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 this composite tract, Late Proterozoic and 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, with local development of extensive thermally altered areas. Many Cu skarn deposits are recognized on the basis of their mineralogy, and association with carbonates adjacent to intrusive contacts. The area is permissive for Cu skarn deposits as described Cox and Theodore (1986).
On the delineation of permissive tracts
Tract boundaries were delineated by the combination of Paleozoic carbonate rocks and Cretaceous and Tertiary intrusive rocks, together with the known distribution of Cu skarns. This tract comprises several tracts that were defined by Brew and others (1991) and whose regional relations were summarized by Brew (1993).
Important examples of this type of deposit
Many Cu skarn deposits (Mt. Andrew, Stevenstown, Mamie, etc.) occur on the Kasaan Peninsula and in the vicinity of the Jumbo Mine on Hetta Inlet, both localities are on Prince of Wales Island. The Alaska Chief deposit is in Glacier Bay National Park.
On the numerical estimates made
Permissive rock types and associations, the many known deposits of this type, and appropriate geochemical patterns were the main basis for the estimates. The minimum number of undiscovered Cu skarn deposits, consistent with the grade and tonnage model of Jones and Menzie (1986), is estimated to be:
Percentile 90 50 10 5 1
Estimated number of deposits 1 4 6 7 8
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., and Theodore, T.G., 1986, Descriptive model of Cu skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p 86.
Jones, G.M., and Menzie, W.D., 1986, Grade and tonnage model of Cu skarn deposits, in Cox, D.P., and Singer, D.A., eds., Mineral deposit models: U.S. Geological Survey Bulletin 1693, p. 86-89.