The Mafic-ultramafic Intrusions In The Huangshan Region Eastern Tianshan, Xinjiang: Petrogenesis And Mineralization Implication

A series of mafic-ultramafic intrusions occur in the Kangguer-Huangshan shear zone in northXinjiang,including Tudun,Xiangshan,Huangshan,Huangshandong and Tulargen economic mineralizedintrsions,Erhongwa and Huangshannan intrsions with variable degrees of copper-nickel sulphidemineralization.In recent years,with the increasing exploration depth and density,reserves has substantialincreased,Kangguer- Huangshan zone has now become the second world-class magmatic copper-nickelsulfide deposit metallogenic zone in China.Erhongwa,Xiangshan,Huangshannan,Huangshan,Huangshandong,Hulu intrusions were selected for detailed study,focusing on the key petrology issues ofmagmatic sulfide deposits:â‘ the nature of magma source and the composition of primary magma;â‘¡whether the intrusion has underwent crustal contamination or not,the type of hybrids and the degree ofcrustal contamination,the relationship between crustal contamination and sulphide segregation;â‘¢fractional crystallization,magma evolution.Systematically comparison between economic mineralizedintrusions and uneconomic mineralized intrusions,oxides deposits and sulfide deposits respectively werecarried out based on petrology,mineralogy,element geochemistry,Nd,Sr,and Pb isotope geochemistry.The following are the main results:(1) The economic mineralized intrusions have clear facies and highly altered,while the uneconomicmineralized intrusions are fresh.there are a few peridotite.(2)Geochemistry characteristics of rare earth element has obvious difference between the economicmineralized intrusions and the uneconomic mineralized intrusions.The economic mineralized intrusionshave significantly higher content of the total rare earth elements than that of the uneconomic mineralizedintrsions,and the degree of the LREEs fractionation of the formers,as well as the HREEs,are also strongerthan that of the latters.(3) The economic mineralized intrusions underwent crustal contamination to some extent.For example,Huangshandong and Hulu intrusion were subjected to comtaminated about 5%,5%～10% byupper-intermediate continental crust.Huangshan intrusion and Xiangshan intrusion contamination hascome from the intermediate-lower crust.In contrast,the uneconomic mineralized intrusions,such asHuangshannan intrusion,only experienced partially contamination,Erhongwa intrusion didnot have theimpact of crustal contamination.(4) The Fo molecules of olivine and Mg^# are used to restrict the MgO content of the primary magma. Rearch proves that the MgO content of the economic mineralized intrusions are higher than that of theuneconomic mineralized intrusions,although the minimum MgO content of Xiangshan intrusion is 5.0%.Among the economic mineralized intrusions,the MgO content of primary magma of Huangshandonginstrusion is 11.6%;the minimum MgO content of primary magma of Huangshan instrusion and Huluintrusion is respectively 9.2%,7.1%,While among the uneconomic mineralized intrusions,the MgOcontent of primary magma of Erhongwa intrusion is 7.1%,and the minimum MgO content of primarymagma of Huangshannan instrusion is 5.7%.(5) Magmatic crystallization and crustral contamination comeing from Si-rich component lead to sulfidesaturation in economic mineralized intrusions.(6) Xiangshanzhong intrusion of Cu-Ni deposit and Xiangshanxi intrusion of V-Ti-Fe deposit have differentwith rock series.Xiangshanzhong intrusion have no primary magnetite,with rich in MgO,low in FeO_T,TiO₂ and positive/negative Eu anomalies.The m/f ratio of rock is 3.97-5.53 and belong to ferruginousultrabasic rocks.However Xiangshanxi intrusion have some primary magnetite,are rich in FeO_T,TiO₂ andhave obvious positive Eu anomalies.The m/f ratio of Fe-Ti gabbro is 0.68-0.90 and belong toferruginous basic rocks.Participating in fluid and magmatic evolution itself are the key to from theCuNi-VTi composite deposits.(7) Nb,Sr,Pb isotope and trace element geochemistry characters indicate that magma source of theseintrusions were similar and composed of wedge matasomasised by subducting slab and aesethenospherecomponents.The mafic-ultramafic intrusions of Huangshan terrane are the result of the lithosphericdelamination at the root and the upwelling of asthenosphere components.