Geochronology and geochemistry of the Zhangjia granitic pluton in the Miaoershan uranium orefield, Northeastern Guangxi Province

Two samples were collected near the Zhagutian uranium ore deposit and Zhangjia uranium ore deposit respectively to carry out LA-ICP-MS zircon U-Pb isotopic dating. The analytical result demonstrates that the formation age of the host rock in the Zhagutian uranium ore district is 218.0±1.4Ma, whereas the formation age of the host rock in the Zhangjia uranium ore district is 226.8±5.7Ma. Furthermore, the Zhangjia granite is characterized by high SiO₂ (74.35%~76.29%), Al₂O₃ (12.54%~14.03%) and (Na₂O+K₂O) (6.95%~9.17%), but low MgO (0.34%~0.45%), CaO (0.68%~1.03%) and TiO₂ (0.106%~0.18%), so it belongs to high-K calc-alkaline series granite. The Zhangjia granite is rich in Rb, and poor in Ba, Sr with high Rb/Sr ratio, so it belongs to low Ba-Sr granite series. The granite is rich in LREEs with negative Eu anomalies. Meanwhile, The granite is rich in U (21.5×10^-6 on average)with low Th/U ratio (1.63 on average), so it is very favourable for uranium mineralization. The granite has high (⁸⁷Sr/⁸⁶Sr)_i (~0.7247), low ε_Nd (t) (-13.95 on average) and its two-stage Nd isotopic model ages are (2.07~2.19Ga). The Zhangjia granite belongs to strongly peraluminous S-type granite. It probably originated from partial melting of Proterozoic sedimentary metamorphic rocks.