Lucky Friday Mine recognized for innovation that transformed deepest U.S. mine

Workers at the Lucky Friday Mine head to the mine. Below, Hecla president and CEO Phillips S. Baker Jr. speaks during the keynote address of MINEXCHANGE 2023. The Murray Innovation Award was presented to Hecla Mining Co. for its innovation of the underhand closed bench (UCB) mining method at the Lucky Friday Mine in Idaho. The 80-year old mine is the deepest underground mine in the United States. It is also a mine with significant seismic activity. Leaning on a culture of innovation, Hecla developed the patent-pending UCB, a mining method that controls the release of seismic energy in a deep, narrow-vein mining front while improving safety and productivity. Hecla Mining Co. president and chief executive officer Phillips S. Baker Jr. and Lucky Friday operations manager Chris Neville accepted the award on behalf of the company and presented the Murray Innovation Lecture during the keynote. Hecla’s commitment to innovation transforms mining at the United States’ deepest mine Baker has been CEO of the 130-year company since 2001 and has continued to lead a culture of innovation that includes among other things, an automated haulage system at the Casa Berardi Mine and ore sorter at the San Sebastian Mine. The journey to manage seismicity at the Lucky Friday Mine began 40 years earlier and has included the underhand longwall with paste backfill trial in 1985, a continuous remote vein miner, and eventually, the UCB in 2020. “What we’ve discovered is that the best ideas are often years in the making, so we appreciate the role of both success and failures in the learning process,” said Baker. “However, we also know that you have to try things out and be willing to fail.” The Lucky Friday Mine is not only the deepest mine in the United States, it is also extremely hot (ambient rock temperature at the bottom of the mine is 155 degrees) and it is seismically active. That seismic activity has changed over time from rock burst to fault slips. Both create safety risks and reduce productivity. Following a seismic event eight years ago, Hecla began to look for ways to reduce stresses around the stopes to keep its workers safe and production moving. Preconditioning ore “We knew that a day or so after we create an excavation by blasting, the area becomes inactive, with no mining and little seismicity. So, we concluded that, if we could precondition the ore in advance of the stopes using large blasts, not only could we physically mine out troublesome faults near the stope and prevent them from slipping, but we could also redistribute stresses into stable, confined rock far in advance of the stope. The result would be to reduce the energy that’s released during mining and control the stresses that are applied to faults in the areas where people are working,” Baker said. Baker said the search for a solution was a search for the Holy Grail of mining — a way to cut the preconditioned rock productively while removing the miner from the face. For a time, the company considered a remote vein miner, but eventually settled on the UCB method. Figure 1 Seismic control improvements from UCB method. The UCB method blasts a longer, deeper area of the stope, releasing the seismic energy during the blast while miners are out of the mine and away from danger. This allows for a safer and more efficient way to muck out the ore. Neville said the UCB blast hole rings are drilled to break 7 m (24 ft) deep along 250 ft (76 m) of the stope using 25,000 lb of explosives to blast 9.1 kt (10,000 st) of rock, rapidly fragmenting the ore below. During the traditional cut-and-fill method, seismic energy is released gradually over 10 weeks. In contrast, with the UCB method, 90 percent of the total seismic energy around the stope is released within 12 hours, distressing the mining zone and greatly reducing risk of further seismic activity. It has also created 100 times more fragmented ore (Fig. 1). With the ore already fragmented by the initial large blast, there is little to no need for further blasting. The ore is mucked out in 3.6-m (12-ft) layers while backfilling the stope with cemented paste. Since the introduction of the UCB, Lucky Friday has recorded its best safety record in its history while improving production 150 percent. During Hecla’s innovation journey, Baker said the company experienced two unexpected events: The first was a labor strike that began in 2017 and stretched on for more than two and half years, ending in January 2020. That was followed closely by the COVID-19 pandemic. Both events were challenging but the silver lining to the dark clouds was that the pause in production also allowed the company time to create and implement the UCB. “During the strike, of course, our engineers developed the new mining method. After the strike, the older, experienced miners retired, leaving the Lucky Friday with a brand-new mining method and a very young, inexperienced crew to implement it,” Baker said. “Still, the mine’s accident rate has dropped from what it was when the experienced miners were there — and it’s dropped dramatically. “Now, with the UCB method, the mine has gone from miner control to engineer and management control. We’ve shifted toward a task-based mining, where management decides how the mining is done. I’m convinced that, without the strike, the UCB method wouldn’t have happened. The work rules would have prevented the very experimentation we needed to make it successful. But with the UCB method, the management at Lucky Friday has created a much safer and a more productive mine,” Baker said. From 2016 to 2022 the mine saw a 68 percent increase in production, and 2023 is forecast to see another 17 percent increase, producing 375,000 st of silver from the mine.

Lucky Friday Mine recognized for innovation that transformed deepest U.S. mine

Authored by:
William Gleason

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