Last Chance; Caribou Mine, Kantishna District, Denali Borough, Alaska, USA
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Location: The Last Chance (sometimes called Caribou) mine is about at the center of the N1/2 NE1/4 of section 22, T. 15 S., R. 17 W., Fairbanks Meridian. The location is accurate within 300 feet. The mine is location 24 of Cobb (1972 [MF 366]), 21 of MacKevett and Holloway (1977), L of Hawley and Associates (1978), 63b of Bundtzen (1981), and 61 of Thornsberry, McKee, and Salisbury (1984).
Geology: The country rock at the Last Chance mine is strongly-deformed, biotite- amphibolite schist of the upper Precambrian Birch Creek Schist ( Bundtzen, 1981; Thornsberry, McKee, and Salisbury, 1984, fig. K-2). The deposit consists of a fault-controlled, mineralized quartz vein that strikes about N 30 E and dips 50-70 NW. The strike of the vein is approximately parallel to the strike of the schist hostrock, but the vein dips NW and the schist dips SE. The vein is 2 to 6 feet thick. Stibnite is the main ore mineral; it occurs in massive form and in elongate crystals mixed with nearly euhedral quartz crystals (Prindle, 1907; Capps, 1919; Bundtzen, Smith, and Tosdal, 1976). Parts of the vein are composed of nearly massive quartz. The stibnite is accompanied by small amounts of pyrite, pyrrhotite, jamesonite, and probably sphalerite. Some of the stibnite is oxidized to stibiconite. The maximum antimony content in samples of the vein is about 26 percent, but the coarse, massive stibnite probably contains more than 50 percent antimony. More than 70 tons of the high-grade stibnite ore has been mined (Cobb, 1980 [OFR 80-363]; Bundtzen, Smith, and Tosdal, 1976). The stibnite ore is weakly auriferous. Prindle (1907) reported that samples assayed as much as 0.12 ounce of gold and 4 ounces of silver per ton, and Hawley and Associates (1978) reported assays of as much as 0.14 ounce of gold per ton. Free gold has been reported; it probably occurs in quartz-rich parts of the vein, inasmuch as high-grade antimony ores generally contain little gold. Thornsberry, McKee, and Salisbury (1984, location 61, v. 2) reported about 100 ppm molybdenum in several samples and as much as 600 ppm zinc. The molybdenum mineral is unknown; the zinc probably is in small amounts of sphalerite.
Workings: The deposit was discovered in 1905 (Prindle, 1907; Brooks, 1916), and developed by open cuts, shallow shafts, and short adits. The shafts were flooded when the prospect was visited by Capps in 1916 (Capps, 1919). The mine operated on a small scale in 1968-1970, 1973-74, and 1984.
Age: The deposit is assumed to be Eocene (see record MM091).
Alteration: Local oxidation of stibnite.
Production: Twelve 12 tons of high-grade stibnite ore reportedly was mined in about 1905. The ore was not shipped, because high antimony prices during the Russo-Japanese War fell abruptly at the end of the hostilities (Wells, 1933, p. 353-354). Buntzen, Smith, and Tosdal (1976) reported a total of 74,360 pounds of antimony recovered from 71.5 tons of ore before 1974. Thornsberry, McKee, and Salisbury (1984) reported a total production of about 70 tons of ore. There were 15 to 30 tons of ore stockpiled at the site in 1983.
Commodities (Major) - Sb; (Minor) - Ag, Au, Mo, Pb, Zn
Development Status: Yes; small
Deposit Model: Simple stibnite deposit (Cox and Singer, 1986; model 27d).
8 entries listed. 7 valid minerals.
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Brooks, A.H., 1916, Antimony deposits of Alaska: U.S. Geological Survey Bulletin 649, 67 p. Bundtzen, T.K., 1981, Geology and mineral deposits of the Kantishna Hills, Mt. McKinley quadrangle, Alaska: M. S. Thesis, University of Alaska, College, Alaska, 238 p. Bundtzen, T.K., Smith, T.E., and Tosdal, R.M., 1976, Progress report--Geology and mineral deposits of the Kantishna Hills: Alaska Division of Geological and Geophysical Surveys Open-File Report AOF-98, 80 p., 2 sheets, scale 1:63,360. Capps, S. R., 1919, The Kantishna region, Alaska: U. S. Geological Survey Bulletin 687, 116 p. Cobb, E. H., 1972, Metallic mineral resources map of the Mount McKinley quadrangle, Alaska: U. S. Geological Survey Miscellaneous Field Studies Map MF-366, 1 sheet, scale 1:250,000. Cobb, E.H., 1980, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Mount McKinley quadrangle, Alaska: U. S. Geological Survey Open-File Report 80-363, 150 p. Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, 379 p. Hawley, C. C. and Associates, Inc, 1978, Mineral appraisal of lands adjacent to Mt. McKinley National Park, Alaska: U. S. Bureau of Mines Open-File Report 24-78, 275 p. (paged by sections). 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. Prindle, L.M., 1907, The Bonnifield and Kantishna regions, Alaska: U.S. Geological Survey Bulletin 314-L, p. 205-226. Thornsberry, V. V., McKee, C. J., and Salisbury, W. G., eds, 1984, 1983 Mineral Resource Studies: Kantishna Hills and Dunkle Mine Areas, Denali National Park and Preserve, Alaska: U. S. Bureau of Mines Open-File Report 129-84. 3 Volumes: v. 1, Text; v. 2, Appendices; v. 3, Maps. Prepared by Salisbury & Dietz, Inc., Spokane, WA. Wells, F. G., 1933, Lode deposits of Eureka and vicinity, Kantishna district, Alaska: U. S. Geological Survey Bulletin 849-F, p. 335-379.