Petrogenesis of ore-forming granites with implications for W-mineralization in the super-large Shimensi tungsten-dominated polymetallic deposit in northern Jiangxi Province, South China

Abstract The Shimensi deposit is a newly discovered, super-large tungsten (W) polymetallic deposit in northwestern Jiangxi Province, South China. In this paper, we reported new zircon U–Pb ages for the ore-bearing porphyritic biotite granite (151.3 ± 2.8 Ma) and fine-grained granite (150.1 ± 1.2 Ma and 150.7 ± 2.4 Ma), which represent the oldest Mesozoic granitic magmatism reported at Shimensi. Our ore-bearing granite porphyry ages (142.7 ± 2.3 Ma and 143.3 ± 1.5 Ma) have better constrained the timing of the Jurassic-Early Cretaceous ore-forming magmatism. Geochemically, the Shimensi granitoids are strongly peraluminous, with high contents of SiO 2 (70.7–78.7 wt%) and K 2 O (>4.0 wt%), P 2 O 5 , Rb, Ta and U, and low contents of Ti, Sr, Ba and HREEs. The rocks also show positive P 2 O 5 vs. SiO 2 correlation, suggesting a highly-fractionated S-type affinity. Different from most W-bearing granites in the Jiangxi region, the calculated zircon eHf(t) (−10.0 to −2.4; two-stage model ages: 1350–1824 Ma) and δ 18 O zircon values (+6.40 to +8.87‰) of the Shimensi granites suggest that the latter were mainly derived from the partial melting of heterogeneous source rocks, probably with combined contributions from the Neoproterozoic Shuangqiaoshan Group metamorphic rocks and Jiuling granodiorite. The calculated zircon Eu/Eu ∗ (0.05–0.58; mean = 0.20) and Ce 4+ /Ce 3+ (3.83–96.49; mean = 20.99) ratios of the granites indicate very low oxygen fugacity ( f O 2 ) for the ore-forming magmas, a highly favorable factor for W mineralization. Potentially W and Cu-rich source rocks, and highly-fractionated and reducing granitic magmas, were important factors that triggered super-large W mineralization at Shimensi.