Ground Geophysical Techniques In Northern Kimberlite Exploration – Recent Innovations
The range of ground geophysical surveys employed in kimberlite exploration has expanded from magnetic field and frequency domain electromagnetic (EM) to include time domain EM, gravity, ground penetrating radar (GPR), capacitively coupled resistivity (CCR) and seismic surveys. Gravity has become a third tool of choice after magnetics and EM in target discrimination following the introduction of BHP Billiton’s Falcon airborne gradiometer system. Responses from kimberlite pipes can be as low as 0.5 mGal and careful field procedures are required to minimize the noise introduced during reductions. These include carrier phase GPS leveling, bathymetry corrections adapted for small lakes, and accurate terrain corrections using digital terrain models. CCR is a useful complement to airborne resistivity surveys and can achieve depths of penetration in the order of 50 to 100 m. GPR can detect distinct reflections from various kimberlite facies to depths of 50 m and has proven most useful in delineating kimberlite pipes located with other surveys. GPR is a primary exploration tool in the search for kimberlite dykes at the head of indicator mineral trains. Finally, advanced 3D potential field and 2D EM interpretation algorithms permit the assessment of target geometry and can improve drilling success rates.