Uncle Sam

Mine, Active

Alternative names

Elm City

Commodities and mineralogy

Main commodities Cu; Fe
Other commodities Au
Ore minerals chalcopyrite; magnetite; pyrite
Gangue minerals calcite; epidote; garnet

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale C-2
Latitude 55.53273
Longitude -132.37517
Nearby scientific data Find additional scientific data near this location
Location and accuracy The location of the Uncle Sam Mine is shown on the USGS 1:63,360-scale topographic map. The mine is near the center of the south boundary of section 17, T. 73 S., R. 86 E.

Geologic setting

Geologic description

The rocks in the vicinity of the Uncle Sam Mine are intensely altered greenstone and sedimentary rocks cut by dacite, granodiorite, and diabase dikes (Wright and Wright, 1908; Warner and others, 1961; Maas and others, 1995). The deposit consists of several irregular masses of chalcopyrite, pyrite, and magnetite in a gangue of epidote, garnet, and calcite. The main ore body is cut off by a steep east-trending fault.
The Uncle Sam Mine was discovered in 1899; some ore was produced prior to 1902 but did not return the cost of mining (Roppel, 1991). About 350 tons of ore were shipped in 1906; this ore returned $22 a ton. The mine closed in the fall of 1907 (Wright and Wright, 1908). Maas and others (1995) indicate that the mine produced 12 metric tons of copper. The workings include an open pit and about 800 feet of underground workings from three adits. The workings are shown in detail on figure 15 of Maas and others (1995).
The Elm City and Skookum claims are near the Uncle Sam Mine (Brooks, 1902). A short tunnel on those claims exposes pyrite and chalcopyrite in a zone 3 feet wide; the ore is reported to contain a half ounce of gold per ton.
The Uncle Sam Mine is one of many copper-iron deposits on the Kasaan Peninsula having similar geology and origin (Warner and others, 1961; Eberlein and others, 1983; Brew, 1996). The rocks on the peninsula consist mainly of andesite ('greenstone' in much of the older literature) interbedded with about 25 percent sedimentary rocks comprising approximately equal amounts of limestone or marble, calcareous mudstone and sandstone, and graywacke and conglomerate. These units are part of the Luck Creek Breccia of Silurian and Devonian age, but many of the sedimentary units are similar to and probably grade into rocks of the Silurian and Ordovician, Descon Formation. The bedded rocks are intruded by a profusion of Silurian or Ordovician dikes, sills, and irregular masses of porphyritic gabbro, basalt, andesite, diorite, dacite, and granodiorite. Near some of the deposits, these intrusions may make up 20 percent or more of the outcrop and usually are associated with the development of tactite and alteration of the greenstone. The area subsequently was intruded by several large Silurian or Ordovician plutons; they are mainly granodiorite but locally are diorite and gabbro.
The ore deposits are typically small and of irregular shape; often the ore bodies form lenses or mantos. Some of the deposits conform to the layering in the greenstone and sedimentary rocks. The principal ore minerals are chalcopyrite, pyrite, and magnetite; hematite is often present and a little molybdenite occurs in some deposits. Most of the deposits are associated with tactite or skarn with varying amounts of actinolite, calcite, chlorite, garnet, diopside, epidote, and hornblende. There was significant by-product silver and gold in the ore that was mined in the past, and the gold values in some deposits are high enough to have encouraged exploration in recent years. Marble is more common in the deposits in the western part of the peninsula, where the gold values are generally higher as well (Wright and Wright, 1908; Wright, 1915; Warner and others, 1961; Myers, 1985; Bond, 1993; Maas and others, 1995).
Early interpretations of the ore deposits on the Kasaan Peninsula emphasize their contact metamorphic origin and their probable Mesozoic age (for example, Warner and others, 1961). However, recent radiometric dating and mapping indicate that the deposits formed in a Silurian or Ordovician, arc-related environment characterized by deposition of andesite and submarine sedimentary rocks that were intruded by swarms of dikes of varying composition, mineralized, and then intruded by large granodiorite plutons (Hedderly-Smith, 1999 [Inventory]).
The copper deposits of the Kasaan Peninsula were known to the Russians and the first claim was staked in 1867. Most of the production and development occurred from about 1900 to 1918, especially from 1905 to 1907, when copper prices soared and a smelter was built at Hadley on the north side of the Kasaan Peninsula. After World War I, copper supply exceeded demand, prices fell, and there has been no further copper production since 1918 (Wright, 1915; Warner and others, 1961; Roppel, 1991; Maas and others, 1995). However, because of the intense and widespread mineralization on the peninsula, the area has repeatedly been re-examined for copper, iron, and gold, notably during WW II (Warner and others, 1961) and in the last several decades.
Geologic map unit (-132.376852959027, 55.5323669771842)
Mineral deposit model Cu-Fe skarn (Cox and Singer, 1986; model 18d).
Mineral deposit model number 18d
Age of mineralization The deposit formed in a Silurian or Ordovician, submarine arc-related environment characterized by the deposition of volcanic and sedimentary rocks, the intrusion of swarms of dikes of diverse composition, and the emplacement of several large plutons.
Alteration of deposit Greenstone and sedimentary rocks are intensely altered; formation of skarn.

Production and reserves

Workings or exploration The workings include an open pit and about 800 feet of underground workings from three adits. The workings are shown in detail on figure 15 of Maas and others (1995).
Indication of production Yes; small
Reserve estimates None.
Production notes The deposit was discovered in 1899; some ore was produced prior to 1902 but did not return the cost of mining (Roppel, 1991). About 350 tons of ore were shipped in 1906; this ore returned $22 a ton. The mine closed in the fall of 1907. Maas and others (1995) indicate that the mine produced 12 metric tons of copper.

Additional comments

The Uncle Sam Mine is on or is surrounded by land whose subsurface rights are held by the Sealaska Corporation.

References

MRDS Number A010082; A010139

References

Anzman, J.R., 1995, Airborne geophysical survey, Kasaan Peninsula, Alaska, 12 p. (Unpublished report held by Sealaska Corporation, Juneau, Alaska).
Bond, R.W., 1993; The mineralogy and geochemistry of the Kasaan Peninsula, iron-copper-silver-gold skarns, Prince of Wales Island, southeastern Alaska: Salt Lake City, University of Utah, M.Sc. thesis, 130 p.
Hedderly-Smith, D.A., 1997, Report on the 1995 and 1996 work on the Kasaan Peninsula-Sealaska minerals project: Sealaska Corporation, 87 p. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
Hedderly-Smith, D.A., 1998, Report of the 1995-1997 work on the Kasaan Peninsula-Sealaska minerals project: Sealaska Corporation, 130 p. (Unpublished report held by the Sealaska Corporation, Juneau, Alaska.)
Hedderly-Smith, D.A., 1999, Inventory of metallic mineral prospects, showings and anomalies on Sealaska lands, 1988 through 1998: Sealaska Corporation, Juneau, Alaska, 217 p. (internal report held by Sealaska Corporation, Juneau, Alaska).
Myers, G.L., 1985, Geology and geochemistry of the iron-copper-gold skarns of Kasaan Peninsula, Alaska: Fairbanks, University of Alaska, M.Sc. thesis, 165 p.
Roppel, Patricia, 1991, Fortunes from the earth: Manhattan, Kansas, Sunflower University Press, 139 p.
Reporters D.J. Grybeck (Applied Geology)
Last report date 5/1/2004