Idaho silver mine shaft sunk to final depth of 9,587 feet

Cementation USA Inc. on Tuesday announced it has completed sinking the deepest shaft in the United States at the mine owned by Hecla Mining outside the town of Mullan in Shoshone county, Idaho.

With a finished diameter of 18 feet, the Lucky Friday #4 Shaft was sunk to a final depth of 9,587 feet (2.92 kilometres) below surface. The project is moving into the furnishing construction phase where shaft steel and the final conveyances will be installed.

Hecla, which is celebrating its 125th year of operations, kicked off the expansion project at a cost of roughly $225 million as far back as late 2008 and completion is scheduled for late 2016.

The Cementation group, which is currently sinking 15 shafts worldwide, has sunk the deepest single lift shaft in the world at South Deep Mine in South Africa, the deepest shaft in Canada at Kidd Mine D No.4 Shaft, the deepest single lift shaft in the United States at the Resolution Copper Project, and now the deepest shaft in the United States.

The Lucky Friday #4 Shaft is a vertical shaft that begins underground, which makes it a Winze in mining terminology. A Winze is an internal shaft which requires the equivalent of a shaft headframe and hoisting system to be installed underground before the excavation activities can occur.

Hecla selected Cementation USA to sink the shaft, excavate accesses, stations and pockets, and install the related infrastructure, which include a state-of-the-art fully automated ~200 ton per hour material handling system, a 500 gallon per minute water pumping system, a centralized refrigeration system with 977 tons of cooling capacity, a batch plant, and other systems.

Hecla produced more than 3 million ounces of silver, 18,300 tons of lead and 8,100 tons of zinc at Luck Friday last year. The mine boasts measured and indicated resources of more than 128 million ounces of silver.

Hecla expects to produce 13.5–14 million ounces of silver this year from mines in the US, Canada and Mexico. The company, headquartered in Coeur d’Alene on Tuesday announced the acquisition of the Montanore project in Montana, considered one of the largest undeveloped silver and copper deposits in North America. The project is 50 miles north of Luck Friday.

Image: Cementation