Identification of Interlayer Oxidation Zones and Analysis of Uranium Mineralisation Conditions of the Changjihe Formation in the Hanshuiquan Area of the Southern Margin of the Santanghu Basin

The sandstone uranium mineralisation found in the Santang Lake Basin is primarily located in the Hanshuiquan area, with the ore-endowed stratigraphy concentrated in the Neoproterozoic Changji River Group. In order to accurately and objectively evaluate the mineralisation conditions and prospects of the Hanshuiquan area in the Santang Lake Basin, the identification of interlayer oxidation zones and an understanding of the uranium mineralisation conditions are crucial. In this paper, the focus is on the Neoproterozoic Changji River Group. In order to identify the yellow sandstones, geochemical indexes of altered sandstones, constant and trace element analyses of rocks and ores, and physicochemical parameters of fluid action are employed. The grey-green, grey and grey-white sandstones containing minerals or anomalies are considered to be the transition zone, while the red sandstones and grey sandstones are the reductive zone. The grey-green, grey and grey-white sandstones are the result of oxidation, while the red sandstones and grey sandstones are the result of reduction. The oxidised red sandstones present in this area are the result of primary deposition under arid climatic conditions, while the yellow sandstones are interlayer oxidation zones formed by post-oxidation and control uranium mineralisation. It would be beneficial to trace the alteration front of the yellow sandstone in order to reduce the cost of exploration. Some of the geochemical indicators provide evidence that this red sandstone is a product of sedimentary diagenesis. This is evidenced by the higher organic carbon (Orgc), CaO, Cu/Al, Ni/Al and Cd/Al contents in the red sandstone than in the yellow sandstone, and the low temperature of fluid action at which it was formed. The in situ pyrite sulfur isotope signature of the microzone indicates an interstratified oxidized zone type of uranium deposit. The very restricted distribution of white and green sandstones suggests a weak but hydrocarbon-influenced influence. The analysis of tectonic, topographic, geomorphological and hydrological conditions, lithology, petrography and post-generation alteration conditions indicates that this area has certain conditions conducive to uranium mineralisation. However, there are some key deficiencies, including insufficient reductant capacity, weak oil and gas dissipation and the absence of uranium ore enrichment.