Unnamed Occurrence (ARDF - MF055; west of Rendu Inlet), Juneau District, Skagway-Hoonah-Angoon Borough, Alaska, USA
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Location: The occurrence is at an elevation of about 2000 feet on the top of the ridge between Rendu Inlet and Glacier Bay about 0.7 miles northwest of VABM Rendu. The location is accurate within a few hundred feet. The location is number 39 of MacKevett and others (1971), number 32 of Cobb (1972), and number 44 of Kimball and others (1978).
Geology: Poddy magnetite-rich skarn deposits occur in limestone-marble units of Devonian-Silurian age at or near medium-coarse-grained intrusions of hornblende quartz diorite of Cretaceous age (Rossman, 1963 B 1121-K; Brew and others, 1978). Calc-silicate rich phases of the skarn consist of tactite composed of grossularite-rich garnet and epidote accompanied by quartz, chlorite, and calcite. Magnetite and pyrite locally form poddy masses. The area is poorly exposed and other deposits--inferred from magnetic anomalies--could be buried by overburden. Based on three samples reported by MacKevett and others, 1971 (locality 39, table 9) the iron content of the skarn ranges from about 5 percent to more than 10 percent. No precious metals were detected and copper and other valuable metals are present at near background levels. Titanium values are low, so magnetite is inferred to be an essentially pure phase.
Workings: There are no workings. MacKevett and others (1971) collected samples and ran magnetic traverses in the occurrence area. Magnetic anomalies of as much as 5500 gammas are attributed to concealed masses of magnetite skarn.
Age: Cretaceous.
Commodities (Major) - Fe
Development Status: No
Deposit Model: Pyrite-magnetite (Fe) skarn (Cox and Singer, 1986; model 18d).
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. Rossman, Darwin, 1963, Geology of the eastern part of the Mount Fairweather quadrangle, Glacier Bay, Alaska: U.S. Geological Survey Bulletin 1121-K, p. K1-K57.
