Operations at Rio Tinto’s flagship copper mine, the Kennecott Utah Copper Bingham Canyon complex near Salt Lake City, Utah, USA, have been severely curtailed by a massive pit-wall failure that occurred April 10. Latest estimates from the company indicate the slide, which took place in the northeast corner of the pit, involved at least 150 million tons of material and filled the bottom of the pit to a depth of 300 ft (91 m) in some areas. The landslide was described by KUC’s president and CEO, Kelly Sanders, as one of the largest in mining history.

KUC said it had been aware of increasing ground movement in the area of the slide and was monitoring the rate of slippage closely for weeks before it occurred. By the time the slide took place, the mine’s visitor-center facility had been closed and removed, employees had been evacuated, control facilities had been relocated and mobile equipment had been shifted to locations considered safe. Even with these precautions, the unexpected magnitude of the slide resulted in burial or damage involving three shovels, 14 haul trucks, and some ancillary equipment including drills, bulldozers and graders.

KUC had previously notified the U.S. Mine Safety and Health Administration (MSHA) of the impending slide, and said MSHA personnel were on-site both before and after the slide occurred. MSHA granted KUC permission for limited access to the mine after the slide had stabilized, and the company said its geotechnical specialists were carefully examining the slide area, using remote-controlled equipment.

Considered the largest excavated hole in the world, Bingham Canyon is one of the top producing copper mines in the industry with 2012 output of 163,200 tons of refined copper, along with 279,000 oz of gold and 9.4 tons of molybdenum. Its annual production accounts for between 1% and 2% of the world’s mined copper production and represents about a quarter of annual copper consumption in the United States.

Although an inevitable production shortfall from the mine isn’t expected to significantly affect world copper supply in 2013, the financial impact of reduced operational levels and possible workforce adjustments could quickly reverberate throughout the northern Utah economy. The mine employs 2,500 people and spent more than $1.2 billion in the state in 2011, including $270 million in wages, benefits and pensions and $765 million in purchases from Utah firms.

Days after the slide occurred, KUC asked its 850 mine employees to consider taking vacation or unpaid time off until it could assess the situation; it later expanded the request to include the entire KUC workforce. Workers who chose to report for work were assigned to jobs, as available, outside the pit. The event also affected a number of contractors working at the mine; for example, Cementation USA Inc., which was conducting underground work in the pit as part of the company’s long-term plan to extend mine life, had to lay off 45 workers after its work area and equipment were completely buried by the slide.

Sanders, at a press conference held on April 25 at an observation point on the pit rim, said early assessments indicated that 90% of the mine’s production equipment was unaffected by the slide, including the in-pit crusher and conveyor-system tunnel that transports 10,000 t/h of crushed ore through a mountainside to the Copperton concentrator. He said that within 48 hours after the slide occurred, workers had restarted operations to excavate and remove overburden from the mine’s Cornerstone layback area, located high on the pit rim and roughly opposite the area of the slide.

Nevertheless, KUC warned that if geotechnical investigation shows that workers may re-enter the pit safely to resume operations, 2013 production is estimated to amount to only 50% of predicted output, and it will take at least a year for the mine to again achieve full production.

Emphasizing that KUC was still in the very early stages of assessing the damage to the mine and investigating geotechnical aspects of recovery, Sanders said the operation faces numerous short-term challenges and decisions before it recovers from the slide. He did not directly address the possibility of worker layoffs at the press conference, but said the company would consult with its unions and hoped to minimize any impact on workers, yet had to closely control its cost structure against the backdrop of reduced production.

He outlined a four-month plan that the company mapped out to return to production. Over the next 30 days, KUC will complete an assessment of pit conditions in regard to safe return of workers for limited ore production. In 60 days, it will develop a strategy for mining-plan recovery and staffing levels, and over the next 120 days will develop a long-term plan to increase mining output from 50% to full production.

(For details of the equipment and technology used by Rio Tinto to monitor ground movement at Bingham Canyon prior to the slide, see “Careful Monitoring: The Key to Pit-Wall Safety,” on p. 32.)