National mineral assessment tract AK-WC08 (Epithermal vein, generic)

Tract AK-WC08
Geographic region West Central, AK
Tract area 57,393sq km
Deposit type Epithermal vein, generic
Deposit age Cretaceous - Tertiary

Rationale

Explained by Bruce M. Gamble, Robert G. Eppinger, John W. Cady, Stanley E. Church, Byron R. Berger, Gregory T. Spanski
On the choice of deposit models
Models for epithermal vein deposits 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 in 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).
On the delineation of permissive tracts
This tract encompasses the Koyukuk Magmatic arc, which consists chiefly of Upper Jurassic(?) and Lower Cretaceous island arc andesitic volcanic rocks (Patton and others, 1989, Nokleberg and others, 1994). Two major suites of intrusions are present: (1) a 79‑89 Ma I-type tonalite to granite, typically granodiorite group in the east; and (2) a 99‑113 Ma S-type group in the west which consists of 2 distinct subtypes: (a) potassic syenites, monzonites, etc., and (b) ultrapotassic nepheline-bearing intrusions (Patton and others, 1989). Anomalous concentrations of As, Sb, Pb, Cu, Au, Ag, and W in stream sediment samples are sometimes clearly related to plutonic rocks, but often there is no evidence of an intrusion. Noteworthy is the “3 day slough” anomaly (Cu, Pb, Cd) in the Kateel River quadrangle, in an area of surficial cover.
Important examples of this type of deposit
No epithermal vein deposits are known in this tract.
On the numerical estimates made
Insufficient data exist to estimate the expected number of undiscovered 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.
Nokleberg, W.J., Moll-Stalcup, E.J., Miller, T.P., Brew, D.A., Grantz, Arthur, Reed, J.C., Jr., Plafker, George, Moore, T.E., Silva, S.R., and Patton, William W., Jr., 1994, Tectonostratigraphic terrane and overlap assemblage map of Alaska: U.S. Geological Survey Open-File Report 94-194, 45 manuscript p., scale 1:2,500,000.
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.
Patton, W.W., Jr., Box, S.E., Moll-Stalcup, E.J., and Miller, T.P., 1989, Geology of west-central Alaska: U.S. Geological Survey Open-File Report 89‑554, 41 p.

Geographic coverage

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