National mineral assessment tract AK-BR15 (Polymetallic replacement)

Tract AK-BR15
Geographic region Brooks Range, AK
Tract area 9,782sq km
Deposit type Polymetallic replacement
Deposit age Cretaceous


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
Numerous small occurrences of contact metasomatic skarns or disseminated and veinlet base metal mineralization associated with felsic plutons are known in the Brooks Range. Petrologic and geochemical information on the plutons is limited, but numerous mineral deposit types are permissive, including polymetallic replacement deposits as described by Morris (1986).
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. These tracts contain variable amounts of carbonate rocks of ?Proterozoic to Paleozoic age which are likely hosts for replacement mineralization. The timing and grade of metamorphism of the carbonate rocks, and their lithologies are not known in enough detail to differentiate areas of higher or lower favorability. The geochemical data from stream sediment samples show anomalous levels of Sn, W, and/or Mo in addition to the base metals Cu-Pb-Zn. There is very little, if any, gold associated with the intrusions.
Important examples of this type of deposit
There are no known examples of polymetallic replacement deposits in this tract.
On the numerical estimates made
There is insufficient geologic information to estimate the numbers of undiscovered mineral deposits for polymetallic replacement deposits in this tract.
Morris, H.T., 1986, Descriptive model of polymetallic replacement deposits, in Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 99.

Geographic coverage

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