U-Pb age of post-ore dykes in the Xiejiagou gold deposit and its constraints on ore-forming age, Northwest Jiaodong, China

The northwest Jiaodong peninsula is one of the largest gold ore concentration areas in China, in which gold resource reserves exceed 4000 tons.Most of the deposits in the area are controlled by Sanshandao, Jiaojia and Zhaoping faults.The Xiejiagou gold deposit is located in the west and the footwall of Zhaoping fault, controlled by NWW- and NEE- secondary faults, which is different from the feature of the deposits which occur in Zhaoping fault such as Dayinggezhuang and Xiadian.Based on the phenomenon of existence of two kinds of dike, i.e., quartz diorite porphyry and granodiorite, which cut though mineralization and alteration in the tunnel, the authors conducted LA-ICP-MS U-Pb dating for the dikes.It is found that the U-Pb ages are 118.0±1.1 Ma and 118.4±0.9 Ma respectively, which suggests that the lower limit age of mineralization is 118 Ma in the Xiegagou gold deposit, and gold mineralization in northwest area of Jiaodong peninsula had been mainly completed by 118 Ma.It is inferred that regional mineralization was more probably related to diorite type intrusives between the formation of Guojialing and Weideshan intrusives.