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

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

3. WHY NOW ? Forward modeling studiesB M N
Forward modeling studies
Multi-electrode array instrumentation

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

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

10. Vertical Resistivity ProfilingM N
Apparent
Resistivity B

11. Borehole intersects sulfides in conductive environment

12. Borehole pass by sulfides in conductive environment

13. Borehole intersects sulfide in resistive environment
Log10

14. Borehole pass by sulfide in resistive environment
Log10

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

16. Borehole to Borehole Electrode ConfigurationM

17. B1 B2
Projection Plane B3

18. B3 B1 B2

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

20. 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

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

22. B3 B1 B2

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

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

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

26. No Electrode Coverage
Zone II
Zone I
No Electrode Coverage

27. 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.

28. 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

29. Conclusions
Detect conductive zones within 30 m range around the borehole
Provide independent estimate of bulk ( 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

30. 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

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