Mapping alteration systems in the eastern Gawler Craton
Adrian Fabris Geological Survey of South Australia
#GSSADD17 Mapping alteration systems in the eastern Gawler Craton
Key points 1. 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.
#GSSADD17 Eastern Gawler Craton Mineral Systems
New data from exiting Dh’s 1. 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
Sampled dh’s
#GSSADD17 Residual gravity IOCG Deposit Class
• Fe oxide-Cu-Au breccia deposits
e.g. Olympic Dam
• Magnetite-apatite deposits (Kiruna-type)
• Iron sulfide Cu-Au deposits Loose classification leads to confusion both to the genetic model and to • Sediment-hosted Fe oxide-Cu-Au deposits understanding the alteration system • Ironstone replacement Au-Cu deposits
• Cu-Au-Fe skarn deposits
• Carbonatite-Fe-oxide-F-REE deposits #GSSADD17• Cu-Au-Fe porphyry (alkalic) deposits Alteration Model Alteration facies Deposit styles Silicification Epithermal (<250°C) • Provides explanation Hematite-group IOCG Low T K-Fe-H-CO2 of why we see an Hem-Kfs/Musc-Carb-Chl- Cu-Au-Ag-REE-U-Mo array of deposit sulfides e.g. Olympic Dam (<350°C) styles IOCG
Mag to Hem transition Polymetallic skarn IOCG Distal to heat source heat to Distal • late shallow, T, Low Based on Great Bear Kfs/Cpx-Grt-Kfs-sulfides Cu-Pb-Zn polymetallic IOCG terrain Potassic e.g. Pernatty Lagoon prospects • Evolving fluid High T K-Fe Magnetite-group IOCG Mag-Bt/Kfs-sulfides Cu-Au-Co e.g. Manxman, Cloncurry elements at each stage stage each at elements IOA Magnetite-apatite High T Ca-Fe ± Mg (+skarn) ealier Amp-Mag ± Cpx-Ap-Ttn IOA Fe, P, V, Th, REE Corriveau, L., Montreuil, J.-F., and Potter, E.G., 2016, Alteration facies (largely barren of sulfides) recharges/discharges or evolves Fluid e.g. Kiruna type, ?Cairn Hill linkages among iron oxide copper-gold, iron (<800°C) oxide-apatite, and affiliated Na ± Ca (albities) deposits in the Great Bear Magmatic zone,
Northwest Territories, Canada: Ab-Scp-Qz-Zrn-Rt High T, deeper, deeper, T, High Economic Geology, v. 111, p. 2045–2072. core Thermal #GSSADD17 Sodic (<600°C) After Corriveau et al., 2016 What are the implications?
Coober Pedy Mapping sodic and potassic alteration in the eastern Gawler
Craton Olympic Dam • Sodic and potassic alteration will provide evidence for this process and give broad footprints Potassic Sodic Background
#GSSADD17 Mapping regional potassic and sodic alteration
MALD1 – Alford West
HyLogger#GSSADD17TM Wallaroo Group Spectral data available
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)
#GSSADD17 Alteration Model Alteration facies Deposit styles Implications Silicification Epithermal • Early stages of alteration (<250°C) provide crucial ground Hematite-group IOCG Low T K-Fe-H-CO2 preparation Hem-Kfs/Musc-Carb-Chl- Cu-Au-Ag-REE-U-Mo sulfides e.g. Olympic Dam • All IOCG’s will have a (<350°C) magnetic response related to IOCG
Polymetallic skarn IOCG Distal to heat source heat to Distal early magnetite-alteration late shallow, T, Low Cu-Pb-Zn polymetallic phase (magnetics ideal Mag to Hem transition e.g. Pernatty Lagoon prospects mapping tool). Kfs/Cpx-Grt-Kfs-sulfides High T K-Fe Magnetite-group IOCG Mag-Bt/Kfs-sulfides Cu-Au-Co e.g. Manxman, Cloncurry elements at each stage stage each at elements IOA Magnetite-apatite High T Ca-Fe ± Mg (+skarn) ealier Amp-Mag ± Cpx-Ap-Ttn IOA Fe, P, V, Th, REE
Corriveau, L., Montreuil, J.-F., and Potter, Fluid evolves or recharges/discharges recharges/discharges or evolves Fluid E.G., 2016, Alteration facies Magnetite (largely barren of sulfides) e.g. Kiruna type, ?Cairn Hill linkages among iron oxide copper-gold, iron (<800°C) oxide-apatite, and affiliated Na ± Ca (albities) deposits in the Great Bear Magmatic zone,
Northwest Territories, Canada: Ab-Scp-Qz-Zrn-Rt High T, deeper, deeper, T, High Economic#GSSADD17 Geology, v. 111, p. 2045–2072. (<600°C) core Thermal After Corriveau et al., 2016 Mapping alteration through magnetic response
Olympic Dam
10km 10km #GSSADD17 Residual gravity Residual magnetics Mapping alteration through magnetic response
Emmie Bluff/Intercept Hill
Intercept Hill Intercept Hill
Structure and probably source
Emmie Bluff Emmie Bluff North North Selected Dh’s Selected Dh’s Emmie Bluff Emmie Bluff South South 10km 5km 5km #GSSADD17 Residual gravity Residual magnetics Mapping alteration through magnetic response
Punt Hill
Groundhog Groundhog Groundhog
Punt Hill
Red Lake 5km
500m Residual magnetics Selected Dh’s Residual gravity Residual magnetics
#GSSADD17 Magnetic inversion Mapping alteration through magnetic response
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. 5km
Residual magnetic s #GSSADD17 Magnetic inversion Scale reduction
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!
#GSSADD17 Forming trace element halos
• 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’.
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- #GSSADD17oxide Cu-Au-(U) mineralization at Olympic Dam, South Australia. Ore Geology Reviews 80 p. 838-859. Mapping trace element halos
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.
#GSSADD17 Prominent Hill Mapping trace element halos Carrapateena Sb
Trace element associations Emmie Bluff • As, Bi, Sb and W show widespread anomalism in the central Olympic Cu-Au Province (cooler phase)
#GSSADD17 Prominent Hill Mapping trace element halos Carrapateena Ce
Trace element associations Emmie Bluff • Elements such as Ce (LREE), Te, Nd, Re are associated with the centre of the system.
Tea Tree Glen
#GSSADD17 Mapping trace element halos
IHAD3 Cu IHAD6 • Widespread Cu anomalism (no clear vector). IHAD5
IHAD2
#GSSADD172km Mapping trace element halos
IHAD3 Sb IHAD6 • low T elements give high values across all holes {As, IHAD5 Bi, Sb, W} IHAD2
#GSSADD172km Mapping trace element halos
IHAD3 Ce IHAD6 • Elements associated with both mag-dom and hem IHAD5 dom mineralisation, and IHAD2 don’t tend to be mobile {Ce, Nd, Re +/- Te). • May demonstrate a greater proportion of magmatic- hydrothermal fluids in the east.
#GSSADD172km Mapping alteration systems in the eastern Gawler Craton
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.
#GSSADD17 Disclaimer
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#GSSADD17 Contact minerals.dpc.sa.gov.au/gssa_dd
Department of the Premier and Cabinet - Mineral Resources Division Geological Survey of South Australia Level 4, 101 Grenfell Street Adelaide, South Australia 5000
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#GSSADD17