ABSTRACT

The recently discovered world-class Shimensi tungsten-polymetallic deposit, located in the Middle-Lower Yangtze River metallogenic belt, has an estimated reserve of 742,500 tons of WO₃ with 0.195% W, which is accompanied by 403,600 tons of Cu and 28,000 tons of Mo. The ore geology, ore mineralogy, structure/texture, alteration, and mineral zoning of the Shimensi deposit are discussed in the paper. Three styles of mineralization are present in the deposit: veinlet-disseminated, quartz vein, and hydrothermal crypto-explosive breccia. The associated hydrothermal alteration includes mainly K-feldsparization, greisenization, chloritization, silicification, and carbonatization. Seven samples of molybdenite from the three ore styles have Re-Os model ages ranging from 145.6 Ma to 139.7 Ma, with an isochron age of 140.6 ± 1.2 Ma and mean square weighted deviation (MSWD) of 1.5. The rhenium content in the molybdenite in the Shimensi deposit varies from 0.8641 × 10^–6 to 22.600 × 10^–6, mostly in n × 10^–6, which indicates that ore-forming elements conform to the characteristics of the tungsten deposit accompanied by Cu and Mo and also implies that the ore-forming materials originate mostly from the crust, with some input from a mantle source. The calculated O isotope and measured H isotope compositions of the quartz veins indicate that the ore-forming fluids had a partially magmatic-hydrothermal origin but were mixed with meteoric water. The geochronology and isotopic chemistry indicate that the Shimensi deposit is related to the Early Cretaceous magmatism that occurred throughout eastern China. The partial melting of the Neoproterozoic Shuangqiaoshan Group, with high-W-background concentrations, and the high degree of fractional crystallization of volatile-rich magma are significant factors in the genesis of the Shimensi tungsten-polymetallic deposit.