Designing Borehole IP Surveys

By Joe Mihelcic, Geophysicist ClearView Geophysics Inc.

Ontario Exploration & Geoscience Symposium “New Ideas, Revisiting Past Discoveries” December 7, 2010

What is Borehole IP (BHIP)?

 Any induced polarization survey that utilizes boreholes to:  Inject current or  Measure potentials

When is BHIP applied?

 Most common scenario is that favourable mineralization intersected in at least one borehole:   Test if target is chargeable Quantify in or around borehole   Determine Orientation/Direction/Extents Prioritize available geophysics and drilling data

How to achieve this with BHIP?

 Many configurations and methods available:   Mise-a-la-masse In-hole Pole-dipole and dipole-dipole   Hole-to-hole Gradient  Etc. etc.

Designing BHIP surveys

 Keep it simple   Configure using basic physics Include external data  Consider cost/risk vs. benefit/reward  E.g., tomographic mode for mineral exploration?

Example:

 Favourable mineralization detected in a number of boreholes spread over wide area  Favoured theory suggests overall mineralizatoin plunges towards the northwest  Attempt BHIP to test this theory from borehole with good intersection  158.2 m -193.6 m

Step 1

 Run a simple dipole-dipole detection log to determine if intersected zone is chargeable:

Step 2

 Charge the target zone with Current Electrodes above and below the zone:  C1 = 162 m (VG at 176 m)  C2 = 225 m  Read potentials on surface  Ensure lines at 90 degrees to BH direction  Tie-in to surface BH’s (bush crash)

Step 2

 Axis ‘A’ identified along chargeability trend

Step 2

 Axis ‘A’ identified along chargeability trend

Step 3

 Compare to available geophysics data

Step 3

 Compare to available geophysics data

Step 3

 Compare to available geophysics data

Step 4:

 Focused post-processing of previously acquired surface pole-dipole geophysics data  Inversion modeling  Overlay drilling locations in 3D

Step 4:

- Not available on website download due to size - Available upon request

Step 5:

 Which boreholes drilled through zone?

 Re-examine logs to find anomaly source  Recommend tighter drilling along source axis if favourable intersections already encountered

Conclusions:

 BHIP requires more customization than standard surface arrays  Inversion modeling useful in some cases, at end of process, especially for 3D visualization  A method to further prioritize surface IP results