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

Abstract

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/Al ratio, but low Y/Nb ratio, which are similar to those of A1-type granite. The large range of zircon εHf(t) values (−2.4 to +3.4), negative correlation between zircon εHf(t) and δ18O values, and unique whole-rock Sr–Nd isotopic compositions (εNd(t) = −3.3 to −3.7; ISr = 0.7063 – 0.7085) suggest that the Shibei granite is likely to originate from a mixed source of pre-existing 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 post-orogenic collapse of the Indosinian orogeny between the SCB and Indochina Block.