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Unnamed Prospect (ARDF - MF069; northeast side of Willoughby Island), Juneau District, Skagway-Hoonah-Angoon Borough, Alaska, USA

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The deposit is in marble of Devonian and Silurian age; mineralization followed emplacement of mafic dikes of probable Late Cretaceous or Tertiary age. The site is in Glacier Bay National Park and Preserve.
Location: The deposit is reported to be on the northeast side of Willoughby Island at an elevation of 450 feet. It is assumed to be about 0.5 mile southwest of Johnson Cove. Accuracy is uncertain. The site is about the same as locality 49 in Cobb (1972) and locality 95 in Kimball and others (1978). The deposit was not found by the U.S. Geological Survey in 1966 (MacKevett and others, 1971).
Geology: The northeastern part of Willoughby Island is underlain by massive and bedded limestone of Devonian and Silurian age, part of a major reefoid mass (Brew and others, 1978). Locally the marble is cut by mafic dikes of Late Cretaceous or Tertiary age. At this prospect, pyrite, loellingite (?) and chalcopyrite form massive replacement layers or lenses in marble. One such massive sulfide deposit was described as 5-feet-thick and traceable on strike for 15 feet (Reed, 1938). At least three other similar occurrences were reported nearby by Reed.
Workings: The deposit has not been found since Reed's visit in the 1930s (Reed, 1938). Workings are unknown, but there probably were shallow pits and trenches on the eight claims staked on the deposit before 1902.
Age: Late Cretaceous or younger.

Commodities (Major) - Cu; (Minor) - As?, Co?
Development Status: No
Deposit Model: Massive sulfide replacement in marble. Distal deposit related to subjacent intr

Mineral List



4 entries listed. 4 valid minerals.

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References

Brew, D.A., Johnson, B.R., Grybeck, D., Griscom, A., Barnes, D.F., Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources of the Glacier Bay National Monument Wilderness Study Area, Alaska: U.S. Geological Survey Open-File Report 78-494, 670 p., 7 sheets. Cobb, E.H., 1972, Metallic mineral resources map of the Mount Fairweather quadrangle, AK: U.S. Geological Survey Miscellaneous Field Study Map MF-436, 1 sheet, scale 1:250,000. Kimball, A.L., Still, J.C., and Rataj, J.L., 1978, Mineral resources, in Brew, D. A., and others, Mineral resources of the Glacier Bay National Monument wilderness study area, Alaska: U.S. Geological Survey Open-File Report 78-494, p. C1-C375. MacKevett, E.M., Jr., Brew, D.A., Hawley, C.C., Huff, L.C., and Smith, J.G., 1971, Mineral resources of Glacier Bay National Monument, Alaska: U.S. Geological Survey Professional Paper 632, 90 p., 12 plates, scale 1:250,000. Reed, J.C., 1938, Some mineral deposits of Glacier Bay and vicinity, Alaska: Economic Geology, v. 33, p. 52-80.

 
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