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Heap leach adds life to Fort Knox: gold mine receives extension to 2019.

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Owners of Alaska's largest gold mine plan to incorporate a heap-leach operation and a pit expansion to the existing hard-rock operation, a capital investment designed to extend the Fort Knox mine life by at least seven years.

That's good news for the 400-person work force currently employed at Fort Knox, located about 25 miles northeast of Fairbanks. The open-pit mine and mill complex began gold production in 1996, surpassing the 3 million ounce mark in 2006.

Without the two capital projects, mining at Fort Knox would stop in 2010, with final gold processing two years later. The planned heap leach and the pit-expansion project will extend mining to 2014, with final gold processing concluding in 2019.

Currently owned and operated by Toronto-based Kinross Gold, Fort Knox continues to dominate Alaska's annual gold production, producing 333,383 ounces of gold in 2006.

To produce gold at that rate, Fort Knox miners moved up to 200,000 tons of material a day, sorted into three categories: rock that contains enough gold to be economic ore for the mill, rock containing smaller amounts of gold too costly to process through milling and barren rock.

Growing swiftly in the last few years at the mine complex are gray-colored stockpiles of gold-bearing rock not economic for milling, currently considered waste. But processing that low-grade material in a low-cost heap leach converts those stockpiles into valuable resources.

"There's an environmental benefit, as well as a business...