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

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20

30

40

0 500 1000 1500 2000

D-Uµg/L

LaJeCreek

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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

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3A

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3B

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2B

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2WB

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6WB

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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

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3B

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2B

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2WB

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6WB

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4WB

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15-0

1WB

D-A

s µg

/L

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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?

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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

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2B

MW

15-0

2WB

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15-0

6WB

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15-0

4WB

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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

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Car

bona

te N

P (k

gCaC

O3/t

)

0.1

1

10

100

1000Granite Schist Gneiss

ABAResultsPastepHvs.%CO3

MW

14-0

5A

MW

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5B

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5WB

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3A

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3B

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2B

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6WB

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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

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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).

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As p

pm

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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

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5WB

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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