Geochronology And Geochemistry Of The Granitoids In The Bayanhar Area, Inner Mongolia

The Bayanhar gold deposit, belonging to Erlianhot- Xilinhot Au, Fe and Cu metallogenic belt, is located Xing’an Mongolian orogenic belt. The region is characterized by widely exposed Precambrian to upper Paleozoicstrata, and the Ondor Sum Group may provide part of metallogenic material. Affected by multiple stage of subductionand collision, the faulting tectonicsextensively developed,and the Jiaoqierductile-shear zones has a close relationship with Baryanhar gold deposits. Multiply magmatic activities, from Caledonian to Yanshanian, provide sufficient source andhydrotherm for gold mineralization. Especially, the late Hercynian to early Indosinianintrusions has close relationships with many deposits in this area.The Bayanher gold deposit is located along the Ondor Sum Groupmica schist that is near the Triassicbiotite-granite and is hosted a lot of epithermalauriferous quartz veins. The orebody is hosted in these quartz veins and the schist on the sides.Some predecessors consider 363Ma(the U-Pb age of Halatugranodiorite) as the age of deposit, which may triger controversy. First, according to the result of secondary anomalies and REE analysis and also the close spatial relationship with ore bodies, consider the Triassicbiotite-granite as the ore-bearing inclusion, which has the U-Pb age of 226.5±4.1Ma. Furthermore, according to the intercalated relationship of the Triassic biotite-granite and the ophiolite mass, also the similar age of gold deposits in same tectonic environment, we consider 226.5±4.1Ma as the ore-forming age.Our study also provides enough attention on Baolidao and Halatugranitoids. According to the data we get, the Baolidao suit belongs to calcium alkaline aluminium granite, and it was ploted in post-collision area in Rb-(Yb+Ta)diagram. With theε Nd(t)<0, we think that it located in the post-collisional tectonic setting in Carboniferous to Permian, which is tectonic transition period. Compare to Baolidao suit, Halatugranitoidsis characterized bystrongly peraluminous, it was also supported by the euhedraloriginalmuscovite found under the microscope. This suit granitoids has a lower Ti、P andε Nd(t)value, and we suggested that it forms in the post orogenicextension environment.