Genesis of the Jiangwan Uranium Deposit, Northern Guangdong: Constraints from Geochronology and Geochemistry of Pitchblende and Pyrite

The uranium metallogenic potential of the Dadongshan–Guidong granite belt in northern Guangdong, especially the Jiangwan area in the eastern Dadongshan pluton, remains unclear, which hinders the evaluation of exploration prospects in this area. In this study, we present new data on the mineralogy, U-Pb geochronology, trace element, and sulfur isotopic compositions of pitchblende and associated pyrite from the Jiangwan uranium deposit (JUD). The uranium ore is dominated by pitchblende, which commonly occurs as crustiform and fine veinlet-like aggregates. Part of the euhedral-to-subhedral pyrite grains are enclosed or partially replaced by pitchblende. LA-ICP-MS analyses of pitchblende yielded a Tera–Wasserburg lower intercept age of 60.2 ± 0.5 Ma (MSWD = 2.6, n = 16), indicating that uranium mineralization occurred during the Paleocene. Additionally, the pitchblende has ΣREE contents of 2489–4960 ppm and high U/Th ratios (>1000), indicating that the pitchblende has a hydrothermal origin, forming under moderate- to low-temperature conditions (T< 350 °C). HREE-enriched patterns suggest that carbonate complexing played an important role in uranium transport. Weak positive Ce anomalies in pitchblende, together with pervasive hematitization, indicate relatively oxidizing conditions for the ore-forming fluid. Pyrite has Co/Ni ratios of 1.03–4.53, indicating a hydrothermal origin. The δ³⁴S values of pyrite, varying from −4.23‰ to −1.21‰, suggest that the sulfur source was unlikely to be derived solely from the granitic host rocks, but may have been influenced by mafic dike-related sulfur and hydrothermal fluid–rock interaction. Combined petrographic and geochemical evidence suggests that pyrite formed before pitchblende and likely acted as an important reductant during uranium precipitation. These results indicate that the JUD records a Paleocene hydrothermal uranium mineralization event, which corresponds to the age of the identified main mineralization period in the Xiazhuang ore field.