National mineral assessment tract AK-SW15 (Polymetallic replacement)

Tract AK-SW15
Geographic region Southwestern, AK
Tract area 6,926sq km
Deposit type Polymetallic replacement
Deposit age Mesozoic - Tertiary


Explained by Marti L. Miller, Thomas K. Bundtzen, Dennis P. Cox, John E. Gray, and Jeffrey D. Phillips.
On the choice of deposit models
In southwestern Alaska and nearby parts of west-central, east-central, and south-central Alaska, carbonate rocks that are locally intruded by small felsic plutons may host polymetallic replacement deposits as described by Morris (1986).
On the delineation of permissive tracts
The areas permissive for polymetallic replacement deposits are defined by Paleozoic carbonate rocks that are locally intruded by Late Cretaceous and Tertiary plutons. The main permissive area lies in the McGrath, Sleetmute, Taylor Mountains, and Lime Hills quadrangles and forms the Farewell terrane (Decker and others, 1994). A smaller permissive area in the Goodnews Bay quadrangle contains blocks of Ordovician, Devonian, and Permian limestone (Hoare and Coonrad, 1978), that may correlate with the Farewell terrane units (R.B. Blodgett, oral commun., 1992). This tract is a continuation of adjacent tracts in west-central, east-central, and south-central Alaska.
Important examples of this type of deposit
No examples of polymetallic replacement deposits are known in this tract.
On the numerical estimates made
No estimate of undiscovered resources was attempted.
Decker, John, Bergman, S.C., Blodgett, R.B., Box S.E., Bundtzen, T.K., Clough, J.G., Coonrad, W.L., Gilbert. W.G., Miller, M.L., Murphy, J.M., Robinson, M.S., and Wallace, W.K., 1994, Geology of southwestern Alaska, in Plafker, G., and Berg, H.C., eds., The geology of Alaska: Boulder, Colorado, Geological Society of America, The Geology of North America, v. G1, p. 285-310.
Hoare, J.M., and Coonrad, W.L., 1978, Geologic map of the Goodnews and Hagemeister Island quadrangles region, southwestern Alaska: U.S. Geological Survey Open-file Report 78-9-B, 2 sheets, scale 1:250,000.
Morris, H.T., 1986, Descriptive model of polymetallic replacement deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 99-100.

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