The mining never stops, but Kennecott’s massive open pit grows — slowly

The scale is astonishing: nearly 100 trucks, each one carrying 320 tons (640,000 pounds) of ore, running 24 hours a day, 365 days a year.

The trucks crawl along at 10 to 15 mph, carrying basketball-size rocks to a 3.5-mile conveyor, which takes them out of the massive hole that is Kennecott’s Bingham Canyon Mine, Utah’s largest mine and the source of 1% of the world’s copper.

And they’ve been doing it for decades, creating an opening 2½ miles across that is visible from space.

But 40 years of satellite photos of the mine raise a question: How does Rio Tinto, the owner of the mine, keep pulling out rock without seemingly making the pit look bigger?

It’s basically about slowly shaving down the walls of the nearly mile-deep hole.

“When we look at an expansion of the mine, it’s really only 1,000 feet at a time,” said Matt Tobey, general manager of projects and engineering at the mine. “And that keeps us [going] for a decade or more.”

With each round, the bottom of the mine gets a little deeper. “You’re really only dropping maybe 300 or 400 feet deep every time.”

Copper for electric vehicles

Copper is an excellent electrical conductor, and demand for electrification, particularly electric vehicles, is pushing copper prices higher. In that environment, Kennecott’s miners can’t pull the rock out too fast. Annual production is 200,000 tons of copper and 2,000 tons of molybdenum.

And with the huge amount of ore that gets processed, even minerals that exist in tiny amounts can be recovered, including about 4 tons of gold and 6 tons of silver each year. The company also started recovering tellurium, which is used to make solar panels more efficient.

How long will the mine keep producing? That’s an open question based on not just what’s left in the mine but also metal prices and mining costs.

“If you get further than like 15 years out, the economics change,” Tobey said. “You can know a lot about the ore body. You can know a lot about your operation, but you don’t always have certainty around what the world’s going to look like.”

He said about half the known ore body is still in the ground. He described that body as resembling a tooth. The top of the tooth has been removed after more than a century of mining, but some long roots remain.

Working around a landslide

The mine’s current permit, which pulls material from the south wall, runs until 2032. The company is pursuing permits for its next phase, which will switch to the northwest wall of the pit. That is expected to keep ore flowing until at least 2040.

The mine’s steep walls require constant watching, as evidenced by a massive 2013 landslide on the northeast side of the pit. The remains of the slide are still obvious because it’s the only wall inside the pit that isn’t terraced by mining.

“One of the things we’re world-class at is monitoring and measuring the movement of the pit,” Tobey said. “And when I say movement of the pit, we’re talking about thousandths of an inch.”

That monitoring gave mine operators time to relocate equipment and ensure workers were safe before that slide sent 165 million tons of earth tumbling.

No mining takes place on the landslide, but that hasn’t stopped work on the other walls.

Getting cleaner

Kennecott’s mine, smelter and refinery are the largest sources of air pollution in the state, but those operations are making progress on that score. According to data from the Utah Department of Environmental Quality, they generated 10,978 tons of the major air pollutants (particulates, nitrogen oxides, sulfur dioxide, volatile organic compounds and carbon monoxide) in 2017. By 2022, that had dropped to 8,110 tons.

The company also has cut its carbon footprint in the state by more than half after it shut down its coal-fired power plant in 2019. It now buys renewable energy from Rocky Mountain Power and recently opened a small solar plant on company property.

But Kennecott also has to expand its massive tailings operation in Magna if it wants to keep mining until 2040, which has brought some blowback from residents.

Kennecott began in 1903 as the Utah Copper Co., and the first mining in Bingham Canyon was underground, although the vast majority of ore has come from more than a century of digging what was once the world’s largest open-pit mine.

Today it employs more than 2,300 employees, including those from four unions, and another 2,200 people who work for contractors.

The company recently returned to underground mining in a tunnel in the pit, but most of the ore still comes from the surface.

It’s a process that has been refined over the decades but is still basically the same: Drill holes in the mine to plant explosives, and then scoop up the rocks left behind after the explosions. Dump the scoops in the massive trucks, which then haul them to the conveyor.

From rock to plate

The conveyor moves the rock to the company’s concentrator, where huge steel balls crush the basketballs into powder. That powder then is processed to pull out a mixture that is around 20% to 25% copper, which is sent several miles through a slurry to Kennecott’s Magna smelter, where the gold and other minerals are removed.

From there, an even higher copper concentrate streams to the refinery at the edge of the Great Salt Lake, where it is refined to 99.999% copper, almost all of which is sold to U.S. customers.

While there is no set date for closing the mine, everyone knows it will eventually shut down. In the meantime, reclamation has already begun.

About 10,000 acres outside the pit on the east side (the part that is visible from the Salt Lake Valley) has been graded to remove the terraces of the mine. It is then covered with topsoil that was removed decades ago and stored at the base. Then it was reseeded with native plants.

That ongoing process will continue across the entire footprint of the mine. At that point, it presumably will be less visible from space, although some sign of disturbance likely will remain for years.

There are no plans to fill the hole.