National mineral assessment tract AK-WC14 (Porphyry Cu, BC-Ak type)

Tract AK-WC14
Geographic region West Central, AK
Tract area 57,404sq km
Deposit type Porphyry Cu, BC-Ak type
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
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 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). In the west, the Peace River porphyry Mo occurrence is associated with the Granite Mountain pluton. In the east are Black Creek, a possible porphyry Cu; Dakli Cu-rich occurrences near the Zane Hills pluton; an occurrence of Mo-bearing quartz veins, also at Dakli; and an unnamed Mo occurrence of unknown type.
On the delineation of permissive tracts
This tract is delineated by the occurrence of intrusive rocks of the appropriate compositions, a known porphyry Mo occurrence, several Cu and (or) Mo occurrences of unknown type, and stream sediment anomalies of As, Sb, Pb, Cu, Au, Ag, and W, some of which are clearly related to intrusions.
Important examples of this type of deposit
The Dakli and Black Creek deposits are examples of porphyry copper occurrences in this tract.
On the numerical estimates made
Insufficient data exist to support estimating the number of undiscovered porphyry copper deposits.
References
Miller T.P., and Elliott, R.L., 1969, Metalliferous deposits near Granite Mountain, eastern Seward Peninsula, Alaska: U.S. Geological Survey Circular 614, 19 p.
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., 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.

Geographic coverage

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