Late Paleozoic To Early Mesozoic Gold-Copper Polymetallic Metallogeny And Metallogenic Regularity In Central Jilin Province,Northeast China

The central Jilin Province is located at the junction between the eastern segment of the Xing’an-Mongolia Orogenic Belt(XMOB)and the northern margin of the North China Plate(NCP),and has experienced the evolution,superposition and transition of the Paleo-Asian and Paleo-Pacific Ocean tectonic domains during the late Paleozoic to early Mesozoic.The special tectonic location,complex tectonic evolution history and multi-period magmatic activities provide favorable geological conditions for different periods and genetic types of endogenetic metallic metallogeny in the area.This area is considered an ideal area for understanding the regional tectonic evolution and metallogenic regularity of both the eastern XMOB and the northern margin of NCP from the Late Paleozoic to early Mesozoic.Compared with the eastern Jilin(Yanbian area)and southern Jilin(Tonghua and Huadian area),studies on typical deposits,regional metallogeny and metallogenic regularity in central Jilin are obviously weak,and the breakthrough of prospecting is insignificant.Therefore,five little-studied gold-copper polymetallic deposits(Shizui,Guokuidingzi,Xiaohongshilazi,Guanma and Cuyu)are studied systematically in terms of their metallogenic geological conditions,geological characteristics,source and evolution of ore-forming fluids,source and enrichment mechanism of ore-forming materials,diagenesis and mineralization ages,and tectonic settings.These studies,combined with the comprehensive comparative studies of gold-copper polymetallic deposits both within and adjacent area,this paper expounds the types and periods of gold-copper polymetallic metallogenesis from the late Paleozoic to early Mesozoic in the area,and summarizes the regional metallogenic regularity and further prospecting directions.Some conclusions have been drawn as follows:Firstly,the early Permian and Early Triassic copper polymetallic mineralization events in the central Jilin Province have been firstly recognized in this paper.The early Permian mineralization is represented by the Shizui skarn copper polymetallic deposit located mainly at the contact zone between the monzogranite and the marble of the late Carboniferous Shizui Formation.The mineralization-related monzogranite at the Shizui deposit yields a zircon U-Pb age of 277.8±0.93 Ma,which is consistent with the molybdenite Re-Os isochron age of 278.0±2.7Ma.The early Triassic mineralization is represented by the Guokuidingzi porphyry copper deposit,which is spatially,temporally,and genetically related to the porphyritic granodiorite with the LA-ICP-MS zircon U-Pb age of 250.7±2.0Ma that coincides well with molybdenite Re-Os isochron age of 247.9±6.9Ma.Secondly,gold-copper polymetallic deposits in the study area have been classified into four genetic types,namely,skarn copper deposits(Shizui and Guanma),porphyry copper deposit(Guokuidingzi),mesothermal magmatic-hydrothermal vein-type gold and polymetallic deposits(Cuyu,the late vein mineralization of the Xiaohongshilazi deposit)and volcanic-associated massive sulfide(VMS)Pb–Zn mineralization(the early stratiform mineralization of the Xiaohongshilazi deposit).The fluid inclusions and isotopic studies show that the ore-forming fluids of different types of deposits(except VMS mineralization)in the area are dominantly derived from magmatic water,and mixed with meteoric water in the late stage of mineralization.During the evolution process of ore-forming fluids,boiling(Shizui and Guokuidingzi deposits),fluid mixing(Guanma and vein type mineralization of the Xiaohongshilazi deposits)and fluid immiscibility(Cuyu deposit)are the main mechanisms of metal precipitation.Thirdly,the material source,petrogenesis and tectonic setting of the metallogenic intrusions of different stages have been determined.The early Permian intrusions associated with skarn copper polymetallic deposits,belong to the island arc calc-alkaline rock series,and formed under the tectonic setting of subduction of the Paleo-Asian Ocean.The early to middle Triassic intermediate-acidic intrusions related to porphyry copper(molybdenum)deposits have the geochemical characteristics of adakitic rocks,and their original magmas were derived from partial melting of thickened juvenile mafic lower-crust,and they are formed in a tectonic setting transitioning from the syn-collisional compression to the post-collisional extension after the final closure of the Paleo-Asian Ocean.The early Jurassic metallogenic intrusions associated with the skarn gold and mesothermal magmatic hydrothermal vein-type Pb-Zn mineralization are characteristic of island arc calc-alkaline magmatic rocks,which can be attributed to the initial stage of subduction of the Paleo-Pacific Ocean.The extensive middle Jurassic intermediate-acidic intrusions related to many mesothermal magmatic hydrothermal vein-type gold deposits and porphyry molybdenum deposits in the area are resulted from large-scale island arc calc-alkaline magmatism under the tectonic setting of intense subduction of the Paleo-Pacific Ocean.Fourthly,the gold-copper polymetallic metallogenesis in the study area,from the Late Paleozoic to early Mesozoic,can be divided into four periods,including early Permian(280-270Ma)skarn copper polymetallic mineralization(represented by Shizui deposit),early to middle Triassic(250-240Ma)porphyry copper(molybdenum)mineralization(represented by Guokudingzi deposit),early Jurassic(200-190Ma)skarn-hydrothermal vein-type gold and polymetallic mineralization(represented by vein mineralization of the Xiaohongshilazi and Guanma deposit),and middle Jurassic(175-160Ma)hydrothermal-porphyry gold and molybdenum mineralization(represented by Cuyu and others gold deposits in the Jiapigou-Haigou gold belt,as well as Jidetun,Daheishan,Fu’anpu molybdenum deposit,etc.)Fifthly,the metallogenic regularities of gold-copper polymetallic deposits in the area are summarized as follows.The contact zone between the late Paleozoic island arc intermediate to acid intrusions and the Carboniferous carbonate is the major geological indicator for prospecting skarn deposits.The early to middle Triassic porphyry copper-molybdenum deposits are mainly distributed along the EW-trending Xar-MoronChanghun fault zone.The middle Jurassic mesothermal magmatic hydrothermal vein-type gold deposits show similarities to the deposits in the Jiapigou-Haigou gold belt,implying this gold belt extends to northwestward to the Panshi area.The NW-trending tensional faults are the major ore-controlling structure in the area.