Elevated Uranium and Arsenic Concentraons in...
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ElevatedUraniumandArsenicConcentra4onsinBaselineWaterQualityattheCoffeeGold
Project:Implica4onsforGeochemicalPredic4ons
JohnDockrey1,DavidFlather1,LauraFindlater1,ScoJJackson,1JordiHelsen1,JamesScoJ2andJennieGjertsen2
1LoraxEnvironmentalServicesLtd.,Vancouver,Canada2GoldcorpInc.,Vancouver,Canada
24THAnnualBCMENDML/ARDWorkshop
November29-30,2017
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Overview• Elevatedmetal(loid)concentra4onsareoRenobservedinsurfaceand
groundwatersurroundingmineraldeposits– Inves4ga4ngelevatedmetalconcentra4onsinthebaselineenvironmenthas
thepoten4altoinformthegeochemicalcharacteriza4onoflocalbedrock
• ThisapproachhasbeenappliedtotheCoffeeGoldProject,whereelevatedUandAsobservedinbaselinewaterquality.
• Thebehaviouroftheseelementscanbeexplainedbyusingacombina4onoffirstprinciplesanddatacollectedaspartofthegeochemicalcharacteriza4onprogram
• Thisunderstandingofthegeochemicalbaselineenvironmenthasanumberofimplica4onsforsourcetermpredic4onsandminewastemanagementstrategies.
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CoffeeGoldProject:LocaQon
• Located130kmsouthofDawsoninwesternYukon• Theprojectisonthetradi4onalterritoryoftheTr’ondëk
Hwëch’inandtheassertedterritoryoftheWhiteRiverFirstNa4on.
Source:Kaminak2016
200 km
Kaminak
Yukon
Alaska
Operating Mines Advanced Projects
Road
Wolverine Mine
Nucleus
Minto Carmacks Copper
Brewery Creek
Eagle Keno Hill
Rackla
Revenue
White Gold
Casino
LWM
Fort Knox
Livengood
Uncle Sam Pogo
Dawson
Whitehorse
Alaska Yukon
Coffee
Beaver Creek
Mines
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CoffeeGoldProject:MineralizaQon
• Goldmineraliza4onatthesiteishydrothermalinoriginandstructurallycontrolled.
• Structuralweaknessesassociatedwithgoldmineraliza4onhaveallowedforextensivein-situweatheringandoxida4onalongnear-ver4calcorridors.Weatheringhorizonsinclude:
– Oxidezone– Transi4onZone– Fresh(unweathered)zone
• Goldbearingstructurestransectthreedis4nctlithologies:
– Gneiss– Schist– Granite
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020406080100
D-Uµg/L LaJeCreek
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D-Uµg/L CoffeeCreek
SurfaceWaterQualityMonitoring:Uranium
• Naturallyelevateduraniumisobservedinsurfacewater– TypicalsurfacewaterinCanadaisbetween1and3µg/L– Sitemaximarangefrom~30to100µg/L
• Uraniumconcentra4onsareregionallyelevatedasshownbyCoffeeCreek• StrongseasonalitytoUconcentra4ons
020406080100
D-Uµg/L
HalfwayCreek
Latte Creek (70 km2)
Coffee Creek (484 km2)
Yukon River
Proposed Mine Pits
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SurfaceWaterQualityMonitoring:Uranium
• Inverserela4onshipexistsbetweenflowandUconcentra4on.– Highflowcondi4ons(freshet,highrunoff);Surfacewaterflow>>>groundwaterdischarge=low[U]– Lowflowcondi4ons(winter,lowrunoff);Surfacewaterflow<<<groundwaterdischarge=high[U]
• IndicatesthatgroundwateristhedominantsourceofUinthesecatchments
Latte Creek
Coffee Creek
Yukon River
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GroundwaterQualityMonitoring:Uranium
Coffee Creek
Yukon River
Gneiss
Schist
Granite Latte Creek
Proposed Mine Pits
GroundwaterWells
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MW
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GroundwaterQualityMonitoring:Uranium
– Uraniumelevatedinalllithologies,withhighestconcentra4onsingneisswells
– PeakUconcentra4onsarenotadjacenttomineraliza4onzones.
GroundwaterUranium
Coffee Creek
Schist GneissGranite
D-Uµg/L Yukon River
Gneiss
Schist
Granite
– Resultsareconsistentwithsurfacewaterdata,whichindicatedthatsourceofuraniumisgroundwaterseepage
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D-A
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GroundwaterQualityMonitoring:Arsenic
• Arsenicconcentra4onsarealsoelevatedingroundwater– HighestAsconcentra4ons
observedingranitewells– IncontrasttoU,peakAs
concentra4onstendtobeadjacenttomineraliza4onzones.
GroundwaterArsenicSchist GneissGranite
D-Asµg/L
Coffee Creek
Yukon River
Gneiss
Schist
Granite
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ArsenicconcentraQoninrelaQontoflow
• Elevated[As]ingroundwaterdoesnotmanifestashigh[As]insurfacewater• Seasonalsignatureofarsenic:
– HalfwayandCoffeeCreeksshowlowestconcentra4onsduringlowflow– LaJeCreekshowspeakconcentra4onsduringlowflow
• DatashowsthatAsgroundwaterloadisbeingaJenuated.
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Latte Creek
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Yukon River
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KeyQuesQons:
• Whatprocessesleadtothemobiliza4onofarsenicanduraniumingroundwater?
• Whydoesuraniumremainelevatedinsurfacewaterwhilearsenicappearstobea=enuated?
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UraniumEnrichmentinBedrock
Uranium– Slightlyelevatedingneissandgranite(1-5xACA);notelevatedinschist(≤1xACA).– OreshowssimilarlydegreeofUenrichmentaswasterock.– ThelackofsignificantUenrichmentbedrockindicatesthatUmustbepresentinaformthatis
readilysolubleingroundwaterandsurfacewater.
AverageCon4nentalAbundance(ACA)=2.7ppm
1xACA5xACA
WasteRockUranium
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UraniumSolubility
UO2(solid)
UO22+
𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑2−
𝐶𝑎↓2 𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑0
Oxida4on
Increasin
gSolubility
Calcium
Alkalinity
U(4+)
U(6+)
UraniumSolubility– Dependentonoxida4onstateandavailability
ofcomplexingligands
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UraniumSolid-PhaseSpeciaQonResults
• Thetwodominantoxida4onstatesofUintheenvironmentare+4and+6
• XANESmeasuredrela4veabundanceofU(6+)andU(4+)– OxideZone: 90%-100%U(6+)– Transi4onZone: 17%-49%U(6+)
– FreshZone: 27%-67%U(6+)
• Resultsshowthateventhoughtheabundanceislowinbedrock,Uispresentintherela4velysolubleU(6+)oxida4onstatethroughoutthedeposit.
uXRFmicrographofFreshGneissWasteRock(67%U6+,33%U4+)
UO2(solid)
UO22+
𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑2−
𝐶𝑎↓2 𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑0
Oxida4on
Increasin
gSolubility
Calcium
Alkalinity
U(4+)
U(6+)
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MW
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UraniumSolubility:AlkalinityAvailability
• InneutralpHenvironmentsthesolubilityofU(6+)isdependentonCO3availability.
• In-situweatheringhasleadtothedeple4onofsulphurmineralsandtheoxida4onofreducedmineralphases,buthasnotremovedcarbonatecontent.
• ElevatedalkalinityinambientgroundwatersupportsU(6+)leachingandmobility.
GroundwaterAlkalinity
UO2(solid)
UO22+
𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑2−
𝐶𝑎↓2 𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑0
Oxida4on
Increasin
gSolubility
Calcium
U(4+)
U(6+)Alkalinity
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ABAResultsPastepHvs.%CO3
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%UraniumasCa2UO2(CO3)30
UraniumSolubility:ModelledSpeciaQon
• Mobilityof𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑2− cans4llbelimitedbysorp4ontomineralsurfaces.
• Forma4onof 𝐶𝑎↓2 𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑0 ternarycomplexfurtherenhancessolubility.– Calciumisthedominantca4oninmostgroundwater
• GroundwaterchemistrysupportsamajorityofUasternaryCa-U-CO3complex.
• Speciesshouldbeequallysolubleinsurfacewaterandgroundwaterenvironments
GroundwaterCalciumUraniumSpecia4on
UO2(solid)
UO22+
𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑2−
𝐶𝑎↓2 𝑈𝑂↓2 (𝐶𝑂↓3 )↓3↑0
Oxida4on
Increasin
gSolubility
Calcium
Alkalinity
U(4+)
U(6+)
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UraniumSolubility:Summary
• Elevateduraniumconcentra4onsinthebaselineenvironmentcanbeaJributedto:– Enrichmentofuraniumingneissandgranitehostrock– Occurrenceofuraniuminoxidized[U(6+)]state– AlkalineandcalciumrichgroundwaterandsurfacewaterwhichsupportsreleaseandmobilityofU(6+)
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ImplicaQonsforUPredicQonandManagement
– Uraniumreleaseandmobilitywillbeenhancedinminewasteenvironmentswithhighalkalinityandcalciuminporewater.
– Incarbonatebufferedwasterockdumps,alkalinityisinlargepartdeterminedbythepar4alpressureofCO2inporegas.Uraniumleachingwillbeacceleratedinenvironmentswithlimitedgasexchange.
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ity(m
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AtmosphericpCO2
calciteequilibrium
Rela4onshipbetweenalkalinityandpCO2undercalciteequilibrium
LowtempandTD
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HightempandTD
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– Conversely,environmentswhereporegasCO2andCaarenotabletoaccumulatewilllimitUrelease(e.g.,pitwallrock).
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ArsenicEnrichmentinBedrock
Arsenic– Elevatedinallrocktypes,withwasterocktypicallyequaltoorexceeding10xACA– OreissignificantlyenrichedinAs(>1,000ppm)comparedtowasterock
1xACA
10xACA
AverageCon4nentalAbundance(ACA)=1.8ppm
WasteRockArsenic
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ArsenicSolidPhaseSpeciaQon
• XANESanalysisfoundAsprimarilypresentprimarilyAs(+5)andAs(-1)
– OxideZone: 100%As(5+)– Transi4onZone: 91%-100%As(5+)– FreshZone: 20%-59%As(5+)
• As(5+)isassociatedwithFe-oxideandFe-arsenateminerals.
SEM micrograph showing occurrence of arsenian pyrite and arsenopyrite within illite matrix.
As(5+)Aerobic
SuboxicAs(3+)
AnaerobicAs(-1)
Dominantoxida4onstateinhostrock
In-situOxida4on
sulphideminerals
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ArsenicSolubility:RedoxControls
• Groundwaterchemistryshowsthatcondi4onsaresufficientlyreducingtosupportreduc4vedissolu4onofFe-oxideminerals
• Reduc4onofAs(5+)toAs(3+)occursconcomitantlywithFereduc4on.
• ElevatedAsingroundwaterislikelyduetogroundwaterbeingsufficientlyreducingtosupportAs(3+)forma4onandstability
GroundwaterIron
As(5+)Aerobic
SuboxicAs(3+)
AnaerobicAs(-1)
ElevatedD-Feingroundwaterindicatessuboxiccondi4ons
Reduc4on
Dominantoxida4onstateofAsinminerock.
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ElevatedD-Feingroundwaterindicatessuboxiccondi4ons
ArsenicSolubility:A]enuaQonProcesses
As(5+)Aerobic
SuboxicAs(3+)
AnaerobicAs(-1)
AerobicsurfacewatersupportAs(5+)forma4on
• Exposuretoatmosphericoxygenwhenwillresultintheoxida4onofAs(3+)andFe(2+)– As(5+)isreadilysorbedbyironoxide
mineralsurfaces• AerobicmetalleachingtestsshowthatAs
solubilityisrelatedtoFecontentandpH.– Supportsviabilityofsorp4onaJenua4on
mechanism
Whyisarsenicabsentfromsurfacewater?
Oxida4on
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ArsenicSolubilitySummary
• Elevatedarsenicconcentra4onsingroundwatercanbeaJributedto:– Highdegreeofarsenicenrichmentinoreandwasterockaroundthedeposit.
– Occurrenceofarsenicinanoxidizedstatewhichispronetoreduc4vedissolu4oninsuboxicgroundwaterenvironments.
• LowarsenicinsurfacewatercanbeaJributedto:– Oxida4onofD-AsandD-Fewhengroundwaterexposedtoatmosphericoxygen.
– AJenua4onofAs(5+):sorp4onontoFe-oxidesurfaces.
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ImplicaQonsforArsenicPredicQonandManagement
– PlacementofmaterialwithhighAsleachingpoten4alinsaturatedenvironmentsshouldbeavoided.
– StorageofAs-richminewasteinunsaturatedenvironmentispreferred.
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Conclusions
• Analysisofbackgrounddatacaniden4fygeochemicalprocessesoccurringatthefieldscale
• Geochemicalcharacteriza4ontes4ngcanprovidedatato
helpexplainsiteobserva4ons,andprovidedataonhowminingac4vi4eswillmodifyoramplifytheseprocesses.
• Overall,datagainedfromfieldobserva4onsreducesuncertaintyaroundpredic4onofmetalbehaviourinafutureminingenvironmentandincreasesconfidenceinwaterqualitypredic4ons
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QuesQons