Protolith-controlled superposition of Sn-(W) and Cu-Mo mineralization: Examples from the Jurassic and Cretaceous granite-related mineralization in the coastal region of southeastern China

Abstract

Sn (W) and Cu-Mo have distinct geochemical behaviors during magmatic evolution, thus these two group deposits are seldom superposed. Specially, the Mesozoic granite-related Sn-W/W-Sn and Mo-Cu/Cu-Mo deposits in south China are spatial overlapped, with some are even temporal-coincided. To reveal the factors controlling the distribution and the locally coeval occurrence of different mineralization types, here we compared the ages, sources compositions, and tectonic settings of the Jurassic Zijinshan Sn-rich granite, the Jurassic Gutian porphyry Mo-Cu deposit, and the Cretaceous Luoboling porphyry Cu-Mo deposit from the southeastern (SE) China. The results indicate that the Jurassic Sn-W and Mo-Cu rich magmas were derived from Paleoproterozoic meta-sedimentary and meta-basaltic rocks, respectively, through partial melting (>850 °C) along the suture zones triggered by asthenospheric upwelling in the intra-plate extensional setting. The Cretaceous porphyry Cu-Mo deposit was formed by water-flux melting (<800 °C) of the mantle wedge metasomatized by the fluids derived from the subducted Paleo-Pacific plate. A protoliths-controlled distribution model was proposed, namely that during Jurassic, the suture zones, where were the ancient continental margins containing both meta-sedimentary and meta-basaltic rocks, favored heat input from upwelling mantle and high temperature melting, which consumed the both protoliths to form W-Sn and Mo-Cu rich magmas in the same region; shift in tectonic setting from intra-plate extension to subduction during Cretaceous, introduced mantle or juvenile crust-derived materials to source, therefore formed Cu-Mo deposits superposing the Jurassic W-Sn and Mo-Cu ores in SE China.