Casino exec calls new pond design a ‘tailings puddle’

The president of the Casino Mining Corporation says the company’s redesigned tailings pond for its proposed copper and gold mine will use 80 per cent less water than the original plan.

The president of the Casino Mining Corporation says the company’s redesigned tailings pond for its proposed copper and gold mine will use 80 per cent less water than the original plan.

Paul West-Sells discussed the company’s new design at the Yukon Geoscience Forum & Trade Show on Monday.

“We’ve gone from having a tailings pond to really having a tailings puddle,” he told audience members.

The redesigned pond would also keep the more dangerous tailings — those that are potentially acid-generating — at the very back of the tailings pond, where they would be least likely to flow into the environment if the dam were ever breached.

According to the original plan, all of the tailings and waste rock would have been covered with water. West-Sells explained that the company originally assumed the dam could never break, so it made sense to use lots of water to cover all the material.

But then the Mount Polley tailings dam breached in B.C. in 2014, releasing 24 million cubic metres of mine waste and water into surrounding waterways.

“In a pre-Mount Polley world, your dam doesn’t fail, so why are you worried about the volume of water?” he said. “In a post-Mount Polley world, you look at that and say ‘How much do I need?’ And that’s where we ended up with that reduction.”

According to the new design, all of the non-acid-generating tailings — about 80 per cent of the total — will be deposited right behind the dam, and won’t be covered with water. The sandy tailings will form a “beach” that extends a kilometre back from the crest of the dam.

Waste rock will be piled behind those tailings, and will be submerged in water after the mine closes. Casino Mining’s senior environmental manager, Mary Mioska, said the water is necessary because the waste rock can release acid and metals if it’s left exposed to the air.

The remaining 20 per cent of the tailings, which would be potentially acid-generating, will be stored behind the waste rock in water, forming a kind of slurry.

“Were there to be a failure, the possibility of that mobilizing is very, very slim,” Mioska said, explaining that the dangerous tailings would have to travel about five kilometres just to reach the front of the dam.

The total volume of water is now estimated at about three million cubic metres, down from 15 million cubic metres in the original design. If the dam did break, water likely wouldn’t come shooting out into the environment, Mioska said.

“Instead of having this wave of material, you’ll have this slump.”

However, the design changes likely won’t have a major impact on the height of the dam, which at 286 metres would be the tallest tailings dam in the world.

Mioska said that’s because the height is largely determined by the volume of waste material, which hasn’t changed.

Still, some of West-Sells’ audience members on Monday seemed unconvinced. He fielded a number of questions about the safety of the tailings pond over the long term.

“These developments are here generally for thousands of years,” one woman said. “I don’t expect you to be here for thousands of years, but is your corporation… working on developing technologies that gives some sort of hope to First Nations that this stuff can be remediated and gone and we can get back to a healthy environment for our future generations?”

West-Sells replied that the company is committed to using the best available technology.

The proposed Casino mine could produce an estimated 8.9 million ounces of gold and 4.5 billion pounds of copper over a 22-year mine life.

Casino Mining submitted a proposal to the Yukon Environmental and Socio-economic Assessment Board in January 2014. But in February 2016, the board bumped the project up to a panel review, the territory’s highest level of assessment, in part because of concerns about the tailings pond.

The mining company plans to complete a new submission to YESAB by the end of 2017, meaning a panel could be struck in 2018. The panel review process includes public hearings.

Contact Maura Forrest at maura.forrest@yukon-news.com

Get local stories you won't find anywhere else right to your inbox.
Sign up here

Just Posted

A Copper Ridge resident clears their driveway after a massive over night snowfall in Whitehorse on Nov. 2, 2020. Environment Canada has issued a winter storm warning for the Whitehorse and Haines Junction areas for Jan. 18. (Crystal Schick/Yukon News file)
Winter storm warning for Haines Junction and Whitehorse

Environment Canada says the storm will develop Monday and last until Tuesday

Maria Metzen off the start line of the Yukon Dog Mushers Association’s sled dog race on Jan. 9. (Gabrielle Plonka/Yukon News)
Mushers race in preparation for FirstMate Babe Southwick

The annual race is set for Feb. 12 and 13.

The Yukon government is making changes to the medical travel system, including doubling the per diem and making destinations for medical services more flexible. (Joel Krahn/Yukon News file)
Subsidy for medical travel doubled with more supports coming

The change was recommended in the Putting People First report endorsed by the government

Chloe Sergerie, who was fined $500 under the <em>Civil Emergency Measures Act</em> on Jan. 12, says she made the safest choice available to her when she entered the territory. (Mike Thomas/Yukon News file)
Woman fined $500 under CEMA says she made ‘safest decision’ available

Filling out a declaration at the airport was contrary to self-isolation, says accused

Yukon University has added seven members to its board of governors in recent months. (Crystal Schick/Yukon News file)
New members named to Yukon U’s board of governors

Required number of board members now up to 17

Yukonomist Keith Halliday
Yukonomist: Your Northern regulatory adventure awaits!

“Your Northern adventure awaits!” blared the headline on a recent YESAB assessment… Continue reading

Yukoner Shirley Chua-Tan is taking on the role of vice-chair of the social inclusion working group with the Canadian Academy of Health Sciences’ oversight panel and working groups for the autism assessment. (Submitted)
Canadian Academy of Health Sciences names Yukoner to panel

Shirley Chua-Tan is well-known for a number of roles she plays in… Continue reading

The Fish Lake area viewed from the top of Haeckel Hill on Sept. 11, 2018. The Yukon government and Kwanlin Dün First Nation (KDFN) announced they are in the beginning stages of a local area planning process for the area. (Crystal Schick/Yukon News file)
Local area planning for Fish Lake announced

The Government of Yukon and Kwanlin Dün First Nation (KDFN) announced in… Continue reading

Whitehorse City Hall. (Joel Krahn/Yukon News file)
City hall, briefly

A look at decisions made by Whitehorse city council this week

Fire damage, photographed on Jan. 11, to a downtown apartment building which occurred late in the evening on Jan. 8. Zander Firth, 20, from Inuvik, was charged with the arson and is facing several other charges following his Jan. 12 court appearance. (Gabrielle Plonka/Yukon News)
More charges for arson suspect

The Inuvik man charged in relation to the fire at Ryder Apartments… Continue reading

The grace period for the new Yukon lobbyist registry has come to an end and those who seek to influence politicians will now need to report their efforts to a public database. (Mike Thomas/Yukon News file)
Grace period for new lobbyist registry ends

So far nine lobbyists have registered their activities with politicians in the territory

Most Read