The Lucky Friday mine, in Idaho
Silver and gold miner Hecla Mining has developed a new, innovative mining method that will allow the Lucky Friday mine, in Idaho, to increase its projected production in 2022 by almost a million silver ounces, CEO Philip Baker announced on Tuesday.
The Underhand Closed Bench (UCB) mining method, which Hecla developed in an effort to control fault-slip seismicity in deep, high-stress, narrow-vein mining, contributed to a 75% increase in silver production in 2021. The mine produced 3.56-million ounces of silver in 2021, up from 2.03-million ounces in 2020.
Overall, Hecla produced 12.9-million silver ounces and 201 327 gold ounces in 2021, meeting its production and cost guidance. The Greens Creek mine, in Alaska, produced 9.24-million silver ounces and 46 088 gold ounces in the year. Casa Berardi, in Quebec, produced 33 572 oz of silver and 134 511 oz of gold.
Lucky Friday’s output is set to increase to between 4.3-million and 4.6-million ounces of silver in 2022, on the back of using the new UCB method. Green’s Creek output is forecast at 8.6-million to 8.9-million, for overall production of 12.9-million to 13.5-million silver ounces.
The company’s full-year sales rose to a record $807.5-million and net income of $35.1-million was reported.
What is the UCB method
The UCB method uses bench drilling and blasting methods to fragment significant vertical and lateral extents of the vein beneath a top cut taken along the strike of the vein and under engineered backfill.
The method is accomplished without the use of drop raises or lower mucking drives which may result in local stress concentrations and increased exposure to seismic events.
Large blasts using up to 35 000 lb of pumped emulsion and programmable electronic detonators fragment up to 350 feet of strike length to a depth of approximately 30 feet. These large blasts proactively induce fault-slip seismicity at the time of the blast and shortly after it.
The blasted corridor is then mined underhand for two cuts. As these cuts are mined, little to no blasting is done to advance them. Dilution is controlled by supporting the hanging wall and footwall as the mining progresses through the blasted ore. The entire cycle repeats and stoping advances downdip, under fill, and in a de-stressed zone.
The method allows for greater control of fault-slip seismic events, significantly improving safety. In addition, a notable productivity increase has been achieved by reducing seismic delays and utilising bulk mining techniques.
In 2021, 86% of the tons mined were produced through the UCB method.