National mineral assessment tract AK-BR04 (Low-sulfide Au-quartz veins)

Tract AK-BR04
Geographic region Brooks Range, AK
Tract area 35,958sq km
Deposit type Low-sulfide Au-quartz veins
Deposit age Cretaceous

Estimates

Confidence Number of
deposits
90% 1
50% 2
10% 5
5% 10
1% 15

Estimators: Schmidt, Kelley, Cady, Berger, Kilburn, Spanski

Rationale

Explained by Jeanine M. Schmidt, Karen D. Kelley, Richard I. Grauch, Byron R. Berger, John W. Cady, Gregory T. Spanski, James E. Kilburn.
On the choice of deposit models
Some low sulfide gold-quartz veins occur, especially in the Wiseman-Chandalar area; placer gold deposits are common, and the geologic setting and host rocks are permissive for additional deposits.
On the delineation of permissive tracts
This tract includes areas of Proterozoic(?) to Paleozoic mixed schists, including many predominately pelitic schists, and lesser quartzitic, mafic, calcareous, and carbonaceous schists.
Important examples of this type of deposit
Low sulfide gold-quartz veins occur in the Wiseman and Chandalar districts (Dillon, 1982; Nokleberg and others, 1987). The Little Squaw (Ashworth, 1983) and Mikado are some of the larger examples of low-sulfide Au-quartz vein deposits.
On the numerical estimates made
Numerous placer gold deposits and some lode gold deposits in the tract suggest the presence of additional lode deposits. The minimum number of undiscovered low sulfide gold-quartz vein deposits of median grade and tonnage expected to occur in the tract is:
Percentile 90 50 10 5 1
Estimated number of deposits 1 2 5 10 15
References
Ashworth, Kate, 1983, Genesis of gold deposits of Little Squaw Mine, Chandalar District, Alaska: Bellingham, Washington, Western Washington University M.S. Thesis, 64 p.
Dillon, J.T., 1982, Source of lode- and placer-gold deposits of the Chandalar and upper Koyukuk districts, Alaska: Alaska Division of Geological and Geophysical Surveys Open-File Report 158, 22 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.

Geographic coverage

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