CO and CO2. So, it can be thought that the basin margins in the direction of hydrocarbon escape and front of the green alteration zone are favorable areas for uranium mineralization and ore finding.