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Mineralization And Geodynamic Setting Of Skarn Gold,Copper,Lead And Zinc Deposits In Ji’an Area,Jilin Province

Posted on:2024-08-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y P LiuFull Text:PDF
GTID:1520307121472074Subject:Mineralogy, petrology, ore deposits
Abstract/Summary:PDF Full Text Request
Liao-Ji Rift(LJR)is one of the regions with relatively developed mineral resources in China.There are more than 100 kinds of mineral resources widely developed,including nonferrous(copper,lead,zinc,molybdenum,cobalt,nickel,antimony,etc.),precious metals(gold,silver),light metals(magnesium,aluminum)and non-metallic deposits(boron,phosphorus,potassium,etc.).It has attracted the attention and research of economic geologists at home and abroad.In order to reveal the metallogenic process and geodynamic background of the regional hydrothermal gold-copper-lead-zinc deposits,this paper selects the Ji’an area in the northeast of LJR,where the hydrothermal gold and copper-lead-zinc polymetallic deposits are developed,and takes the representative Xiahuolong gold deposit,Daqinggou copper deposit and Ji’an lead-zinc deposit as the research objects.The work on deposit geology,fluid inclusions,element-isotopes,diagenetic and metallogenic ages of the three deposits has been systematically carried out.In combination with the research results at home and abroad,the genetic types,mineralization processes and mechanisms of the deposits have been thoroughly demonstrated,alongside the metallogenic background,geodynamic models of hydrothermal systems.The main progress and achievements are summarized as follows:1.Geological study of the deposit revealed that the selected typical deposits were all attached to the contact zone between the ore-forming related granites and carbonate rocks.Among them,the Daqinggou deposit is dominated by magnetite,chalcopyrite and pyrite mineralization,the Xiahuolong deposit is dominated by pyrite and electrum mineralization,the Ji’an deposit is dominated by galena and sphalerite mineralization,followed by chalcopyrite mineralization.Different types and intensities of skarn,lapinization,silicification,sericitization and carbonation were developed.Five metallogenic stages have been distinguished:(I)dry skarn stage,(II)wet skarn stage,(Ⅲ)oxide stage,(IV)quartz-polymetallic sulfide stage,(V)quartz-carbonate sub-stages.Field geological survey and microscopic identification show that relatively complete mineralization and alteration stages can be seen on the surface of Daqinggou deposit,characterized by the development of magnetite and polymetallic sulphide,while Xiahuolong deposit is characterized by sericitization,silicification,and carbonate mineralization,Ji’an deposit is characterized by the development of qingpanitization(epidotization),sericitization,silicification,carbonation and polymetallic sulphide mineralization.2.The study of petrography,micro-thermometry and laser Raman data of mineral fluid inclusions(FIs)shows that the main types of FIs captured in the ore-forming process of the three typical deposits include gas-rich,liquid-rich and liquid-phase FIs.Among them,Daqinggou deposit also has three-phase FIs in the early metallogenic stage.The ore-forming physicochemical characteristics show that:(1)the ore-forming fluids of Daqinggou Cu deposit belong to a H2O-NaCl±CO2 system with medium-high temperature(360~466°C)and medium-high salinity(8.94~57.09wt.%NaCl eqv)in the early stage of mineralization,and the medium-low temperature(218~336°C)and medium-low salinity(2.73~9.6wt.%NaCl eqv)in the middle stage of mineralization,while the fluid properties of the late stage of mineralization is a H2O-NaCl system with low temperature(145~213°C)and low salinity(1.22~4.48wt.%NaCl eqv);(2)The fluid properties of the Xiahuolong gold deposit generally changed from medium-high temperature(273~367°C)and medium-low salinity(4.01~8.67 wt.%NaCl eqv)to low temperature(120~196°C)and low salinity(0.87~3.85 wt.%NaCl eqv).The ore-forming fluid in the main mineralization stage belongs to the H2O-NaCl-CO2system containing CH4;(3)The fluid properties of the main mineralization stage of the Ji’an lead-zinc deposit belong to a H2O-NaCl±CO2 system with low temperature(160~270°C)and low salinity(4~9 wt.%NaCl eqv).3.The data of H-O-S-Pb isotopes reveal that the sources of ore-forming fluid in the three typical deposits all originated from magmatic water and mixed with atmospheric water.Among them,the main metallogenic stage of Daqinggou copper deposit is gray quartz(stage I3):δD=-104.1‰,δ18OH2O=9.7‰,white quartz of stage II2:δDH2O=-95.5‰,δ18OH2O=4.1‰;The characteristics of quartz fluid inclusions in the ore-forming stage Ⅲ of the Xiahuolong gold deposit:stage IV,DH2O=-106.6‰、δ18OH2O=-1.3‰,stage V,δDH2O=-114.3‰,δ18OH2O=-8.4‰;quartz of stage II in the Ji’an lead-zinc deposit:δDH2O=-120.8‰~-114.9‰,δ18OH2O=-2.0‰~-1.9‰;anhydrite of stage Ⅲ:δDH2O=-102.3‰~-100.7‰,δ18OH2O=-12.4‰~12.2‰.In theδ18OH2O-δDH2O diagram,the main metallogenic stage of the Daqinggou copper deposit is injected with mantle water and magmatic water respectively.The latter two components are between magmatic water and atmospheric water,and are closer to the later in the quartz-carbonate stage.The Pb isotope datas are all located between the evolution lines of upper crust and orogenic belt,indicating the attributes of crust source and crust-mantle mixed source of minerals;the in-situ S isotope data further indicates that the ore-forming materials of the deposit originated from magma in the early stages of mineralization,and contributed to varying degrees with the evolution of the ore-forming strata.the Daqinggou copper deposit:206Pb/204Pb=18.053~18.101,207Pb/204Pb=15.584~15.669,208Pb/204Pb=39.151~39.343,δ34S=5.78~18.62‰;Xiahualong gold deposit:206Pb/204Pb=16.858~17.700,207Pb/204Pb=15.63~16.150,208Pb/204Pb=30.32~37.850,δ34S=5.7‰~8.5‰;Ji’an lead-zinc deposit:206Pb/204Pb=17.527~17.591,207Pb/204Pb=15.497~15.516,208Pb/204Pb=39.166~38.237,δ34S=-2.5‰~16.13‰.4.Accurate geochronology shows that the regional diagenesis and mineralization can be divided into paleoproterozoic and Mesozoic periods.To be specific,the U-Pb age of zircon in the alkali feldspar granite related to the mineralization of Daqinggou deposit is 1900±23Ma,and the U-Pb age of hydrothermal apatite in the ore is 1902±11Ma;The zircon U-Pb age of diorite porphyrite related to the mineralization of Xiahuolong gold deposit is 124.1±1.9 Ma,and the hydrothermal apatite U-Pb age is119±22 Ma;The zircon U-Pb age of quartz porphyry related to the mineralization of the Ji’an lead-zinc deposit is 120.5±1.6 Ma,age of granite porphyry is 115.3±1.7 Ma,and the hydrothermal apatite U-Pb age is 119±3.4 Ma.5.Elemental and isotopic geochemistry of magma closely related to mineralization reveal that:(1)The alkali feldspar granite related to the mineralization of Daqinggou belongs to the I-type granite with high potassium and high differentiation,and the total REEs of rocks are medium,with the characteristics of weak negative europium anomaly and strong fractionation of light and heavy rare earth elements.It originated from the tectonic environment of active continental margin,and was formed by the partial melting of neoarchean crustal material caused by the paleoproterozoic arc-continental collision(Longgang block and Nanlin block);(2)The diorite porphyry related to the mineralization of Xiahuolong belongs to the high-potassium calc-alkaline rock series,which is relatively high in REEs of rocks,rich in light rare earth elements,and the light and heavy rare earth fractionation is relatively significant.It originates from the extensional environment formed by the subduction of the Ancient Pacific plate to the East Asian continental margin,and is the product of partial melting of metasomatic mantle wedge from subduction fluid of oceanic plate;(3)The quartz porphyry related to the lead-zinc mineralization in Ji’an belongs to the I-type granite with high-potassium and calc-alkaline,which originated from the product of the subduction of Ancient Pacific plate into the East Asian continent,and is the product by the partial melting of the lower crust under the heating of the basaltic magma in this region,while underwent crystallization differentiation.6.Based on the geological characteristics,fluid inclusions and isotopic geochemistry of the mining area,it is concluded that the genetic type of the Daqinggou copper deposit is a skarn deposit formed in Paleoproterozoic,which originated from the contact metasomatism between the alkali feldspar granite and the marble of Mayihe Formation in the area.The Xiahuolong gold deposit is a skarn deposit formed in Early Cretaceous,which is related to the contact metasomatism between diorite porphyrite and granulite of Dadongcha Formation.The Ji’an lead-zinc deposit belongs to the Early Cretaceous skarn deposit.The two ore blocks of Guojialing and Kuangdongzi discovered at present are the remote products of the deep skarn system.Fluid immiscibility(boiling)and mixing are the main mechanisms leading to the metal precipitation of the deposit,of The former is dominated by the Daqinggou and Xiahuolong deposits,while the latter is more emphasized by the Ji’an deposit.7.Based on the research results of typical deposits and intrusive rocks,combined with the ore-forming dynamics background proposed by predecessors,we have established the diagenetic and geological models and geodynamic diagrams of the skarn hydrothermal system of polymetallic deposits in Ji’an area:(1)Paleoproterozoic arc-continent collision-Diagenesis by the partial melting of the crust-Mineralization of contact metasomatismIt refers to the collision between the Longgang block and the Nanlin block in the LJR in Late Paleoproterozoic.During this process,the tectonic thickening and the radioactive heat generated by the crustal movement have triggered the partial melting of the Neoarchean crustal material in the area,and formed the alkali feldspar granite through the fractional crystallization.The contact metasomatism between the magma and the strata formed the initial ore-bearing fluids,whilst the Daqinggou copper deposit was formed through fluid immiscibility and fluid mixing.(2)Early Cretaceous oceanic plate subduction-Diagenesis of partial melting of mantle wedge-Mineralization of contact metasomatismIt refers to the Early Cretaceous subduction of the Ancient Pacific plate to the northeast continental margin,during which it metasomatism with the overlying mantle and partial melting occurred to form the diorite porphyrite mother magma,The magma invades and occurs the contact metasomatism with granulite of Datongcha Formation whilst formed the initial ore-bearing fluids,alongside the formation of the Xiahuolong gold deposit through fluid immiscibility and mixing.(3)Early Cretaceous oceanic plate subduction-Diagenesis by the partial melting of the crust-Contact metasomatism-Hydrothermal upwellingIt refers to the subduction of Ancient Pacific plate at the northeast continental margin in Early Cretaceous,during which the basaltic magma invaded and heated the crustal material in the area,which caused partial melting and formed the parent magma of quartz porphyry.The parent magma invaded and formed the initial ore-bearing fluids through contact metasomatism with the Cambrian limestone.And the hydrothermal upwelling extracted the ore-forming favorable components and experienced fluid mixing to form the Ji’an lead-zinc deposit.
Keywords/Search Tags:Ji’ an area, Au-Cu-Pb-Zn polymetallic deposit, Diagenetic and metallogenic age, Genesis and mineralization of deposit, Metallogenic geological model
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