Analysis on the Prospecting Potentiality and Cu-Ni Metallogenic Conditions of the Paleozoic Mafic-ultramafic in the Northwestern Margin of Qaidam Basin

The Paleozoic mafic-ultramafic rocks, located in the northwestern margin of the Qaidam Basin, were emplaced in the Paleoproterozoic Jinshuikou Group, which spread in the north-eastern direction with zonal distribution. From west to east, these rocks can be divided into Niubiziliang intrusion, Datonggounanshan intrusion, Qingxinjieshan intrusion, and Qaidam Gate intrusion. These mafic-ultramafic rock bodies are mainly occurred as vein and lenticular, with many rock types, such as, olivine pyroxenolite, websterite and gabbro. From the core to its edge,this complex is composed of peridotite, pyroxenite and gabbro. The mineralization of nickel and copper is closely related to peridotite and pyroxenite. Zircon U-Pb geochronology and geological background research show that Datonggounanshan intrusion and Qaidam Gate inrusionare probably related to the subduction of oceanic crust in the Early Paleozoic (458.3 Ma and 453 Ma), while the Niubiziliang intrusion was formed the Late Paleozoic period (402 Ma) under the setting of from the late stage of the collisional orogenic to the post-orogenic extension.The comprehensive studies of the field observations, petrology and geochemistry show that the crystallization differentiation and crustal contamination were occurred in the magma chamber, implying that these intrusions have good potential of forming the copper and nickel ore. The MgO contents of the intrusions vary from 8.39% to 31.15%, their M/F ratios range from 2.0 to 4.6, with an average of 3.8, indicating that these intrusions belong to the ferruginous ultrabasic rocks. The average value of K₂O/Na₂O is 2.4. The above data shows that the ultramafic rocks have good condition for the mineralization of nickel and copper.