National mineral assessment tract AK-SC22 (Porphyry Cu, BC-Ak type)

Tract AK-SC22
Geographic region South Central, AK
Tract area 37,930sq km
Deposit type Porphyry Cu, BC-Ak type
Deposit age Jurassic - Cretaceous

Estimates

Confidence Number of
deposits
90% 4
50% 15
10% 30
5% 30
1% 30

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 porphyry Cu and associated granitic-magmatism-related deposits because of favorable bedrock geology, three large porphyry Cu deposits and two prospects, and two associated Cu skarn occurrences, geochemical anomalies (Cu, Mo, Bi, Au, As, Ag, Pb, Zn, Co, Fe), and local aeromagnetic anomalies. This porphyry Cu model (17) also includes porphyry Cu (BC-Ak type) (17.1), porphyry Cu skarn (18a), porphyry Cu-Au (20c), and porphyry Cu-Mo (21). Details of the deposit model for this tract and other areas of Alaska and British Columbia are provided by Hollister (1978), Hollister and others (1975), Cox (1986), and Menzie and Singer (1993).
On the delineation of permissive tracts
The favorable geologic units in this two-part tract are 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, Cu skarn, porphyry Cu-Mo, and Cu (Au) skarn, and polymetallic vein, but related deposits could also occur. Local porphyry Cu occurrences exhibit multiple intrusive phases, propylitic and sericitic alteration. About 25 areas of known and possibly concealed granitic plutons (greater than several km 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).
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
Examples 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; Richter and others, 1975). Associated deposits in the same area are the Lemons and Copper King Cu skarn occurrences, and the Nabesna Au (Cu) skarn mine. 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; 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 porphyry Cu mines and occurrences.
On the numerical estimates made
Tertiary and older rocks in the tract are covered locally by extensive ice fields and glaciers, and by Cenozoic sedimentary and volcanic rocks. Additional detailed exploration might result in the discovery of additional deposits or occurrences. The minimum number of undiscovered porphyry Cu deposits, consistent with the grade and tonnage model of Menzie and Singer (1993), is estimated to be:
Percentile 90 50 10 5 1
Estimated number of deposits 4 15 30 30 30
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, 116 p.
Chapin, Theodore, 1918, The Nelchina-Susitna region, Alaska: U.S. Geological Survey Bulletin 668, 67 p.
Capps, S.R., 1916, The Chisana-White River district, Alaska: U.S. Geological Survey Bulletin 630, 130 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.
Cox, D.P., 1986, Descriptive model of porphyry Cu, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p 76.
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.
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.
Hollister, V.F., 1978, Geology of the porphyry copper deposits of the Western Hemisphere: New York, Society of Mining Engineers of the American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc., 219 p.
Hollister, V.F., Anzalone, S.A., and Richter, D.H., 1975, Porphyry copper deposits of southern Alaska and contiguous Yukon Territory: Canadian Mining and Metallurgy Bulletin, v. 68, p. 104-112.
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.
Menzie, W.D., and Singer, D.A., 1993, Grade and tonnage model of porphyry Cu deposits in British Columbia, Canada, and Alaska, U.S.A.: U.S. Geological Survey Open-File Report 93-275, 9 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.

Geographic coverage

Show this information as XML or JSON