Contrasting whole-rock geochemistry and mineralogy of REE- and U-fertile granites: Implications for the formation of regolith-hosted REE and granite-related U deposits

Abstract The origin of both regolith-hosted rare earth elements (REE) and granite-related uranium deposits has been generally suggested to be associated with REE-U-bearing accessory minerals in granitic rocks. However, different mineralization styles are often associated with granites with specific geochemical and mineralogical fingerprints. Here, whole-rock geochemistry and mineralogy of the REE-fertile Zhaibei and U-fertile Aigao granites in southern Jiangxi Province were investigated to decode petrogenesis of granites and their genetic link with the REE and U mineralization. Zircon and monazite-(Ce) U-Pb dating indicates that the Aigao and Zhaibei granites were emplaced at the Triassic (∼231 Ma) and Jurassic (∼191 Ma), respectively. The Aigao granite belongs to low-Ca peraluminous L-type leucogranites with whole-rock 87Sr/86Sr ratios of 0.7059–0.7228 and ɛNd(t) values of −11.4 to −11.5, monazite-(Ce) ɛNd(t) values of −13.2 to −9.7, and Paleoproterozoic Nd model ages, suggesting that the granite was mainly derived from partial melting of ancient continental crust. In contrast, the Zhaibei granite is high in SiO2, (Na2O + K2O)/CaO, FeOT/MgO, and Zr + Nb + Ce + Y, but low in CaO, TiO2, and Sr and shows the affinity of A2-type granites. It has whole-rock 87Sr/86Sr ratios of 0.7016–0.7097 and ɛNd(t) values of −6.4 to −0.6 and monazite-(Ce) ɛNd(t) values of −6.7 to −5.5. These results indicate that the Zhaibei granite was generated by mixing between mantle-derived mafic magma and crustal-derived felsic magma. The Aigao granite, with low whole-rock Th/U and REE/U ratios, is characterized by the association of monazite-(Ce), Th-poor uraninite, and xenotime-(Y), and represents a favorable U source for uranium deposits. The Zhaibei granite exhibits higher REE + Y, Th, Zr, (REE + Y)/U, and Th/U and has primary REE-bearing minerals of monazite-(Ce), U-rich thorite, and zircon. Some magmatic phases have been transformed into the secondary forms (e.g., REE-fluorocarbonates) that are easier to be weathered during deuteric alteration, which sets the stage for regolith-hosted REE mineralization. This study suggests that uraninite-bearing, low-Ca peraluminous granites with U/(REE + Y) >∼0.2 should be considered as high-priority targets for exploration for U deposits, while high-Si (SiO2 >∼74 wt%), low-Ca (CaO <1 wt%) peraluminous granites with the LREE/(HREE + Y) ratio of <∼1.5 and high-Ca granites (CaO >1 wt%) with the LREE/(HREE + Y) ratio of >∼1.5 may have greater regolith-hosted HREE and LREE ore potential, respectively.