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介绍热液沉积

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介绍 热液 沉积
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IntroductiontoHydrothermalDeposits„Sourcesofhydrothermalfluids„Transportofhydrothermalfluids„Solutionandprecipitationofmetals„Paragenesis„Fluid-rockinteraction:alterationFormationofconnatewatersWhatdriveshydrothermalfluidsthroughchannelsandrocks?1.Upwardflowofwarm/hotjuvenilefluids2.Convectionofgroundwatercausedbyheatingbymagmaticintrusion3.ExpulsionofconnatewatersduetoincreaseinlithostaticPandcompactionofburiedsediments4.Sinkingofdensesalinefluids5.Differenceinhydrostaticheadbetweensourceandoutletofanaquifer6.Tectonicallydrivenflow–faultmovementFlowinresponsetothecreationofhydrostaticheadinanareaofuplift.Flowinresponsetorockcompactioninafoldandthrustbelt.Thermallydrivenflowinresponsetohighheatflowatmid-oceanridges.Flowinresponsetofaultmovements.HydraulicConductivity=Theextenttowhichagivensubstanceallowswatertoflowthroughit,determinedbysuchfactorsassortingandgrainsizeandshape.ηρgNdKf2=N=dimensionlessfactordependingonshapeofporespacesd=meangraindiameterg=accelerationduetogravityρf=fluiddensityη=fluidviscositySolubilityofmetals„“theupperlimittotheamountofdissolvedmetalthatahydrothermalfluidcantransport”„Mostmetals/mineralsarenotparticularlysolubleinpurewater„Needtoincreasesolubility–Temperature–Pressure–CompositionTemperatureLigandsHS-I-CN-H2SS2O32-Cl-Br-NH3OH-F-NO3-HCO3-CH3COO-CO32-SO42-PO44-SoftLigandsBorderlineHardLigandsAu+Ag+Cu+Hg2+Cd2+Sn2+Pt2+Pd2+Au3+Tl3+DivalenttransitionmetalsZn2+Pb2+Fe2+etc.Li+Na+K+Rb+Cs+Be2+Sr2+Ba2+Fe3+Ce4+Sn4+Mo4+W4+V4+Mn4+As5+Sb5+U6+SoftMetalsBorderlineHardMetalsDepositionofmetalsfromhydrothermalfluidsMaincontrols:1.Temperaturechange2.Pressurechange3.Chemicalchange:–Reactionwithhostrocks–MixingofsolutionsPrecipitationduetochangeincomposition„Metal-chloridecomplexes:increasepH:CaCO3(solid)+2H+ÙCa2++H2CO3(aq)ZnCln2-n+H2S(aq)ÙZnS(solid)+2H++nCl„Metal-sulfidecomplexes:decreasepH:Zn(HS)3-+4O2(aq)ÙZnS(solid)+3H++2SO42-ParagenesisofSnandWores,BoliviaGuilbert&Park,1986Chalcopyrite,qtz,phyllicalterationCuMolybdenite,huebnerite,scheelite,cassiterite,qtz,potassicalterationMo-W-SnCinnabar,chalcedony,qtz,bar,fluor,carbonatesHgStibnite,qtzSbGold,electrum,acanthite,qtz,chalcedony,adularia,alunite,carbonates,silicification,somepotassic,phyllicandpropyliticalterationAu-AgPotassicalteration,anhydrite,carbonatemineralsBarrenDeep(hypothermal)Chalcopyrite,tennantite-tetrahedrite,qtz,phyllic,propylitic,argillicalterationCu-As-SbSphalerite,qtzw/occasionalcarbonates,advancedargillicargillicZnGalena,qtzw/minorcarbonatemineralsPbIntermediate(mesothermal)Acanthite,rhodochrosite,qtz,carbonates,somephyllic,argillic,propyliticalterationAg-MnQtzandcarbonatemineralsBarrenChalcedony,qtz,barite,fluorite,carbonatemineralsBarrenSurface(epthermal)OreMineralogyandrelatedalterationassemblagesMetalVeinAlterationreactions„Hydrolysis„Hydration-dehydration„Alkalioralkali-earthmetasomatism„Decarbonation„Silication„Silification„Oxidation-reduction„Andsomeothers……..Controlsonnatureofalteration„Temperature„Pressue„Hostrockcomposition„Fluidcomposition„Fluid/rockratioAlterationTypes1.Potassic2.Phyllic(sericitic)3.Propylitic4.Argillic5.Silication6.Silification7.Carbonization8.HematitizationEvans,2001Potassic(K-silicate)„HighT(500–600oC)alterationassemblage„FormationofnewK-sparand/orbiotite„Minorsericite,chloriteandquartz„K+(cation)metasomatism+hydrolysisPhyllic(sericitic)„Verycommoninhydrothermaldeposits„Widerangeoftemperatures„Hydrolysisoffeldsparstoformsericite„Minorquartz,chlorite,pyriteKAlSi3O8+2H+ÙKAl3Si3O10(OH)2+6SiO2+2K+(K-feld)(musc)(qtz)Propylitic„Chlorite,epidote(greenschistassemblage)„Minorclinozoisite,calcite,zoisiteandalbite„Low-intermediateT(200–350oC)„Lowfluid/rockratio„H+metasomatismArgillic/AdvancedargillicArgillic„kaolinite,montmorillonite„LowT(<250oC)„H+metasomatismAdvancedArgillic„kaolinite,pyrophyllite/dickite,alunite„Minorquartz,topaz,tourmaline„Extremebaseleachingbyacidicfluids„Highfluid/rockratioKAlSi3O8+2H+ÙKAl3Si3O10(OH)2+6SiO2+2K+(k-feld)(musc)(qtz)2KAl3Si3O10(OH)2+2H++3H2OÙ3Al2Si2O5(OH)4+2K+(musc)(kaol)Evans,2001Silication„Conversionofcarbonatetosilicate„Cationmetasomatism„Highfluid/rockratio„TypicalofprogradestageinskarnformationSilicification„Formationofnewquartz/amorphoussilica„H+hydrolysisproduct„CationmetasomatismCarbonization„Formationofcarbonateminerals(calcite,dolomite,magnesite,sideriteetc.)„Associatedwithquartz,muscovite,biotite,albiteandchlorite„FluidswithhighPCo2,neutral-alkalinepHHematitization„Oxidizingfluids„FormationofmineralswithhighFe3+/Fe2+e.g.hematite„Assocwithk-spar,sericite,chloriteandepidote
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