|Quadrangle map, 1:250,000-scale||SR|
|Quadrangle map, 1:63,360-scale||D-6|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||The map site of this gold placer mining area is at an elevation of 1,100 feet on Bertha Creek. It is in the SW1/4 section 26, T. 8 N., R. 1 W., of the Seward Meridian. The principal gold-producing ground is at or near the confluence of Bertha and Granite (SR037) Creeks. This is location 149 of Cobb and Richter (1972), location 171 of MacKevett and Holloway (1977), location 21 of Tysdal (1978 [MF-880-B]), location 149 of Cobb and Tysdal (1980), and location P-64 of Jansons and others (1984). This location is accurate to within 300 feet.|
Bedrock in the area is slate and graywacke of the Valdez Group of Late Cretaceous age (Nelson and others, 1985). Bertha Creek occupies a U-shaped valley in its upper portion and a steep, narrow canyon cut mostly in glacial debris and bedrock in its middle section. An alluvial fan below the canyon has been the source of the most of the gold recovered to date (2000). The gravels are poorly sorted and contain abundant clay and boulders. The gold occurs mostly on bedrock (Jansons and others, 1984). Moffit (1906) reported that at the mouth of Bertha Creek, 2.5 to 3 meters of coarse gravel and boulders are overlain by about 1.5 meters of finer material. Bedrock is not exposed. The gold is in the coarse material, which averages about 15 cents per cubic yard (gold at $20.67 per troy ounce). The gold is fine, bright yellow, and smooth (Moffit, 1906).Hand-placer and hydraulic mining occurred between 1902 and 1904, and the area is currently (2000) used for recreational mining. Total gold production since 1902 is estimated to be 300 to 600 ounces, of which less than 35 ounces has been recovered since 1975 (Jansons and others, 1984).
|Geologic map unit||(-149.244146582193, 60.7508326921865)|
|Mineral deposit model||Placer Au (alluvial) (Cox and Singer, 1986; model 39a).|
|Mineral deposit model number||39a|
|Age of mineralization||Quaternary.|
|Workings or exploration||Hand-placer and hydraulic mining occurred between 1902 and 1904. In 1983, the U.S. Bureau of Mines collected samples from lower Bertha Creek (Jansons and others, 1984). A dredge sample yielded 0.0142 ounce of gold per hour. Two bench samples contained 0.0006 and 0.0129 ounce of gold per cubic yard. Traces of gold were recovered from surface gravels on upper Bertha Creek. A concentrate sample contained cinnabar (Jasper, 1967). Recreational suction dredging is currently popular along Bertha Creek within one-eighth mile of the Seward Highway (C.S. Huber, oral communication, 2000).|
|Indication of production||Yes; small|
|Production notes||Total gold production since 1902 is estimated to be 300 to 600 ounces, of which less that 35 ounces has been recovered since 1975 (Jansons and others, 1984).|
Cobb, E.H., and Richter, D.H., 1972, Metallic mineral resources map of the Seward quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-466, 2 sheets, scale 1:250,000.
Cobb, E.H., and Tysdal, R.G., 1980, Summaries of data on and list of references to metallic and selected nonmetallic mineral deposits in the Blying Sound and Seward quadrangle, Alaska: U.S. Geological Survey Open-File Report 80-621, 276 p.
Hoekzema, R.P., and Sherman, G.E., 1983, Mineral investigations in the Chugach National Forest, Alaska (Peninsula study area): U.S. Bureau of Mines in-house report; held at U.S. Bureau of Land Management Alaska State Office, Anchorage, 524 p.
Jansons, Uldis, Hoekzema, R.B., Kurtak, J.M., and Fechner, S.A., 1984, Mineral occurrences in the Chugach National Forest, southcentral Alaska: U.S. Bureau of Mines Mineral Land Assessment 5-84, 218 p., 2 sheets, scale 1:250,000.
Jasper, M.W., 1967, Geochemical investigations, Willow Creek southerly to Kenai Lake region, south central Alaska: Alaska Division of Mines and Minerals Geochemical Report 14, 47 p.
Moffit, F.H., 1906, Gold fields of the Turnagain Arm region: U.S. Geological Survey Bulletin 277, p. 7-52.
Nelson, S.W., Dumoulin, J. A., and Miller, M.L., 1985, Geologic map of the Chugach National Forest, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1645-B, 16 p., 1 sheet, scale 1:250,000.
|Reporters||Jeff A. Huber (Anchorage)|
|Last report date||6/24/2000|