geophysical expressions of ore systems · methodology technique airborne surface borehole marine...
TRANSCRIPT
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© Condor Consulting 2014
Geophysical Expressions of Ore Systems Our Current Understanding
Saskatchewan Geological Open House
December 2, 2014
Ken Witherly
Condor Consulting, Inc.
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© Condor Consulting 2014
The business challenge
MinEx Consulting
Depth of cover for base metals discoveries
(>0.1% Cu-equiv.) made in Western world
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© Condor Consulting 2014
The business challenge
Depth to top of ore body for (>0.1 Moz) gold
discoveries made in Western world
MinEx Consulting
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© Condor Consulting 2014
The business challenge
Average depth of cover for discoveries-all metals
Western world: 2003-2012
MinEx Consulting
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© Condor Consulting 2014
The business opportunity
Jon Hronsky (2009)
Modeling for a Voisey’s Bay style orebody in remote WA (30 Mt @ 2.5% Ni, 2% Cu; 20 m thick, 60° dip)
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The business opportunity
Courtesy of D Wood (after Chitombo)
Planned or possible Super Block Caves
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Defining the Foot Print/Foot Path
Modified from Australian Academy of Sciences (2010)
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© Condor Consulting 2014
Defining the Foot Print/Foot Path
Modified from Australian Academy of Sciences (2010)
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In the range of 0 - 250 m
Ford et al. (2007)
Matrix of geophysical techniques
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In the range of 250 m - 1.5 km
METHODOLOGY TECHNIQUE AIRBORNE SURFACE BOREHOLE MARINE
POTENTIAL FIELDS Magnetics X X X X
Gravity X (limited
bandwidth)
X X X
ELECTROMAGNETICS
(EM)
active source X (limited
bandwidth)
X X limited
passive X (limited
bandwidth)
X ? limited
ELECTRICAL resistivity ø X X limited
chargeability X (limited
bandwidth)
X X limited
SEISMIC seismic ø X X X
Ø = not applicable X = nominal
Matrix of geophysical techniques-II
Condor Consulting
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Some hope…
1.8 km
Conductive
shale ZTEM 2D inversion
ZTEM 3D inversion
ZTEM airborne EM mapping conductive horizon at 1.8 km
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Going to depth…
“We can see deep but things are blurry”
Joel Jansen-Teck
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Logging while drilling
Hillis (2012)
Plans of the DET-CRC; coil tube drilling and log-while drilling
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Cheng et al. (2009)
Logging while drilling…the hope
With more petrophysical information…
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Cheng et al. (2009)
Logging while drilling…the hope
…better subsurface models can be produced with a
higher likelihood of successful testing
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Examples-porphyry Cu-Au-Bingham Deposit-Utah
Steinberger et al. (2013)
Geology
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Examples-porphyry Cu-Au-Bingham Deposit-Utah
Steinberger et al. (2013)
TMI-RTP Geological model derived from TMI-RTP
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Examples-porphyry Cu-Au-Pebble Alaska
Anderson et al. (2013)
TMI-RTP
TMI-RTP
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Examples-porphyry Cu-Au-Pebble Alaska
Anderson et al. (2013) TMI-RTP
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McMonnies and Gerrie (2007)
Examples-porphyry Cu-Au-Resolution Arizona
Geology MT section; unconstrained inversion
MT section; constrained inversion
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Townsend et al. (2010)
Examples-Carlin gold-Carlin Nevada
Mapping structures & stratigraphy
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Unconformity uranium model
JNR Uranium
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Variations in physical properties; density; either high or low.
Jefferson et al. 2006
Low density halo High density halo
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Features not seen before and as yet unexplained
Condor Consulting
~10 km
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Features not seen before and as yet unexplained
Condor Consulting
~10 km
But no conductor!
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Features not seen before and as yet unexplained
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Data Integration
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Data Integration
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Data integration will be critical; but real integration is much more than simply having all your data on the same ‘bus’ (platform)…
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The HR issues are significant!
Condor Consulting
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© Condor Consulting 2014
Where we are…
• The concept of mineral systems in now 20 years old-ideas take time to
gain acceptance.
• The geophysical signatures of mineral systems are now starting to
be recognized.
• Some deposit styles will have larger signatures than others.
• Subsurface information will be critical to effective vectoring.
• Data integration will be judged on the metric that the whole is
greater than the sum of the parts…
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Acknowledgments
• Cam McCuaig, Graham Closs and Richard Schodde have provided much
insight into the issues related to undercover exploration.
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There is hope!
Undercover 2020-Sept 2010
Geologists working with geophysical data to map undercover porphyry Cu-Au systems.