Study On Diagenesis And Mineralization Process Of Ebutu And Kebu Mafic-Ultramafic Intrusions In Central Inner Mongolia

The central Inner Mongolia is located between the North China and the Siberian cratons.Numerous mafic-ultramafic intrusions are widely distributed in the central Inner Mongolia,and many small-to medium-sized copper-nickel sulfide deposits or ore occurrences have been discovered.These mafic-ultramafic intrusions have similar first-level structural units and different second-level structural units,with the tectonic environment and the diagenesis and mineralization processes for further study.In this study,ore-bearing mafic-ultramafic intrusions of the Urad Rear Banner Ebutu and Urad Middle Banner Kebu in the central Inner Mongolia are selected to explore the magmatic evolution,diagenesis and mineralization processes,and tectonic setting by analysis of petrography,mineralogy,geochronology,and geochemistry.The main understandings are as follows:1.The Ebutu pluton is mainly composed of pyroxene peridotite,olivine pyroxenite,Plagioclase-bearing olivine pyroxenite and gabbro,whereas the Kebu pluton is mainly composed of containing feldspar,olivine gabbro and gabbro.Zircon LA-ICP-MS U-Pb dating of olivine pyroxenite(of the Ebutu pluton)and olivine gabbro(of the Kebu pluton)yielded an Early Carboniferous and Middle Permian age of 326.0 ± 2.2 Ma and 267 ± 1.8Ma for their crystallization ages.2.Whole-rock and isotope geochemical results suggest that the Ebutu mafic-ultramafic intrusion was sourced from EMII-type mantle and intensively affected by crustal contamination during magma emplacement,with its parental magma of having relationship with the primitive magma of boninite.The Kebu pluton was derived from EMI-type mantle and mainly affected by middle to lower crustal contamination during magma emplacement,with its parental magma of high-Mg tholeiitic basaltic magma.Both intrusions have experienced different degrees of crystallization differentiation and crustal contamination,which led to the sulfides saturation and dissociation,contributing to forming magmatic dissociated-type copper-nickel sulfide deposit.3.Combining regional tectonic evolution and rock geochemical characteristics,the Ebutu pluton and the Kebu plutonrespectively,with corresponding tectonic setting of subduction-related island arc and post-collisional extension settings(followed by collision of the North China and Siberian cratons).