National mineral assessment tract AK-WC09 (Low-sulfide Au-quartz veins)

Tract AK-WC09
Geographic region West Central, AK
Tract area 37,880sq km
Deposit type Low-sulfide Au-quartz veins
Deposit age Cretaceous - Tertiary

Estimates

Confidence Number of
deposits
90% 1
50% 2
10% 3
5% 5
1% 10

Estimators: Gamble, Church, Cady, Eppinger, Berger, Spanski

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
Low-sulfide gold-quartz veins (Berger, 1986) are known to occur in this tract, and additional deposits are permissive. A large part of the Seward Peninsula is underlain by greenschist (after blueschist) facies rocks containing numerous low-sulfide gold-quartz vein deposits and occurrences (Gamble and others, 1985), and numerous worldclass Au-placer deposits. Local As, Sb, Au and other geochemical anomalies in stream sediment and heavy-mineral concentrate samples are scattered throughout the area.
On the delineation of permissive tracts
The favorable geologic unit defining this tract includes all of the Nome Group exclusive of high-grade (amphibolite and above) parts, which are confined to the mountain ranges. The Nome Group consists chiefly of pelitic schist, calc-schist, pure and impure marble, graphitic quartzite and quartz-mica schist, and mafic schist (Till and others, 1986). The metamorphic grade within the tract is blueschist that has a pronounced greenschist retrograde overprint. Anomalous elements in stream sediment and panned concentrate samples are chiefly As and Sb, and local Au, W, Bi.
Important examples of this type of deposit
Numerous low-sulfide gold-quartz veins and gold placers are present. The Big Hurrah mine produced about 27,000 ounces, chiefly between 1903 and 1907 (Read and Meinert, 1986).
On the numerical estimates made
The estimated minimum number of undiscovered low-sulfide Au-quartz vein deposits consistent with the tonnage and grade model of Bliss (1986) is:
Percentile 90 50 10 5 1
Estimated number of deposits 1 2 3 5 10
References
Berger, B.R., 1986c, Descriptive model of low-sulfide Au-quartz veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 239.
Bliss, J.D., 1986, Grade and tonnage model of low-sulfide Au-quartz veins, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 239‑243.
Gamble, B.M., Ashley, R.P., and Pickthorn, W.J., 1985, Preliminary study of lode gold deposits, Seward Peninsula, in Bartsch-Winkler, Susan, editor, The United States Geological Survey in Alaska, Accomplishments during 1984: U.S. Geological Circular 967, p. 27‑29.
Read, J.J., and Meinert, L.D., 1986, Gold-bearing quartz vein mineralization at the Big Hurrah Mine, Seward Peninsula, Alaska: Economic Geology, v. 81, no.7, p. 1760‑1774.
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.

Geographic coverage

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