ABSTRACT

The Shimensi tungsten-polymetallic deposit, located in Lower Yangtze mineralization province, is a recently-discovered world-class deposit. It is necessary to clarify the source and the evolution of the ore forming fluid. We report Pb isotope results form scheelite, wolframite, molybdenite and chalcopyrite samples as well as K-feldspars from Neoproterozoic biotite granodiorite, and Mesozoic porphyritic biotite granite, fine-grained biotite granite, and granite porphyry. Results show that the Pb isotopes from both the ore minerals and granite K-felspar can be divided into 3 groups. Pb isotope ratios from the ore minerals are similar to those from the early Cretaceous prophyritic biotite granite and fine-grained biotite granite, indicating that the ore components for the Shimensi deposit were mainly originated from these two types of granites. The O isotope equilibrium temperature of the quartz-scheelite ranges from ∼295.89°C to 435.97°C, the δ¹⁸O from ∼7.0‰ to 9.6‰, indicating that the mineralization occurred under the condition of high temperature and O isotope equilibrium exchange. It is concluded that the ore-forming fluids for the Shimensi deposite had a magmatic-hydrothermal origin, related to the Early Cretaceous magmatism in an extensional tectonic environment in East China. The granites themselves were probably generated from partially melting of the Neoproterozoic Shuangqiaoshan Group, which contains of 9.13 ppm high tungsten background content.