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Assessing the applicability of remote sensing techniques to the environmental assessment of mining a

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Title: Assessing the applicability of remote sensing techniques to the environmental assessment of mining a


1
Assessing the applicability of remote sensing
techniques to the environmental assessment of
mining areas experiences from the Witwatersrand
Gold Field, South Africa
  • Henk Coetzee1 Stéphane Chevrel2
  • 1Council for Geoscience, Private Bag X112,
    Pretoria, 0001, South Africa henkc_at_geoscience.org.
    za
  • 2BRGM Land use Planning and Natural Hazards, BP
    6009 45060 Orléans Cedex 2 France,
    s.chevrel_at_brgm.fr

2
Remote Sensing in Mining Environments
  • Poor track record due to
  • Incorrect tools applied to problems
  • Too much faith in black boxes
  • Poor ground truthing
  • Poor understanding of remote sensing by
    environmental practitioners and vice versa.
  • Application in isolation from other techniques
  • Poor communication

3
Interdisciplinary Approach
  • CGS and BRGM cooperation since 1996
  • Involved diverse scientific disciplines and data
  • Remote Sensing, Geophysics, Geology,
    Geochemistry, Mineralogy, Geomorphology,
    Geography, Environmental Science
  • Combined remote sensing with field campaigns for
    sampling, analysis, ground-truthing
  • GIS as an integrating tool

4
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5
Gold and Uranium in the Witwatersrand
  • The Witwatersrand basin has been mined since the
    discovery of gold in 1886.
  • Estimated production
  • 43 500t of gold 1886-present
  • 75 000t of uranium 1953-1995
  • 300km strike length
  • over 40.000 ha of tailings
  • est. 6 billion tons (Rest of the worlds U
    tailings 600 MT...)

6
Environmental concerns
  • Mining residues
  • sulphates
  • heavy metals
  • As
  • cyanides
  • radionuclides
  • AMD
  • etc..

7
Soil and drainage contamination
8
Acid Mine Drainage
9
Objectives
  • Assess environmental damage from mining at a
    regional scale
  • inventory of polluted areas
  • definition of areas susceptible to pollution
  • identification of pollution pathways
  • Develop a remote-sensing and GIS-based assessment
    methodology
  • in a risk assessment persective

10
Required RS- and GIS- Assessment Capabilities
  • Identification, characterisation and mapping of
    pollution sources
  • Identification and mapping of contaminated
    surface areas
  • Identification and mapping of pollution dispersal
    pathways
  • Mapping groundwater vulnerability

11
Contribution of Remote Sensing and GIS
  • Already achieved
  • Base-maps and land-cover maps. (Landsat TM, SPOT,
    IKONOS)
  • Digital Elevation Models and derived quantitative
    morphology products, using image stereopairs
    (SPOT)
  • Direct detection of radioactive pollution using
    airborne geophysics
  • Creation of various environmental base maps
  • Current development
  • Detailed identification of hot spots and
    mining-related surface features (IKONOS)
  • Planned research
  • Identification of seepage zones and run-off or
    wind-blown plumes using hyperspectral data
    (Hyperion and MODIS Airborne Simulator)

12
Scales of Assessment
Traditional Satellite Imagery Basin-scale
assessment
High-resolution satellite imagery regional to
mine-scale assessment
Scanning electron microscope Mineral grain-scale
assessment
Macro
Micro
13
Satellite imagery gt Land-use mapping
14
Airborne Radiometrics gt surface pollution mapping
15
Geophysical anomalies
  • Elevated count rates are detected from wetlands
    downstream of mining areas in airborne
    radiometric surveys

16
Geophysical anomalies
  • Classification of airborne radiometric data finds
    mine residues and downstream wetlands have a
    similar signature
  • 214Bi/208Tl gt 3

17
Use of Digital Elevation Models DEM gt
Drainage Basin
DEM
Drainage Basin feeding Potch
  • Wonderfonteinspruit

TM Image
18
Contamination Pathways
19
Derived Environmental Maps
  • Results of a multi-criteria GIS analysis
  • Takes into account electrical conductivity and
    hydraulic gradiant in weighting calculation
  • Most of tailings dams are implemented over
    unsuitable areas

20
Very High Resolution (IKONOS)
Direct visual detection of mine tailings spilling
into wetlands
Direct visual detection of mining-related
subsidence features
21
MAS - MODIS Airborne Simulator
  • MAS data were collected in 2000 as part of the
    SAFARI 2000 project, using a Lockheed ER2 aircraft

22
RGB Image - Visible spectrum
Parallelepiped classification - dry tailings
Parallelepiped classification - wetlands
Windblown dust plumes
Seepage
Wetland
Possible use of tailings as building material
23
Contributions of Remote Sensing
  • Up-to date land-cover maps of a rapidly changing
    environment
  • Input into terrain modelling - contaminant flow
    paths
  • Direct detection of pollution
  • Derived datasets which can inform environmental
    decisions - pollution risk maps

24
The future
  • Optical remote sensing has so far proved most
    useful as a mapping tool
  • Very high resolution imagery is proposed as a
    tool in environmental impact assessments and
    monitoring in a multi-scale approach
  • Initial work using hyperspectral imagery shows
    promise for quantitative mapping
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