|Quadrangle map, 1:250,000-scale||SD|
|Quadrangle map, 1:63,360-scale||C-5|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The mineralization and workings of what is commonly called the Point Astley prospect occur discontinuously for about 1,500 feet near the shoreline southeast of Point Astley. The center of the workings is near the mine shown on the USGS 1:63,360 scale topographic map about a mile southeast of Point Astley. The location is accurate. The location of the workings and the mineral occurrences are shown on Figures 24 and 25 of Kimble and others (1984).|
The Point Astley prospect has been known since about 1900 (Spencer, 1906). It was intermittently explored by a succession of companies through 1984 (for details, see Spencer, 1906; Buddington, 1925; Herreid, 1962; Race, 1962; Kimble and others, 1984; Redman, 1988). There are two centers of mineralization separated by 700 feet, but much of the area is heavily vegetated and the continuity or extension of the known mineralization is uncertain. The prospect has been developed by 4, now-flooded shafts, one of which probably has a crosscut at depth, and 2 short adits. All of the workings date from before 1925. There has been no production but there was a test shipment to a smelter in about 1925.
The deposit consists of disseminated sulfides and small lenses of massive sulfides oriented along the foliation of the host rock. The massive sulfide lenses are no more than 3 feet long and 1 foot thick. The main sulfides are pyrite and sphalerite with minor galena and chalcopyrite. Locally in the richer portions of the deposit, bornite, chalcocite, covellite and digenite occur; native silver is reported. The host rock is green chloritic phyllite and black slaty phyllite, part of the Cretaceous greenschist unit of Brew and Grybeck (1984). Locally the sulfides have been remobilized and concentrated at the noses of small folds in the metamorphic rocks.
The northwest zone of mineralization has been explored by two shafts and a short the adit. Kimble and others (1984) sampled a 10-foot section of the mineralized rocks along the shoreline. A sample contained 0.48% copper, 0.11 percent lead, 1.65 percent zinc, and 0.2 ounces of silver per ton. A select sample from a lens of pyrite and sphalerite about 1.1 foot thick contained 0.44 per cent copper, 0.31 percent lead, 9.0 percent zinc, 0.17 ounce of gold per ton, and 1.45 ounces of silver per ton.The other zone of mineralization is about 700 feet to the southeast near the shoreline. It has been explored by a shaft and two adits, only one of which was accessible to Kimble and others (1984). They collected a 30-foot sample that contained 0.07 percent copper, 1.72 percent zinc, and 0.18 percent silver. (The 1984 work by Kimble and others was restricted to the mineralization that could be seen then; few of the workings were accessible and they may have exposed higher grade mineralization.)
|Geologic map unit||(-133.634545382727, 57.7087529208685)|
|Mineral deposit model||Metamorphosed, volcanogenic massive sulfide deposit?|
|Age of mineralization||Unclear. The primary mineralization was remobilized during the Cretaceous event that formed the metamorphic host rocks. The age of the protolith is uncertain, as is whether the primary mineralization was syngenetic or epigenetic.|
|Workings or exploration||The prospect has been developed by 4, now-flooded shafts, one of which probably has a crosscut at depth, and 2 short adits. All of the workings date from before 1925. A succession of companies have looked at or owned the property into the 1980s but there probably has been no substantial exploration since the 1920s.|
|Indication of production||None|
|Production notes||No recorded production; there was a test shipment to a smelter in 1925.|
Additional commentsThe prospect is in the Tracy Arm-Fords Terror Wilderness Area which is closed to mineral exploration and mining.
Berg, H.C., and Cobb, E.H., 1967, Metalliferous lode deposits of Alaska: U.S. Geological Survey Bulletin 1246, 254 p.
Brew, D.A., and Grybeck, Donald, 1984, Geology of the Tracy Arm-Fords Terror wilderness study area and vicinity, Alaska, in U.S. Geological Survey and U.S. Bureau of Mines, Mineral resources of the Tracy Arm-Fords Terror wilderness study area and vicinity, Alaska: U.S. Geological Survey Bulletin, 1525, p. 19-52.
Buddington, A.F., 1925, Mineral investigations in southeastern Alaska: U.S. Geological Survey Bulletin 773-B, p. 71-139.
Buddington, A.F., and Chapin, Theodore, 1929, Geology and mineral deposits of southeastern Alaska: U.S. Geological Survey Bulletin 800, 398 p.
Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Sumdum and Taku River quadrangles, Alaska: U.S. Geological Survey Open-File Report 78-698, 64 p.
Eakins, G.R., 1975, Uranium investigations in southeastern Alaska: Alaska Division of Geological and Geophysical Surveys Geologic Report 44, 62 p.
Herreid, G.H., 1962, Preliminary report on geologic mapping in the Coast Range mineral belt: Alaska Division of Mines and Minerals, Geologic Report 1, 33 p.
Houston, J.R., Bates, R.G., Velikanje, R.S., and Wedow, Helmuth, Jr., 1958, Reconnaissance for radioactive deposits in southeastern Alaska, 1952: U.S. Geological Survey Bulletin 1058-A, p. 1-31.
Kimble, A.L., Still, J.C., and Rataj, J.L., 1984, Mineral deposits and occurrences in the Tracy Arm-Fords Terror wilderness study area and vicinity, Alaska, in U.S. Geological Survey and U.S. Bureau of Mines, Mineral resources of the Tracy Arm-Fords Terror wilderness study area and vicinity, Alaska: U.S. Geological Survey Bulletin 1525, p. 105-210.
MacKevett, E.M., Jr., and Blake, M.C., Jr., 1964, Geology of the Sumdum copper-zinc prospect, southeastern Alaska: U.S. Geological Survey Bulletin 1108-E, p. E 1-E31.
Martin, G.C., 1920, The Alaska mining industry in 1918: U.S. Geological Survey Bulletin 712-A, p. 1-52.
Race, W.H., 1962, Preliminary geochemical investigation, Tracy and Endicott Arm area: Alaska Division of Mines and Minerals Mineral Investigation 115-3, 11 p.
Redman, Earl, 1988, History of the mines and miners in the Juneau gold belt: Juneau, Alaska, privately printed, 294 p.
Spencer, A.C., 1906, The Juneau Gold Belt, Alaska; and A Reconnaissance of Admiralty Island, Alaska: U.S. Geological Survey Bulletin 287, 161 p.
U.S. Geological Survey and U.S. Bureau of Mines, 1984, Mineral resources of the Tracy Arm-Fords Terror wilderness study area and vicinity, Alaska: U.S. Geological Survey Bulletin 1525, 308 p.
Wedow, Helmuth, White, M. G., and Moxham, R. M., 1952, Interim report on an appraisal of the uranium possibilities of Alaska: U.S. Geological Survey Open-File Report 52-165, 124 p.
|Reporters||Donald Grybeck (U.S. Geological Survey)|
|Last report date||10/8/2004|