Late Paleozoic-Mesozoic Tectonic Evolution And Regional Metallogenic Regularity Of The Eastern Yanbian Area,NE China

The eastern Yanbian area is located at the eastern Margin of the Xing'an Mongolian Orogenic Belt?EM-XMOB?.Since the Paleozoic,the EM-XMOB has experienced the evolution and transition of the Paleo-Asian and Paleo-Pacific tectonic doMains.Therefore,this area took place multiple periods of tectono-MagMatic activities,which is favorable for the endogenetic metallic metallogenesis.The EM-XMOB has experienced complicated transition of tectonic regime during the Late Paleozoic to Mesozoic,accompanied with intense metallic metallogenesis.The eastern Yanbian is considered an ideal area for exploring the tectonic evolution of the EM-XMOB and the regional metallogenic regularity.Combined with the recent data of the regional tectonic evolution,the geologic and geochemical characteristics of ore-related strata and intrusions from this study,provide new evidence for revealing the regional tectonic evolution of the eastern Yanbian area during the Late Paleozoic to Mesozoic.Furthermore,this paper aims at 3 scheelite deposits?Yangjingou,Wudaogou,and Sidaogou?,3 gold deposits?Yangjingou,Jiusangou,and Duhuangling?and 2 gold-copper deposits?Xiaoxi'nancha and Madidabeishan?,to discuss their geological conditions,geologic characteristics,source of ore-forming fluid and Material,forMation ages,and tectonic settings.Therefore,this paper has concluded several points involving types,epoch,and temporal-spacial regularity of mineralization in eastern Yanbian,as well as indicator and further directions for prospecting.1.This paper sumMarized the Late Paleozoic to Mesozoic tectonic evolution of the eastern Yanbian area.During the Permian,the eastern Yanbian area formed numerous I-type calc-alkaline granitoids,calc-alkaline intermediate-basic volcanic rocks and sedimentary rocks?the protolith of the Wudaogou Group?,all of which were formed in an island arc or active continental Margin setting.This indicated that the eastern Yanbian area is dominated by the subduction of the Paleo-Asian Ocean during the Permian.At the end of the Permian to the beginning of the Early Triassic,the eastern Yanbian region was in a compressional setting dominated by the transition from the final subduction to closure of the Paleo-Asian Ocean,which has been recorded by the mesotherMal vein type gold and tungsten mineralizations.The large-scale Early–Middle Triassic syn-collisional granite belt at the EM-XMOB extends from the middle of Jilin Province to the Wangqing–Hunchun region,and the protolith of the metamorphic rocks of the Wudaogou Group experienced the Early Triassic epidote–amphibolite facies regional metamorphism.Both of them forcefully indicated that the subduction of Paleo-Asian Ocean ceased at the beginning of the Early Triassic.The detrital zircon geochronological data of the metamorphic sedimentary rocks from the Wudaogou Group and the presence of the syn-collisional granite in Wangqing-Hunchun region further imply that the Paleo-Asian Ocean finally closed along the Xra Moron River–Changchun– Wangqing–Hunchun Suture at the end of the Middle Triassic.During the late Early to early Late Cretaceous,island arc calc-alkaline MagMatic rocks and adakitic intrusions formed in eastern Yanbian,accompanied with the forMation of porphyry Au-Cu and epitherMal Au deposits.Therefore,the eastern Yanbian area was in a tectonic setting dominated by the subduction of the Paleo-Pacific Plate beneath the Eurasian Plate.2.This paper firstly recognized the late Paleozoic tungsten and gold mineralization in the Yanbian area,and constrained their forMation ages.Both of the late Paleozoic tungsten and gold mineralization are of mesotherMal vein type,and hosted within the metamorphic rocks of the Wudaogou Group,the Permian intermedium-acid intrusions,and their contact zones.For the tungsten mineralization,the scheelite is the single economic mineral in tungsten ores,the tungsten deposits are characterized by the sulphide-poor scheelite-quartz vein type mineralization,the orebodies are big vein?Wudaogou deposit?or thin stockwork?Yangjingou deposit?type,are controlled by the NW-,NNW-,or S–N-trending faults or fractures in the host strata,and are spatially,temporally,and genetically related to the host I-type tonalite pluton.The gold mineralization is dominated by the altered rock type,as well as minor quartz vein type,and the gold orebodies occur as gold-bearing altered zone,which was controlled by the NNE-trending faults.The new scheelite Sm–Nd isochron age is 251.7±2.9 Ma,which is consistent with the U–Pb emplacement age of the tonalite?251.9±2.2 Ma?,indicating that the tungsten mineralization occurred at 252 Ma.The host intrusion of the Yangjingou gold deposit yielded the U–Pb age of 262±1 Ma,the hydrotherMal muscovite 40Ar/39 Ar plateau age is 241.6±1.2 Ma,molybdenite Re–Os model age is 250.6±1.8 Ma,indicating that the gold mineralization formed at 250 Ma.3.The ore deposits in eastern Yanbian have been classified into three genetic types.The ore deposits in eastern Yanbian are classified into mesotherMal vein type,porphyry and?high-sulfidation?epitherMal deposits.The mesotherMal vein deposits including tungsten deposits?Yangjingou,Wudaogou and Sidaogou?and gold deposits?Yangjingou and Wudaogou?.The porphyry Au-Cu deposits are represented by Xiaoxi'nancha and Madidabeishan.High-sulfidation epitherMal gold deposits include Jiusangou and Duhuangling deposits.Except the forMation ages of the late Paleozoic mineralization stated above,this paper provides some new zircon U–Pb ages of ore-hosting diorite and quartz diorite porphyry from Sidaogou tungsten and Jiusangou gold deposits of 258 ± 3 Ma,and 108.1 ± 1.4Ma,respectively.4.The nature and source of the ore-forming fluids and Materials for the ore deposits of different types have been determined.The RaManspectroscopy,micro-thermometry and C-H-O isotope analyses of fluid inclusions indicated that the ore-forming fluid of mesotherMal vein type deposits is NaCl-H₂O-CO₂±N₂±CH₄ system,which was Mainly derived from MagMatic water,and its carbonaceous Material resulted from oxidation of organic Material in the sedimentary rocks from the Wudaogou Group.The ore-forming fluid of porphyry Au-Cu deposits is hypertherMal NaCl-H₂O-CO₂±CH₄ system,which was derived from MagMatic water,mixed with a little bit of meteoric water,and its carbonaceous Material originated from MagMa.The ore-forming fluid of epitherMal Au deposits is NaCl-H₂O±CO₂±N₂±CH₄ system,which is derived from mixture between the MagMatic and meteoric water.The S,Pb,Sr,and Nd isotopic data indicated that the ore-forming Material of the mesotherMal vein tungsten deposits was Mainly derived from juvenile lower crust Materials that originated from the depleted Mantle,that of the mesotherMal vein gold deposits was also Mantle-derived,while that of porphyry Au-Cu and epitherMal Au deposits contained both Mantle-derived and crustal components.5.Based on the study on tectonic settings of typical ore deposits,the corresponding metallogenic models were established.The squeezing from the transition of the subduction to closure of the Paleo-Asian Ocean induced the partial melting of the juvenile lower crust derived from the depleted Mantle,which resulted from the emplacement of calc-alkaline MagMa enriched in W element.The initial hydrotherMal fluid was differentiated at the end of MagMa crystallization,which ascended through deep faults.In this process,the fluid reacted with the host strata?Wudaogou Group?,and extracted some ore-forming Material.The boiling of the evolved fluid prompted the scheelite to precipitate,thus forming several scheelite deposits in eastern Hunchun.The squeezing also induced the upwelling of the deep-derived gold-bearing fluid.Fluid immiscibility occurred in the NNE-trending fractures,and thus the mesotherMal vein type gold deposits formed.During the late Early Cretaceous,the superimposed processes involving the partial melting of subducted oceanic crust,metasoMatism of Mantle wedge and contamination of continental crust formed the adakitic MagMa,which was rich in Au and Cu.The associated porphyry Au-Cu deposits formed at the joint of faults in different orientations,whereas the epitherMal high-sulfidation Au deposits occurred at the Margin of volcanic fault basin.6.The regional metallogenic regularity,indicator and further directions for prospecting in eastern Yanbian were sumMarized and determined.Two periods of endogenic metallic mineralization can be identified in the eastern Yanbian area,namely end of the Hercynian?the end of Late Permian,252²50 Ma?mesotherMal vein type tungsten and gold mineralization,and the late Yanshanian?the late Early Cretaceous,110¹00 Ma?porphyry Au-Cu and epitherMal Au mineralizations.Spatially,the mesotherMal vein type tungsten and gold deposits were located at the N-S-trending Dabeicheng-Qianshan fault-fold belt,the porphyry Au-Cu deposits were located at the joint of the deep faults in different orientations,whereas the epitherMal high-sulfidation Au deposits were concentrated in the joint between the Margin of Mesozoic volcanic fault basin and the W–E-trending deep fault,and controlled by the breccia pipe and subsidiary fractures.Based on the above studies,as well as the geology,metallogenetic element geochemistry,1/10000 soil and 1/50000 stream sediment survey,this paper ascertained the geological and geochemical indicators for the gold,copper and tungsten deposits,and proposed the further directions for Au-Cu-W prospecting.Furthermore,nine Au-Cu-W prospective regions have been delineated in the Madida–Dabeicheng area,including three A-grade prospective regions.