Geological,Geochemical Characteristics And Geochronology Of The Gabbro Rocks In The Haoyaoerhudong Gold Deposit,Inner Mongolia,China

The Haoyaoerhudong gold deposit is located in the west section of the Mesoproterozoic Bayan Obo rift, northren margin of the North China Craton(NCC). The Hercynian magmatic rocks and veins are wide spread in the gold ore district and have close relationship to gold mineralization. This study focuses on the gabbro intrusion, which is less studied by previeous reserarchers. Based on the geological and geochemical characteristics and the geochronology of the gabbro, the geological significance, regional tectonic evolution, gold mineralization mechanism and prospecting potential are discussed in detail.The whole-rock geochemical data indicate that the gabbro in the deposit is of calc-alkaline K-rich series. High-field strength elements Nb, Zr and Th and heavy rare earth elements are depleted, and large ion lithophile elements Ba and Sr are enriched. The magma underwent a high degree crystallization-differentiation during evolution, and the primary magma may had undergone the crustal contamination.The Sr-Nd-Pb isotopic values are distributed in the mixing area of lower crust and mantle, indicating that the gabbro has a mixed origin of crust and mantle. This suggests the melting of lower crust caused by the underplating of mantel during the magma rising.The gabbro sample yields a zircon SHRIMP U-Pb age of 279±2 Ma. Garnet Sm-Nd isochron age is 285.6±2.4 Ma. These ages are close to the ages of the other magmatic rocks reported by previous researches. The age of the Haoyaoerhudong gold mineralization is basically in line with the ages of the magmatic rocks, indicating a middle and late Hercynian age for the gold mineralization.The mantel underplating during the magma rising resulted in the melting of lower crust, which produced the parental magma of the Haoyaoerhudong gabbro. The gabbro emplacement(279Ma) indicated the end of the collision between the North China Craton and Siberia plate, and the tectonic setting was transformed into intraplate extension. The periphery of gabbro rock is considered as a key area for further prospecting.