The NWT’s Ekati mine is staking its future on the use of large underwater crawlers to extract more diamond-containing kimberlite from pits that would otherwise be uneconomical to mine.
At the moment, conventional open-pit and underground mining at Ekati is set to end in 2024, with the exception of Point Lake – a new open pit currently going through the environmental permitting process.
Arctic Canadian Diamond Company, which bought Ekati from financially troubled former owner Dominion earlier this year, says the switch to underwater mining technology is the only way Ekati can stay open in the long term.
“As we go deeper into those ore bodies, the value does not support continued mining using conventional techniques,” said Rory Moore, Arctic’s president and chief executive, in a presentation at this week’s NWT Geoscience Forum.
“We needed a method that we could mine at a high tonnage but at a measurably lower cost in order to keep Ekati viable.”
A trial of the underwater crawler design will take place in 2023 and 2024, when Arctic will test one at the base of its existing, flooded Lynx pit. A full production trial is then scheduled for the Sable pit from 2026 onward, at which point open-pit mining at Sable will be complete.
Conventional open-pit mining of Point Lake is scheduled from 2023 if the pit is approved. Eventually, Arctic envisages also mining Point Lake by flooding it and using the underwater crawlers.
“Point Lake will be the last of the conventional mining pits that we do,” said Moore. “Once the Point Lake pit is completed, the operation at Ekati will be 100-percent underwater remote mining.”
He projected the technology could extend Ekati’s mine life – currently set to expire by 2030 – by many years.
“If we get this technique right, which I’m very confident we will, we’ve got decades of successful mining ahead for Ekati,” Moore told forum delegates.
‘Prize worth chasing’
The crawler technology blends the huge surface mining machines already used at some mines with underwater mining technology used elsewhere, though not currently at any diamond mines.
Crawlers to be trialled at Ekati are slightly smaller than the giant Cat 793 trucks used at many mines, but will still be large pieces of equipment. They are deployed from floating platforms and powered by electric umbilical cords.
The crawler directly mines kimberlite on the floor of a lake or flooded open pit and sends ore up a pipe to a dewatering plant.
Moore said the crawlers, which use four independently suspended tracks to move across the lake bed, would use biodegradable hydraulics so that “if we have failure, it will not cause undue pollution.”
Each crawler is expected to have a life of seven years. The crawlers will mine during the shoulder seasons and summer, then be taken out of service for maintenance during the winter.
The crawler concept has been discussed for years. Then-owner of Ekati BHP Billiton evaluated underwater crawlers in 2009 but put further research on hold as the cost was considered prohibitive compared to more conventional options.
In 2013, Dominion similarly concluded crawlers were “not suitable as a project at this time.”
Their impact on employment levels at the mine, such as how many people are required compared to conventional forms of mining, is not yet clear – but Moore said the technique would create no waste rock, produce higher-grade material, and allow Ekati to get at kimberlite conventional mining cannot viably reach.
The initial Lynx trial, for example, is expected to generate 150,000 tons of kimberlite and produce $25 million in revenue.
Moore said underwater mining would help Arctic mine 33 million tons of kimberlite in Point Lake that the proposed open pit will not reach, representing an extra 21 million carats.
The Fox pit, said Moore, has 15 million carats of “very high-value diamonds” that can be reached by an underwater crawler, “a prize that is well worth chasing.”
Keeping Ekati alive in some form for decades to come would represent a welcome boost to the Northwest Territories’ economy.
The NWT relies on diamond mines for much of its wealth but the three operational mines – Ekati, Diavik, and Gahcho Kué – are approaching the end of their lives.
At the Geoscience Forum on Wednesday, Diavik boss Richard Storrie said his mine would continue operating until 2025 and was beginning work to help staff plan their careers beyond the mine’s operational life.
Gahcho Kué currently anticipates operation until around 2030, though the mine has one or two options that could extend its life.
Update: November 30, 2021 – 15:09 MT. After this article was first published, Arctic said its production trial is in fact scheduled for 2026 “after two seasons of flooding of the open pit,” not in 2024 as initially suggested. The company added its proposed method will result in no waste rock, not simply less than other methods.