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Sea Level

Past Producer in Alaska, United States with commodities Silver, Gold, Lead, Zinc
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Sections on this page
  1. Identification information
  2. Geographic coordinates
  3. Site location context
  4. Geographic areas
  5. Commodities
  6. Materials information
  7. Alteration
  8. Mineral occurrence model information
  9. Host and associated rocks
  10. Nearby scientific data
  11. Economic information about the deposit and operations
  12. Mining district
  13. Links to other databases
  14. Bibliographic references
  15. General comments
  16. Reporter information

Geologic information

Identification information

Deposit ID 10001589
MRDS ID A012345
Record type Site
Current site name Sea Level
Alternate or previous names Sealevel
Related records 10161269

Geographic coordinates

Geographic coordinates: -131.1937, 55.36864 (WGS84)
Relative position The Sea Level claim extends from the shoreline of Thorne Arm northeastward to an elevation of about 300 feet. The map site is in section 18, T. 75 S., R. 94 E., of the Copper River Meridian, and it coincides with the 'Sealevel Mine' symbol on the 1:63,360-scale, Ketchikan B-4 topographic map (1949 ed., rev. 1973). 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.

Site location context

Political divisions (FIPS codes)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Ketchikan B-4 SW(quadrangle 1:24,000 scale)

Ketchikan SW(quadrangle 1:100,000 scale)

Ketchikan(quadrangle 1:250,000 scale)

Federal lands

Tongass National Forest(National Forest)

National Forest UND(Type of land area)

UND(Federal land areas administered by UND)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Silver Primary
Gold Primary
Lead Secondary
Zinc Critical Secondary

Materials information

Materials Type of material
Galena Ore
Gold Ore
Pyrite Ore
Sphalerite Ore
Muscovite Gangue
Quartz Gangue

Alteration

  • (Local) Most of the quartz veins are bordered by a hydrothermally altered zone up to three feet thick, characterized by generally 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.

Mineral occurrence model information

Model code 273
USGS model code 36a
Deposit model name Low-sulfide Au-quartz vein
Mark3 model number 27

Host and associated rocks

  • Host or associated Host
    Rock type Metamorphic Rock > Schist > Greenschist

Nearby scientific data

(1) -131.1937, 55.36864
ListMap

Economic information

Comments on the geologic information

  • Geologic Description = The country rocks in this part of Revillagigedo Island are marine, interbedded, andesitic and basaltic metavolcanic rocks and subordinate pelitic metasedimentary rocks that are intruded by stocks, sills, and dikes of Cretaceous feldspar-porphyritic granodiorite (Berg and others, 1988). The strata and some of the granodiorite were regionally metamorphosed to greenschist grade in Late Cretaceous time. These regionally metamorphosed rocks subsequently were locally remetamorphosed to hornblende hornfels near the contacts of Cretaceous granodiorite plutons that were emplaced after the regional metamorphism. The premetamorphic age of the strata is uncertain. Berg and others (1988) assign them a Mesozoic or (late) Paleozoic age. Berg (1982) and Crawford and others (in press) assign them to the Gravina belt, of Late Jurassic or Cretaceous age, or to the Taku terrane, of late Paleozoic to Late Triassic age. The metamorphic and intrusive rocks locally are overlain by basalt and andesite lava flows of Quaternary or Tertiary age.? 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 generally 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
  • Geologic Description = 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.? the Sea Level mine was developed in the early 1900s by a three-compartment shaft 125 feet deep, with drifts along the orebody at the 50- and 125-foot levels (Wright and Wright, 1908, p. 144). Total length of these 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). Other surface developments included an inclined tram, a 30-stamp mill, and a pipeline for water power.? 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/ton (Au at $20.67/ounce) (Brooks, 1902, p. 66-67). Maas and others (1995, p. 217) report a mean value of 4940 ppb Au in 38 samples of the Sea Level deposit.
  • Age = 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.

Economic information about the deposit and operations

Development status Past Producer
Commodity type Metallic

Mining district

District name Ketchikan

Comments on the production information

  • 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/ton (Au at $20.67/ounce) (Brooks, 1902, p. 66-67).

Comments on the workings information

  • Workings / Exploration = The Sea Level mine was developed in the early 1900s by a three-compartment shaft 125 feet deep, with drifts along the orebody at the 50- and 125-foot levels (Wright and Wright, 1908, p. 144). Total length of these 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). Other surface developments included an inclined tram, a 30-stamp mill, and a pipeline for water power.? Maas and others (1995, p. 217) report a mean value of 4940 ppb Au in 38 samples of the Sea Level deposit.

Reference information

Bibliographic references

Comments on the references

  • Primary Reference = Brooks, 1902; Maas and others, 1995

General comments

Subject category Comment text
Deposit Model Name = Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Deposit Other Comments = Throughout its history, the name of the property has varied from 'Sea Level' to 'Sealevel.'

Reporter information

Type Date Name Affiliation Comment
Reporter 04-JUL-99 H.C. Berg U.S. Geological Survey

Beyond USGS

Supplemental information added by qvyshift.com. Not part of the original USGS MRDS record.

External references

Maps centered on this site

Authoritative Alaska resources

These are landing pages for further research — the state agencies don't currently expose per-mine deep links.