Chronology And Geochemistry Of Granitoid For The Weilasituo Cupper Polymetal Deposit In Inner Mongolia

Weilasituo Cu polymetal deposit is located in the western slop of middle-southern metallogenic belts in Da Hinggan Mountains of Inner Mongolia, and the previous preliminarily researched and thought that the deposit is magmatic hydrothermal deposit related to the Yanshanian granite. At present this deposit is not well researched, and systematic deposit geochemistry has not started yet.Combined with regional geological background and integrated studies of petrology, geochemistry and SHRIMP U-Pb geochronology for the relationship between the granitic intrusions and deposit, and for the preliminarily analysis of metallogenesis can lead to the following conclusions:(1)According to the SHRIMP U-Pb age, the granitoids in the mining area are granites intruded at c.a. 323Ma and diorites crystallized at c.a. 308～298Ma. Both of them are Hercynian granitoids.(2)The two granitic rocks in the mining area both alkali calcic rocks, with high field strength elements(Ti, Nb, Ta ) depletion and large-ion lithophile elements (Rb, Cs) and high field strength elements (Zr, Hf, Th and U) enrichment. And it is also characterized by low∑REE, weak Eu anomaly, and relatively lower partition of the HREE. Those geochemistry characteristics, together with relatively highεNd(t) values and low ISr values, indicate that the origin of these intrusive rocks are mixtures of continental crust and mantle material, and belong to rich amphibole calc-alkalic granitoids, with subduction-related petrogenesis.(3)According to the subduction of the Paleo-Asian ocean in late Paleozolc in this area, the petrogenesis processes of these two granitic rocks in the mining area are as follows: Partial melted mantle materials are induced by subduction, and then it underplated into crust with a certain depth ( often to the bottom of lower crust); thereafter, these accreted components partial melted during later tectono-thermal event again; during the upwelling of these material, the secular recycled wallrock were heated and melted; those remelting crust materials mixed and assimilated with the accreted components in different degree; and finally the mixed magma emplaced and crystallized.(4) The relationship between the granitoids and deposit in this area are discussed in geochronology and geochemical characteristics, which shows the Hercynian granitoids in this study is not likely to provide mineral-formation materials, hydrothermal fluid or thermodynamic, but can performed as passageway or precipitation space for mineral transportation.(5)Based on the study of the spatial distribution of mineral ore, mineral composition and structural tectonics, wall rock alteration and fluid inclusion, it is thought that the cupper polymetal deposit belongs to mesothermal deposit, and preliminarily deducted that younger hidden rocks mass in the deep could supply mineral materials.