High-tech canary in the copper mine
On the night of April 10, 165 million tons of rock -- equivalent in volume to 735,000 school buses -- ripped down the northeast face of Kennecott Utah Copper's Bingham Canyon mine near Salt Lake City, damaging giant shoveling machines, haul trucks and other mining equipment. The cascade of earth swept away roads and left buildings hanging over a gaping new cliff. But nobody was killed, or even injured, because Kennecott knew the landslide was coming.
Mine landslides have long been a danger, but predicting them, it turns out, is a fairly recent achievement. New monitoring technologies developed in recent years have allowed mine companies like Kennecott to quickly and reliably detect small slope movements -- fractions of an inch -- that signal imminent danger.
These innovations use radar to measure tiny changes in the distance between fixed monitoring stations and the mine face. The changes in distance indicate that the slope is moving and potentially becoming unstable. Kennecott uses two different radar systems. One, made by Italian company IDS and sold in the U.S. since 2009, can take an image of a large area of a mine pit every six minutes, making it useful for identifying hotspots of instability. Another system, made by GroundProbe, uses a TV-satellite-style dish to scan a pencil-sized radar beam across the mine face, typically to keep a closer watch on potentially unstable slopes.
Kennecott says it still uses some of the older techniques, too. Conductive cables inserted into the mine face can indicate when cracks occur (they sense a break in electric current), and microseismic monitors can measure small tremors caused by shifting rock. Lasers can measure the positions of hundreds of small reflectors mounted to the pit wall, indicating if those parts of the slope are moving. But fog and dust interfere with the laser beams, and the radar systems measure millions of points with greater accuracy.
"Some of the bigger (mines) are recognizing the value of radar monitoring, so they're moving away from the traditional (systems)," says David Ogan, the general manager of GroundProbe's American operations. He estimates that 70 of his company's radar units are used in mines in North and South America.
Open pit mines are prone to landslides. "You open up any excavation in the ground and you have movement," says Ogan, "and that's how people get killed." That's why researchers started developing the new radar technologies in the early 2000s, recalls David Long, director of the Center for Remote Sensing at Brigham Young University. "(The new technologies have) given mine owners more comfort, because it's pretty scary when a slope fails," he says. More widespread use of the radar equipment could help prevent disastrous landslides like the one earlier in April at a mine in Tibet, operated by China Gold Group, that covered a 3-square-kilometer area and killed 83 people. But "not everybody can afford" a complete monitoring system, which can cost millions of dollars, says Ogan.
At the Bingham mine, the landslide will cut the mine's production of copper by 50 percent, according to Kennecott. Because the Bingham mine provides about 1 percent of the world's copper, the partial shutdown is expected to increase the price of copper, already nearly $3.50 per pound. The company isn't sure when the mine will re-open, but it announced that the mine visitors' center -- where tourists flock to take in the view of the 2 3/4 mile wide, 3/4 mile-deep mining pit -- won't re-open until sometime in 2014.
The makers of the new radar equipment aren't celebrating the disaster, but the landslide is something of a milestone for them. "We've definitely detected things in the past, but nothing like Kennecott," says Cliff Preston, manager of application technology at IDS North America. The company issued a press release saying "we are proud to announce that our technology has aided (Kennecott) technical staff in the quest to increase mine safety."
Marshall Swearingen is a High Country News intern.
Images courtesy Kennecott Utah Copper.