Study On Metallogenic Regularity And Metallogenic Model Of Gold Deposits In The Ertix Metallogenic Belt,Xinjiang

The Ertix gold metallogenic belt was located in the collision zone between Siberian plate and Kazakhstan-Junggar plate in northern Xinjiang,China.According to petrochemistry,zircon U-Pb dating,fluid inclusions and stable isotope,this thesis makes a detailed study on metallogenetic enviroment of gold deposits in the Ertix tectonic belt.To identify the geological background,metallogenic conditions,ore controlling factors and metallogenic mechanism of gold deposits in the eastern(middle)and western part of the Ertix metallogenic belt,a comparative study of gold deposits in the Ertix metallogenic belt was carried out on the basis of geological anatomy of Jinba gold deposit and Kekesayi gold deposit.The relationship between tectono-magmatic-metamorphic thermal events and mineralization was analyzed.And metallogenic model and prospecting model of gold deposit in the Ertix metallogenic belt was built.Summarizing metallogenic regularity provides basic data and support for further prospecting and prospecting work.Petrogeochemistry of some magmatic rocks related to gold mineralization is studied in the Ertix gold metallogenic belt.The Habahe plagiogranite rock body in western is characterized by high SiO2,intermediate Al2O3 and low Na content.Plagiogranite is right deviation partition curve with light rare earth relative enrichment,and negative Eu anomaly.The trace elements are characterized by enrichment of Rb,Ba,Th,La,Ce and depletion of Ta,Nb,Sr,Zr and Yb.Chronological studies show that zircon U-Pb age of plagiogranite was 431 ± 3.4Ma.Plagiogranite is considered to be the product of subduction zone environment,and the tectonic environment of magmatite might be the volcano island arc environment.The quartz porphyry in Sarbulake gold deposit of middle part in the Ertix gold metallogenic belt are also characterized by high SiO2,intermediate Al2O3 and low Na content.Quartz porphyry is right deviation partition curve with LREE enrichment,and negative Eu anomaly(? Eu=0.27-0.31).The trace elements are characterized by enrichment of Rb,Ba,Th,U,Nb,Sr,Zr,Ce and depletion of Ta,La,Hf and Nd.The quartz porphyry belongs to high-k calc-alkaline series,Zircon U-Pb age of quartz porphyry was 297.8±1.4Ma.It may be the product of intraplate tectonic environment.The volcanic rocks of the Middle Devonian Beitashan Formation in Aktas gold deposit of middle part in the Ertix gold metallogenic belt are mainly basic volcanic rocks.The lithology is mainly basalt,followed by picrite.The volcanic rocks are mainly located in the calc-alkaline series,and some are high potassium calc-alkaline series.The magma source belongs to the tholeiitic series.The volcanic rock has a high content of trace elements and has the characteristics of island-arc volcanic rocks.The fluid inclusion research mainly focus on the Jinba gold deposit in the western part and the Kekesayi gold deposit in the eastern of the Ertix tectonic belt.The fluid inclusions of Jinba gold deposit can be divided into three types:H2O-NaCl inclusions,CO2 inclusions,and few carbonaceous fluid inclusions.The homogenization temperature range of fluid inclusions in early metallogenic stage are 262?401 ?,and main metallogenic stage are 200?280?.Ore-forming fluid system is low salinity H2O-NaCl-CO2 system.The evolution of ore-forming fluids is as follows:CO2-rich medium-high temperature hydrothermal fluid in early and middle periods evolves to low-medium temperature and salinity H2O-NaCl system fluid in the middle and late periods.The fluid inclusions of Kekesayi gold deposit can be divided into H2O-NaCl inclusions and CO2 inclusions.In early shear-schistose stage,the homogenization temperature of fluid inclusions is higher,which reflects the characteristics of medium-high temperature hydrothermal fluid.The fluid inclusions in later metallogenic stage have the characteristics of medium-low temperature.Compared with other gold deposits in the Ertix tectonic belt,such as Saidu gold deposit,Sarbulake gold deposit,etc,the ore-forming fluid were all characterized by medium high temperature and rich CO2 at early stage and evolved into a medium low temperature H2O-NaCl system at the late stage.The diorite and plagiogranite in Jinba gold deposit provide material source for mineralization,the Markakuli ductile shear zone provides a space for mineralization,and the formation of quartz veins preliminarily enriched the intrusion of gold.Metallogenic sulfur source of Jinba gold deposit(?34S=3.42‰?8.71‰,average value=6.30‰)is mainly originates from the deep crust,that is deep source sulfur characteristics.Kalaxianger-Lekalatawu fault and Keziletawu fault control the output and distribution of auriferous ductile shear zone and orebody of Kekesayi gold deposit of eastern part in the Ertix gold metallogenic belt.Structural alteration of shear zone is the main controlling factor of mineralization.At the same time,magmatic hydrothermal alteration plays an important role in mineralization.The S isotope characteristics reflect that the gold deposits in this area have complicated mineralization and the ore-forming materials have multi-source characteristics.According to the regional distribution characteristics of sulfur isotopes,the sulfur isotope of Saidu gold deposit and Jinba gold deposit in the western is relatively rich in heavy sulfur.Gradually,toward Sarbulake gold deposit in the central to Keksayi gold deposit in eastern,sulfur isotopes tend to become lighter.We speculated that the metallogenic material sources of gold deposits in western are more closely related to magmatic activities,while the tectonic metamorphism of gold deposits in eastern has a greater impact on metallogenesis.The H-O isotopes of all these gold deposits indicate that the ore-forming fluids were characterized by metamorphic water(and magmatic water)in the early stage and mixed with atmospheric precipitation in the late stage.Gold mineralization in Ertix metallogenic belt is widely distributed showed belt-like distribution,concentrated on section in secondary fracture zone.The metallogenic structure has the characteristics of divergence from the west and convergence to the east.The mineralization lasted for a long time from Late Devonian to Middle Permian.Devonian sedimentary strata,Carboniferous sedimentary strata and intermediate-acidic rock mass in the middle and late Hercynian period are the main ore bearing surrounding rocks.The mineralization with the characteristics of multi-stage in the Ertix gold metallogenic belt was controlled by ductile shear and magmatic activity.The Ertix tectonic belt with strong magmatic activity,and the volcano eruption and magmatic intrusion is frequently.Frequent volcanic magmatic activity can provide the heat source and some material source needed for mineralization and promote the activation and migration of gold in the formation.The metallogenic fluids in the Ertix gold belt have similar evolution characteristics.The long-term metamorphism and deformation have formed a series of metamorphic superimposition and tectonic superimposition of multiple stages and forms,which has resulted in the reactivation of the rich gold and other ore-forming elements in the formation.In Ertix tectonic magmatic metallogenic belt,gold deposits can be formed when it has a particular position in favor of the formation and plenty of gold source supply.The gold element of the Ertix gold metallogenic belt is activated,migrated and enriched with mixed fluids of magmatic hydrothermal fluid,metamorphic hydrothermal fluid and atmospheric precipitation that mainly in medium and low temperature,medium shallow-medium deep environment.This paper improves the structure of Ertix gold belt metamorphic fluid evolution system,established gold metallogenic model of Ertix tectonic belt.