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Borehole Resistivity Logging and Tomography for Mineral Exploration

Geoserve Logging & Tomography. Borehole Resistivity Logging and Tomography for Mineral Exploration W. Qian, B. Milkereit, G. McDowell, K. Stevens and S. Halladay www.geo-lt.com. B. A. N. M. WHY ?. Continuities of conductors between boreholes Identification of conductors offhole

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Borehole Resistivity Logging and Tomography for Mineral Exploration

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

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

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

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

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

  6. Vertical Resistivity Profiling A M N Apparent Resistivity B

  7. Borehole intersects sulfides in conductive environment

  8. Borehole pass by sulfides in conductive environment

  9. Borehole intersects sulfide in resistive environment Log10

  10. Borehole pass by sulfide in resistive environment Log10

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

  12. Borehole to Borehole Electrode Configuration B A N M

  13. B1 B2 Projection Plane B3

  14. B1 B3 B2

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

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

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

  18. B1 B3 B2

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

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

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

  22. No Electrode Coverage Zone II Zone I No Electrode Coverage

  23. 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.

  24. 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

  25. Conclusions • 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

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

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

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