National mineral assessment tract AK-BR20 (Sandstone hosted Pb-Zn)

Tract AK-BR20
Geographic region Brooks Range, AK
Tract area 59,440sq km
Deposit type Sandstone hosted Pb-Zn
Deposit age Devonian - Mississippian

Rationale

Explained by Jeanine M. Schmidt, Karen D. Kelley, Richard I. Grauch, Byron R. Berger, John W. Cady, Gregory T. Spanski, James E. Kilburn.
On the choice of deposit models
The geologic setting, extensive sandstone and siltstone host rocks, and elevated Pb geochemistry indicate that this tract is permissive for sandstone-hosted Pb-Zn deposits (Briskey, 1986). Several small occurrences, such as Ginnie Creek (Mayfield and others, 1979), Ipnavik River, and Otuk Creek may be of this type.
On the delineation of permissive tracts
This tract includes all known exposures of sedimentary rocks of the Upper Devonian to Mississippian(?) Endicott Group. These rocks include the nonmarine Kekituk and Kanayut Conglomerates, the marine Noatak Sandstone and the Kayak and Hunt Fork Shales. These units generally produce a broad distinct aeromagnetic low, and contain scattered geochemical anomalies of Zn and Pb.
Important examples of this type of deposit
No sandstone-hosted Pb-Zn deposits are known in this tract, but it includes several occurrences of disseminated sphalerite and galena in sandstones (Mayfield and others, 1979), and numerous vein-breccia Zn-Pb-Ag sulfide deposits (Schmidt and Werdon, 1993). Sphalerite and galena also occur infilling diagenetic concretions within the Kayak shale.
On the numerical estimates made
No attempt was made to estimate the number of undiscovered deposits.
References
Briskey, J.A., 1986b, Descriptive model of sandstone-hosted Pb-Zn, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 201.
Mayfield, C.F., Curtis, S.M., Ellersieck, I.F., and Tailleur, I.L., 1979, The Ginny Creek zinc-lead-silver and Nimiuktuk barite deposits, northwestern Brooks Range, Alaska, in Johnson, K.M., and Williams, J.R., eds., The U.S. Geological Survey in Alaska, Accomplishments during 1978: U.S. Geological Survey Circular 804B, p. B11-B13.
Schmidt, J.M., and Werdon, M.B., 1993, Clastic-hosted stratiform, vein-breccia, and disseminated Zn-Pb-Ag deposits of the northwestern Brooks Range, Alaska: Are they different expressions of dewatering of the same source basin? [abs], Geological Society of America Abstracts with Program, volume 25, no. 5, p. 143.

Geographic coverage

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