The Qingchengzi orefield which lies in geotectogene of Liaodong rift is an important polymetallic mineral district in northern China for its clustering several large Pb-Zn, Ag and Au deposits.  LA-ICPMS zircon U-Pb age of (224.2±1.2) Ma was obtained for the Shuangdinggou intrusion. Based on petrological and geochemical data it is inferred that the biotite monzogranitic magma might be derived from the partial melting of a thickened lower crust with prominent garnet and rutile retained in the residual assemblages, and magma mixing is probably involved based on the unusually high Nb/Ta ratio (18.4～21.2). It is suggested that slab break-off during the process of Yangtze Craton and North China Craton continental deep subduction in Late Triassic may be responsible for the ore-related magmatism.