Canadian Mining Journal

Feature

A giant environmental legacy

The Giant mine's legacy in numbers



The numbers are staggering.

In six decades of gold production, the Giant mine, near Yellowknife, N.W.T., yielded more than 7 million oz. – and 237,000 tonnes of toxic arsenic trioxide dust. The arsenic trioxide waste, produced in the roasting process to liberate the gold from the arsenopyrite ore, remains stored onsite in underground chambers. The cleanup bill, which will be fully funded by the federal government, was last estimated at $600 million. But that figure is sure to rise, now that the reclamation and closure plan has been finalized.

That plan has been a long time coming.

The mine’s last owner, Royal Oak Mines, went bankrupt in 1999.

The original reclamation and closure plan was completed in 2007 before being referred to an environmental assessment, a process that was only completed in 2014. Since then, the Giant mine remediation team has been working on incorporating the changes (both mandated and suggested) that came out of the EA. This spring, the team re-applied for a water licence, which is required to complete the remediation work. If the licence is granted, work on final remediation could begin in 2021.

In the meantime, care and maintenance for the site costs about $15 million per year. As the arsenic trioxide waste is water soluble and is stored underground, water must constantly be pumped out of the mine to avoid contamination.

Some remediation work has already been completed at Giant – emergency items such as dismantling the roaster complex on site.

But even once the project gets the permits it needs to execute the reclamation and closure plan, it won’t be the end of the story.

That’s because a permanent solution to securing the arsenic trioxide waste does not yet exist.

The chosen frozen block method will see the waste remain underground, using thermosyphons to keep the ground frozen passively (see page 19).

“This is not considered a permanent solution, but it’s the best solution we have right now,” Natalie Plato, deputy director for the Giant Mine Remediation Project told CMJ in May. “In the meantime, we are funding the Giant Mine Oversight Board to do research into a permanent solution.” These days, mines are required to put up securities that would cover the cost of reclamation in the case of bankruptcy. That is as it should be.

But as long as we’re still contending with the environmental consequences of abandoned projects like Giant, the industry will find itself wrestling with their powerful legacy.


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