The Magmatism Of The Yanshanian And Related Metallogenetic Effects In The Xidaming Mountain Of Guangxi Province

The Xidaming Mountain ore-concentrated area is a new W-Zn-Ag polymetallic ore accumulated area with the favorable economic value.It is located in the east of Xidaming Mountain at the southwest of the Qin-Hang(Qinzhou-Hangzhou)metallogenic belt,which is closely related to the mineralization and magmation of the late Yanshanian in South China.Based on the achievement in the past,we studied the magmatite of the ore-concentrated area,analyse the geochemical characteristics,chronology and rare earth element of the magmatic rocks.We compared it with the other granites in the Danchi metallogenic belt,analysis the genesis and geochemical characteristics of the granodiorite in the Xidaming Mountain and discussed the magmatism and mineralization occured in the late Cretaceous.The granite in the Xidaming Mountain is similar to other granites in the Danchi metallogenic belt.They are the per-aluminous and alkaline A-type granite,which formed at the environment transformed from the collision to the within-plate tectonic environment.In the multielement diagram of trace elements,samples are strongly enriched in the LILEs(e g.Rb,U,Nd,Pb,Th)and loss of HFSEs(Ba,Sr,Ti).The rare earth distribution pattern of samples shows a right-fined "V"-like distribution curve with obvious Eu negative anomaly.The zircon U-Pb dating result is 94.3±1.9 Ma,which is consistent with the age of magmatism and mineralization at the late Yanshanian in South China.The value of granite's ?Hf(t)(-3 ~-7)shows that the granite is derived from the lower crust.The quartz porphyry was altered seriously,the zircon U-Pb age of the quartz porphyry is 93.46±0.46 Ma and the rock belongs to the Yanshanian mass,which is consistent with the age of the magmatism in this area,and have a closely relationship with the mineralization.The dolerite in the Xidaming Mountain is the alkaline oceanic basalt that formed under the extension environment.The rare earth distribution curve shows the right-leaning curve without Eu anomaly,which is characterized by the source of the deep crusts.The dolerite contains high ore-forming elements(e.g.,Mn?Cu?Zn?Ni).The high content of Mn is related to the formation of the Mn-deposit in the area.The U-Pb age of the zircon in this area is about 94 Ma,which is similar to the age of the magmatism and mineralization.Including,the age of the magmatism is equal to the age of large magmatism and mineralization in the South China.The H-O isotopes of the fluid inclusions of the typical deposits in the Xidaming Mountain show that the ore-forming fluids are mainly root in deep magmatic water.The value of ?18O(0.57~9.66‰)and ?D(-74~-55‰)reflect the ore-bearing fluids is magmatic water.The S and Pb isotopes show that the ore-forming materials are from the deep magma.The Pb in the ore is similar to the granite,it reflect the magmatite is closely related to the mineralization in the late Yanshanian.The combination of the ore-forming elements?the ore body distribution characteristics and the feature of geochemical isotopic shows the Xidaming Mountain area is a magmatic hydrothermal metallogenic system with a closely relationship with the deep rock.