| The western slope of the Great Xing'an Range is an epithermal copper-lead-zinc-silver metallogenic belt related to continental volcanic-subvolcanic hydrothermal interaction in China,also known as Derbugan copper-lead-zinc-silver polymetallic metallogenic belt.It's composed of southern Jiawula lead-zinc polymetallic ore cluster and northern Ergu'na lead-zinc-silver polymetallic ore cluster.At present,many large scale polymetallic deposits have been found and proved in the metallogenic belt of China,the main deposits types are porphyry copper-molybdenum deposits(such as Wunugetushan,Badaguan copper-molybdenum deposit),epithermal copper-lead-zinc-silver deposits(such as Jiawula,Chaganbulagen,Sanhe,Dongjun,Erdaohezi,Biliyagu and so on),epithermal manganese-silver deposits(such as Erentaolegai)and so on.Meanwhile,there is often associated with fine vein disseminated copper mineralization or ore deposits in the ore cluster or mining area(ore field).Jiawula copper-lead-zinc deposit is located in the Xin Barag Right Banner,Inner Mongolia Autonomous Region,is one of the large-scale copper-lead-zinc deposits of Derbugan copper(molybdenum)-silver-lead-zinc metallogenic belt in the western slope of the Great Xing'an Range,which is considered as an epithermal deposit related to volcanic-subvolcanic hydrothermal interaction for a long time.However,the recent field researches have found the fine vein disseminated copper mineralization was developed in the deep,to the shallow,copper-zinc,silver-lead-zinc and lead-zinc mineralization were developed in turn,thus forming a porphyry copper-epithermal lead-zinc metallogenicsystem.The stratas outcropped in the mining area are mainly upper Permian Laolongtou formation coarse clastic sedimentary rock series and intermediate-acid volcanic rocks series,Mesozoic Jurassic Shangkuli formation intermediate-acid volcanic rocks series and Quaternary loose deposits;The intrusive rocks in the mining area are Yanshanian granite,granodiorite and intermediate-acid hypabyssal rocks(such as plagiophyre,quartz porphyry,quartz monzonite porphyry and diorite porphyrite);The structures are mainly NW,NWW and near SN trending faults and folds,Among them,the NWW trengding shear crushed zone controlls the output of ore bodies.Lead-zinc ore bodies are developed in the shallow part of the deposit,whose output form is mostly vein-type and the second is lentoid shape,growth with silicification,sericitization,chloritization and carbonatation and so on,mainly developed in NWW trending ore-bearing crushed zone.In the deep,there is mainly developed fine vein disseminated copper mineralization(ore bodies)in the inteior of alkali-rich granite porphyry,which output as fine vein disseminated type,and the alteration types are mainly dilicification,potash feldspathization,sericitization,followed by illitization,carbonatation and kaolinization and so on.The mineralization process can be preliminarily divided into three stages:(?)quartz-pyrite stage,(?)quartz-polymetallic sulfide stage and(?)quartz-carbonate stage.The ore-bearing quartz in Jiawula deposit is mainly developed liquid-rich inclusions,while the pure liquid inclusions are not developed.The?stage fluid inclusions homogeneous temperature are mainly concentrated in 252.3 ? ~ 337.7 ?,the average temperature is 276.0?,the salinity wt%(NaCleqv)ranged from 2.40 to 11.11%,mainly concentrated in 4.63% ~ 6.44%,the fluid density is mainly 0.62 to 0.77g/cm3,the ore-forming pressure is between 18.80 to 33.38 MPa and the mineralization depth is ranged from 0.63 to 1.11km;The ? stage fluid inclusions homogeneous temperature are mainly concentrated in 191.6?~248.0?,the average temperature is 216.1?,the salinity wt%(NaCleqv)ranged from 3.53% to 13.88%,mainly concentrated in 5.70%~7.30%,the fluid density is mainly 0.80 to 0.88g/cm3,the ore-forming pressure is between 16.15 to27.68 MPa and the mineralization depth is ranged from 0.54 to 0.92km;The ? stage fluidinclusions homogeneous temperature are mainly concentrated in 113.7?~189.5?,the average temperature is 162.1 ?,the salinity wt%(NaCleqv)ranged from 2.23% to10.11%,mainly concentrated in 5.70% ~ 7.99%,the fluid density is mainly 0.88 to0.92g/cm3,the ore-forming pressure is between 11.16 to 19.02 MPa and the mineralization depth is ranged from 0.37 to 0.63 km.Laser Raman spectroscopic analysis indicates that the gas phase and liquid phase composition of fluid inclusions are H2 O.In general,the ore-forming fluid belongs to the H2O-NaCl system,and belongs to medium-low temperature,low salinity and medium density fluid,which formed in the middle-low pressure environment,the mineralization depth is medium to shallow.Combined with the sulfide quartz vein hydrogen-oxygen isotope and the S and Pb isotope characteristics of ore minerals,considering that early stage metallogenic fluid mainly comes from deep source magma,while the late stage ore-forming fluid is characterized by the ancient rain water,the ore-forming materials come from the lower crust or upper mantle magma,holding the property of MORB,the original mantle and young upper continental crust mixed source region.The main host rocks of the deposit are granite porphyry,and the characteristics of geochemistry of elements show that the w(SiO2)content of granite porphyry is ranged from 71.59% to 72.36%,w(TiO2)is from 0.46% to 0.58%,w(Al2O3)is from 15.45% to15.92%,w(Fe2O3)is from 0.74% to 0.90%,w(FeO)is from 1.67% to 1.96%,w(MgO)is from 0.55% to 0.89%,w(Na2O+K2O)is from 9.01% to 9.91%,w(K2O/Na2O)is from 1.37 to 2.15,rittmann index(?)is from 2.77 to 3.43,alkalinity index(AR)is from 3.13 to 3.96,indicating that the rocks are shoshonite series,high potassium,peraluminous A type alkali-rich granite porphyry;The total amount of rare earth elements(?REE)is between350.11×10-6 and 408.80×10-6,the ratio of light and heavy rare earth(?LREE/?HREE)is between 11.25 and 11.44,? Eu mainly is concentrated in 0.38 to 0.44,possessing the characteristics of stronger fractionation of light and heavy rare earth and obvious negative Eu anomaly and strong depletion of compatible elements(Ni,Co,Cr,V,Yb,Eu,etc.),enrichment in incompatible elements(Cs,Rb,Pb,U,Th,Zr,Hf,etc.),relative depletion ofLi,Sr and other incompatible elements,and holding higher Rb/Sr(0.93 to 1.31)and Zr/Hf(29.38 to 35.61),which reveals that the original magma is produced by the fluid dominated with CO2 or H2 O metasomatizing lower crustal layer occurring partial remelting,the magmatic process suffered from strongly hybridization with carbonate,and possesses the attribute of providing copper-lead-zinc for ore-forming fluid.According to the characteristics of higher zircon 176Hf/177Hf(0.282800~0.282877)and positive ?Hf(t)values(4.1~6.9)of this kind of rocks,and the single model age(TDM1)and the two stage model age(TDM2)of Hf isotope range are 531 ~ 642 Ma and 680 ~ 836 Ma,considering that the source materials of granite porphyry in this period mainly is formed by the partial melting of the new born crustal material from the depleted mantle in the Neoproterozoic era.In view of the received granite porphyry possessing the characteristics of the magmatic and hydrothermal zircon symbiotic and associate,and the weighted average of magmatic zircon206Pb/238 U age is(146.4±1.6)Ma(MSWD=1.30,n=12)and the weighted average of hydrothermal zircon 206Pb/238 U age is(143.1± 3.9)Ma(MSWD=0.56,n=5),combined with previous research results,we come to conclusion that the mineralization of Jiawula deposit occurred at the initial stage of Early Cretaceous,the magmatism closely related to the mineralization occurred at the end of later Jurassic.Based on this article and previous research results,the metallogenic model of Jiawula deposit can be concluded that: the Early Cretaceous is just at the time when Mongolia—Okhotsk ocean had closed and the orogenic belt stretched stage,thus leading to lithospheric thinning,asthenosphere upwelling and crust-mantle mixing interaction,also triggering massive and intensive volcanic activity in the region.At the same time,a large number of intermediate-acid volcanic rocks and subvolcanic rocks were formed.The magmatic hydrothermal rich in copper-lead-zinc was migrated upon to a certain temperature and pressure condition along the favorable tectonic site,and the ore-bearing fluid was boiling.Druing the fluid continuing intrusion upon,accompanied by a decline in temperature and pressure,meanwhile the atmospheric precipitation constantly mixing,theore-bearing fluid started to unload copper elemengts,and the fine vein disseminated copper mineralization(ore bodies)was developed in the deep at first.The residual magma fluid kept on intrusive,then suffered strongly contamination of circulation atmospheric precipitation in the shallow crust.Thereby,the H2O-NaCl fluid system of medium-low temperature,low salinity and medium density which was dominated by atmospheric precipitation was formed,then lead and zinc elements were removed under favorable physical and chemical conditions.In the end,the medium-low temperature epithermal lead-zinc deposit was formed.From whole it constituted the Jiawula porphyry copper-epithermal lead-zinc metallogenic system. |
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