National mineral assessment tract AK-SE12 (Polymetallic replacement)

Tract AK-SE12
Geographic region Southeastern AK
Tract area 594sq km
Deposit type Polymetallic replacement
Deposit age Cretaceous - Tertiary


Confidence Number of
90% 0
50% 0
10% 0
5% 1
1% 3

Estimators: Brew, Taylor, Jachens, Koch, Grybeck, Drinkwater, Barnes, Drew


Explained by David A. Brew, Cliff D. Taylor, Robert C. Jachens, Richard D. Koch, Donald Grybeck, James L. Drinkwater, David F. Barnes, and Larry J. Drew
On the choice of deposit models
In southeastern Alaska, small polymetallic replacement deposits are possible where Paleozoic carbonate and some clastic rocks are intruded by Cretaceous and Tertiary mesozonal to epizonal subduction- and post-subduction-related calcalkaline granitic plutons and dikes.
On the delineation of permissive tracts
Tract boundaries were delineated by the combination of Paleozoic carbonate rocks and Cretaceous and Cretaceous and Tertiary intrusive rocks (Brew and others, 1991). These criteria are the regional metallogenic factors cited by Brew (1993).
Important example of deposit type
Coronation Island is a Pb-Ag polymetallic replacement deposit in Silurian limestone and marble intruded by Tertiary(?) diorite (Twenhofel and others, 1949).
On the numerical estimates made
Permissive rock types and associations and appropriate geochemical patterns (Brew and others, 1991) were the main basis for the estimates. The minimum number of undiscovered polymetallic replacement deposits, consistent with the grade and tonnage model of Mosier and others (1986), estimated to occur in this tract is:
Percentile 90 50 10 5 1
Estimated number of deposits 0 0 0 1 3
Brew, D.A., 1993, Regional geologic setting of mineral resources in southeastern Alaska, in Godwin, L.H., and Smith, B. D., eds., Economic mineral resources of the Annette Islands Reserve, Alaska: U.S. Dept. of the Interior, Bureau of Indian Affairs, Division of Energy and Mineral Resources Publication, p.13-20.
Brew, D.A., Drew, L.J., Schmidt, L.M., Root, D.H., and Huber, D.F, 1991, Undiscovered locatable mineral resources of the Tongass National Forest and adjacent areas, southeastern Alaska: U.S. Geological Survey Open-File Report 91-10, 370 p., 15 maps at 1:250,000, 1 map at 1:500,000, 11 figs.
Mosier, D.L., Morris, H.T., and Singer, D.A., 1986, Grade and tonnage model of polymetallic replacement deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 101-104.
Twenhofel, W.S., Reed, J.C., and Gates, G.O., 1949, Some mineral investigations in southeastern Alaska: U.S. Geological Survey Bulletin 963-A, 45 p.

Geographic coverage

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