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#GSSADD17
Adrian FabrisGeological Survey of South Australia
Mapping alteration systems in the eastern GawlerCraton
#GSSADD17
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
#GSSADD17
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
#GSSADD17
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
#GSSADD17
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
#GSSADD17
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
#GSSADD17
Mapping alteration through magnetic response
Residual gravity Residual magnetics
Olympic Dam
10km10km
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Mapping alteration through magnetic response
Residual gravity Residual magnetics
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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Mapping alteration through magnetic response
Residual gravity Residual magnetics
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.
Mapping alteration through magnetic response
Magnetic inversion
5km
Residual magnetic s
#GSSADD17
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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Mapping trace element halos
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
#GSSADD17
Mapping trace element halos
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
#GSSADD17
Mapping trace element halos
2km
• Widespread Cu anomalism (no clear vector).
CuIHAD3IHAD6
IHAD5
IHAD2
#GSSADD17
Mapping trace element halos
2km
• low T elements give high values across all holes {As, Bi, Sb, W}
SbIHAD3IHAD6
IHAD5
IHAD2
#GSSADD17
Mapping trace element halos
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
#GSSADD17
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]