Heap leach could add value at Fort Knox

Fort Knox mine near Fairbanks is considering the construction of a heap leach pad to improve its recovery rate and take advantage of soaring gold prices. The project is still in the planning stages, but if mine owner Fairbanks Gold Mining - a subsidiary of Kinross - decides it is viable, the estimated capital cost would be $22 million. Operating costs would be approximately one-third of the current mill operating costs, and the heap leach would be used in addition to the mill processes.

"Heap leaching is being evaluated to improve mine efficiency," Lorna Shaw, community affairs director at Fort Knox, told Mining News. "It would allow us to lower our cut-off grade and process ore that is not economic to mill under current commodity prices." Condemnation drilling in the proposed heap leach location, the north corner of the existing tailings facility, was completed at the end of 2005. "Results are pending to determine whether the Walter Creek drainage area is appropriate," Shaw said. "We need to ensure that the site doesn't contain any economic gold."

Geotechnical studies were completed last summer and all results indicate the technical feasibility of the project, according to Fairbanks Gold Mining. "We need to evaluate the economics to make sure this is a good business decision," Shaw said. "It primarily hinges on the metallurgy and there is current test work being done to determine the recovery characteristics of the material." The mill's recovery rate at present is 86 percent. The metallurgical report on the heap leach project is due to be ready in April.

Ground clearing could begin this year

If the metallurgical results are encouraging, ground clearing could begin later this year and the heap leach could begin working in 2007. Knight Piesold was contracted to do the pad design and Mine and Mill Engineering put together the plant design. "I feel confident that we have a well-designed project. ... If a project like this can't be permitted, then heap leaching can't be permitted anywhere in Alaska," Shaw said. No permit applications have been filed yet.

Cyanide heap leach pads require careful maintenance and have caused problems at other sites where mining companies have gone bankrupt. In Alaska this occurred at the Illinois Creek mine, which was recently reclaimed successfully in a partnership between the state and private industry. Fairbanks Gold Mining already uses cyanide in its mill processes at Fort Knox.