Surveyors at an Alaska gold mine can now track material movement and mine changes effectively at a safe distance
By Don Talend
By Don Talend
Combine Alaska’s vast spaces and the highwalls and large loading and hauling equipment movement inherent in mining, and you don’t exactly have a surveyor’s optimal working environment. A leading gold-mining company recently adopted surveying and digital imaging technology that is allowing surveyors to track material inventories across a mine’s active area. The result is major improvements in surveying productivity and safety.
The Fort Knox open-pit mine, located near Fairbanks, Alaska, originally permitted in 1994, produces about 330,000 oz/y of gold and is one of the largest gold-producing areas in the state. According to the Alaska Department of Natural Resources Division of Land, Mining & Water, the Fort Knox deposit has yielded nearly 179.6 million tons (163 million metric tons) of ore containing 4.61 million oz of gold since 1996.
Toronto-based Kinross Gold Corp. acquired the mine in 1998 and in February 2008, the company’s board of directors approved the construction of a heap leach facility and expansion of the pit in order to extend the life of the mine from 2012 to 2018. More importantly, the expansion was projected to double the remaining life-of-mine production to 2.9 million oz with the heap leach facility adding approximately 65,000 oz/y.
At Fort Knox, Hitachi EX3600 mining shovels excavate raw material from the mine face and the material is placed on a leach pad by Caterpillar 785D, 789 and 793 haul trucks in 30-foot lifts.
The leach pad is designed to be built in five stages and eventually will cover about 310 acres with a total capacity of 161 million tons (about 145 million mt). Pregnant leach solution is stored in a lined holding pond, where it is pumped to a new carbon-in-circuit (CIC) plant at a rate of about 8,000 gallons (30,400 liters) per minute. This process takes the burden off of the mill’s carbon-in-pulp (CIP) plant, which cannot process lower-grade ore economically.
Kinross needed to survey the working faces and keep track of the volume of material extracted from the pit. Cliff Russell, engineer-technician for Kinross, pointed out that the mine can be a hazardous environment for surveying work. “It’s an open-pit mine and we’ve got a lot of really large equipment moving around, 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. If we can have an instrument that allows us to stay far away and still survey the area accurately, it’s a huge improvement,” he said.
To that end, in 2008 the company purchased a Topcon IS robotic total station, which does reflectorless long-range surveying in addition to integrated digital imaging and three-dimensional modeling, from GPS Alaska, a provider of precision positioning equipment for applications such as surveying and construction.
The new technology, which has replaced a Global Navigation Satellite System (GNSS) rover and a conventional total station, allows surveying across longer distances of up to 6,500 ft. At the Fort Knox mine, the instrument is typically used for surveying at distances of 1,000–3,000 ft. “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 said. “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.”
The accuracy and range of the instrument were tested prior to purchase. Bill McClintock, survey sales manager for GPS Alaska, recalled that when the dealer demonstrated the IS for Kinross, a telephone pole was located from about 4,800 ft away. The IS was also used to scan the heap leach pad across the valley at a distance of about 3,500 ft. Up to that point, says McClintock, the mine’s surveyors had been skeptical of claims regarding the instrument’s range.
David Quandt, chief mine engineer for Kinross, said that 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. “The biggest factor is getting the person away from a highwall situation. You’ve got rocks that can come off the wall, you’ve got loading equipment in that area, you’re taking that man away from any and all that danger with the prism-less instrument.”
Illustrating the less-productive method of surveying the mine the old way, Quandt said, “Our surveyors would have to physically walk the area from crestline and toeline, stop and take a shot every 50 or 100 feet. If you were using the conventional total station, you would have a man at the gun and a rod man with a prism doing the same thing: stopping and taking a shot every 50 feet.”
The scanning function has been useful for conducting topographical surveys. The total station is equipped with ImageMaster IS software developed to supplement laser scanning by generating dimensional 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 topography surveys because it was in a valley that had side slopes that were capable of being scanned,” Russell said. “Also, for stockpiles of classified materials; we’ve been able to take scans and create a computerized 3-D model for quantity purposes.”
Another environmental challenge that Kinross’ surveyors face at the Fort Knox mine is extreme cold. In mid-winter, 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,” said Russell. “I’ve left it set up in between 30° and 40° below zero for several hours at a time performing scans and it’s definitely rugged enough to operate at those temperature, but 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. McClintock expects that a new DaySaver external battery pack will improve this situation.
One capability that Kinross eventually may utilize more is controlling the instrument wirelessly. The ImageMaster IS software’s functionality includes WLAN control of the instrument, working in conjunction with a wireless network card. Taking advantage of this functionality would give management the ability to control the instrument from a desktop or laptop computer. Additionally, it would be possible to view a live video feed. Noting that initial experimentation with this functionality used the mine’s existing dispatch network that does not reach all remote areas beyond the mining roads, Russell said that GPS Alaska has a different idea: The dealer has used 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 -40°F weather, according to Russell. During the winter, the surveyors have to take frequent warming breaks in their pickup trucks. Using the WLAN control, they could control the instrument from inside their trucks via laptop computers, significantly improving productivity.
McClintock reports that use of this long-range reflectorless technology is spreading across Alaska. Surveyors in Anchorage, Ketchikan and Fairbanks are using IS instruments for a variety of surveying projects. The Usibelli coal mine in Healy recently purchased an IS system from GPS Alaska and expects increased productivity similar to that experienced by Fort Knox mine management.
Don Talend of Write Results Inc., West Dundee, Illinois, USA, is a freelance writer specializing in technology (www.write-results-p3.com).