Alaska Endicott Mine, Skagway District, Juneau District, Haines Borough, Alaska, USA

Latitude & Longitude (WGS84):	58° 41' 48'' North , 135° 15' 32'' West
Latitude & Longitude (decimal):	58.6966666667, -135.258888889

Location: 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.
Geology: 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).
Workings: 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.
Production: 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.
Reserves: 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).

Commodities (Major) - Ag, Au, Cu
Development Status: Yes; small

Mineral List

4 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Devonian 358.9 - 419.2 Ma

Karheen and Cedar Cove Formations Age: Devonian (358.9 - 419.2 Ma) Description: In Ketchikan quadrangle, consists primarily of massive and thinly bedded dolomitic marble and recrystallized limestone and greenschist facies, locally pyritic, phyllite and semischist derived from graywacke flysch. It also contains feldspathic to arkosic calcareous siltstone and sandstone, conglomerate, calcarenite and limestone breccia, and concretionary dolomite. On Prince of Wales Island consists of flyschlike tuffaceous banded mudstone, graywacke, quartzofeldspathic wacke, and subordinate grit. Gradationally overlain by tuffaceous marlstone, pillow breccia, volcanic conglomerate, carbonate cemented lithic lapilli aquagene tuff, subordinate basaltic to andesitic pillow flows, volcanic breccia, and polymictic conglomerate. In Keete Inlet, consists of volcanic breccia and massive clast- and matrix-supported volcaniclastic conglomerate, interbedded fossiliferous dark gray calcareous argillite and argillaceous limestone. Dark-gray siltstone and dark-gray argillite is the dominant unit. Unit is approximately 1800 m thick between Keete Inlet and Klakas Inlet. The lower 600 m contains subordinate but distinctive dolomitic concretions, usually 0.1 to 3 m thick and a few meters long. The concretions are faintly laminated, and usually parallel to siltstone beds. In Klakas Inlet, includes basal conglomerate or breccia, sandstone, siltstone and mudstone with intercalated basaltic and andesitic flows. Dark gray to black shale and subordinate slate and slatey argillite, with mm-scale laminations and cm-scale compositional layering. Layers of gray mudstone., brown carbonate-rich siltstone, and leucogranodiorite-clast conglomerate up to tens of cm thick are found locally in the section. Graded beds and fine laminations record turbidite deposition. Large slide-block of leucogranodiorite suggest significant topographic relief. Stratigraphic thickness is at least 250 m. These clastic and volcanic rocks are overlain by limestone and the limestone is overlain by black graptolitic shale Lithology: Sedimentary Reference: Wilson, F.H., Hults, C.P., Mull, C.G, and Karl, S.M. (compilers). Geologic map of Alaska. doi: 10.3133/sim3340. U.S. Geological Survey Scientific Investigations Map 3340, pamphlet 196. [21]

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References