Abstract: The Shizhushan deposit (70 millions tons of wollastonite) in Jiangxi is situated in the eastern section of the Qin-Hang metallogenic belt and is recognized as the largest wollastonite deposit in the world. Within this deposit, W-Sn-Cu-Mo polymetallic mineralization is present in the skarns located in the contact zone between the Mengshan granite and the surrounding carbonate rocks. However, research on the formation age and genesis of this mineralization is relatively limited. This paper conducts in situ U-Pb dating and trace element analyses of garnets from different generations to determine the age of formation of the polymetallic mineralized skarns. The findings aim to enhance the understanding of the deposit's genesis and provide further guidance for mineral exploration. Three types of garnets have developed in the skarn: the first type consists of reddish-brown garnet (Grt-1), the second type comprises dark-brown garnet (Grt-2), and the third type features yellowish-green garnet (Grt-3). All three types of garnet belong to the andradite to grossularite solid-solution series; however, Grt-1 and Grt-2 are relatively rich in iron, while Grt-3 is relatively rich in aluminum. The U-Pb ages of Grt-2 and Grt-3 are 234.7 ± 1.6 Ma and 234.4 ± 9.9 Ma, respectively, which align with the ages of the biotite monzogranite from the Mengshan complex, widely exposed in the mining area. This study indicates that both wollastonite mineralization and polymetallic mineralization in the Shizhushan deposit occurred during the Late Triassic and are closely associated with the intrusion of the Mengshan granite. In addition to wollastonite, the Shizhushan deposit also holds significant potential for W-Sn-Cu-Mo polymetallic mineralization.