Reclamation is nearly complete on a part of the Wharf Mine near Lead that is no longer producing minerals, a mine official said Thursday during a tour for state regulators.
The tour was conducted for the state Board of Minerals and Environment, a nine-member regulatory body appointed by the governor. Besides seeing the active parts of the Wharf Mine, where gold and silver are produced, board members also saw the historical Golden Reward Mine, which is almost fully restored to a natural-looking state.
Matt Zietlow, Wharf’s environmental manager, said the last obviously unreclaimed area of the old Golden Reward Mine, just east of Terry Peak, was scheduled to be reclaimed this year. Excessive precipitation got in the way of that plan, Zietlow said, but Wharf expects to have the work done next year.
Standing atop a grassy and tree-dotted hill constructed from waste rock and spent ore, Zietlow said the reclaimed former pit mine is a preview of what the currently mined parts of the Wharf project will look like someday.
“We’re pretty proud of this,” Zietlow said. “The optics speak for themselves.”
Zietlow said parts of the Golden Reward area are roughly in the middle of their 30-year post-closure regulatory phase, during which monitoring is conducted to ensure the site is properly reclaimed and is not polluting the environment. He said dozens of monitoring sites are in place to monitor groundwater, surface water and air quality.
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The Golden Reward area is just southeast of the currently mined parts of the Wharf Mine. Wharf’s corporate parent, Coeur Mining, of Chicago, has 8 square miles of land holdings in the Wharf Mine area and is planning to conduct exploratory drilling with the hope of extending the mine life beyond the currently projected seven years.
Although gold has been mined in the Black Hills since the 1870s, the Wharf Mine is the region's only active large-scale gold mine. Production last year at the Wharf Mine was 76,840 ounces of gold and 50,575 ounces of silver. Coeur’s annual report to investors said combined sales of gold and silver from the Wharf Mine last year were $96.5 million, and the mine had 208 employees.
The heap-leach extraction method is used at the Wharf Mine. Earth is stripped away to get at the gold-bearing ore, and the ore is crushed. The crushed ore is piled in huge mounds, and hoses are laid on the mounds to emit a water-cyanide solution that drips through the crushed ore. The cyanide solution leaches tiny gold particles from the crushed ore, and gold-bearing liquid is collected in pools at the base of the mounds.
Biological processes are then used to denitrify the cyanide solution in ponds, and the resulting water is reused.
Last year, the Wharf Mine stripped away 10.62 million tons of earth (called “waste rock”), mined 4.76 tons of mineral-bearing ore and used 2.04 million pounds of cyanide.