Canadian Mining Journal

Feature

Radical change coming to tailings management



Maybe it’s overstating the case to say the 2014 Mount Polley tailings dam failure changed everything.

It hasn’t yet. But it will.

Today, the mine’s owner, Imperial Metals – which has already spent about $70 million on remediation efforts at Mount Polley – is still cleaning up the site.

Still, the company has been very lucky. That’s because the tailings spill could have been much worse.

If the tailings had been reactive (they are not acid generating, but rather relatively chemically inert) – the damage to the Quesnel water shed, local aquatic life, and the mining industry itself could have been devastating.

Thankfully, they are not, and the effects of the spill have been mostly physical (see page 22).

(While there are some people who don’t completely trust either Imperial or the B.C. government’s work assessing the spill’s effects, a recent independent study by U.K.

researchers published in the journal Applied Geochemistry, concluded that “… transport of Cu from Hazeltine Creek to Quesnel Lake may be slightly higher than before the tailings dam spill. However, given the size of Quesnel Lake, and the relatively low Cu flux from Hazeltine Creek, this additional Cu load should have a negligible impact on lake water quality and ecosystem processes.”)

Regardless, the failure has prompted a search for alternatives to the conventional method of handling tailings via sub-aqueous deposition, or tailings ponds.

A 2015 report by an independent panel investigating the causes of the Mount Polley disaster recommended drier methods of disposal, such as thickening or filtering (dry-stacking) tailings. But these methods are more expensive, especially at a larger scale, and come with their own trade-offs, such as the necessity of added infrastructure (a thickening plant) and difficulties in achieving a consistent and stable end product.

For the moment, companies advancing new mines in Canada are still proposing conventional tailings ponds. But as they make their way through permitting, it would not be surprising if pressure from both the public and regulators causes some of them to change course and adopt different methods.

In the meantime, there is ongoing research on making dewatered tailings solutions viable at a larger scale. For example, Goldcorp’s EcoTails co-mingling tailings technology (see Page 18).

And it is interesting to note that Imperial Metals had investigated other disposal methods at Mount Polley in the past.

“We considered thickened discharge in the 1990s and we were about to trial mixing tailings into the rock storage areas (co-mingling) in 2014,” says Vice-President Environmental Affairs ‘Lyn Anglin. “In fact, Mount Polley had a permit to undertake co-mingling research prior to the breach.” Imperial is likely to go ahead with that research in the future.

The Mount Polley tailings dam failure should never have happened.

But because it did – followed a year later by the much more destructive Samarco failure in Brazil that killed 19 – the days when sub-aqueous deposition is considered the default option for tailings disposal are coming to an end.