|Quadrangle map, 1:250,000-scale||TN|
|Quadrangle map, 1:63,360-scale||A-3|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This site represents about a square-mile area of placer mines, centered on the abandoned town of Woodchopper. For this record, the site is at the junction of Woodchopper Creek and Deep Creek, in the southeast quarter of section 28, T. 3 N., R. 17 W., of the Fairbanks Meridian. The site corresponds to location 25 of Cobb (1972), and to the site for Woodchopper Creek, U.S. Bureau of Land Management MAS number 0020480016.|
The Woodchopper Creek placer mine marks the western end of the Tofty tin belt, a 12-mile long area of cassiterite- and gold-bearing placer deposits that trends east-northeast, between Roughtop Mountain to the north and Hot Springs Dome to the south (Thomas, 1957). Roughtop Mountain and Hot Springs Dome respectively are underlain by Cretaceous (K-Ar age date of 92 +/- 5 Ma) and Tertiary (K-Ar age date of 62 +/- 3 Ma) granitic plutons (Chapman and others, 1982). The plutons intrude and contact metamorphose Mesozoic marine sedimentary strata, which also are cut by diverse faults, including regional-scale, east-northeast-striking, thrust faults (Reifenstuhl and others, 1998). A carbonatite sill(?) is in the Triassic section of these strata and there are exposures of serpentinized, Cretaceous(?) mafic and ultramafic rock, mainly on Serpentine Ridge.
The gold- and tin-bearing creeks flow normal to the trend of the tin belt. They head in the plutonic, metamorphic, and mafic/ultramafic rocks of Roughtop Mountain and Serpentine Ridge, which probably are the source(s) of some of the metalliferous minerals in the placer deposits. Concentrations of gold diminish toward the south, probably due to dispersion (Thomas, 1957).
The pay gravels on Woodchopper Creek occupy a deep channel and lie as deep as 200 feet below the surface (Brooks, 1918). Mertie (1934) described one of the mines on the east side of Woodchopper Creek as containing 20 feet of gravel on bedrock, overlain by 20 feet of muck, then 40 feet more of gravel, capped in turn by 40 feet of muck. These gravels consist predominantly of light phyllite, dark phyllite, and quartzite, with sandstone increasing downstream (Wayland, 1961). Tourmaline-bearing quartz boulders occur in the tailings (Thomas, 1957).
The gold and cassiterite generally occur together. However, Wayland (1961) reported that drilling between 1926 and 1941 by Adolph Brock yielded 5 holes with cassiterite and no gold. Through 1956, Thomas (1957) reported the total production of Woodchopper Creek to be 28,501 ounces of gold, 3,402 ounces of silver, and 40,300 pounds of cassiterite concentrate. The cassiterite generally occurs as rounded pebbles, and at least some of the gold is coarse (Wayland, 1961). Other heavy minerals include ilmenite, picotite, pyrite, and magnetite (Mertie, 1934).Cobb (1977) has summarized the mining history on Woodchopper Creek. Mining on the creek started in 1913 with the discovery of gold gravels near the mouth of the creek (Chapin, 1914). There was large-scale drift mining from 1915 to 1916, employing more than 100 men (Brooks, 1918). This project disbanded, but mining on different claims continued through 1941, and many prospecting holes were dug by different people (Wayland, 1961). Woodchopper Creek was the most productive creek in the Hot Springs district in 1926 (Smith, 1929). The Woodchopper Mining Company drift mined from a 167-foot-deep shaft on the Loraine Claim in 1951 (Williams, 1951). Seven groups held active mining claims on Woodchopper Creek in 1967 (Heiner and others, 1968). Jack Neubauer mined in the area in 1997 (Swainbank and others, 1998).
|Geologic map unit||(-151.014682139777, 65.0510601195389)|
|Mineral deposit model||Placer Au(-Sn) (Cox and Singer, 1986; model 39a).|
|Mineral deposit model number||39a|
|Age of mineralization||Quaternary.|
|Workings or exploration||Cobb (1977) has summarized the mining history on Woodchopper Creek. Mining on the creek started in 1913 with the discovery of gold gravels near the mouth of the creek (Chapin, 1914). There was large-scale drift mining from 1915 to 1916, employing more than 100 men (Brooks, 1918). This project disbanded, but mining on different claims continued through 1941, and many prospecting holes were dug by different people (Wayland, 1961). Woodchopper Creek was the most productive creek in the Hot Springs district in 1926 (Smith, 1929). The Woodchopper Mining Company drift mined from a 167-foot-deep shaft on the Loraine Claim in 1951 (Williams, 1951). Seven groups held active mining claims on Woodchopper Creek in 1967 (Heiner and others, 1968). Jack Neubauer mined in the area in 1997 (Swainbank and others, 1998).|
|Indication of production||Yes; small|
|Production notes||Thomas (1957) reported that 28,501 ounces of gold, 3,402 ounces of silver, and 40,300 pounds of cassiterite concentrate (60 percent tin) were produced from Woodchopper Creek through 1956.|
Chapin, Theodore, 1914, Placer mining in the Yukon-Tanana region: U.S. Geological Survey Bulletin 592-J, p. 357-362.
Chapman, R.M., Yeend, W.E., Brosge, W.P., and Reiser, H.N., 1982, Reconnaissance geologic map of the Tanana quadrangle: U.S. Geological Survey Open-File Report 82-734, 20 p., scale 1:250,000.
Cobb, E.H., 1972, Metallic mineral resources map of the Tanana quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-371, 1 sheet, scale 1:250,000.
Cobb, E.H., 1977, Summary of references to mineral occurrences (other than mineral fuels and construction materials) in the Tanana quadrangle, Alaska: U.S. Geological Survey Open-File Report 77-432, 98 p.
Heiner, L.E., Wolff, E.N., and Lu, F.C.J., 1968, Mining regions and mineral commodities, in Heiner, L.E., and Wolff, E.N. eds., Final Report - Mineral Resources of Northern Alaska: Mineral Industry Research Laboratory, University of Alaska Report No. 16, p. 3-137.
Mertie, J.B., Jr., 1934, Mineral deposits of the Rampart and Hot Springs districts, Alaska: U.S. Geological Survey Bulletin 844-D, p. 163-226.
Reifenstuhl, R.R., Dover, J.H., Newberry, R.J., Clautice, K.H., Pinney, D.S., Liss, S.A., Blodgett, R.B., and Weber, F.R., 1998, Geologic map of the Tanana A-1 and A-2 quadrangles, central Alaska: Alaska Division of Geological & Geophysical Surveys Public Data File 98-37A v. 1.1, 19 p., 1 sheet, scale 1:63,360.
Smith, P.S., 1929, Mineral industry of Alaska in 1926 and Administrative Report: U.S. Geological Survey Bulletin 797-A, p. 1-50.
Swainbank, R.C., Clautice, K.C., and Nauman, J.L., 1998, Alaska's mineral industry, 1997: Alaska Division of Geological and Geophysical Surveys Special Report 52, 65 p.
Thomas, B.I., 1957, Tin-bearing placer deposits near Tofty, Hot Springs district, central Alaska: U.S. Bureau of Mines Report of Investigations 5373, 56 p.
Wayland, R.G., 1961, Tofty tin belt, Manley Hot Springs district, Alaska: U.S. Geological Survey Bulletin 1058-I, p. 363-414.
|Reporters||G.E. Graham (ADGGS)|
|Last report date||1/15/2001|