Mapping alteration systems in the eastern Gawler Craton

24 Pages·2017·3.13 MB·English

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
e
(<250°C)
c e
r t
• Provides explanation u a
o l Hematite-group IOCG
Low T K-Fe-H-CO2 s ,w
of why we see an t Cu-Au-Ag-REE-U-Mo
Hem-Kfs/Musc-Carb-Chl- a o s
e l e
array of deposit sulfides h o lah GC gra e.g. Olympic Dam
c (<350°C) t s O h
styles is la ,T I cs e
s t w id g Polymetallic skarn IOCG
• Based on Great Bear at Mag to Hem transition siD oL /s ats Cu-Pb-Zn polymetallic
o Kfs/Cpx-Grt-Kfs-sulfides e h
g
IOCG terrain P r c e.g. Pernatty Lagoon prospects
a a
h e
• Evolving fluid c t
e a
High T K-Fe r s Magnetite-group IOCG
r t
Mag-Bt/Kfs-sulfides o n
e Cu-Au-Co
s
e m
r v e e.g. Manxman, Cloncurry
e l
o l
i A e
l v
High T Ca-Fe ± Mg (+skarn) a O e IOA Magnetite-apatite
e

Amp-Mag ± Cpx-Ap-Ttn ,r I di Fe, P, V, Th, REE
Corriveau, L., Montreuil, J.-F., and Potter, e e u
(largely barren of sulfides) r p lF e.g. Kiruna type, ?Cairn Hill
E.G., 2016, Alterationfacies o e
(<800°C) c e
linkages among iron oxide copper-gold, iron l d
a
oxide-apatite, and affiliated c Na ± Ca (albities) m ,T
deposits in the Great Bear Magmatic zone, i
d r h
N#orGthweSst STerAritorDies, DCana1da7: o Ab-Scp-Qz-Zrn-Rt eh gi
Economic Geology, v. 111, p. 2045–2072. S (<600°C) T H 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
#GSSADD17
HyLoggerTM 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
e
(<250°C)
• Early stages of alteration c e
r t
u a
provide crucial ground o l Hematite-group IOCG
Low T K-Fe-H-CO2 s ,w
preparation t Cu-Au-Ag-REE-U-Mo
Hem-Kfs/Musc-Carb-Chl- a o s
e l e
• All IOCG’s will have a s(<u3lf5id0e°Cs) h ot lahs GCO grah e.g. Olympic Dam
magnetic response related to la ,T I cs e
t w id g Polymetallic skarn IOCG
s a
early magnetite-alteration iD oL /s ts Cu-Pb-Zn polymetallic
e
phase (magnetics ideal Mag to Hem transition g h
r c e.g. Pernatty Lagoon prospects
a a
mapping tool). Kfs/Cpx-Grt-Kfs-sulfides h e
c t
e e a
t High T K-Fe r s Magnetite-group IOCG
r t
i o n
t Mag-Bt/Kfs-sulfides e Cu-Au-Co
s
e e m
n re vl e e.g. Manxman, Cloncurry
o l
i A e
g High T Ca-Fe ± Mg (+skarn) la O ve IOA Magnetite-apatite
a e
M Amp-Mag ± Cpx-Ap-Ttn ,r I di Fe, P, V, Th, REE
Corriveau, L., Montreuil, J.-F., and Potter, e e u
(largely barren of sulfides) r p lF e.g. Kiruna type, ?Cairn Hill
E.G., 2016, Alterationfacies o e
(<800°C) c e
linkages among iron oxide copper-gold, iron l d
a
oxide-apatite, and affiliated Na ± Ca (albities) m ,T
deposits in the Great Bear Magmatic zone,
r h
N#orGthweSst STerAritorDies, DCana1da7: Ab-Scp-Qz-Zrn-Rt e g
h i
Economic Geology, v. 111, p. 2045–2072. (<600°C) T H After Corriveau et al., 2016
Mapping alteration through magnetic response
Olympic Dam
10km 10km
Residual gravity Residual magnetics
#GSSADD17