The Xiaokelehe Mo-Cu Deposit is a porphyry deposit newly discovered in the north of Greater Khingan Mountains in recent years and is located at the junction of Erguna massif and Khingan massif.In order to determine the chronology,petrogenesis,magma source and tectonic settings of the monzonite in the area,zircon U-Pb dating and whole rock analysis of the monzonite is conducted.The zircon U-Pb dating results show that the monzonite yields a Paleocene age,that is 57.8 Ma±0.3 Ma(MSWD=2.0).The whole rock analysis results show that the monzonite is characterized by low Mg（w（MgO）is 1.89 %-2.06 %） and high alkali(w（K₂O＋Na₂O）is 8.02 %-8.68 %）concentrations,indicating it is aluminous and shoshonite rock;the samples are rich in LILEs (Rb,Ba,K),depleted in HFSEs (Nb,Ta,Ti),consistent with the magmatic characteristics of subduction zone;they have low Mg#(35.07-36.46),Co(w（Co）is 9.80×10-6-11.66×10-6） and Ni(w（Ni） is 1.22×10-6-3.25×10-6）,and relatively high ratios of w（La）/w（Nb）value(1.87-2.97）,w（Th）/w（La）value(0.21-0.28）and w（Th）/w（Nb）value(0.43-0.66）,similar to the characteristics of crustal magmatic rocks,which is supposed to be the product of partially melting of the basic metamorphic rocks in the lower crust.Based on the previous research results of regional tectonic setting,it is considered that the monzonite formed in the regional extensional tectonic setting caused by the withdrawal of the Pacific subduction plate.