In-situ Microscale Geochronology and Elemental Analysis of Pitchblende from Tangdong Area, Northern Guangdong: Constraints on Uranium Ore-forming Processes

The Tangdong area is located in the southern segment of the Zhuguang-Taoshan uranium metallogenic belt and the northern part of the Changjiang uranium ore field, with favorable geological conditions for uranium mineralization. To investigate the precise geochronology and genesis of uranium mineralization in this region, based on detailed petrographic observations, electron microprobe U-Th-Pb chemical dating and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in-situ U-Pb isotopic dating were used to conduct geochronological and elemental analyses on pitchblende, and the ore genesis was discussed. The results show that the in-situ chemical U-Th-Pb ages of pitchblende determined by electron microprobe are consistent with the LA-ICP-MS in-situ U-Pb isotopic ages. The mineralization age of pitchblende is approximately 55 Ma, indicating a Paleocene-Eocene uranium mineralizing event. The rare earth element (REE) patterns of pitchblende are characterized by slight enrichment in light rare earth elements (LREEs), indistinct differentiation between LREEs and heavy rare earth elements (HREEs), distinct negative Eu anomalies, and weak positive Ce anomalies. These features are comparable to those of vein-type uranium deposits, suggesting that the mineralization formed under low-temperature, low-to-moderate salinity and reducing conditions. The REE distribution patterns of pitchblende correspond well with those of the Changjiang pluton, implying that the Changjiang pluton likely represents the principal uranium source. Uranium mineralization is controlled by multi-stage lithospheric extension and rifting in South China, and occurred geodynamically during lithospheric extension and thinning at 55-45 Ma. The NE-trending Tangdong fault-depression zone provids favorable structural conditions for uranium mineralization.