Genetic relationship between the two-period magmatism and W mineralization in the Dahutang ore-field

The Dahutang ore-field is a newly discovered world-class W-polymetallic ore cluster in South China. It is located in the middle part of the Jiangnan orogenic belt, at the junction of Wuning, Xiushui and Jing'an counties of Jiangxi Province. Dahutang ore field covers an area of about 500km(2) and reserves nearly two million tons of W0(3) resources (associated Cu and Mo). This area is characterized by a large area of exposure of Jinning Period granitoids, while the Yanshanian granitoids are completely concealed. The former one is the main vein-disseminated scheelite carrier, and the latter one is consistent with the W mineralization in time. It is of important significance whether there is a genetic connection between the two-period magmatism and how they contribute to the W mineralization. On the basis of studies of ore-field geology, petrology and geochemistry, this paper is a comparative research of geochronology, Hf isotoic and trace elemental geochemistry of the zircons from the Jinning Period and Yanshanian granotoids. The results show that Shimensi granite has zircon U-Pb ages of is 147. 7Ma, Jing'an W desposit has molybdenite Re-Os ages of is 134. 9Ma, and the age of ore-host Jinning Period granite is 815. 8Ma in Dahutang W ore-field. The granitoids of the two-period are all peraluminous and S-type series. Some inherited zircons are discovered in Shimensi Yanshanian granite, which have similar Hf isotopes and trace element compositions with the Jinning Period magmatic zircons, indicating the Jinning Period granitoids and Yanshannian granite may have an inheritance relationship. The Meso-Neoproterozoic basement, including the Jinning Period granitoids could take part in the original remelting source of the Mesozoic granite. The trace element of zircon indicates that the crystallization temperature of the two-period granitic magma were both around 700 degrees C, then experienced low oxygen fugacity and water saturated molten during magma evolution. In Mesozoic, large-scale remelting of the middle and upper crust formed granitic magma under the background of lithospheric extension in South China. The W-bearing hydrothermal fluid accumulated following the Yanshanian granitic magma intrusion and metasomatized with the surrounding Jinning Period granitoids (rich in W and Ca), which became the necessary condition for the formation of large scale veinlet-disseminated type scheelite-dominated mineralization.