New mining method improves safety and productivity at depth

The Society for Mining, Metallurgy and Exploration (SME) presented Hecla Mining with the Robert E. Murray Innovation Award at its annual meeting, which was held in Denver, during February. What follows is an edited version of the presentation that Phillips S. Baker, Jr., CEO, Hecla Mining, and Chris Neville, operations manager for the Lucky Friday mine, delivered during the keynote session before accepting the award.

Thanks in part to the Underhand Closed Bench (UCB) method, the Lucky Friday mine, located in Wallace, Idaho, USA, now produces more than 4 million ounces per year (oz/y) of silver. “In 2001, when I arrived at Hecla Mining Co., the mine’s future was uncertain,” Baker said. “At the time, the price of silver was $4.10/lb, while the cost of production without capital expenditures was $5.50/lb. Some believed Lucky Friday should be shut down and allowed to flood – a step that, at best, would have closed the mine for a very long time, and at worst, would have ended the opportunity to mine there forever.”

Others, however, recognized its potential. Lucky Friday was Hecla’s second largest resource, and one that had at least 10 more years of production. Silver deposits of this size are rare. Today, the Lucky Friday is the 12th largest primary silver reserve in the world. “Because silver resources are so hard to find, develop, and operate, I was convinced that we needed to try to keep the mine open,” Baker said. “Since then, we’ve worked hard not only to keep it open, but to make it safer and more productive. Remarkably, since 2001, the Lucky Friday mine has produced around 50 million oz. Based on what we know today, it likely has another 100 million oz in reserves.”

Innovations like the UCB method do not happen by accident, Baker explained. “They are the result of a long-term mindset, the commitment of a skilled and experienced team, a willingness to make the most of opportunities and challenges, and the relentless drive to improve,” Baker said. “That’s what saved Lucky Friday, and it’s what defines the culture of our 132-year-old company.

“We are honored to receive the Robert E. Murray Innovation Award,” Baker said. “I knew Bob Murray personally, and I believe he’d be pleased with the UCB method because, at its core, it’s not just about increasing production — it’s about protecting the miners.”

132 Years of Innovation

Hecla is the oldest U.S.-based precious metals mining company. The company operates three primary silver mines, the Lucky Friday, Greens Creek in Alaska, and Keno Hill in Yukon — as well as the Casa Berardi gold mine in Québec. It also has half a dozen development projects.

“Back in 1891, when Patsy Clark, Mace Campbell, and John Finch founded the Hecla Mining Co., they made a key decision – hiring James McCarthy as the CEO,” Baker said. “A mining engineer, McCarthy continually brought new ways of operating to the company. During his tenure, Hecla led the way in electrification. He served as CEO for 27 years, yet his commitment to innovation continued to shape the company long beyond his tenure. Over the years, Hecla deployed deep shafts and new equipment of every type.

“One of the unique features of Hecla is the long tenure of its employees and CEOs — something that’s critical to both a long-term mindset and a culture of innovation,” Baker said. “My predecessor, Art Brown, was the CEO for 16 years, and I am only the 11th CEO over the past 132 years with nearly half of Hecla’s existence has been with just three CEOs.”

It’s not just the leadership that’s committed to longevity, Baker explained. “Countless Hecla employees have served the company for years, providing skills, experience, and expertise that are critical to its success. Although we’re focusing on the Lucky Friday mine today, our people continually drive innovation across the company.”

Hecla has fostered a company culture that values continuous learning, remains open to new ideas, and is willing to adapt to change. “What we’ve discovered is that the best ideas are often years in the making, so we appreciate the role of both successes and failures in the learning process,” Baker said. “We also know that you have to try things out and be willing to fail.”

As he started to tell the story behind the UCB mining method, Baker wasn’t sure where to begin so he started with Wilson Blake. “Back in the 1970s, Blake was studying seismicity at Asarco’s Galena mine in the Silver Valley while he earned his Ph.D.,” Baker said. “In those days, Bill Anderson was general manager for the Star mine, and that mine eventually played a major role in where we find ourselves today. Brown was also central to the story because everything that happened at the Lucky Friday in the late 1970s and 1980s was at his direction.”

In the late 1970s, the Bureau of Mines put out a request for a study on how to control rock bursts in the Silver Valley. While the bureau would fund this research, the industry needed to build it, Baker explained. Blake and a young engineer, Mark Board, reviewed the work of nickel miners in Sudbury and proposed a method of controlling seismicity. Board approached several mining companies in the Silver Valley to do some basic research. 

Hecla expects to safely double production from deepest part of the mine during the next decade.

Anderson agreed to support the research, and they began testing a method that Wilson called “preconditioning the rock,” at the Star mine. This work led to two new mining methods: the Lucky Friday Underhand Longwall (LFUL) methods in the 1980s and the UCB today. 

Hecla constructed the No. 2 Shaft at Lucky Friday, which became operational in 1960. The shaft offered the only access to the Lucky Friday vein, a mile below the surface until about 1984, when the Silver Shaft was completed. This one-mile-deep, circular concrete-lined shaft allowed for several innovations: the shaft itself, paste backfill and rubber-tired equipment, and the new mining method called the LFUL. “This was a significant adaptation of the early trials at the Star,” Baker said. “The engineer who led these efforts was Fred Brackebush. Another engineer, George Sturgis who worked for a contractor on the Silver Shaft, was the principal leader of the Lucky Friday’s No. 4 shaft. This shaft, almost two miles below the surface, gives access to Lucky Friday’s deep highly stressed ore.”

In 1998, Hecla began mining the Gold Hunter Vein at Lucky Friday, a vein that outcrops about 8,000 feet at the surface. When Baker joined Hecla, all the Lucky Friday mining was on the Gold Hunter Vein. “The LFUL method worked reasonably well for the next 15 years, since the Gold Hunter is a weak argillite vein that squeezes rather than bursting,” Baker said. “However, the vein also has the complication of more faults that risk slipping without warning.

Overcoming the Challenges Deep Mining Presented

Lucky Friday presented a unique set of challenges, Baker explained. The mine is very deep. In fact, it’s the deepest mine in the United States. Only two mines in all North America are deeper. Second, it’s extremely hot. At the bottom of the mine, the ambient rock temperature is 155°F. The mine is well known to be seismically active. “When the mine was at full production using the LFUL method, about 25% of the time we had to shut down certain stopes for a shift or two to safely allow for seismic activity,” Baker said.

“Work rules with the union were yet another challenge at Lucky Friday,” Baker said. “These rules allowed the senior miners to determine where they worked and who they worked with. Inevitably, the more experienced and capable miners would end up working in the easiest and most profitable stopes. That meant we had to mine more slowly in some stopes, which resulted in poor geometries and led to greater seismic potential.”

About eight years ago, the Lucky Friday mine experienced a seismic event that emphasized the need to find a new mining method. As they mined, the activity put stresses into the rock that would ultimately cause the faults to slip. Hecla began to look at ways to reduce the stresses around stopes.

“We knew that a day or so after we create an excavation by blasting, the area becomes inactive, with no mining and little seismicity,” Baker said. “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. The next question was: How to best safely mine the heavily preconditioned rock in advance of the stope?”

That’s when Hecla took a huge leap. To cut the preconditioned rock productively, while removing the miner from the face, they decided to develop a mechanical mining machine, the Remote Vein Miner (RVM), that could rapidly cut the preconditioned rock. Hecla had hired Clayr Alexander a couple of years earlier, and he had already led a team at Rio Tinto that developed a rock-cutting machine with Atlas Copco (now Epiroc).

Baker said he has been asked how they were able to get the company to move forward with the RVM. “Frankly, it was a balancing act between believing that it could work and believing that, even if it didn’t, we would learn,” Baker said. “And, we knew we had to innovate.” On several occasions, Baker compared the RVM investment to exploration, saying “most work associated with exploration is unsuccessful, but it’s still a necessary part of reaching a successful outcome.” The RVM was no different.

Ultimately, Hecla opted for the UCB method over the RVM. “The way I saw it was that the RVM was a single point of failure,” Baker said. “A failure of the machine would stop production. And, as this one was the first, it would take time to make it operate consistently.”

With the UCB method, on the other hand, Baker could see several advantages. The Lucky Friday had already experienced success with the UCB method, which had evolved during the time that they were developing the RVM. Theoretically, the production from the UCB method should far outstrip the hoisting and milling capacity of the mine. And finally, the transition from LFUL to UCB would be faster and more straightforward than the transition to a continuous miner.

Lucky Friday sees production increase with the implementation of the UCB mining method.

Two unexpected challenges bought Baker and his team more time to research and explore the options before making a decision. “When the union went on strike at Lucky Friday in 2017, we had extra time without the pressures of ongoing production,” Baker said. “Workers didn’t return until 2020. Which, of course, is when the world was hit with the COVID-19 pandemic. It gave us the time and space to do the preconditioning blast. And, in the end, COVID-19 supply chain issues prevented us from shipping the RVM to the Lucky Friday mine. That reduced the pressure to bring the RVM online.

After the strike, many of the older, more experienced miners retired, leaving the Lucky Friday with a new mining method and a very young, inexperienced crew to implement it. “Still, the mine’s accident rate has dropped from what it was when the experienced miners were there,” Baker said. “And, it’s dropped dramatically.”

The UCB method changed the mine from miner controlled, to engineer and management controlled, Baker explained. “We’ve shifted toward task-based mining, where management decides how the mining is done,” Baker said. “Without the strike, the UCB method wouldn’t have happened. The work rules would have prevented the experimentation needed to make it successful. But with the UCB method, the management at Lucky Friday has created a much safer and more productive mine.”

Baker recognized the support Hecla received from several organizations. Orica provided blasting technology, including the i-kon detonators that assured the timing and consistent detonation; ESG improved the seismic monitoring; Northwest Energy Services supplied the Orica product; and Boart Longyear provided the long hole drilling. Baker turned the presentation over to Chris Neville, operations manager at the Lucky Friday mine.

A Safer Approach to Deep Mining

During his younger days, Neville said they could feel the rock bursts from the Lucky Friday mine at the high school in Wallace. “This was well before cell phones, so the notification to mobilize the voluntary ambulance crew was a siren that could be heard across town,” Neville said. “Unfortunately, it was all too common for that siren to sound shortly after the windows rattled at the school, and soon the ambulance would be at the Lucky Friday mine.” He said he shared that perspective, so the audience could understand how truly excited he is about what they have accomplished at the Lucky Friday with the UCB.

The mine is accessed by the 6,100-ft-deep Silver Shaft, which was first used to mine the Lucky Friday veins. The internal 3,700-foot No. 4 Shaft sits a mile to the northwest and accesses the Gold Hunter veins to the 8300 level where the shaft bottom is approximately 10,000 feet below surface.

The mine has three generations of mining methods:

• The conventional overhand cut-and-fill in the Lucky Friday Vein, down to the 5100 level;

• The mechanized Lucky Friday Underhand Longwall (LFUL), which started in 1985 and mitigated pillar rock bursting with a single mining front that greatly improved safety; and

• The UCB, which has now been used very successfully for the past three years and has further improved safety by mitigating structural seismicity.

Lucky Friday is well known for its mining induced seismicity. The mine is one of the most challenging in the world, having higher stress concentration levels than the seismically active mines of South Africa at about one-half the depth. The Lucky Friday is deep, at 2.3 km, with a major horizontal stress approximately 1.5 times the vertical stress. Combine this with numerous faults near the mining front that are prone to unstable slip, and mining a near vertical narrow vein create the right conditions for some significant seismicity.

“There are multiple ways to manage seismicity — monitoring, exclusion protocols, adjusting mining geometry to eliminate pillars (e.g., underhand mining), extraction rate, and use of heavy, dynamic ground support,” Neville said. “The story here is really all about de-stressing and preconditioning, and the development of a mining technique in which they are an integral part of the method.

This series of photos shows the transition in mining conditions.

“In 2017, a 2.15 moment magnitude event occurred in 15 stope caused by a floor wedge bounded by faults cutting through the vein beneath the stope,” Neville said. “The event heaved 80 ft of stope floor 6 to 9 ft. Seismicity like this is what pushed us to continue looking for a better way to mine.”

In 2019, de-stressing and preconditioning came to the forefront, which was the final catalyst for developing the UCB. The lagging underhand 12 stope above 15 stope created a 90-ft tall, stress-concentrating corner pillar that was a seismic problem. Hecla developed a de-stress plan using a single row of 4-in. holes, 60-ft deep on a tight pattern to attempt to crush the corner zone and remove its capability to store energy. At the same time, 15 stope continued to have floor heave. A preconditioning pattern of widely spaced blast holes was implemented.

Neville explained the difference between the two. “Preconditioning is only intended to disrupt fault structures that would store energy versus de-stressing that would crush the area completely,” Neville said.

To crush the rock, the powder factor was increased to 2.5 emulsion per ton of rock. The embedded ground support on drill cuts, 6-ft bolts on 4-ft centers was increased to 8-ft bolts on 3-ft centers.

The 12 slope de-stress blast produced a swell of broken rock with large boulders. “When that happened, it was like a bell rang and light bulbs flashed,” Neville said. He said he clearly remembered everyone thinking, ‘What if we used just a few more holes and broke the rock down more?’

The LFUL method focused on eliminating pillars causing rock bursts. The UCB method focuses on blasting through faults that cause seismicity, and it represents a significant change in the mining method.”

Seismic Control is Key

The UCB blasts a longer, deeper area of the stope releasing seismic energy during blasting. Blasthole rings are drilled to break 24 ft deep along 250 feet of the stope floor. Using 25,000 lb of emulsion, a powder factor of 2.5, 10,000 tons of ore is pulverized below the floor.

The traditional cut-and-fill method releases seismic energy incrementally over 10 weeks, the duration of mining two cuts. The UCB method releases more than 90% of the total seismic energy around the stope within 12 hours, or one shift. It creates 100 times more fragmented ore versus the traditional method and de-stresses the mining zone.

With the ore already fragmented by the large blast, clearing the ore requires little to no additional blasting. Miners safely muck out the swell in two 12-foot cut layers back filling the stope with cemented paste. Once operations return to a solid floor, the UCB process is ready to repeat.

“We have not eliminated seismicity,” Neville said. “We simply have dictated when it would occur creating a safer and more productive environment for the miners. Since we have fully implemented the UCB method, no damaging seismic events have occurred at the active mining front.

Hecla had to overcome some major challenges in developing UCB. Production drilling had to be able to follow
the ore blindly for 24-ft vertically, or two 12-ft cuts of rock. Definition drilling was on 150-ft centers, so they initiated a major diamond drilling campaign down to 50-ft centers. This improved vein location. Without the increased definition drilling, staying in the ore would have been impossible.

Another major challenge was the ability to break the rock for the depth of two cuts. “The use of electronic detonators gave us confidence that all explosives were initiated,” Neville said. “Without electronic detonators, this method would have been challenging.

“It took a lot of failure to get to this point,” Neville said. “And, we were allowed to fail. We also failed fast. At one point, we had three different types of blast patterns and timing in one stope just to figure out what worked. Of course, we ultimately figured it out. Due to the heavy ore and a choke style of blast, a lot of explosives are required.”

They knew when they had finally succeeded with blasting when closure in the stopes went from 2 in. up to 7-, 8-, and more than 9-in. immediately after the blasts. That normally would have taken 10 to 12 weeks using the LFUL method. The closure, however, created another challenge: keeping the backfill from crushing overhead. Neville and his team increased embedded ground support from 6-ft bolts on 4-ft centers to 8-ft bolts on 3-ft centers on drill cuts.

The final major challenge was keeping the paste backfill from saturating the broken rock, Neville explained. “Again, we failed multiple times, and we failed fast,” Neville said. “Similar to the situation with blasting, sometimes we tested several methods in the same cut of a stope. Ultimately, we determined a 12-in. layer of compacted broken ore worked effectively as a barrier.

“The safety improvement alone that the UCB method has provided is a remarkable achievement,” Neville said. “Rarely does improving safety with seismicity increase production. However, that’s exactly what UCB has done. From 2016 to 2022, Lucky Friday has had a 68% production increase in its main mining zone, the 30 Vein. In 2023, we expect another 17% increase in tonnage.”

The invention of the UCB mining method is a testament to Hecla’s dedication to continuous improvement and innovation. “We stand on the shoulders of many predecessors, beginning with those who tested de-stressing at the Star mine in the late 1970s and early 1980s,” Neville said. “At Lucky Friday, the circular concrete Silver Shaft, the first in the district, positioned the mine for the long haul. Through the years, our knowledge grew through the LFUL method and continued de-stressing practices. New technology in electronic detonators also contributed to the success of UCB. Even the vision to change the work rules in 2017 was necessary to facilitate the new mining method.”

With the UCB mining method, the Lucky Friday mine is positioned to safely produce more than 5 million oz/y of silver, Neville explained, and that makes these the best years the Lucky Friday has ever had.