Fort Knox keeps it clean, safe, efficient

Out of an average 157,800 tons of rock, with the assistance of 30 tons of explosives, 6.7 tons of lime and 20,506 gallons of diesel fuel, Fort Knox mine produces 900 ounces of gold per day. Trucks with giant tires that cost $10,000 each carry 150 tons of ore to the crusher every three minutes. The ore comes out of a pit that is 1,100 feet deep and will be a mile long and half a mile wide by the time mining comes to an end in 2010. The mine operates 24/7, 365 days a year and its electricity bill is $1.9 million per month.

Recovering the precious gold from these vast quantities of rock is big business in all senses.

It's expensive, it can be very profitable when the price of gold is high and it carves out a whole new landscape in this patch of Interior Alaska. Like all mines in the state, Fort Knox is expected to uphold the highest standards of environmental responsibility; but perhaps even more so than the rest, because it is only a few miles by road from Fairbanks, and everything the mine does can be closely scrutinized by the city's residents.

The ore at Fort Knox is "exceptionally clean," Delbert Parr, the mine's environmental manager, told Mining News.

If it weren't for slightly elevated levels of arsenic and antimony (0.03-0.04 parts per million and 0.06-0.08 parts per million respectively), the water in the tailings facility would almost meet drinking water standards, he added.

Levels of cyanide are also extremely low, according to Parr: in the summer the cyanide is almost non-existent due to the effect of sunlight, and in winter it climbs to three or four parts per million.

The mine's permits allow the level of cyanide to reach 10 parts per million.

If necessary, the mill can use a cyanide destruction process, but this is rarely required and involves putting copper, sulfate and nitrates into the water which ideally should not be in there.

Computerized dispatch system installed in 2005

The mining process itself has been improved with the installation of a computerized dispatch system in 2005, which cost about $1 million and was developed by Tucson-based Modular Mining Systems.

About 16 to 20 employees, some of whom were formerly truck drivers, have now been trained as dispatchers.

The system has resulted in a roughly 10 percent improvement in efficiency, as the computer now assigns trucks to routes, ensuring that they are filled with rock at almost all times, instead of waiting in line.

The computer also knows what all the truck drivers are doing, from talking to a supervisor to refueling to taking a bathroom break.

At the same time as the computerization, Fort Knox also purchased nine new haul trucks, a shovel, a grader and two loaders.

The trucks dump ore into the primary crusher, which reduces the rock from up to 60 inches to less than six inches. The crusher is a huge rotating bell-shaped mantle lined with manganese steel that gets harder the more it wears, and can work for four months before being changed out.

A Tramac hydraulic hammer is controlled by the crusher operator and can move or break up oversized rocks. The crushed rock is then transported up a half-mile conveyor belt to the stockpile, and from there onto another conveyor belt that takes it into the mill. Crusher operators have to climb 187 stairs up to the conveyor belt's drive tower and then walk its entire length regularly for inspections.

Mine achieved 1 million manhours without lost-time accident

Fort Knox recently achieved 1 million manhours without a lost-time accident, for the fourth time since operations began in 1997, according to Bob Taylor, the mine's acting general manager. Taylor, who is Toronto-based Kinross Gold's vice president for North American operations, took the Fort Knox position temporarily after John Wild resigned May 1.

While Fort Knox is planning for the construction of a heap leach facility, which could enable the mine to recover more of the remaining gold at a lower price, reclamation and closure of the mine is also looming closer.

The pit, which is dewatered during operations, will be allowed to flood naturally, forming a 150-acre lake. The waste rock dumps will be graded and revegetated to create a rolling-type topography. The tailings impoundment will be a mixture of shallow open water and wetlands habitat.

"The water in the tailings will be pumped to the pit and replaced with clean run-off," Parr said. "Within a couple of cycles the water will clean up." Reclaiming the heap leach pad should also be fairly straightforward, Parr believes. He has closed three heap leach facilities already, including at the nearby Ryan Lode, which was acquired by Kinross but never mined by the company. Kinross also operates Round Mountain mine in Nevada, one of the largest heap leach mines in the country.