Abstract: The authors discovered the Xiaoyinuogaigou granite-porphyry in the southern margin of the Ergun block,where the Xiaoyinuogaigou gold deposit is located. The research confirms that:1)the Xiaoyinuogaigou granite-porphyry was formed in middle Jurassic;2)the ore-bearing rock and the host rock of the Xiaoyinuogaigou gold deposit are the Xiaoyinuogaigou granite-porphyry;3)the Xiaoyinuogaigou gold deposit is a mesothermal deposit;and 4)the Ergun ductile shear zone is the passageway for the Xiaoyinuogaigou granite-porphyry,and the secondary fracture of the Ergun ductile shear zone is the host structure of the Xiaoyinuogaigou gold deposit.