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FAIRBANKS - A Fairbanks gold mine will seek permission to use heap leaching to extract gold from ore.
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The plan by Fairbanks Gold Mining for the Fort Knox Mine would pile low-grade ore in a creek valley and leach gold from the ore using a sodium cyanide solution. The ore and solution would be contained by a plastic liner.
Representatives from the company, the Army Corps of Engineers, and the departments of Natural Resources and Environmental Conservation will discuss the project, answer questions and accept public comment on the proposal Monday night.
The open pit gold mine is 26 miles northeast of Fairbanks. It produces more than 400,000 ounces of gold annually. The mine is primarily on state and Alaska Mental Health Trust lands. The mine and mill employs about 400 employees and operates two shifts, 24 hours per day, 365 days per year.
According to the company, a dramatic increase in the cost of electricity led the mine to consider the alternate method. Heap leaching would require less energy than mill processing and enable the mine to process ore at about one-third the cost.
Two other Alaska mines have used heap leach facilities, according to Rich Hughes, who tracks mining for the state's Department of Commerce, Community and Economic Development. One produced gold in the mid-1980s on Ester Dome. The other, south of Galena, was developed in the mid-1990s and reopened in the early 2000s.
Hughes said the two facilities have not caused any environmental problems.
Tom Crafford, mining coordinator at the Department of Natural Resources' large mine permitting team, said concerns associated with permitting demanded close review by the agencies.
"You need to be diligent in looking at the company's application and subject them to an adequate level of scrutiny," he said.
Crafford said the two state agencies have reviewed the Fairbanks Gold Mining applications and documentation and likely will approve the proposal unless major issues arise.
"We anticipate that we can proceed to the issuance of final permits," he said.
According to Crafford, the proposal will require additional review because of the steep slopes in the valley but is buoyed by the mine's active state of operation. Also, heap leach would be upstream from the mine's tailings pond. Any accidentally released chemicals would be captured in the pond, he said.
"It's kind of a backstop," he said.
The heap leach facility would be built by clearing trees, brush and soil from a section of the Walter Creek drainage, grading the area and laying down a fine-grained, low-permeability material in a one-foot layer, according to the company. An impermeable plastic liner nearly 3 inches thick would be laid over that and covered with three feet of crushed rock. Ore would be piled on top of that.
The facility would be built in phases and ultimately cover 310 acres. According to spokeswoman Lorna Shaw, the company is completing a cost estimate for the project.
After gold is recovered from the ore, the heap would be rinsed, re-graded, covered with the removed soil, and planted with native vegetation.
Hughes, who said he plays a role in the Department of Natural Resource's large mine permitting team, said the Fort Knox proposal looks sound.
"They've done their homework," he said. "We don't expect any problems with it."