Owhat (Cobalt Creek)

Site Name

Primary: Owhat (Cobalt Creek)

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Commodity

Primary: Tin
Primary: Antimony
Primary: Gold
Primary: Copper
Secondary: Silver
Secondary: Bismuth
Secondary: Zinc
Secondary: Lead
Secondary: Cobalt

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Location

State: Alaska
District: Aniak

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Land Status

Not available

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Holdings

Not available

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Workings

Not available

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Ownership

Not available

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Production

Not available

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Deposit

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

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Physiography

Not available

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Mineral Deposit Model

Model Name: Polymetallic veins

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Orebody

Not available

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Structure

Not available

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Alterations

Alteration Type: L
Alteration Text: Silicification and tourmalinization.

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Rocks

Name: Quartz Monzonite
Role: Associated
Age Type: Associated Rock
Age Young: Pliocene

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Analytical Data

Not available

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Materials

Ore: Aramayoite
Ore: Stephanite
Ore: Stetefeldite
Ore: Tetrahedrite
Ore: Arsenopyrite
Ore: Bismuth
Ore: Bornite
Ore: Chalcopyrite
Ore: Galena
Ore: Pyrite
Ore: Bismutite
Ore: Pekoite
Ore: Sphalerite
Ore: Gladite
Ore: Marcasite
Ore: Gold
Gangue: Tourmaline
Gangue: Axinite
Gangue: Quartz

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Comments

Comment (Deposit): Model Name = Polymetallic veins (Cox and Singer, 1986; model 22c)

Comment (Reserve-Resource): Reserves = Assuming dimensions, in feet, of 4.4 x 280 x 870, Bundtzen and Laird (1991) estimate that the resource at this prospect is 63,000 tons of material with average grades of 5.3 ppm gold, 13.4 percent arsenic, 0.21 percent antimony, 0.39 percent copper, 0.07 percent tin, 0.05 percent zinc, and 0.017 percent cobalt.

Comment (Workings): Workings / Exploration = Three shallow shafts as much as 40 feet deep and several surface trenches and pits explore about 800 feet of strike length of this deposit.

Comment (Geology): Geologic Description = The Owhat, or Cobalt Creek prospect was discovered by Native prospectors before 1900 (Maddren, 1915; Holzheimer, 1926). The deposits include 8 to 10 sulfide-tourmaline-axinite-quartz veins or greisens in syeno-monzonite (Bundtzen and Laird, 1991). The individual greisens are several inches to more than 3 feet thick in a zone that is 5 to 26 feet thick; the average width of the zone is about 8 feet ,and it has been traced more than 280 feet vertically. The greisens trend northwest and dip steeply northeast near a contact with an axinite-bearing andesite porphyry dike. The mineralized zone has been traced on the surface for a distance of 870 feet, and extensions totaling 650 feet in both directions are indicated by the distribution of mineralized float. The deposit is mineralogically complex and includes arsenopyrite, aramayoite, bismuth, bismuthite, bornite, chalcopyrite, galena, gold, marcasite, pekoite or gladite, pyrite, sphalerite, stephanite, stetefeldite and tetrahedrite in the sulfide-rich material in the quartz-tourmaline-axinite greisen. Multiple episodes of mineralization are indicated by cross-cutting relations among the veins. Late-forming minerals include arsenopyrite, chalcopyrite, and pyrite, but the youngest cross-cutting assemblages include bornite, stephanite, tetrahedrite, sphalerite, and lead-bismuth sulfides (Bundtzen and Laird, 1991). Microprobe analyses indicate that arsenopyrite contains 0.1 to 0.2 weight percent gold in lattice structures. Bundtzen and Laird (1991) collected 16 chip-channel samples averaging 4.4 feet wide, along 860 feet of the greisen zone. The samples average 5.3 ppm gold, 13.4 percent arsenic, 0.21 percent antimony, 0.39 percent copper, 0.07 percent tin, 0.05 percent zinc, and 0.017 percent cobalt. Assuming dimensions, in feet, of 4.4 x 280 x 870, Bundtzen and Laird (1991) estimated that the resource at this prospect is 63,000 tons of material with the stated average grades. The syeno-monzonite host rocks are part of the Upper Cretaceous intrusive complex of the Russian Mountains (Bundtzen and Laird, 1991).

Comment (Reference): Primary Reference = Bundtzen and Laird, 1991

Comment (Geology): Age = Late Cretaceous or Tertiary. Veins crosscut part of the intrusive complex of the Russian Mountains. Quartz monzonite from this complex has yielded a K/Ar age of 70.3 +/- 2.1 Ma (Bundtzen and Laird, 1991).

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References

Reference (Deposit): Maddren, A.G., 1915, Gold placers of the lower Kuskokwim with a note on copper in the Russian Mountains: U.S. Geological Survey Bulletin 622-H, p. 292-360.

Reference (Deposit): Hoare, J M., and Cobb, E.H., 1972, Metallic mineral resources map of the Russian Mission quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-444, 1 sheet, scale 1:250,000.

Reference (Deposit): Hoare, J.M., and Cobb, E.H., 1977, Mineral occurrences (other than mineral fuels and construction materials) in the Bethel, Goodnews, and Russian Mission quadrangles, Alaska: U.S. Geological Survey Open-File Report 77-156, 98 p.

Reference (Deposit): Bundzten, T.K., and Laird, G.M., 1991, Geology and mineral resources of the Russian Mission C-1 Quadrangle, southwest Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 109, 24 p.

Reference (Deposit): Hoare, J M., and Cobb, E.H., 1972, Metallic mineral resources map of the Russian Mission quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-444, scale 1:250,000.

Reference (Deposit): Holzheimer, F.W., 1926, Lode prospects in the Russian Mountains, Kuskokwim River region: Alaska Territorial Department of Mines Miscellaneous Report 81-1, 15 p.

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