Greens Creek (Big Sore Mine), Admiralty Mining District, Juneau, Alaska, USAi

Regional Level Types
Greens Creek (Big Sore Mine)	Creek
Admiralty Mining District	Mining District
Juneau	City Borough
Alaska	State
USA	Country

A Ag-Au-Cu-Pb-Zn-Ba-Bi occurrence/mine started February, 1989. Owned by Greens Creek Mining Co. (subsidiary of BP Minerals America, Inc. + 3 minor interests). Hecla Mining holds a 29.73% interest in the Greens Creek mine with Kennecott Greens Creek Mining Company. Kennecott Greens Creek is the operator of the mine.

History: The Greens Creek deposit was discovered in 1973 by following up a zinc stream-sediment anomaly (Crafford, oral commun., 2000). The underground mine and concentrator facility began operation in 1989, but was placed on standby in 1993, followed by a $114 million modernization and redevelopment investment over a three-year period. Operations resumed in 1996 (Kennecott Minerals Company, 2001). The deposit is serviced by 13 miles of road. In addition to the mine, there is an ore concentrating mill, a tailings impoundment area, a ship-loading facility, camp facilities, and a ferry dock at Hawk Inlet. Kennecott Greens Creek currently (2001) is mining approximately 1,680 tons per day from the 200 South, the Southwest, and the West ore zones. Ore from this underground trackless mine is milled at the mine site. The mill produces gold-silver ore.

Location: The Greens Creek Mine is at an elevation of 1,500 feet on the south side of Greens Creek. The mine is marked on the Juneau A-2 topographic map in the NW¼ sec. 9, T44S, R66E, CRM. The location is accurate.

Age: Fossils in calcareous black-argillite clasts intercalated with pyritic massive-sulfide ore are Late Triassic in age (Crafford, 1989).

Mineralization: Mineralization is a sulfide deposit (Deposit Model: Kuroko massive sulfide deposit (Cox and Singer, 1986; model 28a).

Alteration: The most intense alteration is found closest to the copper-rich portions of the orebody and consists of intense silica-pyrite alteration.

Geology: The Greens Creek deposit occurs discontinuously along the contact between a structural hanging wall of thinly laminated, quartz-mica-carbonate phyllite and a structural footwall of black, graphitic, meta-argillite. Fossils in calcareous, black-argillite clasts in pyritic massive sulfide ore are Late Triassic in age (Crafford, 1989). The most intense alteration is found closest to the copper-rich portions of the orebody and consists of intense silica-pyrite alteration. Three main types of ore have been recognized at the Greens Creek deposit: massive, black, and white. Massive ore is the most common and contains more than 50 percent sulfides, chiefly pyrite, sphalerite and galena, in a matrix of locally barite-bearing silica-carbonate rock. Less-abundant ore minerals include chalcopyrite, tetrahedrite, freibergite, proustite, and electrum. The pyrite content of the massive ore varies from 80 to 90 percent in base-metal-poor ore to 10 to 15 percent in base-metal-rich ore. The black ore is similar to the massive ore, except that it contains appreciable graphite. White ore varies depending upon whether the gangue is primarily barite, silicates, or carbonates. The white ore is pyrite-poor and contains coarse-grained tetrahedrite-tennantite, bornite, freibergite, proustite, galena, sphalerite, chalcopyrite and acanthite. Very high precious metal values are common in base-metal-rich massive sulfides near the stratigraphic hanging wall contact, but gold is common in all three types of ore (Newberry and others, 1997).

Workings: The underground mine and concentrator began operation in 1989. The deposit is serviced by 13 miles of road. In addition to the mine, there is an ore concentrating mill, a tailings impoundment area, a ship-loading facility, camp facilities, and a ferry dock at Hawk Inlet. Kennecott Greens Creek currently (2001) is mining approximately 1,680 tons per day from the 200 South, the Southwest, and the West ore zones. Drilling in 1999 added sufficient reserves to the 200 South and other orebodies to replace production. Similar production replacement resulted from drilling in 2000. As of December 31, 2000, there were 268 employees at the Greens Creek Mine (Hecla Mining Company, 2001). Exploration efforts are ongoing along the trend of the deposit.

Production: Ore from this underground, trackless mine is milled at the mine site. The mill produces gold-silver dor.

Reserves: Current (2001) reserves are 13 million tons of ore with 12 percent zinc, 4 percent lead, 414 grams of silver per ton, and 6 grams of gold per ton (Hecla Mining Company, 2001).

Other Regions, Features and Areas containing this locality

References