Explained by Warren J. Nokleberg, Richard J. Goldfarb, and Warren Yeend.
On the choice of deposit models
This tract, in the southern Yukon-Tanana Upland, is permissive for Late Cretaceous and early Tertiary Au-Sb vein deposits (Berger, 1993) because of favorable bedrock geologic units, known deposits, and stream-sediment geochemical anomalies (Sb, Pb, Au, As, Ag, Bi, W). The features of known deposits are typical of the gold-antimony deposit model of Berger (1993).
On the delineation of permissive tracts
The favorable geologic units for Au-Sb veins in this tract are the Devonian and Mississippian metasedimentary and lesser metavolcanic rocks of southern Yukon-Tanana terrane where metamorphosed to greenschist facies during major regional metamorphic event(s) ending in the mid-Cretaceous, and intruded by Upper Cretaceous and lower Tertiary granitic plutonic rocks of the Kluane arc. Two K-Ar ages suggest that granitic plutonism and associated Au-Sb vein mineralization occurred between 48.3 (Bundtzen, 1981) and 81 Ma. The metasedimentary rocks in the region were mainly quartz-rich shale and siltstone, quartz sandstone, minor limestone, and marl. The metavolcanic rocks in the region were mainly andesite, but ranged in composition from rhyolite to basalt.
The distribution of the geologic units defining the tract is adapted from Nokleberg and others (1994). The distribution of this belt of mineral deposits is adapted from MacKevett and others (1978) and Nokleberg and others (1987, 1993). This tract is the same area as for tract SC35 for plutonic porphyry Au deposits and tract SC-52 for porphyry Cu deposits. Mineral resource assessments of 250,000-scale quadrangles within the tract were done by Richter and others (1975), Singer and others (1977), Cox and others, 1989, and Nokleberg and others (1990).
Important examples of this type of deposit
Au-Sb veins occur at Kansas Creek in the Healy quadrangle (Cox and others, 1989), and at Slate Creek, Eagles Den, Caribou Creek, and Stampede in the Kantishna district in the McKinley quadrangle (Capps, 1919; White, 1942; Barker, 1963; Bundtzen, 1981, 1983a). Local gold placer deposits in the Kantishna district in the tract may be derived in part from veins of this deposit type (Capps, 1919; Cobb, 1973; Bundtzen, 1981).
On the numerical estimates made
The tract is a large area that is partly covered by extensive glacial loess and dense vegetation. The existence of Au-Sb veins in the Healy and McKinley quadrangles in the northwestern part of the tract suggests that at least two undiscovered deposits probably occur in this tract. The mineral resource team estimated the minimum number of undiscovered Au-Sb vein deposits, consistent with the grade and tonnage model of Berger (1993), to be:
Percentile 90 50 10 5 1
Estimated number of deposits 2 4 10 10 10
Barker, Fred, 1963, Exploration for antimony deposits at the Stampede mine, Kantishna district, Alaska: U.S. Geological Survey Bulletin 1155, p. 10-17.
Berger, V.I., 1993, Descriptive, and grade-tonnage model for gold-antimony deposits: U.S. Geological Survey Open-File Report 93-194, 24 p.
Bundtzen, T.K., 1981, Geology and mineral deposits of the Kantishna Hills, Mount McKinley quadrangle, Alaska: Fairbanks, Alaska, University of Alaska, M.S. thesis, 237 p, 4 sheets, scale 1:63,360.
Bundtzen, T.K., 1983a, Mineral resource modeling Kantishna-Dunkle Mine Study, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 83-12, 51 p.
Capps, S.R., 1919, The Kantishna region, Alaska: U.S. Geological Survey Bulletin 687, 118 p.
Cobb, E.H., 1973, Placer deposits of Alaska: U.S. Geological Survey Bulletin 1324, 213 p.
Cox, D.P., Light, T.D., Csejtey, Béla, and Campbell, D.L., 1989, Mineral resource assessment map of the Healy quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2058-A, scale 1:250,000.
MacKevett, E.M., Jr., Singer, D.A., and Holloway, C.D., 1978, Maps and tables describing metalliferous mineral resource potential of southern Alaska: U.S. Geological Survey Open-File Report 78-1E, 2 sheets, scale 1:1,000,000, 45 p.
Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, Donald, Robinson, M.S., Smith, T.E., and Yeend, Warren, 1987. Significant metalliferous lode deposits and placer districts of Alaska: U.S. Geological Survey Bulletin 1786, 104 p.
Nokleberg, W.J., Bundtzen, T.K., Grybeck, Donald, Koch, R.D., Eremin, R.A., Rozenblum, I.S., Sidorov, A.A., Byalobzhesky, S.G., Sosunov, G.M., Shpikerman, V.I., and Gorodinsky, M.E., 1993, Metallogenesis of mainland Alaska and the Russian Northeast: Mineral deposit maps, models, and tables, metallogenic belt maps and interpretation, and references cited: U.S. Geological Survey Open-File Report 93-339, 222 pages, 1 map, scale 1:4,000,000; 5 maps, scale 1:10,000,000.
Nokleberg, W.J., Lange, I.M., Singer, D.A., Curtin, G.C., Tripp, R.B., Campbell, D.L., and Yeend, Warren, 1990, Mineral resource assessment maps of the Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1996-A, 4 sheets, scale 1:250,000, 22 p.
Nokleberg, W.J., Moll-Stalcup, E.J., Miller, T.P., Brew, D.A., Grantz, Arthur, Reed, J.C., Jr., Plafker, George, Moore, T.E., Silva, S.R., and Patton, William W., Jr., 1994, Tectonostratigraphic terrane and overlap assemblage map of Alaska: U.S. Geological Survey Open-File Report 94-194, 45 manuscript p., scale 1:2,500,000.
Richter, D.H., Singer, D.A., and Cox, D.P., 1975, Mineral resources map of the Nabesna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-655-K, 1 sheet, scale l:250,000.
Singer, D.A., Curtin, G.C., and Foster, H.L., 1977, Mineral resources map of the Tanacross quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-767-E, 1 sheet, scale l:250,000.
White, D.E., 1942, Antimony deposits of the Stampede Creek area, Kantishna district, Alaska: U.S. Geological Survey Bulletin 936-N, p. 331-348.