Sea Level

Mine, Undetermined

Alternative names

Sealevel

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Pb; Zn
Ore minerals galena; gold; pyrite; sphalerite
Gangue minerals muscovite; quartz

Geographic location

Quadrangle map, 1:250,000-scale KC
Quadrangle map, 1:63,360-scale B-4
Latitude 55.3683
Longitude -131.1899
Nearby scientific data Find additional scientific data near this location
Location and accuracy
The Sea Level mine extends from the shoreline of Thorne Arm northeastward to an elevation of about 300 feet. The mine is in section 18, T. 75 S., R. 94 E., and it coincides with the 'Sealevel Mine' symbol on the 1:63,360-scale, Ketchikan B-4 topographic map (1949 ) The site corresponds to loc. 92 in Elliott and others (1978), and to loc. 301 (1-5) in Maas and others (1995). The location is accurate within a hundred or so feet.
Also see Additional comments.

Geologic setting

Geologic description

The history of the Sea Level Mine has been researched in some detail by Roppel (2005). The deposit was found in 1897 and by 1898 a 35-foot tunnel was driven along a vein from which $10,000 in rich ore was recovered. Following considerable interest in the property, I.B. Hammond began developing the property in 1901 as the Sealevel Mining and Milling Company. Soon it was the most active mine in southern southeastern Alaska and about 800 feet of workings were driven on the vein, a large camp had been erected, and a 30-stamp mill was built. The mill began operation in May of 1902 and ran for 3 weeks before shutting down. After more underground exploration, the mill ran intermittently but ceased operation in July of 1903 for lack of ore, and the assets of the Sealevel Mining and Milling Company were foreclosed on in 1906. There were several attempts to put the property back in operation from 1906 to 1925, but by 1913 the buildings were already deteriorating. From 1926 to 1929, there was considerable activity by the Peerless Consolidated Mining Company to put the mine back in operation, including the construction of a new camp and power plant and the construction of a new 50-ton mill. About 300 tons of ore went through the mill in 1929 and 47 ounces of gold was produced. But the Peerless Company was reorganized soon after and what followed was mainly management changes and legal actions through the rest of the 1930s. There was little if any mining or milling beyond 1929 and eventually the patented claims were sold for their timber.
The total length of the workings was more than 1200 feet. A short tunnel with winze was also driven on the (main) vein at a point 350 feet N60E of the shaft house. The vein was exposed at several other points by opencuts and prospect tunnels, and it appears to continue northeastward for at least 2000 feet, onto the adjoining Sea Breeze claim (KC094).
The rocks in the area of the Sea Level Mine are mainly phyllite and semischist derived from pelitic sedimentary rocks and andesitic or basaltic volcanic rocks, intruded by Cretaceous granodiorite (Berg and others, 1988). The premetamorphic age of the strata is speculative. On the basis of various criteria, the rocks have been interpreted as Mesozoic or late Paleozoic (Berg and others, 1988) and Permo-Triassic or Jurassic-Cretaceous (Crawford and others, 2000). The bedded rocks and some of the granodiorite were regionally metamorphosed to greenschist grade in Late Cretaceous time and subsequently remetamorphosed to hornblende hornfels near contacts of Cretaceous granodiorite plutons emplaced after the regional metamorphism. The metamorphic and intrusive rocks are overlain by Quaternary or Tertiary andesite and basalt.
The Sea Level deposit consists of sulfide-bearing quartz fissure veins. The veins cut hydrothermally altered mafic metavolcanic (greenstone schist) country rocks, and a 25-foot-thick body that either is an intrusive dike of altered porphyry ('blue porphyry' of Brooks, 1902, p. 65-67; and Wright and Wright, 1908, p. 144-146), or a zone of hydrothermally altered mafic metavolcanic rock (Maas and others, 1995, p. 210-218). The principal workings were on two parallel veins 15 feet apart. One is 5 feet thick and one 1-2 feet thick; both strike NE and dip steeply SE, at an acute angle to the NW strike of the foliation of the metamorphic country rocks. The veins consist of coarsely crystalline, milky quartz and minor muscovite, and contain (auriferous) pyrite, galena, and sphalerite, and sparse flakes of native gold. Pyrite cubes also are common in the altered wallrocks of the veins. Included in the veins are large breccia fragments of altered country rocks that reportedly carried as high values in precious metals as the quartz. Locally conspicuous, open-space-filling textures indicate quartz deposition at shallow crustal levels. In addition to the faulting that preceded vein formation; some of the veins in turn are sheared and offset by small faults. The quartz in the veins, however, is not recrystallized, and they thus are probably younger than most or all of the Late Cretaceous regional metamorphism (Maas and others, 1995, p. 215).
Most of the quartz veins are bordered by a hydrothermally altered zone up to three feet thick, characterized by fine-grain, light-gray to bluish-gray, massive, carbonate- and sericite-bearing rock that commonly contains cubic pyrite crystals up to an inch across (Maas and others, 1995, p. 215). Maas and others (1995) interpret this zone as hydrothermally altered mafic metavolcanic rock. Early miners called this altered rock 'blue porphyry,' which they interpreted as crosscutting altered dikes that predate the quartz veins, but are closely associated with some of the orebodies (Brooks, 1902, p. 65; Wright and Wright, 1908, p. 143). Gold content of these pyritic altered zones is high adjacent to the quartz veins and diminishes away from them. Weathered altered rocks have a reddish-brown, oxidized rind up to three inches thick.
An unknown amount of gold and silver was produced from the Sea Level mine in the early 1900s, when the ore reportedly averaged $5.35 of gold per ton (at $20.67 per ounce of gold) (Brooks, 1902, p. 66-67). Forty-seven ounces of gold was produced in 1929 from 300 tons of ore.
Geologic map unit (-131.191593809096, 55.3679599870183)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization The quartz in the veins is not recrystallized (Maas and others, 1995, p. 215). The veins thus are probably younger than most or all of the Late Cretaceous regional metamorphism.
Alteration of deposit Most of the quartz veins are bordered by a hydrothermally altered zone up to three feet thick, characterized by fine-grain, light-gray to bluish-gray, massive, carbonate- and sericite-bearing rock that commonly contains cubic pyrite crystals up to an inch across (Maas and others, 1995, p. 215). Maas and others (1995) interpret this zone as hydrothermally altered mafic metavolcanic rock. Early miners called this altered rock 'blue porphyry,' which they interpreted as crosscutting altered dikes that predate the quartz veins, but are closely associated with some of the orebodies (Brooks, 1902, p. 65; Wright and Wright, 1908, p. 143). Gold content of these pyritic altered zones is high adjacent to the quartz veins and diminishes away from them. Weathered altered rocks have a reddish-brown, oxidized rind up to three inches thick.

Production and reserves

Workings or exploration
The history of the Sea Level Mine has been researched in some detail by Roppel (2005). The deposit was found in 1897 and by 1898 a 35-foot tunnel was driven along a vein from which $10,000 in rich ore was recovered. Following considerable interest in the property, I.B. Hammond began developing the property in 1901 as the Sealevel Mining and Milling Company. Soon it was the most active mine in southern southeastern Alaska and about 800 feet of workings were driven on the vein, a large camp had been erected, and a 30-stamp mill was built. The mill began operation in May of 1902 and ran for 3 weeks before shutting down. After more underground exploration, the mill ran intermittently but ceased operation in July of 1903 for lack of ore, and the assets of the Sealevel Mining and Milling Company were foreclosed on in 1906. There were several attempts to put the property back in operation from 1906 to 1925, but by 1913 the buildings were already deteriorating. From 1926 to 1929, there was considerable activity by the Peerless Consolidated Mining Company to put the mine back in operation, including the construction of a new camp and power plant and the construction of a new 50-ton mill. About 300 tons of ore went through the mill in 1929 and 47 ounces of gold was produced. But the Peerless Company was reorganized soon after and what followed was mainly management changes and legal actions through the rest of the 1930s. There was little if any mining or milling beyond 1929 and eventually the patented claims were sold for their timber.
The total length of the workings was more than 1200 feet. A short tunnel with winze was also driven on the (main) vein at a point 350 feet N60E of the shaft house. The vein was exposed at several other points by opencuts and prospect tunnels, and it appears to continue northeastward for at least 2000 feet, onto the adjoining Sea Breeze claim (KC094).
Indication of production Yes; small
Production notes An unknown amount of gold and silver was produced from the Sea Level mine in the early 1900s, when the ore reportedly averaged $5.35 in gold per ton (at $20.67 per ounce of gold) (Brooks, 1902, p. 66-67). In 1929, 300 tons of ore was milled to recover 47 ounces of gold (Roppel, 2005).

Additional comments

Throughout its history, the name of the property has varied from 'Sea Level' to 'Sealevel.'
In the 1930s, the management of the Sea Level Mine was frequently combined with that of the the nearby Goo Goo Mine (KC096) and they shared their many legal and operational problems.

References

MRDS Number A012345

References

Roppel, Patricia, 2005, Striking it rich! Gold mining in southern Southeastern Alaska: Greenwich, Connecticut, Coachlamp Productions, 286 p.
Reporters H.C. Berg (USGS); D.J. Grybeck (Port Ludlow, WA)
Last report date 3/4/2008