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Flooding at Minto stalls copper excavation

The high grade copper at the bottom of the Minto mine is stuck underwater.

The high grade copper at the bottom of the Minto mine is stuck underwater.

“Excess water, over and above what could be contained in the (water) storage pond, was directed into the open pit during freshet in order to prevent a non-compliant discharge,” reads a July 15 Capstone Mining Corporation press release.

“The snowpack was greater than usual, resulting in more water diverted into the open pit than planned,” says the release by Capstone—the Vancouver-based company that owns the Minto mine north of Carmacks.

Excavation machinery can’t get to the most lucrative copper at the bottom of the mine, said Capstone president Stephen Quinn.

“It’s just the way the deposit is,” said Quinn on Thursday. “All the ore is at the bottom.”

The Minto mine has plenty of copper stockpiles to mill, so Capstone decided to fill its open-pit mine with wastewater runoff instead of dumping it in the Yukon River, he said.

On July 2, the company received approval from the Yukon Water Board to discharge 300 million litres of wastewater into the Yukon River over 45 days, and has already begun emptying the pond.

“What we’ve done is discharge from our water storage pond first,” said Quinn.

Capstone will begin pumping water from the mine to the pond in the “next few days,” said Quinn.

Capstone’s profits are taking a hit because of the water-filled pit.

In the second quarter of this year, the Minto mine pumped out 12.75 million pounds of copper, he said.

That’s a 15 per cent drop from its expected 15 million pounds of copper per quarter.

“The timing of the discharge will affect the timing of the re-entry into the open pit and therefore access to the higher-grade ore in the pit bottom,” says the July 15


“In the meantime, milling operations continue uninterrupted from the available stockpile,” it says.

But the stockpiled copper is of lower quality than the ore in the pit.

The output during the first half of 2009 will be lower than expected, says the release, but the second half will eclipse expectations.

The Minto mine should hit normal production levels in the second half of the year “provided we get sufficient water out to get the ore—that’s the caveat,” said Quinn.

The Minto mine is meant to produce 60 million pounds of copper a year. The ore is trucked to Skagway and then shipped to Japan where it gets smelted.

Capstone must file a new water management plan today as part of the Yukon Water Board’s approval of the wastewater discharge.

“We will be filing an amended plan for them,” said Quinn on the eve of the deadline.

Its parent company, Capstone, owns another copper mine in central Mexico, after a merger between two Vancouver-headquartered companies occurred earlier this year.

Contact James Munson at