National mineral assessment tract AK-SC32 (Cu (Au) skarn)

Tract AK-SC32
Geographic region South Central, AK
Tract area 37,930sq km
Deposit type Cu (Au) skarn
Deposit age Jurassic - Cretaceous

Estimates

Confidence Number of
deposits
90% 1
50% 2
10% 6
5% 6
1% 6

Estimators: Nokleberg, Goldfarb, Cox, Campbell, Koch, Yeend

Rationale

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 Jurassic and Early Cretaceous Cu (Au) skarn deposits (Cox and Theodore, 1986; Jones and Menzie, 1986). Supporting data include the favorable areas underlain by carbonate rocks of Late Paleozoic and Late Triassic age, two known occurrences, associated porphyry Cu deposits, anomalously high concentrations of Cu, Mo, Bi, Au, As, Ag, Pb, Zn, Co, and Fe in stream-sediment and heavy-mineral-concentrate samples, and local aeromagnetic anomalies.
On the delineation of permissive tracts
The favorable geologic units in this two-part tract are the Late Jurassic and Early Cretaceous granitic rocks that intrude the Gravina-Nutzotin belt and adjacent sedimentary and volcanic rocks of Wrangellia terrane, and carbonate rocks altered to skarn in areas where intruded by the Jurassic and Early Cretaceous granitic rocks. The principal mineral deposit models are porphyry Cu and Cu skarn, but related deposits could also occur. Areas of known and possibly concealed granitic plutons (greater than several kilometers 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 25 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 Lemons and Copper King deposits in the Nabesna quadrangle (Richer and others, 1975) are examples of a Cu skarn deposits in this tract. Associated deposits in the tract are the Baultoff, Orange Hill, Horsfeld, Bond Creek, and Carl Creek porphyry Cu and Cu-Mo deposits and occurrences, all in the Nabesna quadrangle (Van Alstine and Black, 1946). Associated placer gold deposits in the Chisana, Chistochina, Delta River, Nizina, and Valdez Creek districts in the tract (Moffit, 1914; Chapin, 1918; Capps, 1916, 1919; Tuck, 1938; Smith, 1941, 1970; Rose, 1965, 1967; Cobb and Matson, 1972; Richter and Matson, 1972; Cobb, 1973; Cobb and MacKevett, 1980; Yeend, 1981a, b; Bressler and others, 1985; Fechner and Herzog, 1990; Nokleberg and others, 1990; Reger and Bundtzen, 1990) may be partly derived from gold-bearing Cu skarn occurrences.
On the numerical estimates made
Because of two known Cu-(Au) skarn occurrences and associated porphyry Cu deposits, an excellent possibility exists that further 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 1 2 6 6 6
References
Bressler, J.R., Jones, W.C. and Cleveland, Gaylord, 1985, Geology of a buried channel system of the Denali Placer Gold Mine: Alaska Miner, January, 1985, p. 9.
Capps, S.R., 1916, The Chisana-White River district, Alaska: U.S. Geological Survey Bulletin 630, 130 p.
Capps, S.R., 1919, The Kantishna region, Alaska: U.S. Geological Survey Bulletin 687, 118 p.
Chapin, Theodore, 1918, The Nelchina-Susitna region, Alaska: U.S. Geological Survey Bulletin 668, 67 p.
Cobb, E.H., 1973, Placer deposits of Alaska: U.S. Geological Survey Bulletin 1324, 213 p.
Cobb, E.H., and MacKevett, E.M., Jr., 1980, Summaries of data on and lists of references to metallic and selected nonmetallic mineral deposits in the McCarthy quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-885, 156 p.
Cobb, E.H., and Matson, N.A., 1972, Metallic mineral resources map of the Valdez quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-438.
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.
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.
Fechner, S.A. and Herzog, D.A., 1990, Gold- and PGM-bearing conglomerate of the Valdez Creek mining district, Alaska: U.S. Bureau of Mines Open File 12-90, 52 p.
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.
Moffit, F.H., 1914, Geology of the Hanagita-Bremner region, Alaska: U.S. Geological Survey Bulletin 576, 56 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.
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.
Reger, R.D. and Bundtzen, T.K., 1990, Multiple glaciation and placer gold formation, Valdez Creek Valley, Western Clearwater Mountains, Alaska: Alaska Division of Geological and Geophysical Surveys Professional Paper 107, 29 p., 1 sheet, scale 1:63,360.
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., 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.
Smith, T.E., 1970, Gold resource potential of the Denali bench gravels, Valdez Creek Mining District, Alaska: U.S. Geological Survey Professional Paper 700-D, p. D146-D152.
Tuck, Ralph, 1938, The Valdez Creek mining district, Alaska, in 1936: U.S. Geological Survey Bulletin 897-B, p. 109-131.
Van Alstine, R.E., and Black, R.F., 1946, Copper deposits of the Kotsina-Kuskulana district, Alaska: U.S. Geological Survey Bulletin 947-G, p. 121-141
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.

Geographic coverage

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