National mineral assessment tract AK-WC27 (Sedex Zn-Pb)

Tract AK-WC27
Geographic region West Central, AK
Tract area 37,919sq km
Deposit type Sedex Zn-Pb
Deposit age Paleozoic

Rationale

Explained by Bruce M. Gamble, Robert G. Eppinger, John W. Cady, Stanley E. Church, Byron R. Berger, Gregory T. Spanski
On the choice of deposit models
Several mineral occurrences on the Seward Peninsula consist, at least in part, of stratiform stringers of galena and (or) sphalerite in metasedimentary rocks, chiefly carbonates and argillites. These occur in the mixed unit of the Nome Group, and have alternatively been interpreted as vein, polymetallic replacement, sedimentary exhalative Zn-Pb, and kuroko volcanogenic deposits. Therefore, the area is considered permissive for syngenetic base metal mineralization including sedimentary exhalative Zn-Pb deposits.
On the delineation of permissive tracts
This tract includes all of the Nome Group, including high-grade rocks, and is essentially equivalent to the Seward terrane (Till and others, 1986). Anomalously high concentrations of elements in stream-sediment and panned-concentrate samples include As, Sb, Au, Cu, Pb, Zn, Ag, Ni, Co, Ba, and Mn. The stratiform galena and(or) sphalerite stringers are within this tract.
Important examples of this type of deposit
A metamorphosed sulfide deposit at Hannum Creek has been interpreted as a sedimentary exhalative Zn-Pb deposit (Nokleberg and others, 1987), or alternatively as a vein deposit (Herreid, 1966). Other examples of possible sedex deposits include Galena, Aurora Creek, and Quarry in the Nome quadrangle (Mulligan and others, 1965).
On the numerical estimates made
No estimate of the number of undiscovered deposits was attempted because of uncertainty of deposit type.
References
Herreid, Gordon, 1966, The geology and geochemistry of the Inmachuk River map area, Seward Peninsula, Alaska: Alaska Division of Mines and Minerals Geologic Report No. 23, 25 p., scale 1:63,360, 1 sheet.
Mulligan, J.J., and Hess, H.D., 1965, Examination of the Sinuk Iron Deposits: U.S. Bureau of Mines Open-File Report, 34 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.
Till, A.B., Dumoulin, J.A., Gamble, B.M., Kaufman, D.S., and Carroll, P.I., 1986, Preliminary geologic maps and fossil data, Solomon, Bendeleben, and southern Kotzebue quadrangles, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 86‑276, 62 p., scale 1:250,000.

Geographic coverage

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