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
Slightly metamorphosed Paleozoic clastic sedimentary and minor volcanic rocks on Prince of Wales Island contain sparse thin lenses of sulfide minerals. These units are permissive for Besshi massive sulfide deposits (Cox, 1986).
On the delineation of permissive tracts
This tract is delineated by the outcrop areas of Silurian turbidite and minor volcanic rocks, and by favorable geochemical data, on Prince of Wales Island (Brew and others, 1991; Brew, 1993).
Important example of deposit type:
The McCullogh deposit may be an example of a Besshi massive sulfide (Brew and others, 1991).
On the numerical estimates made
Permissive rock types and associations and appropriate geochemical patterns were the main basis for the estimates. The team estimated the minimum number of undiscovered Besshi massive sulfide deposits, consistent with the grade and tonnage model of Singer (1986), to be:
Percentile 90 50 10 5 1
Estimated number of deposits 0 0 0 0 1
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., 1986, Descriptive model of Besshi massive sulfide, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 136.
Singer, D.A., 1986, Grade and tonnage model of Besshi massive sulfide deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 136-138.