Explained by Warren J. Nokleberg, Dennis P. Cox, Richard J. Goldfarb, David L. Campbell, 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 plutonic porphyry Au deposits (Hollister, 1992) because of favorable bedrock geology, a known mine, and geochemical anomalies (Au, As, Au).
On the delineation of permissive tracts
The tract is delineated by the distribution of deposits and of the Upper Cretaceous and possibly lower Tertiary (80-100 Ma) granitic plutons, dikes, and sills of the Kluane arc. The plutonic prophyry Au deposits are associated with polymetallic vein and Sb-Au polymetallic veins. Some known and possibly concealed granitic plutons in the tract are delineated by large, blotchy magnetic highs and (or) eU or eTh cells interpreted from sparse data on radiometric maps. For simplicity, the tract is restricted to the area east of the Delta River and north of the Tanana River where deposits of this type are known.
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 coincident with tracts described as permissive for porphyry Cu deposits and for gold-antimony vein 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
The Democrat mine in the Richardson district (Bundtzen and Reger, 1977; Nokleberg and others, 1993) is an important example of this deposit type, and may be similar to the Fort Knox plutonic porphyry Au deposit near Fairbanks(Robinson and others, 1990; Hollister, 1992). Placer Au mines in the Bonnifield, Delta River, and Kantishna districts in the region (Capps, 1912, 1919; Smith, 1941; Rose, 1965; Cobb, 1973; Gilbert and Bundtzen, 1979; Bundtzen, 1981; Nokleberg and others, 1990) may in part be derived from plutonic porphyry Au deposits.
On the numerical estimates made
Much of the tract is covered by glacial loess and dense vegetation, which may obscure additional porphyry Au deposits. Favorable geological and geochemical data suggest that at least one additional undiscovered deposit probably occurs in the tract. The mineral resource team estimated the minimum number of undiscovered deposits, consistent with a tonnage and grade model constructed from deposit data reported by Hollister (1992), to be:
Percentile 90 50 10 5 1
Estimated number of deposits 1 5 7 7 7
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., and Reger, R.D., 1977. The Richardson lineament, a structural control for gold deposits in the Richardson mining district, interior Alaska. In Short Notes on Alaska Geology - 1977. Alaska Division of Geological and Geophysical Surveys Geologic Report 55, p. 29-34.
Capps, S.R., 1912, The Bonnifield region, Alaska: U.S. Geological Survey Bulletin 501, 64 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.
Gilbert, W.G., and Bundtzen, T.K., 1979, Mid-Paleozoic tectonics, volcanism, and mineralization in north-central Alaska Range, in Sisson, A., ed., The relationship of plate tectonics to Alaskan geology and resources: Alaska Geological Society, Symposium, 1977, p. F1-F21.
Hollister, V.F., 1992. On a proposed plutonic porphyry gold deposit model. Non-renewable resources, 1, p. 293-302.
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, 53 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.
Rose, A.W., 1965, Geology and mineral deposits of the Rainy Creek area, Mt. Hayes quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 14, 51 p.
Robinson, M.S., Smith, T.E., and Metz, P.A., 1990, Bedrock geology of the Fairbanks mining district: Alaska Division of Geological and Geophysical Surveys Professional Report 106, 1 sheet, scale 1:63,360.
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.
Smith, P.S., 1941, Mineral industry of Alaska in 1939: U.S. Geological Survey Bulletin 926-A, p. 1‑106.