LA-ICP-MS Zircon U-Pb Age of the Brittle-Ductile Shear Zones in Hougou Gold Orefield, Northwestern Hebei Province

Synthetic study shows that there are near NE brittle-ductile shear zones in the Hougou gold deposit. In order to study its forming age, the authors made a mineralogical and U-Pb geochronologic study on the zircons from the mylonitized quartz syenite located to the north of the Shiduokou village in the shear zones. Two types of zircons, magmatic and hydrothermal origin are recognized. The magmatic zircons are characterized by euhedral-subhedral with clear magmatic oscillatory zones on cathodeluminescence (CL) images. Their U-Pb results gave a weighted mean 206Pb/238U age of (383.4±2.8) Ma. The hydrothermal zircons are mainly irregular form and fill in the rim or interior of the magmatic zircons, dark-gray (non-luminescent) on the CL images. Their LA-ICP-MS zircon U-Pb age is (154.4±1.3) Ma, which indicates a Late Jurassic tectonic event. Combining with the geological facts, the authors suggest that the former age indicates intrusive time of the eastern part of the Shuiquangou alkaline complex, and the latter implies the age of the NE direction brittle-ductile shear zones. Considering the time gap of the ore forming age (140 Ma) of the Dongping gold deposit and the brittle-ductile shear zones age (154 Ma), the authors propose that there are multistage structural-magmatic activities and hudrothermal ore-forming events in the Dongping and Hougou deposit fields, and the main mineralization stage of Au deposits is the Yanshanian peroid. Aand the gold deposits formation is mostly related to the magmatic activities of the intermediates acid small rock bodies in the Yanshanian period.