Acta Petrologica et Mineralogica

Uraninite is a typical mineral of uranium-bearing granite and the most important source mineral of uranium for the formation of granite-related uranium deposits. Understanding its compositional characteristics and crystallization age is significant for revealing the uranium mineralization process. The Xiazhuang uranium ore field in northern Guangdong is an important granite-related uranium deposit in China. In this study, textures and chemical ages of uraninite from the Xiazhuang granite and the altered granite at the Shituling uranium deposit were investigated using EPMA. The results indicate that uraninite in the Xiazhuang granite (Urn-1) is enclosed in rock-forming minerals, and the uraninite near the ore granite of the Shituling uranium deposit (Urn-2) is intergrown with pyrite and occurs between rock-forming minerals. EPMA data yielded the chemical ages of 233±3 Ma and 156±2 Ma for Urn-1 and Urn-2, respectively. The former is consistent with the zircon U-Pb age of the Xiazhuang granite, indicating that Urn-1 is of magmatic origin. Hydrothermal alteration of the altered granite mainly includes muscovitization and chloritization, corresponding to the early stage of uranium mineralization of the Shituling deposit. These altered samples have higher whole-rock U contents (55.5×10^-6~118×10^-6) and lower Th/U ratios (0.15~0.35) relative to the fresh rocks, indicating that these samples were influenced by uranium-rich fluids, and Urn-2 crystallized from that fluid, suggesting a hydrothermal origin. The chemical age of Urn-2 further indicates that uranium mineralization of the Shituling uranium deposit took place at the Late Jurassic. Some uraninites have been altered, and UO₂ contents of the altered domains are 33.83%~56.01%, obviously lower than the unaltered domains (UO₂=86.21%~95.91%), which may suggest the mobilization and mineralization of uranium related to hydrothermal activity.

Xiazhuang granite; uraninite; northern Guangdong; uranium mineralization; chemical ages