National mineral assessment tract AK-WC25 (Zn-Pb skarn)

Tract AK-WC25
Geographic region West Central, AK
Tract area 11,026sq km
Deposit type Zn-Pb skarn
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
The presence of intermediate to felsic plutonic rocks intruding carbonate rocks suggest that this tract is permissive for Zn-Pb skarn deposits as described by Cox (1986).
On the delineation of permissive tracts
This tract encompasses all the Seward Peninsula plutons, exclusive of tin-granites. There are three distinct suites of plutonic rocks (Till and others, 1986): (1) 99-108 Ma alkaline, nepheline-bearing intrusions; (2) 90‑96 Ma sub-alkaline to alkaline plutons, typically monzonite, quartz monzonite, monzogranite, and granodiorite; and (3) 81‑83 Ma calc-alkaline plutons, typically quartz monzodiorite, granodiorite, and monzogranite. Metacarbonate rocks are widespread throughout the tract. Known mineral deposits (Gamble, 1988; Gamble and Till, 1988) include the Kugruk Fe-Cu skarn; Independence Ag-Pb polymetallic vein; Windy Creek porphyry Mo; Omilak East and Foster Ag-Pb polymetallic veins(?); Cu-rich polymetallic veins of the upper Niukluk River; and many deposits/occurrences, chiefly Ag-Pb-(Zn), of unknown type. Stream-sediment and heavy-mineral-concentrate samples from within the tract contain anomalous Ag, Cu, Pb, Zn, Mo, Sn, As, Sb, and rare Au.
Important examples of this type of deposit
No Zn-Pb skarn deposits are known in this tract.
On the numerical estimates made
Insufficient data exist to estimate the expected number of undiscovered Zn-Pb deposits for this tract.
Cox, D.P., 1986, Descriptive model of Zn-Pb skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 90.
Gamble, B.M., 1988, Non-placer mineral occurrences in the Solomon, Bendeleben, and parts of the Kotzebue quadrangles, western Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF 1838-B, 1 sheet, scale 1:250,000, 13 p.
Gamble, B.M., and Till, A.B., 1993, Maps showing metallic mineral resources of the Bendeleben and Solomon quadrangles, western Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF 1838-D, 3 sheets, scale 1:250,000, 22 p.
Till, A.B., Dumoulin, J.A., Gamble, B.M., Kaufman, D.S., and Carroll, P.I., 1986, Preliminary geologic maps and fossil data, Solomon, Bendeleben, and southern Kotzebue quadrangles, Seward Peninsula, Alaska: U.S. Geological Survey Open-File Report 86‑276, 62 p., scale 1:250,000.

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