One of Alaska’s largest gold mines seeks to extend its life by a decade.
The Kensington Mine is one of Southeast Alaska’s biggest private employers. Chicago-based Coeur Mining wants to invest in an expansion to extend operations at least through 2034.
“The mine was originally designed for a 10-year mine life and we’ve exceeded that,” Kensington’s General Manager Mark Kiessling told CoastAlaska on Friday.
The underground mine’s tailings storage area is expected to be full by 2024. The mine projects to be out of waste rock storage space even sooner: 2022.
Coeur Alaska has applied to the U.S. Forest Service to increase its footprint in the Tongass by 150 acres. That would expand three existing waste rock storage sites and add a fourth to boost overall capacity by about 5 million tons.
The mine employs nearly 400 people — with more than 40 percent living in Southeast. The Kensington Gold Mine is located 45 miles north of Juneau in the Tongass National Forest of Alaska. It opened in 2010.
“We hope to stick around in the community, we plan to stick around,” Kiessling said. “We hope to find the additional reserves and keep people here in Southeast Alaska employed and working at Kensington Mine.”
After the gold is extracted, the leftover mine waste — known as tailings — are kept underwater in Lower Slate Lake. The lake appears on company maps as a “tailings treatment facility.”
That’s through a legal precedent set in 2009 by the U.S. Supreme Court allowing mine waste to be submerged in inland waters. But since the mine’s now running out of space, the lake’s dam needs to be raised by 36 feet.
The company also wants to raise its cap on daily production from 2,000 to 3,000 tons per day.
Critics of the expansion include the Southeast Alaska Conservation Council. The nonprofit environmental group’s Guy Archibald says climate research projects heavier rainfall and extreme weather.
The organization’s staff scientist says he’s worried the lake could overflow and mine waste would spill over into nearby streams.
“What we used to call 200-year storm events are happening at a weekly or monthly basis nowadays,” Archibald said.
SEACC was among the environmental groups that unsuccessfully fought court battles to keep Lower Slate Lake from being used as a tailings pond.
“They’re not considering global climate change, they’re not taking the precautionary steps to prevent a catastrophic failure of that dam,” he added.
But Kiessling says concerns like these will be addressed in the mine’s environmental impact statement to come.
“These are things that will consider as we go through the scoping process,” Kiessling said, “and as we go through the permitting process, so nothing is finalized yet.”
When the mine does shut down it’ll need to keep the mine waste from leaching out into the surrounding watershed.
The reclamation plan calls for keeping the tailings submerged in water in both Lower Slate Lake and the adjacent Upper Slate Lake.
“We’d allow those two lakes to merge and then it would just become become one large lake,” Kiessling said.
But he says both lakes would have to meet water quality levels acceptable to state and federal regulators — that means restoring fish habitat lost during operations.
The mining company was recently fined $500,000 by the Environmental Protection Agency for allowing the release of acid rock drainage into Lower Slate Lake and other lapses in monitoring, assessments, inspections and trainings, federal regulators said.
The first stage of Kensington’s proposed expansion plan is out for public review. The Forest Service is taking public comment through Nov. 7.
Once the 45-day scoping period is concluded, the mine’s expansion plan will undergo a formal environmental review with additional hearings and public comment.