geological survey of south australia€¦ · magnetic data map the roots of an iocg system and...

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Adrian FabrisGeological Survey of South Australia

Mapping alteration systems in the eastern GawlerCraton

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Key points1. Na and K alteration provides broad alteration footprints around IOCG’s and

that there are distinct trends in the eastern Gawler that demonstrate a range of crustal depths.

2. Magnetics and gravity map alteration associated with IOCG’s. Magnetic data map the roots of an IOCG system and provide an understanding of fluid pathways.

3. Trace element geochemistry can be used to map footprints and vector in IOCG systems.

Mapping alteration systems in the eastern Gawler Craton

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New data from exiting Dh’s1. Re-assaying of select intervals

(>2700) from 112 diamond drillholes (2012-2015)

2. Multi-element geochemistry (65 elements)

3. Spectral mineralogy (>300 dh’s HyLogged)

4. Petrophysical properties

Eastern Gawler Craton Mineral Systems

Residual gravity

Sampled dh’s

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IOCG Deposit Class

• Fe oxide-Cu-Au breccia deposits

e.g. Olympic Dam

• Magnetite-apatite deposits (Kiruna-type)

• Iron sulfide Cu-Au deposits

• Sediment-hosted Fe oxide-Cu-Au deposits

• Ironstone replacement Au-Cu deposits

• Cu-Au-Fe skarn deposits

• Carbonatite-Fe-oxide-F-REE deposits

• Cu-Au-Fe porphyry (alkalic) deposits

Loose classification leads to confusion both to the genetic model and to understanding the alteration system

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Alteration ModelDeposit styles

Corriveau, L., Montreuil, J.-F., and Potter, E.G., 2016, Alteration facieslinkages among iron oxide copper-gold, iron oxide-apatite, and affiliateddeposits in the Great Bear Magmatic zone, Northwest Territories, Canada:Economic Geology, v. 111, p. 2045–2072.

Epithermal

Hematite-group IOCGCu-Au-Ag-REE-U-Moe.g. Olympic Dam

Polymetallic skarn IOCGCu-Pb-Zn polymetallice.g. Pernatty Lagoon prospects

Magnetite-group IOCGCu-Au-Coe.g. Manxman, Cloncurry

IOA Magnetite-apatiteFe, P, V, Th, REEe.g. Kiruna type, ?Cairn Hill

IOA

IOC

G

Silicification(<250°C)

Low T K-Fe-H-CO2Hem-Kfs/Musc-Carb-Chl-sulfides(<350°C)

Mag to Hem transitionKfs/Cpx-Grt-Kfs-sulfides

High T K-FeMag-Bt/Kfs-sulfides

High T Ca-Fe ± Mg (+skarn)Amp-Mag ± Cpx-Ap-Ttn(largely barren of sulfides)(<800°C)

Na ± Ca (albities)Ab-Scp-Qz-Zrn-Rt(<600°C) Th

erm

al c

ore

Hig

h T

, de

ep

er, e

alie

rD

ista

l to

he

at s

ou

rce

Low

T, s

hal

low

, lat

e

Alteration facies

Flu

id e

volv

es o

r re

char

ges/

dis

char

ges

ele

me

nts

at

eac

h s

tage

After Corriveau et al., 2016

• Provides explanation of why we see an array of deposit styles

• Based on Great Bear IOCG terrain

• Evolving fluid

Po

tass

icSo

dic

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Mapping sodic and potassicalteration in the eastern GawlerCraton

• Sodic and potassic alteration will provide evidence for this process and give broad footprints

What are the implications?

Potassic

Sodic

Background

Coober Pedy

Olympic Dam

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Mapping regional potassic and sodic alteration

MALD1 – Alford West

Wallaroo GroupHyLoggerTM

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Spectral data compiled• Spectral data provides a powerful tool for mapping alteration mineralogy. It is now

available within a single spreadsheet making it more user friendly (Simon van der Wielen)

• Spreadsheets – TIR 143 columns (>125 000 metre intervals), SWIR/VNIR 112 columns (>209 000 metre intervals)

Spectral data available

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Alteration ModelDeposit styles

Corriveau, L., Montreuil, J.-F., and Potter, E.G., 2016, Alteration facieslinkages among iron oxide copper-gold, iron oxide-apatite, and affiliateddeposits in the Great Bear Magmatic zone, Northwest Territories, Canada:Economic Geology, v. 111, p. 2045–2072.

Epithermal

Hematite-group IOCGCu-Au-Ag-REE-U-Moe.g. Olympic Dam

Polymetallic skarn IOCGCu-Pb-Zn polymetallice.g. Pernatty Lagoon prospects

Magnetite-group IOCGCu-Au-Coe.g. Manxman, Cloncurry

IOA Magnetite-apatiteFe, P, V, Th, REEe.g. Kiruna type, ?Cairn Hill

IOA

IOC

G

Silicification(<250°C)

Low T K-Fe-H-CO2Hem-Kfs/Musc-Carb-Chl-sulfides(<350°C)

Mag to Hem transitionKfs/Cpx-Grt-Kfs-sulfides

High T K-FeMag-Bt/Kfs-sulfides

High T Ca-Fe ± Mg (+skarn)Amp-Mag ± Cpx-Ap-Ttn(largely barren of sulfides)(<800°C)

Na ± Ca (albities)Ab-Scp-Qz-Zrn-Rt(<600°C) Th

erm

al c

ore

Hig

h T

, de

ep

er, e

alie

rD

ista

l to

he

at s

ou

rce

Low

T, s

hal

low

, lat

e

Alteration facies

Flu

id e

volv

es o

r re

char

ges/

dis

char

ges

ele

me

nts

at

eac

h s

tage

After Corriveau et al., 2016

Implications• Early stages of alteration

provide crucial ground preparation

• All IOCG’s will have a magnetic response related to early magnetite-alteration phase (magnetics ideal mapping tool).

Mag

net

ite

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Mapping alteration through magnetic response

Residual gravity Residual magnetics

Olympic Dam

10km10km

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Emmie Bluff/Intercept Hill

5km10km 5km

Emmie Bluff South

Emmie Bluff North

Intercept Hill

Selected Dh’sSelected Dh’sEmmie Bluff South

Emmie Bluff North

Intercept Hill

Structure and probably source

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Punt Hill

Magnetic inversion

5km

Red Lake

Groundhog

Punt Hill

GroundhogGroundhog

Selected Dh’s

500m

Residual magnetics

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Take home message• Magnetics and gravity data are critical in mapping alteration in IOCG systems.

Magnetics also provide an understanding of the fluid pathways and regions that have seen the paragenetically early or deeper part of an IOCG system.


Magnetic inversion

5km

Residual magnetic s

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How to determine if it’s a significant system?• Sodic and potassic alteration give regional trends

• Magnetics and gravity narrow down the search space but…. one of the challenges is not just understanding where we are in the alteration system, but whether it is a significant system

• Trace element chemistry can certainly help!

Scale reduction

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• Process of feldspar alteration in these systems leads to porosity that is filled with numerous and varied inclusions including Fe oxides, Fe sulfides. E.g. pyrite

= mechanism of forming trace element footprints

• Widespread alteration = large trace element ‘footprints’.

Forming trace element halos

Kontonikas-Charos A, Ciobanu CL, Cook NJ, Ehrig K, Krneta A and Kamenetsky VS 2017. Feldspar evolution in the Roxby Downs Granite, host to Fe-oxide Cu-Au-(U) mineralization at Olympic Dam, South Australia. Ore Geology Reviews 80 p. 838-859.

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Trace element associations• Integration of alteration and chemistry can be used to define elements associated

with each deposit style (Fabris et al., 2013)

• Hematite-dominated IOCG: Au, Ag, As, Ba, Bi, Cd, Ce, Co, Cu, Fe, La, Mn, Mo, Nd, REE, Re, S, Sb, Se, Te, W± U

• Magnetite-dominated IOCG: Au, Ca, Ce, Co, Cu, Fe, Mo, Nd, P, Pb, REE, Re, S, Se, Te, U, Zn

• Magnetite-dominated systems lack strong association with As, Ag, Bi, Sb and W

i.e. elements typically associate with lower T fluids in hydrothermal systems.

Mapping trace element halos

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Trace element associations• As, Bi, Sb and W show

widespread anomalism in the central Olympic Cu-Au Province (cooler phase)

SbProminent Hill

Carrapateena

Emmie Bluff

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Trace element associations• Elements such as Ce (LREE), Te,

Nd, Re are associated with the centre of the system.

Ce

Tea Tree Glen

Prominent HillCarrapateena

Emmie Bluff

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2km

• Widespread Cu anomalism (no clear vector).

CuIHAD3IHAD6

IHAD5

IHAD2

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2km

• low T elements give high values across all holes {As, Bi, Sb, W}

SbIHAD3IHAD6

IHAD5

IHAD2

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2km

• Elements associated with both mag-dom and hem dom mineralisation, and don’t tend to be mobile {Ce, Nd, Re +/- Te).

• May demonstrate a greater proportion of magmatic-hydrothermal fluids in the east.

CeIHAD3IHAD6

IHAD5

IHAD2

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Conclusions

1. Na and K alteration trends demonstrate the range of crustal depths in the eastern Gawler and therefore style of IOCG’s to look for.

2. Magnetic data map the roots of an IOCG system and provide an understanding of fluid pathways.

3. Trace element geochemistry can be used to vector within an IOCG system with certain elements potentially indicating the source of low T and high T fluids.

Mapping alteration systems in the eastern Gawler Craton

#GSSADD17

Disclaimer

The information contained in this presentation has been compiled by the Department of the Premier and Cabinet (DPC) and originates from a variety of sources. Although all reasonable care has been taken in the preparation and compilation of the information, it has been provided in good faith for general information only and does not purport to be professional advice. No warranty, express or implied, is given as to the completeness, correctness, accuracy, reliability or currency of the materials.

DPC and the Crown in the right of the State of South Australia does not accept responsibility for and will not be held liable to any recipient of the information for any loss or damage however caused (including negligence) which may be directly or indirectly suffered as a consequence of use of these materials. DPC reserves the right to update, amend or supplement the information from time to time at its discretion.

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minerals.dpc.sa.gov.au/gssa_ddContact

Department of the Premier and Cabinet - Mineral Resources DivisionGeological Survey of South Australia

Level 4, 101 Grenfell StreetAdelaide, South Australia 5000

T: +61 8 8463 3000E: [email protected]

geological survey of south australia€¦ · magnetic data map the roots of an iocg system and...

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