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Borehole Resistivity Logging and Tomography for Mineral Exploration W. Qian, B. Milkereit, G. McDowell, K. Stevens and S. Halladay www.geo-lt.com Geoserve Logging & Tomography

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WHY ? A B M N Continuities of conductors between boreholes Identification of conductors offhole Mapping perfect conductors Mapping poor conductors

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WHY NOW ? A B M N Forward modeling studies Multi-electrode array instrumentation

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Very easy to deploy Can acquire vast amount of data rapidly Battery power Easy data QC Rugged design Advantages of the System

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Zn, Pb and Ag (Modest Conductor) Ni-Cu (Super Conductor)

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Vertical Resistivity Profiling A B M N Apparent Resistivity

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Borehole intersects sulfides in conductive environment

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Borehole pass by sulfides in conductive environment

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Log10 Borehole intersects sulfide in resistive environment

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Log10 Borehole pass by sulfide in resistive environment

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VRP survey in a single hole will provide: Bulk background resistivity Information about off-hole conductors

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Borehole to Borehole Electrode Configuration A B M N

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B3 B1 B2 Projection Plane

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B3 B2 B1

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Deeper Ore zone in B2 QC Electric Current Injected between B2 and B3 Current Electrodes in B3 Current Electrodes in B2

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Deeper Ore zone in B2 Ore zone shadow in B3 Current Electrodes in B3 Current Electrodes in B2 QC Electric Current Injected between B2 and B3

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Deeper Ore zone shadow in B3 QC Electric Current Injected between B1 and B3 Current Electrodes in B3 Current Electrodes in B1

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B3 B2 B1

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Massive Sulfide Zone Top Bottom Electric Current between two adjacent electrodes in B2

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Ore zone in B2 Ore zone shadow in B3 Electric Potential between two adjacent electrodes in B3 [mV] 1 mA of current is injected between two adjacent electrodes in B2

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Deeper Zone I Zone II QC Electric Current Injected between B1 and B3

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No Electrode Coverage Zone II Zone I

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A: alteration bleached, no significant Zn mineralization or Pyrite-content, resistivity larger than 40 ohm.m B: brecciation, matrix Pyrite rich ( 5 – 10 % Pyrite), less than 1% Zn content, resistivity between 15 and 40 ohm.m C: strong brecciation, often more than 5% Zn content, resistivity less than 15 ohm.m.

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Inverse Modeling Strategy VRP pseudo section as starting model Sharp inversion of only VRP data (Initial model is the main constraint) Build a model from the two sharp inversion models Fix the near borehole properties and let the tomography inversion work on the resistivity in the central region. The resistivity values can be fixed, semi- fixed (fixed in a narrow range) or completely floating Fine tuning the inversion model with different geological / petrophysical constraints

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Detect conductive zones within 30 m range around the borehole Provide independent estimate of bulk (4 - 100 m) resistivity data for calibration / interpretation of other EM datasets Map conductive zones between the boreholes 180 m apart Works for all conductivity contrasts Very easy field operation procedures Conclusions

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Field test 3D tomography methodologies Develop IP data interpretation Move towards simultaneous data acquisition in multiple boreholes Build cables to deploy in deeper boreholes Outlook

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Nash Creek, Slam Exploration Sudbury, Camiro, NSERC, CVRD, Xstrata, First Nickel Acknowledgement

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