National mineral assessment tract AK-SC18 (Synorogenic-synvolcanic Ni-Cu)

Tract AK-SC18
Geographic region South Central, AK
Tract area 25,441sq km
Deposit type Synorogenic-synvolcanic Ni-Cu
Deposit age Late Triassic

Rationale

Explained by Warren J. Nokleberg, Richard J. Goldfarb, and David L. Campbell.
On the choice of deposit models
This tract, in the eastern Alaska Range, Nutzotin, and Wrangell Mountains, is permissive for Late Triassic gabbroic Ni-Cu deposits because of favorable bedrock geology, one known deposit, geophysical anomalies, and geochemical anomalies (Cu, Ni). The gabbroic Ni-Cu deposit type is a modification by Nokleberg and others (1987) of the synorogenic-synvolcanic Ni-Cu deposit type of Singer and others (1986) in Cox and Singer (1986).
On the delineation of permissive tracts
The favorable geologic units for the tract are the Upper Triassic Nikolai Greenstone and subjacent units of the Wrangellia terrane where intruded by coeval mafic and ultramafic plutons, dikes, and sills, such as the Fish Lake complex in the Mount Hayes quadrangle (Nokleberg and others, 1992). In the eastern Alaska Range, Nutzotin Mountains, and Wrangell Mountains, the Nikolai Greenstone, which also contains coeval mafic and ultramafic rocks, is up to 4350 m thick and consists mainly of massive, subaerial, amygdaloidal basalt flows, lesser pillow basalt flows, and thin beds of argillite, chert, and mafic volcaniclastic rocks (Nokleberg and others, 1994c, d). The flows are predominantly intermixed aa and pahoehoe flows; individual units range from 5 cm to more than 15 m thick. The Nikolai Greenstone is a thick and vast unit of submarine and subaerial Middle and Upper Triassic tholeiitic basalt and associated mafic and ultramafic sills and that forms a major part of the Wrangellia terrane. The Nikolai Greenstone and associated mafic and ultramafic plutonic rocks are interpreted as forming during a short-lived period of rifting or oceanic plume activity within the Wrangellia island arc terrane (Nokleberg and Lange, 1985; Nokleberg and others, 1984, 1985; 1987, 1989, 1994c, d, e, Plafker and others, 1989).
The distribution of the geologic units defining the tract is adapted from Nokleberg and others (1994d, e; 1997). The distribution of this belt of mineral deposits is adapted from MacKevett and others (1978), and Nokleberg and others (1987, 1993, 1994a, b, 1996, 1997). Mineral resource assessments of 250,000-scale quadrangles within the tract were done by Richter and others (1975), Singer and others (1977), Reed and others (1979), Cox and others (1989), and Nokleberg and others (1990, 1991).
Important examples of this type of deposit
The Fish Lake and Wellgreen deposits are classified by Nokleberg and others (1996) as gabbroic Ni-Cu deposits. The Fish Lake gabbroic Ni-Cu deposit (63 13 00N, 146 48 00W: Nokleberg and others, 1984; I.M. Lange and W.J. Nokleberg, unpublished data, 1985; Nokleberg and others, 1991, 1996) consists of chromite, disseminated and in wispy layers, in serpentinized olivine cumulate. The occurrence occupies a zone up to 15 km long along strike and up to 2 km wide, and contains locally anomalous Cu and Ni in stream-sediment and rock samples. Isolated grab samples contain greater than 0.5% Cr and up to 0.3% Ni. This gabbroic Ni-Cu occurrence is hosted by small- to moderate-size gabbro plutons and local cumulate mafic and ultramafic rocks. The mafic and ultramafic rocks intrude the Nikolai Greenstone and older rocks, and are interpreted as being co-magmatic with the mafic magmas that formed the Middle and Upper Triassic Nikolai Greenstone.
The Wellgreen gabbroic Ni-Cu deposit (61 28 00N, 139 31 18W: Campbell, 1976; Nokleberg and others, 1984; Hulbert and others, 1988; EMR Canada, Nokleberg and others, 1989, 1991, 1996; Mining Review, 1991) contains reserves of 50 million tonnes grading 0.36% Ni, 0.35% Cu, 0.51g/t Pt, 0.34 g/t Pd. The deposit consists of massive pyrrhotite, pentlandite, chalcopyrite and magnetite lenses that are scattered along the footwall contact of a steeply dipping fault zone in gabbroic rocks of the Upper Triassic Quill Creek Complex. The deposit occurs within a 130 km belt of Ni-Cu-Co-PGE occurrences that are hosted in the Pennsylvanian Skolai Assemblage that includes the Canalask deposit at White River. Cu-Ni sulfides are disseminated within mafic dikes and peridotite. Production occurred in 1972-73. The deposit age is interpreted as Late Triassic.
On the numerical estimates made
Because only two widely-separated deposits are known, and because the occurrence of mafic and ultramafic plutons, dikes, and sills in the Nikolai Greenstone is very erratic, this tract is considered to be permissive. No estimate of undiscovered gabbroic Ni-Cu was attempted.
References
Campbell, S.W., 1976, Nickel-copper sulphide deposits in the Kluane Ranges, Yukon Territory: Department of Indian and Northern Affairs, Open File Report EGS 1976-10, 17 p.
Cox, D.P., and Singer, D.A., 1986, eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, 329 p.
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.
EMR Canada, 1989, Canadian mineral deposits not being mined in 1989: Energy, Mines and Resources Canada, Mineral Resource Sector, MR 223, 625 p.
Hulbert, L.J., Carne, R.C., Gregoire, D.C., and Paktunc, D. ,1992, Sedimentary nickel, zinc, and platinum-group-element mineralization in Devonian black shales at the Nick Property, Yukon, Canada: A new type of deposit: Exploration, Mining and Geology, Canadian Institute of Mining and Metallurgy, v. 1, no. 1, p. 39-62.
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.
Mining Review, 1991, British Columbia and Yukon Chamber of Mines, v. 11, no. 3, p. 24-33.
Nokleberg, W.J., Aleinikoff, J.N. Lange, I.M., Silva, S.R., Miyaoka, R.T., Schwab, C.E., and Zehner, R.E., 1992, Preliminary geologic map of the Mount Hayes quadrangle, eastern Alaska Range, Alaska: U.S. Geological Survey Open-File Report 92-594, 1 sheet, scale 1:250,000, 39 p.
Nokleberg, W.J., and Lange, I.M., 1985, Metallogenetic history of the Wrangellia terrane, eastern Alaska Range, Alaska [abs.]: U.S. Geological Survey Circular 949, p. 36-38.
Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, Donald, Robinson, M.S., Smith, T.E., Yeend, Warren, 1994a, Metallogeny and major mineral deposits of Alaska, 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, p. 855-904.
Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, Donald, Robinson, M.S., Smith, T.E., Yeend, Warren, and 54 contributors, 1994b, Metallogenic map of significant metalliferous lode deposits and placer districts of Alaska, 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 11, scale 1:2,500,000.
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., Dawson, K.M., Eremin, R.A., Goryachev, N.A., Koch, R.D. Ratkin, V.V., Rozenblum, I.S., Shpikerman, V.I., Frolov, Y.F., Gorodinsky, M.E., Melnikov, V.D., Ognyanov, N.V., Petrachenko, E.D., Petrachenko, R.I., Pozdeev, A.I., Ross, K.V., Wood, D.H., Grybeck, Donald, Khanchuk, A.I., Kovbas, L.I., Nekrasov, I.Ya., and Sidorov, A.A., 1996, Significant metalliferous lode deposits and placer districts for the Russian Far East, Alaska, and the Canadian Cordillera U.S. Geological Survey Open-File Report 96-513-A (paper format), 385 p.
Nokleberg, W.J., Bundtzen, T.K., Dawson, K.M., Eremin, R.A., Ratkin, V.V., Shpikerman, V.I., Goryachev, N.A., Khanchuk, A.I., Koch, R.D., Rozenblum, I.S., Gorodinsky, M.E., Frolov, Y.F., Pozdeev, A.I., Parfenov, L.M., and Sidorov, A.A., 1997, Mineral deposit and metallogenic belt maps of the Russian Far East, Alaska, and the Canadian Cordillera: U.S. Geological Survey Open-File Report 97-161, 2 sheets, 5 million scale; 5 sheets, 10 million scale).
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., Foster, H.L., and Aleinikoff, J.N., 1989, Geology of the northern Copper River Basin, eastern Alaska Range, and southern Yukon-Tanana Basin, southern and east-central Alaska, in, Nokleberg, W.J., and Fisher, M.A., eds., Alaska Geological and Geophysical Transect: Field Trip Guidebook T104, 28th International Geological Congress, p. 34-63
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., and Roback, R.C., 1984, Preliminary accretionary terrane model for metallogenesis of the Wrangellia terrane, southern Mount Hayes quadrangle, eastern Alaska Range, Alaska, in Reed, K.M., and Bartsch-Winkler, Susan, eds., The United States Geological Survey in Alaska: Accomplishments during 1982: U.S. Geological Survey Circular 939, p. 60-65.
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., 1994d, Tectonostratigraphic terrane and overlap assemblage map of Alaska: U.S. Geological Survey Open-File Report 94-194, 53 p., scale 1:2,500,000.
Nokleberg, W.J., Parfenov, L.M., and Monger, J.W.H., and Baranov, B.V., Byalobzhesky, S.G., Bundtzen, T.K., Feeney, T.D., Fujita, Kazuya, Gordey, S.P., Grantz, Arthur, Khanchuk, A.I., Natal'in, B.A., Natapov, L.M., Norton, I.O., Patton, W.W., Jr., Plafker, George, Scholl, D.W., Sokolov, S.D., Sosunov, G.M., Stone, D.B., Tabor, R.W., Tsukanov, N.V., Vallier, T.L. and Wakita, Koji, 1994c, Circum-North Pacific tectono-stratigraphic terrane map: U.S. Geological Survey Open-File Report 94-714, 221 pages, 2 sheets, scale 1:5,000,000; 2 sheets, scale 1:10,000,000.
Nokleberg, W.J., Plafker, George, and Wilson, F.H., 1994e, Geology of south-central Alaska, in Plafker, George, and Berg, H.C., eds., The Geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G-1, p. 311-366.
Plafker, George, Nokleberg, W.J., and Lull, J.S., 1989, Bedrock geology and tectonic evolution of the Wrangellia, Peninsular, and Chugach terranes along the Trans-Alaska crustal transect in the Chugach Mountains and southern Copper River Basin, Alaska: Journal of Geophysical Research, v. 94, p. 4255-4295.
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., 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., 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.
Singer, D.A., Page, NJ., and Menzie, W.D., 1986, Descriptive model of synorogenic-synvolcanic Ni-Cu, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 28-31.

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