The Dexing porphyry copper deposit in Jiangxi Province is the largest porphyry copper deposit in southeastern China. This paper carried out the SHRIMP U-Pb geochronologic analyses for zircons from the diorite porphyrite veins in the Tongchang mine deposit, yielding a good concordant ²⁰⁶Pb/²³⁸U weighted mean age of (153.5±2.4) Ma (2σ, MSWD=2.5). The result shows that the magmatism occurred in the Late Jurassic, land formed likely in a back-arc or intra-arc extension environment triggered by the subduction of palaeo-Pacific plate. Hf and Nd isotopic analysis produced high εNd(t) (～0.5) and εHf(t) values (～4.73), indicating that these intrusions have a crust-mantle mixing source.