Genesis of the Jinguanchong perigranitic uranium deposit, South China: constraints from whole-rock geochemistry and in-situ pitchblende analyses

The Jinguanchong deposit is the typical perigranitic uranium deposit located in the eastern Hunan Province, south China. The ore bodies primarily occur within the exocontact zone of the Yajiangqiao pluton and in the Qiziqiao Formation, with pitchblende being the predominant uranium mineral. The detailed mineralogical, mineral chemistry, geochronology, and whole-rock geochemistry of the Jinguanchong deposit have been conducted, in order to elucidate its genetic mechanism. Two uranium mineralization stages have been organized based on the mineralogical characteristics and LA-ICP-MS U-Pb dating on pitchblende. The first mineralizing stage occurred during Late Cretaceous, with a weight mean age of 72.6 ± 0.4 Ma (MSWD = 0.96). The second mineralizing stage occurred during Early Paleogene, with a weight mean age of 59.9 ± 0.5 Ma (MSWD = 0.23). The Yajiangqiao pluton exhibits a strongly peraluminous character with relatively low Th/U ratios, which is characteristic of a good U source for the mineralization. Combined whole-rock and in-situ trace-REE geochemistry of pitchblende, indicate that the Yajiangqiao pluton, Qiziqiao Formation, and Lengjiaxi Group served as uranium sources for the Jinguanchong deposit. According to the mineral paragenetic association and geochemistry of pitchblende, the ore-forming fluids of the first mineralizing stage in the Jinguanchong deposit should be rich in HCO 3 – , CO 2 , and Ca 2+ , with moderate to high salinity and high temperatures. Ore-forming fluids of the second mineralizing stage are characterized by lower salinity and middle to low temperatures, mainly originated from meteoric water. Deeply-rooted faults and a series of fault breccia zones were formed under an extensional tectonic setting in the Mingyuefeng area. These zones provided pathways for the circulation of ore-forming fluids. Fluid cooling, degassing, and changes in geochemical conditions are the key factors leading to the reduction and precipitation of uranium from uranyl complexes in the ore-forming fluids. The findings of this study will contribute to establishing a mineralization model for the Jinguanchong deposit, and provide a theoretical basis for the future exploration of perigranitic uranium deposit in the Mingyuefeng area.