Flooding Snap Lake diamond mine could take more than a year, says De Beers

De Beers has fleshed out plans to flood its closed Snap Lake diamond mine in a care and maintenance proposal filed this week to the Mackenzie Valley Land and Water Board.

The company suspended operations at the underground mine 220 km kilometres northeast of Yellowknife in December 2015 with the projected loss of more than 400 positions. De Beers said poor market conditions made the Snap Lake operation unviable.

The company says the length of the temporary closure may be three years or more, depending on market conditions.

Opting to flood the mine — which must first be approved by the Mackenzie Valley Land and Water Board — means De Beers can save cash by turning off expensive pumps currently keeping the mine as dry as possible.

According to De Beers' proposal, its plan will save the company money while lessening the site's environmental impact and keeping alive hopes of reopening the mine. De Beers says flooding Snap Lake will reduce effluent sent downstream, limit winter road traffic and lower emissions.

The company also says choosing to flood the mine will reduce operating costs, buying more time "until the markets improve or technological or operational efficiencies increase and the mine can be reopened by De Beers or another qualified operator."

The flood would take between 213 and 398 days to complete. If the mine reopens in future, De Beers says pumping it dry and resuming operations would take around 420 days.

"Temporarily flooding a mine is not unknown. It's been done before. It's not a fatal flaw in a temporary closure plan," said independent mine closure consultant Rick Siwik.

Examples of mines allowed to flood in the N.W.T. include Yellowknife's Con gold mine, which closed in 2003. The now-abandoned Ptarmigan gold mine just outside Yellowknife was dewatered to allow its reopening in the 1980s, according to Tom Hoefer, executive director of the NWT and Nunavut Chamber of Mines. The Bellekeno silver mine in Yukon was also dewatered prior to resuming commercial production in 2011.

Surface monitoring

According to Siwik, if the mine is flooded, the environmental focus will shift to the waste materials left at ground level.

"From an environmental perspective, once you remove all the equipment, the oils, the lubricants and the solvents, the issue becomes more what's happening on the surface," he said.

"Now you have a lot fewer people surveying the operation when it's on standby, so you have to monitor all those dykes, piles and dams up on the top.

"If there is a rainfall event, you have to go and inspect to make sure they're safe and performing properly."

De Beers plans a remote monitoring network to keep an eye on Snap Lake if no workers are on-site during care and maintenance.

'Hard number' needed?

Alex Power, regulatory specialist for the Yellowknives Dene First Nation, expressed concern that De Beers' proposal has no defined end point.

"It's unclear that there's any limit as to how long the site will remain in care and maintenance. As long as the site is in care and maintenance, it is not being remediated," said Power.

"Everybody knows the mine is a bit of a dud. It's hard to imagine a buyer that would be interested. Maybe they'll find someone in the market for a mine with a leaky roof and all the easy diamonds removed — but take that for what it is.

"The Yellowknives Dene would like to see a hard number on how long you can just essentially let a site sit fallow."