Dane Gibson
Northern News Services

NNSL (Oct 04/99) - It's one of the largest abandoned mine sites in Canada.

It also holds the distinction of being the highest source of mercury contamination, both for quantity and concentration, in Canada.

Discovery mine, located 90 kilometres north of Yellowknife on the shore of Giauque Lake, was abandoned in 1968 after 19 years of operation.

When no more gold could be blasted out of the earth, Discovery Mines Ltd. pulled out leaving one million tonnes of highly contaminated tailings piled on the surface.

The Department of Indian Affairs and Northern Development (DIAND) is now attempting to mitigate the effects the unattended tailings are having on the water, fish, and plants in the area.

They are half-way through an $8 million, three- year project designed to put a giant clay and crushed rock lid over the exposed tailings.

Because the area is so large, they need 250,000 cubic metres of clay and gravel to do it.

"All this happened before there were land-use regulations, water acts, or even an awareness of what the danger could be (of extracting gold out of ore using mercury)," said DIAND land-use administrator Ed Hornby.

"We're not doing this with 100 per cent certainty it's going to work, which is why environmental monitoring is done to validate the process, but I think the capping will provide a long-term solution in that it will isolate the mercury from the surrounding environment."

One of the most disturbing findings at the site is that fully one-third of the tailings on the land has leached into Giauque Lake.

Because of that, the bottom of the lake around the mine is layered with tailings. The cap they are constructing extends into the lake.

"Giauque Lake is connected to the Yellowknife River system. Fortunately, mercury isn't tremendously soluble, so there's very little sign of mercury itself in the water," Hornby said.

"We know if we can stop it (contamination) at the source, we have a far better chance at success in ensuring it doesn't turn into a problem downstream."

Hornby said the reason 30 years went by before a reclamation project at Discovery was begun is that the site wasn't even a blip on DIAND's radar screen until the 1980s.

When Discovery started showing up in their risk analysis processes, it was put on the top of the list. But they then had to wait until funding from the Arctic Environmental Strategy was made available to start the massive project.

"After we had a handle on the problem, we set down some alternatives to treat it. Once the (capping process) was selected we decided on an engineering design and got to work," Hornby said.

Back when the mine was operating, it was common for a company to be created to mine one prospect. Unfortunately, Discovery Mines Ltd. is long gone.

"When the deposit was depleted, the company had no more assets so they folded," Hornby said.

"If a major company was involved in Discovery that still operated today, DIAND would be trying to recover some of the clean-up costs."

Michael Nahir, of Public Works Canada, is the Discovery design and project manager.

He said the first goal of the program is to minimize the spreading of tailings that occurs through wind and wave erosion. The second is to promote rain and snow drainage off-site to cut the transport of contaminants into Giauque Lake.

He said that to date, everything in the lake from the highest order of fish, such as whitefish and lake trout, down to the smallest lichens and plants have been affected to some extent by mercury contamination.

"Mercury doesn't really go away. All you can do is distribute it across the planet. We're not getting rid of the contamination, we're stopping it from affecting the environment further," Nahir said.

"The whole purpose of this is to bring back Giauque Lake and the only way we can do that is to allow the natural systems to take hold and rejuvenate themselves. That's going to take a long time but it will occur."