Fortymile River (from mouth of Franklin Creek to Canadian border)

Mines, Active

Commodities and mineralogy

Main commodities Au
Other commodities Sn; W
Ore minerals cassiterite; gold; scheelite

Geographic location

Quadrangle map, 1:250,000-scale EA
Quadrangle map, 1:63,360-scale B-1
Latitude 64.3086
Longitude -141.4069
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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).

Geologic setting

Geologic description

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 1800s and early 1900s, 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 1970s caused a renewed interest in placer mining throughout Alaska, and numerous floating suction dredge operations appeared on the Fortymile River in the 1980s and 1990s; 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.
Geologic map unit (-141.409194727613, 64.3082881470946)
Mineral deposit model Placer Au (Cox and Singer, 1986; model 39a).
Mineral deposit model number 39a
Age of mineralization Quaternary.

Production and reserves

Workings or exploration
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 1800s and early 1900s, 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 totaled 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 Franklin 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 1970s caused a renewed interest in placer mining throughout Alaska, and numerous floating suction dredge operations appeared on the Fortymile River in the 1980s and 1990s; 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.
Indication of production Yes; medium
Production notes 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).

References

MRDS Number A015161

References

Reporters M.B. Werdon; R.L. Flynn
Last report date 5/1/2002