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Another, but much smaller landslide Friday at Kennecott's Bingham Canyon Mine resulted in the evacuation of about 100 workers.
Company spokesman Kyle Bennett said a "minor bench failure," measuring about 150 across and 150 feet tall, occurred about 12:30 p.m. along the northeast face of the gigantic pit.
It was not too far, he said, from a massive landslide April 10 that filled the bottom of the pit with waste rock about 300 feet deep.
The 100 miners were working to clear more of that debris Friday when a supervisor saw evidence of movement in the terraced wall above them. Monitoring equipment also sensed ground movement, Bennett said, so the company "evacuated everyone from the lower portion, as a precaution."
Those miners were sent home when their afternoon shift ended, he noted, and the evening shift was informed not to come in until contacted. Bennett expected the work call to go out sometime Friday night.
Miners working on the southern end of the pit were not impacted, he added.
"This does happen in open-pit mines, any time you're dealing with gravity," Bennett said. "Fortunately, we have many levels of protection. Our workers are all trained to observe their surroundings and we have the radar system and can use that data to make real-time decisions."
Earlier this week, University of Utah geophysicists said that two rock avalanches 90 minutes apart on April 10 produced what "probably was the biggest nonvolcanic slide in North America's modern history."
Their study determined the slides reached a speed of up to 100 mph and triggered 16 small earthquakes, the first time that cause-and-effect has been documented.
The April 10 slide weighed about 165 million tons and moved 2.3 billion cubic feet of rock.
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