National mineral assessment tract AK-SE20 (Porphyry Cu-Mo)

Tract AK-SE20
Geographic region Southeastern AK
Tract area 9,382sq km
Deposit type Porphyry Cu-Mo
Deposit age Tertiary

Estimates

Confidence Number of
deposits
90% 0
50% 0
10% 1
5% 4
1% 5

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

Rationale

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
A few porphyry Cu (Cox, 1986a), porphyry Cu-Mo (Cox, 1986b), and porphyry Cu, skarn related (Cox, 1986c) deposits are known in the Cretaceous and Tertiary calcalkaline granitic plutons and dikes in southeastern Alaska.
On the delineation of permissive tracts
Tract boundaries were delineated by the combination of Paleozoic carbonate rocks and Tertiary intrusive rocks (Brew and others, 1991; Brew, 1993). This multi-part tract includes most of the Tertiary subduction- and post-subduction-related calcalkaline granitic plutons in southeastern Alaska, and the tract boundaries are those of the areas known or interpreted to be underlain by those rocks. The tract also includes some similar plutons of middle Cretaceous age. In detail, Paleozoic clastic and carbonate rocks are intruded by mesozonal to epizonal Cretaceous and Tertiary granitic dikes, with local fracturing and alteration.
Important examples of this type of deposit
The most important known porphyry Cu deposit in southeastern Alaska is the Margerie Glacier deposit, in Glacier Bay National Park. Minnesota Ridge, in Glacier Bay National Park, is the best example of a porphyry Cu, skarn related, deposit. Muir Inlet Nunatak, Bruce Hills, and Threesome Mountain in Glacier Bay National Park; and Shakan Bay on Prince of Wales Island are porphyry Cu-Mo deposits.
On the numerical estimates made
Permissive rock types and appropriate geochemical patterns were the main basis for estimating the number of undiscovered deposits. The minimum number of undiscovered porphyry Cu; porphyry Cu, skarn related; and porphyry Cu-Mo deposits, consistent with the grade and tonnage models of Singer and others (1986b), Singer and others (1986a), and Singer (1986), respectively, is estimated to be:
Percentile 90 50 10 5 1
Estimated number of deposits 0 0 1 4 5
References
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.
Cox, D.P., 1986a, Descriptive model of porphyry Cu, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 76.
Cox, D.P., 1986b, Descriptive model of porphyry Cu-Mo, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 115.
Cox, D.P., 1986c, Descriptive model of porphyry Cu, skarn-related deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 82.
Singer, D.A., 1986, Grade and tonnage model of porphyry Cu, skarn-related deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 82-85.
Singer, D.A., Cox, D.P., and Mosier, D.L., 1986a, Grade and tonnage model of porphyry Cu-Mo deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 116-119.
Singer, D.A., Mosier, D.L., and Cox, D.P., 1986b, Grade and tonnage model of porphyry Cu, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 77-81.

Geographic coverage

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