The Sanhetun gold deposit is a ductile shear zone type gold deposit in the Nenjiang County, Heilongjiang Province. Zircons from the granitic mylonite collected in the ductile shear zone are dated by LA- ICP- MS U- Pb analysis to study the timing of the shear zone and relations with the gold mineralization. A weighted U- Pb age of ~162 Ma is obtained from the rims of hydrothermal zircons from the studied mylonite. Thus, the shear deformation is defined in Late Jurassic, which is correlated with previous research on the deformation time of the Keluo- Xinkailing complex and the sinistral strike- slip time of the Badahan- Nenjiang fault. Taking into consideration previous studies on gold mineralization epoch, we propose that the Sanhetun gold deposit was formed in Early Cretaceous, after the Late Jurassic ductile shear deformation. The core zone of zircons from the granitic mylonite which have inherited zircon features represent a Late Triassic magmatic activity. The result also reveals the ductile deformation time of the Keluo complex is in Late Jurassic, rather than Late Triassic. It provides the basic condition for the formation of the Sanhetun gold deposit. The Lu- Hf isotopic analysis from the granitic mylonite in this study reveals a source of juvenile crust related to depleted mantle.