Zircon U-Pb dating, Hf isotope of magmatic rocks from Qibaoshan Cu polymetallic deposit, Hunan Province

The Qibaoshan Cu-polymetallic deposit in Liuyang is belong to the west section of Qinzhou-Hangzhou metallogenic belt,and it is the largest Cu-polymetallic deposit in northeastern Hunan Province. The quartz-porphyry is on a great contribution of the mineralization of the Qibaoshan Cu-polymetal-lic deposit. The zircons from quartz-porphyry are typical magmatic zircons. LA-ICP-MS U-Pb dating of the zircons shows the age of 154.8±1.8 Ma, which represents the crystallization age of quartz-porphyry, and indi-cate it was Late Mesozoic intrusion. The new born zircons have intermediate 176Hf/177Hf of 0.282120 ~0.282539,εHf (t) of-19.8~-4.9, model age of crust tDM2 from 1519 to 2450 Ma, indicating that the rock was formed by the partial melting of the Paleoproterozoic to Mesoproterozoic crust. Through the comprehensive study of crystallization age and Hf isotope model age of the zircons, the crustal magma formed the quartz-por-phyry was from a mixed magma from the crust source and the mantle source or form a mixed magma with the characteristics of the depleted mantle, which may containing the very old continental crust (the Hadean crust). In 175 ~ 145 Ma, an extensive rocks related to the porphyry and skarn copper deposit intruded of Qinzhou-hangzhou metallogenic belt. And these rocks were the product of the heyday of the system of temper-ature increasing and pressure depressing after the Izanagi Plate subducting toward northwest into the South China Block. The study of the geochemical characteristics of the quartz-porphyry before shows that the magma also having the the mantle source. All these data suggest the magma from the partial melting material of Paleo-proterozoic to Mesoproterozoic crust or even much older crust was in the magma chamber already, the as-thenospheric mantle fluid upwelling into the magma chamber and they mixed inhomogenously by the effects of the delamination of lithosphere and asthenosphere upwelling. And then the magma intruded upward to form the quartz porphyry.