Duke Island Prospects, Duke Island, Ketchikan Mining District, Prince of Wales-Hyder Census Area, Alaska, USAi

Regional Level Types
Duke Island Prospects	Group of Prospects
Duke Island	Island
Ketchikan Mining District	Mining District
Prince of Wales-Hyder Census Area	Census Area
Alaska	State
USA	Country

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.
Location: 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.
Geology: 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.
Workings: 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.
Age: Cretaceous

Commodities (Major) - Cr, Fe; (Minor) - Cu, Ni, PGE
Development Status: None
Deposit Model: Alaska PGE (Cox and Singer, 1986; model 9)

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Link to USGS - Alaska:	PR001

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References