Grand Island-Caribou District

Site Name

Primary: Grand Island-Caribou District
Secondary: Caribou
Secondary: Cardinal
Secondary: Eldora
Secondary: Nederland
Secondary: Grand Island

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Commodity

Primary: Gold
Primary: Lead
Primary: Silver
Secondary: Copper
Secondary: Zinc
Tertiary: Titanium
Tertiary: Uranium

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Location

State: Colorado
County: Boulder
District: Grand Island-Caribou District

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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: District
Operation Category: Past Producer
Operation Type: Surface-Underground
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

Type: L
Description: ore shoots localized at vein junctions and by changes in dip or strike

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Alterations

Alteration Type: L
Alteration Text: silicified, pyritized, argillized, and chloritized wall rock

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Rocks

Name: Granitoid
Role: Associated
Age Type: Associated Rock
Age Young: Tertiary

Name: Gneiss
Role: Associated
Age Type: Associated Rock
Age Young: Precambrian

Name: Schist
Role: Associated
Age Type: Associated Rock
Age Young: Precambrian

Name: Monzogabbro
Role: Host
Age Type: Host Rock
Age Young: Precambrian

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Analytical Data

Not available

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Materials

Ore: Argentite
Ore: Chalcopyrite
Ore: Galena
Ore: Pyrargyrite
Ore: Silver
Ore: Sphalerite
Ore: Titaniferous Magnetitite
Ore: Pitchblende
Ore: Cerargyrite
Gangue: Pyrite
Gangue: Quartz

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Comments

Comment (Commodity): Gangue contains carbonate minerals.

Comment (Location): The district is centered on the old town of Caribou, NE/4 sec. 8, T1S, R73W, about 4 miles NW of Nederland; it lies in the northwest quarter of the township. Most mines and veins are in and adjacent to a Tertiary(?) stock just west of Caribou and on Boulder County Hill a mile east. To the east, the district abuts the west end of the Boulder Tungsten district.

Comment (Location): The district includes mines and deposits at Grand Island, Caribou, and Cardinal, but excludes those at Eldora (a separate district). The district includes the Caribou Consolidated District and Caribou Gold and Silver District of Calais Resources.

Comment (Production): Total value of production from 1869 to 1924 is estimated at $6 million, mostly silver, plus some lead and gold. In the early days, very rich silver ore was produced from upper levels of the Caribou and other mines on the NE slope of Caribou Hill. There was little activity in the district from 1900 to 1948, when the Caribou mine was reopened and produced about $0.5 million through 1951. Work on a small scale at the Cross mine, from 1977 to 1982, resulted in production valued at $2.1 million.

Comment (Reserve-Resource): Sunshine Mining Co. evaluated the Caribou mine, in 1980 and in 1994, and concluded that no more work be done. Extensive files on the Caribou and Cross mines include various reports, assays and maps dated from 1919 to 1994 that may have dated or optimistic resource estimates.

Comment (Reserve-Resource): As of 2005, Calais Resources reports a total resource (measured, indicated, and inferred) of: 437,240 oz Au and 12,575,240 oz Ag, contained in 1,058,000 tons of mineralized material for the Caribou/Cross project. The company continued exploration in the district in 2004 and 2005.

Comment (Commodity): Silver is the main economic product; lead and gold are of secondary importance. Titanium might be recovered from titaniferous iron deposits at Caribou. Uranium has been found at the Caribou Mine, but production is negligible.

Comment (Geology): The Grand Island-Caribou district is underlain by igneous and metamorphic rocks of Precambrian age and intrusive rocks of Tertiary(?) (Laramide) age. The dominant structure at Caribou is a NNE-trending anticline that controlled emplacement of the Caribou stock. Veins trending NE and east-west form an interconnecting system that contains the silver-lead ore deposits at Caribou; gold-bearing veins trending NW lie to the east. Three ore deposit types are lead-silver veins, pyritic gold veins, and titaniferous magnetite bodies in the Caribou stock.

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References

Reference (Commodity): Harrer, C.M., and Tesch, W.J., Jr., 1959, Reconnaissance of iron occurrences in Colorado, U.S. Bureau of Mines Information circular 7918, 82 p.

Reference (Deposit): Smith, D. A., 2003, Silver saga, the story of Caribou, Colorado (rev. ed.): Boulder, University Press of Colorado, 230 p.

Reference (Deposit): Sunshine Mining Co. Colorado exploration files, unpublished data, Colorado Geological Survey.

Reference (Deposit): MINE MAP REPO # 409114

Reference (Deposit): Vanderwilt, J.W., 1947, Mineral resources of Colorado: State of Colorado Mineral Resources Board, 547 p.

Reference (Names): Dunn, L.G, 2003, Colorado mining districts: A reference: Golden, Colo., Colorado School of Mines Library, 364 p.

Reference (Reserve-Resource): Calais Resources corporate info., accessed from internet on 12/20/2005.

Reference (Commodity): Moore, F. B., Cavender, W. S., and Kaiser, E. P., 1957, Geology and uranium deposits of the Caribou area, Boulder County, Colorado: U.S. Geological Survey Bulletin 1030-N, pp. 517-552.

Reference (Geology): Lovering, T. S., and Goddard, E. N., 1950, Geology and Ore Deposits of the Front Range, Colorado: U.S. Geological Survey Professional Paper 223, 319 p.

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