Fort Knox/True North
Environmental and Community Issues
The Fort Knox mine complex currently consists of two open pit gold mines - Fort Knox and True North - and the Fort Knox mill, where gold is recovered through the cyanide vat leach process. Fort Knox began operations in 1996 as a stand-alone mine. It was converted to a regional gold processing facility with the permitting and development of the True North satellite open pit mine in 2001. The Fort Knox mine is operated by Fairbanks Gold Mining, Inc. (FGMI), a wholly owned subsidiary of Kinross Gold Corporation. A Canadian gold company, Kinross is currently the world's seventh largest primary gold producer.
Location
Fort Knox Mine, Fairbanks, AK |
The Fort Knox mine is located approximately 25 miles northeast of Fairbanks, Alaska's third largest city, and two miles from the community of Cleary Summit, consisting of a small downhill ski facility, an aurora-viewing business and bunkhouse, and several year-around residences. Its satellite mine, True North, is situated on the western side of Pedro Dome, 11 miles northwest of Fort Knox. A dedicated ore haul road connects the two properties.
Type of Ore and Current Production
The Fort Knox deposit is a low-grade gold deposit hosted in and along the margins of quartz veins, shears, fractures, and pegmatites within a granite intrusion. Gold is associated with anomalously high bismuth and it is a low-sulfide deposit. In seven years of operation Fort Knox has produced 2.7 million ounces of gold from 99 million tons of ore. Average grade of ore is 0.024 ounces/ton. As of December 31, 2002, the current proven and probable reserve (based on a gold price of $300/ounce) is 2.4 million ounces of gold contained in 100 million tons of ore. Fort Knox's current mine life estimate is eight years.
The True North deposit is hosted in felsic schists in a structurally complex zone trending northeast. The gold is very fine-grained and is closely associated with the sulfide minerals pyrite (iron), arsenopyrite (arsenic), and stibnite (antimony) in unoxidized zones. In its first two years of operation, True North produced approximately 228,000 ounces of gold from 5.7 million tons of ore. Average grade of ore is 0.044 ounces/ton. As of December 31, 2002, the current proven and probable reserve (based on a gold price of $300/ounce) is 312, 400 ounces of gold contained in 7.1 million tons of ore. Present True North reserves are expected to be depleted by 2005.
Operation
True North open pit mine |
Mining at the two deposits is done by conventional open pit methods, seven days a week, year around. The Fort Knox pit covers approximately 332 acres, and is roughly a half a mile wide by a mile long. Mining takes place below the water table, thus there are dewatering pumps that keep the pit dry during mining. At True North, mining is currently done only above the water table, in an oxidized ore zone. At 352 acres, the True North pit is slightly larger than Fort Knox; at end of mine life, the pit will stretch nearly a mile and ½ on its longest axis. The stripping ratio (waste to ore) at Fort Knox is 1:1; at True North it ranges from 2: 1 to 5:1. In 2002, Fort Knox produced nearly 12 million tons of waste rock, while True North produced 7 million tons. Waste rock is stored in massive rock dumps on each property.
True North ore is continuously hauled to Fort Knox by seven 85-ton trucks with trailers. The 11-mile haul road, which is mostly closed to the public, runs roughly 1200 feet below the Skiland and Cleary Summit subdivisions. Once at Fort Knox, True North ore is stockpiled and mixed - one part to three parts - with Fort Knox ore as it is fed into the rock crusher.
The Fort Knox mill uses cyanide to recover gold from the ore; it processes between 35,000 and 50,000 tons of ore a day. First, the ore is crushed to a fine powder, then, after thickening, it flows into leach tanks, where cyanide dissolves the gold. Next, activated carbon is used in the Carbon-in-Pulp (CIP) circuit to absorb the gold from the cyanide solution. Screening removes the gold-laden carbon from the slurry - which is then piped to the tailings impoundment.
The Fish Creek dam
and the lower tailings impoundment |
The 1,177-acre tailings impoundment, created by the construction of an earthen dam, is the upper Fish Creek drainage. The dam, keyed into bedrock, is raised each year as more and more tailings are stored behind it. In its final configuration, it will require approximately 23 million cubic yards of fill, and measure 350 vertical feet from the toe of the dam. A series of pump-back wells installed below the dam keep tailings fluid from seeping into ground water. During mine life, Fish Creek is diverted around the impoundment.
Mine Reclamation and Bonding
As of 2002, reclamation plans for both mines were current. At end of mine life at both mines, in accordance with Alaska regulations for mine reclamation, FGMI must stabilize the pits, waste rock dumps, and the Fort Knox tailings impoundment so as to ensure long-term protection of land and water resources. The Fort Knox pit will be left open and allowed to fill with ground water, creating a pit lake. With the exception of some areas that will be back-filled with waste rock, the True North pits will be left open as dry pits. Pit headwalls will be stabilized to prevent injury to public and wildlife from falling rock. Waste rock dumps will be re-contoured, covered with stockpiled organic material, and revegetated. An engineered wetland will be constructed from the Fort Knox tailings impoundment. Currently, the Fort Knox reclamation bond, which includes a bond for the freshwater dam and for the solid waste permit covering the tailings impoundment is $12,150,414 while the bond for True North is $2,456,874 for a total bond amount for the Fort Knox mine complex of $14,607,288.
Satellite Open Pit Development
The True North open pits are the first in a series of satellite open pits that Fairbanks Gold Mining, Inc. plans to develop as additional feed sources for the Fort Knox gold mill. The company is acquiring rights to and exploring additional lode gold occurrences located throughout the Fairbanks and surrounding areas of Ester, Chatanika, and Cleary Summit. These are identified gold occurrences that are either not large enough or of high enough grade to support a stand-alone mine. Among the company's current exploration targets with the greatest potential to become satellite open pits are the Ryan Lode and Curlew deposits, on Ester Dome 35 miles from Fort Knox, the NOAA target, located on the Gilmore Tracking Station approximately three miles west of the Fort Knox pit, and the Gil, eight miles northeast of the Fort Knox mill. Additionally, International Freegold, a junior exploration company with interests in the nearby Golden Summit property on Cleary Summit, is actively pitching the property to FGMI as a satellite feed source; it is also highly likely that the True North mine life will be extended as additional reserves are confirmed.
Fort Knox Photo Gallery
True North Photo Gallery
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