Alaska Endicott

Mine, Inactive

Commodities and mineralogy

Main commodities Ag; Au; Cu
Ore minerals chalcopyrite; pyrite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale C-4
Latitude 58.6968
Longitude -135.2589
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mine is at an elevation of about 300 feet, on a west tributary to the Beardsley River. It is on the west side of Lynn Canal 1/2 mile south-southwest of the head of William Henry Bay, in the NE1/4 section 1, T. 37 S., R. 61 E. of the Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

The Alaska Endicott Mine is in well-foliated greenstone intercalated with fine-grained clastic rocks and muscovite schist. The clastic rocks are mostly graywacke, dark gray argillite, and black phyllite (Clough and Redman, 1989). The mine workings follow a quartz-calcite vein in sheared greenstone. The vein strikes about west and dips 58-85 south. It pinches and swells from nil to 25 feet, averaging 5 feet thick. The vein is predominantly calcite which has been crushed and brecciated and subsequently annealed with quartz. Chalcopyrite and pyrite make up about 1% of the vein. The sulfides are concentrated near the vein margins. The Alaska Endicott deposit was discovered prior to 1915 and developed by more than 2,400 feet of underground workings, including an 1,800-foot adit, and several drifts, raises, and stopes. A 30-stamp mill was in-place by 1919. A new 15-stamp mill from the Comet mine (JU036) was in operation by 1922 and a small flotation plant was also built. The prospect was diamond-drilled in 1922. A 100-ton smelter sample that averaged 1.7% copper was shipped in 1917; production records indicate that 48 ounces of gold and 20 ounces of silver were recovered from 200 tons of ore. A U.S. Bureau of Mines sample of the quartz-calcite vein contained 1.7% copper, 5.6 ppm silver and 0.04 ppm gold (Clough and Redman, 1989). They estimate that the deposit contains a resource of 20,000 tons of ore with an average grade of 0.46% copper.
The general area is underlain by metamorphosed Silurian and Devonian clastic rocks, limestone, and volcanic units; Permian limestone and siltstone; and small plutons of Tertiary and Cretaceous granodiorite (Brew and Ford, 1985).
Geologic map unit (-135.26071298459, 58.6964698496488)

Production and reserves

Workings or exploration The Alaska Endicott deposit was discovered prior to 1915 and developed by more than 2,400 feet of underground workings, including an 1,800-foot adit, and several drifts, raises, and stopes. A 30-stamp mill was in-place by 1919. A new 15-stamp mill from the Comet mine (JU036) was in operation by 1922 and a small flotation plant was also built. The prospect was diamond-drilled in 1922. A 100-ton smelter sample that averaged 1.7% copper was shipped in 1917; production records indicate that 48 ounces of gold and 20 ounces of silver were recovered from 200 tons of ore.
Indication of production Yes; small
Reserve estimates The U.S. Bureau of Mines estimate that the deposit contains a resource of 20,000 tons of ore with an average grade of 0.46% copper (Clough and Redman, 1989).
Production notes A 100-ton smelter sample that averaged 1.7% copper was shipped in 1917; production records indicate that 48 ounces of gold and 20 ounces of silver were recovered from 200 tons of ore.

References