National mineral assessment tract AK-WC21 (Polymetallic vein)

Tract AK-WC21
Geographic region West Central, AK
Tract area 57,404sq km
Deposit type Polymetallic vein
Deposit age Cretaceous - Tertiary


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
Polymetallic vein deposits are associated with hypabyssal intrusions of nearly any age and a wide range of compositions, in sedimentary and metamorphic terranes (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, do not appear to fit into other similar categories.
On the delineation of permissive tracts
This tract encompasses the Koyukuk magmatic arc, which chiefly consists of Upper Jurassic(?) and Lower Cretaceous island arc andesitic volcanic rocks (Patton and others, 1989, Nokleberg and others, 1994). Two major suites of intrusive rocks are present: (1) a 79‑89 Ma I-type tonalite to granite in the east; and (2) a 99‑113 Ma S-type group in the west containing potassic syenites and monzonites, and ultrapotassic nepheline-bearing intrusive rocks (Patton and others, 1989). Stream sediment anomalies include As, Sb, Pb, Cu, Au, Ag, and W. Some of these anomalies are spatially associated with intrusions.
Important examples of this type of deposit
Polymetallic veins are known at Granite Mountain, Quartz Creek, at Hawk River in the Shungnak quadrangle, and in the Selawik area (Miller and Ferrians, 1968; Nokleberg and others, 1987).
On the numerical estimates made
Because of the lack of data for this tract, no attempt was made to estimate the number of undiscovered polymetallic vein deposits.
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, T.P., and Ferrians, O.J., 1968, Suggested areas for prospecting in the central Koyukuk River region, Alaska: U.S. Geological Survey Circular 570, 12 p.
Nokleberg, W.J., Bundtzen, T.K., Berg, H.C., Brew, D.A., Grybeck, Donald, Robinson, M.S., Smith, T.E., and Yeend, Warren, 1987. Significant metalliferous lode deposits and placer districts of Alaska: U.S. Geological Survey Bulletin 1786, 104 p.
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.
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.

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