|Quadrangle map, 1:250,000-scale||MF|
|Quadrangle map, 1:63,360-scale||B-2|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This placer deposit is at the terminus of Brady Glacier at Taylor Bay; it extends southerly onto broadly-exposed tide flats. The coordinate location is the approximate center of the glacier front as drawn on the Mt. Fairweather B-2 quadrangle, which was mapped from aerial photographs taken in 1948. The placer deposits occur in an arcuate zone about 3 miles long south of the glacier. Small, transient placer deposits could occur throughout the broad tide flats south of the terminus of the glacier.|
Brady Glacier occupies a major north-northwest-aligned boundary between Paleozoic strata intruded by granitic rocks of Cretaceous age on the east and rocks of Cretaceous and Tertiary age to the west (Brew and others, 1978). The Brady Glacier nickel-copper deposit (MF003) is in the western province and within the drainage basin of the glacier. Glacial erosion of the sulfide and oxide deposits of the Crillon-LaPerouse layered mafic intrusion, the host of the Brady Glacier deposit, would furnish titanium and PGEs to the glacial outflow. Gold deposits similar to the LeRoy mine (MF022) could exist in the Cretaceous rocks in the eastern terrane.
Gold, in extremely fine-grained form, ilmenite, PGEs, and zircon locally are concentrated in transient placers at the front of the glacier.Placer samples collected from the outwash fan by the U.S. Bureau of Mines contained as much as 0.15 ppm gold (Kimball and others, 1978) and 6.15 percent titanium (Foley and others, 1995).
|Geologic map unit||(-136.611860694966, 58.349633271752)|
|Mineral deposit model||Placer: Low-grade glacial outwash reworked on tidal flat.|
|Age of mineralization||Holocene.|
|Workings or exploration||
Small, transient placers on the outwash plain were worked during the early years of the twentieth century (Rossman, 1963, B 1121-K, p. K51-52). The U.S. Bureau of Mines (Kimball and others, 1978, p. C126) detected gold content in stream-sediment-type samples of up to 0.15 ppm (0.004 oz/ton) along with traces of silver, copper, cobalt, and nickel. The gold is extremely fine-grained, but local concentrations could have been rich. The gold is so fine that recovery is difficult.Foley and others (1995, sample no. 319) determined that ilmenite (titanium) and zircon (zirconium) were present in one sample in anomalous amounts. The sample contained 4.95 percent and 6.15 percent titanium, respectively, in a head split and a spiral concentrate. Zirconium was reported as 720 ppm in the head split and 1084 ppm in the spiral concentrate.
|Indication of production||Yes; small|
Additional commentsThe placer sites are in Glacier Bay National Park and Preserve.
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.
Foley, J.Y., La Berge, R.D., Grosz, A.E., Oliver, F.S., and Hirt, W.C., 1995, Onshore titanium and related heavy-mineral investigations in the eastern Gulf of Alaska region, southern Alaska: U.S. Bureau of Mines Open-File Report 10-95, 125 p.
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.
|Reporters||C.C. Hawley (Hawley Resource Group)|
|Last report date||4/15/1999|