National mineral assessment tract AK-SW16 (Polymetallic vein)

Tract AK-SW16
Geographic region Southwestern, AK
Tract area 229,939sq km
Deposit type Polymetallic vein
Deposit age Mesozoic - Tertiary

Rationale

Explained by Marti L. Miller, Thomas K. Bundtzen, Dennis P. Cox, John E. Gray, Jeffrey D. Phillips
On the choice of deposit models
Polymetallic vein deposits can be associated with intrusive rocks of any age and a wide range of compositions (Cox, 1986). Polymetallic veins may also be spatially related to a large number of other types of deposits, thus making their permissive area quite extensive. This model also serves as somewhat of a catch‑all for deposits of unknown type that, given minimal information, are not clearly described by other deposit models.
On the delineation of permissive tracts
This tract includes most of southwestern Alaska and extends into the northwest corner of the Alaska Peninsula. It is drawn on the basis of the distribution of known and inferred plutonic rocks in sedimentary and metamorphic terranes. The tract was extended to include the covered areas of Dillingham, Marshall, Black, and Kwiguk quadrangles on the basis of geophysical data (gamma ray and aeromag), which indicate the possibility of shallow plutons.
The area contains numerous scattered gold-sulfide mineral occurrences, which (on the basis of available data) do not fit other model types, so are tentatively classified as polymetallic veins.
Important examples of this type of deposit
Although insufficient data are available for definitive classification, the Fortyseven Creek lode occurrence in Sleetmute quadrangle (Miller and others, 1989) may be a polymetallic vein deposit (Bundtzen and Nokleberg, 1987).
On the numerical estimates made
Due to the paucity of geologic data in most of the area, no estimate of undiscovered resources was made.
References
Bundtzen, T.K., and Nokleberg, W.J., 1987, Significant metalliferous lode deposits, west-central Alaska, in Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, Donald, Robinson, M.S., Smith, T.E., and Yeend, Warren, Significant Metalliferous Lode Deposits and Placer Districts of Alaska: U.S. Geological Survey Bulletin 1786, p. 23-31.
Cox, D.P., 1986, Descriptive model of polymetallic veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 125.
Miller, M.L., Belkin, H.E., Blodgett, R.B., Bundtzen, T.K., Cady, J.W., Goldfarb, R.J., Gray, J.E., McGimsey, R.G., and Simpson, S.L., 1989, Pre-field study and mineral resource assessment of the Sleetmute quadrangle, southwestern Alaska: U.S. Geological Survey Open-File Report 89-363, 115 p., 3 plates, scale 1:250,000.

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