Abstract：Through continuous laser stepwise heating 40Ar/39Ar dating of two mica samples from auriferous phyllic mylonite of the Kekesayi and Alatasi gold deposits hosted in the Bu’ergen shear zone, the authors obtained plateau ages of 274.5±2.2 and 282.6±2.2 Ma and corresponding isochron ages of 275.8±5.2 and 283.1±5.2 Ma for the two deposits respectively. These ages suggest that the ductile-brittle shear of the Bu’ergen shear zone and formation of gold deposits occurred at the beginning of the Early Permian. These chronological data combined with regional geological data show that the formation and evolution of the Bu’ergen gold-bearing shear zone were mainly controlled by the tectonomagmatic event related to the regional sinistral ductile shear of the huge Irtysh (Ertix) strike-slip shear zone on the southern margin of the Siberian plate, and its tectonic setting is the post-collisional extensional environment of the Altay orogeny.