The Fort Knox mine near Fairbanks, Alaska, produces about 330,000 ounces of gold annually, making it one of the largest gold-producing areas in the state. According to the Alaska Department of Natural Resources Division of Mining, Land & Water, the Fort Knox deposit has yielded nearly 179.6 million tons of ore containing 4.61 million ounces of gold since 1996.
The mine was acquired by Kinross Gold Corp. in 1998. At the time, it was expected to produce gold through 2012. In February 2008, the company’s board of directors approved an expansion of the open-pit mine and the construction of a heap leach facility to process low-grade ore and mineralized waste material. The expansion will extend the life of the mine to 2018. More importantly, with the heap leach facility increasing the amount of low-grade material that can be processed each year, the project is expected to double the life-of-mine production to 2.9 million gold ounces and increase annual production to an average 370,000 gold ounces between 2010 and 2015.
Throughout the mining and construction process, Kinross needs to keep track of the volume of material extracted from the pit and survey the dig faces. However, it’s not an easy working environment. “It’s an open-pit mine, and we’ve got a lot of really large equipment moving around,” says Cliff Russell, engineering technician for Kinross, “so the farther back we can stay from work areas and not be right in the middle of the mix of equipment running around, the better.”
To accomplish its material tracking goals while boosting the safety and productivity of its surveyors, Kinross is using advanced equipment that provides both long-range surveying and scanning.
High-Tech Prospecting ToolsBefore embarking on the expansion project, Kinross purchased a Topcon IS robotic total station--an instrument that integrates digital imaging and 3D modeling with reflectorless long-range surveying. The new technology, which replaces a GNSS rover and a conventional total station, is capable of covering distances of up to 6,500 feet, or 1.2 miles.
Kinross surveyors and engineers were initially skeptical of claims regarding the instrument’s range, recalls Bill McClintock, PLS, CFedS, survey sales manager for positioning-equipment provider GPS Alaska Inc. However, when he demonstrated the Topcon IS for Kinross, it located a telephone pole from about 4,800 feet away. The IS was also used to scan the heap leach pad across the valley at a distance of about 3,500 feet. These demonstrations were enough to convince the decision makers at Kinross.
At the Fort Knox mine, the Topcon IS is typically used for surveying at distances of 1,000 to 3,000 feet. “When we mine down benches, we lose access to those upper benches, and there’s only so far we can shoot with the previous instrument,” Russell notes. “Based on the continuously changing topography of the pit and basically constant new-road construction, access can be tricky at times. There are a lot of areas that have limited or no access. The IS has a more powerful [electronic distance measuring device] with a greater range than our existing instrument. That has reduced the number of setups we need to make to get an area surveyed and has expedited a lot of the surveying that we do.”
Besides distance, another challenge that Kinross’ surveyors face at the Fort Knox mine is extreme cold. In midwinter, temperatures in the Fairbanks area routinely plummet to deadly levels. So far, the surveyors have gotten continuous, though somewhat limited, operation from the instrument. “I’ve been really impressed with its ability to withstand the cold,” Russell says. “I’ve left it set up in [temperatures] between 30 and 40 degrees below zero for several hours at a time performing scans, and it’s definitely rugged enough to operate at those temperatures. The only thing is, you’ve got to be there to swap out the lithium-ion batteries at a higher-than-normal rate because they consume the batteries a lot faster in the cold.” He estimates that he gets about half the battery life during the winter as in the summer. Kinross hopes to extend the battery life this coming winter by using a DaySaver external battery pack recommended by McClintock.
Modeling SuccessAccording to David Quandt, chief mine engineer for Kinross, the mine has experienced major increases in productivity and safety since adopting the new technology. He estimates that surveying time has decreased by about one-third because fewer redeployments of the instrument are needed. “[Using a conventional total station,] our surveyors would have to physically walk the area from crestline and toeline, stop and take a shot every 50 or 100 feet,” he says.
In regard to safety, Quandt points out that the biggest factor is keeping workers away from the highwall areas. “You’ve got rocks that can come off the wall. You’ve got loading equipment in that area,” he says. “You’re taking that man away from any and all that danger with the prismless instrument.”
Additionally, the instrument’s scanning function has been useful for conducting topographic surveys. The Topcon IS total station is equipped with ImageMaster IS software developed to supplement laser scanning by generating 3D images. The total station collects points, and the software is used to develop real-time images based on triangulated irregular networks (TINs) consisting of irregularly spaced points and breaklines with their own x and y coordinates and z (surface) values. “In the heap leach project, the scanning became advantageous for doing topographic surveys because it was in a valley that had side slopes that were capable of being scanned,” Russell explains. “Also, for stockpiles of classified materials, we’ve been able to take scans and create computerized 3D models for quantity purposes.
“Having an instrument that allows us to stay far away and still survey the area accurately is a huge improvement.”
Sidebar 1: Heap LeachingFort Knox currently mines and stockpiles large volumes of low-grade ore and mineralized waste material that cannot be economically processed at Kinross’ existing carbon-in-pulp mill. The heap leach facility will allow the mine to process some of these low-grade materials as well as zones of lower-grade ore that have not yet been mined.
In heap leaching, the mined ore is crushed into small chunks and heaped onto a leach pad where it is irrigated with a dilute cyanide solution. The solution percolates through the heap and leaches out the gold in molecular form. The leach solution containing the dissolved gold is collected in a lined holding pond and pumped to a carbon-in-circuit (CIC) plant. The plant injects carbon into the mixture, which bonds with and captures the gold molecules. Afterward, the gold is washed off with a superheated water solution to ready it for further processing.
Kinross began putting ore on the new heap leach pads in August 2009 and was on schedule to produce the first gold from the facility in the fourth quarter.
Sidebar 2: The Wireless ElementThe ImageMaster IS software’s functionality includes wireless local area network, or WLAN, control of the instrument working in conjunction with a wireless network card. Taking advantage of this functionality would give Kinross management the ability to control the instrument using a desktop or laptop computer. Additionally, it would be possible to view a live video feed.
A current limitation of this approach at the Fort Knox mine is that the mine's existing dispatch network does not reach all of the remote areas beyond the mining roads. However, GPS Alaska Inc. has an idea to improve coverage. The dealer has suggested using an external router that acts as a repeater for the wireless network card. The manufacturer is also equipping newer models with a more-powerful wireless transmitter.
Using this capability would provide a major advantage in minus-40-degree weather, according to Cliff Russell, engineering technician for Kinross. “During the winter, we have to take frequent warming breaks in our pickup trucks,” he says. “Using the WLAN control, we could control the instrument from inside our trucks with laptop computers, which would significantly improve productivity.”
Kinross has not yet made a decision on whether to implement the technology at the Fort Knox mine.