The Early Jurassic Fe-Sn metallogenic event and its geodynamic setting in South China: Evidence from Re-Os, U-Pb geochronology and geochemistry of the Dading magnesian skarn Fe-Sn deposit

The South China Block (SCB) is one of the largest W-Sn-polymetallic metallogenic district over the world, with most of the deposits formed during the Mesozoic. The Early Jurassic of SCB was considered as a magmatic and metallogenic quiescence stage, as response to the tectonic transition from the paleo-Tethyan to the paleo-Pacific geodynamic domains. The Dading Fe-Sn deposit is a quite rare Early Jurassic deposit recognized in SCB. SIMS Zircon U-Pb and molybdenite Re-Os dating indicate that the Dading Fe-Sn deposit (185.9 +/- 4.9 Ma) and related Shibei granite (189.0 +/- 1.5 Ma) formed at the Early Jurassic, which provides convincing evidence for a previously unrecognized Early Jurassic Fe-Sn metallogenic event in SCB. Geochemical data show that the Shibei granite has high SiO2, Nb, Zr + Nb + Ce + Y concentrations and high Ga/AI ratio, but low Y/Nb ratio, which are similar to those of A l -type granite. The large range of zircon epsilon(Hf)(t) values ( -2.4 to + 3.4), negative correlation between zircon epsilon(Hf) (t) and delta O-18 values, and unique whole-rock Sr-Nd isotopic compositions (epsilon(Nd)(t) = -3.3 to - 3.7; I-sr = 0.7063 - 0.7085) suggest that the Shibei granite is likely to originate from a mixed source of preexisting crust and juvenile material with OIB-like isotopic composition. Combining with the spatial distribution of the volcanic-intrusive rocks, sedimentary basins, and tectonic deformation styles, we suggest that the Early Jurassic Fe-Sn mineralization occurred in an extensional environment, which was probably linked to the postorogenic collapse of the Indosinian orogeny between the SCB and Indochina Block.