Duke Island

Prospect in Alaska, United States with commodities Chromium, Iron, Copper, Nickel, PGE

Geologic information

Identification information

Deposit ID 10308989
MRDS ID A012398
Record type Site
Current site name Duke Island
Related records 10094044

Geographic coordinates

Geographic coordinates: -131.31574, 54.92274 (WGS84)
Relative position This site represents the locations of all prospects and occurrences of magnetite- and chromite-bearing ultramafic rocks on Duke and adjacent islands for which there either are U.S. Bureau of Mines (1974) claim records, or other published descriptions (Irvine, 1959; Taylor and Noble, 1960; Clark and Greenwood, 1972; Elliott and others, 1978, locations 159-174; Cobb and Elliott, 1980, p. 137). The coordinates are for the approximate center of the estimated 48-square-mile outcrop area of the ultramafic complex and are accurate within about 0.25 mile. (The 16 prospects and occurrences represented by this site are in both the Prince Rupert D-4 and D-5 quadrangles; the coordinates of the center of the site are in the D-4 quadrangle.) Also see Additional Comments field.
(click for info)

Geographic areas

Country State
United States Alaska

Commodities

Commodity Importance
Chromium Primary
Iron Primary
Copper Secondary
Nickel Secondary
PGE Secondary

Materials information

Materials Type of material
Chalcopyrite Ore
Chromite Ore
Magnetite Ore
Pentlandite Ore
Pyrite Ore
Pyrrhotite Ore

Mineral occurrence model information

Model code 23
USGS model code 9
Deposit model name Alaskan Cr-Pt (PGE)
Mark3 model number 120

Nearby scientific data

(1) -131.31574, 54.92274

Comments on the geologic information

  • 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.
  • Age = Cretaceous

Economic information

Economic information about the deposit and operations

Development status Prospect
Commodity type Metallic

Comments on exploration

  • Status = Probably inactive

Mining district

District name Ketchikan

Comments on the workings information

  • 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.

Reference information

Links to other databases

Agency Database name Acronym Record ID Notes
USGS Alaska Resource Data File ARDF PR001
USGS Mineral Resources Data System MRDS A012398
USGS Mineral Resources Data System MRDS A012399
USGS Mineral Resources Data System MRDS A012400
USGS Mineral Resources Data System MRDS A012401
USGS Mineral Resources Data System MRDS A012402
USGS Mineral Resources Data System MRDS A012403
USGS Mineral Resources Data System MRDS A012404
USGS Mineral Resources Data System MRDS A012405
USGS Mineral Resources Data System MRDS A012406
USGS Mineral Resources Data System MRDS A012407
USGS Mineral Resources Data System MRDS A012408
USGS Mineral Resources Data System MRDS A012409
USGS Mineral Resources Data System MRDS A012410
USGS Mineral Resources Data System MRDS A012411
USGS Mineral Resources Data System MRDS A012412
USGS Mineral Resources Data System MRDS A012413

Bibliographic references

  • 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.

  • 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.

  • Deposit

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

  • 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.

  • 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.

  • 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.

Comments on the references

  • Primary Reference = Irvine, 1959; Cobb and Elliott, 1980

General comments

Subject category Comment text
Deposit Model Name = Alaska PGE (Cox and Singer, 1986; model 9)
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.

Reporter information

Type Date Name Affiliation Comment
Reporter 02-FEB-1999 H.C. Berg U.S. Geological Survey