Geochronology, petrogenesis and metallogeny of Piaotang granitoids in the tungsten deposit region of South China

抄録

The tungsten deposit region of South China is well known as the world's leading tungsten (W) producer. The Piaotang tungsten deposit in the region is such a representative large-scale quartz vein type tungsten polymetallic deposit that is closely associated with granitoids. In the present study we present precise LA-ICP-MS zircon U-Pb dating and LA-MC-ICPMS zircon Hf isotopic data for the samples from exposed quartz diorite body and buried granite stock in the Piaotang tungsten deposit area. Zircon U-Pb dating results indicate that the quartz diorite body was formed in Early Paleozoic time at 439 ± 2 Ma, whereas the granite body was emplaced in Early Yanshanian time at 158 ± 3 Ma. Both the quartz diorite and granite have negative ε_Hf(t) values, with similar two-stage zircon Hf model ages ranging from 1.8 to 2.1 Ga. Through integration of our new data with the isotope data of Precambrian basement rocks in western Cathaysia, we suggest that the Paleoproterozoic Hf model ages (1.8-2.1 Ga) might be an average age which resulted from mixing of continental materials of different ages. Both the Piaotang Early Paleozoic quartz diorite and Early Yanshanian granite are produced by reworking of the heterogeneous Neoproterozoic crust. Our zircon ages, together with the geochemical data and geological features and ore-forming ages of this tungsten deposit, indicate that the buried Early Yanshanian granite, rather than the exposed quartz diorite, is genetically associated with tungsten mineralization. The distinct metallogeny difference between the Piaotang Early Paleozoic quartz diorite and Early Yanshanian granite can be ascribed to the different degrees of magma differentiation. The Early Yanshanian granite is highly differentiated rock and similar to the other W-Sn deposits generating granitoids in South China. The extents of magma differentiation depend on the tectonic setting and the mechanism of magma generation. On the basis of the relationship between two different stages of magmatism and W mineralization in the Piaotang tungsten deposit, and the similarities with other granite related W-Sn deposits in the same region, it is proposed that the regional tectonic setting and lithosphere dynamics are the key factors controlling the metallogenic capacity of granitoids in South China.