Petrogenesis of Yanshanian granites in the Guidong complex, Northern Guangdong: Implications for uranium mineralization

Abstract

The Guidong complex in northern Guangdong constitutes a key segment of the Nanling Metallogenic Belt and hosts significant granite-related uranium deposits. However, the petrogenesis of the Yanshanian intrusions in its western part remains poorly constrained because of insufficient high-precision geochronological and mineralogical data. This limitation hinders a comprehensive understanding of regional metallogenesis. To address this, we conducted an integrated study of the Siqian two-mica granite and the Changping biotite granite, incorporating zircon U–Pb geochronology, whole-rock geochemistry, Hf–Nd isotope analysis, and mineral chemistry. Our objectives were to determine their emplacement ages and to investigate their petrogenesis and relationship with uranium mineralization. Zircon U–Pb dating indicates that the Siqian and Changping granites formed at 160 ± 1 Ma and 156 ± 1 Ma, respectively, suggesting both were emplaced during the Early Yanshanian magmatic event. These high-K calc-alkaline rocks are peraluminous (A/CNK = 1.04–1.44), enriched in large-ion lithophile elements (LILEs; e.g., Rb, Th, U), and depleted in high-field-strength elements (HFSEs; e.g., Ba, Nb, Ta). They exhibit negative zircon ε_Hf(t) values ranging from – 15.4 to – 8.4, with corresponding crustal model ages of 1668–2142 Ma. Whole-rock samples show ε_Nd(t) values from –11.2 to –9.1 and Nd model ages of 1693–1860 Ma. These isotopic features indicate that both plutons represent moderately differentiated S-type granites derived from partial melting of Paleo- to Mesoproterozoic metasedimentary sources (e.g., pelitic and psammitic rocks), accompanied by fractional crystallization of minerals such as ilmenite and apatite. Integrated geochemical and mineralogical data reveal that the Siqian and Changping granites are characterized by low Th/U ratios, high F contents, and low magmatic oxygen fugacity—signatures typical of U-rich granites. These attributes provided a favorable lithogeochemical environment for uranium enrichment and acted as primary sources for uranium-bearing, high-temperature hydrothermal fluids, thereby playing a critical role in regional uranium mineralization.