The Snap Lake mine site will need another decade to be fully decommissioned and may not be finally abandoned to nature until almost 2050, owner De Beers believes.

Operations at the diamond mine were shut down in December 2015, when De Beers decided Snap Lake was no longer economically viable.

A year later, the mining giant essentially gave up on finding a buyer and flooded the site’s underground chambers, ending any realistic chance of the mine reopening.

The company submitted its final closure and reclamation plan, estimated to cost around $85 million, at the end of March. The plan was made public by regulator the Mackenzie Valley Land and Water Board on April 12.

In the plan, De Beers says Snap Lake’s closure will need two phases.

“First, during the eight-year closure phase, mine facilities will be decommissioned or demolished, water management systems will be adapted for closure, and the land will be reshaped and revegetated,” the plan – which is almost 200 pages long, excluding appendices – reads.

“Second, during the post-closure phase, which is expected to continue for a minimum of 10 years, monitoring programs will be put in place to check that the Snap Lake mine is meeting closure goals and ensuring the successful long-term closure of the site.”

The initial eight-year phase is not expected to begin until 2021, as the relevant permits must first be acquired.

Documents presented to the regulator by De Beers suggest it could be 2048 before the “post-closure phase” is considered complete.

De Beers says its overall goal for the mine site – 220 km northeast of Yellowknife – is “to return the site and affected areas around the mine to technically viable and, where practicable, self-sustaining ecosystems that are compatible with a healthy environment and with human activities.”

The company aims to keep dust levels down, leave the site stable, ensure both humans and wildlife like caribou can cross the site safely, and reintroduce vegetation where possible.

To fully close the now-flooded underground mine area, surface features leading underground will be sealed, while ventilation systems will be capped with concrete.

Remaining buildings and hazardous materials will be removed, including the decontamination of the site’s processing plant before it is demolished.

The airstrip will be revegetated.

The post-closure monitoring phase, at least a decade long, will assess dust levels, mine stability, water quality, vegetation regrowth, and effects on wildlife.

Once the regulator is satisfied the site has been safely closed and nothing more need be done – potentially two decades from now or more – the land leases for Snap Lake may be returned to the Crown.

Importantly, De Beers aims to ensure there is no need for “active long-term care and maintenance at the site.”

In other words, the company plans to leave the site in sufficiently stable condition that there is no need for indefinite monitoring or remediation work.

Trickier, costlier

At the moment, the territorial government holds a financial security from De Beers of just under $80 million according to the closure plan documentation.

De Beers estimates the full clean-up will cost around $85 million, including a $7-million contingency fund.

Securities are paid by mining companies to governments to ensure clean-up operations can be funded if the companies themselves will not or cannot do it (as has happened many times in the past, when legislation was not as robust – most notably at Giant Mine, outside Yellowknife).

The closure plan includes a proposal for security money held by the NWT to be returned to De Beers as work is completed, with most handed back after eight years and a small remainder gradually returned over a further two decades.

In full: Read the Snap Lake final closure and reclamation plan

The overall plan remains in draft form. De Beers’ application for a water licence to carry out the work in the plan has been received by the regulator, and will now be reviewed by relevant governments and organizations.

A public hearing is scheduled to follow in September. If the process remains on schedule, a final decision on the water licence would be issued in April 2020.

Around 400 jobs were lost when Snap Lake ceased production in late 2015, having been open since 2008.

The mine had initially been expected to remain in operation until 2028, but underground mining at the site, beneath Snap Lake itself, proved trickier and costlier than expected. At the same time, diamond prices dipped.