issue 83 Sept 2006

Catching the nickel boom �

Catchingthe nickel boom

New synthesis will aid nickel explorersDean Hoatson, Subhash Jaireth and Lynton Jaques

InAugust2006,atonneofnickelwaswortharecord$US34750ontheworldmarket,a7.7-foldincreasefrom2001—anastoundingperformancedrivenmainlybytheurbanisationandindustrialisationofChina.Atthatprice,globalstockpilesofnickelhavevirtuallydisappeared,whileexplorationexpenditureandactivityareatall-timehighsasAustralia’snickelindustryexperiencesa‘boomphase’ofunparalleledopportunities.

TosupportAustralianexplorers,GeoscienceAustraliahasjustpublishedNickel sulfide deposits in Australia: characteristics, resources and potential,acomprehensivesynthesisinwhichwereviewthegeologicalsettingsandresourcesofAustralia’snickelsulphidedepositsatanationalscaleandplacetheminaglobalcontextforthefirsttime.Thepapersummarisesthekeyfactorsthatdeterminethefertilityofnickel-bearingmagmaticsystems,withapredictivefocusthatshouldbeofconsiderableinteresttocompaniesexploringfornickeldeposits.

Evolution of Australia’s nickel sulphide industry and global statusThediscoveryofmassivenickel–coppersulphidesatKambaldanearLakeLefroyintheEasternGoldfieldsofWesternAustraliaonthe28January1966heraldedthebeginningofthenickelindustryinAustralia.ThesulphidesatKambaldaassayed8.3%Niand0.5%Cuover2.7metres,andwerehostedbyunusualultramaficigneousrockscalledkomatiites—rocksrichinmagnesium,ironandthemineralolivine.Explorationsince1966hasdefinedatotalresource(totalproductionplusremainingreservesandresources)ofnickelmetalfromsulphideoresofapproximately12.9Mt,andfiveworld-classdeposits(eachcontainingatleast1Mtofnickelmetal).In2006–07,productionfromnickelsulphideandlateritedepositswillreach212000tonnesofnickelandearnaroundA$4.2billioninexportrevenue(ABARE2006),makingAustraliatheworld’sthirdlargestproducerofnickelafterRussiaandCanada.

Morethan90%ofthenation’stotalknownresourcesofnickelmetalfromsulphidedepositsweredefinedduringtherelativelyshortperiodfrom1966to1973,andproductionfrommanykomatiite-

hosteddepositsintheEasternGoldfieldsbeganwithintwoyearsofdiscovery.Australiaisparticularlywellendowedwithworld-classkomatiite-associateddepositsatMtKeith(3.4Mt),Perseverance(2.5Mt),Yakabindie(1.7Mt),Kambaldaregion(1.4Mt),andHoneymoonWell(1Mt),alongwithsmallerhigh-gradedeposits(assaying5–9%Ni)atCosmos,Prospero,Long,SilverSwanandVictor.Incontrast,thenickelresourcesinAustralia’stholeiiticmafic–ultramaficintrusions(containingmoresiliceousigneousrocksthankomatiites)aresubstantiallysmallerthanthoseinthemajorforeigndeposits.

Explorationfornickelsulphideshasbeenveryactivesince2001inmostPrecambrianprovincesofAustralia.RecordnumbersofexplorationcompaniesareactiveinWesternAustralia(morethan170in2006),accountingformorethan90%ofthenation’sNi–CuexplorationbudgetofA$168.1million(ABS2006).ThemainareasofinterestincludeArchaeangreenstonebeltsintheYilgarnCraton(nearKambalda,Leonora,LeinsterandSouthernCross),

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Catching the nickel boom �

thenorthernmarginsofthatcraton,thewesternpartofthePilbaraCraton,andtheProterozoicMusgrave,Kimberley,Albany–FraserandHamersleyprovinces.Recentexplorationsuccessesinclude:

increasedresourcesatpreviouslyknowndeposits(manydepositsnearKambalda,CarnilyaHill,FlyingFoxTZerotoT5,RadioHill,SallyMalay)

delineationofdeepandcoveredmineralisedkomatiitesequences(CosmosDeeps,Prospero,Wedgetail,FlyingFoxT5)

newmineralisedPrecambrianmafic±ultramaficintrusions(Nebo–Babel,Copernicus,BillyRay)

newstylesofmineralisationand/ornewprovinces(Collurabbie,Sinclair,KoolyanobbingNorth,Beasley,andAveburyinwesternTasmania).

Classification of Australia’s nickel sulphide depositsAustralia’snickelsulphidedepositsareassociatedwithultramaficand/ormaficigneousrocksinthreemajorgeotectonicsettings:

Archaeankomatiitesemplacedinriftzonesofgranite–greenstonebelts

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Precambriantholeiiticmafic–ultramaficintrusionsemplacedinriftzonesofArchaeancratonsorProterozoicorogens

hydrothermal-remobilisedoccurrenceswithnoapparentageortectonicconstraints.

Mostdepositscanbeclassified(table1)intotwoorthomagmaticassociationsthatreflectthedominantchemicalaffinitiesofthehostmagma(komatiiticortholeiitic)andathirdassociationthatencompasseshydrothermal-remobilisedmineralisingsystems.ThelargestandmosteconomicallyimportantdepositsareassociatedwithArchaeankomatiiticrocksinthegreenstonebeltsoftheYilgarnCratonofWesternAustralia.Thesedepositsaccountforapproximately82%ofthenation’snickelproduction;minorcontributionscomefromtholeiiticmafic–ultramaficintrusions(~3%)andlaterite(~15%)sources.

Theworld’skomatiite-associatedNi–CudepositsareofspecificArchaeanandProterozoicage,withthelargestformedat~2700Maand~1900Ma(figure1).Incontrast,basalNi–Cusulphidedepositsdonotappeartobeagedependent.Largedeposits/miningcampsassociatedwithcontinentalfloodbasalt(Noril’sk)andastrobleme(Sudbury)eventsappeartohaveaveryrestrictedrepresentationinthegeologicalrecord.The

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Figure 1. Time-nickelsulphidemetallogeniceventplotshowingapproximateagesandrelativesizesofnickelsulphidedepositsandnickelsulphidecamps/provincesintheworld.

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Table 1. ClassificationofAustralia’snickelsulphidedeposits

Association Deposits/prospects Age (Ma) Metal association Ni:Cu

1. Komatiitic 1A.Massiveand/ormatrixsulphidesatbaseofolivinecumulate(peridotite)sequencesinpreferredlavapathways

Kambalda, WAMaggieHays,WACosmos,WA

~2900–2700 Ni-Cu±Au±PGE±Co 7-20

1B.Disseminatedsulphidesincentralpartsofthickolivinecumulate(dunite)sequencesinpreferredlavapathways

Mt Keith, WABlackSwan,WAHoneymoonWell,WA

~2900–2700 Ni-Cu±PGE±Co >20

Other komatiitic depositsSulphidesatbasalcontactofolivinecumulatesequencesassociatedwithcomagmaticfloodbasalts

• Beasley, WA ?2770 Ni-Cu-PGE NA

PGE-enrichedsulphidesassociatedwithkomatiiticandtholeiiticmafic-ultramaficrocks

• Collurabbie, WA ?Daltons,WA

?2900–2700 PGE-Ni-Cu <2

2. Tholeiitic 2A.Massiveanddisseminatedsulphidesinfeederconduitand/ordepressionsalongbasalcontactsofmafic±ultramaficintrusions

Radio Hill, WASallyMalay,WAMtSholl,WANebo-Babel,WA

~2925–2700,~1850,~1080

Ni-Cu-Co±PGE 0.5-7

2B.Stratabounddisseminatedsulphidesnearultramafic-gabbroiczonecontactsofmafic-ultramaficintrusions

Munni Munni, WAWeldRange,WAWindimurra,WA

~2925–2800,?1850

PGE-Cu-Ni <2

2C.Strataboundchromititelayersnearultramafic-gabbroiczonecontactsofultramafic-maficintrusions

Panton, WAEastmansBore,WASaltCreek-Plumridge,WA

~1850,~1300 PGE-Ni-Cu-Au-Cr 5

2D.Discordantbronzititebrecciapipesinmafic-ultramaficintrusions

Carr Boyd Rocks, WA ?2700 Ni-Cu 3

3. Hydrothermal-remobilised 3A.Hydrothermal-remobilised—ultramafichostor?skarn

Avebury, Tas ?360 Ni Ni>>Cu

3B.Hydrothermal-remobilised—metasedimentaryrockhost

Sherlock Bay, WACruickshank,WA

~2925–2700 Ni-Cu 5

Other hydrothermal-remobilised depositsHydrothermal-remobilised—felsic±mafic±ultramaficrockhosts

• Elizabeth Hill, WA?Andover,WA

<2870 Ag-Pb-Ni-Cu±PGE NA

Remobilised-metamorphic—metagabbrohost

• Corkwood, WABowRiver,WA

~1865 Ni-Cu-Co 3

Hydrothermalarsenical-auriferous-bearingquartz-carbonateveins

• Mt Martin, WABamboo,WA

NA Ni-As-Au Ni>>Cu

Typeexamplesofdeposits/prospectsareindicatedinitalics.NA–notavailable

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Catching the nickel boom �

Al-undepletedchemicalaffinities(Al2O3/TiO2=15to25),andformcompoundsheetflowswithinternalpathwaysandduniticcompoundsheetflowfacies.Thepreferredpathways(figure2)assistinfocusinglargevolumesofprimitivemagmaflow(i.e.high-magmafluxenvironments)andfacilitateinteractionofthemagmawithapotentialsulphur-bearingsubstrate.Theidentificationofmagmaticfaciesinkomatiiticsystemsisthereforeimportantforassessingeconomicprospectivity.Thereisconsiderablepotentialforfurtherdiscoveryofkomatiite-hosteddepositsinArchaeangranite–greenstoneterranes,includinglargeandsmallerhigh-gradedeposits(5–9%Ni),thatmaybeenriched(2–5g/t)inplatinum-groupelements(PGE),especiallywherethehostultramaficsequencesarepoorlyexposedundershallowcoveroryoungerbasinalsequences.

Incontrasttokomatiitic-mineralisingsystems,thebroadcriteriaforassessingthenickelprospectivityoftholeiiticmafic±ultramaficintrusionsandtheirprovincesarelessclear.However,asignificantexplorationadvantageforinvestigatingbasalNi–Cu–Cosulphidedeposits(suchasatSallyMalay,RadioHillandNebo–Babel)isthattheycanoccurinsmall-tomedium-sized,sulphur-saturatedmaficbodiesofvariousages.MostPrecambrianprovincesinAustraliaand,inparticular,

agesofAustralia’smajordepositscorrelatewithatleastthreemajorglobal-scalenickelmetallogeniceventsat~3000Ma(3000Mato2875Ma),~2700Ma(2705Mato2690Ma)and~1900Ma(2060Mato1840Ma).Theseeventscorrespondwithmajorperiodsofjuvenilecrustalgrowthandthedevelopmentoflargevolumesofprimitivekomatiiticandtholeiiticmagmas.Theyarethoughttohavebeencausedbymantleoverturneventsassociatedwithmantleplumesorlargersuperplumes(figure1).

Fertile versus barren magmatic systems, and prospectivityAnalysisoftheworld’smajorkomatiiteprovincesrevealsthatthemostfertilekomatiitesequencesaregenerallyoflateArchaean(~2700Ma)orPalaeoproterozoic(~1900Ma)age,havedominantly

Figure 2. Komatiiticmineralisingsystems.Schematicsectionthroughaninflationarykomatiiteflowfieldthatdevelopedthroughsustainederuptionofkomatiite.ThespatialrelationshipsbetweenvariouskomatiitefaciesandtypesofnickelmineralisationareshownfortheMtKeith(sectionA–B),Kambalda(C–D),andBeasley(E–F)typedeposits.ModifiedafterDowling&Hill(1998).

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Catching the nickel boom �

Proterozoicorogenicbelts,containanabundanceoftheseintrusionsthathavenotbeenfullyinvestigated.TheMusgraveProvince,HallsCreekOrogen,Albany–FraserOrogen,AruntaBlock,andwesternpartsoftheYilgarn,PilbaraandGawlercratonsareconsideredthemoreprospectiveprovinces.ThemajorexplorationchallengesforfindingbasalNi–Cu–Cosulphidedepositsaretodeterminethepredeformationalgeometriesandyoungingdirectionsoftheintrusions,andtolocateundercover,favourableenvironments(e.g.,structuralirregularitiesanddepressionsinbasalcontactsandfeederconduits)thatconcentratetheeconomicallyimportantmassivesulphides(figure3).

Hydrothermal-remobilisednickelsulphidedepositshavediversegeologicalsettingsandmetalassociationsthatreflectthedifferentcompositionsofthesourcerocksandfluids.Typically,mosthydrothermaldepositsaresmalltonnageandofloweconomicimportance.TheunusualAveburydepositinwesternTasmaniahasincreasedawarenessofhydrothermal-typetargetsinPhanerozoicprovincesthatwerepreviouslyconsideredtohavelowprospectivity.

AustraliahaslargeareasofArchaeantoPhanerozoiccontinentalfloodbasalts,butno‘Noril’sk-type’Ni–Cu–PGEdepositsassociatedwiththeserockshaveyetbeendiscovered.Hence,thereisalsosomepotentialfortheseunderexploreddepositsinlargeigneousprovinces,suchasthelateArchaeanFortescueGroupbasaltsofthePilbaraCraton,PalaeoproterozoicHartDolerite–CarsonVolcanicsoftheKimberleyBasin,andMesoproterozoicWarakurnadolerites/intrusionsandCambrianKalkarindjibasaltsofwesternandnorthernAustralia.

Figure 3. Tholeiiticandhydrothermalmineralisingsystems.Schematicdistributionoforthomagmaticandhydrothermal-remobilisednickelsulphidedepositsassociatedwiththoleiiticmafic±ultramaficintrusion.

A . Stratabound,basal,anddiscordantNi–Cu–CoandPGE–Ni–Cudepositsinmafic–ultramaficintrusion.Australiandeposits(showninnormaltype)areMunniMunni,RadioHill,MtSholl(westPilbaraCraton);CarrBoydRocks(YilgarnCraton);andPantonandSallyMalay(HallsCreekOrogen).Foreigndeposits(italics)areMerenskyReefandUG–2Chromitite(BushveldComplex,SouthAfrica);J–MReef(StillwaterComplex,USA);MSZ(MainSulphideZone–GreatDyke,Zimbabwe);andJinchuanIntrusion(China).

B . MassiveNi–Cu–Cosulphidedepositsinthefeederconduitofmafic-dominatedintrusion:Nebo–Babel(MusgraveProvince,WA)andVoisey’sBay(Canada).

C . Hydrothermal-remobilisedNi–Cu–±Ag±PGEandothermetaldepositshostedby:serpentinisedultramafic(Avebury),deformedmafic(Corkwood),metasedimentary(SherlockBay,MtMartin),andigneous(ElizabethHill)rocks.

issue 83 Sept 2006

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Catching the nickel boom �

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phone DeanHoatsonon+61262499593email dean.hoatson@ga.gov.au

Related websites/articles

Nickel sulfide deposits in Australia: characteristics, resources and potentialwillappearinOreGeologyReviews,volume29,No.3–4,October2006link www.sciencedirect.com

AusGeo News 79Nickelsulphidemetallogenicprovinces:resourcesandpotentiallink www.ga.gov.au

ResourcesAustralia’snickelendowment(PDF)link www.ga.gov.au

ReferencesABARE(AustralianBureauofAgriculturalandResourceEconomics).2006.AustralianMineralStatistics.ABARE,Junequarter2006,Canberra,339–341.ABS(AustralianBureauofStatistics).2006.MineralandpetroleumexplorationAustralia.8412.0,ABS,Decemberquarter2005(reissue),16March2006.DowlingSE&HillRET.1998.Komatiite-hostednickelsulphidedeposits,Australia.SpecialjubileeissueofAustralianGeologicalSurveyOrganisationJournal17(4):121–127.