SUPERIOR — There is no copper being mined from Resolution Copper’s East Plant, several miles beyond the town of Superior. But within Shaft Nos. 9 and 10, work continues in maintaining the vast underground network of pipes, corridors and control systems necessary to keep the mine in ready shape for its eventual purpose.

Shaft No. 9 is left over from the original Magma Mine operation, which shut down in 1982 — the other eight original shafts are now abandoned and were separated with thick concrete barriers from the new operation. Resolution drilled the 10th shaft itself, and the two hoist towers sit atop a hill looking out over Oak Flat. At the time of its completion in 2014, Shaft No. 10 was the deepest in the United States.

The latter goes down over 7,000 feet, well below sea level and down to a layer where the Earth is so hot that water seeps into the hole at nearly 175 degrees Fahrenheit. To keep the mine in workable condition requires a vast network of pumps, fans, trains and electric equipment that must be constantly maintained.

The most important of that from the miners’ perspective may be the air pumps and chillers, which not only provide breathable air but keep the mine shaft cooled at the lowest levels so that the heat and humidity is kept at bay. When PinalCentral was shown around the bottom level of the mine, it was roughly 80 degrees.

At that depth, water seeps in through the walls and ceiling, pooling in puddles at the bottom of the shaft. Despite the cooling system, the water is still hot to the touch. A series of pumps “dewaters” the mine at the rate of nearly 500 gallons per minute. The mine would quickly fill with water otherwise, and that excess is pumped out to Resolution’s West Plant, closer to Superior, where it is treated to be used for agriculture.

“The deeper you get, the more you get into the water tables,” said Bo Deen, construction superintendent at Resolution’s West Plant. Deen said that when Resolution took over, it had to remove water from the flooded-out remains of the Magma mine. In addition, when Resolution began to sink the 10th shaft, it encountered more water than anticipated, which caused a two-year delay as it worked out how to increase pump capacity even further. Another work stoppage occurred when they had to install underground air-conditioning units due to the extreme heat.

At the bottom, the mine is surprisingly bright through the hot mist, as the corridors are well-lit and all miners wear a headlight on top of their hard hats. Despite some corrosion and rust along the pipes and metalwork, which the mining team has to contend with as part of regular maintenance, there isn’t a whole lot within the tunnels that calls attention to the extreme depth. Even thousands of feet below sea level, there is still Wi-Fi access.

In addition to the bottom level, PinalCentral was guided through the “never sweat” level, at “only” 1,100 feet below the surface. That level, much colder than the bottom, is where train lines run with excess sludge material that accumulates several miles through the mountains until the tunnel opens out onto the rolling hillsides of Resolution’s West Plant, closer to Superior.

The train can carry workers between the two sites as well. Deen calls the ride “pretty amazing,” and the ceiling is low. Several workers say they will occasionally jog the route for fun.

“When most people think of underground mines, their reference is from 100 years ago,” said Andrew Lye, Resolution Copper project director. “The underground mines of today contain modern technology and people are really surprised when they get underground to see something more like a factory. Even with modern technology and automaton, we still need people to operate and maintain the operations, and people to construct. Building these skills to operate and maintain modern mines is something for which I am proud.”

Half a mile from the twin shafts sits an ore body of copper that has become a focal point of furious contention over the past decade. In the future, Resolution Copper hopes to drill out to the ore and mine the copper using a block-caving process that will permanently damage the site directly above, Oak Flat, which happens to be a popular camping ground and, more importantly, a site of religious significance for the local San Carlos Apache tribe.

At the moment, Resolution is doing exploratory drilling to more accurately pinpoint the location of the ore, which is deep underground but above the lowest level of the mine.

“In mining, if they don’t have the technology, or it costs too much to mine, they won’t do it,” Deen said. “They have calculated the profit down to the penny.”

Superior was the site of the world’s first mine shaft cooling towers, built in the 1930s. But the technological progress in mine worker safety and ventilation, as well as environmental rehabilitation, has kept pace with the ability to scale up projects so that their local impacts remain contentious.

According to the company’s website, sensors monitor employees and equipment at all times, comprehensive data systems provide up-to-the-minute analysis, and battery-powered vehicles within the mine reduce the need for cables or power connections. The data, as well as connectivity between mine shafts, mean in an emergency, miners have more time to escape danger.

The anticipated water consumption once copper drilling commences — even assuming a best-case scenario for the company in terms of permitting, that is still a decade away — could be enormous. But even with no mining going on, a report from 2019 estimates that the operations for dewatering and refrigeration require 2,400 megawatts.

Lye did note that the company is purchasing renewable energy certificates, which offset 100% of their electrical usage in 2020, and that partnering with the Salt River Project utility allowed them to supply 25% of their present power usage directly from solar.

Superior Mayor Mila Besich said that overall the Copper Corridor of Pinal County is a great “testing ground” for state-of-the-art mining technologies.

“I find what they do for workers and miner safety is incredible,” Besich said. “The fact that they are bringing in robotics so workers can work at safe levels, once again it ensures Superior will lead the way in how mines operate. I think that is fascinating.”

Besich noted that in addition to being the site of the first air-conditioned mine, a lot of innovation started within Superior and the Copper Corridor, and she hopes to continue that with the city’s proposed Enterprise and Innovation Center Project, funding for which is included in the recent infrastructure bill making its way through Congress.

“I like working at Resolution,” Deen said. “They’re a great company, they care a lot about their employees and mining. When I first started in the early Eighties, safety was barely what it is today.”


Aaron Dorman is the Casa Grande reporter at PinalCentral, covering government, schools, business and more. He can be reached at

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