Multi-information Metallogenic Prediction Of Gold Deposits In Jiapigou Metallogenic Belt,Jilin Province

The Jiapigou metallogenic belt,located in Huadian City,Jilin Province,is one of the important gold-producing districts in the Peri-Pacific metallogenic zone.Belonging to the eastern section of the northern margin of the North China Craton?NCC?and the eastern section of the Central Asian Orogenic Belt?CAOB?,the NW-trending main ductile shear zone controls the distribution of deposits and mineralization points in the belt,showing a good metallogenic potential.At present,there are a number of large and medium-sized ore deposits in the area,such as Erdaogou,Xiaobeigou,Bajiazi,Sandaogou,Sidaocha,Xiaxitai,Banmiaozi,etc.With the continuous consumption of proven resources and reserves in mining,it is urgent to find alternative resources.At the same time,the previous understanding of the genesis of ore deposits,metallogenic control factors,major predictive factors?indicators?,metallogenic enrichment laws and other aspects is controversial,which restricts the smooth development of prospecting work.In order to alleviate the resource crisis of the China National Gold Group Corporation?CNGC?and the Jiapigou Mining Corporation,CNGC,has established the scientific research project of"multi-information prospecting and prediction of Jiapigou gold metallogenic belt".Based on the project,guided by the metallogenic prognosis theories in exploration areas and mineral resources prognosis of synthetic information,and on the basis of previous studies,we select three representative gold deposits?Erdaogou,Xiaobeigou and Bajiazi?to make a systematic research on geological,geochemical characteristics,and genesis,etc.The metallogenic geological conditions and ore-controlling factors of Jiapigou metallogenic area are systematically analyzed,and the metallogenic regularity is summarized.Based on field observation and interpretation of aeromagnetic,gravity,geochemical data and comprehensive information of this project,the prediction factors of gold deposits are determined.Finally,the positioning/quantitative prediction of mineral resources in the area was carried out based on the weight of evidence model,and the evaluation target of resource potential was finally realized in the prospective area.The main results achieved in this paper are as follows.1.Taking the typical deposit research as a means,the geological characteristics and genesis of the gold deposit in the study area are summarized,and the metallogenic model is established.Geological characteristics of deposits reveal that the ores are mainly of the gold-bearing quartz vein and secondarily altered rock types,and are strictly controlled by secondary faults.The gold deposits are hosted in the Jiapigou Group composed of amphibolites and granitic gneiss.Four stages of mineralization in the gold deposit have been identified:milky quartz,pyrite-quartz,native gold-quartz-pyrite,and quartz-carbonate.The studies of fluid inclusion and H-O isotopes show that the ore-forming fluids belong to the NaCl-H₂O-CO₂ system with medium-temperature,medium-to low-salinity immiscibility fluids.The initial ore-forming fluid consisted of magmatic water produced by the partial melting of lower crustal material containing a mantle component,and mixed meteoric water during the mineralization progresses.The ore-forming fluids subsequently evolved into meteoric waters in the late stage.The results of S isotopes indicate that metallogenic material was derived predominantly from the mantle containing a crust component,and it extracted only a small amount of metallogenic material from host rocks during the process of upward migration.Magmatic zircon LA-ICP-MS U-Pb dating indicates that the samples within the study area were emplaced during the Late Permian?ca.252 Ma?and Late Triassic?ca.230²13Ma?.Combined with the geochronology data within the Jiapigou-Haigou gold belt,gold metallogenic event in the Jiapigou area occurred during late Indosinian?240²10 Ma?and early Yanshanian?180¹60 Ma?,which coincided with the regional tectono-magmatic events.In view of this,Jiapigou gold deposit is determined to be a mesothermal magmatic hydrothermal deposit.According to the characteristics of regional tectonic evolution,it is considered that the metallogenesis was formed in the tectonic environment of the transition from compression to extension in the northern margin of the NCC to the eastern margin of the CAOB.2.The geological conditions and ore-controlling factors of gold deposits in Jiapigou metallogenic area are determined,and the regional metallogenic essential factors are summarized.The NW-trending main ductile shear zone controls the distribution of deposits in the belt.According to geological and geophysical interpretations,it is confirmed that TTG in the southwestern part of the NW-trending main ductile shear zone constitutes a circular dome structure.The early stage of the Jiapigou NW-trending shear zone is the stratum contact zone between TTG dome and Jiapigou Group.The inheritance of Late Paleozoic-Mesozoic developed into a regional NW-trending ductile shear zone,which controlled the NW-trending zonal distribution of gold deposits in the area.The NE and NW structures control the tectonic framework of the area,and jointly control the spatial distribution of ore bodies in the area and constitute the structural ore-controlling factors.The amphibolite and amphibolite gneiss in the Sandaogou Formation of Jiapigou Group are the main ore-hosting rocks of gold ore bodies in space.The content of gold and other metallogenic elements and multivariate statistical analysis show that they provide material sources for gold mineralization and constitute the lithologic elements of gold ore-forming strata.The regional granitic magmatic activities in Indosinian and early Yanshanian period controlled the occurrence and distribution of ore bodies in terms of time,space,hydrothermal source,mineralizing material source and metallogenic dynamic characteristics,thus constituting the metallogenic magmatic rock conditions.The formation of gold deposits in Jiapigou metallogenic area is the product of the above-mentioned synthetical action of structure,stratum lithology and magmatism conditions.Based on the interpretation results of comprehensive information of geology,aeromagnetism and gravity,the types and characteristics of ore-forming geological bodies,ore-forming structural planes and ore-controlling structures in Jiapigou metallogenic area are determined,which lays a foundation for the subsequent evaluation of ore-prospecting potential.3.Based on field observation and interpretation of comprehensive information of geology,aeromagnetism,gravity and geochemical exploration,the predictive factors of gold deposits in Jiapigou gold metallogenic area are determined.The study of known deposits confirms that the geological indicators are silicification,pyritization,potassium,sericitization,sericitization,chloritization,epidotetization and carbonation;the NW trending structure and its derivative low-order NW trending and NE trending fault structures,and the concentrated development area of ore-forming related veins are also geological indicators of gold mineralization prediction.The Jiapigou NW-trending structure and its derivative low-order NW-trending and NE-trending faults,as well as the concentrated development of ore-forming related veins,are also geological indicators of gold metallogenic prognosis.Geochemical data show that Au,Ag,Zn,Mo,Sb,Hg,Pb and Cu are the main metallogenic elements?according to coefficient of variation?,and Au,Ag,Pb,Zn,As,U and Mo show a main metallogenic period?stage?,while Cu,Bi,W,Sb,Hg,Sn and Th show two or more metallogenic periods?stage?.The metallogenic elements are divided into Ag-Cu-Pb-Zn,Co-Ni-Ti-V,Au-Bi-W,F-Mo-Th,As-B-Sb,Mn-Sn and Hg-U elements assemblages,which indicate that the metallogenic elements in the area are characterized by multi-source and multi-stage superimposed enrichment.The elements anomalies of Au,Bi,W,Ag,Pb,Zn,Cu,Sb,Mn and Au-Bi-W,Ag-Cu-Pb-Zn assemblage anomalies are the geochemical indicators for gold prospecting.The regional aeromagnetic and gravity data are interpreted to extract the information of linear and annular structure.According to the spatial dependence of gold deposits and gravity-magnetic interpretation structure,the gravity and magnetic interpretation of NW-trending structures,NE-trending structures?physical interface?and their intersection sites,NW-trending structures and annular structures control the spatial distribution of ore bodies,and determine their geophysical indicators for gold prospecting.4.According to the distribution characteristics of gold deposits in Jiapigou metallogenic area and their relationship with lithology,structure,magmatic rocks,linear and annular structure of ore-controlling strata,the metallogenic regularity of regional gold deposits is summarized.It is pointed out that the spatial distribution of gold deposits?spots?in this area have obvious heterogeneous mineralization,concentrated distribution and equal spacing in the spatial distribution,which are mainly controlled by strata lithology of Jiapigou Group,NW or NE-trending ductile shear zone,Archaean TTG and Mesozoic granite.The relationship between geophysical interpretation results and gold mineralization shows that the gold deposits?spots?in Jiapigou metallogenic belt are mainly located in the position of occurrence change of annular structure?or metallogenic geological body?,the intersection area of annular and linear structure,and the intersection of NW-and NE-trending structures.Gold mineralization was formed in Indosinian and early Yanshanian periods.5.Based on the regional mineral resources comprehensive information evaluation system?MRAS?based on GIS platform and using the weight of evidence model,the metallogenic information such as geology?stratigraphic lithology,structure and magmatic rocks?,mineral resources and prediction information?indicators?such as gravity,aeromagnetism and geochemical prospecting were extracted,and the metallogenic prediction research of comprehensive information of gold deposits was carried out,and 5A type,8 B type and 11 C type metallogenic prospecting areas were outlined.Finally,the quantitative theory I model is used to estimate the total amount of gold resources in the study area,and the total amount of gold resources in the study area is 348t.