The Yukon government is in the first phase of closing and remediating the abandoned Minto mine.
Officials with the Department of Energy, Mines and Resources said during a technical briefing on Sept. 28 that contractors are removing equipment and other infrastructure from the underground portion of the mine, after which pumps will be removed and the space will be allowed to naturally flood.
It's a common closure and remediation practice, said Darren Stahl, director of assessment and abandoned mines.
"It's been done at Keno mine — it's been flooded and dewatered several times over its life," he said.
The water, according to Stahl, will remain contained in the underground space, which has a capacity of approximately one million cubic metres or the equivalent of 400 Olympic-size swimming pools. It won't overflow due to the water table in the area, and also isn't expected to contaminate that water table or the surrounding soil.
The flooding is set to begin in November.
Longer-term reclamation plans include placing unwanted surface material into two above-ground pits that also have water in them and, when the water hits a certain level, having it flow down an engineered channel to a treatment plant before releasing it into Minto Creek. As well, crews will need to cover waste-rock piles with a top-coat that vegetation can grow on and do other landscaping to return the site to a more natural state.
Equipment sits in the underground portion of the Minto mine during a site tour in July 2023. As part of reclamation work, crews will be removing infrastructure from the underground and then allowing it to naturally flood. (Government of Yukon)
The reclamation and closure work is happening as receiver PriceWaterhouseCoopers is soliciting bids for the mine, which the now-defunct Minto Metals Corp. suddenly abandoned on May 12.
The Yukon government took over the site the next day.
Stephen Mead, the assistant deputy minister of mineral resources and geoscience services, said that while the government knew at the time that Minto needed to expand its operations to remain profitable, it had "absolutely no warning" that the company would leave.
"People, sort of, I think, perhaps are rightfully skeptical… But being the person in the room when that call came in, it was a complete surprise and we spent the rest of that first day on the phone trying to mobilize resources," he said.
Mead said it took several weeks to make sure the site's "daily needs" were taken care of, particularly with the heavy spring melt. By July though, he said the government and Selkirk First Nation, on whose land the mine sits on, were in a position to plan for the site's future.
Lesson learned from other abandoned mine, Mead says
On top of wanting to protect the environment, Mead said the decision to start closure and reclamation activities was influenced by how another recent mine abandonment played out.
"I mean, the lesson from Wolverine is that we act quickly," he said, referring to a mine in southeast Yukon that its owner gradually let fall into disrepair, forcing the territorial government to step in when its underground flooded and overflowed in 2017.
"So one of the benefits, I would suggest, of moving ahead with reclaiming and closing the site is that action is reducing the liability — it's reducing the environmental liability."
The reclamation work started before Minto Metals was put into receivership and the sales process began, but Mead said he didn't think the two were "incompatible," explaining that a potential buyer now doesn't need to worry about dealing with that liability.
To date, the government has spent $7.87 million on work at Minto, and in total has signed $20.72-million-worth of contracts to cover potential work up to May 2024, though it may not all be needed.
Minto Metals, before going under, had furnished $75.2 million in security, which the government will be tapping into to cover costs.
While there's room for improvement, Mead said he believes the government has been "successful" in its handling of the Minto abandonment so far.
"I think the system that is in place right now allowed us to react the way we should react to these circumstances," he said, adding that it's impossible to prevent companies from ever abandoning mines, but having fail-safes in place reduces the negative impacts.
Mead also said his department would like to see a new owner at the site in the future, and though he wouldn't "speculate" about the operations financial viability, he noted there were still copper deposits nearby and that mining is an "important part of Yukon's economy"
"If there is real opportunity in the minerals that are available in that area, we would always like to see a responsible and sustainable mine," he said.
PriceWaterhouseCoopers, according to a sales process document, is accepting initial bids for Minto until Oct. 6 and hopes to get court approval of a sale by early next year.
In the meantime, dozens of contractors have added their names to a list of creditors that Minto Metals, at last count, collectively owed $66 million in unpaid bills.