Explained by Warren J. Nokleberg, Dennis P. Cox, David L. Campbell, and Warren Yeend.
On the choice of deposit models
Tract AK-SC05 in the Alaska Range and Wrangell Mountains is permissive for Cu-Ag quartz vein deposits because of favorable bedrock geology, known mines and occurrences, geochemical anomalies (Cu, As, Au, Ag, Hg), and locally abundant chalcopyrite and bornite in stream-sediment samples. The Cu-Ag quartz vein deposit type (Nokleberg and others, 1993) consists of Cu sulfides and accessory silver in quartz veins and disseminations in weakly regionally metamorphosed mafic igneous rocks, mainly basalt and gabbro, and in lesser andesite and dacite. The depositional environment is low-grade metamorphic belts. The veins are generally late-stage metamorphic. The deposit minerals include chalcopyrite, bornite, lesser chalcocite, and rare native copper. Alteration minerals include epidote, chlorite, actinolite, albite, quartz, and zeolites.
On the delineation of permissive tracts
This tract is delineated by the distribution of deposits and by the outcrop areas of Upper Triassic sedimentary and mafic volcanic rocks, and of older sedimentary and volcanic rocks of Wrangellia terrane that show pervasive, lower greenschist facies metamorphism of probable mid-Cretaceous age. This deposit type was established for this tract (Nokleberg and others, 1987, 1993); the deposits may be associated with formation of Kennecott Cu deposits (Tract AK-SC01) (Nokleberg and others, 1993).
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 others (1977, 1980), Cox and others (1989), and Nokleberg and others (1990).
Important examples of this type of deposit
The Nugget Creek and Nikolai occurrences (Moffit and Capps, 1911; Miller, 1946; MacKevett, 1976) in the McCarthy quadrangle, and the Kathleen-Margaret mine in the Mount Hayes quadrangle (MacKevett, 1965) are examples of Cu-Ag quartz vein deposits in the tract. Many other smaller occurrences and prospects of this deposit type occur in the tract.
On the numerical estimates made
No tonnage and grade model exists for the Cu-Ag quartz vein deposit type, and no estimate of the number of undiscovered deposits was attempted.
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., 1965, Ore controls at the Kathleen-Margaret (Maclaren River) copper deposit, Alaska: U.S. Geological Survey Professional Paper 501c, p. C116-C120.
MacKevett, E.M., Jr., 1976, Mineral deposits and occurrences in the McCarthy quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-773B, 2 sheets, 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.
Miller, D.J., 1946, Copper deposits of the Nizina district, Alaska: U.S. Geological Survey Bulletin 947-F, p. 93-140.
Moffit, F.H., and Capps, S.R., 1911, Geology and mineral resources of the Nizina district, Alaska: U.S. Geological Survey Bulletin 448, 111 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.
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.