Seventymile River Mines, Eagle Mining District, Southeast Fairbanks Census Area, Alaska, USAi

Regional Level Types
Seventymile River Mines	Group of Mines
Eagle Mining District	Mining District
Southeast Fairbanks Census Area	Census Area
Alaska	State
USA	Country

Location: 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).
Geology: 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, 18.21percent 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).
Workings: 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).
Age: Quaternary.
Production: 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.

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

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Link to USGS - Alaska:	EA025

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References