The origin of uranium deposits related to the Huangmeijian A-type granite from the Lu-Zong volcanic basin, South China: Constraints from zircon U-Pb geochronology and mineral chemistry

Abstract

Although most of granite-related uranium deposits in South China are spatially and genetically associated with S-type granites, few are related to A-type granites. In this study, we present whole-rock major and trace elements, zircon U-Pb geochronology, and mineral chemistry data for the Huangmeijiang A-type granite in the Lu-Zong volcanic basin (South China) to investigate the origin of uranium deposits related to this pluton. The uranium ore bodies mainly occur within the Jurassic Luoling formation close to the Huangmeijian pluton. Whole-rock and biotite geochemistry indicates that the F-rich alkaline magmas with relatively high fO2 prompted the partitioning of U into the fluids released from the Huangmeijian pluton with an affinity of A-type granites, which would set the stage for the later concentration of the U into the Jurassic Luoling formation. Thorite, zircon, apatite, and bastnäsite are the dominant accessory minerals that host U in this pluton. Backscattered electron (BSE) images suggest that some zircon and thorite grains can be divided into the unaltered domains and altered domains. The textural features are interpreted as a later hydrothermal event superimposed on the magmatic zircon and thorite. In situ LA-ICP-MS U-Pb dating on the unaltered domains and altered domains of zircon grains yielded weighted mean ages of 127.8 ± 1.0 Ma and 65.7 ± 5.3 Ma, respectively. The former age represents the emplacement age of the Huangmeijian pluton, and the latter one overlaps the timing of a uranium mineralization event (∼66.6 Ma) in this area. The altered domains of thorite and high-(U + Th) zircon grains have lower U contents than those of the unaltered domains, indicating that uranium was mobilized from thorite and zircon during fluid infiltration, which might be the main source of uranium for the ∼ 66.6 Ma uranium mineralization. Our study suggests that the Huangmeijian pluton was the primary source of uranium for the formation of uranium deposits in this area.