Petrogenesis of Jurassic Granite from the Shuitou Pluton in South Jiangxi Province, South China: Implication for Ion-adsorption REE Enrichment

Ion-adsorption rare earth deposits are mainly formed by the weathering and leaching of the granite ore-forming parent rocks, and the heavy rare earth resources in the world dominantly occur within this type of deposits. In this study, we take the Shuitou pluton, the Late Jurassic rare earth element (REE) ore-forming parent rocks, as the research object, and elucidate the REE enrichment process in the granites through the chronology, rock geochemistry and isotope geochemistry analyses‌. The results show that the zircon U–Pb age of the Shuitou pluton is ~150 Ma, and the monazite U–Pb age is ~145 Ma, both indicating the pluton was formed in the Yanshan Stage. The rocks have high content values of SiO2 (72.85–75.55 wt%), Al2O3 (12.85–14.63 wt%), and K2O (4.46–5.27 wt%), with the A/CNK values of 1.05–1.19, the differentiation index (DI) values of 87.48–95.59, the zircon saturation temperature values of 689–746 ℃, the Nb/Ta ratios of 2.72–9.54, and the Zr/Hf ratios of 7.12–26.11; besides, the rocks also contain peraluminous minerals muscovite and garnet. All these indicate that rocks belong to highly fractionated S-type granite. The εHf(t) values of zircon and monazite range from –10.04 to –6.78 and –9.3 to –8.2, respectively, indicating that the magma mainly originated from the Proterozoic crustal metamorphic sedimentary rocks. In the extensional tectonic setting of South China, high temperature promotes the melting of the REE-enriched accessory minerals, and the higher content value of F increases the solubility of the REEs in the molten mass. The presence of the heavy rare earth minerals such as garnet in the rocks makes the rocks have a high heavy rare earth element (HREE) content, and the REE-enriched minerals such as titanite, bastnäsite, and allanite provide the material conditions for the formation of the ion-adsorption REE deposits.