he Duolong copper (gold) ore concentration district, located in the north of Bangong Co—Nujiang suture zone, is the most outstanding oreprospecting achievement in recent years. It is the first discovered superlarge epithermal porphyry Cu (Au) deposit in Xizang (Tibet). Methods:This articale did the first study to the monzonitic granite porphyries via LAMCICPMS ziron UPb dating and whole rock geochemistry analysis collected from the Dibaonamugang deposit in the Duolong copper (gold) ore concentration district.Results:The monzonitic granite porphyries in the district belong to potassium calcalkaline and weakly peraluminous rocks. They have SiO2 values of 66.31% to 67.31%, Al2O3 values of 15.16% to 15.33% , MgO values of 1.30% to 1.47%, CaO values of 1.53% to1.65%, TFe2O3 values of 3.29% to 3.74%, K2O values of 3.72% to 3.98%, Na2O values of 4.48% to 4.96%. These rocks show K2O/Na2O ratios of 0.80 to 0.89, A/CNK ratios of 1.00 to 1.07, Terman index of 2.82 to 3.43. The monzonitic granite porphyries are systematically enriched in largeion lithophile elements(LILE: Th、U、K、Pb and Rb) and LREE, relatively deplted in high strength elements(HFSE:Ta、Nb、Ti and Zr) and HREE. Total Coneentartion of REE range from 131.81×10-6 ~ 151.59×10-6, with LREE/HREE 10.67~10.97, (La/Yb)N 14.03~15.23 and middle negative Eu anomalies(δEu=0.75~0.78). The geochemical characteristics of these intrusions are consistent with those of arctype magmas worldwide. This indicates the arc granitic magma was generated by partial melting of mantle wedges replaced by the fluid which is formed by the dehydration of the oceanic crust subdution plate in the subdution zone. In addition, its high La/Nb ratios (3.36~3.50) and high La/Ta ratios (40.71~42.79) suggest that the magma might be contaminated by crustal mantle. Zicrons coming from the monzonitic granite porphyry have obvious oscillatory zone, yielding Th/U ratios of 0.56 to 1.10. Its have zircon LAMCICPMS UPb age of 112.6±1.3Ma. Conclusions:Combined with the published data, this ore concentration district contains two obvious main diagenesis stage (117~124Ma, 107~112Ma, respectively), suggesting Bangong Co—Nujiang ocean basin was still subducting during ca. 112.6 Ma and the closure time of the ocean should be later than early Cretaceous (112.6±1.3Ma).