Unnamed Mines (ARDF - MF042; Gulf of Alaska coast: Includes Topsy Creek; Dagelet River; and Oregon King Consolidated claims), Yakutat District, Skagway-Hoonah-Angoon Borough, Alaska, USA
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Location: The deposit is a beach placer that extends southeasterly for about 13.5 miles, from 2.5 miles southeast of Harbor Point, at the south side of the mouth of Lituya Bay, to the northwest foot of LaPerouse Glacier. The approximate coordinates of the northwest limit are 58.60 and 137. 59. The southeast limit in the Mt. Fairweather B-4 quadrangle is approximately at 58.48 and 137.31. The coordinates for this site are for the approximate mid-point of the placer which is 2.25 miles southeast of the mouth of Topsy Creek, reported to be its most productive area. The site includes location numbers 66 and 67 of Cobb (1972, MF-436). Location 67 was reported as the Oregon King Consolidated placer by MacKevett and others (1971, p. 67-68); it is the part of the placer immediately northwest of LaPerouse Glacier.
Geology: A nearly continuous beach placer is exposed for about 13.5 miles northward from LaPerouse Glacier to the headland south of Harbor Point. Associated fossil beach placers occur on an approximate an 1/2-mile wide plain northeast of the beach placers. The modern beaches were produced by winnowing of deposits brought down by LaPerouse Glacier and the Crillon River. The glacier and river tap the Crillon-LaPerouse and related layered mafic complexes, which are the ultimate source of much of the titanium, iron, and PGEs contained in the placer deposits. Some gold may have been brought down from the hydrothermally altered zones at the head of Topsy Creek reported by Rossman (1959); these zones appear to be the continuation of the auriferous hydrothermal areas in Fall Creek in Lituya Bay (MF043). Economic deposits of gold are thin, lenticular transient deposits related to storm concentration of the heavy sands. Deposits of ilmenite, magnetite, and small amounts of rutile and zircon occur in substantially thicker deposits, which have been sampled in several studies conducted by the Bureau of Mines and by Rossman (1957) of the Geological Survey. (Related deposits are described in MF040 and MF041.) Kimball and others (1978, p. C72-73) reported a maximum of 1.9 percent ilmenite and a trace of gold in samples contained on line 15. This location is at the mouth of Topsy Creek. At line 16, which corresponds closely to the mid-point coordinates of the placer deposit, as much as 15.2 percent ilmenite was found in a tube sample, and 30.3 percent ilmenite in a grab sample. Maximum gold content at line 16 in a tube sample was 0.0009 ounce per cubic yard. At the Bureau's line 17 near the mouth of the Dagelet River (p. C74-75) as much as 3 percent ilmenite was found in a channel sample and as much as 11.5 percent in a tube sample. Gold was found in a grab sample (0.0043 ounce of gold per cubic yard). Trace amounts of gold and as much as 1.7 percent ilmenite were found in line 18, one mile northwest of LaPerouse Glacier.
Workings: Surface workings: Sluice box, rockers, long toms on mostly transient deposits. Workings date back to at least 1894 (Mertie, 1933). Probably, small-scale activity continued every year until World War II, as documented in Annual resource reports by Brooks, Smith, Mertie, and a few others. Government investigations include those by Rossman in 1952 (Rossman, 1957), Thomas and Berryhill (1962), Kimball and others (1978), and Foley and others (1995). Thomas and Berryhill (1962) found relatively good values of titania in the beaches south of Lituya; one sample (no. 123) collected below a northern outlier of LaPerouse Glacier contained 89.5 pounds/cubic yard of titania. The most extensive and detailed investigations were conducted from 1975 to 1977 by the U.S. Bureau of Mines (Kimball and others, 1978). In those investigations, sample lines were run about 3 and 3.5 miles south of Harbor Point (lines 13 & 14), at Topsy Creek (line 15), two miles south of Topsy Creek (line 16), about 1/2 mile north of the Dagelet River (line 17), and about one mile north of LaPerouse Glacier (line 18). In the Harbor Point north line (13), as much as 2.8 pounds/cubic yard of ilmenite was recovered in auger or PVC tube from fine to medium sand. Maximum gold was reported as 0.0003 ounce/cubic yard. Ilmenite and gold were much more abundant two miles south of Topsy (line 16). Gold was present there in four tube samples and was reported as 0.0024 ounce/cubic yard in a select grab sample. Ilmenite content was more than 2 pounds/cubic yard in 8 of 10 tube samples and was a maximum of 15.2 percent (495 pounds/cubic yard). The gold-bearing grab sample contained 30.3 percent ilmenite. Ilmenite is also relatively abundant near Dagelet River, with a maximum of 11.5 percent in one tube sample. Gold content there was 0.0043 ounce/cubic yard in a grab sample. Ilmenite content was as much as 1.7 percent in line 18 north of LaPerouse Glacier . Foley and others (1995) collected 7 samples along the placer, beginning with sample no. 303 near line 14 and continuing through numbers 305-310. Sample 303 had 0.056 gram/tonne gold in the head split. Sample 307 contained 4.37 percent ilmenite in the head split and 10.48 percent ilmenite in the spiral concentrate. Gold was present in several of the samples.
Production: Gold production is probably in the thousand-ounce range. Minor amounts of platinum have been recovered.
Reserves: The Bureau of Mines (Kimball and others, 1978) calculated about one million cubic yards of material based on the sampled lines representative of this placer. Block 7 (line 16) has a calculated resource of about 664,000 cubic yards of material containing 4 percent ilmenite and 0.0002 oz/yd gold.
Commodities (Major) - Au, Fe, Ti; (Minor) - Cr?, PGE, Zr
Development Status: Yes; small
Deposit Model: Placer: Modern beach, active beach, back beach; marine terrace and possibly flu
6 entries listed. 5 valid minerals.
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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. Cobb, E.H., 1972, Metallic mineral resources map of the Mount Fairweather quadrangle, AK: U.S. Geological Survey Miscellaneous Field Study Map MF-436, 1 sheet, scale 1:250,000. Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Mt. Fairweather and Skagway quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-316, 123 p. Cook, D.J., 1969, Lituya Bay, in Heavy minerals in Alaskan beach sand deposits: University of Alaska, Mineral Industry Research Laboratory Report 20, p. 47-57. Foley, J.Y., La Berge, R.D., Grosz, A.E., Oliver, F.S., and Hirt, W.C., 1995, Onshore titanium and related heavy-mineral investigations in the eastern Gulf of Alaska region, southern Alaska: U.S. Bureau of Mines Open-File Report 10-95, 125 p. Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources, in Brew, D. A., and others, Mineral resources of the Glacier Bay National Monument wilderness study area, Alaska: U.S. Geological Survey Open-File Report 78-494, p. C1-C375. MacKevett, E.M., Jr., Brew, D.A., Hawley, C.C., Huff, L.C., and Smith, J.G., 1971, Mineral resources of Glacier Bay National Monument, Alaska: U.S. Geological Survey Professional Paper 632, 90 p., 12 plates, scale 1:250,000. Mertie, J.B., Jr., 1933, Notes on the geography and geology of Lituya Bay: U.S. Geological Survey Bulletin 836-B, p. 117-135 Rossman, Darwin, 1957, Ilmenite-bearing beach sands near Lituya Bay, Alaska: U.S. Geological Survey Open-File Report 149, 10 p. Rossman, Darwin, 1959, Geology and ore deposits in the Reid Inlet area, Glacier Bay, Alaska: U.S. Geological Survey Bulletin 1058-B, p. 33-58. Rossman, Darwin, 1963, Geology and petrology of two stocks of layered gabbro in the Fairweather Range, Alaska: U.S. Geological Survey Bulletin 1121-F, p. F1-F50. Thomas, B.I., and Berryhill, R. V., 1962, Reconnaissance studies of Alaskan beach sands, eastern Gulf of Alaska: U.S. Bureau of Mines Report of Investigations 5986, 40 p.