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1、EconomicGeologyVol.95,2000,pp.143–182TheHydrothermalGeochemistryofTungsteninGranitoidEnvironments:I.RelativeSolubilitiesofFerberiteandScheeliteasaFunctionofT,P,pH,andmNaClSCOTTA.WOOD†DepartmentofGeologyandGeologicalEngineering,UniversityofIdaho,Moscow,Idaho83844-3022ANDIAINM.SAMSONDepa
2、rtmentofEarthSciences,UniversityofWindsor,Windsor,Ontario,CanadaN9B3P4AbstractThecharacteristicsofgranitoid-relatedtungstendepositshostedinsiliceous(carbonate-free)rocks(e.g.,Panasqueira,CliggaHead,PastoBueno)arereviewedandtherangesofphysicochemicalparametersoftheore-formingfluidsaresu
3、mmarized.Thetwoimportanttungstenmineralsinthesedepositsarewolframiteandscheelite,whichweredepositedmostlybetween200ºand500ºCand200and1,500bars.Thesalinitiesofthemineralizingfluidsweretypicallylessthan15wtpercentbutcommonlyweresignificantlyhigher(upto55wt%).Thetwopredominantdissolvedcom
4、ponentsareNa+andCl–withsubordinateCa2+,K+,andcarbonatespecies(CO2–/HCO–).ThecontentsofCOarehighlyvariable,butXvaluestypicallyrangefrom0to0.1.332CO2LimitedpHandfOestimatesindicateamoderatelyacidicfluidwithoxygenfugacitiesbetweenthoseofthe2QFMandHMbuffers.Theseparameterswereusedtoguideso
5、lubilityandspeciationmodelingofWinhy-drothermalfluidsingranitoidenvironments.Experimentallyderivedthermodynamicdataforscheelite,ferberite,aqueousCa,Fe,andWspecies,andotherrequiredaqueousspecieswerecriticallyevaluatedandthemostreliabledatawereadopted.Wherenec-essary,missingdatawereestim
6、ated.TheresultantthermodynamicdatabaseprovidesabasisforsolubilityandspeciationcalculationsinthesystemCa-Fe-W-Cl-O-H.ThesimultaneoussolubilitiesofscheeliteandferberiteinNaCl-HCl-H2Osolutionswerecalculatedattemperaturesfrom200ºto600ºC,pressuresfrom500to1,000bars,pHfrom3to6,andmNaClfromto
7、0.1to5.0moles/kgH2O.ThesolubilitymodeltakesaccountofthespeciesH+,OH–,Na+,Cl–,NaCl0,HCl0,NaOH0,HWO0,HWO–,WO2–,Fe2+,FeCl+,FeCl0,FeOH+,FeO0,24442HFeO–,Ca2+,CaCl+,CaCl0,CaOH+,NaHWO0,andNaWO–.Thecalculationsindicatethefollowing:(1)sol-2244ubilitiesofscheeliteand/orferberitecanattainvalues
