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Fortymile River Mines (from mouth of Franklin Creek to Canadian border), Fortymile District, Southeast Fairbanks Borough, Alaska, USA

Latitude: 64°18'30"N
Longitude: 141°24'25"W
Location: The Fortymile River is the major river cutting through the Fortymile mining district. This record includes all references to placer mining on the Fortymile River, from the mouth of Franklin Creek (see EA116) downstream to the Canadian border. The coordinates are arbitrarily placed at the Taylor Highway bridge on the lower Fortymile River. The lower Fortymile River is locations 60, 62, 64, and 65 of Cobb (1972 [MF-393]), location 28 of Eberlein and others (1977), and locations 35 to 69 of Burleigh and Lear (1994).
Geology: The Fortymile River is the major river cutting through the Fortymile mining district, and it is a significant producer of placer gold. The lower Fortymile River follows an entrenched meandering course in a steep-walled canyon that cuts through Paleozoic amphibolite-facies metamorphic rocks that have been intruded by Tertiary to Mesozoic plutons and dikes (Foster, 1976). The Fortymile River has a gradient of about 9 feet per mile (Yeend, 1996). Placer gold is the primary commodity recovered from the Fortymile River valley, but cassiterite and scheelite are locally found in concentrates. Placer gold has been recovered primarily from gravel bars along the Fortymile River, but gold has also been recovered from riffles in the active river channel and from gravels on terrace benches. There are extensive terrace gravel deposits along both sides of the river, located on benches that are as high as 230 meters above the valley bottom (Pinney, 2001). The Fortymile River has at least 10 gold-bearing tributaries in Alaska that contribute gold to it. Placers of the Fortymile River are naturally renewing, with new material added during each flood (Cobb, 1973 [B 1374]). Cracks and crevices in fractured bedrock provide an excellent surface for retaining gold (Prindle, 1909). Bedrock with steeply dipping foliation that is obliquely transverse to the river and locally abundant potholes trap gold on the Fortymile River (Yeend, 1996). Gold in the Fortymile River occurs as fine flakes and can almost always be recovered when sampling gravel at the gravel-bedrock contact in the floodplain (Yeend, 1996). Gravels are largely restricted to bars scattered along the river. Well-rounded to subrounded boulders and cobbles elsewhere are generally 4 to 8 inches in diameter and locally form a pavement on the valley floors. The gravel thickness in the river bed is generally 1 meter or less, although locally it is as thick as 33 feet. Porter (1912) observed that near the mouth of Franklin Creek, gold seemed not to be deposited across the entire bed of the stream but mainly along the sides or inside edges of curves. Placer gold was discovered near the mouth of the Fortymile River in the Yukon Territory, Canada, in 1886, and gravel bars were mined. Gold was discovered on Franklin Gulch (EA116) in Alaska in 1887 (Spurr, 1898). In the late 1800's and early 1900's, Fortymile River bars were worked using rocker boxes and small-scale hydraulic methods, utilizing water from tributaries. Several dredges have operated on the lower Fortymile River at various times (Yeend, 1996). Winter mining has occasionally been carried out on the Fortymile River. The gravel bar opposite Smith Creek was first worked in 1887 and produced approximately $500,000 in gold in the early years of work. Discovery Bar, located about 2 miles downstream from Canyon Creek (EA143), produced approximately $80,000 in gold in the early years of mining on the Fortymile River (Prindle, 1909). About 35 miners produced gold valued at $25,000 on the Fortymile River in 1893 (Spurr, 1898). (All the early mined gold was valued at $20.67 per ounce.) There are reports of bar mining on the Fortymile River in most years between 1903 and 1940. In 1907, a dredge was operating on the Fortymile River near the international border, and another dredge was in the process of being installed on Pump Bar below the mouth of Franklin Creek (see EA116) (Prindle, 1908). Production from Fortymile River bars totalled 2,228 fine ounces of gold from 1904 to 1907 (Prindle, 1908). The dredge on Pump Bar was wrecked by spring flooding in 1908 (Brooks, 1909). A small dredge operated near the border on the Fortymile River in 1910 (Ellsworth and Parker, 1911). In 1911, the small dredge near the border was sunk in spring breakup, and the Mulvane dredge began operation at Pump Bar (Porter, 1912). In 1912, in addition to bar mining, there was bench mining at Bonanza and Discovery Bars, a small dredge operating near the border, and the dredge near Franlklin Creek working upstream (Ellsworth and Davenport, 1913). Gold placers were found in bench deposits near the mouth of Steele Creek in 1916 (Brooks, 1918). In 1917, a small dredge operated near the town of Franklin, and bench mining on the Fortymile River was proving very good (Martin, 1919). There are no reports of dredging or other extensive operations on the lower Fortymile River after 1917, although reports of bar mining continue for most years until 1940. Saunders (1957) reported an active placer gold mining operation just downstream of the Taylor Highway bridge in 1957. The gold price rise in the late 1970's caused a renewed interest in placer mining throughout Alaska, and numerous floating suction dredge operations appeared on the Fortymile River in the 1980's and 1990's; there were as many as 20 separate operations on the Fortymile River in 1992 (Yeend, 1996). Suction dredging continues to be actively pursued on the Fortymile River in 2002.
Workings: Placer gold was discovered near the mouth of the Fortymile River, in the Yukon Territory, Canada in 1886 and gravel bars were mined. Gold was discovered on Franklin Gulch (see EA116) in Alaska in 1887 (Spurr, 1898). In the late 1800's and early 1900's, Fortymile River bars were worked using rocker boxes and small-scale hydraulic methods, utilizing water from tributaries. Several dredges have operated on the lower Fortymile River at various times (Yeend, 1996). Winter mining has occasionally been carried out on the Fortymile River. The gravel bar opposite Smith Creek was first worked in 1887 and produced approximately $500,000 in gold in the early years of work. Discovery Bar, located about 2 miles downstream from Canyon Creek (see EA143), produced approximately $80,000 in gold in the early years of mining on the Fortymile River (Prindle, 1909). About 35 miners produced gold valued at $25,000 on the Fortymile River in 1893 (Spurr, 1898). (All the early mined gold was valued at $20.67 per ounce.) There are reports of bar mining on the Fortymile River in most years between 1903 and 1940. In 1907, a dredge was operating on the Fortymile River near the international border, and another dredge was in the process of being installed on Pump Bar, below the mouth of Franklin Creek (EA116; Prindle, 1908). Production from Fortymile River bars totalled 2,228 fine ounces of gold from 1904 to 1907 (Prindle, 1908). The dredge on Pump Bar was wrecked by spring flooding in 1908 (Brooks, 1909). A small dredge operated near the border on the Fortymile River in 1910 (Ellsworth and Parker, 1911). In 1911, the small dredge near the border was sunk in spring breakup, and the Mulvane dredge began operation at Pump Bar (Porter, 1912). In 1912, in addition to bar mining, there was bench mining at Bonanza and Discovery Bars, a small dredge operating near the border, and the dredge near Franlklin Creek (EA116) working upstream (Ellsworth and Davenport, 1913). Gold placers were found in bench deposits near the mouth of Steele Creek in 1916 (Brooks, 1918). In 1917, a small dredge operated near the town of Franklin, and bench mining on the Fortymile River was proving very good (Martin, 1919). There are no reports of dredging or other extensive operations on the lower Fortymile River after 1917, although reports of bar mining continue for most years until 1940. Saunders (1957) reported an active placer gold mining operation just downstream of the Taylor Highway bridge in 1957. The gold price rise in the late 1970's caused a renewed interest in placer mining throughout Alaska, and numerous floating suction dredge operations appeared on the Fortymile River in the 1980's and 1990's; there were as many as 20 separate operations on the Fortymile River in 1992 (Yeend, 1996). Suction dredging continues to be actively pursued on the Fortymile River in 2002.
Age: Quaternary.
Production: The gravel bar opposite Smith Creek was first worked in 1887 and produced approximately $500,000 (dollar value at that time) in gold in the early years of work (Prindle, 1909). Discovery Bar, about 2 miles downstream from Canyon Creek (see EA143), produced approximately $80,000 (dollar value at that time) in gold in the early years of mining on the Fortymile River (Prindle, 1909). A mining population of 35 produced $25,000 (1893 dollars) on the Fortymile River in 1893 (Spurr, 1898).

Commodities (Major) - Au; (Minor) - Sn, W
Development Status: Yes; medium
Deposit Model: Placer Au (Cox and Singer, 1986; model 39a).

References

Brooks, A.H., 1903, Placer gold mining in Alaska in 1902: U.S. Geological Survey Bulletin 213, p. 41-48. Brooks, A.H., 1907, The Alaskan mining industry in 1906: U.S. Geological Survey Bulletin 314-A, p. 19-39. Brooks, A.H., 1909, The mining industry in 1908: U.S. Geological Survey Bulletin 379-A, p. 21-62. Brooks, A.H., 1915, Mineral resources of Alaska; report on progress of investigations in 1914: U.S. Geological Survey Bulletin 622, 380 p. Brooks, A.H., 1916, Mineral resources of Alaska, report on progress of investigations in 1915: U.S. Geological Survey Bulletin 642, 279 p. Brooks, A.H., 1918, Mineral resources of Alaska, 1916: U.S. Geological Survey Bulletin 662, 469 p. Brooks, A.H., 1923, The Alaska mining industry in 1921: U.S. Geological Survey Bulletin 739-A, p. 1-50. Brooks, A.H., and Capps, S.R., 1924, The Alaska mining industry in 1922: U.S. Geological Survey Bulletin 755-A, p. 1-56. Bundtzen, T.K., Green, C.B., Deagen, J.R., and Daniels, C.L., 1987, Alaska's mineral industry, 1986: Alaska Division of Geological and Geophysical Surveys Special Report 40, 68 p. 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., 1972, Metallic mineral resources map of the Eagle quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-393, 1:250,000 scale, 1 sheet. Cobb, E.H., 1973, Placer deposits of Alaska: U.S. Geological Survey Bulletin 1374, 213 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. Ellsworth, C.E., and Davenport, R.W., 1913, Placer mining in the Yukon-Tanana region: U.S. Geological Survey Bulletin 542-F, p. 203-222. Ellsworth, C.E., and Parker, G.L., 1911, Placer mining in the Yukon-Tanana region: U.S. Geological Survey Bulletin 480-F, p. 173-217. 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. Foster, H.L., 1976, Geologic map of the Eagle quadrangle, Alaska: U.S. Geological Survey Miscellaneous Investigations Series, Map 922, 1 sheet, scale 1:250,000. Martin, G.C., 1919, Alaska Mining Industry in 1917: U.S. Geological Survey Bulletin 692-A, p. 11-42. Mertie, J.B., Jr., 1930, Mining in the Fortymile district: U.S. Geological Survey Bulletin 813-C, p. 125-142. Mertie, J.B., Jr., 1938, Gold placers of the Fortymile, Eagle, and Circle districts, Alaska: U.S. Geological Survey Bulletin 897-C, p. 133-261. Moffit, F.H., 1927, Mineral industry in Alaska in 1925: U.S. Geological Survey Bulletin 792-A, p. 1-39. Pinney, D.S., 2001, Surficial-geologic map of the Eagle A-2 quadrangle, Fortymile mining district, Alaska: Alaska Division of Geological and Geophysical Surveys Preliminary Interpretive Report 2001-3c, 1 sheet, scale 1:63,360. Porter, E.A., 1912, Placer mining in the Fortymile, Eagle, and Seventymile River districts: U.S. Geological Survey Bulletin 520-G, p. 211-218. Prindle, L.M., 1905, The gold placers of the Fortymile, Birch Creek, and Fairbanks regions, Alaska: U.S. Geological Survey Bulletin 251, 89 p. Prindle, L.M., 1906, Yukon placer fields: U.S. Geological Survey Bulletin 284, p. 109-127. 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. Prindle, L.M., 1909, The Fortymile quadrangle, Yukon-Tanana region, Alaska: U.S. Geological Survey Bulletin 375, 52 p. Saunders, R.H., 1957, Report on the La Flamme copper prospect (South Fork Lodge and Chicken Creek) Alaska Territorial Department of Mines Property Examination PE 60-6, 6 p. Smith, P.S., 1926, Mineral industry of Alaska in 1924: U.S. Geological Survey Bulletin 783-A, p. 1-30. Smith, P.S., 1929, Mineral industry of Alaska in 1926: U.S. Geological Survey Bulletin 797, p. 1-50. Smith, P.S., 1930, Mineral industry of Alaska in 1927: U.S. Geological Survey Bulletin 810-A, p. 1-64. Smith, P.S., 1930, Mineral industry of Alaska in 1928: U.S. Geological Survey Bulletin 813-A, p. 1-72. Smith, P.S., 1932, Mineral industry of Alaska in 1929, in Smith, P.S., and others Mineral resources of Alaska, report on progress of investigations in 1929: U.S. Geological Survey Bulletin 824-A, p. 1-81. Smith, P.S., 1933, Mineral industry of Alaska in 1931: U.S. Geological Survey Bulletin 844-A, p. 1-81. Smith, P.S., 1936, Mineral industry of Alaska in 1934: U.S. Geological Survey Bulletin 868-A, p. 1-91. Smith, P.S., 1937, Mineral industry of Alaska in 1935: U.S. Geological Survey Bulletin 880-A, p. 1-95. Smith, P.S., 1939, Mineral industry of Alaska in 1937: U.S. Geological Survey Bulletin 910-A, p. 1-113. Smith, P.S., 1939, Mineral industry of Alaska in 1938: U.S. Geological Survey Bulletin 917-A, p. 1-113. Smith, P.S., 1941, Mineral industry of Alaska in 1939: U.S. Geological Survey Bulletin 926-A, p. 1-106. Smith, P.S., 1942, Mineral industry of Alaska in 1940: U.S. Geological Survey Bulletin 933-A, p. 1-102. Spurr, J.E., 1898, Geology of the Yukon gold district, Alaska, with an introductory chapter on the history and conditions of the district to 1897 by H.B. Goodrich: U.S. Geological Survey 18th Annual Report, Part 3, p. 87-392. Swainbank, R.C., Bundtzen, T.K., and Wood, J.E., 1991, Alaska's mineral industry, 1990: Alaska Division of Geological and Geophysical Surveys Special Report 45, 78 p. Swainbank, R.C., Bundtzen, T.K., Clough, A.H., Henning, M.W., and Hansen E.W., 1995, Alaska's mineral industry 1994: Alaska Division of Geological and Geophysical Surveys Special Report 49, 77 p. Yeend, W.E., 1992, Gold placers, gold source, and high terrace gravels in the Fortymile River area, Alaska, in Bradley, D.C., and Ford, A.B., eds., Geological studies in Alaska by the U.S. Geological Survey, 1990: U.S. Geological Survey Bulletin 1999, p. 228-230. Yeend, W.E., 1996, Gold placers of the historical Fortymile River region, Alaska: U.S. Geological survey Bulletin 2125, 75 p., 1 sheet, 1:250,000 scale.

Mineral List

Cassiterite
Gold
Scheelite


3 entries listed. 3 valid minerals.

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