iron oxide copper-gold

Iron Oxide Copper Gold Deposits

(IOGC)Cory Cunningham

IOCGIOCG

Geologically diverseGeologically diverse– Age, geochemical signature, mineralogy, Age, geochemical signature, mineralogy,

host rocks, local geologic settingshost rocks, local geologic settings Recent recognition of deposit groupRecent recognition of deposit group

– Since Olympic Dam Discovery (1975)Since Olympic Dam Discovery (1975) Globally distributedGlobally distributed Many initial perspectives were falseMany initial perspectives were false

IOCGIOCG

ClassificationClassification Space/Time Global distributionSpace/Time Global distribution Metal Contents and Deposit SizesMetal Contents and Deposit Sizes Significant DistrictsSignificant Districts

– GlobalGlobal– CanadaCanada

ClassificationClassificationCommon Key featuresCommon Key features Presence of Cu +/- AuPresence of Cu +/- Au Hydrothermal vein, Hydrothermal vein,

breccia, and/or breccia, and/or replacement ore replacement ore stylesstyles

Abundant magnetite Abundant magnetite and/or hematite and/or hematite (except where (except where cogenetic deposits cogenetic deposits occur)occur)

Iron oxides with low Iron oxides with low Ti contents compared Ti contents compared to most igneous to most igneous rocksrocks

Absence of clear Absence of clear spatial associations spatial associations with igneous with igneous intrusions (excluding intrusions (excluding deposits directly deposits directly associated with associated with carbonatite carbonatite intrusions)intrusions)

http://gsc.nrcan.gc.ca/mindep/synth_dep/iocg/index_e.php#t1

ClassificationClassificationOther FeaturesOther Features Broad Broad

space/time space/time association with association with batholitic batholitic granitoidsgranitoids

Crustal settings Crustal settings with very with very voluminous and voluminous and alkali alkali metasomatismmetasomatism

Ores enriched in Ores enriched in combinations of combinations of F, P, Co, Ni, As, F, P, Co, Ni, As, Mo, Ag, Ba, LREE Mo, Ag, Ba, LREE and U and U

Ores depleted in Ores depleted in Zn, PbZn, Pb


Spatial DistributionSpatial Distribution

Occurring on all continentsOccurring on all continents Various tectonic settingsVarious tectonic settings

Spatial DistributionSpatial Distribution

Various host rocksVarious host rocks

Time distributionTime distribution

No obvious No obvious time time dependencedependence

Ages poorly Ages poorly constrainedconstrained

Time distributionTime distribution No obvious No obvious

time time dependencedependence

Ages poorly Ages poorly constrainedconstrained

Age relation- Age relation- ships within ships within individual individual provinces are provinces are complexcomplex

Spatial-Temporal Distribution Spatial-Temporal Distribution RelationshipsRelationships

Late Archean CarajLate Archean Carajás province exceptionally Cu-ás province exceptionally Cu-Au richAu rich

Australia and North America host the best Mid Australia and North America host the best Mid Proterozic SystemsProterozic Systems

Mid to late Paleozoic IOCG provinces occur mainly Mid to late Paleozoic IOCG provinces occur mainly along the Altaid-related belts in central to west along the Altaid-related belts in central to west asiaasia

Large numbers of Mesozoic-Cenozoic Cu +/- Au Large numbers of Mesozoic-Cenozoic Cu +/- Au deposits along the east coast of China, the deposits along the east coast of China, the American Cordillera and Eastern United StatesAmerican Cordillera and Eastern United States

Cenezoic IOCG-affinity systems are best known Cenezoic IOCG-affinity systems are best known for their Fe production or Fe potentialfor their Fe production or Fe potential

Metal Contents and Deposit Metal Contents and Deposit SizesSizes

Largest IOCG Largest IOCG systems contain systems contain more than 1 Gt of more than 1 Gt of Fe/Cu-Au oreFe/Cu-Au ore

Significant Significant accessory element accessory element quantities as well quantities as well (P, REE, Co, Ag and (P, REE, Co, Ag and U)U)

Usually full suites Usually full suites of chemical data of chemical data do not occurdo not occur

Fe and Cu typically Fe and Cu typically do not occur do not occur togethertogether




Iron ore Iron ore depositsdeposits

Copper ore Copper ore depositsdeposits

Fe gradesFe grades Average Average between 30 between 30 and 70 wt %and 70 wt %

Average Average between 15 between 15 and 25 wt %and 25 wt %

Cu gradesCu grades May be up to May be up to 0.1 wt %0.1 wt %

Average Average between 0.5 between 0.5 and 4 wt %and 4 wt %

Cu/FeCu/Fe ~1/500 to ~1/500 to 1/501/50

~1/15~1/15

Cu/AgCu/Ag N/AN/A Within a Within a factor of 5 of factor of 5 of crustal valuescrustal values

Copper ore deposits Copper ore deposits may contain may contain significant amounts significant amounts of Fe, but do not of Fe, but do not coincide with the Cu coincide with the Cu orebodiesorebodies

Cu grades may form Cu grades may form an approximate an approximate continuum between continuum between deposit typesdeposit types

Deposit type often Deposit type often controlled by metal controlled by metal of interestof interest

MineralogyMineralogy


MineralogyMineralogy

Alteration zones characteristic of Alteration zones characteristic of IOCG depositsIOCG deposits– 3 types:3 types:

Calc-sodicCalc-sodic– Regional in scaleRegional in scale– Usually preceed further alterationUsually preceed further alteration

IronIron– Influx of magnetite +/- biotiteInflux of magnetite +/- biotite

PotassicPotassic– Ore stage is associated with potassium-iron Ore stage is associated with potassium-iron

alterationalteration

TexturesTextures

Considerable Considerable variationvariation– Best to look at Best to look at

individual examplesindividual examples

Significant DistrictsSignificant Districts

In General:In General:►Highly variable in age, composition, Highly variable in age, composition,

size, alteration associations, host size, alteration associations, host rocks, mineralization associations, rocks, mineralization associations, geochemical signature, and physical geochemical signature, and physical properties – More so than other classes properties – More so than other classes of hydrothermal oresof hydrothermal ores

Significant DistrictsSignificant DistrictsExamples of deposits in Examples of deposits in

significant districtssignificant districts

► Salobo (Archean)Salobo (Archean) CarajCarajás district in Brazilás district in Brazil

► Ernest Henry Ernest Henry (Proterozoic)(Proterozoic) Concurry district of Concurry district of

AustraliaAustralia► Olympic Dam Olympic Dam

(Proterozoic)(Proterozoic) Gawler craton of South Gawler craton of South

AustraliaAustralia► Candelaria-Punta Candelaria-Punta

(Mesozoic)(Mesozoic) Coastal belt of ChileCoastal belt of Chile

► Manto Verde (Mesozoic)Manto Verde (Mesozoic) Chile coastal beltChile coastal belt

► Raul-Condestable Raul-Condestable (Mesozoic)(Mesozoic) Peru coastal beltPeru coastal belt

Carajas DistrictCarajas District

CarajCarajás district - Saloboás district - Salobo

SaloboSalobo► ArcheanArchean► Very low sulphur, magnetite-dominated systemVery low sulphur, magnetite-dominated system

CarajCarajás district - Saloboás district - Salobo► Salobo group is intruded by young and old graniteSalobo group is intruded by young and old granite► Various dating methods imply primary mineralization occurring about Various dating methods imply primary mineralization occurring about

the time of emplacement of the old granitethe time of emplacement of the old granite► Principle hosts are exceptionally Fe enriched rocks composed of:Principle hosts are exceptionally Fe enriched rocks composed of:

Magnetite, fayalite, Fe-rich amphiboles, almandine, and biotite Magnetite, fayalite, Fe-rich amphiboles, almandine, and biotite containing some disseminated copper sulfides. containing some disseminated copper sulfides.

CarajCarajás district - Saloboás district - Salobo

► Other deposits in the Other deposits in the CarajCarajás district show ás district show many aspects of variation from the Salobomany aspects of variation from the Salobo

Cloncurry DistrictCloncurry District

Cloncurry districtCloncurry district

► IOCG Deposits occur in two IOCG Deposits occur in two major supracrustal major supracrustal deformed and deformed and metamorphosed metamorphosed sequences: cover sequence sequences: cover sequence 2 and cover sequence 3.2 and cover sequence 3.

► Stratabound, breccia or Stratabound, breccia or fault controlledfault controlled

► Potassic alterationPotassic alteration► Many different metals Many different metals

occuring, such as Cu, Ag, occuring, such as Cu, Ag, Au, Bi, Co, WAu, Bi, Co, W

► epigeneticepigenetic

Cloncurry district – Ernest Cloncurry district – Ernest HenryHenry

►Most resourceful of the IOCG deposits Most resourceful of the IOCG deposits in the Cloncurry districtin the Cloncurry district

►Breccia-hostedBreccia-hosted►Magnetite dominatedMagnetite dominated►Strongly altered basic to felsic Strongly altered basic to felsic

metavolcanic rocks metavolcanic rocks ►Structural deformation in the vicinity Structural deformation in the vicinity

of the deposit.of the deposit.

Cloncurry district – Ernest Cloncurry district – Ernest HenryHenry

Concurry district – Concurry district – Earnest HenryEarnest Henry

► The complexity and degree of alteration The complexity and degree of alteration is a result of mutiple stagesis a result of mutiple stages Sodic and/or sodic calcic alteration Sodic and/or sodic calcic alteration

affecting the entire regionaffecting the entire region Premineralization, spatially associated Premineralization, spatially associated

with the deposit, in veins with K-, Fe-, and with the deposit, in veins with K-, Fe-, and Mn- bearing mineralsMn- bearing minerals

Mineralization associated with a strong Mineralization associated with a strong brecciation eventbrecciation event

► Display a range of texturesDisplay a range of textures► Contain imbricated elliptical clasts, Contain imbricated elliptical clasts,

suggesting formation in a brittle-ductile suggesting formation in a brittle-ductile regimeregime

► Significant matrix gangue minerals include Significant matrix gangue minerals include calcite, quartz, biotite, garnet, and chloritecalcite, quartz, biotite, garnet, and chlorite

► Chalcopyrite and native Au are the only Chalcopyrite and native Au are the only significant ore mineralssignificant ore minerals

PostmineralizationPostmineralization

Gawler craton, Gawler craton, AustraliaAustralia

► Contains the Giant Contains the Giant Olympic Dam Cu-Olympic Dam Cu-Au-U deposit.Au-U deposit.

► IOGC deposits in IOGC deposits in this district are this district are similar in age to similar in age to their host rock and their host rock and appear to be appear to be emplaced at emplaced at shallow crustal shallow crustal levelslevels

Olympic damOlympic dam

Olympic DamOlympic Dam

► ProterozoicProterozoic► Hematite dominated (also some magnetite as Hematite dominated (also some magnetite as

well)well)► 3, 810 Mt of global resource3, 810 Mt of global resource

1.0 wt % Cu1.0 wt % Cu 0.5 g/t Au0.5 g/t Au 400 g/t U400 g/t U33OO88

Significant source of Ag, F, Ba and LREESignificant source of Ag, F, Ba and LREE

► Deposit is within a Brecciated and altered Deposit is within a Brecciated and altered rock within a single graniterock within a single granite

Olympic damOlympic dam► Pipe-like barren Pipe-like barren

hematite quartz hematite quartz breccia in the corebreccia in the core

► Surrounded by Surrounded by progressively complex progressively complex zone of heterogeneous zone of heterogeneous multiphase breccia and multiphase breccia and hematized granitehematized granite

► Hematite rich breccias Hematite rich breccias host most of the orehost most of the ore They are mostly matrix They are mostly matrix

supported with clasts in supported with clasts in the order of 20 cm, the order of 20 cm, however some may be however some may be tens of meterstens of meters

Olympic damOlympic dam

► Alteration is mostly Alteration is mostly sericite-hematitesericite-hematite

► Uranium is closely Uranium is closely related to Cu, and related to Cu, and occurs as fine-occurs as fine-grained to grained to amorphous uraniteamorphous uranite

► High Cu grades High Cu grades occur close to the occur close to the bornite-chalcopyrite bornite-chalcopyrite interfaceinterface

Olympic DamOlympic Dam

►Fluid Inclusions associated with Fluid Inclusions associated with paragenetically early magnetic, pyrite paragenetically early magnetic, pyrite and siderite indicate higher and siderite indicate higher temperatures of formation than main-temperatures of formation than main-phase mineralization (400-500 Celsius)phase mineralization (400-500 Celsius)

►Main phase mineralization was from Main phase mineralization was from cooler fluids with variable salinitycooler fluids with variable salinity

►Nd isotope data suggest a mantle Nd isotope data suggest a mantle component of REE in the orecomponent of REE in the ore

IOCG deposits in CanadaIOCG deposits in Canada

► Relatively recent exploration programRelatively recent exploration program

IOCG deposits in CanadaIOCG deposits in Canada► NICO - 42 Mt Co-Au-BiNICO - 42 Mt Co-Au-Bi► Sue-Dianne - 17 Mt Cu-AgSue-Dianne - 17 Mt Cu-Ag

Directions for further Directions for further researchresearch

►Genetic modelGenetic model►Sources of ore and fluidsSources of ore and fluids►Understanding variations within IOCG Understanding variations within IOCG

classclass►ExplorationExploration

QuestionsQuestions

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iron oxide copper-gold

Documents

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