|Quadrangle map, 1:250,000-scale||EA|
|Quadrangle map, 1:63,360-scale||A-1|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||Twelvemile Creek is a small north tributary of the Walker Fork of the Fortymile River, located about 7 miles west of Boundary. Placer workings extend from one-half mile to one mile upstream of the mouth of Twelvemile Creek. The coordinates are the approximate midpoint of the placer workings, in section 32, T. 27 N., R. 21 E., of the Copper River Meridian; the location is accurate within 500 feet. Twelvemile Creek is locality 59 of Eberlein and others (1977) and locality 98 of Burleigh and Lear (1994). In the northeast Eagle quadrangle, Excelsior Creek (see EA032) was formerly known as Twelvemile Creek.|
Bedrock along Twelvemile Creek consists of Paleozoic amphibolite-facies paragneiss, orthogneiss, amphibolite, schist, quartzite, and marble (Szumigala and others, 2002). These metamorphic units are intruded by sparse granitic pegmatite dikes of probable Jurassic age. The north-south trend of Twelvemile Creek spatially corresponds to a strong north-south-trending conductive zone in the airborne geophysical data (Alaska Division of Geological and Geophysical Surveys and others, 1999). This trend also follows a prominent north-south-trending, high-angle fault (Szumigala and others, 2002). Terrace-gravel benches along the north side of Walker Fork near Twelvemile Creek are present as much as 300 feet above Walker Fork and above the level of placer workings in Twelvemile Creek (Yeend, 1996).In the early 1930s, Twelvemile Creek was prospected extensively, but with little results (Powers, 1935). A bucket-type dredge operated on Walker Fork about a mile above the mouth of Twelvemile Creek from 1907 to 1909. Prospecting and possibly some mining occurred in the 1960s and 1970s on Twelvemile Creek (Eberlein and others, 1977). A small open-cut mining operation was active on Twelvemile Creek from 1982 to 1984 (Norm LaFramboise, Boundary Explorations, Inc., written communication, 2000).
|Geologic map unit||(-141.340475379652, 64.080785414992)|
|Mineral deposit model||Placer Au (Cox and Singer, 1986; model 39a).|
|Mineral deposit model number||39a|
|Age of mineralization||Quaternary.|
|Workings or exploration||In the early 1930s, Twelvemile Creek was prospected extensively, but with little results (Powers, 1935). A bucket-type dredge operated on Walker Fork about a mile above the mouth of Twelvemile Creek from 1907 to 1909. Prospecting and possibly some mining occurred in the 1960s and 1970s on Twelvemile Creek (Eberlein and others, 1977). A small open-cut mining operation was active on Twelvemile Creek from 1982 to 1984 (Norm LaFramboise, Boundary Explorations, Inc., written communication, 2000).|
|Indication of production||Yes; small|
Burleigh, R.E., and Lear, K.G., 1994, Compilation of data for Phase I of the mineral resource evaluation of the Bureau of Land Management Black River and Fortymile subunits: U.S. Bureau of Mines Open-File Report 48-94, 116 p.
Cobb, E.H., 1977, Summary of references to mineral occurrences in the Eagle quadrangle, Alaska: U.S. Geological Survey Open-File Report 77-845, 122 p.
Eberlein, G.D., Chapman, R.M., Foster, H.L., and Gassaway, J.S., 1977, Map and table describing known metalliferous and selected nonmetalliferous mineral deposits in central Alaska: U.S. Geological Survey Open-File Report 77-168-D, 132 p., 1 sheet, scale 1:1,000,000.
Foster, H.L., 1969, Reconnaissance geology of the Eagle A-1 and A-2 quadrangles, Alaska: U.S. Geological Survey Bulletin 1271-G, p. G1-G30.
Powers, J.B., 1935, Synopsis and history of early day mining and prospecting on the Fortymile River and its bars and low benches: Alaska Territorial Department of Mines Miscellaneous Report 60-2, 19 p.
Prindle, L.M., 1908, The Fortymile gold-placer district, in Brooks, A.H., ed., Mineral Resources of Alaska, Report on progress of investigations in 1907: U.S. Geological Survey Bulletin 345, p. 187-197.
|Reporters||R.L. Flynn; M.B. Werdon|
|Last report date||5/1/2002|