Abstract: In order to determine the metallogenic epoch and ore-forming environment of the Bainaimiao copper deposit, the au-thors carried out research on isotope geochronology and geochemistry of ore-bearing intermediate-acid rocks. LA-MC-ICPMS zir-con U-Pb dating shows that the ages of three ore-bearing granodiorites samples are 421.5±1.8Ma, 438.6±3.4Ma and 459.3±3.6Ma respectively. These rocks have peraluminous calc-lkaline characteristics, and are enriched in LREE. There is a weak positive anomaly of Eu. The trace elements are obviously depleted in Ta and Nb. According to comprehensive ages and geochemical characteristics of ore-bearing granodiorites and the regional tectonic background, the authors consider that the Bainaimiao copper deposit was on the whole formed in the early Paleozoic and characterized by multi-period mineralization. In addition, the metallogenesis was related to the subduction event of ancient Mongolia Ocean in the Early Paleozoic.