There are many success stories attributed to revisiting of historic diamond projects that resulted in new resources and diamond mines. The Letseng mine in Lesotho was initially operated on a small scale by several major diamond mining companies starting in 1968. However, it was deemed uneconomic and subsequently shut down in 1982. It was not until 2006 that Gem Diamonds, the third company to undertake mining at the site, realized the full potential of the deposit and recovered significant quantities of some of the highest-value diamonds in the world. Another example would be the AK6 kimberlite in Botswana which was evaluated in the early 1970s and deemed uneconomic by a major. It was only after 2010 that it was developed into the Karowe mine which produces the world’s largest diamonds. Closer to home in the NWT, the Kennady North project was initially explored and discovered in the late 1990s by multiple companies that eventually left the ground. It was not until 2012 that Kennady Diamonds developed the geology of multiple pipes, ultimately proving up a resource of 20.97 million carats with an estimated value of 1.76 billion USD.
The two biggest challenges facing explorationists revisiting diamond projects in the NWT and Nunavut are the remote, pristine, and undeveloped nature of the environment and navigating through the large amount of data related to kimberlites compiled for more than 30 years. Revisiting kimberlite projects requires a prioritized approach, considering not only geological aspects but also economic factors, mining, and regulatory framework considerations. This contribution will focus specifically on the geological criteria.
When considering revisiting a historic diamond project area, the following should be considered: position on the craton and structural setting, neighbouring kimberlites, glacial geology and thickness of overburden, country rock geology, glacial sediment sampling results, and available geophysics. If kimberlites exist within the project area of interest, the distribution and representivity of the drillcores are extremely important as well as sampling methods (for microdiamonds, mineral chemistry, etc.). If bulk sampling has been completed and macrodiamond information is available, updated valuations of the diamonds must be completed.
Once the data for a particular area has been compiled, the reinterpretation exercise begins. Our understanding of geological processes, exploration methods, evaluation, and diamond mining has significantly evolved in the NWT and Nunavut over the last 30 years. The NWT and Nunavut are considered mature kimberlite mining districts where multiple successful mining operations (EKATI, Diavik and Gahcho Kue) have been developed as well as mining project failures (Jericho and Snap Lake), all of which have contributed significantly to our knowledge and understanding of what an economic diamond deposit looks like. Application of this knowledge and reinterpretation of the available historical data revealed opportunities, and this presentation focused on specific geological developments that needed to be considered when reviewing historic projects.
