ReducingReducing MechanismsMechanisms PotentiallyPotentially InvolvedInvolved inin FormationFormation ofof AthabascaAthabasca BasinBasin UraniumUranium Deposits:Deposits: RelevanceRelevance toto ExplorationExploration

GaryGary YeoYeo1 && EricEric PotterPotter2 1 Corp. 2 Geological Survey of

1 Original Title – this would take a lot more than 20 minutes to cover! ReducingReducing MechanismsMechanisms PotentiallyPotentially InvolvedInvolved inin FormationFormation ofof ‘‘BasinBasin-- RelatedRelated’’ UraniumUranium Deposits:Deposits: RelevanceRelevance toto AthabascaAthabasca BasinBasin

GaryGary YeoYeo1 && EricEric PotterPotter2 1 Denison Mines Corp. 2 Geological Survey of Canada

2 We’re just a couple of geologists

Us geochemists? Narf!

Note that this is not a geochemist’s review of the 3 Athabasca reductant problem 3

TheThe AthabascaAthabasca BasinBasin DepositDeposit ModelModel

 ThreeThree componentscomponents inin thethe conventionalconventional modelmodel forfor AthabascaAthabasca deposits:deposits: 1. At sub-Athabasca unconformity, 2. Associated with reverse faults 3. Associated with graphitic pelites

 QuestionQuestion (Mike(Mike Gunning):Gunning): AreAre graphiticgraphitic pelitespelites essentialessential toto thisthis model?model?

 If Yes: focus exploration along the Key Lake – Rabbit Lake corridor associated with basal Wollaston graphitic pelites; drill conductors  If No: much more of is prospective; deposits not necessarily associated with graphitic pelite conductors 4 From Cuney (2009) 5

HoeveHoeve && SibbaldSibbald (1978)(1978) DiageneticDiagenetic-- HydrothermalHydrothermal ModelModel “…“… oxidizingoxidizing diageneticdiagenetic solutionssolutions…… reactedreacted withwith graphiticgraphitic rocksrocks toto yieldyield reducingreducing solutionssolutions containingcontaining carboncarbon dioxidedioxide andand methanemethane……..

MineralizationMineralization resultedresulted fromfrom interactioninteraction ofof flowsflows ofof methanemethane--bearingbearing reducingreducing solutionssolutions andand ofof oxidizingoxidizing diageneticdiagenetic solutionssolutions carryingcarrying oreore constituentsconstituents……..”” 6 ImportanceImportance ofof GraphiticGraphitic PelitesPelites

 StructuralStructural  Basement graphitic pelites localized Trans-Hudson ductile deformation as well as syn- and post-

Athabasca brittle faulting Athabasca brittle faulting

 PotentialPotential reducingreducing mechanismmechanism

 Graphite, or CH4/CO2 generated from graphite, considered the reductant for U6+ in oxidizing basinal

fluids (Hoeve & Sibbald , 1978; Cuney, 2009; IAEA, fluids (Hoeve & Sibbald, 1978; Cuney , 2009; IAEA, 2009; Belyck, 2010) 2009; Belyck, 2010)  Many recent reviews, however, are (deliberately?) not specific about the reducing mechanism (e.g.,

Jefferson et al., 2007; Kyser & Cuney, 2008; Skirrow et al., 2009; Burrows, 2010) 7

WhyWhy thethe westernwestern WollastonWollaston graphiticgraphitic pelitespelites??

What is special about the Key L – Eagle Point corridor?

8 WhyWhy thethe westernwestern WollastonWollaston graphiticgraphitic pelitespelites?? WollastonWollaston StructuralStructural CrossCross--sectionsection (Tran,(Tran, 2001)2001)

Structurally, Wollaston Domain is a broad synclinorium; hence basal Wollaston strata are structurally elevated along its western extent 9 WhyWhy thethe westernwestern WollastonWollaston graphiticgraphitic pelitespelites?? WollastonWollaston ChronostratigraphyChronostratigraphy

Wollaston Supergroup is a classic foreland basin succession: 1. Starved basin facies: black shales, ironstone, carbonates & marls; 2. Flysch (pelites and psammopelites)

3. Molasse (meta-arkose)

(Yeo & Delaney, 2007)

10 ReducingReducing MechanismsMechanisms suggestedsuggested forfor AthabascaAthabasca depositsdeposits

 CarbonCarbon--basedbased reducingreducing mechanismsmechanisms  Intrabasinal fluid hydrocarbons (Alexandre & Kyser, 2006)

 Basement graphite or graphite-derived CH4 or CO2 (Hoeve & Sibbald, 1978; Wallis et al., 1985; Alexandre et al., 2005)

 InorganicInorganic--basedbased reducingreducing mechanismsmechanisms  H2S from pyrite (Cheney, 1985; Ruzicka, 1993)  Fe2+ from chloritization of biotite or illitization of

hornblende (Wallis et al., 1985; Alexandre et al., 2005)

11 IntrabasinalIntrabasinal hydrocarbonshydrocarbons (fluid(fluid hydrocarbons)hydrocarbons)

 FluidFluid hydrocarbonshydrocarbons consideredconsidered potentialpotential reductantsreductants inin manymany sandstonesandstone--hostedhosted depositsdeposits  South Texas coastal plain (Adams & Smith, 1981)

 Ordos & Tarim basins, China

 Late Cret.-Cenozoic Chu-Sarya & Syr-Darya basins in Kazakhstan (Jaireth et al., 2008) Kazakhstan (Jaireth et al., 2008)  ProterozoicProterozoic hydrocarbonshydrocarbons (from(from 1.541.54 GaGa DouglasDouglas Fm)Fm) commoncommon inin AthabascaAthabasca Basin,Basin, butbut postpost--datedate 1.591.59 GaGa U1U1 mineralizationmineralization (Wilson(Wilson etet al,al, 2007)2007)  Exception: At Dufferin Lake, 1.54 Ga hydrocarbons are intimately associated with 1.54 Ga are intimately associated with 1.54 Ga uranium (Alexandre & Kyser, 2006) 12

BasementBasement--derivedderived hydrocarbons:hydrocarbons:

1.1. CHCH4 oror COCO2 associatedassociated withwith graphiticgraphitic pelitepelite

 CHCH4 stablestable inin CC--CHCH4--HH2OO--COCO2 systemsystem >800C>800C (Price,(Price, 1997)1997)

 SurvivalSurvival ofof prepre--metamorphicmetamorphic CHCH4 inin highhigh--TT metamorphismmetamorphism favouredfavoured by:by:

 Presence of water  High fluid pressure  Closed system

 CouldCould sufficientsufficient CHCH4 survivesurvive metamorphismmetamorphism toto bebe aa significantsignificant reductantreductant??

 IfIf CHCH4 survivedsurvived metamorphism,metamorphism, couldcould itit bebe releasedreleased fromfrom graphitegraphite toto actact asas aa reductantreductant??

13 BasementBasement--derivedderived hydrocarbons:hydrocarbons:

2.2. CHCH4 oror COCO2 derivedderived fromfrom graphiticgraphitic pelitepelite

 CHCH4 andand CO2CO2 potentiallypotentially alsoalso generatedgenerated byby hydrolysishydrolysis ofof graphitegraphite byby basinbasin--derivedderived fluids:fluids: 2C2C ++ 2H2H2OO == CHCH4 +CO+CO2

2H2H2OO +CO+CO2 == CHCH4 +2O+2O 2 13  lowlow δδ CC valuesvalues inin graphitegraphite andand pyrobitumenpyrobitumen atat AthabascaAthabasca depositsdeposits suggestsuggest bitumenbitumen waswas formedformed byby radiolysisradiolysis ofof graphite;graphite; notnot fromfrom CHCH4 ((KyserKyser etet al.,al., 1989)1989)

14 BasementBasement--derivedderived hydrocarbons:hydrocarbons:

2.2. CHCH4 oror COCO2 derivedderived fromfrom graphiticgraphitic pelitepelite

 AtAt McArthurMcArthur River,River, CHCH4 (ca.(ca. 11 mm fromfrom ore)ore) andand CC2 HH6 && COCO2 (ca.(ca. 1010 mm fromfrom ore)ore) werewere interpretedinterpreted toto bebe fromfrom postpost--oreore radiolysisradiolysis ofof CC ((DeromeDerome etet al.,al., 2003)2003)

 KyserKyser etet al.al. (1989)(1989) andand DeromeDerome etet al.al. (2003)(2003) concludedconcluded graphitegraphite andand potentiallypotentially derivedderived hydrocarbonshydrocarbons diddid notnot havehave aa majormajor rolerole inin reducingreducing uranium,uranium, butbut……

15 BasementBasement--derivedderived hydrocarbons:hydrocarbons: 3.3. DirectDirect reductionreduction ofof UU6+ byby graphitegraphite

6+  AlexandreAlexandre etet al.al. (2005)(2005) suggestedsuggested thatthat UU6+ waswas directlydirectly reducedreduced byby radiolysisradiolysis ofof graphite:graphite:

6+ + UU ++ 3H3H2OO ++ 11⁄⁄2C2C →→ UOUO2 ++ 11⁄⁄2CO2CO2 ++ 6H6H

 IfIf thisthis isis thethe case,case, wewe shouldshould commonlycommonly seesee anan intimateintimate associationassociation betweenbetween graphiticgraphitic pelitepelite andand uranium.uranium. DoDo wewe seesee this?this?

16 BasementBasement--derivedderived hydrocarbons:hydrocarbons: 3.3. DirectDirect reductionreduction ofof UU6+ byby graphitegraphite

 LittleLittle oror nono graphiticgraphitic pelitepelite atat RabbitRabbit LakeLake (graphitic(graphitic arkosearkose present),present), EagleEagle Point,Point, RavenRaven--Horseshoe,Horseshoe, CluffCluff Lake,Lake, CentennialCentennial  UraniumUranium moremore stronglystrongly associatedassociated withwith otherother lithologieslithologies atat KeyKey LakeLake && SheaShea CreekCreek  ThisThis suggestssuggests graphitegraphite isis notnot aa directdirect reductantreductant forfor UU6+

17 BasementBasement--derivedderived hydrocarbons:hydrocarbons: 3.3. DirectDirect reductionreduction ofof UU6+ byby graphitegraphite

Key Lake: Deilmann Pit (Harvey, 2007)

•Ore zone restricted to SE Ore zone side of graphitic Graphitic zone pelite •Associated with Key Lake Fault

18 BasementBasement--derivedderived hydrocarbons:hydrocarbons: 3.3. DirectDirect reductionreduction ofof UU6+ byby graphitegraphite

Key Lake: Gartner Pit Graphitic pelites (Wheatley et al, 2006)

•Ore zone mainly SE of graphitic pelites •Associated with Key Lake Fault

19 InorganicInorganic reductants:reductants: HH2SS fromfrom pyritepyrite

H2S from breakdown of pyrite (e.g. pyrite to pyrrhotite) is a potential reductant:

FeS2 + H2 = FeS +H2S

H2S from pyrite suggested as the reductant in:  Boomerang Lake prospect, NWT (Beyer et al., 2010)

 Athabasca deposits (Cheney, 1985)  Wollaston graphitic schists are favourable because they are sulphide-rich (pyritic black shale protolith)

20 InorganicInorganic reductants:reductants: FeFe2+2+ fromfrom pyritepyrite

Fe2+ from oxidation of pyrite is a potential reductant: 2+ 2- + 1. FeS2 +7/202 +H2O = Fe + SO4 +2H

6+ 2+ + 2. U + 5H 2O + 2Fe = UO2 + Fe2O3 + 10H

On reduction of Fe2+ to Fe3+, the latter goes to hematite, but where does the sulphate go?  Aluminium phosphate sulphate minerals? 34  δ34S values of ore zone sulphides at McClean Lake are

comparable to those of basement pyrite, suggesting derivation of ore zone sulphur from basement (Bray et al., 1982)  Ore zone sulphides, however, occur late in paragenetic sequence

21 InorganicInorganic reductants:reductants: FeFe2+2+ fromfrom silicatessilicates FeFe2+ fromfrom chloritizationchloritization ofof biotitebiotite oror illitizationillitization ofof hornblendehornblende isis aa potentialpotential reductantreductant ((AlexandreAlexandre etet al.,al., 2005)2005) ::

+ 2+ + biotite + H + H2O + Mg => chlorite + K + SiO2 + Fe2+ or hornblende + K+ + H+ => illite +Na+ + Ca2+ + Fe2+ + 2+ Mg + SiO2 +H2 O

and then 6+ 2+ + U + 5H2O + 2Fe = UO2 + Fe2O3 + 10H

22 InorganicInorganic reductants:reductants: FeFe2+2+ fromfrom silicatessilicates

• ChloritizationChloritization ofof biotitebiotite resultsresults inin significantsignificant volumevolume lossloss (via(via replacementreplacement ofof KK layerslayers byby Mg(OH)Mg(OH)2 layers;layers; KogureKogure && BanfieldBanfield,, 2000)2000) creatingcreating potentialpotential spacespace forfor anan oreore zonezone

• Chlorite,Chlorite, illiteillite andand hematitehematite alterationalteration typicallytypically closelyclosely associatedassociated withwith primaryprimary uraniumuranium mineralizationmineralization atat AthabascaAthabasca deposits,deposits, bothboth spatiallyspatially andand parageneticallyparagenetically

23 TypicalTypical AthabascaAthabasca sandstonesandstone alterationalteration (Thomas(Thomas etet al.,al., 2006)2006)

24 TypicalTypical AthabascaAthabasca basementbasement alterationalteration (Thomas(Thomas etet al.,al., 2006)2006)

25 AlterationAlteration atat KeyKey LakeLake

Chloritized pelite & pegmatite Ore zone

26 HematiteHematite capcap aboveabove oreore && greygrey chloritechlorite--illiteillite alterationalteration atat RoughriderRoughrider

Hathor Exploration news release 21 Oct., 2010 27 ParagenesisParagenesis:: AthabascaAthabasca BasinBasin (Hiatt(Hiatt && KyserKyser,, 2007)2007)

 MineralsMinerals associatedassociated withwith U1U1 event:event:  Formation of C1/C2 chlorite

(and I1 illite*) is potential Fe2+ source;  H2 hematite (and I1 illite*) is Fe3+

sink

* hornblende => illite + Fe2+; plagioclase + Fe2+ => illite

28 ParagenesisParagenesis:: Athabasca,Athabasca, ThelonThelon && KombolgieKombolgie basinsbasins (Jefferson(Jefferson etet al.,al., 2007)2007) U1 Mineralization

Athabasca U1 mineralization :  Formation of C1/C2 chlorite (& illite?) is potential Fe2+ source; 29  H3/H4 hematite (& illite?) is Fe3+ sink

ConclusionsConclusions

2+  ReducingReducing mechanismsmechanisms involvinginvolving FeFe2+ areare moremore likelylikely thanthan thosethose involvinginvolving graphitegraphite  CloseClose spatialspatial andand parageneticparagenetic associationassociation ofof chlorite,chlorite, illiteillite && hematitehematite alterationalteration withwith oreore suggestssuggests FeFe2+ fromfrom silicates;silicates; notnot pyritepyrite

30 ConclusionsConclusions

 BiotiteBiotite--richrich rocksrocks ((pelitespelites)) areare thethe keykey favourablefavourable lithologylithology forfor localizationlocalization ofof unconformityunconformity--typetype

depositsdeposits  InIn answeranswer toto MikeMike GunningGunning’’ss question:question:  graphitic pelites are not essential to create a chemical trap

 much more of Athabasca Basin is prospective than just the Key L – Rabbit L corridor

 GraphiticGraphitic pelitespelites areare stillstill importantimportant asas controlscontrols onon reactivatedreactivated faultsfaults whichwhich actedacted asas fluidfluid

conduits,conduits, butbut theirtheir presencepresence isis notnot essentialessential

31 ThankThank youyou

… maybe someone in the crowd will take our bait and explain the whole mess for us!

32 ReferencesReferences

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34