Geochemical characteristics, zircon U-Pb age and Hf isotope of the gabbro in the Huanghuatan Cu-Ni deposit, Darhan Muminggan Joint Banner, Inner Mongolia

Located in Darhan Muminggan Joint Banner of Inner Mongolia, the Huanghuatan Cu-Ni deposit is hosted in the contact zone of the gabbro and gneiss which lies in the Bayan Obo rift system on the northern margin of the North China Craton.LA-ICP-MS zircon U-Pb dating of Huanghuatan gabbro yielded a weighted average age of 268.7±1.1 Ma (MSWD=0.44, n=32), which suggests that the Huanghuatan Cu-Ni deposit is a product of Middle Permian magmatic activity.The Huanghuatan gabbro, belonging to calc-alkaline series, is characterized by high Al₂O₃ (17.72%~19.81%), rich alkali (K₂O+Na₂O=4.37%~5.09%), low P₂O₅ (0.28%~0.42%) and low Ti₂O (0.83%~1.21%).The REE content ranges from 144×10^-6 to 167×10^-6, showing strong fractionation between LREE and HREE (La_N/Yb_N=7.43~8.85), with slightly negative Eu anomalies (δEu=0.84~0.88).The gabbro is distinctively enriched in LILE (Rb, Ba, K, Sr)but depleted in HFSE (Nb, Ta, Ti).The zircons have concentrated negative ε_Hf(t) values (-17.69~-12.53) and two-stage Hf isotopic crust model ages (t_Hf2=2082~2411 Ma).The geochemical characteristics reveal that the parental magma of Huanghuatan gabbro was derived probably from the mantle, which was subjected to abundant crustal contamination.The crustal materials were probably formed by the partial melting of Sertengshan Group.Combined with the regional tectonic setting, the authors propose that the Huanghuatan gabbro was mantle origin and formed in an extensional regime of the Late Paleozoic.