Stevenstown

Mine, Active

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale C-1
Latitude 55.5173
Longitude -132.28821
Nearby scientific data Find additional scientific data near this location
Location and accuracy The location of the Stevenstown Mine is shown on the USGS 1:63,360-scale topographic map. The mine is near the northeast corner of section 26, T. 73 S., R. 86 E.

Geologic setting

Geologic description

The rocks at the Stevenstown Mine consist mainly of an irregular layer, 50 feet or more thick, of greenstone altered to tactite that forms the roof of a large diorite stock (Wright, 1915; Warner and others, 1961). The tactite and diorite are cut by several diorite, diorite porphyry, and dacite dikes. Most of the ore is confined to a nearly-flat, undulating layer near the surface; it is about 8 to 25 feet thick, 300 feet long, and 200 feet wide. The layer contains disseminated pyrite and chalcopyrite and scattered pockets of higher-grade chalcopyrite, magnetite, and pyrite that commonly are intergrown with coarse-grained hornblende and chlorite. There is relatively little magnetite in the mine but several bodies of magnetite with disseminated pyrite and chalcopyrite occur nearby.
The Stevenstown Mine consists of two large and two small glory holes and a 550-foot tunnel about 50 to 60 feet below the glory holes (Wright (1915; Warner, 1961; Roppel, 1991; Maas and others, 1995; Hedderly-Smith, 1999 [Inventory]). There is another adit nearby that did not encounter ore and there are numerous trenches and pits and a shallow shaft.
The mine was active from 1906 to 1908 and produced about 42,000 tons of ore with an average grade of 2.88 percent copper, 0.0308 ounce of gold per ton, and 0.264 ounce of silver per ton. In 1915 the property was acquired by the Granby Consolidated Mining Company and was mined until 1918.
Warner and others (1961) and Wright and Tolonen (1947) estimate that the Mount Andrew (CR071), Stevenstown, and Mamie (CR073) mines have a combined resource of 2,684,000 long tons of ore, but indicate that about 80 percent of that is at the Mount Andrew Mine and most of the rest is at the Mamie Mine. This material has an average grade of 47.8 percent iron, 0.32 percent copper, and 0.011 ounce of gold and 0.55 ounce of silver per ton (Wright and Tononen, 1947).
The Stevenstown 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 (-132.289892145444, 55.5169385762002)
Mineral deposit model Cu-Fe skarn (Cox and Singer, 1986; model 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 Pervasive development of tactite.

Production and reserves

Workings or exploration The Stevenstown Mine consists of two large and two small glory holes and a 550-foot tunnel about 50 to 60 feet below the glory holes. There is another adit nearby that did not encounter ore and there are numerous trenches and pits and a shallow shaft.
Indication of production Yes
Reserve estimates Warner and others (1961) and Wright and Tolonen (1947) estimate that the Mount Andrew (CR071), Stevenstown, and Mamie (CR073) mines have a combined resource of 2,684,000 long tons of ore, but indicate that about 80 percent of that is at the Mount Andrew Mine and most of the rest is at the Mamie Mine. This material has an average grade of 47.8 percent iron, 0.32 percent copper, and 0.011 ounce of gold and 0.55 ounce of silver per ton (Wright and Tononen, 1947).
Production notes The Stevenstown Mine was active from 1906 to 1908 and produced about 42,000 tons of ore with an average grade of 2.88 percent copper, 0.0308 ounce of gold per ton, and 0.264 ounce of silver per ton. In 1915 the mine was acquired by the Granby Consolidated Mining Company, who operated it and the Mamie Mine until 1918.

Additional comments

In 1998, Sealaska Corporation purchased the patented ground that covers the Mamie and Stevenstown mines and they hold the subsurface rights to the land around them.

References

MRDS Number A010145

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).
Hedderly-Smith, D.A., 1999, Results of 1998 work on the Kasaan Peninsula-Sealaska minerals reconnaissance project: Sealaska Corporation, 40 p. (Unpublished report held by the 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.
Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1915: U.S. Bureau of Mines Bulletin 142, 65 p.
Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1916: U.S. Bureau of Mines Bulletin 153, 89 p.
Reporters D.J. Grybeck (Applied Geology)
Last report date 5/1/2004