Regional geochemical survey of concealed sandstone-type uranium deposits using fine-grained soil and groundwater in the Erlian basin, north-east China

Abstract

The Erlian basin is a very important uranium-bearing basin in China; that is located in the famous Central Asian Mobile Belt. It contains several concealed sandstone-type uranium deposits in sandstone and mudstone of Mesozoic-Cenozoic strata. Sampling of soil profiles over the Nuheting concealed U deposit in this basin shows that fine-grained soil collected from the horizon at depth of 15–30 cm has an obvious geochemical anomaly relative to background areas. Regional geochemical survey using fine-grained soil at a density of approximately 1 site per 4 km2 and groundwater at a density of approximately 1 site per 16 km2 or greater was carried out in the Erlian basin in an area of approximately 6400 km2. The survey results indicate that geochemical anomalies of U in the soil have a corresponding relationship with uranium-bearing geological bodies, including concealed uranium ore mineralization and granitic intrusions. Furthermore, groundwater chemistry determined from samples collected from wells is an effective supplementary means for exploration of concealed sandstone-type U deposits. The soil and groundwater geochemical anomalies may reduce the drilling density required to explore regionally, making them two effective and potentially cost-saving alternatives to regional geochemical exploration for concealed sandstone-type uranium deposits in basins. The formation of large-scale regional U anomalies in soil is a complicated process. A uranium vertical migration model for sandstone-type uranium was built for this study, where the water plays an important role in carrying soluble U in the form of uranyl through transport channels from mineralized bodies to Earth's surface under the action of groundwater motion and evapotranspiration. The study of the methods and anomaly formation mechanism is necessary for sandstone-type uranium exploration and will greatly enhance U resource exploration in covered arid terrains worldwide.