Geological And Geochemical Study Of Typical Deposits And Metallogenic Mechanism Of The East Kunlun Mountains Ditch GOLD Pool

Eastern Kunlun orogenic belt, located in the northeastern margin of Qinghai-Tibet Plateau, is an important part of the Central Orogenic belt. Its complex geological evolutionary history contributed the study area with rich mineral resources, gold, salt and copper polymetallic minerals. Gouli gold metallogenic district is in the east of Eastern Kunlun orogenic belt, at present, some gold deposits have been found in this region such as Guoluolongwa gold deposit (large), Asiha deposit (medium), Annage gold deposit (medium), Walega gold deposit (small) and Dalijigetang gold point, and it shows there are the potential of super large gold fields in the study area. In this paper, based on the collection and sorting out the previous data, starting from some aspects of the typical gold deposit in Gouli gold metallogenic district:the ore-forming geological background, geological characteristics of the deposit, and combined with the structural evolution history in the study area, taking trace and rare earth elements, fluid inclusions, isotope geochemical (S, Pb, H-O), Magmatic rock’s petrology and geochemistry, diagenesis and mineralization chronology as research methods, This paper analysed that Guoluolongwa and Asiha gold deposits’geological features, metallogenic material source, property of mineralizing fluid, origin and evolution, ore-forming processes and the migration direction of the ore-forming fluid, metallogenic epoch and preliminary determined the genetic type of ore deposit, established a practical metallogenic model. The main results are as follows:1. The study on the regional metallogenic background shows that the Gouli gold metallogenic district, with complex tectonic features, intensive magmatism, mostly metamorphism and deformation, has the geological conditions for the formation of superlarge gold deposits. The Kunlun orogenic movement and the medium-acid magma in Indosinian played an important role in ore controlling factors of regional gold deposits.2. The study on the geological characteristics of Guoluolongwa and Asiha gold deposits shows that:①Guoluolongwa gold deposit is hosted in the Nachitai Group metamorphic rocks, and ore bearing lithology is mainly formed by dynamic metamorphism phyllonite, secondary with green mud quartz phyllite, black hornblende schist, siliceous slate, carbonaceous sericite quartz phyllonite, sericite chlorite phyllite and ash mixed color conglomerate. The deposit is controlled by Kunlun central large fault and NW-trending structure in the mining area, with well developed basic dykes and often accompanied by ore bodies. Orobodies occur as nearly EW, south bending, dip angles between45°～75°differently, and occurrence is consistent with the strata. Ore types are quartz vein type, phyllite type, fracture zone type (oxidation broken fracture zone type, belt type and tectonic altered rock type) and altered rock type. Wall rock alterations are silicification, sericitization, pyritization, chlorite, carbonate rock (calcilization), brass mineralization, kaolin etc. Hydrothermal mineralization periods include four stages:quartz vein silicification stage (Ⅰ), quartz polymetallic sulfide stage (Ⅱ), quartz lean sulphide stage (III) and quartz carbonate (IV).②Asiha gold deposit is hosted in granite diorite-diorite structure fracture zone, controlled by the Kunlun central lagre fault and NNE and NNW-NW trending fault zone in the mining area. Orobodies occur as nearly NNE and NNW-NW, mostly SE to NE, dip angles generally75°. Ore types are altered rock type and quartz vein type (A few). Wall rock alterations are silicification, sericitization, pyritization, chlorite, carbonate rock (calcilization), brass mineralization, kaolin etc.. Hydrothermal mineralization periods include four stages:quartz pyrite arsenopyirite stage (Ⅰ), quartz polymetallic sulfide stage (Ⅱ), quartz sulfide stage (Ⅲ) and quartz carbonate (Ⅳ).3. The study on the geochemical characteristics of Guoluolongwa and Asiha gold deposits shows that:①The metallogenic elements analysis shows:The varied strata and intrusive rock have varied Au content, lower than that of the crustal abundance or similar rocks, namely common dilution, which may provide part of the metal ore. In addition, the factor and cluster analysis show that the different assemblages indicate the diversity of mineralization.②The study on rare earth elements shows:Medium-acid magmatic rock (diorite), acidic magmatic rocks (granite porphyry), Nachitai group metamorphic rocks, ores and gold-bearing pyrite, rare earth elements possess the characters of LREE enrichment and negative Eu anomalies and their distribution patterns are similar. Therefore, Guoluolongwa and Asiha gold deposits may underwent similar mineralization processes with same ore-forming materials source.③The fluid inclusion petrography, microthermometry and component analysis results show that:Fluid inclusions in quartz crystals are well developed in the mineralization period and can be classified into aqueous two-phase, CO2-rich three-phase inclusions and CO2-pure single-phase inclusions. The ore-forming fluids of main mineralizing stage belonged to the H2O-CO2-NaCl-CH4±N2system of medium-high temperature (130～425.6℃), medium-low salinity(1.83to20.1lwt%NaCl.eqv), low density (0.14-1.03g.cm3) which suggests the origin of ore-forming fluid is related with medium-high temperature and medium-low salinity fluids system.④The hydrogen, oxygen isotope test results indicates that:the8D value of water in the ore’s quartz is from-117.7%o to-59.6%o,518OV-SMOW of11.3～19.1‰, calculated hydrothermal fluid result of δ18OH2o2.7～10.7‰. It indicates that the ore-forming fluid is dominated by magmatic water, and mixed with meteoric water.⑤The sulfur isotope test results show that:The δ34S value of the sulfide in Guoluolongwa gold deposit is range from-5.95%o to+5.23%o, and is range from+5.0%o to+7.66%o in Asiha deposit. The sulfur in ore-forming fluids is dominantly acidic magma sulfur and is mixed with seawater’s sulfur.⑥The lead isotope of the ore and sulfide test results in Guoluolongwa and Asiha gold deposits show that:The samples’206Pb/204Pb,207Pb/204Pb and208Pb/204Pb are separately between18.057-18.235,15.524-15.605and37.901-38.321, typical for radiogenic plumbum. In the Zartman R E and Doe B R (1981) plumbum structure diagrams, all samples fall into the mantle evolution and the evolution of an orogenic belt line, and by the evolution of orogenic side of the line, which show that the ore-forming fluids in the plumbum is mainly originated from the ancient crust.⑦Petrology, geochemistry and geochronology of magmatic rock study shows that:Formed in the416.2Ma, Guoluolongwa gold deposit basic dykes belong to the altered strong alkaline basalt series, produced in the proto Tethys ocean subtractive subduction background, and no direct genetic link to Guoluolongwa gold deposit. Asiha gold deposit diorite belongs to high potassium calc alkaline rocks, with crust and mantle mixing characteristics, produced in the oceanic crust subduction environment, rock crystallization age of232.6Ma, which may provide space for ore-forming only as the ore bearing rock. Asiha gold deposit granite porphyry belongs to high potassium calc alkaline peraluminous granite, magma emplaced in the228.5Ma, a little later than Asiha diorite, produced in the mechanical properties transition of late collisional orogenic, orogenic stretch back. Its emplacement may not only provide heat power for mineralization, but also can provide some ore-forming materials. Study on metallogenic chronology shows that:Guoluolongwa and Asiha gold deposits were formed in the210-232Ma, belonging to the Indo Chinese epoch.4. Based on the analysis of ore-forming geological background, geological and geochemical characteristics of typical deposits, reveals the deposit mineralization mechanism:The gold deposits’ore-forming materials of Gouli gold metallogenic district is mainly from the lower crust, also extracting some ore-forming materials from flowing through rock and ore-bearing country rock. The ore-forming fluid is dominated by magmatic water and is partly mixed with meteoric water. The ore-forming fluids belong to the H2O-CO2-NaCl-CH4±N2system, containing N2, CH4and Cl-, SO42-, F,-NO3reducing gas and anion.Gold migrates often in the form of sulfur hydrogen complexes.The Au in Guoluolongwa gold deposit transports in the form of single AuHS(H2S)30, Au(HS)2-or thiosulfate complexes, such as [Au(S2O3)]-,[Au(S2O3)]3-.The Au in Asiha gold deposit is in Au(AsS2)0, Au(AsS3)2-and Au(Sb2S4) and other complex forms. Fluid immiscibility (boiling) is the main precipitation mechanism of ore-forming fluid, and the main driving force is the Indosinian tectonic thermal events.From late Variscan to Indosinian (about210-232Ma), the strong subduction and collision orogenic effect in the study area, not only formed a series of regional faults, large shear zones, folds and faults-fractured level ore control structure, but also promoted the enrichment of ore-forming fluid migration and activation metallogenic material.The large ductile shear zone often changed from toughness to ductile brittle and brittle tectonic environment in the study area, in this process, a large number of various medium acidic magma underwent emplacement generated with the melting or anatexis and accompanied by deep fluid migration, in the process of migration, extracting metamorphic water and atmospheric precipitation and other sources of fluid confluence continuously. When the fluid carrying a lot of ore-forming material intruded into the favorable tectonic area, due to tectonic environment and temperature, pressure and the physical and chemical conditions changed, fluid immiscibility, mixed different properties of fluid and water rock reaction and other factors, prompted the gold material deposition and formed gold deposits.5.On the basis of the analysis of the metallogenic geological background, two typical gold deposits geological-geochemical characteristics, magma petrology, geochemistry and geochronology, through a comparative study of mineral deposit, with detailed evidence, determined the genetic type of gold deposit in the study area are hydrothermal vein type gold deposit in acid formation in the orogenic process, and Indosinian intermediate magmatic rocks related, belongs to the orogenic type gold deposit. Meanwhile, tectonic evolution and metallogenic model of gold deposit in line with local realities are established.