Explained by Warren J. Nokleberg, Dennis P. Cox, Richard J. Goldfarb, David L. Campbell, and Warren Yeend.
On the choice of deposit models
Parts of the Alaska Range and Wrangell Mountains are permissive for late Paleozoic Cu-Au skarn deposits as described by Cox and Theodore (1986) and Jones and Menzie (1986). The bedrock geology is favorable, two porphyry Cu occurrences and one associated Cu skarn occurrence are known, and stream-sediment and heavy-mineral-concentrate samples contain anomalously high concentrations of Cu, Mo, Au, As, Ag, Bi, Pb, Zn, Co, and Fe. The principal mineral deposit models are Cu skarn and porphyry Cu, but related deposits could also occur.
On the delineation of permissive tracts
The favorable geologic units in this tract are the Late Paleozoic granitic plutons of Skolai arc that intrude Permian and older rocks of Wrangellia terrane, and carbonate rocks altered to skarn in areas where intruded by late Paleozoic igneous rocks. Areas of known and possibly concealed granitic plutons (greater than several km in diameter) in the tract are delineated by large, blotchy magnetic highs on the aeromagnetic map of Alaska (Godson, 1994) and (or) by K and eU or eTh highs interpreted from sparse data on radiometric maps (J.D. Phillips and F. Riggle, written commun., 1994). About 15 annular aeromagnetic high anomalies, possibly indicative of granite porphyry plutons, exist in this tract.
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). Mineral resource assessments of 250,000-scale quadrangles within the tract were done by Richter and others (1975), MacKevett (1976), Singer and MacKevett (1977), Singer and others (1980), Reed and others (1979), Cox and others (1989), and Nokleberg and others (1990).
Important examples of this type of deposit
The Rainy Creek deposit in the Mount Hayes quadrangle (Rose, 1966; Nokleberg and others, 1991) is an example of a Cu skarn deposit in this tract. Associated porphyry Cu occurrences and minor base metal polymetallic vein occurrences also occur in the tract. Associated placer gold deposits in the Chisana, Chistochina, and Delta River districts in the tract (Capps, 1916; Smith, 1941; Rose, 1965, 1967; Richter and Matson, 1972; Yeend, 1981a, b; Nokleberg and others, 1991) might be partly derived from gold-bearing Cu skarn occurrences.
On the numerical estimates made
Tertiary and older rocks in the tract locally are covered by extensive ice fields and glaciers, and by overlying Cenozoic sedimentary and volcanic rocks. Because deposits are known in the tract, additional detailed exploration might result in the discovery of additional deposits. The minimum number of undiscovered deposits, consistent with the grade and tonnage model of Jones and Menzie (1986), is estimated to be:
Percentile 90 50 10 5 1
Estimated number of deposits 0 0 1 2 3
Capps, S.R., 1916, The Chisana-White River district, Alaska: U.S. Geological Survey Bulletin 630, 130 p.
Cox, D.P., and Theodore, T.G., 1986, Descriptive model of Cu skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p 86.
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.
Godson, Richard H., 1994, Composite magnetic anomaly map of Alaska and adjacent offshore area, in Plafker, G. and Berg, H.C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America: The Geology of North America, v. G1, plate 10, scale 1:2,500,000.
Jones, G.M., and Menzie, W.D., 1986, Grade and tonnage of Cu skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p 86-89.
MacKevett, E.M., 1976, Mineral deposits and occurrences in the McCarthy quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-773B, scale 1:250,000, 2 sheets.
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., Roback, R.C., Yeend, Warren, and Silva S.R., 1991, Map showing locations of metalliferous lode and placer mineral occurrences, deposits, prospects, and mines, Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Map MF-1996-C, 42 p., 1 sheet, scale 1:250,000
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.
Reed, B.L., Nelson, S.W., Curtin, G.C., and Singer, D.A., 1979, Mineral resources map of the Talkeetna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-870-D, l sheet, scale l:250,000.
Richter, D.H., and Matson, N.A., Jr., 1972, Metallic mineral resources map of the Nabesna quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-422.
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.
Rose, A.W., 1966, Geological and geochemical investigations in the Eureka Creek and Rainy Creek areas, Mt. Hayes quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 20, 37 p.
Rose, A.W., 1967, Geology of the upper Chistochina River area, Mt. Hayes quadrangle, Alaska: Alaska Division of Mines and Minerals Geologic Report 28, 41 p.
Singer, D. A., Csejtey, Bèla, Jr., and Miller, R.J., 1980, Map and discussion of the metalliferous and selected non-metalliferous mineral resources of Talkeetna Mountains quadrangle, Alaska: U.S. Geological Survey Open-File Report 78-558-Q, 34 p., 1 sheet, scale 1:250,000.
Singer, D.A., and MacKevett, E.M., Jr., 1977, Mineral resources map of the McCarthy quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-773-C, l 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.
Yeend, Warren, 1981a, Placer gold deposits, Mt. Hayes quadrangle, Alaska, in Silberman, Miles and others, eds., Proceedings of the Symposium of Mineral Deposits of the Pacific Northwest: U.S. Geological Survey Open-File Report 81-355, p. 74-83.
Yeend, Warren, 1981b, Placer gold deposits, Mount Hayes quadrangle, Alaska, in Albert, N.R.D., and Hudson, Travis, eds., The United States Geological Survey in Alaska: Accomplishments during 1979: U.S. Geological Survey Circular 823-B, p. B68.