Next Generation Mineral Mapping: Queensland Airborne HyMap and Satellite ASTER Surveys ...

160 Pages·2009·15.94 MB·English

Next Generation Mineral Mapping:
Queensland Airborne HyMap and
Satellite ASTER Surveys 2006-2008

Thomas Cudahy1, Mal Jones2, Matilda Thomas3, Carsten Laukamp4,
Mike Caccetta1, Rob Hewson1, Andrew Rodger1 and Mike Verrall1

CSIRO Exploration & Mining Report P2007 / 364

18 December 2008

1 CSIRO Exploration and Mining, ARRC, PO Box 1130, Bentley, WA 6102, Australia
2 Geological Survey of Queensland, 80 Meiers Road, Indooroopilly, QLD 4068, Australia
3 Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia
4 James Cook University, Economic Geology Research Unit, Townsville, QLD 4811 Australia

Enquiries should be addressed to:
Dr Thomas Cudahy
Geologist and Group Leader for Minerals and Environmental Sensing
CSIRO Exploration and Mining
Australian Resources Research Centre (ARRC)
Street: 26 Dick Perry Avenue, Kensington, WA, Australia, 6151
Postal: PO Box 1130, Bentley, WA, Australia, 6102
phone: [phone]
mobile: [phone]
fax: [phone]
email: [email protected]
http://www.csiro.au/csiro/content/standard/ps16a,,.html
http://www.em.csiro.au/NGMM

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Which way to go?
CONTENTS
SUMMARY................................................................................................................. 1
INTRODUCTION........................................................................................................ 4
Mineral Systems............................................................................................... 4
Mineral Mapping............................................................................................... 4
Next Generation Mineral Mapping.................................................................. 7
OBJECTIVES............................................................................................................. 8
EXPECTED DELIVERABLES.................................................................................... 8
STRATEGY................................................................................................................ 9
DATA AND COVERAGE........................................................................................... 9
Airborne HyMap sensor................................................................................... 9
Airborne HyMap data coverage.................................................................... 10
Satellite ASTER sensor ................................................................................. 11
SWIR Cross-talk effect......................................................................................12
Airborne geophysics ..................................................................................... 12
Field sampling................................................................................................ 12
Laboratory Analyses...................................................................................... 12
Reflectance.........................................................................................................12
Emissivity...........................................................................................................13
X-Ray Fluorescence..........................................................................................13
X-Ray Diffraction................................................................................................13
Mineral interpretation...........................................................................................13
Clay identification.................................................................................................13
Scanning electron microscope........................................................................14
Electron microprobe..........................................................................................14
IMAGE PROCESSING............................................................................................. 14
HyMap.................................................................................................................15
Atmospheric correction........................................................................................15
Multi-scene information extraction.......................................................................16
Survey calibration................................................................................................17
ASTER.................................................................................................................19
Multi-scene cross-calibration...............................................................................19
Multi-scene information extraction.......................................................................19
Output Image Format........................................................................................19
Queensland Mineral Mapping 2006-2008 i
VALIDATION............................................................................................................ 19
ASTER cross calibration...................................................................................19
HyMap.................................................................................................................21
LABORATORY VALIDATION STUDIES................................................................. 21
White mica physicochemistry....................................................................... 22
White mica from Mount Isa...............................................................................22
Tschermak substitution....................................................................................24
Illite crystallinity.................................................................................................24
XRD analysis.......................................................................................................25
Al-smectite mineralogy.................................................................................. 28
Mineral mapping and spectral resolution.................................................... 29
Information extraction................................................................................... 32
White mica..........................................................................................................32
REMOTE GEOSCIENCE INFORMATION PRODUCT VALIDATION...................... 35
Iron oxide content.......................................................................................... 36
Al-clay content............................................................................................... 38
Vegetation effects.......................................................................................... 40
Lichen effects................................................................................................. 43
Signal to Noise............................................................................................... 45
Compensation for atmospheric residuals.................................................... 45
Surveying wet ground ................................................................................... 46
Along track noise........................................................................................... 48
Wavelength calibration.................................................................................. 50
RELEASED GEOSCIENCE PRODUCTS................................................................ 52
ASTER............................................................................................................. 52
HyMap............................................................................................................. 54
Field and laboratory data .............................................................................. 55
CASE HISTORIES................................................................................................... 56
Proterozoic IOCG Mineral System Analysis................................................ 56
Starra location and geology.............................................................................57
IOCG mineral system model.............................................................................58
ii Queensland Mineral Mapping 2006-2008
Fluid source.........................................................................................................59
Depositional environment....................................................................................60
Fluid pathways.....................................................................................................61
Mineral system summary.....................................................................................63
ASTER mapping..................................................................................................63
Summary.............................................................................................................64
Using the geology to analyse mineral maps................................................ 64
Quartzites around the Mount Isa Pb-Zn and Cu deposits..............................65
Background..........................................................................................................65
Current mineral mapping results..........................................................................66
White mica crystallinity and the Termite Range “growth” fault....................71
Snapshots of open pit mines............................................................................72
FURTHER WORK.................................................................................................... 76
ACKNOWLEDGEMENTS........................................................................................ 77
COMMUNICATIONS RELATED TO THE PROJECT.............................................. 77
REFERENCES......................................................................................................... 80
APPENDIX 1............................................................................................................ 85
Descriptions of the HyMap Blocks for all the Stage 1 and Stage 2 survey
areas...................................................................................................................85
APPENDIX 2............................................................................................................ 87
HyMap Flight line Datum and Projections.......................................................87
APPENDIX 3............................................................................................................ 88
Stage 1 flight line survey times........................................................................88
Stage 2 flight line survey times........................................................................90
APPENDIX 4............................................................................................................ 94
Bureau of Meteorology weather records for Mount Isa, August 2007..........94
APPENDIX 5............................................................................................................ 95
HyMap band centres for Stages 1 and 2 as well as the difference between95
APPENDIX 6............................................................................................................ 96
Stage 1: Field data and laboratory analyses...................................................96
Stage 2: Field data and laboratory analyses.................................................110
APPENDIX 7...........................................................................................................133
HyMap Mineral Mapping Products – Stage 1 (3 August 2007).....................133
HyMap Mineral Mapping Products – Stage 2 (9 December 2008)................140
APPENDIX 8...........................................................................................................148
ASTER Geoscience Products (27 November 2007)......................................148
Queensland Mineral Mapping 2006-2008 iii
APPENDIX 9...........................................................................................................152
Log of cross-track correction of flight-lines (C) and levelling between
blocks (L) for Stage 2 HyMap processing.....................................................152

iv Queensland Mineral Mapping 2006-2008
SUMMARY
This two year collaborative project was established in July 2006 with the overall aim of
developing, validating, evaluating and delivering a suite of publicly available, pre-competitive
mineral mapping products from airborne HyMap hyperspectral imagery and satellite
multispectral ASTER imagery. Moreover, it was important to establish whether these mineral
maps would complement other precompetitive geological and geophysical data and provide
valuable new information for enhanced mineral exploration by the Australian resources
community.
The project was in several parts, including:
• Generating a suite of 15 mineral group maps of the Mount Isa Block (~500K km2)
from satellite multispectral ASTER imagery (~140 scenes);
• Stage 1 (2006-2007): acquisition and generation of a suite of 22 mineral abundance
and mineral composition maps derived from airborne HyMap hyperspectral imagery
(88 flight-lines) covering five structural/mineralised corridors (each about 15 km wide
and 50 km long and covering 8250 km2 ) across the Mount Isa Block; and
• Stage 2 (2007-2008): acquisition and generation of a suite of 29 mineral abundance
and mineral composition maps derived from airborne HyMap hyperspectral imagery
(204 flight-lines) covering four geological provinces (Mount Isa, Georgetown, Charters
Towers and Hodgkinson) across geological/structural/mineralised corridors (each
about 12 km wide and 50 km long and covering 16,000 km2) in north Queensland.
The image processing methodology used to generate the current suite of mineral mapping
products was designed to process multiple flight-lines/images based on a physical model that
does not rely on levelling but instead normalises most/all of the inherent complications typical
of remote sensing data (i.e. topographic shading, surface directional scattering, solar
illumination, residual atmospheric/instrument effects). Furthermore, this methodology aims
to be transferable, i.e. applicable to other similar data, and easily implemented by others
wanting to reproduce similar products.
The mineral mapping processing methodology is based on the assumption that a given
mineral abundance (or composition) is proportional to the normalised continuum-depth
(wavelength, width, and asymmetry) of its diagnostic absorption bands, with zero abundance
equal to no absorption developed. Currently, multiple masks are used to remove possible
overlapping mineral absorptions and other effects like vegetation.
Even with this processing methodology, there remain significant product quality issues
associated with instrument, atmospheric and pixel-unmixing effects. These include: (1) not
all mosaics being seamless; and (2) masks/thresholds not transferable from one date of
acquisition to another. These problems were caused by:
• Different HyMap instrument response functions for each airborne campaign
producing different systematic residual effects;
• Water vapour (and other atmospheric) residuals with intensity proportional to the
amount of water vapour. These generate along-track (flight-line), inter-block and
inter-campaign errors;
• Small wavelength shifts (~1 nm) during the 2007 HyMap survey which produced
along-track (flight-line) errors;
Queensland Mineral Mapping 2006-2008 1
• Lichen, which affected the green vegetation masking;
• Vegetation mixing effects, both green and dry components, which affects the
accuracy of the mineral abundances; and/or
• Environmental effects, including collecting airborne imagery while the ground was
drying after rainfall.
• A new method for green vegetation masking was developed based on measuring leaf
water rather than NDVI because of spectral complications associated with lichen. A
new method was also developed to unmix the effects of green and dry vegetation.
This method was validated and resulted in a new product for release, namely
Unmixed Al-clay content. The other issues described above were characterised and
where possible solutions implemented.
The mineral mapping products have been made available as JPEGs, ECW or TIFF by ftp via
the www.em.csiro.au/NGMM webpage (~10 Gigabytes). The HyMap radiance and
reflectance data, as well as the processed mineral map image files (BSQ format), are
available from the Geological Survey of Queensland by external hard drive (~1 Terabyte).
At this stage, the associated product descriptions provide only a qualitative assessment of
accuracy and what other effects may complicate the geoscience information. Ideally, all
products require more quantitative error analysis, especially if the products are to be
considered as standards. More objective methods are also required: (1) for establishing
product threshold levels, especially with different instrument calibration; and (2) quality
control of products in the processing chain, as there currently exists too much reliance on
specialist interpretation.
As part of the mineral mapping product validation, over 200 field sites were visited and 500
samples collected and measured in the laboratory, including (1) reflectance spectra; (2)
X-ray diffraction (XRD); (3) whole rock chemistry using X-ray fluorescence; (4) scanning
electron microscopy including elemental analysis; (5) electron microprobe analysis of mineral
chemical data; and (6) stable carbon isotopes. Among the key mineral information targeted
in these studies were the (1) white mica (illite-muscovite) crystallinity based on the XRD 001
hkl peak width, which has been used by other workers as a measure of temperature/
pressure of formation; (2) white mica composition, especially the degree of Tschermak
substitution (primarily driven by the tetrahedral Si-content); (3) and smectite clay
composition. The validation work showed that all the tested remote mineral information
products are significantly correlated with the ground validation data, including clay and iron
oxide abundances and different clay mineralogies.
A mineral systems approach was used to appreciate the value of these mineral maps for
exploration. That is, unlocking the value from these mineral maps is not simply by looking for
the red bulls-eyes. Instead, mineral products need to be selected on the basis of critical
parameters, such as what minerals are expected to develop as fluids migrate from source
rocks to depositional sites and then to outflow zones with each associated with different
physicochemical conditions (e.g. metasomatic metal budget, nature of the fluids, water-rock
ratios, lithostatic pressure, pore fluid pressure, REDOX, pH, and temperature). Key products
include: (1) opaques, which are a useful measure of reduced rock; and (2) white mica and
Al-smectite compositions, which are useful for tracking chemical gradients; and (3) kaolin
composition, which is useful for mapping regolith materials, especially “transported” from “in
situ”. Two of the key messages are recognising mineral-chemical gradients and cross-
cutting effects.
2 Queensland Mineral Mapping 2006-2008