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The Characteristics Of Ore-forming Fluid And Genesis Of The Xihuashan Tungsten Deposit In Southern Jiangxi

Posted on:2014-11-04Degree:MasterType:Thesis
Country:ChinaCandidate:T XuFull Text:PDF
GTID:2250330392472840Subject:Mineral reconnaissance and exploration
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Xihuashan tungsten deposit is a famous large quartz-vine type wolframite deposit in SouthernJiangxi Province’China.Tectonic position lies in Caledonian uplift area in south Jiangxi of theCaledonian fold belt of South China.Based on the Pervious researehers and detail field investigation,Inorder to clarify the properties and source of ore fluids,the source of metallogenic material and depositgenesis of Xihuashan,We selected the Xihuashan deposit to conduct the detail study,Foeusing on thegeologieal charaeteristies,fluid inclusions Geochemistry,isotope composition Geochemistry studyetc,The main advance achievements from this study are as followings:(1)The results of study indicate the Xihuashan composite granite had three stage:the first stage islike-porphyritic medium-grained biotite granite,formed at152.6±2.1Ma;the second is themedium-grained biotite granite,formed at150.3±2.2Ma.(2)Three types of Xihuashan tungsten fluid inclusions:NaCl-H2O(I type),NaCl-H2O-CO2(Ⅱtype),pure liquid phase CO2(III type).Then,NaCl-H2O(I type)can also be divede into Threeforms:rich liquid inclusion(I a),pure liquid phase inclusions(I b),rich gas phase inclusions(I c).(3)The NaCl-H2O(I type)temperatures of homogenization of the fluid inclusions varyremarkably from125.8℃to461.1℃, average is249.46℃,The temperatures freezing point ranging from-1.2℃to-17.6℃, peak freezing point temperatures range from-6℃~-9℃; TheNaCl-H2O-CO2(Ⅱtype)temperatures of homogenization of the fluid inclusions vary remarkably from210.9to290.7℃,averageis249.46℃,Mainly in210℃~240℃, the early thawing temperature ranging from-57.6to-56.3℃;Mostof the salinity of the ore-forming fluids concentrated in the7.89%~13.95%NaCl,average is10.73%which belongs to a low-salinity fluid;Ore-forming fluid density range from0.628g/cm3to0.895g/cm3,average is0.795g/cm3;According to the salinity and temperature of fluid inclusions,thepressure and depth can be calculated,being31.7to129.32MPa and3.17to9.47km respectively,averageis respectively64.01MPa,6.45km.Through analysis “fluid inclusion assemblage”,we divide theXihuashan tungsten deposit into two mineralization stages and four hydrothermal activity,of whichformer three stages are metallogenic period hydrothermal activity, formed primary inclusions;whilefollowed one peroids are hydrothermal activived after mineralization,formed secondary inclusions.(4)In the Liquid phase composition,Na+is the highest of cation,Mainly presents thecharacteristics of Na+>K+,the content of Ca2+and Mg2+is very low,The anions is mainly to Cl-,Mainlypresents the characteristics of Cl->SO2-4>F-,and F-content in all samples are lower than Cl-and SO2-4,andthere is a positive correlation exist between the concentration of tungsten and fluorine in the solution,thefluid ion type is approximately Na+-K+Cl-+SO2; The main gas phase composition of fluid inclusions isH2O,followed by CO2,the content of CO,H2and CH4is very low.The fluid inclusions reductionparameter of gaseous components is low,averaging is0.0022,it indicate ore-forming fluid come fromoxidizing environment. (5)The content of REE in fluid inclusions changes Large of Xihuashan tungsten deposit,Mostsamples show rich in LREE,a few rich in HREE,they have similar REE distribution patterns exceptindividual samples,LREE have high fractionating degree than HREE,Most of the samples showednegative δCe and δEu,Ore-forming fluid system under the influence of strata water (ancientseawater).Trace Elements ratio(Mo/W、Th/U、Zr/Hf、Ga/Tl、Co/Ni)of fluid inclusions in quartzof Xihuashan tungsten deposit shows that ore-forming fluid in later low-temperature hydrothermal stageof fluid evolution,Metallogeic material derived from volcanic magma,at the same time some wasleached predominantly from wall-rocks by deeply circulating meteoric water.(6)The H-O-C isotope shows that the ore-forming fluid is mainly from magmatic water,and hasthe low meteoric precipitation,Along with the continuous evolution of the ore-forming fluid,Meteoricprecipitation affected significantly in the later mineralizations stage.The S-Pb isotope shows that themetallogenic material is mainly from granitoid magma of the upper crust,in other words,Magmaticemplacement of upper crust provided some ore-forming materials for mineralization.(7)In Yanshan period,From compressive regime to extensional regime of controlled deposit faultstructure in Xihuashan,all kinds of fault structure up to the shallow of tectonic level,deep watercirculation,Groundwater pumping down from the surface crack and provided channels involved inmineralization,Make the upward migration of magmatic water gradually Joined with a large number ofmeteoric precipitation,Meteoric precipitation with the magma fluid of tungsten mixed prompt fluidsystem oxidation,Lead to PH increase further,temperature,Ligand activity reduced,Break down thecomplex of tungsten stability,Forcing Wolframite deposits.the partial melting degree of upper crustformation rich tungsten granitoid magma,Influence of Tectonism,Magma gradually along with fractureto shallow crust migration,temperature and pressure decrease in the migration process,Prompted acidvolatile nonvolatile and oxygen fugacity rise,complex of tungsten in oxidizing environment,Generatetungsten minerals.With the further evolution of the magma,The medium-grained biotite granite and finegrained mica granite by extensive enrichment of the tungsten,thus formed the main ore-bearing rocks ofXihuashan area.
Keywords/Search Tags:Tungsten deposit, fluid inclusions, isotope composition, ore-forming fluid, Metallogenicmaterial, deposit genesis, Xihuashan
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