The world-class mid-Mesozoic Jiangnan tungsten belt, South China: Coeval large reduced and small oxidized tungsten systems controlled by different magmatic petrogeneses

Abstract

The 500 km-long NE-trending Jiangnan tungsten belt formed at 140–150 Ma at the northern margin of the Yangtze craton and has a total resource of approximately 6.0 Mt WO3. Most deposits are of granite-related porphyry/vein-style and skarn type. The three large W systems at Zhuxi, Shimensi and Shiweidong in the southwestern part of the belt are the most important. These deposits have reduced affinity and are related to ilmenite-series S-type granites. The many smaller W-Mo deposits in the northeastern part of the belt have oxidized affinity and are related to magnetite-series I-type granites. Based on geological features, magma formation temperatures, bulk-rock and biotite compositions, Sr-Nd-Hf isotope data and trace element modeling, we propose a model in which large, reduced W-related granitic magmas formed by crustal partial melting induced by intrusion of mantle-derived mafic magmas, followed by internal magmatic evolution. In contrast, the more oxidized W-Mo-related granitic magmas formed by hybridization of crustal melts and sills of mantle-derived mafic magma in hot zones, with minor magmatic evolution. This model explains the metallogenic features of the coeval large W and small W-Mo deposits in the Jiangnan belt and reveals that the magma source and corresponding oxidation state are the main controls on the significant size difference between the reduced and oxidized tungsten systems, although the general geodynamic situation is the same.