矿床地球化学国家重点实验室知识库

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 SiO2 (70.7-78.7 wt%) and K2O (> 4.0 wt%), P2O5, Rb, Ta and U, and low contents of Ti, Sr, Ba and HREEs. The rocks also show positive P2O5 vs. SiO2 correlation, suggesting a highly-fractionated S-type affinity. Different from most W-bearing granites in the Jiangxi region, the calculated zircon epsilon Hf(t) (-10.0 to -2.4; two-stage model ages: 1350-1824 Ma) and delta O-18(zircon) values (+ 6.40 to + 8.87 parts per thousand) 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 Ce4+/Ce3+ (3.83-96.49; mean = 20.99) ratios of the granites indicate very low oxygen fugacity (fO(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.