Diavik mine's ability to recoup $159M security at risk from Ekati expansion: Rio Tinto

The owner of one N.W.T. diamond mine is worried future environmental impacts from a neighbouring diamond mine could prevent the company from getting back all of its $159-million clean-up security from the territorial government.

Rio Tinto's northern subsidiary, Diavik Diamond Mines Inc. (DDMI), operates the Diavik mine about 300 kilometres northeast of Yellowknife. The nearby Ekati diamond mine is 20 kilometres to the north of Diavik.

In a presentation filed with the Mackenzie Valley Environmental Impact Review Board, DDMI says a new open pit proposed for Ekati may cause changes to the environment that will keep caribou from returning to the Diavik site after the Diavik mine's closure.

Rio Tinto has given the N.W.T. government $159 million in reclamation security — money held by the government in case the company can't clean up the mine once it shuts down. Diavik's cleanup is slated to begin in 2024, wrapping up by 2030. 

One of several factors that will determine how much of that money Rio Tinto gets back is the degree to which caribou return to the remediated Diavik site.

"It will be difficult for DDMI to demonstrate an increase in caribou use of the reclaimed mine areas if the Jay project continues to affect caribou movement," the company wrote.

"Consequently it will be difficult to demonstrate closure performance...and successfully relinquish financial security."

Rio Tinto and DDMI want the review board to say that Jay "is likely to cause adverse effects to DDMI as the operator" of Diavik, and they want the territorial government to recognize those impacts when reviewing DDMI's closure of Diavik

DDMI cites a section of the N.W.T. Water Act that says existing developments shouldn't be negatively affected by environmental changes caused by new developments.  

Same company owns stakes in both mines

Rio Tinto owns a 60-per-cent stake in the Diavik mine.

The Ekati mine is owned by Dominion Diamond Corporation, which owns the other 40-per-cent stake in the Diavik mine.

DDMI wants the review board to require Dominion to "engage with DDMI to develop mutually acceptable monitoring and mitigation to effectively eliminate these effects to DDMI."

Neither company granted CBC an interview.

'Something affecting caribou other than harvesting'

Dominion is already under much pressure in trying to open its new Jay open pit at Ekati, which will add 10 years to the mine and help sustain an N.W.T. mining economy that's already looking at the bottom half of its life. Reserves at Ekati are currently expected to run out in 2019.

Contract renewal talks with nearly 500 Ekati workers are not going well, and groups like the Tlicho Government and the Yellowknives Dene First Nation have also expressed fears about what Jay — which is located within a key migration and habitat area for the Bathurst caribou herd — could mean for the future of the herd. Preliminary results from a recent aerial survey point to the herd's continued decline.

"The numbers indicate that, without us harvesting, the number's still going down," said Yellowknives Dene chief Ed Sangris. "So there is something that's affecting the caribou other than harvesting."

Dominion has reduced the overall footprint of Jay and has proposed ideas on how to reduce the disturbance to the herd, including caribou crossings along Jay's access road.

"We look forward to working with all parties, including DDMI, to address the remaining questions concerning the Jay project…" the company wrote CBC News.

The Mackenzie Valley Environmental Impact Review Board will hold a multi-day public hearing on the Jay project in Yellowknife next month.

It will then attach conditions that Dominion has to meet when proceeding with the Jay project.