dec tanami – north australia project wraps up · provided in-depth knowledge of the geology of...

Tanami – North Australia Project wraps up �

issue 84 Dec 2006

Tanami– North Australia Project wraps upNew datasets reveal geological evolution and mineral systems of North Australian CratonDavid Huston

Asix-yearcollaborativestudyhasproducedmajorchangesinourunderstandingofthegeologicalmake-upandmineralpotentialoftheNorthAustralianCraton.NowavailableonCD-ROMfromGeoscienceAustralia,thisnewwindowintotheevolutionandmetallogenesisofthisimportantregionistheresultoftheTanami–NorthAustraliaNationalGeoscienceAccordProjectinvolvingGeoscienceAustralia,theNorthernTerritoryGeologicalSurvey(NTGS)andtheGeologicalSurveyofWesternAustralia(GSWA).

Extensive collaborationTheNorthAustraliaProjectbeganinJuly2000,whenNTGSgeoscientistsbriefedGeoscienceAustraliageoscientistsonthegeologyoftheAruntaregionduringa10-dayfieldtrip.TheNTGSprovidedin-depthknowledgeofthegeologyoftheareagainedfromregionalandmoredetailedmapping,whileGeoscienceAustraliaaddedspecialistknowledgeingeochronology,geochemistryandmetallogenesis.In2004,theGSWAjoinedtheprojecttomapthe

westernTanamiregion,makingtheNorthAustraliaProjectoneofthefirstNationalGeoscienceAccordprojectstocrossstateboundaries.

ForGeoscienceAustralia,amajorfocusintheprojecthasbeenthecollectionofnewgeochronologicaldata,includingdatatoconstraintheageandcorrelationofsupracrustalvolcanicandsedimentaryunits,felsicandmaficintrusivebodies,andmineraldeposits.Thisprogram,whichinvolvedcollaborationwiththeNTGS,theAustralianNationalUniversityandCurtinUniversity,increasedthegeochronologicaldatabasefortheArunta,TanamiandTennantregionsbyover300dates.Theseregionsnowhavewellover500dates,makingtheNorthAustralianCratononeofthebeststudiedProterozoicprovincesintheworld.Thesedatawillserveasacornerstoneforfuturesynthesisstudiesandprovideabasisfordevelopingexplorationmodels.

AnothersignificantresultwasthecorrelationoftheLander‘package’ofturbiditicsedimentaryrockswiththeTanamiGroup,themajorhostforgoldintheTanami

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Figure 1. MapshowingtheNorthAustralia-TanamiProjectarea.

Tanami – North Australia Project wraps up �

issue 84 Dec 2006

goldprovince.Thecorrelationsuggeststhatpotentialforlode-goldmineralisationextendssouthintothepoorlyexposedwesternandnorthernArunta.ThispotentialhasbeenconfirmedbyTanamiGold’srecentsuccessattheTekapoprospect,whichreturnedanintersectionof16metresgrading3.4g/tAu.

New models for Tanami goldAsecondmajorfocusoftheprojecthasbeentherefinementofgeology,geochronology,geochemistryandcontrolsonlode-goldmineralisationintheTanamiregion.Thisprogram,whichinvolvedclosecollaborationwiththeNTGSandGSWA,extendedregionalgeologicalmappingtoincludestudiesonthefluidhistory,geochemistry,structureandorecontrolsoflode-golddeposits.ThishasledtodescriptivemodelsfordepositsinTheGranites,DeadBullockSoakandTanamigoldfieldsandholisticmodelsofstructural,stratigraphicandgeochemicalcontrolsongoldmineralisation.TheresultshavebeenpublishedinNTGS Report 17andinanupcomingMineralium DepositaspecialissueontheTanamigoldprovince.

Ourgeological,geochronologicalandgeochemicalstudiesoftheTanamiregionhavebeenfollowedupbytheacquisitionof720kilometresoflandseismicdata(figure1)toestablishthearchitectureofthismajorProterozoicgoldprovince.Twomajorconclusionsofthisstudy,tobedescribedinmoredetailinthenextissueofAusGeo News,includetheidentificationofamajorsuturebetweentheTanamiandAileronprovincesandtherecognitionthatmineraldepositsintheregionareassociatedwithmajorcrustpenetrating

shearzonesand/oranticlinalstacks(figure2).Thesuture,whichcorrespondsspatiallytotheWillowragravityridge,hasaclassiccrocodileformandjuxtaposesAileronprovincecrustwithacharacteristicnorth-dippingstructuralgrainagainstTanamicrusttothenorthandwest.AsrocksofthecorrelatedTanami–Landerpackageblanketthissuture,collisionoftheTanamiandAileroncrustisinterpretedtohavehappenedpriorto~1840Ma.

Firmer dates for Tennant magmatismOutsidetheTanamiregion,theprojectundertookworkintheTennantandAruntaregions(figure1).IntheTennantregion,datingoffelsicmagmaticrocks,includinggranitesandporphyries,hasindicatedthattheTennantmagmaticeventwasrestrictedintimetobetween1850and1845Ma.Thisresult,althoughconsistentwithpreviousresultsofCompston(1995),indicatesamuchtighterconstraintontheageofgraniteemplacement.

RecalculationofAr–Arisotopicdatingresultsforore-relatedmuscovitefromCompstonandMcDougall(1994)toaccountforupdatestostandardsanddecayconstantsyieldedagesbetween1850and1845Ma.Thissuggeststhatgold–copper–bismuth(Au–Cu–Bi)mineralisationatTennantCreekcoincidedwithfelsicmagmatismoftheTennantmagmaticevent(figure3).

“majorconclusionsofthisstudy,includetheidentificationofamajorsuturebetweentheTanamiandAileronprovinces”

Figure 2. Seismicdataandinterpretationofline05GA-T1,Tanamiregion,northwesternAustralia.

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Arunta region potentialOneofthefirststudiesundertakenaspartoftheNorthAustraliaProjectwasanassessmentoftheAruntaregionformafic–ultramaficorthomagmaticnickel–copper–platinumgroupelements(Ni–Cu–PGE)mineralisation.InitialresultssuggestedthatthewesternAruntahasmoderatepotentialforVoisey’sBay-typebasalNi–Cusegregations,whereastheeasternAruntahasmoderatepotentialforMerenskyReef-typestrataformPGE-bearingsulphidelayers.Associatedgeochronologicalstudiessuggestthatthemafic–ultramaficbodieswereemplacedduringthreemajorperiods:1811–1803Ma

(duringtheStaffordEvent),1787–1774Ma(duringtheYambahEvent)and1639–1633Ma(duringtheLiebigEvent).Forwardmodellingofpotentialfielddataindicatesthatmanyoftheultramafic–maficintrusionsareunderrelativelyshallowcover.

Toestablishtheoriginandpotentialofsmallbasemetal±golddepositsintheStrangwaysRangesoftheeasternArunta,NTGSandGeoscienceAustraliaundertookasystematicprogramofmappingandsamplingthedeposits.Basedonthosestudies,itwasconcludedthat,aspreviouslyinterpretedbyWarrenandShaw(1985),manyofthedepositswerevolcanic-hostedmassivesulphidedepositsthatformedwithin1810–1801MavolcaniclasticrocksthatweredepositedduringtheStaffordigneousevent.However,severalprospectsassociatedwithmassiveironstonebodies,includingJohnnie’sRewardandpossiblysomeoftheJervoisdeposits,wereinterpretedasironoxide–Cu–AudepositsformedduringtheYambahigneouseventat1795–1780Ma.Inaddition,theOonagalabiCu–Znprospectwasinterpretedasacarbonate-replacementdepositformedduringanInkamullahigneouseventat1760–1740Ma.

Results synthesised for North Australia CratonThefinalaspectoftheprojectwastosynthesiseindividual

Figure 3. Space-timediagramshowingbasinforming,magnetic,structuralandmineralisingeventsintheTanami,AruntaandTennantregionsbetween1870and1680Ma.

Tanami – North Australia Project wraps up �

issue 84 Dec 2006

resultsintoanoverallunderstandingofthegeologicandmetallogenicdevelopmentoftheNorthAustraliaCraton.Theresultsofthissynthesisarepresentedinfigure3.Between~1865and~1800Ma,theTanami–Tennant–Aruntaregionwascharacterisedbythedevelopmentofthreebasinsystemsat~1865–1860Ma,1840–1835Maand1815–1800Ma.AlthoughtheearliestbasinsystemappearstoberestrictedtotheTanamiandTennantregions,thetwolaterbasinphasesarepresentinallregions.Sedimentaryrocksdepositedduringthesecondphasearemostwidespread,makinguplargepartsofallregions.

Allthermotectonicevents—withthepossibleexceptionoftheLiebigevent—intheTanami,TennantandAruntaregionsareassociatedwithsignificantmineralisation.Ironoxide–copper–golddepositsintheTennantCreekandRovergoldfieldsareassociatedwiththeTennantigneouseventat1850–1845Ma.Thesedepositsproducedover5millionouncesofgoldinadditiontosignificantcopper,bismuthandselenium.Theirhighgradeandpolymetalliccharactermakethemattractiveexplorationtargets,particularlyintheRoverfield,whichuntilrecentlyhadnotbeenactivelyexploredforseveraldecades.

ThemajormineralisingeventintheTanamiregionoccurredattheendoftheStaffordeventat1803–1791Ma.Thislode-goldeventproducedaglobalgoldresourceofover12milliontroyounces,andiscurrentlyinterpretedtorelatetotheshiftfromconvergencealongthenorthwestmarginoftheNorthAustraliaCratontoconvergencealongthesouthernmargin.ItislikelythatsmalldiscoveriesinthenorthandwestArunta(Tekapo,DodgerandFalchion–Sabre)areassociatedwiththisevent,andrecentdatingofdeposits(Rasmussenetal2006)inthePineCreekregiontothenorthindicatessimilar(withinerror)butslightlyyoungerages(~1780Ma).

Results publishedTheNorthAustraliaandTanamiprojectshavegeneratedextendeddatasetsthatprovideabetterunderstandingofthegeologicalevolutionandmineralsystemsoftheNorthAustraliaCraton.AcompilationofthesenewdataandresultshasbeenpublishedasGeoscienceAustraliaRecord2006–17(availableonCD-ROM),whileGISdatasetsfortheTanami–northArunta,TennantandsouthAruntaregionsareavailableonDVD.AllproductsareavailablefromtheGeoscienceAustraliaSalesCentreonFreecall1800800173(withinAustralia)or+61262499966(emailmapsales@ga.gov.au).

For more information

phone BruceGoleby+61262499404

email bruce.goleby@ga.gov.auor

phone DavidHuston+61262499577

email david.huston@ga.gov.au

Related articles and websites

EvolutionandmetallogenesisoftheNorthAustralianCratonconferenceabstractsNorthAustraliaProjectresultsandproductswww.ga.gov.au/minerals/research/regional/nap/NAP_results_products.jsp

link

ReferencesCompstonD.1995.TimeconstraintsontheevolutionoftheTennantCreekBlock,northernAustralia.PrecambrianResearch71:315–346.CompstonDandMcDougallI.1994.40Ar-39ArandK-ArageconstraintsontheEarlyProterozoicTennantCreekBlock,northernAustralia,andtheageofitsgolddeposits.AustralianJournalofEarthSciences41:606–616.RasmussenB,SheppardS,&FletcherIR.2006.TestingoredepositmodelsusinginsituU-Pbgeochronologyofhydrothermalmonazite:PaleoproterozoicgoldmineralizationinnorthernAustralia.Geology34:77–80.WarrenRG&ShawRD.1985.VolcanogenicCu-Pb-ZnbodiesingranulitesofthecentralAruntaBlock,centralAustralia.JournalofMetamorphicGeology3:481–499.

“Thesedepositsproducedover5millionouncesofgold”