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The Bureau of Land Management is analyzing the environmental impacts of a proposed heap-leach mine in the remote southwest corner of Tooele County, where a historic mining district has tapped deposits of valuable metals for a century and a half.

Desert Hawk Gold Corp., based in Spokane, Wash., seeks to develop the Kiewit Mine Project on 104.5 acres of private, state and federal land in the Clifton Hills, about four miles outside the town of Gold Hill, according to a draft environmental assessment released earlier this week. The public has until March 12 to submit comments on the project, which aims to drill 350 to 500 exploratory holes over a 660-acre area to determine the extent of silver and gold deposits.

Kiewit covers the existing Herat Mine, a small operation acquired by Desert Hawk from Dumont Nickel Inc., which had invested at least $7 million developing mining claims there before running out of funding, according to Desert Hawk President Rick Havenstrite. His project would also tap lands and claims owned by Utah-based Clifton Mining Co.

"We've used Dumont data for our design and permitting. We have the whole array of permits," said Havenstrite, who intends to start operations once he and his associates obtain the BLM's record of decision authorizing the mine.

"We want to drag this out of the ground like they used to in the good old days," Havenstrite added. "This is one of the best unproduced silver districts around."

For the first two years, the Kiewit project would produce 2 million tons of ore and 3 million tons of waste rock by drilling, blasting and digging a 16.5-acre pit to a depth of 160 feet, the BLM's environmental assessment reported. The mine would yield ores of oxidized silver and gold that would be processed on a 17-acre cyanide heap-leach pad on private land.

Operators would pile crushed ore on the pad and soak it with up to 100,000 gallons of barren cyanide solution a day. Cyanide is a toxic carbon-nitrogen compound that bonds with atoms of gold and other precious metals as it filters through the ore onto collection liners. The Kiewit operation would gather this "pregnant" solution in a 61,000-square-foot pond that could fill to a depth of 16 feet.

The company expects to complete mining and ore processing in six years, followed by a three-year reclamation program.

The project area, west of the Dugway Proving Grounds and north of the Deep Creek Mountains, is part of the Clifton-Gold Hill Mining District that saw the development of 50 mines in the second half of the 19th century. Surface deposits of silver and lead were extracted initially, and later tungsten and arsenic were mined. Many of those old mines are within the Kiewit project area, Havenstrite said.