Early Yanshanian metallogenesis of the Banjing tungsten deposit in Ganxian, Jiangxi province, China: Constraints from geochemistry, Sr-Nd isotopes, zircon U-Pb, molybdenite Re-Os, and mica 40Ar-39Ar dating

The Banjing tungsten deposit, which has been discovered recently, is located in the northernmost part of the Dabu pluton, southern Jiangxi Province, China. In this study, zircon LA-ICP-MS U-Pb dating of the fine-grained porphyritic biotite granite indicate that it was formed in the early Yanshanian (159.4 +/- 2.5 Ma-161.6 +/- 0.8 Ma). Whole-rock geochemical studies have shown the fine-grained porphyritic biotite granite has SiO2 of 75.82%-76.84%, Al2O3 12.50%-12.87%, MgO 0.07%-0.20%, and CaO 0.64%-1.09%, with A/CNK of 1.017-1.038. It has a total rare earth elements content of 93.9-118.9 ppm with strong negative Eu anomalies (delta Eu = 0.021-0.081). The biotite granite is enriched in Rb, Th, U, Nd and depleted in Ba, Sr, Nb, Ti. These data suggest the Dabu pluton belongs to S-type granite. This pluton has I-Sr of 0.71212-0.72929 and epsilon(Nd)(t) from -9.60 to -10.62 with Nd model ages concentrated in 1732-1838 Ma. These isotopic data in combination with zircon Hf isotopes suggest the biotite granite originated from partial melting of the Middle Proterozoic metamorphic supracrustal rocks in South China, with a minor contribution from juvenile crust. Meanwhile, this study has obtained Re-Os isochron ages of the intrusion-related and quartz vein-type molybdenum mineralization are 156.3 +/- 2.7 Ma and 157.0 +/- 1.1 Ma in the Banjing tungsten deposit, respectively. Sericite from the greisen-type tungsten-molybdenum ore has an 40Ar-39Ar plateau age of 156.4 +/- 1.0 Ma, interpreted as the formation age of this deposit. Collectively, the Banjing tungsten deposit is considered as a product of the early Yanshanian large-scale peak mineralization in South China, which was formed in an extensional intracontinental environment caused by the subduction of the Palaeo-Pacific Plate.