Duke Island

Site Name

Primary: Duke Island

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Commodity

Primary: Chromium
Primary: Iron
Secondary: PGE
Secondary: Copper
Secondary: Nickel

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Location

State: Alaska
District: Ketchikan

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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: Alaskan Cr-Pt (PGE)

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Orebody

Not available

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Structure

Not available

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Alterations

Not available

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Rocks

Not available

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Analytical Data

Not available

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Materials

Ore: Chalcopyrite
Ore: Chromite
Ore: Magnetite
Ore: Pentlandite
Ore: Pyrite
Ore: Pyrrhotite

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Comments

Comment (Deposit): Model Name = Alaska PGE (Cox and Singer, 1986; model 9)

Comment (Geology): Age = Cretaceous

Comment (Exploration): Status = Probably inactive

Comment (Reference): Primary Reference = Irvine, 1959; Cobb and Elliott, 1980

Comment (Deposit): Other Comments = The following names, most probably names of claims, (Elliott and others, 1978) have been used for some of the prospects on Duke and adjacent islands (location numbers are from Elliott and others, 1978): Dud, loc. 163; Sec 14, T. 80 S., R. 93 E., of the Copper River Meridian; Peter?, loc. 164; Sec 13, T. 80 S., R. 93 E., of the Copper River Meridian; Red, loc. 165; Sec 13, T. 80 S., R. 93 E., of the Copper River Meridian; Ditto?, loc. 166; Sec 14, T. 80 S., R. 93 E., of the Copper River Meridian; Cave, loc. 167; Sec 23, T. 80 S., R. 93 E., of the Copper River Meridian; Camp, loc. 169; Sec 27, T. 80 S., R. 93 E., of the Copper River Meridian; Richard, loc. 171; Sec 31, T. 80 S., R. 94 E., of the Copper River Meridian; Creek?, loc. 173; Sec 7, T. 80 S., R. 95 E., of the Copper River Meridian; and Ted, loc. 174; Sec 3, T. 81 S., R. 95 E., of the Copper River Meridian.

Comment (Geology): Geologic Description = Duke Island and adjacent islands (Irvine, 1959; Taylor and Noble, 1960, p. 178-180; Berg and others, 1988) are underlain by metamorphosed undivided Silurian or Ordovician intermediate and mafic intrusive rocks; by Triassic gabbro, which intrudes the metamorphic rocks; and by a Cretaceous ultramafic complex, which intrudes the gabbro. The ultramafic complex is roughly concentrically zoned outward from a core of dunite and peridotite, succeeded by shells of olivine pyroxenite and hornblende pyroxenite. The complex is distinguished by locally conspicuous graded layering and other cumulate features, especially in the dunite, peridotite, and olivine pyroxenite. Metalliferous minerals include chromite, which occurs in the dunite and peridotite as individual crystals and as small veins and clots; titaniferous magnetite, which locally accompanies pyroxene in graded layers in the hornblende pyroxenite; and rare specks of pyrrhotite, pyrite, pentlandite, and chalcopyrite (Irvine, 1959; Cobb and Elliott, 1980, p. 137). Analyses of 22 samples (Clark and Greenwood, 1972, p. 159) showed averages of 0.037 ppm Pt (10 samples), 0.033 ppm Pd (16 samples), and 0.010 ppm Rh (6 samples). The acid-soluble iron content of 261 samples of pyroxenite (Berg and others, 1978, p. 25) ranged from 8 to 18% and averaged about 12%. Several of the prospects have been drilled by private interests, but no data on potential iron resources have been made public. The site includes the 16 claims and prospects scattered over the ultramafic complex that have been described in the literature (and are located individually in the 'Additional comments' field). However, chromite, magnetite, and disseminated sulfides are pervasively distributed throughout the complex, rather than only at a few specific locations.

Comment (Workings): Workings / Exploration = Analyses of 22 samples (Clark and Greenwood, 1972, p. 159) showed averages of 0.037 ppm Pt (10 samples), 0.033 ppm Pd (16 samples), and 0.010 ppm Rh (6 samples). The acid-soluble iron content of 261 samples of pyroxenite (Berg and others, 1978, p. 25) ranged from 8% to 18% and averaged about 12%. Several of the prospects have been drilled by private interests, but no data on potential iron resources have been made public.

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References

Reference (Deposit): Berg, H.C., Elliott, R.L., and Koch, R.D., 1978, Map and tables describing areas of metalliferous mineral resource potential in the Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-73-M, 52 p., 1 sheet, scale 1:250,000.

Reference (Deposit): Cobb, E.H., and Elliott, R.L., 1980, Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in the Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-File Report 80-1053, 154 p.

Reference (Deposit): Irvine, T.N., 1959, The ultramafic complex and related rocks of Duke Island, southeastern Alaska: Pasadena, California Institute of Technology, Ph.D. dissertation, 320 p.

Reference (Deposit): U.S. Bureau of Mines, 1974, Claim map, Prince Rupert quadrangle: U.S. Bureau of Mines Map 122, scale 1:250,000.

Reference (Deposit): Elliott, R.L., Berg, H.C., and Karl, Susan, 1978, map and table describing metalliferous and selected nonmetalliferous mineral deposits, Ketchikan and Prince Rupert quadrangles, Alaska: U.S. Geological Survey Open-file Report, 78-73-B,17 p., scale 1:250,000.

Reference (Deposit): Clark, A.L., and Greenwood, W.R., 1972, Geochemistry and distribution of platinum-group metals in mafic to ultramafic complexes of southern and southeastern Alaska: U.S. Geological Survey Professional Paper 800-C, p. C157-C160.

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