HIGH RESOLUTION RESISTIVITY A NEW OPAL EXPLORATION TOOL Jingping Zhe,( ZZ Resistivity Imaging Pty Ltd) Brian J. Morris (Principal Geologist, PIRSA Geological Survey Branch)
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HIGH RESOLUTION RESISTIVITY
A NEW OPAL EXPLORATION TOOL
Jingping Zhe,( ZZ Resistivity Imaging Pty Ltd)Brian J. Morris (Principal Geologist, PIRSA Geological Survey Branch)
CONTENTS• Current Opal Exploration Status
• Available Geophysical Methods for Opal
Exploration
• Resistivity Method and Its New
Developments
• Field experiments
• Conclusions
Current Opal Exploration Status
• Almost no geophysical methods are used
• other miners’ mining information
• surface specified vegetation distribution
• randomly digging
That’s why the probability to find opal so small !
Geological features of opal mining area
Opal-hosted structure
• Impermeable layers permitting groundwater pooling
• local traps with sedimentary structure ( bedding
irregularities, floored by impermeable layers, porous
material, voids)• faults, fractures, cracks, silica-bearing groundwater
Sedimentary rocks
weathered sandstone, alluvium with silcrete pebbles,
impermeable or permeable claystone, gypsum, silt-clay,
shales, …
Available geophysical methods
• Seismic method --- high resolution, but high cost
• EM method --- conductive targets (iron, copper ore bodies)
• Air magnetic method --- larger scale exploration
• Ground magnetic method --- regional lithology mapping,
• Resistivity method --- high resolution, low cost
• Ground penetration radar --- high resolution, limited depth
Resistivity Method and our New Developments
• Traditional resistivity method: sounding,
profiling, well-logging
• New developments of the method: high
resolution imaging (subsurface, crosshole)
• Our development: FlashRES64 – an advanced
high resolution resistivity exploration system
Principle of the
resistivity method
Traditional resistivity method
New developments of resistivity method
For high resolution imaging
• Large number data collection (equipment)
• Subsurface true resistivity reconstruction
(softwares)
Our development: FlashRES64 – an advanced high resolution resistivity exploration system
Practical Advantages of the ZZ Resistivity Imaging System
• Easy to operate, no special train needed
• Can quickly collect 60k data points
• 2D true resistivity distribution cross section gives a
view of underground geological structure
Coober Pedy Trials
Site 1: Resistivity imaging result
•Good correlation between resistivity and lithology•Low opal prospectivity: smooth resistivity contours
Site 2: Resistivity imaging result
•correlation between resistivity and lithology•high opal prospectivity: low resistivity intrusions
Site 3: Resistivity imaging result
•correlation between resistivity and lithology•high opal prospectivity: low resistivity intrusions
Lightening Ridge Trials (NSW)
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• very similar to Coober Pedy sites 2 & 3: high opal prospectivity: low resistivity intrusions
Comparison
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High opal prospectivity
low opal prospectivity
CONCLUSIONS
• Trial results: good correlation between resistivity and lithology,
delineate subsurface structure for opal exploration, indicates low
or high opal prospectivity
• Opal miners need some advanced exploration tools to change the
random digging habit and increase the chance to find opal
• Resistivity imaging method is a most cost effective method among
various geophysical methods
• FlashRES64 is an advanced high resolution resistivity exploration
tool, which is affordable for opal miners and can produce a relative
accurate geological cross-section for easy interpretation.
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