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Red Bluff Bay Prospects, Chicagof District, Sitka Borough, Alaska, USA

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The complex is now in the South Baranof Wilderness Area which is closed to mineral exploration and mining. MAS number: 0021160001.
Location: The Red Bluff Bay mafic-ultramafic complex forms an elliptical outcrop about 4 miles long that is exposed at the mouth and north of the mouth of Red Bluff Bay. The coordinates are at about the center of the body which is near the center of section 9, T. 58 S., R. 68 E.
Geology: The Red Bluff Bay ultramafic complex forms an elliptical outcrop about 4 miles long that consists mainly of partly serpentinized, dunite and wehrlite in gradational contact (Guild and Balsley, 1942; Holdsworth and Williams, 1953; Himmelberg and Loney, 1995). Irregular masses of clinopyroxenite in sharp contact with the dunite and wehrlite make up a large part of the northwest portion of the complex. The complex is surrounded by greenschist and phyllite with minor amphibolite of the Kelp Bay Group of Late Jurassic and Early Cretaceous age (Loney and others, 1975). There is no indication of contact metamorphism around the complex and it may be largely in fault contact with the surrounding metamorphic rocks. The complex is layered but it is not zoned; Himmelberg and Loney (1995) interpret it as 'Alaskan-type' ultramafic complex. Chromite was first recognized in the complex in 1933 and 28 claims were staked in 1935 (Smith, 1937 [B 880-A]). The Alaska Juneau Mining Company held the claims until 1940. Subsequently, several government agencies examined the complex but there has been little or no exploration by industry since WWII. Eight mineralized zones up to 30 feet wide and several hundred feet long have been identified in the dunite. These zones contain disseminated chromite and lenses of chromite up to 3 feet wide and 40 feet long (Guild and Balsley, 1942; Bittenbender and others, 1999). Guild and Balsley identified an inferred resource of 30,000 tons of material in the complex with an average grade of 12 percent Cr2O3. There is no indication that the ultramafic rocks have significant concentrations of copper, nickel, or platinum-group elements. The bodies are small and the chrome to iron ratio is low. The deposit is considered too small and too low grade to be a viable resource (Bittenbender and others, 1999). In addition, the complex is now in the South Baranof Wilderness Area which is closed to mineral exploration and mining.
Workings: Chromite was first recognized in the complex in 1933 and 28 claims were staked in 1935 (Smith, 1937). The Alaska Juneau Mining Company held the claims until 1940. Subsequently, several government agencies examined the complex but there has been little or no exploration by industry since WWII.
Age: If the complex is an Alaskan-type body as proposed by Himmelberg and Loney (1995), it is probably about 110 Ma.
Alteration: The dunite and wehrlite are largely altered to serpentine.
Reserves: Eight mineralized zones up to 30 feet wide and several hundred feet long have been identified in the dunite. These zones contain disseminated chromite and lenses of chromite up to 3 feet wide and 40 feet long (Guild and Balsley, 1942; Bittenbender and others, 1999). Guild and Balsley identified an inferred resource of 30,000 tons of material in the complex with an average grade of 12 percent Cr2O3. There is no indication that the ultramafic rocks have significant concentrations of copper, nickel, or platinum-group elements. The bodies are small and the chrome to iron ratio is low. The deposit is considered too small and too low grade to be a viable resource (Bittenbender and others, 1999). In addition, the complex is now in the South Baranof Wilderness Area which is closed to mineral exploration and mining.

Commodities (Major) - Cr
Development Status: None
Deposit Model: Chromite in Alaska-type ultramafic complex.

Mineral List



1 entry listed. 1 valid mineral.

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References

Bittenbender, P., Still, J.C., Maas, K., and McDonald, M., Jr., 1999, Mineral resources of the Chichagof and Baranof Islands area, southeast Alaska: Bureau of Land Management, BLM-Alaska Technical Report 19, 222 p. Cobb, E.H., 1972, Metallic mineral resources map of the Port Alexander quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-464, 1 sheet, scale 1:250,000. Cobb, E.H., 1978, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Port Alexander quadrangle: U.S. Geological Survey Open-File Report 78-787, 33 p. Guild, P.W., and Balsley, J.R., Jr., 1942, Chromite deposits of Red Bluff Bay and vicinity, Baranof Island, Alaska: U.S. Geological Survey Bulletin 936-G, p. 171-187. Himmelberg, G.R., and Loney, R.A., 1995, Characteristics and petrogenesis of Alaskan-type ultramafic-mafic intrustions, southeastern Alaska: U.S. Geological Survey Professional Paper 1564, 47 p. Holdsworth, P.R., and Williams, J.A., 1953, Magnetic investigations of chromite deposits at Red Bluff Bay, Baranof Island: Alaska Territorial Department of Mines, Mineral Investigation 116-1, 2 p. Kennedy, G.C., and Walton, M.S., Jr., 1946, Geology and associated mineral deposits of some ultrabasic rock bodies in southeastern Alaska: U.S. Geological Survey Bulletin 947-D, p. 65-84. Loney, R.A., Brew, D.A., Muffler, L.J. B., and Pomeroy, J.S., 1975, Reconnaissance geology of Chichagof, Baranof, and Kruzof Islands, southeastern Alaska: U.S. Geological Survey Professional Paper 792, 105 p. Nelson, G.E., 1942?, Chromite at Red Bluff Bay: Unpublished report, 4 p. (On file at the Juneau Mineral Center, U.S. Bureau of Land Management, Juneau, Alaska.) Smith, P.S., 1937, Mineral industry of Alaska in 1935: U.S. Geological Survey Bulletin 880-A, p. 1-95. Smith, P.S., 1938, Mineral industry of Alaska in 1936: U.S. Geological Survey Bulletin 897-A, p. 1-107. Twenhofel, W.S., 1953, Potential Alaskan mineral resources for proposed electrochemical and electrometallurgical industries in the upper Lynn Canal area, Alaska: U.S. Geological Survey Circular 252, 14 p.

 
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