Borehole radar application to kimberlite delineation at Finsch diamond mine

Abstract

Finsch Mine is a world class diamond mine in the Northern Cape province of South Africa, producing roughly 2.4 million carats annually. The mine is currently busy with a project aimed at determining the feasibility of exploiting the resource below the current extraction level located 630 m below surface (Block 5). In order to assist with delineating complex kimberlite pipe morphology at depth, the mine embarked on a project to evaluate borehole geophysical techniques that could be applied to detect and map the contact of the kimberlite pipe. To this effect, GeoMole borehole radars (BHR) were deployed down two boreholes at 650 m level to perform single hole profiling as well as cross-hole scanning surveys. The objective of the BHR survey was to determine whether coherent reflection from the kimberlite?country rock interface could be obtained, and to establish the limits on the operational parameters such as range and resolution. After data processing, using GeoMole?s SeisWin software, a coherent reflection from the kimberlite pipe contact was clearly observed from distances up to 60 m through the dolomite country rock. The kimberlite interface appears to be quite sharp, cemented, smooth and curved. The BHR results indicated that the kimberlite pipe surface did not resemble a smooth cone, but revealed three horizontal rounded ridges, penetrating 4 m to 8 m into the country rock, across the imaged flank of the pipe. The range, resolution and accuracy obtained from the BHR surveys at Finsch Mine are of such high quality that it enhances the detail of and confidence in, pipe morphology significantly. This allows for more accurate geological modelling and resource estimations, resulting in meaningful project evaluation, tunnel design and ultimately sound investment decisions.