LAUSR

Abstract The Dongbulage porphyry Mo-dominant and Taibudai Cu-(Mo) deposits are located in the central–southern Great Xing’an Range, Inner Mongolia, northeastern China, and are associated with granite porphyry and monzogranite intrusions, respectively. Re–Os isotope data for five molybdenite samples from the Dongbulage Mo deposit give a weighted mean model age of 164.3 ± 1.2 Ma, which is in accordance with a zircon U–Pb age of 164.5 ± 1.7 Ma for the host granite porphyry, indicating that the deposit formed at the end of the Middle Jurassic. The zircon U–Pb age of the Taibudai ore-bearing monzogranite is 137.9 ± 1.7 Ma, indicating that the deposit formed in the Early Cretaceous. Whole-rock geochemical data indicate that the Dongbulage granite porphyry and the Taibudai monzogranite are high-K calc-alkaline, and have REE patterned light rare earth elements (LREEs) enriched and heavy rare earth elements (HREEs) depleted. Both plutons show Ba, Nb, and Ti depletions on normalized trace element diagrams, and the Dongbulage granite porphyry shows strongly negative Eu anomalies which are absent in the Taibudai intrusion. The geochemical differences between the two intrusions suggest that the Dongbulage granite porphyry is the result of more advanced fractional crystallization, which led to the formation of a Mo-dominant deposit, whereas the lesser degree of crystal fractionation in the Taibudai monzogranitic magma resulted in the formation of a Cu deposit. The relatively listric-shaped REE patterns of Taibudai rocks suggest more hydrous parental magmas than that of Dongbulage rocks. Therefore, fractional crystallization and magma water content exert a significant control on the styles of mineralization (Mo- versus Cu-dominant) in the central–southern Great Xing’an Range.