Abstract:

Sandstone uranium deposits in the basins of South China are integral to China’s sandstone-type uranium deposits. Significant progress has been made in genetic research on sandstone-type uranium deposits in North China, while research on sandstone-type uranium deposits in South China remains predominantly descriptive, representing a critical gap in uranium genesis studies. The Xinjiang Basin in Jiangxi is a representative uranium-rich basin in South China, where Xiaojia sandstone-type and multiple sandstone-type uranium mineralization have been discovered. This study takes Xinjiang Basin as an example to investigate the ore-forming characteristics and controlling factors of sandstone-type uranium deposits in South China. It aims to perform comparative studies on ore-forming mechanisms and provide a theoretical basis for understanding sandstone-type uranium mineralization in China through literature review, field surveys, microscopic observations, and trace element analysis. The results indicate that uranium mineralization in the Xinjiang Basin primarily occurs in the grey layers sandwiched between the red layers of the Upper Cretaceous Maodian, Zhoutian, Hekou, and Tang-bian Formations. The ore-bearing rocks include grey, grey-white, grey-green, bluish-grey conglomerates, sandstone conglomerates, sandstones, silty sandstones, and silty mudstones. The selectivity of mineralization based on stratigraphic and lithological characteristics is not significant. Spatially, sandstone uranium mineralization is primarily located at the central and western ends of the Xinjiang Basin, near the deep-seated source rock of the Lower Cretaceous Lengshuiwu Formation or its periphery. The intensity of mineralization correlates with the organic matter content in the rocks. It is concluded that sandstone uranium mineralization is controlled by multiple factors: (1) Rocks in basin depression areas control the sources of ore-forming materials; (2) Grey layers sandwiched between red layers determine the extent of uranium mineralization; (3) Anticline structures’ axes concentrate uranium body formation; (4) Neotectonic fault structure activity governs mineral deposit localization. The mineralization involves the activation of uranium and other elements in deep source rocks due to fault activity, migrating along fault channel to rock layers or tensile fractures (fracture belts) near shallow anticline axes. When uranium-bearing deep reducing fluids enter shallow, more oxidized environments, uranyl organic complexes dissociate. Elements such as uranium precipitate due to these reducing agents, forming uranium mineralization or deposits.

Key words: sandstone-type uranium deposit, gray layer, neotectonics activity, Xinjiang Basin