Groundwater Geochemistry In TheKoongarraoredeposit

8/8/2019 Groundwater Geochemistry In TheKoongarraoredeposit

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Geochemicalournal,Vol. 29,pp. 1 to 29, l995

Groundwatereochemistryin theKoongarraoredeposit,Australia(I):Implicationsforuraniummigration

NOBUYUKIYANASE,1TIMOTHY E.PAYNE2andKEIICHISEKINE11Eenvironmentaleochemistryaboratory,Japan AtomicEnergyResearchInstitute,Tokai-mura,Ibaraki319-11,Japan

2EnvironmentalcienceProgram,AustralianNuclearScience&Technologyrganisation,NewIllawarraRoad,LucasHeights,NSW 2234,Australia

(ReceivedFebruary25,1994;AcceptedSeptember9, 1994)

Groundwatereochemistryatthe Koongarrauraniumoredepositwasinvestigatedin orderto gain adetailedunderstandingofthemigrationofuraniumin ahighlyweatheredwaterrocksystem. Koongarragroundwatersare quitedilutewiththe totaldissolvedsolidsusuallybelow200 mg/l. The pH is slightlyacidicorneutral,and the majorchemicalcharacteristicsaredominatedbymagnesiumand bicarbonatePartialpressuresofCO2 in the deepergroundwatersaresubstantiallyelevatedrelativeto those ofsurfacewatersGroundwaterin themineralizedzonesexhibitselevatedlevels ofuraniumup to three orders ofmagnitudebovebackgroundevels. Totalorganiccarbonlevelsaregenerallylow,suggestingthaturaniumcomplexationy organicspeciesplaysaminorrole. Due to thehighbicarbonateoncentration,uraniumappearsto bemobilein theweatheredzone as uranylcarbonatecomplexes Otherinorganicuraniumcomplexantsre notpresentatlevelssufficienttoinfluenceuraniumspeciation,withthepossibleexceptionof phosphateOn the basis ofchemicaland isotopicevidence,there aretwo majorinputs ofgroundwatero the

system. The first of these is flowsfrom thevicinityof the Koongarrafault into theCahillformation,whichhosts theuraniummineralization A secondmajorsource is infiltratingwaterswhichpermeatedownwardromthe surface,andcausea gradualmixinganddilutionofthecharacteristicsofgroundwatersfromthemineralizedzone. The migrationofuranium in groundwateris not onlyperpendicularto thefault,butincludesacomponentat an angleto it. In the vicinityofborehole Cl (due south of the orezone),uraniumconcentrationsre comparativelyigh,giventhedistancefromtheorebody Movingawayfrom the orezonetothe south-east,there is agradualdecreaseofgroundwaterraniumoncentrationsobackgroundlevelsoverapproximately00 meters,whichcoincideswiththeuraniumdistributionin thesolid phase. Therefore,atKoongarra,uraniumseemsto havemigratedover distancesofapproximately200m towardthe south-eastoveratimeperiodestimatedto be 1 to 1.5 millionyears.


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Groundwater Geochemistry In TheKoongarraoredeposit

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