National mineral assessment tract AK-BR11 (Porphyry Cu, BC-Ak type)

Tract AK-BR11
Geographic region Brooks Range, AK
Tract area 9,782sq km
Deposit type Porphyry Cu, BC-Ak type
Deposit age Cretaceous

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
Petrologic and geochemical information on Proterozoic, Devonian or Cretaceous granitic plutons in the Brooks Range is limited or absent, but numerous mineral deposit types are permissive, including porphyry Cu as described by Cox, (1986a), porphyry Cu-Au deposits (Cox, 1986b), or porphyry Cu-Mo deposits (Cox, 1986c). Numerous small occurrences of contact metasomatic skarns or disseminated and veinlet base metal mineralization are also known in the area.
On the delineation of permissive tracts
This tract comprises all the Proterozoic, Devonian or Cretaceous granitic plutons in the Brooks Range, and includes all potential host rocks within 5 km of the plutons. The geochemical data from stream sediment samples show anomalous levels of Sn, W, and/or Mo in addition to the base metals Cu, Pb, and Zn. There is very little, if any, gold associated with the intrusions.
Important examples of this type of deposit
There are no known porphyry copper deposits in this tract, but there are numerous small occurrences of contact metasomatic skarns or disseminated and veinlet base metal mineralization. The Bear Mountain occurrence in the Table Mountain quadrangle, eastern Brooks Range, contains both Mo and W porphyry mineralization (Barker and Swainbank, 1986).
On the numerical estimates made
There is insufficient geologic or mineral deposit information to estimate the numbers of undiscovered mineral deposits for any of the permissive deposits in this tract.
References
Barker, J.C., and Swainbank, R.C., 1986, A tungsten-rich porphyry molybdenum occurrence at Bear Mountain, Northeast Alaska: Economic Geology v. 81, p. 1753 - 1759.
Cox, D.P., 1986a, 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., 1986b, Descriptive model of porphyry Cu-Au, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 110.
Cox, D.P., 1986c, Descriptive model of porphyry Cu-Mo, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 115.

Geographic coverage

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