integrated spectral mapping of gold related...
TRANSCRIPT
GSWA OPEN DAY 2016, 26 FEBRUARY
MINERALS RESOURCES
‘Promoting the Prospectivity of Western Australia’
M. A. WELLS, C. LAUKAMP AND L. HANCOCK
Integrated Spectral Mapping of Gold Related Alteration Mineral Footprints, Nanjilgardy Fault, WA.
Acknowledgments
GSWA Perth Core Library Northern Star Resources Ltd. CSIRO – MR Colleagues
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Geological setting: Capricorn Orogen
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Mt Olympus
Paulsens
10GA-CP1
50 km
Wyloo Group Shingle Creek Gp
Dolerite sills
Capricorn Orogen: General Stratigraphy
Au at Mt Olympus in meta-sediments of the McGrath Formation • Duck Creek Dolomite • Dated at 1740 Ma
(xenotime analysis)
Carlin-style deposit • Solid-solution, inclusions of
Au in pyrite
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Johnson et al., 2013
Johnson et al., 2013*
WylooGroup
Ashburton Fm. Mudstone, siltstone, wacke, conglomerate
Duck Creek Dolomite
Dolomite, siltstone, chert
Mount McGrath Fm.
Ferruginous epiclasticsedimentary rocks
Cheela Springs Basalt
Basalt, subordinate tuff and sandstone
Beasley River Quartzite
Quartz sandstone
Angular Unconformity
- Mount Olympus, Stynes,Marcus, Zeus, Styx, Hermes
- Amphitheatre, AugustusAu
mineralisation
- West Olympus
WylooGroup
ShingleCreekGroup
Johnson et al., 2013 Australian Journal of Earth Sciences, 60, 681–705
Johnson et al. 2013
Alteration Mineralogy Au-related to strong sulfide alteration and variously: • Quartz or quartz-sericite • Silica, sericite and carbonate
Other minerals? Sulfates, kaolin minerals • Low-T, hydrothermal alteration
Strongly spectrally active: • SWIR, 1.0–2.5 µm • TIR, 6–14.5 µm
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GSWA HyLogger-3. Photo from Lena Hancock
Project Objectives
Opportunity to develop 3D mineral characterisation of potential structurally related, alteration footprints that may be associated with Au-mineralisation along the NF corridor Integrate HyLogging-3™ and remotely sensed data (ASTER), within a validated mineralogical framework: • Approach follows a ‘bottom-up’ methodology • Adds value to GSWA’s precompetitive spectral data
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HyLogging
Validation: XRD and Geochemistry
Core-scale alteration mineralogy
Deposit scale 3D-visualisation
Local scale alteration patterns (ASTER, regolith geochem)
Proximal Sensing
Remote Sensing
Regional scale alteration patterns (ASTER, AEM, regolith geochem)
Hydrothermal Alteration: Mineral Indicators
Two mineral groups used as indicators of hydrothermal alteration: • Al-clay minerals (white
mica, kandites) • Sulphates (alunite,
jarosite)
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Parameter Mineral Group Geological environment Active wavelength range [nm]
Advanced argillic alteration Pyrophyllite Porphyry ~ 2160
Advanced argillic alteration Alunite Epithermal ~ 1480, ~ 1760
(Advanced) argillic alteration
Kaolinit/Dickite Epithermal ~ 2160/2180, ~ 2200
Tschermak exchange due to pH and/or T
White mica, Al-smectites Hydrothermal (metamorphic?)
~ 2200
Spectral parameters of ‘indicator’ mineral groups and examples of the associated geological environment.
HyLogging and Spectral Mineralogy Sulfates • Alunite, KAl3(SO4)2(OH)6
• Jarosite, KFe33+(SO4)2(OH)6
– Increasing T favours Na-alunite over K-alunite
Absorption features are relatively unique • Spectral separation of sulfate types • In the core sulfate phases hard to distinguish
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Jarosite K-alunite Na-alunite
Alteration Mineralogy vs. Au mineralisation (MOD4) Siltstones interlayered with carbonates, dolomites and sandstones
Au in sandstone and siltstone • 33 ppm @54 and 82 m
Jarosite (proximal) to Au mineralisation altered to Na/K-alunite
Kaolinite with alunite
More distally kaolinite replaced by dickite+mus • No carbonate or chlorite
detected • No major changes in quartz
abundance (TIR data)
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MOD4: 190.6 m (11.7–202.3 m), above interval 70–95 m
Mineralised zone81–85 m
Au (p
pm)
kaolinite
dickite
alunite and/or kaolin group
kaolin group
white mica
Na-alunite
K-alunite
jarosite
Kaol
inite
+K-
Alun
ite
Kaol
inite
K-Al
unite
Na-A
luni
te
Na-A
luni
te+
Jaro
site
Jaro
site
Dick
ite
Dick
ite
Kand
ite
Musc
ovite
Kaol
inite
+Na
-Alu
nite
Kand
ite
K-Al
unite
Na-A
luni
te
K-Al
unite
Kaol
inite
+Na
-Alu
nite
Kaol
inite
+Na
-Alu
nite
Kand
ite
Musc
ovite
Musc
ovite
Quar
tz
Alun
ite an
d/or
kaol
in
grou
p ab
unda
nce
inde
x
Al-c
lay
abun
danc
e in
dex
Sulp
hate
ab
unda
nce
inde
x
Sulp
hate
ab
unda
nce
inde
x
B
C
D
Sandstone Siltstone Qtz-veinA
E
Mineralisation Styles Au-related mineral alteration patterns identified in common rock types at Mount Olympus • Sandstone (Type-A, B) • Siltstone (Bright/Black) • Conglomerate
Potential hydrothermal minerals interpreted as: • Na/K-alunite (proximally) • Well-ordered kaolinite, dickite and pyrophyllite
– (indicative of advanced argillic alteration) • Muscovite
– (indicative of phyllic alteration) • Fe/Mg-chlorite and carbonate (distally)
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Mt Olympus
Paulsens
10GA-CP1
50 km
Wyloo Group
Shingle Creek Gp
Dolerite sills
Visualisation of Alteration Mineralogy
Deposit-scale alteration patterns Only drill holes closest to Mt Olympus included • 17 drill holes
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Shingle Creek Gp
Wyloo Gp
3D modelling: Au and sulphate Zoe Fault steeply inclined, striking NW-SE • Most significant structural feature
Isovolumes define: • Highest sulphate abundance (yellow) (A) • Au (>0.5 ppm) and sulphate abundance (B) • Largest Au zone exhausted(?) • Mt Olympus pit
Smaller, poddy zones of Au mineralisation plunging to the SE (intersected by Zoe Fault) • Similar trend for sulphates
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Plunge +20° Azimuth 073°
500 m
Plunge +44° Azimuth 075°
300 m
MOD4
White-mica and chlorite visualisation Al-poor white-mica proximal and shows a similar trend as Au and sulphate alteration
Al-rich white mica in Mt Olympus pit associated with main Au zone
Fe-rich chlorite ‘envelopes’ Al-poor white mica
Change to Mg-rich chlorite proximal to the largest zone of Au mineralisation
In the pit ore zone • Fe-rich chlorite in the upper part • Underlying Mg-rich chlorite
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Plunge +20° Azimuth 073°
300 m
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ASTER vs. HyLogger: Spectral Mineralogy Hyperspectral indicator minerals as ASTER products • Diagnostic mineral features ‘lost’ in
ASTER data
• 1480 nm alunite feature not detected
• Kaolin Group Index Product maps only ‘Kaolinite/Alunite’
• Still ‘track’ white-mica and chlorite related features
14 |
HyLogger ASTER
ASTER Alteration Mapping Patterns in MgOH Group Content and Opaques Index • Correlated with major structures around Mt
Olympus • Widespread, elevated MgOH content related to
pervasive white mica+chlorite assemblages • Close to joint/fault intersections (black arrow)
Elevated Opaques Index values coincident to elevated MgOH values • Potential occurrence of black shales, e.g., in
MOD13
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MgOH
Mt Olympus
Opaques
Mt Olympus
ASTER vs. AEM Correlating remotely sensed mineral patterns to deeper, sub-surface features • Inversion modelling of AEM data • FID59 Tempest line
No significant change in the MgOH Group Content along NF • High conductivity domain (South)
separated from low conductivity domain (North)
3 conductivity highs between OF1 and NF (pink arrows) continue East and West, mapped by MgOH Group Content Product
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Lower Wyloo Grp
Upper Wyloo Grp
NN
A B
C
D
NMOD005NMOD004
NMOD002MOD04
SPD001
2200 m Mt Olympus
Shingle Creek Group
Wyloo Group
ASTER MgOH Group Content product (blue - low content, red -high content) over greyscale DEM
ASTER vs. Regional Geochemistry ASTER Silica Index, Ferric Oxide Content and AlOH Group showed coherent patterns related to distinct lithologies South of NF, high Silica Index values may follow WNW-trending lithologies • Correlate with modelled high SiO2 contents
Shingle Creek Grp, low/void of Silica Index • Matches high MgOH/Carbonate abundances
North of NF (Hamersley Basin), low/void Silica Index values • Correlates with modelled low SiO2 contents
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Mt Olympus
Conclusions HyLogger characterisation identified four Au-mineralisation alteration patterns • Logged lithology and gold assay data • Validation through XRD and compositional analyses
Potential hydrothermal alteration phases in common rock types along the Nanjilgardy Fault are: • Na/K-alunite, kaolin (kaolinite, dickite), pyrophyllite, white mica and chlorite
(proximal) (distal)
New alteration mineralogy identified • Sulfate-white mica-kaolin
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Conclusions White mica and chlorite were widespread • White mica has a characteristic hydrothermal spectral signature and occurs throughout
alteration footprints for all mineralisation types
Chlorite abundance increased away from mineralisation • Difficult to differentiate between regional metamorphic and later hydrothermal types
Kaolinite and dickite occurred proximally to all four mineralisation types • Distribution restricted to certain intervals in drill cores
Jarosite probably formed during sulfide oxidation
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Conclusions Identified small-scale hydrothermal mineral footprints (metre-decametre) in proximal (HyLogging) data
Some ASTER mineral products (MgOH Group Content), AEM data, mapped distinct, conductive, sub-surface geological domains • Define structures (faults, lithological contacts, bedding-parallel shear zones) not previously mapped
Evidence for significant alteration zonation associated with NF not found in multispectral, remotely sensed (ASTER) data • ASTER may not be sensitivity enough (spectrally/spatially) to detect small-scale alteration systems • Future exploration programmes use available airborne, hyperspectral (AMS or Hymap) data or soon to be
launched hyperspectral satellites (e.g. EnMAP) for detecting potential, small-scale alteration associated with large-scale structures, such as the Nanjilgardy Fault
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Thank you
Mineral Resources
Martin Wells Research Geologist: Iron Ore/Ni laterite t +61 8 6436 8812 e [email protected] w www.csiro.au
“Coffee time….”
References
Johnson, S.P., Thorne, A.M., Tyler, I.M., Korsch, R.J., Kennett, B.L.N., Cutten, H.N., Goodwin, J., Blay, O., Blewett, R.S., Joly, A., Dentith, M.C., Aitken, A.R.A., Holzschuh, J., Salmon, M., Reading, A., Heinson, G., Boren, G., Ross, J., Costelloe, R.D. and Fomin, T. 2013. Crustal architecture of the Capricorn Orogen, Western Australia and associated metallogeny. Australian Journal of Earth Sciences, 60, 681–705.
Sener, A.K., Young, C., Groves, D.I., Krapez, B. and Fletcher, I.R. 2005. Major orogenic gold episode associated with Cordilleran-style tectonics related to the assembly of Palaeoproterozoic Australia? Geology, 33 (3), 225–228.
Tyler, I.M., Johnson, S.M., Thorne, A.M. and Cutten, H.N. 2011. Implications of the Capricorn deep seismic survey for mineral systems. Capricorn Orogen seismic and magnetotelluric (MT) workshop 2011, 115–120.
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Extra Slides
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Chlorite Spectral Chemistry Changes in Fe:Mg ratio occur as a shift in the wavelength of the ≈2250 nm absorption feature Chlorite absorption feature shifts to longer wavelengths as %Fe content increases
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Fe-rich
Mg-rich
Wavelength in nm1400 18001600 2000 2200 2400
Ref
lect
ance 1415
1406
1907 1992
1907 2008
22612360
2251
2345
Fe absorption near 1100 nm causes variable gradients in this region
Increasing Fe content
Chlorite Chemistry: Spectral vs. XRD validation
Influence of Fe substitution in chlorite • Odd-numbered (001 and 003),
basal peaks weaker (less intense) • Even-numbered (002 and 004),
basal peaks stronger
With increasing Mg content • odd-numbered peaks increase • even-numbered peaks decrease in
intensity
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Mica Chemistry: Spectral composition Tschermak exchange in micas (AlIVAlVISiIV-1(Fe,Mg)VI
-1) reflects hydrothermal fluid composition (e.g., T and pH conditions): • muscovite = more acidic vs. phengite
= less acidic • muscovite = low-T recharge zones vs.
phengite = high T hydrothermal fluids
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Wavelength in nm2200 2300 2400 250021002000
Reflectance(offset
forclarity)
2207
2189
Paragonite
Muscovite
Position of 2200 nm feature not related to Na-K exchange between paragonite-muscovite. Related more to decrease in AlVI content with replacement by Mg/Fe: • high-Al/low-Si micas (e.g. muscovite) to low-Al/high-Si micas (e.g. phengite)