Petrogenesis of U-rich two-mica granite from the Mesozoic Reshui pluton (Nanling Range, South China) with implications for uranium mineralization

Muscovite-bearing granites are the dominant rock type associated with metallic deposits in South China. Some of these granites are rich in U and considered potential sources for subsequent hydrothermal uranium mineralization. Although widely studied, the petrogenesis of muscovite-bearing granites remains obscure. The Reshui pluton contains fine-grained biotite granite and coarse grained two-mica granite (CGTG). CGTG exhibits high U concentrations (5.07-40.15 ppm, average 15.94 ppm) and is typical of U-rich granite in South China. We conducted detailed petrographic, geochemical and biotite mineralogical analyses of the CGTG from the Reshui pluton. Our findings provide new insights into the petrogenesis of U-rich granites in South China and their significance for uranium mineralization. LA-ICP-MS zircon U-Pb dating shows that the CGTG were formed at 167.3 +/- 1.7 Ma. Integrated petrological, whole-rock geochemical and biotite geochemical data, the negative and limited variation of the epsilon Nd(t) values (from- 10.8 to- 9.6) and a two-stage Paleoproterozoic model age (1.72 to 1.83 Ga), suggest the U-rich S-type CGTG formed by partial melting of Paleoproterozoic clay-rich pelitic rocks and underwent extensive fractional crystallization. The U-rich pelitic magma sources characterized by relatively low oxygen fugacity and temperature, relatively high degree of magmatic differentiation and F content are the main factors controlling U enrichment in the Reshui pluton CGTG. The petrologic and whole-rock geochemical characteristics, together with the biotite chemical compositions and disseminated U-rich accessory minerals including uraninite, indicate that the CGTG in the Reshui pluton has a high uranium mineralization potential and should be given more attention in further explorations.