National mineral assessment tract AK-BR18 (Cu (Au) skarn)

Tract AK-BR18
Geographic region Brooks Range, AK
Tract area 9,782sq km
Deposit type Cu (Au) skarn
Deposit age Cretaceous

Rationale

Explained by Jeanine M. Schmidt
On the choice of deposit models
Numerous small occurrences of contact metasomatic skarns or disseminated and veinlet base metal mineralization are known in the area (Nokleberg and others, 1987). Petrologic and geochemical information about the plutons is limited or absent, but numerous mineral deposit types are possible, including Cu-(Au) skarn deposits.
On the delineation of permissive tracts
This multi-part tract comprises all the known and inferred Proterozoic, Devonian or Cretaceous granitic plutons in the Brooks Range, and all potential host rocks within a 5 km distance from the plutons. These tracts contain variable amounts of carbonate rocks of ?Proterozoic to Paleozoic age which are likely hosts for skarn 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 these intrusions.
Important examples of this type of deposit
No Cu-(Au) skarn deposits are known in this tract.
On the numerical estimates made
There is insufficient geologic and mineral deposit information to estimate numbers of undiscovered Cu-(Au) skarn deposits in this tract.
References
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.

Geographic coverage

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