|Quadrangle map, 1:250,000-scale||GU|
|Quadrangle map, 1:63,360-scale||D-1|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||Grubstake Creek (Cobb, 1979 [OF 79-1247 p. 11-12] flows west and joins Ahtell Creek about 2 miles south of the Dome. The creek was mainly mined in a section of its canyon about 0.8 to 1.2 miles above its mouth. Grubstake Creek is locality 10 of Richter (1966), locality 17 of Richter and Matson (1972), and locality 16 of MacKevett and Holloway (1977). The location is accurate to within 500 feet; it is in the SE1/4SW1/4, section 26, T. 12 N., R. 7 E., Copper River Meridian.|
The rocks along Grubstake Creek consist of granitic rocks of the Pennsylvanian to Permian, Ahtell pluton and altered volcanics and minor sedimentary rocks of the Pennsylvanian to Permian, Tetelna Formation. Jurassic diorite forms small bodies that intrude the volcanic section and possibly the Ahtell pluton. Richter and Matson (1968) proposed that the source of the placer was the Jurassic diorite; earlier Richter (1966) had assumed that the source was the Permian, Ahtell intrusive.The placer deposit consisted of poorly sorted gravels with occasional boulders. The discovery of an economic placer was made in 1934. The gravel section reported then was more than 16 feet thick and bedrock had not been reached (Moffit, 1936, p. 139-141). The country rock was volcanic and limestone with Permian fossils. Native gold was accompanied by significant amounts of native copper and native silver. The native metals found in the placer, are rough and some are dendritic, indicating a local source. Ilmenite was found in concentrates, and magnetite occurred locally in flattened slabs more than 1 foot across. Moffit (1937, p. 106-107) later reported that sheared diorite was encountered in bedrock under the placer.
|Geologic map unit||(-144.051191450843, 62.7846097346358)|
|Mineral deposit model||Placer Au (Cox and Singer, 1986; model 39a)|
|Mineral deposit model number||39a|
|Age of mineralization||Holocene placer.|
|Alteration of deposit||Rocks nearby have iron-stained, pyrite-rich zones and and there is local hydrothermal alteration of the Ahtell pluton and its wall rocks.|
|Workings or exploration||Gold was found in sub-economic concentrations early in the history of the district. An economic deposit was found in 1934 and was mined on at least a small scale until World War II (Moffit, 1936, 1937,1938; Smith, 1942; Moffit, 1942; Thorne, 1946). It was subsequently worked on a small scale after the war.|
|Indication of production||Yes; small|
|Production notes||Placer deposits in Grubstake and Slope Creeks (GU007) have been mined intermittently since 1934. The total gold production from both creeks is probably less than $30,000 (about 857 ounces) (Richter and Matson, 1968).|
Additional commentsSee also Slope Creek (GU020). The placer in upper Grubstake Creek probably overlies a disseminated lode gold deposit (GU019).
Cobb, E.H., 1979, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Gulkana quadrangle, Alaska: U.S. Geological Survey Open-File Report 79-1247, 36 p.
MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000.
Moffit, F.H., 1936, Upper Copper and Tanana Rivers: U.S. Geological Survey Bulletin 868-C, p. 135-143.
Moffit, F.H., 1937, Recent mineral developments in the Copper River region: U.S. Geological Survey Bulletin 880-B, p. 97-109.
Moffit, F.H., 1938, Geology of the Slana-Tok district, Alaska: U.S. Geological Survey Bulletin 904, 54 p.
Moffit, F.H., 1944, Mining in the northern Copper River region, Alaska: U.S. Geological Survey Bulletin 943-B, p. 25-47.
Nokleberg, W.J., and (seven) others, 1994, Metallogeny and major mineral deposits of Alaska and Metallogenic map of significant metalliferous lode deposits and placer districts of Alaska, in Plafker, G. and Berg, H.C., eds., The Geology of Alaska: Geological Society of America, DNAG, The Geology of North America, Vol.. G1, p. 855-904, Plate 11, scale 1:2,500,000.
Richter, D.H., 1966, Geology of the Slana district, southcentral Alaska: Alaska Division of Geological and Geophysical Surveys Geological Report 2l, 54 p., 3 sheets, scale 1:63,360.
Richter, D.H., and Matson, N.A., Jr., 1968, Distribution of gold and some base metals in the Slana area, eastern Alaska Range, Alaska: U.S. Geological Survey Circular 593, 20 p.
Richter, D.H., and Matson, N.A., Jr., 1972, Metallic mineral resources map of the Gulkana quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-419, 1 sheet, scale 1:250,000.
Smith, P.S., 1942, Mineral industry of Alaska in 1940: U.S. Geological Survey Bulletin 933-A, p. 1-102.
|Reporters||W.T. Ellis (Alaska Earth Sciences), C.C. Hawley (Hawley Resource Group), and W.J. Nokleberg (U.S. Geological Survey)|
|Last report date||12/20/2000|