ElevatedUraniumandArsenicConcentra4onsinBaselineWaterQualityattheCoffeeGold
Project:Implica4onsforGeochemicalPredic4ons
JohnDockrey1,DavidFlather1,LauraFindlater1,ScoJJackson,1JordiHelsen1,JamesScoJ2andJennieGjertsen2
1LoraxEnvironmentalServicesLtd.,Vancouver,Canada2GoldcorpInc.,Vancouver,Canada
24THAnnualBCMENDML/ARDWorkshop
November29-30,2017
Overview• Elevatedmetal(loid)concentra4onsareoRenobservedinsurfaceand
groundwatersurroundingmineraldeposits– Inves4ga4ngelevatedmetalconcentra4onsinthebaselineenvironmenthas
thepoten4altoinformthegeochemicalcharacteriza4onoflocalbedrock
• ThisapproachhasbeenappliedtotheCoffeeGoldProject,whereelevatedUandAsobservedinbaselinewaterquality.
• Thebehaviouroftheseelementscanbeexplainedbyusingacombina4onoffirstprinciplesanddatacollectedaspartofthegeochemicalcharacteriza4onprogram
• Thisunderstandingofthegeochemicalbaselineenvironmenthasanumberofimplica4onsforsourcetermpredic4onsandminewastemanagementstrategies.
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
CoffeeGoldProject:MineralizaQon
• Goldmineraliza4onatthesiteishydrothermalinoriginandstructurallycontrolled.
• Structuralweaknessesassociatedwithgoldmineraliza4onhaveallowedforextensivein-situweatheringandoxida4onalongnear-ver4calcorridors.Weatheringhorizonsinclude:
– Oxidezone– Transi4onZone– Fresh(unweathered)zone
• Goldbearingstructurestransectthreedis4nctlithologies:
– Gneiss– Schist– Granite
020406080100
D-Uµg/L LaJeCreek
0
50
100
2009 2010 2011 2012 2013 2014 2015 2016
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
01020304050
0 2000 4000 6000 8000
D-Uµg/L
FlowL/s
CoffeeCreek
0
10
20
30
40
0 500 1000 1500 2000
D-Uµg/L
LaJeCreek
0
50
100
0 500 1000 1500
D-Uµg/L HalfwayCreek
SurfaceWaterQualityMonitoring:Uranium
• Inverserela4onshipexistsbetweenflowandUconcentra4on.– Highflowcondi4ons(freshet,highrunoff);Surfacewaterflow>>>groundwaterdischarge=low[U]– Lowflowcondi4ons(winter,lowrunoff);Surfacewaterflow<<<groundwaterdischarge=high[U]
• IndicatesthatgroundwateristhedominantsourceofUinthesecatchments
Latte Creek
Coffee Creek
Yukon River
GroundwaterQualityMonitoring:Uranium
Coffee Creek
Yukon River
Gneiss
Schist
Granite Latte Creek
Proposed Mine Pits
GroundwaterWells
MW
14-0
5A
MW
14-0
5B
MW
15-0
5WB
MW
14-0
3A
MW
14-0
3B
MW
14-0
2B
MW
15-0
2WB
MW
15-0
6WB
MW
15-0
4WB
MW
15-0
1WB
D-U
µg/
L
0
100
200
500
600 Granite Schist Gneiss
GroundwaterQualityMonitoring:Uranium
– Uraniumelevatedinalllithologies,withhighestconcentra4onsingneisswells
– PeakUconcentra4onsarenotadjacenttomineraliza4onzones.
GroundwaterUranium
Coffee Creek
Schist GneissGranite
D-Uµg/L Yukon River
Gneiss
Schist
Granite
– Resultsareconsistentwithsurfacewaterdata,whichindicatedthatsourceofuraniumisgroundwaterseepage
MW
14-0
5A
MW
14-0
5B
MW
15-0
5WB
MW
14-0
3A
MW
14-0
3B
MW
14-0
2B
MW
15-0
2WB
MW
15-0
6WB
MW
15-0
4WB
MW
15-0
1WB
D-A
s µg
/L
0
100
200
1500
2000 Granite Schist Gneiss
GroundwaterQualityMonitoring:Arsenic
• Arsenicconcentra4onsarealsoelevatedingroundwater– HighestAsconcentra4ons
observedingranitewells– IncontrasttoU,peakAs
concentra4onstendtobeadjacenttomineraliza4onzones.
GroundwaterArsenicSchist GneissGranite
D-Asµg/L
Coffee Creek
Yukon River
Gneiss
Schist
Granite
0
0.5
1
1.5
0 2000 4000 6000 8000
D-Asµg/L
FlowL/s
CoffeeCreek
ArsenicconcentraQoninrelaQontoflow
• Elevated[As]ingroundwaterdoesnotmanifestashigh[As]insurfacewater• Seasonalsignatureofarsenic:
– HalfwayandCoffeeCreeksshowlowestconcentra4onsduringlowflow– LaJeCreekshowspeakconcentra4onsduringlowflow
• DatashowsthatAsgroundwaterloadisbeingaJenuated.
0
0.5
1
1.5
0 500 1000 1500
D-Asµg/L
HalfwayCreek
0
0.5
1
1.5
0 500 1000 1500 2000
D-Asµg/L LaJeCreek
Latte Creek
Coffee Creek
Yukon River
KeyQuesQons:
• Whatprocessesleadtothemobiliza4onofarsenicanduraniumingroundwater?
• Whydoesuraniumremainelevatedinsurfacewaterwhilearsenicappearstobea=enuated?
Oxi
de
Tran
.
Fres
h
Oxi
de
Tran
.
Fres
h
Oxi
de
Tran
.
Fres
h
U p
pm
0.1
1
10
100 Granite Schist Gneiss
UraniumEnrichmentinBedrock
Uranium– Slightlyelevatedingneissandgranite(1-5xACA);notelevatedinschist(≤1xACA).– OreshowssimilarlydegreeofUenrichmentaswasterock.– ThelackofsignificantUenrichmentbedrockindicatesthatUmustbepresentinaformthatis
readilysolubleingroundwaterandsurfacewater.
AverageCon4nentalAbundance(ACA)=2.7ppm
1xACA5xACA
WasteRockUranium
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
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+)
MW
14-0
5A
MW
14-0
5B
MW
15-0
5WB
MW
14-0
3A
MW
14-0
3B
MW
14-0
2B
MW
15-0
2WB
MW
15-0
6WB
MW
15-0
4WB
MW
15-0
1WB
Alka
linity
mg/
L
0
200
400
600Granite Schist Gneiss
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
Oxi
de
Tran
.
Fres
h
Oxi
de
Tran
.
Fres
h
Oxi
de
Tran
.
Fres
h
Car
bona
te N
P (k
gCaC
O3/t
)
0.1
1
10
100
1000Granite Schist Gneiss
ABAResultsPastepHvs.%CO3
MW
14-0
5A
MW
14-0
5B
MW
15-0
5WB
MW
14-0
3A
MW
14-0
3B
MW
14-0
2B
MW
15-0
2WB
MW
15-0
6WB
MW
15-0
4WB
MW
15-0
1WB
Ca
mg/
L
050
100150200250300 Granite Schist Gneiss
050100150200250300
0%20%40%60%80%100%
Cam
g/L
%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+)
UraniumSolubility:Summary
• Elevateduraniumconcentra4onsinthebaselineenvironmentcanbeaJributedto:– Enrichmentofuraniumingneissandgranitehostrock– Occurrenceofuraniuminoxidized[U(6+)]state– AlkalineandcalciumrichgroundwaterandsurfacewaterwhichsupportsreleaseandmobilityofU(6+)
ImplicaQonsforUPredicQonandManagement
– Uraniumreleaseandmobilitywillbeenhancedinminewasteenvironmentswithhighalkalinityandcalciuminporewater.
– Incarbonatebufferedwasterockdumps,alkalinityisinlargepartdeterminedbythepar4alpressureofCO2inporegas.Uraniumleachingwillbeacceleratedinenvironmentswithlimitedgasexchange.
0
100
200
300
400
500
600
0.0% 0.2% 0.4% 0.6% 0.8% 1.0%
Alkalin
ity(m
gCaC
O3/L)
poregasCO2(%)
AtmosphericpCO2
calciteequilibrium
Rela4onshipbetweenalkalinityandpCO2undercalciteequilibrium
LowtempandTD
S
HightempandTD
S
– Conversely,environmentswhereporegasCO2andCaarenotabletoaccumulatewilllimitUrelease(e.g.,pitwallrock).
Oxi
de
Tran
.
Fres
h
Oxi
de
Tran
.
Fres
h
Oxi
de
Tran
.
Fres
h
As p
pm
1
10
100
1000
10000Granite Schist Gneiss
ArsenicEnrichmentinBedrock
Arsenic– Elevatedinallrocktypes,withwasterocktypicallyequaltoorexceeding10xACA– OreissignificantlyenrichedinAs(>1,000ppm)comparedtowasterock
1xACA
10xACA
AverageCon4nentalAbundance(ACA)=1.8ppm
WasteRockArsenic
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
MW
14-0
5A
MW
14-0
5B
MW
15-0
5WB
MW
14-0
3A
MW
14-0
3B
MW
14-0
2B
MW
15-0
2WB
MW
15-0
6WB
MW
15-0
4WB
MW
15-0
1WB
D-F
e µg
/L
0
4000
8000
12000Granite Schist Gneiss
ArsenicSolubility:RedoxControls
• Groundwaterchemistryshowsthatcondi4onsaresufficientlyreducingtosupportreduc4vedissolu4onofFe-oxideminerals
• Reduc4onofAs(5+)toAs(3+)occursconcomitantlywithFereduc4on.
• ElevatedAsingroundwaterislikelyduetogroundwaterbeingsufficientlyreducingtosupportAs(3+)forma4onandstability
GroundwaterIron
As(5+)Aerobic
SuboxicAs(3+)
AnaerobicAs(-1)
ElevatedD-Feingroundwaterindicatessuboxiccondi4ons
Reduc4on
Dominantoxida4onstateofAsinminerock.
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
ArsenicSolubilitySummary
• Elevatedarsenicconcentra4onsingroundwatercanbeaJributedto:– Highdegreeofarsenicenrichmentinoreandwasterockaroundthedeposit.
– Occurrenceofarsenicinanoxidizedstatewhichispronetoreduc4vedissolu4oninsuboxicgroundwaterenvironments.
• LowarsenicinsurfacewatercanbeaJributedto:– Oxida4onofD-AsandD-Fewhengroundwaterexposedtoatmosphericoxygen.
– AJenua4onofAs(5+):sorp4onontoFe-oxidesurfaces.
ImplicaQonsforArsenicPredicQonandManagement
– PlacementofmaterialwithhighAsleachingpoten4alinsaturatedenvironmentsshouldbeavoided.
– StorageofAs-richminewasteinunsaturatedenvironmentispreferred.
Conclusions
• Analysisofbackgrounddatacaniden4fygeochemicalprocessesoccurringatthefieldscale
• Geochemicalcharacteriza4ontes4ngcanprovidedatato
helpexplainsiteobserva4ons,andprovidedataonhowminingac4vi4eswillmodifyoramplifytheseprocesses.
• Overall,datagainedfromfieldobserva4onsreducesuncertaintyaroundpredic4onofmetalbehaviourinafutureminingenvironmentandincreasesconfidenceinwaterqualitypredic4ons
QuesQons