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Study On Geological Characteristics And Genesis Of Asiha Gold Deposit,East Kunlun,Qinghai Province

Posted on:2013-08-17Degree:MasterType:Thesis
Country:ChinaCandidate:X ShenFull Text:PDF
GTID:2230330371485272Subject:Mineralogy, petrology, ore deposits
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Asiha gold ore deposit is located in the eastern part of middle uplifted basementand granitic belt, adjacent to the central Kunlun fault. It is a vein-type gold depositsformed in the early Indosinian. The strata outcropped in the mining area is simple, justthe Palaeoproterozoic Jinshuikou group only.The ore bodies are controlled by earlyIndosinian tectonic and magmatic activities. Fault structure is the main structure in themining area,nearly EW trending faults and different grades of secondary faultswidely distributed in the area, while the NNE and NW trending faults are the mainlyore-bearing structures.Intrusive rocks are widely distributed, mainly for the earlyIndosinian granodiorite, diorite batholith and granite stock.Vein rocks mainly forminette.There are more than ten different scales of gold altered fracture (veins) found inthe mining area,1#vein and2#vein are the most important veins, followed by4#vein.1#vein was controlled by the NNE trending left lateral tension-torsional fault,while2#vein was controlled by the NW trending right lateral compression-torsional fault.Ore types can be classified into quartz vein type and structurally altered rocktype,maily of quartz vein type. Ore minerals are pyrite, chalcopyrite, arsenopyrite,galena, native gold, galenobismutite and gustavite, etc. Gangue minerals are quartz,sericite, plagioclase, calcite, chlorite and biotite, etc. Major ore textures are anhedralgranular texture, euhedral-subhedral granular crystal texture, cataclastic texture andmetasomatic texture,etc. Ore structures are mainly disseminated structure, massivestructure, vein structure and net-vein structure,etc. Alteration consists of sericitization, silicification, chloritization and carbonation,etc. Mineralization can be divided intoquartz pyrite arsenopyrite stage, quartz polymetallic sulfide stage and quartzcarbonate stage from early to late.As the ore-bearing wall rocks of Asiha gold deposit, diorite-granodiorite andgranite show the characteristics of pre-collisional(late stage of subduction) activecontinental margin and post-collisional granite through the rock geochemistry studies.The northward subduction and collage effect of Kunlun oceanic crust lead to theunderplating process that makes the mafic magma from the mantle provide hugeamount of thermal dynamic and leads the crustal material to melt,then formlarge-scale granitic rock band in this area. The granitic rocks content low grade ofgold,are not likely to provide the main mineral for the mineralization. The minette isclosely associated with veins in space and it may originate from the metasomaticenriched mantle.We speculate that its tectonic setting is the relative relaxation stage ofcompression converting to extension which is after the continent-continent collisionand orogenesis.This is nearly consistent with the deposit in time and closelyassociated with its genesis.Fluid inclusions of quartz crystals can be classified into aqueous two-phase andCO2-rich three phase. Ore-forming fluids are characterized by low salinities,Low-densities and medium temperatures. The salinities of fluid inclusions range from1.83to8.13wt%NaCl.eqv,the densities of fluid inclusions range from0.69to0.87g/cm3, and the homogenization temperatures of fluid inclusions range from155.3℃to425.6℃. The main gas-phase of fluid inclusions make up of CO2,CH4, N2and H2O, it belongs to the H2O-CO2-N2-CH4system. In Mineralization Stage Ⅰ, fluidinclusions characterize by low salinity, high-temperature, and CO2-rich. InMineralized stage Ⅱ, CO2-rich fluid inclusions and gas-liquid two-phase inclusionscoexist, because of immiscibility or boiling characterized by CO2escaping, whichleads to salinity increasing of the residual fluid. Fluid inclusions in mineralized stageⅢ are the gas-liquid two-phase inclusions.The variation range of δ18O、δDV-SMOW and δ18OH2Oof gold-bearing quartz veinfrom Asiha gold deposit is respectively11.3‰15.1‰,-59.6‰-117.7‰and 2.7‰9.2‰. Hydrogen oxygen isotopes and laster Raman spectroscopy of fluidinclusion research shows that ore-forming fluid of Asiha gold deposit is mainly frommagmatic fluid which contains mantle material and rich in CO2, organic water such asmeteoric water interfused at late ore-forming stage.The δ34S values of pyrites varybetween+5.0‰and+7.4‰, average value is+5.8‰.Both the characteristic of sulfurisotope and the close relationship which lamprophyre dykes and ore vein have inspace show that the metallogenic material is mainly from deep mantle-derivedmagma,which extract metallogenic material from stratum and rocks at the process ofrise and migration.By the genesis study of Asiha gold deposit,the author considers that themineralization may occurs in the transition period from compression to extensiontectonic environment during the intracontinental orogenic movement in the earlyIndosinian, the mineralization phases should be a little later than the emplacementtime of granitoid magma. In the aspect of ore genesis, Asiha gold deposit’scharacteristic is similar to the orogenic gold deposits, the metallotectonic setting isintracontinental orogeny. The genetic type of ore deposit is mesozonal orogenic golddeposit.
Keywords/Search Tags:Fluid inclusion, stable isotope, lithogeochemical characteristics, ore genesis, Asihagold deposit, East Kunlun
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