Omilak

The Omilak is a silver, lead, and antimony mine located in Alaska.

About the MRDS Data:

All mine locations were obtained from the USGS Mineral Resources Data System. The locations and other information in this database have not been verified for accuracy. It should be assumed that all mines are on private property.

Mine Info

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Site Name

Primary: Omilak

Commodity

Primary: Silver
Primary: Lead
Primary: Antimony
Secondary: Gold
Secondary: Copper

Location

State: Alaska
District: Council

Land Status

Not available

Holdings

Not available

Workings

Not available

Ownership

Not available

Production

Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^146.83 Oz/Ton Ag, 76.9%Pb, No Au Value Given
Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^0.36 Oz/Ton Au, 53.05 Oz/Ton Ag, 25.1% Pb
Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^0.075 Oz/Ton Au, 44.28 Oz/Ton Ag, 30.3% Pb
Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^0.075 Oz/Ton Au, 40.75 Oz/Ton Ag, 28.3% Pb
Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^0.05 Oz/Ton Au, 58.75 Oz/Ton Ag, 38.5% Pb
Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^0.364 Oz/Ton Au, 70.1 Oz/Ton Ag, 40.8% Pb
Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^0.1 Oz/Ton Au, 114.03 Oz/Ton Ag, 66.0% Pb
Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^0.15 Oz/Ton Au, 105.58 Oz/Ton Ag, 56.4% Pb
Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^No Au Value Given, 111.23 Oz/Ton Ag, 65.0% Pb
Year: 1881
Material type: ORE AG PB
Description: Ap_Grade: ^0.1 Oz/Ton Au, 133.89 Oz/Ton Ag, 72.0% Pb
Year: 1889
Material type: ORE AG PB
Description: Ap_Grade: ^No Au Value Given, 142.19 Oz/Ton, Ag, 74.7% Pb
Year: 1889
Material type: ORE AG PB
Description: Ap_Grade: ^0.1 Oz/Ton Au, 49.69 Oz/Ton Ag, 44.5% Pb
Year: 1889
Material type: ORE AG PB
Description: Ap_Grade: ^0.1 Oz/Ton Au, 76.1 Oz/Ton Ag, 49.0% Pb
Year: 1889
Material type: ORE AG PB
Description: Ap_Grade: ^0.1 Oz/Ton Au, 92.9 Oz/Ton Ag, 48.3% Pb
Year: 1890
Time Period: 1881-1890
Material type: ORE AG PB
Description: Cp_Grade: ^Ave. 53% Pb, 4800 G/T Ag

Deposit

Record Type: Site
Operation Category: Past Producer
Operation Type: Unknown
Years of Production:
Organization:
Significant:

Physiography

Not available

Mineral Deposit Model

Model Name: Polymetallic veins
Model Name: Polymetallic replacement

Orebody

Not available

Structure

Not available

Alterations

Alteration Type: L
Alteration Text: The deposits are variably oxidized with secondary iron oxides and lead carbonates developed.

Rocks

Not available

Analytical Data

Not available

Materials

Ore: Silver
Ore: Galena
Ore: Cerussite
Ore: Chalcopyrite
Ore: Stibnite
Gangue: Arsenopyrite
Gangue: Limonite
Gangue: Pyrite
Gangue: Pyrrhotite

Comments

Comment (Geology): Geologic Description = The Omilak mine is one of the oldest in Alaska (Cobb, 1975). It was discovered before 1880, claims were staked in 1881, ore shipments took place between 1881 and 1890, and the claims were patented in 1884 (Brooks and others, 1901; Mendenhall, 1901; Smith and Eakin, 1911). Forty- one tons of galena were shipped in 1890; they contained 74.7 % Pb, 142.2 ounces/ton Ag, and 0.1 ounces/ton Au (Smith and Eakin, 1911). Nine assays of ore shipped in the 1880's ranged from 60.7 to 173.0 ounces/ton Ag and 10.27 to 82.0 % Pb and some contained up to 0.4 ounces/ton Au (Smith and Eakin, 1911). The mineral deposits consist of discontinuous lenses or veins of argentiferous galena and cerussite in fractured marble. Samples from the shaft dump contain limonite after pyrite or pyrrhotite (and possibly chalcopyrite) and marble cut by veinlets of calc-silicate minerals with disseminated pyrrhotite and pyrite(?). Typical specimens of high grade ore from the shaft dump contained 55.2 % Pb, 12.1 % Fe, 1.0 % Sb, 0.15 % Cu, 0.2 % Sn, 0.1 % Zn, 0.13 ounces/ton Au, and 88.01 ounces/ton Ag (Mulligan, 1962). Thin stibnite veinlets and disseminations are scattered through marble float on the dump of a caved prospect shaft 350 feet southeast of the main shaft (Herreid, 1965; Briskey, 1983). A specimen from this dump contained 0.06 % Pb, 3.4 % Fe, 31.7 % Sb, 0.05 ounces/ton Au, and 0.19 ounces/ton Ag (Mulligan, 1962). The host rock is slightly recrystallized, partly dolomitic marble intercalated with schist in the core of a small anticline that plunges northwest and is overturned to the northeast (Herreid, 1965). The Omilak mine had a 180 foot main shaft, two working levels, and a 500 foot adit. Smith and Eakin (1911) estimated about 600 feet of workings in the main mine area and Herreid (1965) suggested that the adit may have not reached the ore zone due to an inferred plunge of the mineralization. This is a polymetallic vein and replacement in high grade metasedimentary rocks of probable Lower Paleozoic or Precambrian age (Till and others, 1986).

Comment (Commodity): Ore Material = argentiferous galena

Comment (Geology): Age = Cretaceous ; Epigenetic mineralization in metamorphic rocks of Seward Peninsula is primarily of Cretaceous age.

Comment (Exploration): Status = Inactive

Comment (Production): Production Notes = Smith and Eakin (1911) estimate that a total of 300 to 400 tons of high grade ore was shipped from the Omilak mine. Forty-one tons of galena shipped in 1890 contained 74.7 % Pb, 142.2 ounces/ton Ag, and 0.1 ounces/ton Au (Smith and Eakin, 1911). Nine assays of ore shipped in the 1880's ranged from 60.7 to 173.0 ounces/ton Ag and 10.27 to 82.0 % Pb and some contained up to 0.4 ounces/ton Au (Smith and Eakin, 1911).

Comment (Reference): Primary Reference = Smith and Eakin, 1911

Comment (Workings): Workings / Exploration = The Omilak mine had a 180 foot main shaft, two working levels, and a 500 foot adit. Smith and Eakin (1911) estimated about 600 feet of workings in the main mine area and Herreid (1965) suggested that the adit may have not reached the ore zone due to an inferred plunge of the mineralization. Some stopes are now caved to the surface. An inclined prospect shaft (now caved) is 350 feet southeast of the main shaft.

Comment (Deposit): Model Name = Polymetallic vein or replacement in marble (Cox and Singer, 1986; model 19a or 22c ?)

Comment (Deposit): Model Number = 19a (?), 22c (?)

References

Reference (Deposit): Herried, G.H., 1965, Geology of the Omilak-Otter Creek area, Bendeleben quadrangle, Alaska: Alaska Division of Mines and Minerals Geological Report 11, 12 p., 1 sheet, scale 1:63,360.

Reference (Deposit): Briskey, J.A., 1983, Summary of field observations on Seward Peninsula mineral deposits: U.S. Geological Survey, unpublished administrative report, 34 p.

Reference (Deposit): Smith, P.S. and Eakin, H.M., 1911, Mineral resources of Alaska 1910: U.S. Geological Survey Bulletin 480, 333 p..

Reference (Deposit): Mulligan, J.J., 1962, Lead-silver deposits in the Omilak area, Seard Peninsula, Alaska: U.S. Bureau of Mines Report of Investigations 6018, 44 p.

Reference (Deposit): Cobb, E.H., 1972, Metallic mineral resources map of the Bendeleben quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-417, 1 sheet, scale 1:250,000.

Reference (Deposit): Cobb, E.H., 1975, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Bendeleben quadrangle, Alaska: U.S. Geological Survey Open-File Report 75-429, 123 p.

Reference (Deposit): Till, A.B., Dumoulin, J.A., Gamble, B. ., Kaufman, D.S., and Carroll, P.I., 1986, Preliminary geologic map and fossil data, Soloman, Bendeleben, and southern Kotzebue quadrangles, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 86-276, 10 p., 3 plates, scale 1:250,000.

Reference (Deposit): Brooks, A.H., Richardson, G. B., and Collier, A. J., 1901, Reconnaissance in the Cape Nome and Norton Bay regions, Alaska, in 1900: U.S. Geological Survey Special Publication, p. 1-180.

Reference (Deposit): Mendenhall, W.C., 1901, A reconnaissance in the Norton Bay region, Alaska, in 1900, in Brooks, A.H., Richardson, G.B., Collier, A.J., and Mendenhall, W.C., Reconnaissance in the Cape Nome and Norton Bay regions, Alaska, in 1900: U.S. Geological Survey Special Publication, p. 181-222.

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