Geochemical and stratigraphic tools for exploration undercover · 2020. 6. 16. · Geochemical and...

NAP WRAP 2006

Australian Government

Geoscience Australia

Lex Lambeck

Geochemical and stratigraphic tools for exploration undercover: Tanami region, Northern Australia

speak goldWORLD GOLD COUNCIL

NAP WRAP 2006

Overview:

Gold-hosting units in the Tanami region have been geochemically fingerprinted and placed in a stratigraphic model which has important implications for regional exploration

NAP WRAP 2006

Geology of north-central

AustraliaTanami Region

AProterozoic

Basin

NT

Crusade

Browns Range Dome

Frankenia Dome

CallieTitania

Black

Peak

Groundrush

Bluebush

Sup

plej

ack

Tanami

TANAMI GOLDFIELD

Coomarie Dome

DEAD BULLOCKSOAK GOLDFIELD

WA

Coyote

Kookaburra

THE GRANITESGOLDFIELD

WA

NT

SA

QLD

NSW

ACTVIC

TAS

TANAMI BASEMENT GEOLOGY

Mount Winnecke Formation

Nanny Goat Volcanic

Mount Charles Formation

ARCHAEAN

Dead Bullock Formation

Pargee SandstoneFault

Gold deposit

0 30 km

Geological contact

Killi Killi FormationWareGroup

TanamiGroup

Tanami Group (undifferentiated)

Wilson and Century Formation

D

D

6

5

Fredrick Suite

Grimwade Suite

Birthday Suite

Birrindudu Group

04-234-1 21°

20°

19°130°129°

CoyoteTitania

Groundrush

CallieDead Cat

Challenger

AnomalyMagellan

Kookaburra

Old Pirate

Drill or outcrop logs

Sunline

CashelCashel 39km east of Anomalyin undifferentiated Tanami Group{ }

NAP WRAP 2006

Gold in the Tanami occurs in:

Shallow level, epizonalmineralisation

Deep level, meso-thermal mineralisation, hosted by:

iron formationsmetamorphosed mafic sillturbiditeshosted by decarbonised siltstone, World-Class Callie deposit (> 6 MOz)

75% of gold in the Tanami occurs in siltstone or fine greywackes

NAP WRAP 2006

Evolution of Tanami basinGeochronology results

Pargee Sst. < 1760 Ma.

Mt Charles Formation.

Ware Group < 1820 Ma.

Killi Killi Formation 1840 Ma. Maximum depositional age

Dead Bullock Formation 1838 6 Ma. Depositional age

Bald Hill 1864 3 Ma. Magmatic crystallisation age

+

+

Need to use geochronology in conjunction with geochemistry to help elucidate the full story

NAP WRAP 2006

Stratigraphic distribution of goldRegional Stratigraphy Au* (tonnes)

Pargee Sandstone Nil

Mt Charles Formation 50.6

Ware Group 2.3Killi Killi Formation 27.4

Dead Bullock Formation 270

Bald Hill Sequence 3.5

Tanami Groupcontaining Callie

stratigraphy}Au* tonnage calculated as a sum of gold resources, production and stockpile


NAP WRAP 2006

Obstacles to Overcome

• Rocks that do outcrop are generally fine-grained greywackes or black shales

• Lack of outcrop in the Tanami

• Relatively shallow exploration holes

• Relating mine stratigraphy nomenclature to regional stratigraphy

NAP WRAP 2006

Approach• Downhole geochemistry to distinguish gold-bearing lithologies

• Use Th/Sc combined with Cr values to define the gold-bearing lithologies

•High Cr indicative of a mafic provenance

•High Th/Sc indicative of a felsic provenance

• Build composite cores of Dead Bullock & Mt Charles Formations

• Dead Bullock & Mt Charles Formations which contain in excess of 320 tonnes of gold combined

NAP WRAP 2006

Approach

• Use isotopic data to differentiate between Dead Bullock & Mt. Charles Formations• Log grain size and sedimentary features from diamond drill cores & limited outcrop logs

• Use Sequence stratigraphy to predict where we can find possible gold-bearing fine-grained greywackes and black shales within the Tanami

NAP WRAP 2006

Th/Sc vs. Au Tonnes

0

1

2

3

4

5

1 10 100 1000Au tonnes

Th/S

c

The Granites

Callie

TanamiGoldfields

Coyote

Bald Hill

Groundrush

Kookaburra

Titania

* Au tonnage calculated as a sum of gold resources, production and stockpile

NAP WRAP 2006

Regional framework

• How do the composite drill holes at Callie and Tanami Gold fieldsrelate to the regional stratigraphy?

• Can we use whole-rock and isotope geochemistry to distinguish the regional stratigraphy in relation to the Callie and Mt Charles stratigraphy?

NAP WRAP 2006

Cr (ppm) Th/Sc Lith1 1000 0.1 15

Callie composite coreCr (ppm) Th/Sc Lith

1 1000 0.1 15 claysilt

sand

Mt. Charles composite core

claysilt

sand

Major

units

not true thickness for Mt Charles Fm.max thickness~1200m

0

300 m

{ }

0

gold-bearing

1100 m

NAP WRAP 2006

A kinked continuumCompositional variations due to change in provenance

Major gold-bearingunits

0.01

0.1

1

10

1 10 100

Felsic provenanceM

afic

prov

enan

ce

Dead Bullock Fm.Killi Killi Fm.

Bald Hill

Ware Group

Pargee Sst.Mt. Charles Fm.

Zr/Sc

Th/S

c

NAP WRAP 2006

Mafic sedimentsAu tonnes (56.6)n = 57

Mafic sedimentsAu tonnes (270)n = 102

Felsic sedimentsAu tonnes (27.4)n = 76



Felsic sedimentsAu tonnes (Nil)n = 2

La Ce Pr Nd Sm Eu Gd Tb Ho Er Yb Lu

REE

/PA

AS

REE

/PA

AS

REE

/PA

AS

REE

/PA

AS

REE

/PA

AS

REE

/PA

AS

Bald HillSequence

Dead BullockFormation

Killi KilliFormation

WareGroup

Mt CharlesFormation

PargeeSandstone

RegionalStratigraphy:

Rare earth element traces

Minimum

MaximumAverage

NAP WRAP 2006

εNd values

-12

-10

-8

-6

4

0 2 4 6Th/Sc

ApertawongaDead Cat RockSunlineCashelMt Charles BasaltMt Charles FormationWare GroupKilli Killi CoyoteKilli Killi DBSDead Bullock Formation

Bald Hill Basalt & Dolerite

2

-4

0

-2

ε Nd

Groundrush

Bald Hill Sequence

NAP WRAP 2006

NT

Crusade

Browns Range Dome

Frankenia Dome

CallieTitania

Black

Peak

Groundrush

Bluebush

Sup

plej

ack

Tanami

TANAMI GOLDFIELD

Coomarie Dome

DEAD BULLOCKSOAK GOLDFIELD

WA

Coyote

Kookaburra

THE GRANITESGOLDFIELD

WA

NT

SA

QLD

NSW

ACTVIC

TAS

TANAMI BASEMENT GEOLOGY

Mount Winnecke Formation

Nanny Goat Volcanic

Mount Charles Formation

ARCHAEAN


Pargee SandstoneFault

Gold deposit

0 30 km

Geological contact

Killi Killi FormationWareGroup

TanamiGroup

Tanami Group (undifferentiated)

Wilson and Century Formation

D

D

6

5

Fredrick Suite

Grimwade Suite

Birthday Suite

Birrindudu Group

04-234-1 21°

20°

19°130°129°

CoyoteTitania

Dead Cat

Challenger

AnomalyMagellan

Kookaburra

Old Pirate

Cross-sections constructed using whole-rock and isotope geochemistry

Drill or outcrop logs

N-S cross-section

GroundrushSunline

NW-SE cross-section

NAP WRAP 2006

Jasper Hills

Challenger Trig Titania

Callie

Sunline

Outcrop samples

Cr1 800

Th/Sc1 10 Lith

200

TT(m

)

SUNLINE Lith

TT(m

)

JASPER HILLS

GROUNDRUSH

Lith

TT(m

)

CHALLENGER TRIG POINT

Cr1 800

Th/Sc1 10 Lith

150

200

250

300

350

TT(m

)

TITANIA 058

Cr1 800

Th/Sc1 10 Lith

50

100

150

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

TT

Lith

TT(m

)

DEAD CAT ROCK

Outcrop samples

Metres ?

Cr1 800

Th/Sc1 10 Lith

250

300

350

400

450

500

TT(m

)

Sandstonemedium tovery coarse

Sandstonevery fineto fine

Sandy siltstone

Siltstone

Shale

Conglomerategranule toboulder

Lithology Legend

TUFF CHERT BRECCIA

SILICICLASTICSQUARTZO-FELDSPATHIC

SILICICLASTICSLITHIC

SILICICLASTICSCARBONACEOUS

(VARIABLY DOLOMITIC)

SILICICLASTICSTUFFACEOUS

DOLOMITICSILICICLASTICS

CARBONATES

METAMORPHIC

Dololutite

Dolosiltite

Silty dolarenite

to finevery fineDolarenite

very coarse

Dolarenitemedium to

bouldergranule to Dolorudite

IGNEOUSCRYSTALLINECARBONATES

mineralogyundifferentiated

Dead Cat Rock

Groundrush

FerdiesLowerCallieSequence

Sediments above this line are interpreted as

Killi Killi Formation

Sediments below this line are interpreted as


Groundrush is interpreted by the NTGS to be stratigraphically belowCallie however, the stratigraphicdistance separating the units is notknown.

N S

Sandstone very fine to fine

Siltstone

Conglomerate granule to boulder

Sandstone medium to very coarse

Sandy siltstone

Shale

ChertFault Breccia

CHERT

d

v v v v v v v v

+ + + + + + ++ + + + + + + Dolerite

North south Tanami transect

Metres ?

Cr Th/Sc

Mafic provenance

Felsic provenance

TitaniaChallenger

TrigJasperHillsSunline

NAP WRAP 2006

Cr1 800

Th/Sc1 10 Lith

50

100

150

200

250

300

350

TT(m

)

COYOTE COMPOSITE

Cr1 800

Th/Sc1 10 Lith

50

100

TT(m

)

OLD PIRATE

Lith

TT(m

)

APERTAWONGA

Cr1 800

Th/Sc1 10 Lith

50

100

150

200

250

300

350

400

450

500

550

600

650

700

750

800

850

900

950

1000

1050

TT(m

)

DBD COMPOSITE

Lith

TT(m

)

DEAD CAT ROCK

Cr1 800

Th/Sc1 10 Lith

150

200

TT(m

)

MAGELLAN

Cr1 800

Th/Sc1 10 Lith

200

250

300

TT(m

)

ANOMALY

Cr1 800

Th/Sc1 10 Lith

100

TT(m

)

CASHEL

Cr1 800

Th/Sc1 10 Lith

200

250

300

350

TT(m

)

BALD HILLCr

1 800

Th/Sc1 10 Lith

150

200

TT(m

)

KOOKABURRA


Siltstone



Sandy siltstone

Shale

ChertFault Breccia

CHERT

d

v v v v v v v v

+ + + + + + ++ + + + + + + Dolerite

North west– south east

Tanami transect

BaldHill Kookaburra

Cashel

Anomaly

Magellan

DeadCat

Rock

Callie

Apertawonga

Old Pirate

Coyote

Outcrop samples

Sediments above this line are

interpreted as Killi Killi Formation

Sediments below this line are interpreted as


Black shales can occur in the Killi Killi Formation, felsic geochemistry

The Bald Hill Sequence has a depositional ageThat is older than Callie but the distance separating the units is not known.

NW SE

Cr Th/Sc

Mafic provenance

Felsic provenance

NAP WRAP 2006


Siltstone



Sandy siltstone

Shale

ChertFault Breccia

CHERT

d

v v v v v v v v

+ + + + + + ++ + + + + + + Dolerite

Aggradation

ProgradationKilli Killi

Formation

1100mTransgression

World classdeposit

Ferdies LowerCallie

Sequence

Cr (ppm) Th/Sc Lith1 1000 0.1 15

Callie compositecore

Callie composite core displayssupersequence scale stratigraphy

NAP WRAP 2006

Stratigraphic model for Tanami region

Callie

Coyote

Tanami Group

WA NTPlatformmarginKimberly?

Platform

Paleosource ofsediment ?

Killi Killi Formation1840Ma(felsic source, Proterozoic source)

FerdiesMember(mixed mafic felsic soure,Archean Provenance)

?

Callie Member1838 6 Ma

? ? ?

??

+ + + + + + + + + + + + + + + + + +

Basement+

+ +

Bald Hill1864 3 Ma+_

+-

UnconformityCorrelative conformityCanyon systems

Basin floor fans

Platformmargin

Kimberley?

NAP WRAP 2006

• Suggests Dead Bullock Formation (black shales) largely restricted to NT

Black shale distribution

NT.

NAP WRAP 2006

Conclusions

Effective discriminators define the strongly mineralised mafic group:

High Cr valuesLow Th/Sc values

Light REE depletionLow εNd values

Geochemistry:

NAP WRAP 2006

Conclusions

Stratigraphic Model for the Tanami Region:

The Killi Killi Formation may represent a series of Low Stand prograding diachronous turbiditic packages.

Ferdies Lower Callie Sequence represents a sediment-starved, deep water environment distal to land.

The Bald Hill Sequence could form part of these earlier diachronous packages or it could be part of a unit not recognized in the Northern Territory.

NAP WRAP 2006

Questions that remain?• Correlating logs over a

large area?• We only have a very basic basin structure

• Can only identify super sequence scale packages

• This technique only works where end members of the Stratigraphy are of different compositions

NAP WRAP 2006

This work could not have gone ahead without the help and support of:

David HustonPeter SouthgateDavid ChampionAndrew CrossDavid MaidmentJohn PykeLara SedgmenGA North Australia ProjectAndrew Crispe (NTGS)Leon Bagas (GSWA)Geoff Lowe (Newmont)Eric Whitaker (Newmont)Chris Campbell (Newmont)Tim Smith (Tanami Gold)Luc English (Tanami Gold)Jim Anderson (Tanami Gold)

NAP WRAP 2006

Samarium and Neodymium datingWhat is it and how do we measure it?

• Over geologic time, the decay of 147Sm to 143Nd results in changes in the abundance of 143Nd relative to the other Ndisotopes.

• These small variations are measured precisely by mass spectrometers.

•Samarium (147 Sm) is radioactive and decays to neodymium (143Nd).

• Decay process is very slow as the half life of 147Sm is 106 billion years.

NAP WRAP 2006

Sedimentary Rocks

Studies show that Nd isotopic characteristics are a good indicator ofSediment provenance, and that the information is complementary to that provided by other methods of provenance determination.

Studies also show confirm that interlayed coarse-grained beds and fine grained beds give the same isotopic results. Important because it is almostImpossible to determine provenance of fine grained sediments petrographically

Mixing is a special process in that isotopic ratios in the endmembercompositions of a mixture may be different, so in the process of mixingone component into an other, shifts the isotopic ratio as well as shifts chemical composition

NAP WRAP 2006

Downhole geochemistry of Callie composite core

Killi KilliFormation


FelsicProvenance

MaficProvenance

Intermixingbetween provenances

0 2 4 6 8

Th/Sc

Dep

th

0 250 500 750 1000 1250

Cr

Corra Dolerite

1100 m

High Th/Sc indicativeof a felsic provenance

High Cr indicativeof a mafic provenance

NAP WRAP 2006

Geology of north-central

Australia

Tanami Region


Geochemical and stratigraphic tools for exploration undercover · 2020. 6. 16. · Geochemical and...

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