Research On Metallogenesis And Geological Model Of The Mesozoic Hydrothermal Au-Ag,Mo And Fe-Cu Polymetallic Deposits In Helong Of Yanbian Aera,Jilin Province

Helong of Yanbian area is located in the eastern part of the northern margin of the North China Craton.It consists of two major tectonic units,the Longgang block and the accretionary zone of the northern margin of the North China Craton.Affected by the superposition of the Paleo-Asian oceanic tectonic domain and the Paleo-Pacific structural domain,multiple structures and magmatism made this area become a multi-metal metallogenic area,which is dominated by molybdenum deposits.Based on the existing data of the Helong area,this paper systematically studied the regional geodynamic evolution of this area.On this basis,the representative deposits?points?were selected to carry on the study of geological characteristics,fluid inclusions,isotopic geochemical characteristics and chronological characteristics to determine the genesis of the deposits.At the same time,on the basis of studying the relationship between magma and mineralization,the evolution of ore-forming fluids,and the source of ore-forming materials,the mineralization was discussed and typical ore-forming model was established.Finally,a regional metallogenic model was established based on the regional geodynamic background.The main progress and conclusions are as follows:1.The studied area has experienced three stages:the formation and evolution of the Early Cambrian crystalline basement,the evolution of the Paleo-Asian ocean tectonic domain?subduction,closure,extension?and the evolution of the Paleo-Pacific structural domain.At the end of the Neoarchean period,the cratonization ended and entered the process of systemic extension.In the Middle Triassic,North China Craton and Xingmeng orogenic belts were collaged in this area,and the evolution of the Paleo-Asian Ocean tectonic domain ended.After the closure of the ancient Asian Ocean in the late Triassic,the studied area is in the stretched background.In the Early-Middle Jurassic,the studied area is in the tectonic setting of the westward subduction of the Paleo-Pacific plate to the Eurasian plate,indicating the beginning of the evolution of the Pacific tectonic domain.2.For the first time,the hydrothermal deposits in the study area are classified into four types:medium-temperature hydrothermal vein type,porphyry type,skarn type and superimposed type.Among them,Bailiping Silver Mine is a medium-temperature hydrothermal vein type deposit,Jinchengdong gold deposit is a medium-temperature hydrothermal vein type deposit,Shimadong molybdenum ore and Huajiling molybdenum deposit are porphyry molybdenum deposits,Baishidong iron deposit is a skarn type deposit,and the Shajingou gold deposit is a superimposed deposit,which is intrusion related gold deposit superimposed with moderate-temperature hydrothermal vein-type gold mineralization.3.Study of microscopic petrography,chemical composition and hydrogen-oxygen isotope on fluid inclusions reveal that the fluid inclusions of Bailiping silver deposit include three types:gas-liquid two-phase inclusion,CO₂-rich three-phase inclusion and multi-phase daughter mineral bearing inclusions.In the main ore-forming stage,the uniform temperature of the inclusions ranges from 233°C to 296°C,the salinity is 3.1%³7.2%NaCleqv.,the density is 0.75¹.08 g/cm³,which is medium temperature,medium and low salinity,medium and low density CO₂-NaCl-H₂O ore-forming fluid system,which is derived from magmatic water and with some addition of atmospheric precipitation in the late stage.The fluid inclusion types of Jinchengdong Gold Mine include gas-liquid two-phase inclusions and CO₂-rich three-phase inclusions.The average temperature of inclusions in the main metallogenic stage is 251³12°C,the salinity is0.5%¹1.2%NaCleqv,and the density is 0.50⁰.87 g/cm³,which is a medium-high temperature,medium-low salinity,low-density CO₂-NaCl-H₂O ore-forming fluid system,which is derived from magmatic water and mixed with atmospheric precipitation in the late stage;The types of fluid inclusion in the Shimadong molybdenum ore mainly include gas-liquid two-phase inclusions,a small amount of CO₂ three-phase inclusions and daughter mineral bearing inclusions.The uniform temperature of inclusions in the main metallogenic stage ranges from 242°C to 338°C.The salinity is 6.9%¹0.7%NaCleqv,and the density is 0.75⁰.90 g/cm³,which is medium-high temperature,medium-low salinity,medium-low density CO₂-NaCl-H₂O ore-forming fluid system.The ore-forming fluid is derived from magmatic water and may be mixed with atmospheric precipitation in the late stage;The types of fluid inclusions in Huajiling molybdenum ore mainly include gas-liquid two-phase inclusions and CO₂-rich three-phase inclusions,and a small amount of daughter mineral bearing inclusions.The uniform temperature of inclusions in the main metallogenic stage ranges from 250°C to 347°C.The salinity is 6.0%¹3.6%NaCleqv,and the density is 0.62⁰.88 g/cm³.The laser Raman results show that the main component of the ore-bearing fluid is H₂O and CO₂,containing a small amount of N₂,which is medium-high temperature,medium-low salinity,medium low-density NaCl-H₂O ore-forming fluid system containing CO₂ and N₂,which is derived from magmatic water and mixed with atmospheric precipitation in the late stage;The types of fluid inclusion in Baishidong iron ore are mainly gas-liquid two-phase inclusions and daughter mineral bearing inclusions,with a small amount of CO₂-rich three-phase inclusions,and the uniform temperature of inclusions in garnets of skarn ranges from 297°C to 445°C,the salinity is 4.2 to 50.4%NaCleqv,and the density is 0.65 to 1.11 g/cm³.The quartz-sulfide phase fluid inclusions have a uniform temperature range of 154²87°C,a salinity of4.2%²0.2%NaCleqv,and a density of 0.76¹.00 g/cm³,indicating high temperature,high salinity,and high density mineralization in the early stage,and low temperature,medium salinity,medium and low density NaCl-H₂O ore-forming fluid system in the late stage;The first phase of fluid inclusions types in the Shajingou gold deposit include daughter mineral bearing inclusions,gas-liquid two-phase inclusions and pure CO₂inclusions.The uniform temperature of the inclusions in the main metallogenic stage range from 265 to 425°C,and the salinity is 6.4%¹6.5%NaCleqv,with the density of0.56¹.01 g/cm³,medium-high temperature,medium-low salinity,medium-low density CO₂-NaCl-H₂O ore-forming fluid system;The second phase of fluid inclusions include CO₂-rich three-phase inclusions,rich-gas inclusions and pure CO₂ inclusions.The uniform temperature range of the inclusions in the main metallogenic stage is 249³25°C,and the salinity is 3.5%¹1.5%NaCleqv,with the density of 0.62⁰.89g/cm³.It is a medium-temperature,medium-low salinity,low-density CO₂-NaCl-H₂O ore-forming fluid system with some atmospheric precipitation in the late-stage.4.The results of S,Pb,Re-Os isotopes and related elements in ore minerals indicate that the?³⁴S value of the Bailiping silver mine pyrite varies from 2.07‰to 4.93‰,with an average of 3.88‰,indicating that the ore-forming materials are mainly from deep magma;?³⁴S value of pyrite in Jinchengdong gold deposit varies from 3.0‰to 4.3‰.Pb isotope composition of ²⁰⁶Pb/²⁰⁴Pb is 16.845¹7.173,²⁰⁷Pb/²⁰⁴Pb is 15.48¹5.519,²⁰⁸Pb/²⁰⁴Pb is 36.864³8.52,revealing that ore-forming material is derived from deep source magma or crust-mantle mixed source;The Re content of the molybdenite in the Shimadong molybdenum deposit is between 26.9×10^-633.8×10^-6,indicating that the ore-forming material is the crust-mantle mixed source;the?³⁴S value of the Huajiling molybdenum pyrite sample ranges from 2.0‰to 4.2‰,the Re content of molybdenum ore is between 19.564×10^-623.128×10^-6,indicating that the ore-forming material is mainly from deep source magma or crust-mantle mixed source;The diorite in Baishidong iron deposit,closely related to the mineralization,originated from a mixed source of new crust and ancient materials or most of the ore-forming material is derived from the mixed source of the mantle and the lower crust;In Shajingou gold deposit,the?³⁴S value of pyrite in the first phase varies from-0.08‰to 1.92‰,and the ore-forming material is mainly from mantle.The?³⁴S value of pyrite in the second phase varies from 0.49‰to4.90‰,and the corresponding lead isotope composition of ²⁰⁶Pb/²⁰⁴Pb is 18.270¹8.281,²⁰⁷Pb/²⁰⁴Pb is 15.569¹5.580,and ²⁰⁸Pb/²⁰⁴Pb is 38.256³8.301,indicating that the ore-forming material has a property of crust-mantle mixed source.5.The chronology study of diagenesis and mineralization shows that the zircon U-Pb age of the diabase porphyrite,closely related with the Bailiping silver mineralization,is243.5±2.6Ma.The weighted average age of molybdenite Re-Os of Shimadong molybdenum deposit and the Huajiling molybdenum mine are 163.1±0.9 Ma and178.0±1.1 Ma respectively.The zircon U-Pb age of the diorite which is closely related to Baishidong mineralization is 164.6±1.4 Ma.Combined with the relevant research results,it is concluded that the mineralization of Bailiping silver deposit,related with the diabase porphyrites,occurred in the Middle Triassic.The mineralization of Jinchengdong gold deposit occurred in the Middle Jurassic,and metallogenic processes are related to the lamprophyre and the diorite porphyry.The ore-forming of the Shimadong and Huajiling porphyry molybdenum deposits occurred in the Middle Jurassic,and metallogenic processes are related to the monzonitic granites.The mineralization of the skarn-type iron ore occurs in the Middle Jurassic,and metallogenic processes are related to diorite.The first-phase mineralization of the Shajingou gold deposit is related to the Middle Jurassic diorite,and the second-phase mineralization is closely related to the Early Cretaceous diorite porphyry.According to this,the Mesozoic hydrothermal deposits in the study area are divided into three metallogenic periods,namely the mineralization of the Indosinian?Middle Triassic?silver deposits,the polymetallic formation in the early Yanshanian?early-Middle Jurassic?and polymetallic mineralization in the late Yanshanian?Early Cretaceous?.6.From the perspective of diagenesis and mineralization,it is initially determined that the mineralization of the Indosinian?Middle Triassic?is the product of the closure of the ancient Asian Ocean,with the collision of the North China Craton and the Xingmeng orogenic belt,shortening and thickening of the lithospheric plate in Yanbian area.Under this condition,part of the lithospheric mantle is melted to form basaltic magma,magma underplating and heating the lower crust,which is partially melted to form a magma chamber.After further evolution,it is placed in the shallow part of the crust.At the late stage,with the evolution of magma,the fluid was dissolved and carried a large amount of Ag,Au and other ore-forming material to migrate along the brittle fracture.At the same time,a small amount of ore-forming material such as Ag and Au were extracted from the strata.The fluid and ore-forming material was unloaded in the near-surface ductile shear zone or other structure-weak areas;During the early Yanshanian?Early-Middle Jurassic?,mineralization occurred in the tectonic setting of the Pacific plate subduction westward under the Eurasian plate.Dehydration and degassing of the subduction oceanic crust caused partial melting of the lithospheric mantle to form basaltic magma.The underplating and heating of the lower crust promote the partial melting of the pre-existing ancient matter of the lower crust.Together with the mixing of the new basaltic magma,a mixed magma chamber was formed.Mixed magma crystallization differentiation during the during the ascending process,and formed a series of medium-acid magmatic rocks near surface,which are closely related to mineralization of Mo,Fe and Au.Hydrothermal fluids formed in the late stage of magma differentiation migrated along brittle fractures in structural weak zones,unloading and precipitating to form a series of hydrothermal deposits such as Mo,Fe and Au;During the late Yanshanian?Early Cretaceous?,mineralization occurred in the tectonic setting of the extensional background of the Pacific plate subduction westward under the Eurasian plate.The high-density mantle-derived C-H-O fluid carrying a large number of macro and trace elements rose along the fault structure and underwent crystallization differentiation in the lower crust.Part of the fluid formed the calcium-alkaline ultrabasic magma,after a small amount of crustal material assimilation and crystallization differentiation,emplacement in the shallow part of the crust.Another part of the fluid is relatively silicate-rich C-H-O fluid,forming the ore-bearing hydrothermal fluid at the different level of the earth's crust.The ore-bearing hydrothermal fluid migrates along the brittle fracture.The ore-bearing material migrated along brittle fractures in structural weak zones,unloading and precipitating to form a series of hydrothermal deposits at the shallow crust.