Latitude & Longitude (WGS84):
58° 53' 24'' North , 161° 46' 47'' West
Latitude & Longitude (decimal):
Mindat Locality ID:
198423
Long-form identifier:
mindat:1:2:198423:4
Location: This location is the modern beach extending from the mouth of the Salmon River north 9 miles to the Hageimeister Island quadrangle boundary. The map site is at Flat Cape, about 2 miles north of the mouth of Salmon River. It is location 4 of Cobb (1972 [MF 362]; 1980 [OF 80-909]).
Geology: This location is the modern beach extending from the mouth of the Salmon River north 9 miles to the Hagemeister Island quadrangle boundary. The modern beach is a 75- to 140-m-wide sandy gravel veneer over older unconsolidated deposits. From north to south, the landward margin of the beach is against 4 miles of bluffs to 8 m high of poorly sorted, stratified, pebble and cobble gravel with some thin discontinuous sand lenses; 1.5 miles of talus and bedrock of the Red Mountain ultramafic pluton; and 3.5 miles of bluffs to 16 m high of unconsolidated pebble gravel, clay- and silt-rich deposits with some iron-cemented gravel, and local sand- and peat-bearing sections (Mertie, 1940). Black sand streaks and lenses are present locally along the beach. These were tested by panning early in the exploration of the area but only traces of platinum were found (Mertie, 1940, p. 36). Systematic sampling and evaluation of the beach sands was later accomplished by Berryhill (1963), Bond (1982), Ulrich (1984), and Fechner (1988). Berryhill (1963) collected auger or shovel samples at 16 locations and Fechner (1988) collected mini-sluice or hydraulic concentrator heavy mineral concentrates at 20 locations. Berryhill (1963) showed that chromite was a major constituent of the heavy mineral concentrates, but that both gold and platinum were commonly present only in trace amounts. One sample collected about 2 miles north of the mouth of Salmon River contained 0.0736 ounce of gold and 0.0573 ounce of platinum per cubic yard. A composite sample of black sands from beaches throughout the Kuskokwim Bay-Chagun Bay area contained 33.8 percent acid-soluble iron, 12.1 percent Cr2O3, and less than 0.02 ounce of Au, Pt, and Ag per ton (Berryhill, 1963, p. 13). Analytical data reported by Fechner (1988) showed that the beach sands commonly contained detectable Pt and Au. The highest values, 0.26 ounce of PGM per cubic yard and 0.1029 ounce of Au per cubic yard, were from the Flat Cape area between the mouth of Salmon River and Red Mountain. Microprobe analyses of the PGM grains showed that they comprise 0.5 to 4.5 percent Rh, 0.2 to 1 percent Ru, 32 to 89.1 percent Pt, 1.6 to 47.8 percent Ir, 0.8 to 15.9 percent Os, and 3.2 to 8.9 percent Fe; the gold fineness ranged from 548 to 863 (Fechner, 1988, p. 24). Fechner (1988) also collected samples of older unconsolidated materials in the bluffs along the beach and showed that small amounts of Pt and Au are present in these deposits both north and south of Red Mountain. Hessin and others (1978 [OF 78-9-J; OF 78-9-K; OF 78-9-L; OF 78-9-P]) and Coonrad and others (1978) showed that samples of bottom sediments collected offshore of the present beach contained anomalous concentrations of Cr, Co, Ni, Hg, Au, and Pt in several places. Mertie (1940) noted that the lack of higher Pt concentrations in beach sands nearer the Red Mountain ultramafic outcrops could indicate that the lode sources were not uniformly distributed in this pluton and/or that the beach erosion along this part of the pluton is very recent. Fechner (1988) and Ulrich (1984) concluded that the better Pt concentrations in the modern beach sands reflected the presence of higher Pt concentrations in the unconsolidated deposits of the nearby bluffs, particularly in the Flat Cape area. In this area, Fechner (1988) estimated that there are 39,000 cubic yards of material that average 0.0073 ounce of Pt per cubic yard and 0.0033 ounce of Au per cubic yard.
Workings: All work on the modern beach has been spot sampling for heavy mineral concentrates by auger, portable sluice, hydraulic concentrator, hand shovel and panning. This type of work has been repeated several times by early prospectors, and by Mertie (1940), Berryhill, (1963); Bond (1982), Ulrich (1984), and Fechner (1988).
Age: Holocene.
Reserves: Fechner (1988) estimated that there are 39,000 cubic yards of material that average 0.0073 ounce of Pt per cubic yard and 0.0033 ounce of Au per cubic yard in the Flat Cape area.
Commodities (Major) - Cr; (Minor) - Au, Pt
Development Status: No
Deposit Model: Placer PGE-Au; modern beach (Cox and singer, 1986; model 39b)
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This is a list of exploitable or exploited mineral commodities recorded at this locality.Mineral List
3 valid minerals.
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List of minerals arranged by Strunz 10th Edition classification
List of minerals for each chemical element
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References
Berryhill, R.V., 1963, Reconnaissance of beach sands, Bristol Bay, Alaska: U.S. Bureau of Mines Report of Investigations 6214, 48 p. Bond, S.C., 1982, Origin and distribution of platinum-enriched heavy mineral accumulations in a beach placer near Platinum, Alaska: Austin, University of Texas, M.A. thesis, 63 p. Cobb, E.H., 1972, Metallic mineral resources map of the Hagemeister Island quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-362, 1 sheet, scale 1:250,000. Cobb, E.H., 1980, Summaries of data and lists of references to metallic and selected nonmetallic mineral deposits in fifteen quadrangles in southwestern and west-central Alaska: U.S. Geological Survey Open-File Report 80-909, 103 p. Coonrad, W.L., Hoare, J.M., Clark, A.L., Grybeck, Donald, and Barnes, P.W., 1978, Geochemical distribution and abundance of platimun and gold in the vicinity of Platinum, Goodnews, and Hagemeister Island quadrangles region, southwestern Alaska: U.S. Geological Survey Open-File Report 78-9-S, 1 sheet, scale 1:250,000. Fechner, S.A., 1988, Bureau of Mines mineral investigation of the Goodnews Bay mining district, Alaska: U.S. Bureau of Mines Open-File Report 1-88, 230 p., 3 sheets. Hessin, T.D., Taufen, P.M., Seward, J.C., Quintana, S.J., Clark, A.L., Grybeck, Donald, Hoare, J.M., and Coonrad, W.L., 1978, Geochemical and generalized geological map showing distribution and abundance of chromium in the Goodnews and Hagemeister quadrangles region, southwestern Alaska: U.S. Geological Survey Open-File Report 78-9-J, 2 sheets, scale 1:250,000. Hessin, T.D., Taufen, P.M., Seward, J.C., Quintana, S.J., Clark, A.L., Grybeck, Donald, Hoare, J.M., and Coonrad, W.L., 1978, Geochemical and generalized geological map showing distribution and abundance of cobalt in the Goodnews and Hagemeister quadrangles region, southwestern Alaska: U.S. Geological Survey Open-File Report 78-9-K, 2 sheets, scale 1:250,000. Hessin, T.D., Taufen, P.M., Seward, J.C., 
