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IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND MAGMATIC HYDROTHERMAL ORIGIN

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Page 1: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

IOCG DEPOSITS

DEFINITION, NATURE, TECTONIC

SETTING AND MAGMATIC

HYDROTHERMAL ORIGIN

Page 2: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

• Extreme confusion in literature as defined

• Some have no significant Cu nor Au• Vary over several orders of magnitude

WHAT ARE IRON OXIDE COPPER-

GOLD DEPOSITS?

• Vary over several orders of magnitude in Cu and Au grade

• Have non-consistent timing and tectonic setting

• Clearly not a coherent genetic group

Page 3: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

Age(Ma)

EARLYPROTEROZOIC

ARCHEAN

Pea Ridge

Malmberget

IRON-OXIDE ASSOCIATED DEPOSITS: SIZE AND AGEFrom Williams et al. (2005)

Kiruna

Olympic Dam

Vergenoeg

Alemao SossegoSalobo

Cristalino

1500

2000

2500

3000

Cu

Maincommodity

Fe

Reported resource (Mt)Candelaria

KorshunovskoeSarbai

ChimiwungoGole Gohar

Kalengwa

Khetri

IronSprings

Ernest HenryBenson Mines

Kacharskoe

Marcona

Sokolovkoe combinedLATE PROTEROZOIC

MIDDLEPROTEROZOIC

PALEOZOIC

MESOZOIC &CENOZOIC

Pea Ridge

200015001000500 2500 30000

500

1000

1500

Page 4: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

IOCG deposits:

Geko

IRON-OXIDE ASSOCIATED DEPOSITS: SIZE VS COPPER GRAD EFrom Williams et al. (2005)

StarraSantos

Punta del CobreDistrict

ErnestHenry

Candelaria

%C

u

Cristalino

GrasbergGrasbergGrasbergGrasberg

OlympicDam

BinghamBinghamBinghamBinghamSalobo

Manto Verde (oxide)

1

10

IOCG deposits:main commodity

Porphyry Cu deposits

CuFe

Key depositsCu-(Au-Mo)Calc-alkaline

Cu-Au alkaline

Au-Cu dioritic

Reported resource (Mt)

%

Goroblagadot

Cornwall

Marcona

Kacharoe

10,0001,0001001010.1.01

0.1

0.1 Mt

1 Mt

10 Mt

Page 5: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

• Cu + Au as economic metals (NOT simply Fe deposits)

• Hydrothermal characteristics and structural controls: breccias common

DEFINITION OF IOCG SENSU STRICTO

structural controls: breccias common• Abundant low-Ti Fe oxides

(magnetite, hematite) and/or Fe silicates (grunerite, Fe actinolite) and/or Fe carbonates (siderite)

Page 6: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

• REE enrichment and low-S sulfides(NOT pyrite deposits as for most other hydrothermal Cu-Au deposits)

• Syn-sulfide quartz veins and SiO2 alteration absent to rare

DEFINITION OF IOCG SENSU STRICTO

alteration absent to rare• Temporal relationship to magmatism

(commonly alkaline to sub-alkaline) but no spatial relationship to causative intrusions

Page 7: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

GROUPING OF IRON-OXIDE ASSOCIATED DEPOSITS INTO SUB GROUPS

Age

Cenozoic El Laco Iron SpringsCerro de MercadoCortez, Yerington

Mesozoic Chilean Iron Belt CandelariaManto Verde

MarconaPampa de PongoRaul CondestableHangkowCornwall, GraceKorshunovsk, Tagar

Paleozoic Kachar, Sarbai, SokolovskTeyskoe, AmpalyskoeTashtagolMagnitogorsk

Subgroup 1Iron-oxide (P)

Subgroup 3IOCG

sensu stricto

Subgroup 4Skarn

Subgroup 5High-grade

Au (Cu)

Subgroup 2Iron-oxidelithophileelements

MagnitogorskGoroblagodat, PerschanskChogart

Neoproterozoic Kasempa Jabal IsasMesoproterozoic Benson Mines

Pea RidgeBayan Obo Olympic Dam

AcropolisErnest Henry(Boss-Bixby 70mt)SinghbhumO’okiep

(Dover 26mt)(Osborne 11mt)

StarraTick Hill

Paleoproterozoic KirunaMalmbergetSvappavaara

Vergenoeg Palabora Grangesberg WarregoNobels NobWhite DevilPeko

Neoarchean SaloboCristalinoSossego-SequerinhoAlemao-Igarape Bahia

Page 8: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

TONNAGE, GRADE AND AGE OF IOCG SENSU -STRICTO DEPOSITS >100MT

Province

Coastal Cordillera CandelariaManto Verde

470230

1.070.55

0.220.11

ca 115 Maca 115 Ma

Rajasthan KhetriOthers

140140

1.01.3

0.50.4

ca 850 Maca 850 Ma

O’okiep 106 1.71 - ca 1040 MaNamaqualand

Deposit Cu (%) Au(g/t) AgeSize (mt)

Cloncurry Ernest Henry 167 1.1 0.54 ca 1530 Ma

Gawler Craton Olympic DamProminent Hill

3810283

1.00.89l

0.50.81

ca 1590 Maca 1590 Ma

Northern Province Palabora 350 0.52 0.01 ca 2040 Ma

SaloboCristalinoSossegoIgarape Bahia-AlemaoCento et Dezoito

789500355219170

0.961.01.11.41.0

0.520.30.280.860.3

ca 2570 Maca 2570 Maca 2570 Maca 2570 Maca 2570 Ma

Carajas

Page 9: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

Tick Hill

50.0

10.0

5.0

1.0

Aug/t

HIGH-GRADE DEPOSITS(Tennant Creek and Cloncurry)

Warrego

PekoStarra

Prominent Hill

Olympic Dam

GOLD VS COPPER GRADES FOR IRON-OXIDE ASSOCIATED DEP OSITS

Ernest Henry

Iron skarns

Iron (P, K)

Nobels NobWhite Devil

0.5

0.1

0.05

0.01

0.01 0.05 0.1 0.5Cu%

1.0 5.0 10.0

Olympic Dam

Rajasthan

Candelaria

Manto Verde PHANEROZOIC IOCG

PRECAMBRIAN IOCG

Carajas Deposits

PalaboraO'okiep MAGMATIC

ENDMEMBERS(?)

Page 10: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

80

70

60

40

Benson Mines

PeaRidge Carajas Gp

(Salobo, Khetri

Kiruna,Malberget

TECTONIC/LITHOSPHERIC SETTING OF IRON-OXIDE ASSOCIATED DEPOSITS

Neoproterozoic/Phanerozoic

SkarnsIOCG sensu stricto deposits Iron (P,F,REE) deposits

Paleo-Mesoproterozoic Archean

20

0

-20

-40

-120 -80 -40 0 40 80 120

(Salobo,Cristalino etc)

CandelariaManto Verde

El Romeral

O'okiep

Vergenoeg Palabora

ChimiwungoKasempaTenantCreek

Olympic Dam, Prominent Hill

ErnestHenry,Starra

Khetri

Page 11: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

Location of the Carajás Mineral Province: - Margin of both Archean crust (craton margin) & worlds largest A-type granitoid province.

(Santos et al., 2000)

Page 12: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

The Itacaiúnas

Belt -Carajás Mineral Mineral Province

Page 13: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

IRONIRON--OXIDE CuOXIDE Cu--Au DEPOSITSAu DEPOSITS

Igarape Bahia: Ring Like Breccia Bodies; Others Near-Vertical Pipe or Dyke-Like Bodies

grunerite

magnetite

siderite

chalcopyrite

Typical Fe-Oxide Cu-Au Ore from Cristalino

Page 14: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

MODELMODEL –– IOCGIOCG (Fe(Fe--OXIDEOXIDE CuCu--Au)Au)Inferred volc anic se tting & hydro thermal system,Olympic Dam

Inferred volcanic setting & hydrothermal system,Olympic Dam

OLYMPIC DAMMAAR

DEPOSIT MODEL FOR GIANT OLYMPIC DEPOSIT MODEL FOR GIANT OLYMPIC DAM DEPOSITDAM DEPOSIT

WORLDWORLD--CLASS POTENTIALCLASS POTENTIAL

Olympic DamBreccia ComplexOlympic DamBreccia Complex

BasaltBasalt

DykeDyke

Basalt-derivedgroundwaterBasalt-derivedgroundwaterInferred intrusiveInferred intrusive

Roxby Downs GraniteRoxby Downs GraniteDeeply circulated ormagmatic waterDeeply circulated ormagmatic water

CDB1188 7/ 97

Page 15: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

ALTERED LAMPROPHYRE DYKES IN IRONALTERED LAMPROPHYRE DYKES IN IRON --OXIDEOXIDE --COPPERCOPPER--GOLD ORE AT OLYMPIC DAMGOLD ORE AT OLYMPIC DAM

EuSm

Page 16: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

DEPOSIT SHAPE & SIZE

1 km

Olympic Dam

Palabora

200 m

1 kmN

Volcanic rock

Breccia / oreMafic dykes

Carbonatites

1 kmGranite / gneiss

Breccia

Igarape Bahia

Sedimentary rock

Pyroxenite

N

Pegmatoid

Page 17: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

Roc

k / C

hond

rite

10000

1000

100

REE Data: FeREE Data: Fe--Oxide CuOxide Cu--Au Au vsvs PalaboraPalabora((CarbonatiteCarbonatite))

La Pr Pm Eu Tb Ho Tm Lu

Roc

k / C

hond

rite

10

Ce Nd Sm Gd Dy Er Yb1

Olympic Dam hematite breccias

Alemão magnetite-chalcopyrite-bornite Cu-Au oreIgarapé Bahia magnetite breccia Au-Cu ore

Salobo iron-stone Cu-Au orePalabora carbonatite (range)

most REE-

enrichedsamples

Page 18: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

VERGENOEGGIANT MAARS:

A FEATURE OF ALKALINE MAGMATIC ACTIVITY?

2 km

A

B

ARGYLELAMPROITEPIPE

Ore body: F for A. Diamonds for B. Cu-Au for C.

Breccia

Associated rocks:

Ignimbrite for A. Tuff for B. Granite breccia for C.

Sedimentary or volcaniclastic rocks

500 m

C OLYMPIC DAM

2 km

Page 19: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

80

70

60

40

Benson Mines

PeaRidge Carajas Gp

(Salobo, Khetri

Kiruna,Malberget

TECTONIC/LITHOSPHERIC SETTING OF IRON-OXIDE ASSOCIATED DEPOSITS

Neoproterozoic/Phanerozoic

SkarnsIOCG sensu stricto deposits Iron (P,F,REE) deposits

Paleo-Mesoproterozoic Archean

20

0

-20

-40

-120 -80 -40 0 40 80 120

(Salobo,Cristalino etc)

CandelariaManto Verde

El Romeral

O'okiep

Vergenoeg Palabora

ChimiwungoKasempaTenantCreek

Olympic Dam, Prominent Hill

ErnestHenry,Starra

Khetri

Page 20: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

Longevity of Kaapvaal Craton Surrounded by Proterozoic Mobile Belts

LONGEVITY OF ARCHAEAN CRATON LONGEVITY OF ARCHAEAN CRATON MARGINSMARGINS

O’R

eilly

(200

3)

Buoyant Archaean Sub-Continental Lithosphere

Page 21: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

TECTONIC SETTING OF IOCG DEPOSITSTECTONIC SETTING OF IOCG DEPOSITS

Page 22: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

IOCGS : MAGMATISM FROM METASOMATISED IOCGS : MAGMATISM FROM METASOMATISED SCLMSCLM

Page 23: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

TEMPORAL DISTRIBUTIONS: RESOLUTION OF TEMPORAL DISTRIBUTIONS: RESOLUTION OF PROPOSED GENETIC CONNECTIONPROPOSED GENETIC CONNECTION

Page 24: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

• No > 100mt IOCG deposits known from this period• NICO in Great Bear Magmatic Zone, Canada has

42mt of 0.5%Au, 0.1%Co, 0.12%Bi adjacent to 1500mt of 35%Fe

• Sue Diane in same Zone has 17mt at 0.72%Cu,

IOCG-LIKE DEPOSITS ASSOCIATED WITH

GIANT IRON-OXIDE AT CA. 1.9 – 1.8GA

• Sue Diane in same Zone has 17mt at 0.72%Cu, 2.7glt Au

• Kolari District, Finland, including Hannukainen, is developing district in a province dominated by giant to world-class Fe-oxide deposits

• Tennant Creek Cu ± Au ± Bi deposits in same period

Page 25: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

DEPOSIT STYLES IN CARAJAS PROVINCE

• Iron-oxide Cu-Au Deposits Include Igarape-Bahia/Ale mao, Salobo, Cr Cristalino and Sossego-Sequeirinho. − Size: 170-1000 Mt of 0.95-1.4% Cu and 0.3-0.85 g/t Au. − Features: Extreme Fe and LREE Enrichment; Anomalous U and

Co; Quartz- and Sulfur- Deficient; Pipe or Ring-Like Ore Bodies; Hosted in Range of Lithologies (Mostly Lower Volcani c Sequences and Gneisses) at Varying Metamorphic Grad es.

• Copper-Au ± Sn ± W ± Bi Deposits Include Breves, AquasClaras and Gameleira . Claras and Gameleira . − Size: <50 Mt at < 1% Cu and < 1 g/t Au in Hypogene O re. − Features: Quartz-Bearing; More Sulfur-Rich Fe-Cu Sul phides;

Greisen to Ring-Like Bodies; Hosted Mainly by Upper Sedimentary Sequences.

• Gold-PGE Deposits at Serra Pelada. − Estimated Size………. − Features: Mainly Supergene Mineralogy; Fold Hinge i n

Carbonaceous Shales; Magnetite-Rich Breccias and Ma ssive Hematite; Anomalous U, Co and LREE.

• Minor Au-Cu at Formiga Garimpo in Breccias Rich in Fe -Oxides.

Page 26: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

1600

2000

24002800

0.4

0.6

206 P

b / 23

8 U

27800.55

0.60

Hydrothermal Monazites

2575±12Ma (MSWD = 1.19)

AGE OF IGARAPE BAHIA DEPOSITAGE OF IGARAPE BAHIA DEPOSITAGE OF IGARAPE BAHIA DEPOSITAGE OF IGARAPE BAHIA DEPOSITAGE OF IGARAPE BAHIA DEPOSITAGE OF IGARAPE BAHIA DEPOSITAGE OF IGARAPE BAHIA DEPOSITAGE OF IGARAPE BAHIA DEPOSIT

800

1200

0.0

0.2

0 5 10 15207Pb / 235U

206

25002540

25802620

26602700

27402780

0.40

0.45

0.50

0.55

10 11 12 13 14

Strong Agreement With Re-Os Age of Salobo Early Mol ybenite at 2576±8 Ma, Pb-Pb Age of Cu-Fe Sulphides at 2579±71 Ma and U-Pb Zircon Age of 2573±2 Ma for Old Salobo granite (Reqvia et al., 2003).

Page 27: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

AGE OF BREVES DEPOSITAGE OF BREVES DEPOSITAGE OF BREVES DEPOSITAGE OF BREVES DEPOSITAGE OF BREVES DEPOSITAGE OF BREVES DEPOSITAGE OF BREVES DEPOSITAGE OF BREVES DEPOSIT

1980

19401900

1800

1760

0.28

0.32

0.36

0.40

4.5 5.0 5.5 6.0207Pb / 235U

206

Pb

/ 238

U

2000

0.4

Xenotime

19601940

1900

1800

0.34

0.36

0.38

206P

b / 23

8U

Monazite

1600

1200

800

400

00.0

0.1

0.2

0.3

0 2 4 6207Pb / 235U

206P

b / 23

8U

Xenotime1800

1760

0.30

0.32

4.6 4.8 5.0 5.2 5.4 5.6 5.8 6.0207Pb / 235U

206

Weighted Mean Age of 1872±7 Ma (MSWD = 1.2) is in E rror of Weighted Mean SHRIMP U-Pb Zircon Age of Breves Gran ite at 1878±8 Ma (MSWD = 1.1) and of Breves Episyenite at 1882±7 Ma.

Page 28: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

AGE OF SERRA PELADA AuAGE OF SERRA PELADA AuAGE OF SERRA PELADA AuAGE OF SERRA PELADA AuAGE OF SERRA PELADA AuAGE OF SERRA PELADA AuAGE OF SERRA PELADA AuAGE OF SERRA PELADA Au--------PGE PGE PGE PGE PGE PGE PGE PGE

DEPOSITDEPOSITDEPOSITDEPOSITDEPOSITDEPOSITDEPOSITDEPOSIT

• 17 Hydrothermal Monazite Grains Analyzed• Only 8 Grains Have Common-Pb Corrected Values <3%• These Yield Imprecise Age of • 1861±45 Ma (MSWD = 2.3)• Hydrothermal Biotite Occurs in• Hydrothermal Biotite Occurs in

Distal Alteration Zone• Presumed Related to Au-PGE

Ore• 40Ar/ 39Ar Age of Five Biotites is

1882±3 Ma• Cigano Granite has U-Pb Zircon Age of 1883 ±2 Ma

(Machado et al., 1991)

Page 29: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

AGE OF FORMIGA GRANITEAGE OF FORMIGA GRANITEAGE OF FORMIGA GRANITEAGE OF FORMIGA GRANITEAGE OF FORMIGA GRANITEAGE OF FORMIGA GRANITEAGE OF FORMIGA GRANITEAGE OF FORMIGA GRANITE

Archean and Proterozoic Xenocrystic Zircons Reset at Ca 550Ma

Page 30: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

IMPLICATIONS OF CARAJAS STUDYIMPLICATIONS OF CARAJAS STUDYIMPLICATIONS OF CARAJAS STUDYIMPLICATIONS OF CARAJAS STUDYIMPLICATIONS OF CARAJAS STUDYIMPLICATIONS OF CARAJAS STUDYIMPLICATIONS OF CARAJAS STUDYIMPLICATIONS OF CARAJAS STUDY

• Two Major and One Minor Periods of Au-Cu Mineraliza tion in Carajas Mineral Province: Suggest Inheritance in Sou rce.

• All Have Strong REE Enrichment and Enhanced LREE.

• Trend From Low-SiO 2, Low-S to Quartz-Bearing and More S-Rich Systems with Time.

• Cannot be Significant Connate/Basinal Fluid Involved : All Hosts Metamorphosed Before Mineralization: Some Amphibolite .Metamorphosed Before Mineralization: Some Amphibolite .

• Mineralization Events Correspond to Three Periods o f Alkaline/Subalkaline magmatism at ca 2.57 Ga, ca 1.88 Ga and ca 0.55 Ga. Magmatic Association is Compelling.

• Largest Fe-Oxide Cu-Au Deposits Show Least Obvious Spatial Relationships to Intrusions (Deep Alkaline Intrusio ns?): Compare With Other Fe-Oxide Cu-Au Deposits.

• Suggest That Magmas and Ore Fluids Derived From Lon g-Lived Metasomatised Sub-Continental Lithosphere Beneath Am azon Craton Margin: Compare With Other Precambrian Fe-Oxi de Cu-Au Deposits.

Page 31: IOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING …media.kenanaonline.com/files/0006/6986/Talk 12 Intrusion Related Gold.pdfIOCG DEPOSITS DEFINITION, NATURE, TECTONIC SETTING AND

• IOCG has become a garbage-can term for a variety of deposits

• True IOCG deposits mostly have Cu-Au grades with <1% Cu and < 1gltAu and high tonnages

• They have low-Ti iron-oxides, silicates or carbonates, low-SiO2, low-S sulfides and REE enrichment (LREE –rich)

• Precambrian examples occur within 100km of older craton

SUMMARY

• Precambrian examples occur within 100km of older cratonmargins: Phanerozoic examples have less-clear tectonic setting

• There is a close temporal but not spatial relationship to magmatism in intracratonic settings

• The most likely genetic model is association with alkaline magmatism derived from metasomatised lithosphericmantle