Unnamed (Gulf of Alaska beaches, Yakutat quadrangle segment)

Mine, Undetermined

Commodities and mineralogy

Main commodities Au; Fe; PGE; Ti
Other commodities Cr; Fe; Garnet; REE; W; Zr
Ore minerals ilmenite; magnetite; monazite; native gold; pge; rutile; scheelite; zircon
Gangue minerals apatite; garnet; hornblende; olivine; pyroxene; sphene

Geographic location

Quadrangle map, 1:250,000-scale YA
Quadrangle map, 1:63,360-scale B-5
Latitude 59.45
Longitude -139.62
Nearby scientific data Find additional scientific data near this location
Location and accuracy This site is the segment of the Gulf of Alaska beach placer system that exists on the Yakutat quadrangle. The coordinates are the approximate center of the beach in the quadrangle. The beach extends from 141. 0 longitude and 59.753 latitude at the west edge of the quadrangle to 138.16 longitude and 59.0 latitude where the Yakatut quadrangle abuts the Mt. Fairweather quadrangle. West of Yakutat, the beach placer is interrupted by Yakutat Bay, about 18 miles wide at its mouth. Beach placers occur within Yakutat Bay on the west side of Khantaak Island (YA003) and on the west facing Logan Beach (YA004) near the head of Yakutat Bay. The Yakutat segment includes the Akwe (YA006), Situk (YA007), Blacksand (YA008), also Blacksand Island (YA009) beach placers, all of which have been described separately here and by Cobb (1972). Data on the Logan, Khantaak, Yakutat, Blacksand, Blacksand Island, and Akwe beach placers are also summarized by MacKevett and Holloway (1977, p. 84; also map 77-169A).

Geologic setting

Geologic description

The Yakutat beaches in general are well sorted sandy to gravelly sand to sandy boulder beaches with abrupt back beaches bounded by wave-cut cliffs. Economic beach placer deposits of the system are formed in a high- energy beach environment changing significantly on a seasonal, or occasionally, on a daily basis (Foley and others, 1995).
There are several sources for the heavy minerals contained in the placer deposits. The westernmost beaches of the system are cut in glacial moraine and outwash brought down by Malaspina Glacier. Placer sources are also in the streams arising from the glacier, examples named west to east: Fountain, Alder, Manby, Kame, and Grand Wash. These streams bring down tremendous quantities of alluvium which is then density-separated by beach and long shore currents. Tertiary rocks of the Malaspina area are also a secondary source of heavy-minerals incorporated in the placer deposits (Plafker and Miller, 1957, 1958). The placers on the east side of Yakutat Bay, the Logan Beach and Khantaak, and the deposits further east, such as the major Yakutat beach, are developed on unconsolidated deposits of Holocene age. These sediments, in turn, derived some of their heavy minerals from poorly consolidated rocks of Tertiary age (Reimnitz and Plafker, 1976; Tarr, 1909; Miller, 1961; and Wright, 1969 and 1972) .
The ultimate sources of most of the placer minerals are the crystalline and intrusive rocks that lie northeast of the Gulf of Alaska Tertiary province (Hudson, Plafker, and Lanphere, 1977; Hudson, Plafker, and Turner, 1977), and this material is distributed and locally concentrated by alluvial and marine processes. In the southeast part of the system, the Alsek River could intersect mafic-ultramafic source materials that would furnish Ti, Fe, Cr, and PGE to the system.
Production from the beaches has been small, but has occurred over a long interval of time, dating back to before 1890 (Spencer and Schrader, 1901; Brooks, 1904; Blackwelder, 1907; Tarr, 1906; Tarr and Butler, 1909; Brooks, 1918; Brooks, 1923). Most of the production has come from small-scale placer operations operating on heavy-mineral concentrate layers less than a foot to several feet thick, but the beaches contain concentrations of up to several percent of 'valuable heavy minerals' defined as ilmenite + rutile + zircon, that constitute a medium- to large-scale resource (Thomas and Berryhill, 1962; Foley and others, 1995) which could be exploited on a larger scale. Locally, the deposits contain concentrations of monazite and scheelite, sources respectively of REEs and tungsten. PGEs are local trace components of some of the heavy-mineral placers (Foley and others, 1989).
Offshore concentrates almost certainly exist, as do onshore inland concentrations produced at varying seastands. Some indication of the extent of the fossil beaches preserved on the upland is given in the Yakutat and Akwe River drainage areas where MacKevett and Plafker (1970, p. 1) locally show the preserved upland beaches. Some of the placer deposits have magnetic signatures (Johnson and Plafker, 1969).
Some of the beach placer system, as at Yakutat, is on native-owned or U.S. Forest Service land where it might be exploited commercially.
Geologic map unit (-139.621684910051, 59.4496953086083)
Mineral deposit model High-energy beach sand deposits derived from steep upland terrane.
Age of mineralization Holocene

Production and reserves

Workings or exploration Workings have been mostly small scale using pans, rockers, and sluices. Some attempts have been made to process the resource on a larger scale but have not been successful. Exploration work, mostly by the U.S. Bureau of Mines, has been by hand and powered augers and hand-dug cuts and trenches. The studies by Thomas and Berryhill (1962) and Foley and others (1995) have concentrated on the industrial metals iron, titanium, and zirconium instead of the gold or PGEs sought by the small-scale miners. The Bureau demonstrated that significant placer resources exist; probably the most promising deposit is the Yakutat beach. Churn drill testing for heavy mineral concentrates, by private companies, with uncertain results, reportedly occurred in 1957 (Thomas and Berryhill, 1962; Foley and others, 1995, p. 23).
Indication of production Yes; small
Reserve estimates
Resources have been calculated (Foley and others, 1995) in the Yakutat area, based on an assumption of a placer deposit that is 300 m wide by 24 km long with a wedge shaped beach ranging from 0 to 11 m thick. This volume contains 36 million cubic meters of beach sand equivilent to 57 million metric tons of sand that contains an average of 3.4 percent valuable heavy minerals (ilmenite + rutile + zircon). The range in values found along the beach was from 0.2 to 14.8 percent valuable heavy minerals. The resource contains native gold and PGEs of uncertain amount (Foley and others, 1995).
A less-quantified resource from the Situk River southeasterly to Boussole Bay (the latter bay is in the Mt. Fairweather quadrangle) consists of about 192 million metric tons of sand containing about 3 percent valuable minerals. This segment is fed by glaciers and rivers whose source is in the mafic-ultramafic complex region of the Fairweather Range.
Production notes Production of 3700 ounces of gold is reported for the region from Yakutat Bay to Lituya Bay (Reimnitz and Plafker, 1976).

Additional comments

The titanium resource is relatively low grade and consists mostly of ilmenite rather than rutile. The placer deposits were formed by high-energy single pass systems rather than by complex transgressions and regressions that produced the rutile-based titanium placers characteristic of beach placers derived from the erosion of stable regions. Nevertheless, the resources are significant, and could be important if the high-titanium placer deposits are depleted. Clifton and Luepke (1987) have studied the Yakutat beach placers as part of their comprehensive study of the Pacific beach placers from Alaska to Baja California.
Other minerals and metals, such as gold and PGEs will add value, as could garnet, now not considered as a valuable mineral. Large-scale mining might also produce tungsten (scheelite), REEs (from monazite), and chromite. Some of the gold and PGEs and other valuable minerals are very fine-grained; Cook (1969) has studied flotation and ultrafine gravity techniques on the recovery of the fine-grained minerals.
The offshore potential is essentially unevaluated. Equipment used for operations offshore, as well as those on the modern beach, needs to be able to withstand, or move quickly from the paths, of major storms.
Some of the deposits, as those in Wrangell-St. Elias National Park, the Logan Beach in the Russell Fiord Wilderness area, and those southeast of Dry Bay in Glacier Bay National Park and Preserve are withdrawn from mineral entry. Placer deposits northwest of Dry Bay, extending westerly to past Yakatut, are in non-wilderness Tongass National Forest or on native-owned lands and might be developed.

References

MRDS Number 10308481

References

Clifton, H.E., and Luepke, G., 1987, Heavy-mineral placer deposits of the continental margin of Alaska and the Pacific Coast States, Chapter 30 in Scholl, D.W., Grantz, Arthur, and Vedder, J.G., eds., Geology and resource potential of the continental margin of western North America and adjacent ocean basins, Beaufort Sea to Baja California: Circum-Pacific Council for Energy and Mineral Resources, Earth Science Series, v. 6, p. 691-738.
Wright, F.F., 1969, Sedimentation and gold distribution, Yakutat Bay, Alaska: University of Alaska Marine Science Report R69-9, 23 p.
Reporters C. C. Hawley (Hawley Resource Group)
Last report date 2/4/1999