Dry-stacking versus wet storage at mines

The province has asked the proposed Harper Creek mine near Vavenby to submit alternatives to wet-tailings facilities

Cam Fortems – Kamloops This Week

While a panel that studied the Mount Polley mine tailings-pond failure pointed to dry-stack tailings as a way to prevent future disasters, an Ontario engineering expert said costs are higher and may prevent some mines from being viable.

Eric Domingue, an engineer and manager of operations and environment with DST Consulting Engineers, spoke on March 26 at Thompson Rivers University on tailings and their management. He outlined storage options for the slurry that remains after ore is separated in the milling process.

Those options include pouring them in the sea in some case; dewatering and dry stacking; backfilling mining shafts and pits; and placing material underwater in artificial lakes — the latter used at Mount Polley and the de facto standard in this province.

Domingue said all have advantages and disadvantages based on the site, amount of precipitation and cost.

“Tailings will be there forever,” he warned. “Once the mine has closed, tailings will stay there … You’d better do it right the first time.”

The Mount Polley panel pointed to Greens Creek, Alaska, which uses filtered, or dry-stack tailings, as best practice and the only way to eliminate risk of collapse that occurred at Mount Polley. The Cariboo mine’s tailings dam collapsed in August last year, sending millions of gallons of contaminated water into Polley and Quesnel lakes.

In its wake, the province has asked all projects, including the proposed Ajax mine in Kamloops and the proposed Harper Creek mine in the North Thompson near Vavenby, to submit alternatives to wet-tailings facilities.

KGHM Ajax originally proposed dry-stack tailings, but moved to wet storage. It is now costing a potential reversion to a dry-stack plan.

Domingue recently worked on a mine project in Saudi Arabia that uses dry-stack tailings, primarily due to the arid climate and operating cost of diesel-powered trucks that transport it to a storage site.

“Diesel is seven cents a litre — they don’t care,” he said.

Other advantages include water conservation. But, there are downsides, Dominigue said, including dust control for tailings that may contain complex mineral elements and chemical traces used in the concentrate process.

“It’s site by site,” he said of preference of tailings storage. “You need to evaluate your specific situation.”

Domingue said dry-stack tailings are more costly and such an imposition may make some projects uneconomical.

 

The engineering expert appeared as a guest of Kamloops Exploration Group, which sponsors a number of industry speakers.