Case; Grant Lake Mine, Hope District, Kenai Peninsula Borough, Alaska, USA
There are abundant references to this mine in the literature, but most of them refer only to ongoing work and give no details.
Location: The mine is located in the NE1/4 section 29, T. 5 N., R. 1 E., of the Seward Meridian, on the north side of Grant Lake; the workings extend into the south half of section 20, T. 5 N., R 1 E., in the C-7 quadrangle. The workings are accessible from Moose Pass by the Grant Lake trail that begins either at the railroad bridge on the west shore of Upper Trail Lake or half a mile south of the railroad bridge on the west shore of Upper Trail Lake. (The public is not allowed to walk across to the trail (northern entrance) on the railroad bridge. The southern entrance to the trail is accessed by boat.) The mine camp is at an elevation of 700 feet. The mine workings are about half a mile north-northeast of the camp between elevations of 1,500 and 1,600 feet. This is location 36 of Cobb and Richter (1972), location 45 of MacKevett and Holloway (1977), location 66 of Cobb and Tysdal (1980), and location S-231 of Jansons and others (1984). Cobb and Tysdal (1980) summarized the relevant references under the name Case. This location is accurate to within 300 feet.
Geology: The deposit at this mine consists of quartz veins in interbedded slate and graywacke of the Valdez Group of Late Cretaceous age (Cobb and Tysdal, 1980). The veins occur in three orientations. One set generally parallels the north-northwest strike of the country rock and dips about 70 west. This set of veins contains pods and lenses within a shear zone that follows bedding. The hanging wall of the veins is slate, and the foot wall is graywacke. The veins range from 12 to 36 inches wide and average about 16 inches. The strike length varies, but in the adit at 1,540 feet elevation, this vein was more than 100 feet long. Ore minerals include arsenopyrite, chalcopyrite, galena, and pyrite; gold is also present. The second set of veins strikes roughly east-west and dips 80S. These veins range in width from less than a foot to more than 5 feet. A majority of the material mined came from these veins. They are hosted in graywacke and are truncated on both ends by left lateral faults (Hoekzema and Sherman, 1983). Samples collected by the U.S. Bureau of Mines in 1980 assayed as much as 1.11 ounces of gold per ton (Hoekzema and Sherman, 1983). The third set of veins strikes northwest and dips 65 NE. These veins appear to be discontinuous and barren (Hoekzema and Sherman, 1983).
Workings: The mine workings consist of three adits, at elevations of 1,500,1,540, and 1,600 feet. The 1,500-level adit is 12 feet long and follows a quartz vein that pinches out at the face. The 1,540-level adit is the main working. It is 170 feet long and has two 30- to 40-foot-long crosscuts that follow the east-west-trending veins. The western crosscut is stoped to the surface (Hoekzema and Sherman, 1983). The 1,600-foot adit is about 40 feet long and follows the northwest-trending vein (Hoekzema and Sherman, 1983). Samples collected by the U.S. Bureau of Mines in 1980, assayed as much as 1.11 ounces of gold per ton (Hoekzema and Sherman, 1983). Sampling by the U.S. Forest Service as part of a patent examination showed sporadic gold grade as much as 2.10 ounces per ton, interspersed with barren samples.
Age: Cretaceous or younger; the veins cut rocks of the Valdez Group of Late Cretaceous age.
Production: Production is estimated at 972 ounces of gold and 123 ounces of silver (Jansons and others, 1984).
Reserves: The proven reserves at this mine are reported to be 270 tons of ore having a grade of 0.78 ounce of gold per ton and 0.2 ounce of silver per ton (Hoekzema and Sherman, 1983). The U.S. Bureau of Mines suggested that this deposit has a moderate potential for development as a small mine. The mine was examined both by a private consulting geologist and by a government mineral examiner as part of the patent process. U.S. Government mineral examiners concluded in 1993 that mineralization exposed to that date would not support a small-scale mining operation. The private consulting geologist suggested that further work could define a down-dip extension of the known deposit.
Commodities (Major) - Ag, Au; (Minor) - Cu, Pb
Development Status: Yes; small
Deposit Model: Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
ReferencesBerg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p. Brooks, A.H., 1915, Mineral resources of Alaska; report on progress of investigations in 1914: U.S. Geological Survey Bulletin 622, 380 p. Brooks, A.H., 1918, Mineral resources of Alaska, 1916: U.S. Geological Survey Bulletin 662, 469 p. Brooks, A.H., and Capps, S.R., 1924, The Alaska mining industry in 1922: U.S. Geological Survey Bulletin 755-A, p. 1-56. Cobb, E.H., and Richter, D.H., 1972, Metallic mineral resources map of the Seward quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-466, 2 sheets, scale 1:250,000. Cobb, E.H., and Tysdal, R.G., 1980, Summaries of data on and list of references to metallic and selected nonmetallic mineral deposits in the Blying Sound and Seward quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-621, 276 p. Garrett, C.R., 1972, Grant Lake Development Co. report of mineral examination: U.S. Forest Service; held at the Chugach National Forest office, Anchorage, 19 p. Hoekzema, R.P., and Sherman, G.E., 1983, Mineral investigations in the Chugach National Forest, Alaska (Peninsula study area): U.S. Bureau of Mines in-house report; held at U.S. Bureau of Land Management Alaska State Office, Anchorage, 524 p. Jansons, Uldis, Hoekzema, R.B., Kurtak, J.M., and Fechner, S.A., 1984, Mineral occurrences in the Chugach National Forest, southcentral Alaska: U.S. Bureau of Mines Mineral Land Assessment 5-84, 218 p., 2 sheets, scale 1:250,000. Johnson, B.L., 1919, Mining on Prince William Sound: U.S. Geological Survey Bulletin 692-C. MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000. Smith, P.S., 1937, Mineral industry of Alaska in 1935: U.S. Geological Survey Bulletin 880-A, p. 1-95. Smith, P.S., 1938, Mineral industry of Alaska in 1936: U.S. Geological Survey Bulletin 897-A, p. 1-107. Smith, P.S., 1939, Mineral industry of Alaska in 1937: U.S. Geological Survey Bulletin 910-A, p. 1-113. Smith, S.S., 1917, The mining industry in the Territory of Alaska during the calendar year 1915: U.S. Bureau of Mines Bulletin 142, 65 p. Tuck, Ralph, 1933, The Moose Pass-Hope district, Kenai Peninsula, Alaska: U.S. Geological Survey Bulletin 849-I, p. 469-530. Tysdal, R.G., 1978, Mines, prospects, and occurrences map of the Seward and Blying Sound quadrangles, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-880-A, 2 sheets, scale 1:250,000.
6 entries listed. 6 valid minerals.
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