Post-magmatic hydrothermal origin of late Jurassic Liwu copper polymetallic deposits, western China: Direct chalcopyrite Re-Os dating and Pb-B isotopic constraints

The Liwu copper polymetallic deposits are located in the Jianglang Tectonic Dome in the southeastern Songpan-Ganzi Fold Belt. The deposits contain more than 0.8 million tonnes (Mt) of Cu, 0.5 Mt of Zn, 133 t of Ag and 1300 t of Co. However, the detailed geologic features, formation ages and metallogeny of these deposits remain poorly understood. Our new analyses indicate that the Liwu-type copper polymetallic deposits (LTCPD) are epigenetic hydrothermal deposits. The major copper polymetallic orebodies were emplaced in the Late Jurassic (ca. 151.1 ± 4.8 Ma), approximately 4–2.5 Myr later than the local granites (ca. 160.9 ± 1.0 Ma–159.3 ± 0.9 Ma). The ores show variable Pb isotopic compositions, with initial 206 Pb/ 204 Pb ratios of 18.048–18.420, 207 Pb/ 204 Pb ratios of 15.595–15.724, and 208 Pb/ 204 Pb ratios of 38.335–38.795, similar to those of local plutons but significantly lower than those of the ore-hosting rocks. The ore-associated tourmalines are dravitic and relatively homogeneous and exhibit similar δ 11 B values (between −15.47 ± 0.83 and −5.91 ± 0.67 ‰). These geological and Pb-B isotopic features suggest that the deposits at Liwu have a post-magmatic hydrothermal origin, similar to the stratiform skarn deposit. The major ore-forming source is dominantly related to the coeval upper crust-derived magmatism in the region.