GSWA-IntegratedSpectralMapping_MartinWells.pdf

Integrated Spectral Mapping of Gold Related Alteration Mineral Footprints

1. GSWA OPEN DAY 2016, 26 FEBRUARY
MINERALS RESOURCES
‘Promoting the Prospectivity of Western Australia’
M. A. W ELLS, C. LAUKAMP AND L. HANCOCK

Integrated Spectral Mapping of Gold Related Alteration
Mineral Footprints, Nanjilgardy Fault, WA.

2. Acknowledgments
GSWA
Perth Core Library
Northern Star Resources Ltd.
CSIRO – MR Colleagues
Nanjilgardy | GSWA Open Day 2016 2 |

3. Geological setting: Capricorn Orogen
Nanjilgardy | GSWA Open Day 2016 3 |
Mt Olympus
Paulsens
10GA-CP1
50 km
Wyloo
Group
Shingle
Creek Gp
Dolerite
sills

4. 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
Nanjilgardy | GSWA Open Day 2016 4 |
Johnson et al., 2013
Johnson et al., 2013*
Wyloo
Group
Ashburton Fm.Mudstone, siltstone,
wacke, conglomerate
DuckCreek
Dolomite
Dolomite, siltstone, chert
Mount McGrath
Fm.
Ferruginous epiclastic
sedimentary rocks
CheelaSprings
Basalt
Basalt, subordinate tuff
and sandstone
Beasley River
Quartzite
Quartz sandstone
Angular Unconformity
-Mount Olympus, Stynes,
Marcus, Zeus, Styx, Hermes
-Amphitheatre, Augustus
Au
mineralisation
-West Olympus
Wyloo
Group
Shingle
Creek
Group
Johnson et al., 2013 Australian Journal of Earth Sciences, 60, 681– 705
Johnson et al. 2013

5. 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
Nanjilgardy | GSWA Open Day 2016 5 |
GSWA HyLogger-3. Photo from Lena Hancock

6. 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
Nanjilgardy | GSWA Open Day 2016 6 |
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)

7. Hydrothermal Alteration: Mineral Indicators

Two mineral groups
used as indicators of
hydrothermal
alteration:
•Al-clay minerals (white
mica, kandites)
•Sulphates (alunite,
jarosite)
Nanjilgardy | GSWA Open Day 2016 7 |
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.

8. HyLogging and Spectral Mineralogy
Sulfates
•Alunite, KAl
3(SO
4)
2(OH)
6
•Jarosite, KFe
3
3+(SO
4)
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
Nanjilgardy | GSWA Open Day 2016 8 |
Jarosite K-alunite Na-alunite

9. 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)
Nanjilgardy | GSWA Open Day 2016 9 |
MOD4: 190.6 m (11.7– 202.3 m), above interval 70– 95 m
Mineralised zone
81–85 m
Au (ppm)
kaolinite
dickite
aluniteand/or
kaolin group
kaolin
group
white mica
Na-alunite
K-alunite
jarosite
Kaolinite+
K-Alunite
Kaolinite
K-Alunite
Na-Alunite
Na-Alunite+
Jarosite
Jarosite
Dickite
Dickite
Kandite
Muscovite
Kaolinite+Na-Alunite Kandite
K-Alunite
Na-Alunite
K-Alunite
Kaolinite+
Na-Alunite
Kaolinite+
Na-Alunite
Kandite
Muscovite
Muscovite
Quartz
Alunite and/or kaolin
group abundance
index
Al-clay
abundance
index
Sulphate
abundance
index
Sulphate
abundance
index
B
C
D
Sandstone
Siltstone
Qtz-vein
A
E

10. 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)
Nanjilgardy | GSWA Open Day 2016 10 |

11. 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
Nanjilgardy | GSWA Open Day 2016 11 |
Shingle Creek Gp
Wyloo Gp

12. 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
Nanjilgardy | GSWA Open Day 2016 12 |
Plunge +20°
Azimuth 073°
500 m
Plunge +44°
Azimuth 075°
300 m
MOD4

13. 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
Nanjilgardy | GSWA Open Day 2016 13 |
Plunge +20°
Azimuth 073°
300 m

14. Nanjilgardy | GSWA Open Day 2016
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

15. 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
Nanjilgardy | GSWA Open Day 2016 15 |
MgOH
Mt
Olympus
Opaques
Mt Olympus

16. 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
Nanjilgardy | GSWA Open Day 2016 16 |
Lower
Wyloo Grp
Upper
Wyloo Grp
N
N
A B
C
D
NMOD005
NMOD004
NMOD002
MOD04
SPD001
2200 m Mt
Olympus
Shingle
Creek Group
Wyloo
Group
ASTER MgOH Group Content
product (blue - low content, red -
high content) over greyscale DEM

17. 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 SiO
2 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 SiO
2 contents
Nanjilgardy | GSWA Open Day 2016 17 |
Mt
Olympus

18. 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

Nanjilgardy | GSWA Open Day 2016 18 |

19. 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
Nanjilgardy | GSWA Open Day 2016 19 |

20. 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
Nanjilgardy | GSWA Open Day 2016 20 |

21. Nanjilgardy | GSWA Open Day 2016
Thank you
Mineral Resources
Martin Wells
Research Geologist: Iron Ore/Ni laterite
t [phone]
e [email protected]
w www.csiro.au
“Coffee time….”

22. 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.
Nanjilgardy | GSWA Open Day 2016 22 |

23. Extra Slides
Nanjilgardy | GSWA Open Day 2016 23 |

24. 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
Nanjilgardy | GSWA Open Day 2016 24 |
Fe-rich
Mg-rich
Wavelength in nm
1400 18001600 2000 2200 2400
Reflectance
1415
1406
19071992
1907
2008
2261
2360
2251
2345
Fe absorption near
1100 nm causes variable
gradients in this region
Increasing
Fe content

25. 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
Nanjilgardy | GSWA Open Day 2016 25 |

26. Mica Chemistry: Spectral composition
Tschermak exchange in micas
(Al
IV
Al
VI
Si
IV
-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
Nanjilgardy | GSWA Open Day 2016 26 |
Wavelength in nm
2200 2300 2400 250021002000
Reflectance
(offset
for
clarity)
2207
2189
Paragonite
Muscovite
Position of 2200 nm feature not related to Na-K exchange between paragonite-muscovite.
Related more to decrease in Al
VI
content with replacement by Mg/Fe:
•high-Al/low- Si micas (e.g. muscovite) to low- Al/high- Si micas (e.g. phengite)