National mineral assessment tract AK-BR21 (Sediment-hosted Cu)

Tract AK-BR21
Geographic region Brooks Range, AK
Tract area 183,781sq km
Deposit type Sediment-hosted Cu
Deposit age Paleozoic - Mesozoic

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
There are numerous small chalcopyrite occurrences in this tract, often in quartz veinlets, and often associated with the Hunt Fork Shale or Noatak sandstone parts of the clastic Endicott Group (Schmidt and Allegro, 1980). The host rocks and geologic setting of this tract are permissive for Kupferschiefer type shale-hosted copper deposits (Cox, 1986) as well as for red-bed type sandstone-hosted deposits.
On the delineation of permissive tracts
This tract includes all outcrop areas of Proterozoic(?), Paleozoic, and Mesozoic sedimentary and metasedimentary rocks that are prospective for sedimentary or diagenetic Cu deposits. The lithologies included are shale, black shale, sandstone, siltstone, off-platform carbonate rocks, pelitic, quartzitic and carbonaceous schists, and marbles. No specific geochemical information was used to define this tract.
Important examples of this type of deposit
No sediment-hosted Cu deposits are known in this tract, but numerous small Cu occurrences hosted in sedimentary rocks are known.
On the numerical estimates made
No estimate of the number of undiscovered deposits was attempted.
References
Cox, D.P., 1986, Descriptive model of sediment-hosted Cu, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 205.
Schmidt, J.M., and Allegro, G.L., 1980, Mineral occurrences and indicators in the Baird Mountains quadrangle, Alaska: USGS Miscellaneous Field Studies Map MF1992, 1 plate, scale 1:250,000, 19 p.

Geographic coverage

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