National mineral assessment tract AK-SE05 (Sierran Kuroko mass. sulf.)

Tract AK-SE05
Geographic region Southeastern AK
Tract area 797sq km
Deposit type Sierran Kuroko mass. sulf.
Deposit age Late Triassic

Estimates

Confidence Number of
deposits
90% 1
50% 3
10% 7
5% 9
1% 13

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
Upper Triassic and inferred Upper Triassic intermediate, felsic, and some mafic volcanic rocks occur in heterogeneous and locally metamorphosed units. Local altered areas are present. Geochemical patterns and mineral occurrences suggest Sierran kuroko massive sulfide deposits (Singer, 1992).
On the delineation of permissive tracts
This three-part tract is delineated mainly by the distribution of volcanic and metavolcanic units, and the distribution of known deposits and occurrences (Brew and others, 1991; Brew, 1993).
Important examples of this type of deposit
Mount Henry Clay(?), Orange Point in Glacier Bay National Park, Greens Creek, Sumdum Glacier in Tracy Arm-Fords Terror Wilderness Area, and Castle Island(?) are all known or inferred to be Sierran kuroko massive sulfide deposits.
On the numerical estimates made
Permissive rock types and associations, appropriate geochemical patterns, and the occurrence of known deposits were the main basis for the estimates. The mineral resource team estimated the minimum number of undiscovered deposits, consistent with the grade and tonnage model of Singer (1992), to be:
Percentile 90 50 10 5 1
Estimated number of deposits 1 3 7 9 13
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.
Singer, D.A., 1992, Grade and tonnage model of Sierran kuroko massive sulfide deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 2004, p. 29-32.

Geographic coverage

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