Lucky Friday silver-lead-zinc project is a historic underground mine located in Coeur d’Alene Mining District of northern Idaho, US.
Hecla Mining Company acquired the mine, which has been operational since 1942, in 1958 and has been operating it since then.
Hecla completed sinking of the number four shaft at the mine to a depth of 9,587ft below surface in 2016, making it the deepest mine in the US. The number four shaft construction was completed in 2017.
The shaft enables to reach lower mining levels and increase operational flexibility. The shaft development is anticipated to extend the life of the mine by 23 years.
The underground mine produced 173,627 ounces (Oz) of silver in the first quarter of 2019.
Lucky Friday silver-lead and zinc project location and geology
Lucky Friday silver-lead-zinc project is situated close to Mullan in Shoshone County, North Idaho, and Coeur d’Alene, Idaho.
The mine site consists of two ore containing structures namely Lucky Friday vein and Lucky Friday expansion area.
The Lucky Friday expansion area is located in the Wallace Formation. Hecla is conducting mining operations at the ore structure since 1997 through its subsidiary Silver Hunter Mining Company (Silver Hunter).
Gold Hunter property, located approximately 5000ft from the mine, comprises several mineralised structures containing high-grade silver ores.
Lucky Friday reserves
The proven and probable ore reserves at the Lucky Friday silver-lead-zinc project are estimated to be 5.61 million tons (Mt), grading 14.4oz/ton of silver, 9.1% lead, and 4.0% zinc. It is estimated to contain 81 million ounces (Moz) of silver, 510,800t of lead and 225,260t of zinc, as of December 2018.
Mining and ore processing at Lucky Friday silver-lead and zinc project
Underground mining method with underhand and overhand technique is currently performed at the Lucky Friday silver-lead-zinc project . The underground mine is accessed through the 18ft diameter concrete-lined silver shaft.
Ramp access, cut-and-fill method is primarily used at the underground Lucky Friday mine. The veins are accessed by using rubber-tired equipment through ramps constructed outside the ore body.
Production at the mine takes place by ramps and usage of jumbo drills, mechanised mining, and truck haulage to the silver shaft.
The mining activity involved extracting ore from a cut along the strike of the vein, followed by backfilling with cemented tailings. Same procedure is applied at the next cut, which is accessed from the ramp system.
The ore is processed at the surface processing plant, with a capacity of 1,000tpd. The ore undergoes crushing, grinding, and flotation to produce lead and zinc concentrates. The concentrates produced are currently treated in Teck Cominco Metals smelter in Trail, British Columbia, Canada.
Lucky Friday Number 4 shaft details
The number four shaft, which is an internal shaft of the project, provides access to the highest-grade ore in the mine’s history. Hecla invested approximately $225m for the shaft development.
The newly developed shaft comprises a fully-automated 200 ton per hour (tph) material handling system, a 500 gallon per minute water pumping system, and a centralised refrigeration system with 977t of cooling capacity.
Other associated tasks included lateral development, excavation, and construction of an underground hoist station, 70ft-tall ore bins, hoisting plant, and underground sinking equipment.
Cementation conducted the design and sinking of the number four shaft of the Lucky Friday mine. The company is also involved in preparing the pre-feasibility costing, scheduling, and preliminary design work of the internal shaft.