Partial-melting of fertile metasedimentary rocks controlling the ore formation in the Jiangnan porphyry-skarn tungsten belt, south China: A case study at the giant Zhuxi W-Cu skarn deposit

Abstract

The Zhuxi W-Cu deposit, located in the Jiangnan porphyry-skarn W belt, is a world-class W deposit. We studied three coeval mineralization-related intrusions composed of biotite monzogranite, fine-grained granite, and granite porphyry in the Zhuxi mine. These rocks contain peritectic garnet and K-feldspar. The LA-ICP-MS U–Pb dating of zircon from the biotite monzogranite, fine-grained granite, and granite porphyry yields average ages of 149.38 ± 0.86 Ma, 149.0 ± 1.0 Ma, and 148.30 ± 1.4 Ma, respectively. The Zhuxi granites are enriched in Cs, Rb, and U and depleted in Ba, Sr, and Ti, with ASI [molar Al2O3 / (CaO + Na2O + K2O)] values of 1.03–2.15. The fine-grained granite exhibits initial 87Sr/86Sr values of 0.716–0.717 and εNd(t) values ranging from −9.61 to −9.21. The εHf(t) values of the biotite monzogranite and fine-grained granite range from −8.83 to −6.30 and from −9.86 to −7.62, respectively. The Sr–Nd–Hf isotopic compositions of these rocks are similar to those of the fertile Neoproterozoic metasedimentary rocks in the Jiangnan W belt.The Zhuxi granites are S-type granites based on their mineral assemblages and geochemical characteristics. The Hf isotopic compositions, Sr–Nd isotopic characteristics, and trace element modelling suggest that the studied granites formed from the dehydration melting of fertile Neoproterozoic metasedimentary rocks caused by the Late Jurassic underplating of OIB-like basaltic magma.