Seventymile River

Mines, Probably inactive

Commodities and mineralogy

Main commodities Au
Other commodities Pt
Ore minerals gold

Geographic location

Quadrangle map, 1:250,000-scale EA
Quadrangle map, 1:63,360-scale D-2
Latitude 64.9302
Longitude -141.8419
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Seventymile River is approximately 60 miles long and drains into the Yukon River about 10 miles northwest of the town of Eagle. Most mining on the Seventymile River occurred just above the falls of the Seventymile River, about 20 miles upstream of its mouth. The coordinates for these mines are placed at this point ,in section 9, T. 1 N., R. 29 E., of the Fairbanks Meridian. The location is accurate. The Seventymile River is localities 19 and 23 to 25 of Cobb (1972 [MF-393]), locality 53 of Eberlein and others (1977), and localities 9 and 11 of Burleigh and Lear (1994).

Geologic setting

Geologic description

The rocks along the middle portion of the Seventymile River are Paleozoic gneiss, amphibolite, schist, and greenschist and Upper Cretaceous to Pliocene terrigenous sedimentary rocks (Foster, 1976). The main trace and subsidiary strands of the Tintina Fault run along and parallel the Seventymile River.
The falls of the Seventymile River are located about 20 miles upstream of the Yukon River; they are about 9 feet high (Prindle, 1905). Above the falls well-developed gravel benches are found on both sides of the river; low benches are best developed on the north side of the river. By 1936, small-scale mining had been carried out intermittently for many years on gravel on the lower benches (Mertie, 1938). One hundred holes were drilled on low benches on the north side of the river, from the falls upstream to within a mile of Barney Creek. The depth to bedrock averaged 19 feet to bedrock, with a maximum depth of 27 feet. Two assays of placer gold from the Seventymile River averaged of 828 parts of gold and 163 parts of silver per thousand. A sample of placer gold from the Seventymile River at the mouth of Broken Neck Creek contains 80.59 percent gold, 18.21 percent silver, and 0.20 percent platinum (Mertie, 1942). No platinum grains were observed; the platinum is presumably alloyed with gold and silver. Placer gold has been produced on many of the tributaries entering the Seventymile River, including Rock Creek (EA030), Fox Creek (EA021), Crooked Creek (EA026), Broken Neck Creek (EA024), Canyon Creek (EA027), Sonickson Creek (EA022), Barney Creek (EA019), Nugget Creek (EA014), Alder Creek (EA011), and Flume Creek (EA008).
In 1902, a hydraulic plant was used to mine on the Seventymile River about 15 miles upstream from the Yukon River (Brooks, 1903). Bar mining and sniping are reported on the Seventymile River in most years from 1902 to 1940. A small hydraulic outfit operated at the falls in 1903 (Brooks, 1904; Prindle, 1905), and in 1910 placer mining occurred at the falls and Curtis Bar (Ellsworth and Parker, 1911). Mining at the falls ceased in 1912, but more mining took place at Curtis Bar than in any recent year (Ellsworth and Davenport , 1913). In 1936, a drilling crew of Gold Placers, Inc. prospected benches along the Seventymile River. They drilled 100 holes above the falls, but results of the drilling were not as encouraging as had been expected (Mertie, 1938).
Geologic map unit (-141.844225297017, 64.9298862499826)
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 In 1902, a hydraulic plant was used to mine on the Seventymile River about 15 miles upstream from the Yukon River (Brooks, 1903). Bar mining and sniping are reported on the Seventymile River in most years from 1902 to 1940. A small hydraulic outfit operated at the falls in 1903 (Brooks, 1904; Prindle, 1905), and in 1910 placer mining occurred at the falls and Curtis Bar (Ellsworth and Parker, 1911). Mining at the falls ceased in 1912, but more mining took place at Curtis Bar than in any recent year (Ellsworth and Davenport , 1913). In 1936, a drilling crew of Gold Placers, Inc. prospected benches along the Seventymile River. They drilled 100 holes above the falls, but results of the drilling were not as encouraging as had been expected (Mertie, 1938).
Indication of production Yes
Production notes Two assays of placer gold from the Seventymile River averaged of 828 parts of gold and 163 parts of silver per thousand. A sample of placer gold from the Seventymile River at the mouth of Broken Neck Creek contains 80.59 percent gold, 18.21percent silver, and 0.20 percent platinum (Mertie, 1942). No platinum grains were observed; the platinum is presumably alloyed with gold and silver.

References

MRDS Number A015128; M045367

References

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