Located in the middle part of the Tethys-Himalaya, the Zhaxikang Pb-Zn polymetallic deposit is the biggest ore deposit in this belt. The Zhaxikang ore veins are controlled by several normal faults nearly striking NS, developed at the post-collision stage of the Tibet Plateau. Two stages of mineralization has been identified, and the first phase, Pb-Zn mineralization, has been overprinted by Sb-bearing that happened later. Among the mineral assemblage of the calcite- pyrite stage during Sb-bearing mineralization, sericite has been found coexist with quartz, calcite, pyrite and minor sphalerite. Dating of the sericite using Ar-Ar isotopes shows that plateau age of this mineral is 12.28±0.45 Ma, and its isochron age is 11.7±3.1 Ma. Two dated ages have the same deviation range, indicating the geological validity of the dating, and therefore the age of Sb-bearing mineralization. Tethys Himalaya has developed an Au(Ag) mineralization event in main collisional orogenic setting, while the Ar-Ar age of Zhaxikang indicates that mineralization in late collisional stage would continue to 12Ma.The mineralization developed in the NS fault belt suggests that the fault system should predate this age,earlier than 12Ma. The first stage of Pb-Zn mineralization has experienced compression supported by broken rocks distributed among the belt, while the late phase of Sb-bearing mineralization develops along the veins, manifesting that the NS-striking fault system has undergone extension since 12Ma.