Geochemical characteristics and uranium-thorium mineralization mechanism of the Shanqi granite in the Xiaotian-Mozitan Basin, Anhui Province

In recent years, a series of granite-related uranium-thorium mineralization occurrences have been discovered in the Xiaotian-Mozitan Basin of Anhui Province, demonstrating excellent uranium metallogenic potential in this area. Conducting research on the uranium-thorium mineralization mechanism is of great significance for revealing the regional uranium-thorium metallogenic theory and guiding prospecting efforts. This paper selects the Shanqi area of the basin as the research object, and conducts petrography, whole-rock major and trace element, and mineral compositional analyses to investigate the characteristics of uranium-thorium mineralization, and preliminarily reveal the petrogenesis of granite and the mechanism of uranium-thorium mineralization. The mineralization is located at the contact zone between the Shanqi granite and metamorphic rock strata. The U and Th contents of the mineralization samples range from 216×10-6 to 7 374×10-6 and from 2 291×10-6 to 43 109×10-6, respectively, both have reached industrial grades of U and Th. The dominant uranium-bearing and thorium-bearing mineral is uranothorite, with U and Th contents of 2.12%~5.51% and 66.05%~73.41%, respectively. The Shanqi pluton is a muscovite monzogranite, characterized by high silica content (SiO2 = 76.69%~77.22 %), a high differentiation index (DI = 96~98), and strongly peraluminous features (A/CNK = 1.14~1.22). It exhibits a light rare earth element (LREE)-enriched pattern with pronounced negative Eu anomalies and is geochemically characterized by enrichment in Rb, Th, U, and K, depletion in Ba, Ta, Sr, P, and Ti. The study reveals that the Shanqi pluton belongs to highly fractionated S-type granites. Zircons from the granite exhibit porous structure and lack oscillatory zoning in cathodoluminescence (CL) images, with high concentrations of U (avg. 13 452×10-6) and Th (avg. 14 121×10-6), likely resulting from metasomatism by U-Th-rich hydrothermal fluids. This study concludes that the uranium-thorium mineralization in the Shanqi area is closely related to high-temperature hydrothermal activity associated with highly differentiated granite. This study suggests that fractured zones with hematitization within the contact zones between highly fractionated granites and metamorphic strata should be considered as high-priority targets for uranium exploration in Xiaotian-Mozitan Basin.