The Study Of Genetic Difference Between Cu And W Deposits In Southern Hunan

Baoshan and Huangshaping deposits are the typical representative of porphyry skarn-hydrothermal vein type Cu polymetallic and W-Sn polymetallic mineralization in the southern Hunan, located in the central part of Qinzhou-Hangzhou ore belt. The Cu-Pb-Zn deposits are associated with granodiorite porphyries whereas the W-Sn deposits occur within granite porphyry. In order to further discuss the differences of porphyry skarn-hydrothermal vein type Cu polymetallic and W-Sn polymetallic mineralization, the geological characteristics, mineral chemistry and petrographic of the Baoshan granodiorite porphyry and granodioritic cryptoexplosion breccia have been investigated, and then compared with Huangshaping granite porphyry closely related with the W-Sn deposit.The zircon LA-MC-ICP-MS U-Pb dating results show that the zircon U-Pb ages of the Baoshan granodiorite porphyry, granodioritic cryptoexplosion breccia and Huangshaping granite porphyry are 156.3±0.9 Ma,157.1±1.8 Ma and 155.2±0.4Ma respectively. It is well coincident with Baoshan, indicating the Late Jurassic magmatism.In addition, we found that granite porphyry and granodiorite porphyry have differnces in factors of formation, souces, the degree of magmatic differentiation and oxygen fugacity from the geological survey and petrogeochemistry and mineral micro-zone analysis. The results suggest that Baoshan granodiorite porphyry belongs to I-type granite with the same remelted granite. Huangshaping granite porphyry belongs to S-type and has the characteristics of more higher evolution differentiation.The Baoshan granodiorite porphyry was formed by the partial melting of Paleoproterozoic crustal material with a mixed source of crust and mantle. The Huangshaping granite porphyry was formed by the partial melting of Proterozoic crustal material, the source is crust, little even no mantle souces.The significant depletions in Ba, Sr, Eu, and Ti shown in the spider diagrams indicate significant fractional crystallization during the formation of the Huangshaping granite porphyry. In addition, the high Rb/Sr and Sm/Nd ratios, and low Th/U and Ba/Rb ratios also indicate that the Huangshaping granite magma underwent intensive fractional crystallization. In contrast, there was no obvious fractional crystallization during the formation of the Baoshan granodiorite porphyry.The zircons from the Huangshaping granite porphyry have an average Ce4+/Ce3+ ratios of 8, the zircon 8Eu values is 0.003. The zircons from the Baoshan granodiorite porphyry have an average Ce4+/Ce3+ ratios of 355, the zircon 8Eu values of the Baoshan is 0.42. It is suggesting that the granodiorite porphyry have relatively high oxygen fugacity than granite porphyry.The magma relatively high oxygen fugacity and no obvious fractional crystallization of granodiorite porphyry may be the key to Cu polymetallic deposit, and the high fractional crystallization and low oxygen fugacity of granite porphyry perhaps was important to W-Sn minerallization.