National mineral assessment tract AK-SW13 (Plutonic porphyry Au)

Tract AK-SW13
Geographic region Southwestern, AK
Tract area 67,723sq km
Deposit type Plutonic porphyry Au
Deposit age Mesozoic - Tertiary

Estimates

Confidence Number of
deposits
90% 3
50% 6
10% 10
5% 15
1% 20

Estimators: Miller, Bundtzen, Cox, Gray, Phillips

Rationale

Explained by Marti L. Miller, Thomas K. Bundtzen, Dennis P. Cox, John E. Gray, and Jeffrey D. Phillips.
On the choice of deposit models
This tract contains numerous Cretaceous and Tertiary calc-alkaline stocks that may host plutonic porphyry Au deposits as described by Hollister (1992). Quartz stockwork vein systems that locally carry gold, scheelite, molybdenite, and bismuth (Bundtzen and others, 1992; Bundtzen and Miller, 1997) are associated with some of the stocks.
On the delineation of permissive tracts
This tract trends northeast from the Bethel quadrangle to the McGrath quadrangle, and continues into the west-central region. The tract is defined by the Kuskokwim Mountain belt, which features volcano-plutonic complexes (and related stocks), gold-quartz vein deposits, and favorable geochemical data (Bundtzen and Miller, 1997).
Important examples of this type of deposit
This tract contains several gold deposits including those at Chicken Mountain and Golden Horn (Bundtzen and others, 1992) in the Iditarod quadrangle, and at Vinasale Mt. (DiMarchi, 1993) in the McGrath quadrangle. Although these deposits are plutonic-related, it is not clear what model(s) they represent.
On the numerical estimates made
Assuming a mean tonnage and grade of about 15 million tons averaging 1 gram per ton Au, similar to the size of the Chicken Mountain deposit (Bundtzen and others, 1992), estimates of the minimum number undiscovered deposits are as follows:
Percentile 90 50 10 5 1
Estimated number of deposits 3 6 10 15 20
References
Bundtzen, T.K., and Miller, M.L., 1997, Precious metals associated with Late Cretaceous-early Tertiary igneous rocks of southwestern Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral deposits of Alaska, Economic Geology Monograph 9, p. 242-286.
Bundtzen, T.K., Miller, M.L., Laird, G.M., and Bull, K.F., 1992, Geology and mineral resources of Iditarod mining district, Iditarod B-4 and eastern B-5 quadrangles, southwestern Alaska: Alaska Division of Geological and Geophysical Surveys Professional Report 97, 46 p. scale 1:63,360 and 1:770.
DiMarchi, J.J., 1993, Geology, alteration, and mineralization of the Vinasale Mountain gold deposit, west-central Alaska, in Solie, D.N., and Tannian, Fran, eds., Short Notes on Alaskan Geology 1993: Alaska Division of Geological and Geophysical Surveys Professional Report 113, p. 17-29.
Hollister, V.F., 1992, On a proposed plutonic porphyry gold deposit model: Nonrenewable Resources, v. 1, no. 4, p. 293-302.

Geographic coverage

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