Independent report details causes of last year’s Eagle mine failure in Yukon

Board of experts was appointed by territory to study catastrophic heap leach slide, make recommendations

Last year’s catastrophic slide at the Eagle mine site in Yukon was caused by “the accumulation of a series of adverse conditions and events,” according to a new independent report on the incident.

The 156-page report — with an additional 760 pages of appendices — was done by a three-person independent review board appointed by the territorial government last fall and released on Wednesday. It details some of the technical factors that led to the slide in June 2024 and also includes recommendations “for improved practices by industry and the regulators.”

Yukon’s Mines Minister John Streicker said in a statement on Wednesday that his government is “committed to taking appropriate action in response” to the board’s report.

“The report makes clear that multiple factors contributed to the heap leach failure, but that overall a layer of ore within the heap was not draining as it should and the layer above it became saturated, leading to the catastrophic slide,” Streicker said.

Following the release of the report, the First Nation of Na-Cho Nyäk Dun said in a statement that it is still calling for a full public inquiry into the mine’s collapse.

It said the report leaves “unanswered questions” about the root causes of the slide and how “regulatory negligence and lax governmental oversight” factored in.

The slide happened early on the morning of June 24, 2024, at the mine’s heap leach facility. The report says a “substantial failure” on the south slope of the facility resulted in nearly six million cubic metres, or about 11.3 million dry tonnes, of ore spilling down the slope. Nearly 1.8 million dry tonnes of material left containment and cyanide solution spilled into a nearby valley, contaminating local groundwater and Haggart Creek.

Work is still being done at the site to try to contain the damage. The report says contaminated water from the site continues to flow out into the environment.

The review board, made up of engineers and geotechnical experts, studied the mine’s design and operational documents, interviewed current and former employees of Victoria Gold (the mine’s owner at the time of the slide), studied some of the material used at the site, among other things.

It described how a stack of “low-permeability” ore, combined with a rising water table triggered a “local slope failure” in part of the facility that then, seconds later, “triggered deep static liquefaction of the saturated and nearly saturated ore within the heap.”

The board ruled out other things, including an earthquake or a foundation failure, as possible causes.

Speaking to CBC News on Wednesday, Streicker said the government is still reviewing the report and recommendations.

“Public confidence is lost quickly and built slowly. So I think that we have to continue that hard work, and I think one of those steps is to see how we respond to this report,” he said.