This paper presents a 40Ar-39Ar chronological study of the Qiyugou gold deposit, an explosion-breccia type deposit in the Xiong'ershan area, Songxian County, Henan Province. The 40Ar-39Ar ages of K-feldspar formed in the ore veins show that the main metallogenic stage occurred during 115~125 Ma, and the gold mineralization lasted 10 Ma. Combined with the studies by other researchers, the authors suggest that it took about 30 Ma from the formation of regional granite to the development of the explosion-breccia and the beginning of the main metallogenic epoch. The Qiyugou gold deposit got into form at the same time as the development of the regional extensional tectonics, when the activity of deep fluids became intensive and frequent. The deposit is a component part of the large-scale gold mineralization in late Mesozoic in eastern China.