Rio Tinto aims for 'something that not many others have done': successful closure of an N.W.T. mine

Rio Tinto is still two years away from ending production at its Diavik diamond mine in the N.W.T. and alreadythere are signs of how nature may reclaim East Island in the years to come.

Fireweed and flowers were growing near the mine's main campbuilding during a media tour of the site last Friday, and green plant life could be seen in spots along the gravel roadways.

"The suggestion was to make the site neither an attraction or a deterrence neutral to wildlife," said Gord Stephenson, Diavik's manager of surface operations and closure, reflecting on engagement that's been happening with neighbouring Indigenous communities about the mine's shutdown.

He said the companywas still working with partners to figure out what to plant and where if at all moving forward. Part of that process, he said, was actually testing in designated spots to see what could regrow in crushed granite and till.

"We can return the land to a state that is able to be used by wildlife, by people in the future," said Matt Breen, Diavik's chief operating officer. "Hopefully when people come across this in another hundred, 200 years, that it just looks like part of the landscape."

Dixter Wedawin, a Tch man who works at the mine and drove a bus during the media tour, is hoping for the same,in the nearer future.

"Hopefully my kids, grandkids, will come here to this site one day ... with my family coming up here, going hunting, fishing."

What does Diavik's closure look like?

The Wek'eezhii Land and Water Board hasn't approved Rio Tinto's final closure and reclamation plan yet, but mine officials say they've been working on closure since before production beganat Diavik in 2003 and have a good sense of what it'll look like when the last of the buildings have been torn down.

Breen said open-pit mining has already ended. The A154 and A21 pits are still being mined underground, he said, while the A418 pit has been completely mined and is now being used to store processed kimberlite.

Stephenson said the plan isto start flooding Diavik's three pits with water from Lac de Gras in the fall of 2026. The process will be done with pipes and it'll be slow it's expected to take between six andeight months. Then, once the water has met yet-to-be-determined criteria, the dikes holding the lake back will be perforated.

Large, mobile equipment that isn't being used is already being shipped off site, he said. Hazardous material is being taken off site too. Material from demolished buildings will be disposed of at the site's landfill and then covered with 4.5 metres of rock, said Stephenson.

Diavik is also hoping that some infrastructure can be salvaged or repurposed.

"We've got a great camp, it's in great shape. We've got a great runway that we think that is well-situated to support, you know, future road development if that were to happen," said Stephenson. But time to sort that all out is dwindling.

"We're looking for answers by the end of 2025," he said.

A 2022 version of the closure and reclamation plan says that some areas the processed kimberlite containment facility (PKC) and the waste rock storage areas will "remain as significant landscape features" once the site is closed.

On Friday, officials said the PKC had already been 67 per cent covered with granite, while closure of the North Country Rock Pile (one of the waste rock storage areas) was 97 per cent finished and had become a point of pride after a herd of caribou used it as a place to bed down in the spring.

"They were there for a couple weeks, kind of grazing and going up and down that slope," said Stephenson. "It shows what can be done and shows that the wildlife that lives up here is comfortable in the environment."

What parts of the plan still need to be sorted out?

Though there's enough certainty about what closure will look like for Rio Tinto to create a 3D model of the site after 2030, there are aspects of the plan that haven't been sorted out yet, officials said.

For one thing, a solar farm at the mine site just became operational this year. The company is hoping it can be deployed elsewhere once it closes, but hasn't said where that will be yet.

Water containment ponds around the site will eventually be flooded using the same process as for the open pits, but water quality criteria for that hasn't been nailed down yet, said Stephenson.

"We need to iron out those criteria so that we have a pathway towards relinquishment, which right now does not exist and that's the biggest challenge," he said.

Breen said the company is "really sort of finding our feet in this process, in a process [that] isn't well-defined." The successful relinquishment of a mine is "something that not many others have done," he said.

Breen said he wants to sit down with the territorial government and the Wek'eezhii Land and Water Board to make sure everyone is on the same page.

"If we're having separate conversations, we're going to come to separate conclusions and then we're going to have a [closure plan] that's not fit for purpose for everyone."

Stephenson said it's also unclear at this point how long, exactly, scientific and traditional monitoring will continue after the site is relinquished. He said it could be between 10 to 20 years, but that hasn't been decided yet either.

He hopes Diavik is remembered as the first successfully-closed mine in the N.W.T.