Evolution of kimberlite exploration – systematic exploration using a ground geophysical toolbox for kimberlites, Slave Craton, NT, Canada

Abstract

Diamond exploration in the Slave Craton within the Northwest Territories of Canada has been ongoing since the first kimberlite discovery at Point Lake kimberlite in 1991. Thousands of sediment samples have been collected and hundreds, if not thousands, of geophysical surveys have been completed over the past three decades. The results of which have, at times, perplexed explorers, demonstrating that the search for kimberlites is complex and that no silver bullet exists for their discovery. Recently, a more systematic approach to exploration has shown that despite these challenges, there is still great potential to discover economic kimberlites in the Slave Craton. The Kennady North Project (a wholly-owned subsidiary of Mountain Province Diamonds Inc.) has established that a program that methodically incorporates drill targeting and drill hole results systematically with till sampling, airborne geophysics and a toolbox of ground-based geophysics is critical to kimberlite discovery. Applying this systematic approach has led to the discovery of the Kelvin and Faraday kimberlites, which had previously eluded explorers, at least partially due to the bias of searching for the classic “vertical carrot-style” emplacement model. The Kelvin and Faraday kimberlites instead demonstrate emplacement at inclined angles, which produce different geophysical responses, have much smaller surface expressions, yet still contain significant economic potential. A tailored ground geophysical toolbox comprising electromagnetics [horizontal loop (HLEM)], gravity, resistivity surveys [capacitively-coupled (CCR) and snowmobile-towed] and magnetics helped to guide drill targeting at the Kennady North Project. This drill targeting assisted with the identification and delineation of the Kelvin kimberlite into an 8.5 million tonne indicated resource with 13.62 million carats and the Faraday 2 and 3 kimberlites into an inferred resource of 3.94 million tonnes with 7.35 million carats (Vivian et al. 2019).