National mineral assessment tract AK-SE11 (Cyprus massive sulfide)

Tract AK-SE11
Geographic region Southeastern AK
Tract area 1,374sq km
Deposit type Cyprus massive sulfide
Deposit age Triassic


Confidence Number of
90% 0
50% 0
10% 0
5% 0
1% 2

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
Triassic greenstones, derived from pillow basalts of the Wrangellia terrane, contain local concentrations of Cu-sulfide minerals interpreted to be Cyprus massive sulfide deposits, as described by Singer (1986). Except for the part of the tract that is in the Coast Mountains, any connection with ophiolitic complexes is tenuous.
On the delineation of permissive tracts
This tract was delineated mainly by the distribution of Triassic meta-pillow basalts and by favorable geochemical patterns (Brew and others, 1991; Brew, 1993).
Important examples of this type of deposit
The Northern Copper Co. deposit on Kupreanof Island is a Cyprus massive sulfide (Brew and others, 1991).
On the numerical estimates made
Permissive rock types and associations, a few known deposits, and appropriate geochemical patterns were the main basis for the estimates. The team estimated the minimum number of undiscovered deposits, consistent with the grade and tonnage model of Singer and Mosier (1986), to be:
Percentile 90 50 10 5 1
Estimated number of deposits 0 0 0 0 2
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.
Singer, D.A.., 1986, Descriptive model of Cyprus massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 131.
Singer, D.A., and Mosier, D.L., 1986, Grade and tonnage model of Cyprus massive sulfide deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 131-135.

Geographic coverage

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