National mineral assessment tract AK-SC25 (Placer Au)

Tract AK-SC25
Geographic region South Central, AK
Tract area 266,047sq km
Deposit type Placer Au
Deposit age Cenozoic

Rationale

Explained by Warren J. Nokleberg Dennis P. Cox, Richard J. Goldfarb, and Warren Yeend
On the choice of deposit models
Placer gold can be expected to occur in unconsolidated deposits downstream from any of the gold‑bearing deposit types. Therefore the permissive area for placer and paleoplacer gold is quite broad.
On the delineation of permissive tracts
Excluded from being permissive are the following areas: (1)prohibitively steep modern stream gradients; (2) elevations above approximately 1,600 m; (3) extensive ice-covered terrain; and (4) upper Tertiary and Quaternary volcanic rocks.
Important examples of this type of deposit
Eleven placer districts in the region have produced substantial placer gold (Cobb, 1964; MacKevett and others, 1978). The most important of these is the Valdez Creek District, which has produced nearly 1/2 million ounces of gold (Bundtzen and others, 1994).
On the numerical estimates made
Because of the relative ease of exploring for placer gold deposits, much of the state has been thoroughly explored. There is a low probability that major new placer districts will be discovered, but it is likely that a few relatively small new deposits will be found in the known districts. No estimate of the number of undiscovered deposits was attempted.
References
Bundtzen, T.K., Swainbank, R.C., Clough, A.H., Henning, M.W., and Hansen, E.W., 1994, Alaska’s Mineral Industry: Alaska Division of Geological and Geophysical Surveys Special Report 48, 84 p.
Cobb, E.H., 1964, Placer gold occurrences in Alaska: U.S. Geological Survey Mineral Investigations Resources Map MR-38, scale 1:250,000.
MacKevett, E.M., Jr., Singer, D.A., and Holloway, C.D., 1978, Maps and tables describing metalliferous mineral resource potential of southern Alaska: U.S. Geological Survey Open-File Report 78-1E, 2 sheets, scale 1:1,000,000, 45 p.

Geographic coverage

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