National mineral assessment tract AK-WC18 (Polymetallic replacement)

Tract AK-WC18
Geographic region West Central, AK
Tract area 11,026sq km
Deposit type Polymetallic replacement
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
Numerous felsic to intermediate composition intrusions and metacarbonate rocks occur throughout the Seward Peninsula. Polymetallic vein deposits are locally present, such as the Billiken (Kugruk) Fe-Cu skarn suggesting that polymetallic replacement deposits as described by Morris (1986) are possible for this tract.
On the delineation of permissive tracts
This tract encompasses the Seward Peninsula plutons, exclusive of tin-granites. Three distinct suites of plutonic rocks are present (Till and others, 1986; Gamble, 1988, Gamble and Till, 1988): (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. All of these suites intrude units known to contain metacarbonate lithologies. Anomalous stream sediment and concentrate geochemistry includes: Ag, Cu, Pb, Zn, Mo, Sn, As, Sb, and rare Au.
Important examples of this type of deposit
No polymetallic replacement deposits are known.
On the numerical estimates made
Insufficient data exist to estimate the expected number of undiscovered polymetallic replacement deposits in this tract.
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.
Morris, H.T., 1986, Descriptive model of polymetallic replacement deposits, in Cox, D.P., and Singer, D.A., eds., 1986, Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 99.
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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