Late Jurassic Gold Mineralization Events Identified by the Hydrothermal Xenotime and Apatite in the Southern Margin of the North China Craton, Central China

The Niutougou ore area (~31 t Au) is located in the Xiong’ershan district at the southern margin of the North China Craton (NCC). From north to south, the Niutougou ore area is divided into three main parts, corresponding to the gold deposits in the Songligou altered rocks, the J25-J26 breccia, the Vein VII lode gold deposit, and the Shangzhuang altered rocks. The timing of gold mineralization and the formation age of the J26 breccia pipe have not been well constrained in this ore area. Hydrothermal xenotime and apatite are closely related to gold mineralization. The in situ xenotime U–Pb ages of the J26 breccia pipe and Vein VII show U–Pb lower intercept ages of 151.2 ± 2.0 Ma and 155.9 ± 1.6 Ma, respectively. The in situ U–Pb age of the Shangzhuang apatite shows a U–Pb lower intercept ages of 153.4 ± 2.6 Ma. The U–Pb concordia ages and weighted mean ages of the cement zircons from the J26 breccia pipe are 155.8 ± 0.4 Ma, and 155.9 ± 0.8 Ma, respectively, determined via sensitive high-resolution ion microprobe (SHRIMP) analysis. The molybdenite veins in the J26 breccia pipe cut the cement and different types of breccia and have a Re–Os isochron age of 155.9 ± 2.9 Ma and weighted mean age of 155.9 ± 1.1 Ma. Thus, the formation age of the breccia pipe is Late Jurassic. The subduction of the paleo-Pacific Plate beneath the NCC and the back-arc extensional setting in the Late Jurassic might have caused gold mineralization in the southern margin of the NCC.