Explained by Warren J. Nokleberg, Dennis P. Cox, Richard J. Goldfarb, David L. Campbell.
On the choice of deposit models
This tract, in the Bering Glacier region of coastal south-central Alaska, is permissive for sedimentary exhalative (SEDEX) Zn-Pb deposits of Cenozoic age because it has anomalous concentrations of Ba, Zn, Cu, Mo, and Pb in stream sediment samples (Pickthorn and others, 1985), barite occurs locally in heavy-mineral concentrates, and dark marine shale locally is interlayered with basalt of the Yakutat terrane. However, this type of deposit typically is in Carboniferous and older rocks (Briskey, 1986).
On the delineation of permissive tracts
The favorable geologic unit in the tract is the Cenozoic marine dark shales and interlayered basalts of the Yakutat terrane. Barite and sphalerite occur in stream-sediment samples.
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 MacKevett (1976), Singer and others (1977, 1980), Tysdal and Case (1982), Goldfarb and others (1992), and Madden-McGuire and Winkler (1993).
Important examples of this type of deposit
The geologic setting is permissive for Sedex Zn-Pb deposits but no deposits of this type are known in the tract.
On the numerical estimates made
The tract is locally covered by extensive ice fields and glaciers, and is partly bounded by the southern Alaska coast. Because no deposits or occurrences are known, and because most SEDEX deposits are Carboniferous or older, no attempt was made to estimate the number of undiscovered deposits.
References
Briskey, J.A., 1986, Descriptive model of sedimentary exhalative Pb-Zn, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p 211-213.
Goldfarb, R.J., Case, J.E., Plafker, George, and Winkler, G.R., 1992, Maps showing areas of potential for mineral resources in the Cordova and Middleton Island 1° x 3° quadrangles, southern Alaska: U.S. Geological Survey Miscellaneous Field Investigations Map MF-2190. 1 sheet, scale 1:250,000.
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.
Madden-McGuire, D.J., and Winkler, G.R., 1993, Mineral resource maps of the Anchorage quadrangle, southern Alaska: U.S. Geological Survey Miscellaneous Investigations Map MI-2393, scale 1:250,000, 3 sheets.
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., 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.
Pickthorn, W.J., Goldfarb, R.J., O’Leary, R.M., Sutley, S.J., and Weaver, Sarah, 1985, Kayak Island-Analysis of a geochemical anomaly, in Barsch-Winkler, Susan, and Reed, K.M., eds., The United States Geological Survey in Alaska: Accomplishments in 1983: U.S. Geological Survey Circular 945, p. 82-83.
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., 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.
Tysdal, R.G., and Case, J.E., 1982, Metalliferous mineral resource potential of the Seward and Blying Sound quadrangles, southern Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-880H, 2 sheets, scale l:250,000, 23 p.
