Kensington gold mine review moves forward

State and federal regulatory agencies released a draft version of a supplemental environmental impact statement Jan. 23 for the Kensington underground hard rock gold mine.

Project developer Coeur Alaska Inc., a subsidiary of Coeur d'Alene Mines Corp., one of the world's largest silver producers, wants to build mine and mill facilities that would produce approximately 2,000 tons of gold-rich ore per day, requiring a year-round work force of about 225 people.

It's the third time agencies have reviewed the Kensington project under the National Environmental Policy Act since the original plan of operations was submitted in 1990. While receiving past regulatory approval, no mine has ever been built at Kensington, 45 miles north of Juneau and a few miles inland from Comet Beach on Lynn Canal.

Coeur has been involved in the Kensington project since 1990, developing initial plans with partner Echo Bay Exploration. Now, Coeur is the sole developer of the project.

Development proposal

Public meetings to discuss the proposed project and three alternatives outlined in the draft supplemental EIS will be held Feb. 24 in Juneau and Feb. 26 in Haines. Written comments are due March 8 to the lead agency, the U.S. Forest Service.

The company has proposed building a hardrock mill and administration facilities in the Johnson Creek drainage, in the vicinity of the Jualin Mine, which is a little more than two miles south of the Kensington deposit.

Coeur proposes constructing a 12,000 foot tunnel to access both the Jualin and the Kensington mineralized areas, and mining only higher-grade material from the two deposits.

Ore would be processed using flotation and cyanidation circuits, and non-mineralized rock or tailings would be disposed of in a sub aqueous tailings storage facility built in the Lower Slate Lake. Tailings would be transported via a buried pipeline, and the total tailings disposal would be 4.5 million tons.

Employees would access the mine via a daily ferry service that would operate between Cascade Point and Slate Creek Cove, where a marine terminal to receive supplies and to ship ore would be constructed in the cove off of Berners Bay.

An existing five-mile road from the water terminal to the Jualin Mine would be upgraded to handle mine traffic, and a 3.5 mile pipeline access road and a one-mile cutoff road connecting the other two roads would be constructed.

Mining operations that would employ an estimated 225 workers would last an estimated 10 years, following an 18-month construction period. Construction workers would range from 135 to 179 people.

Three other options

Three other options have been included in the environmental review, prepared by Tetra Tech Inc., a third party contractor under the direction of the Forest Service, the Environmental Protection Agency, the U.S. Army Corps of Engineers and the Alaska Department of Natural Resources.

The no-action alternative reflects a previous action by agencies, which is the project approved in a 1997 record of decision.

Major changes to that previously approved plan include the location of mill and administration facilities, disposal of tailings and construction of on-site employee housing. Supply and freight access would be from a marine terminal on Comet Beach, on Lynn Canal.

Production rate would be 4,000 tons of ore per day, and 400 tons of waste rock per day. No ore would be processed through an on-site cyanidation circuit.

An alternative to that no-action option involves a reduced mining and tailings production rate, equal to the production rate proposed by the company. The life of the operation would be reduced to 10 years, following an estimated two-year construction period.

A third option would involve a ferry transportation dock at Echo Cove, using that access rather than Cascade Point. A landing craft ramp at the Slate Creek Cove terminal would be eliminated.

Water would not be recycled from the tailings facility to the mill circuit. Instead, diversion channels would be constructed to direct flow from Mid-Lake East Fork Slate Creek and overland runoff from undisturbed areas around the tailing disposal. Diverted water would discharge to a spillway at the top of the tailings dam.