Metallogenesis And Geodynamic Setting Of The Typical Gold Deposits In The Liuhe Area Of The Huadian City,Jilin Province

The Liuhe area,approximately 55 kilometers southeast of the Huadian City,is located on the side of the craton at the junction of the Central Asian Orogenic Belt?CAOB?and the northern margin of the North China Craton?NCC?,and lies to the south of the Jiapigou mining district?JMD?,which is a world-famous gold-producing district in China and even in the world.In recent years,with the increase of the prospecting intensity and the deepening of research work in the JMD and adjacent regions,many new gold deposits have been discovered in the Liuhe area,such as the Toudaoliuhe,Liupiye,Zhemagou,Jiancaogou,Binghugou,Laoling,Laoling'erduan,Naizhigou deposits,and a series of ore occurrences and metallogenic prospect area.According to incomplete statistics,the total gold reserves in the Liuhe area have exceeded 70 tons,which indicates that this area is expected to become a large to superlarge gold field comparable to Jiapigou gold field.However,due to relatively late discovery,exploration and mining of the gold deposits in this area,the research on the ore geology,metallogenesis,metallogenic process and geodynamic setting is still unclear,which seriously restricts the prospecting direction and exploration in this area,as well as regional metallogenic regularity and prospecting breakthrough.Hence,on the basis of previous studies,we select three representative gold deposits,i.e.,Toudaoliuhe,Binghugou,and Liupiye deposits,to make a systematic research on the geological characteristics of deposits,ore geochemistry,fluid inclusions,Diagenetic-metallogenic age,as well as chronology,elemental geochemistry and Hf isotope geochemistry of the intrusive rocks genetically related to mineralization.These new data,in combination with the regional geological observations,we draw the following main achievements.1.The geological characteristics of the three typical gold deposits in the Liuhe area reveal that the deposits and orebodies are mainly controlled by a series of NW-,NE-striking ductile-brittle and brittle faults,and by breccia pipe at the intersection of NW-,NE-and EW-striking faults.The orebodies are mainly of breccia-type?i.e.,Toudaoliuhe and Binghugou?and quartz vein-type?i.e.,Liupiye,Jiancaogou and Laoling?.The gold mineralization can be divided into three stages:quartz–pyrite?the early stage?,quartz–polymetallic sulfides?the main stage?and quartz–carbonate?the late stage?.The wallrock alteration mainly include K-feldspathization–biotitization,silicification,sericitization,chloritization–epidotization and carbonatization.Ore mineral is mainly associated with a pyrite+galena+sphalerite+native gold/electrum/küstelite+chalcopyrite±arsenopyrite±pyrrhotite±bornite assemblage.The dominant gangue minerals are quartz,feldspar,sericite,chlorite,epidote,and carbonate.2.The early-and main-stage fluid inclusions?FIs?of the three typical gold deposits in the Liuhe area are mainly PC-type?pure CO₂?,C-type?CO₂–H₂O–NaCl?and W-type?NaCl–H₂O?,whereas the late-stage FIs are mainly W-type.The result of the microthermometry,laser Raman spectroscopy and H–O isotopes revealed that initial ore-forming fluids of these gold deposits belong to the CO₂-NaCl-H₂O system with moderate-temperature,moderate–low-salinity and weak reduction.The fluid-rock interaction widely exists between ore-forming fluid and wallrock during metallogenic process.The fluid boiling is dominant mechanism for the precipitation of gold in the Louhe area.With the gradual decrease of temperature and the continuous injection of meteoric water,the ore-forming fluids have gradually evolved into the H₂O-dominated fluids.3.The H-O isotope results show that the initial ore-forming fluids of the three typical gold deposits have common source,i.e.,deep-seated magmatic water with mantle-derived magmatic property,and mixed meteoric water during the late stage.The S-Pb-Sr isotope results reveal that ore-forming materials were provided by crustal and mantle sources,i.e.,a deep crust-mantle Mixed Source with the characteristics of the Enriched Mantle I.4.The sulfide Rb-Sr isochron age from the Toudaoliuhe gold deposite is 177.7±1.7Ma,whereas the ages of the intrusive rocks genetically related to mineralization are in the range of 174?177 Ma.The pyrite Rb-Sr isochron age from the Binghugou gold deposite is 176.4±2.2 Ma,whereas the ages of the hydrothermal breccia and intrusive rocks genetically related to mineralization are 176.4±2.2 Ma and 174?177 Ma,respectively.The intrusive rocks related to mineralization from the Liupiye gold deposit are in the range of 173?176 Ma.By comparing with the chronological data from mineralization?include the intrusive rocks genetically related to mineralization?in the JMD,we believe that the gold mineralization occurred during the Middle Jurassic?171?178 Ma?and coincided with the gold mineralization age of these gold depsits in the JMD.These results revealed that the gold mineralization in the Liuhe area and even in the JMD is not an independent event,but a regional gold mineralization event occurred during the Middle Jurassic?170?178 Ma?,which is directly related to the regional intermediate-acid magmatism.5.Based on the zircon U-Pb ages,element geochemistry and Hf isotope geochemistries of metallogenic-related intrusive rocks in the Liuhe area,as well as regional geological observations,we concluded that these intrusive rocks formed in an active continental margin setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.The granitic rocks were likely derived from partial melting of thickened ancient crust heated by the underplating of mantle-derived basaltic magmas,whereas dioritic rocks are derived from a neutral magmas,which was the product of the mixing of the mantle-derived basaltic magma and the crustal acid magma.6.Combined with ore geology,ore-controling structure,magmatism,fluid evolution,and geodynamic setting,we have established a geodynamic evolution model for the metallogenic/rock of the mesothermal gold deposits in the Liuhe area.?1?During the Late Triassic?>210 Ma?,the study area was in an extensional tectonic environment that followed the closure of the Paleo-Asian Ocean.During this period,voluminous mantle-derived magma upwelling resulted in partial melting of lithospheric mantle and formed the basic-ultrabasic intrusive rocks.The crust-mantle interaction in this process could promote the initial enrichment of Au-Cu elements.And the NW-striking Jiapigou ductile shear zone occurred dextral shearing,resulting in forming a series of NW-,NE-,NEE-and EW-striking secondary faults.These secondary faults could provided the channels for ore-forming fluid transportation,and emplacement spaces for the metallogenic-related intrusive rocks.?2?During the Early Jurassic?198?180 Ma?,the mantle-derived basaltic magma were derived from the mantle wedge metasomatized by the subduction fluid.This magma ascended to the bottom of the lower crust and provided hydrothermal fluid,which resulted in partial melting of the ancient lower crust,forming the granitic magma.this magma emplaced and formed intermediate-acid intrusive rocks dominated by monzogranite.This process may have contributed to the enrichment of metallogenic elements in the lower crust.?3?During the Middle Jurassic?178?170 Ma?,the subduction plate fluids metasomatize the lithospheric mantle,resulting in partial melting of the lithospheric mantle and the formation of the basaltic magma with a large amount of metallogenic elements and CO₂-rich fluids.The basaltic magma underplated and heated the thickened ancient lower crust,prompting partial melting of the thickened ancient lower crust to form adakitic acid magma chamber.During this process,basaltic magma and adakitic magma were mixed to form neutral magma chambers.And the interaction between the two end-member magmas could promote the continuous migration and enrichment of metallogenic elements in the magma source.This two end-member magmas migrated upward to shallow regions of the crust,and then underwent immiscibility and formed the initial CO₂-and H₂O-rich ore-forming fluids.Subsequently,the ore-forming fluid migrated upward along the secondary faults?mainly NW-and NE-trending faults?,and reacted with wallrocks,resulting in a series of hydrothermal alterations.With decompression and cooling,ore-forming fluids underwent fluid boiling,forming early sulfide quartz veins in the shallow crust.Accompanied by the changes in physicochemical condition,i.e.,cooling or decompression,resulting in escape of massive volatiles such as CO₂ and H₂S?brecciation occurred locally?.Subsequently,the stability of the Au-S complex was destroyed,and then the gold and other sulfides precipitated,resulting in the formation of the numerous mesothermal gold deposits in the Liuhe area.