SALT LAKE CITY (AP) -- Kennecott Utah Copper has suspended mining inside one of the world's deepest open pits as geologists assess a landslide the company says it anticipated for months.
Shovel and haul operators were pulled back earlier Wednesday before the landslide tore loose around 9:30 p.m. inside the nearly mile-deep Brigham Canyon Mine, Kennecott spokesman Kyle Bennett said Thursday.
"This slide was self-contained within the mine," he said.
The outside walls of the mining pit, which stretch 2 1/2 miles from rim to rim, are holding with no danger to housing developments several miles away, he said.
For more than a century, miners have reduced a mountaintop about 20 miles southwest of Salt Lake City to a deep hole. Kennecott, the latest in a succession of owners, is digging into a tooth-shaped volcanic core that has yielded millions of tons of copper and small amounts of gold and silver.
Normally, Kennecott operates the mine all day, every day, with electric-powered shovels capable of scooping up 98 tons of crushed rock at a bite. Bennett said the company continues to operate a copper concentrator, refinery and smelter.
The landslide tore loose not far from a visitor center on the rim of the pit that was closed earlier this month as a precaution.
The first sign of a possible slide was detected in February, when sensors measured ground movement at fractions of an inch. That increased to up to 2 inches a day earlier this week. Then, in rainfall Wednesday night, the slide broke loose. Kennecott couldn't immediately provide details about its size or dimensions.
"We had anticipated this slide and were carefully monitoring that area for some time," Bennett said. "We re-routed roads, utilities and even buildings out of way."
Mining operations have been suspended indefinitely as geologists assess the stability of the step walls inside the pit.
"Movement like this slide we saw last night is very infrequent, but it's something we monitor every day" with special instruments, Bennett said.