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Cosna Dome

Prospect in Alaska, United States with commodities Silver, Lead, Tin, Gold, Copper, Antimony, 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. Nearby scientific data
  10. Economic information about the deposit and operations
  11. Mining district
  12. Links to other databases
  13. Bibliographic references
  14. General comments
  15. Reporter information

Geologic information

Identification information

Deposit ID 10307705
Record type Site
Current site name Cosna Dome

Geographic coordinates

Geographic coordinates: -152.00002, 64.50857 (WGS84)
Relative position The Cosna Dome Pb-Ag and Sn prospects are situated on a 2,026-foot-high rounded hill on the north flank of the Bitzshtini Mountains. The approximate center of the 1-square-mile area that contains the two prospects is in NE1/4SW1/4 section 6, T. 5 S., R. 22 W., of the Fairbanks Meridian. The Pb-Ag prospect is situated along a west-flowing tributary of the Cosna River that drains the southwest side of hill 2,026. The Sn prospect is situated at the top of hill 2,026. The Cosna Dome prospects are accessible by the Cosna River and an airstrip, 1,100 feet long, on the south flank of the dome.

Site location context

Political divisions (FIPS codes)

Yukon-Koyukuk(Census area)

Alaska(state)

United States(country)

North America(continent)

Land(continent)

USGS map quadrangles

Kantishna River C-4(quadrangle 1:63,360 scale)

Kantishna River NE(quadrangle 1:100,000 scale)

Kantishna River C(quadrangle 1:250,000 scale)

Hydrologic units (watersheds)

Alaska(hydrologic region)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Silver Primary
Lead Primary
Tin Critical Primary
Gold Secondary
Copper Secondary
Antimony Critical Secondary
Zinc Critical Secondary

Materials information

Materials Type of material
Arsenopyrite Ore
Cassiterite Ore
Chalcopyrite Ore
Galena Ore
Pyrite Ore
Sphalerite Ore
Stibnite Ore
Chlorite Gangue
Quartz Gangue
Sericite Gangue
Tourmaline Gangue

Alteration

  • (Local) Burleigh (1989 [OFR 11-89]) reported sericite flakes in the vein material and wall rock, indicating hydrothermal alteration.

Mineral occurrence model information

Model code 47
USGS model code 15b
Deposit model name Sn veins

Nearby scientific data

(1) -152.00002, 64.50857
ListMap

Economic information

Comments on the geologic information

  • Geologic Description = The Cosna Dome area is characterized by low rounded hills having less than 1percent outcrop (Burleigh, 1989 [OFR 11-89]). The country rocks are Precambrian to Cambrian quartzite, metasiltstone, slate, phyllite, and grit (Chapman and others, 1975). Regionally, the area contains a system of northeast-trending strike-slip and related conjugate faults associated with Cretaceous to Tertiary plutonic rocks and coeval or younger volcanic rocks (Clautice and others, 1993). The Cosna Dome prospects are sparsely intruded by thin aplitic dikes (Burleigh, 1989 [OFR 11-89]). . The Pb-Ag prospect is characterized by numerous east-trending subparallel zones of limonite-stained vuggy quartz veins in open-space fractures. The quartz veins contain hydrothermal sericite and various combinations of galena, chalcopyrite, pyrite, sphalerite, and stibnite. Massive galena samples from two prospect pits contained 65 to 147 ounces Ag per ton. A cobble of stibnite from a trench contained 0.7 ppm Hg, 0.8 ppm Ag, and 68.95 percent Sb. Some of the best assays of galena yield 71percent Pb, 91.3 ounces Ag per ton, and 0.06 percent Sn. A pan concentrate from gravels downstream of the prospect contained 7 ppm Ag, and 1,150 ppm Pb (Burleigh, 1989 [OFR 11-89]). The Sn prospect is characterized at the surface by subtle linear benches and depressions trending approximately 145 degrees. These benches and depressions contain brecciated graywacke with irregular quartz stringers, goethite-limonite gossan, and some quartz-tourmaline veining. An iron-stained quartz-veined breccia sample contained 45 ppm Ag, 830 ppm Sn, 2,200 ppm Pb, and 181 ppm As. A sample consisting of gossan and quartz-chlorite veins crosscutting a massive quartz lens contained 54 ppm Ag, 5,800 ppm Pb, 897 ppm As, 0.320 ppm Au, and less than 200 ppm Sn. A zone of dense gossan material contained 20,000 ppm Sn, 110 ppm Ag, 2,130 ppm As, and 3,950 ppm Pb. Regional stream-sediment sampling has found detrital cassiterite. A pan concentrate from gravels downstream of the prospect contained 0.090 ppm Au, less than 5 ppm Ag, 2,100 ppm Sn, and 195 ppm Pb (Burleigh, 1989 [OFR 11-89]). The regional northeast-trending fault and plutonic system that characterizes Cosna Dome and the Bitzshtini Mountains also characterizes Haystack Mountain (KH004) approximately 20 miles southwest and the Chitanatala Mountains to the north and northwest. Silberman and others (1978) determined a K-Ar biotite age of 64.2 plus or minus 1.9 Ma for the pluton on Haystack Mountain, and a K-Ar biotite age of 91.3 plus or minus 2.7 Ma and a K-Ar hornblende age of 92.5 plus or minus 2.8 Ma for the pluton in the Chitanatala Mountains. Results of airborne radiometric and magnetic surveys of the Bitzshtini Mountains are similar to the geophysical expression of the Haystack Mountain pluton and associated hornfels. Burleigh (1989 [OFR 11-89]) interprets the Bitzshtini Mountains, including Cosna Dome, as the surface expression of an
  • Geologic Description = aureole of hornfels around a shallow, unexposed pluton with high-level felsic dikes and Pb-Ag-Sn mineralization. It is reported that Tom Arnstrom first discovered lode cassiterite at the head of a gulch on the northwest flank of Cosna Dome. It is unclear what year the discovery occurred. Using information supplied by Arnstrom, Charles Holky prospected the area for tin (Burleigh, 1989 [OFR 11-89]). Holky reported good prospects of placer cassiterite in the headwaters of the Cosna River (Joesting, 1943). Holky and Colbert discovered lead and silver vein mineralization at the Pb-Ag prospect and hand-dug a 100-foot adit, three trenches, and several prospecting pits. The U.S. Bureau of Mines conducted a brief examination, consisting of rock, soil, and pan concentrate sampling, of the Pb-Ag and Sn prospects in 1964 and a follow up Cu-Pb-Zn soil survey in 1966. In 1980, the Department of Energy completed 1:250,000-scale airborne radiometric and magnetic reconnaissance surveys for the region. During and after 1985, Charles Woodruff conducted various trenching operations and constructed a 1,100-foot airstrip on Cosna Dome. There is no reported production for the Cosna Dome Pb-Ag and Sn prospects (Burleigh, 1989 [OFR 11-89]).
  • Age = the vein mineralization is most likely related to mid- to Upper Cretaceous plutonism in the Bitzshtini Mountains similar to that in the nearby Haystack Mountain and Chitanatala Mountains (Burleigh, 1989 [OFR 11-89]).

Economic information about the deposit and operations

Development status Prospect

Comments on exploration

  • Status = Inactive

Mining district

District name Hot Springs (Cosna)

Comments on the production information

  • Production Notes = There is no reported production for the Cosna Dome Pb-Ag and Sn prospects (Burleigh, 1989 [OFR 11-89]).

Comments on the workings information

  • Workings / Exploration = It is reported that Tom Arnstrom first discovered lode cassiterite at the head of a gulch on the northwest flank of Cosna Dome. It is unclear what year the discovery occurred. Using information supplied by Arnstrom, Charles Holky prospected the area for tin (Burleigh, 1989 [OFR 11-89]). Holky reported good prospects of placer cassiterite in the headwaters of the Cosna River (Joesting, 1943). Holky and Colbert discovered lead and silver vein mineralization at the Pb-Ag prospect and hand-dug a 100-foot adit, three trenches, and several prospecting pits. The U.S. Bureau of Mines conducted a brief examination, consisting of rock, soil, and pan concentrate sampling, of the Pb-Ag and Sn prospects in 1964 and a follow up Cu-Pb-Zn soil survey in 1966. In 1980, the Department of Energy completed 1:250,000 scale airborne radiometric and magnetic reconnaissance surveys for the region. During and after 1985, Charles Woodruff conducted various trenching operations and constructed an 1,100-foot airstrip on Cosna Dome (Burleigh, 1989 [OFR 11-89]).

Reference information

Bibliographic references

Comments on the references

  • Primary Reference = Burleigh, 1989 (OFR 11-89)

General comments

Subject category Comment text
Deposit Model Name = Plutonic related mesothermal, Sn veins (?) (Cox and Singer, 1986; model 15b).

Reporter information

Type Date Name Affiliation Comment
Reporter 08-NOV-99 Cameron S. Rombach Alaska Division of Geological and Geophysical Surveys

Beyond USGS

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

Maps centered on this site

Authoritative Alaska resources

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