Yukon disaster one of two ‘most catastrophic’ in heap-leach mining history: expert

The spill of about two million tonnes of cyanide-soaked ore at a Yukon gold mine was one of the two “most catastrophic failures” in the 45-year history of the heap-leaching mining process, an engineer tasked with reviewing it said.

Mark Smith said the disasters last year, the other occurring in Turkey, would “define the next 10 or 20 years for heap-leach practices,” in which minerals are extracted from piles of ore by running liquid chemicals through them.

Smith is a member of the independent review board that examined the disaster at the Eagle Gold Mine in June 2024, when an ore slope failed, leading to the contamination of local groundwater in central Yukon.

He told a briefing hosted by the Yukon government on Tuesday that the board found several underlying causes along with a trigger for the disaster.

Those factors included the poor quality of ore, an “over-steepened” slope and a rising water table at the facility, as well as the “impairment” of a gravel layer that was meant to collect and move liquid, Smith explained.

Together they led to the large-scale liquefaction of saturated ore that triggered the massive failure in a matter of 10 seconds, he said.

“All five of those things had to happen at the same time for this catastrophe to happen. If we only had the first four, and no liquefiable ore, it would have been a failure, but it wouldn’t have been a catastrophe,” he said.

The mine located about 85 kilometres north of Mayo has not operated since the collapse and Victoria Gold was placed in receivership in August 2024.

Smith said the board found irrigation of part of the heap that started in April 2024 was raising the water table and would have caused material to start moving in the weeks prior to the massive slide on June 24.

“Probably around June 1st, there would have been some evidence of distress on that slope. But there are no operators down there,” he said.

“This is not an area where people were going routinely … and there was no instrumentation on the slope. So, they didn’t know this was happening.”

If the irrigation sprinklers had been turned off, “it may have stopped the failure completely,” Smith said.

He said the site that had been operated by Victoria Gold Corp. had “almost no surveillance,” something that is “far too common” in the industry.

“We need better surveillance of these facilities across the board.”

Smith told the briefing he hopes the board’s findings and recommendations will extend beyond the territory, steering the heap-leach industry toward better practices that lower the risks of failures.

Asked if other mining companies had reached out to him after the disaster at the Eagle Gold Mine, Smith said he was receiving calls “as often as daily” in the months that followed. He also hears from regulators, insurance companies and investors asking about the future of heap leaching, he added.

Smith said he is the lead editor on the first-ever guidelines on heap and dump leaching, which are funded by industry and set for publication in 2027.

While there may always be a risk of failure, he said heap-leach facilities should aim to reduce not only the risk but also the consequences of failure.

“Things can go wrong, but they don’t go badly wrong. They don’t become catastrophic failures,” he said.

The heap-leach disaster in Turkey last year resulted in deaths, he noted.

The review board for the Eagle Gold Mine failure makes 50 recommendations in its report released this month, and Smith said none of them would be “particularly expensive” to implement.

“I’m pretty sure that the cost burden that’s now been put on the Yukon taxpayers for the Eagle Gold failure would fund all of our recommendations on every mining project that will ever be proposed in the Yukon,” he said.

“I think cost-wise, it’s nothing in comparison.”

If he had to pick, Smith said his top recommendation would be requiring independent technical review boards for all significant heap-leach projects.

Yukon officials have said the territory is reviewing the board’s report.

This report by The Canadian Press was first published July 8, 2025.

Brenna Owen, The Canadian Press