National mineral assessment tract AK-AP05 (Epithermal vein, generic)

Tract AK-AP05
Geographic region AK Peninsula & Aleutians
Tract area 20,011sq km
Deposit type Epithermal vein, generic
Deposit age Cenozoic

Estimates

Confidence Number of
deposits
90% 5
50% 10
10% 30
5% 30
1% 30

Estimators: Wilson, Church, Saltus, Drew, Menzie

Rationale

Explained by Frederic H. Wilson, Stanley E. Church, Richard W. Saltus, Lawrence J. Drew, and W. David Menzie.
On the choice of deposit models
Epithermal vein deposit models in the conterminous US have been divided into several types based largely on the underlying basement rocks (Cox and Singer, 1986). For the most part, information about Alaska is inadequate to classify individual epithermal gold vein types. Therefore, we have combined deposit models for Creede epithermal veins (Mosier and others, 1986b), Comstock epithermal veins (Mosier and others, 1986c), Sado epithermal veins (Mosier and others, 1986a), and epithermal quartz-alunite gold (Berger, 1986a) into a generic epithermal vein model. We evaluated the permissive area for undiscovered deposits of all types of epithermal veins based on this generic model, which includes gold and/or silver veins associated with intermediate to felsic volcanic rocks similar to those described by Panteleyev (1987).
Occurrences known in the Aleutian Islands may or may not display structural control, can occur in rocks ranging from basalt to dacite or in volcanically-derived sedimentary rocks adjacent to felsic intrusive igneous rocks, and may contain variable, although typically small, amounts of base metal sulfides.
On the delineation of permissive tracts
The Aleutians Islands are a poorly mapped area of volcanic and volcaniclastic rocks of Tertiary and Quaternary age intruded by plutons of Oligocene, Late Miocene, and possibly other ages. The geologic setting is permissive for epithermal gold veins and there are several small occurrences, such as the one at Pyramid Peak on Unalaska Island.
Important examples of this type of deposit
Pyramid Peak on Unalaska Island is an example of an epithermal vein deposit (Simpson, 1986).
On the numerical estimates made
Additional undiscovered epithermal vein deposits are expected to occur in this tract, and would be about the same size as the deposits known on the Alaska Peninsula (i.e., Apollo and Shumagin); that is, about 500,000 tons of ore containing 3-5 million grams of gold (90,000 to 160,000 ounces of gold). The minimum number of undiscovered deposits has been estimated as:
Percentile 90 50 10 5 1
Estimated number of deposits 5 10 30 30 30
Large tracts of volcanic rocks, for which existing records sporadically describe areas of alteration, suggest that there is a high probability that several additional deposits of this type exist within the tract. Although limited geochemical sampling has been published, unpublished data indicate a high potential in the region for epithermal vein deposits.
References
Berger, B.R., 1986a, Descriptive model of epithermal quartz-alunite Au, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 158.
Berger, B.R., 1986b, Descriptive model of hot-spring Au-Ag, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 143.
Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 130.
Mosier, D.L., Berger, B.R., and Singer, D.A., 1986a, Descriptive model of Comstock epithermal veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 154.
Mosier, D.L., Sato, Takeo, Page, N.J., Singer, D.A., and Berger, B.R., 1986b, Descriptive model of Creede epithermal veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 145.
Mosier, D.L., Singer, D.A., and Berger, B.R., 1986c, Descriptive model of Comstock epithermal veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 150.
Panteleyev, Andrejs, 1987, A Canadian cordilleran model for epithermal gold-silver deposits, in Roberts, R.G., and Sheahan, P.A., Ore Deposit Models: Geoscience Canada Reprint Series 3, p. 31-43.
Simpson, D.F., 1986, Aleutian Islands project 1985 final report, Kennecott-Alaska Exploration: unpublished report available from The Aleut Corporation, 54 p.

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