Study On The Diagenesis And Metallogenic Characteristics Of Yejili Mafic-ultramafic Intrusions In Beidashan Mountains Of Gansu

The Yejili mafic-ultramafic intrusion is located in the southwestern margin of Alxamassif，the place is at the top of Alxa arc tectonic belt and structural convergence position,favoring for mineralization. It is similar structural place between Yejili intrusion in Beidashanand Jinchuan mafic-ultramafic intrusion in Longshoushan.The Yejili ultramafic intrusion ismainly composed of plagioclase pyroxene peridotite, olivine pyroxenite, olivine gabbro,gabbro, diorite, the types of metal sulfides are chalcopyrite, pentlandite, pyrrhotite, and pyrite.The Yejili mafic intrusion is mainly consisting of is gabbro; the metal minerals are magnetite,ilmenite, minor chalcopyrite and pyrite. The Yejili mafic-ultramafic intrusion is similar toXiangshan intrusion in the East Tianshan, hosting the potential of forming Cu-Ni, Ti-Femineralization. Presently, few researches have been done on the Yejili mafic-ultramaficintrusion. In this thesis, I have done a lot of research on the mineralogy, petrology,lithogeochemistry, petrogenic age et al, discussing on the mineral genesis, petrogenesis andmagma source and the mineralization potential. Conclusions are as followed:1、The zircon SHRIMP U-Pb dating for gabbros of Yejili mafic-ultramafi rock intrusion is286.6±2.5Ma, which proves that the intrusion is formed at late Carboniferous-early Permian,maybe relating to post-orogenic extensionl events in the Central Asian Orogenic Belt.2、Copper-nickel mineralization occurs in Yejili ultramafic intrusion (North part), the majorelements, trace elements and Nd-Sr-Pb isotope indicate the parental magma is high-Mg tholeiiticmagma, coming from depleted mantle (similar to lithophere), the magma has experienced by about5~10%contamination of middle-upper crust during ascending to the crust.3、Titanium-iron oxide mineralization occurs in Yejili ultramafic intrusion (south part), themajor elements, trace elements and Nd-Sr-Pb isotope indicate the parental magma is Titanium-ironrich, coming from depleted mantle (similar to asthenosphere), the magma has experienced by lessthan5%contamination of middle-upper crust during ascending to the crust.4、The Yejili mafic-ultramafi intrusion is located at the structural convergence position, themetallogenic material is hyperactive in this area, favoring for mineralization; The Yejili ultramaficintrusion (North part) is favor of forming copper-nickel mineralization through its geology andgeochemical features; The Yejili mafic intrusion (north part) has been prospected as a small scaleTitanium-iron oxide deposit.