Mengya’a is a typical skarn-porphyry Pb-Zn deposit, located in the eastern part of the northern Gangdese Pb-Zn-Ag-Fe-Mo-W polymetallic belt (NGPB). Constraining the mineralization age of Mengya’a deposit is crucial to understand the genesis and geodynamic processes of this deposit and is important to estimate the metallogenic potential of the NGPB. Previous studies on the mineralization age of this deposit are mainly focused on the granite porphyry or lead isotopic composition of the sulfides, which are still disputed. According to the type of the mineralization, the orebodies of Mengya’a deposit can be divided into skarn and porphyry styles, and the main economic orebodies are skarn style. Based on the geological characteristics of this deposit, we present the Ar-Ar dating results of muscovite collected from the skarn orebody, which is symbiosis with sphalerite. Muscovite from the Mengya’a skarn orebody yielded a well-defined 40Ar/39Ar plateau age of 54.60 ± 0.40 Ma and an isochron age of 54.45 ± 0.67 Ma. These ages suggest that Mengya’a skarn orebody were developed in the period of the main India-Eurasia collision. Combined with the former research, we suggest that there existed two phases mineralization of Mengya’a deposit: the early skarn type and the late porphyry type, and the geodynamic processes which controlled the formation of the skarn mineralization was the rollback of the Neo-Tethys slab.