Unnamed Occurrence (ARDF - MF086; between Curtis Hills and Bruce Hills), Juneau District, Skagway-Hoonah-Angoon Borough, Alaska, USA
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Location: Poorly-defined northwest-trending area between the Curtis Hills and Bruce Hills. It is north of Plateau Glacier and south of Burroughs Glacier. The area is approximately 2 to 3 miles long and 1 mile wide. The coordinates are for the approximate midpoint of the area. The site is location number 73 of Kimball and others (1978) and number 23 of MacKevett and others (1971).
Geology: The area is underlain by schist, hornfels, and marble derived mainly from sedimentary rocks of Paleozoic age. The sedimentary rocks were metamorphosed by the intrusion of a granitic batholith of Cretaceous age (Brew and others, 1978). The metasedimentary rocks are cut by mafic dikes and lie between the granitic Curtis and Bruce Hills. The area has recently been denuded by melting of the Plateau and Burroughs Glaciers. The mineral occurrences of the area are mainly low-sulfide quartz-calcite-ankerite veins that formed on the contacts of mafic dikes that cut the metasedimentary rodk. Grab samples of various occurrences contained as much as 300 ppm lead, 700 ppm copper, and 15 ppm silver (MacKevett and others, 1971, location 23, table 9; Kimball and others, 1978, location 73, p. C316-317). Other elements, including chromium, iron, and titanium, are locally geochemically anomalous in the veins; these elements possibly were contained in or contributed to the veins by the mafic dikes. Titanium content exceeded 1 percent in one sample and was 1 percent in several others. Veins of the area could be distal structures to a buried contact zone between granite and the metasedimentary rocks.
Workings: No workings. MacKevett and others (1971, location 23) found as much as 700 ppm copper and chromium and 1 percent titanium in iron-stained vein zones along mafic dikes. Kimball and others (1978, p. C316-317) reported 300 ppm lead and 15 ppm silver in a 0.3 foot thick quartz-calcite vein and more than 1 percent titanium in one wider (5 ft.) chip sample.
Age: Cretaceous or younger.
Alteration: Propylitic (?).
Commodities (Major) - Ag, Cu, Pb; (Minor) - Cr, Fe, Ti
Development Status: None
Deposit Model: Distal low-sulfide quartz-carbonate veins: Possible trace element contribution f
3 entries listed. 3 valid minerals.
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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. 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.