Geochemical characteristics and petrogenesis of uranium-bearing and barren granites in the Miao'ershan Batholith, South China: Implications for U mineralization

Abstract

The Miao'ershan batholith in South China is an important domain for granite-hosted uranium mineralization, comprising both uranium-bearing (Douzhashan) and barren (Yangqiaoling and Xiangcaoping) granites. However, the processes governing uranium enrichment in granitic systems, as well as the factors responsible for the contrasting fertility of these granites remain poorly understood. This study integrates zircon UPb geochronology, zircon trace element geochemistry, and in situ chemical analysis of both discrete apatite grains and apatite inclusions within zircon to elucidate the petrogenetic processes and physicochemical conditions that distinguish uranium-bearing from barren granite. Zircon UPb dating constrains the crystallization ages of the Yangqiaoling, Xiangcaoping, and Douzhashan granites to 218.6 ± 1.8 Ma, 223.3 ± 1.9 Ma, and 213.5 ± 1.8 Ma to 212.2 ± 1.6 Ma, respectively. Variations in apatite Cl/F ratios, combined with published whole-rock geochemical data, indicate that the Douzhashan granite is a strongly peraluminous S-type granite derived from the partial melting of meta-sedimentary rocks, whereas the Yangqiaoling granite reflects a mixed magmatic source involving both meta-sedimentary and meta-igneous components, and the Xiangcaoping granite exhibits intermediate characteristics. Apatite trace element compositions reveal that the Douzhashan granite underwent a higher degree of magmatic differentiation than the barren granites, as evidenced by lower concentrations of Sr, Th, and light rare earth elements (LREE), reduced (La/Yb)_N and (Sm/Yb)_N ratios, and elevated contents Y and Mn. Geochemical proxies from both zircon and apatite, including (Eu/Eu*)_N, Ce/Nd, and Y/ΣREE ratios, suggest that all three granites crystallized under low oxygen fugacity conditions. Therefore, uranium enrichment in the Douzhashan granite was driven by a combination of distinct source characteristics, advanced magmatic differentiation and reduced magmatic conditions, which collectively enhanced uranium solubility and retention in the melt. These results provide new insights into the petrogenetic controls on granite-hosted uranium mineralization and establish a geochemical framework for guiding future uranium exploration in similar geological settings.