|Quadrangle map, 1:250,000-scale||TN|
|Quadrangle map, 1:63,360-scale||A-2|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This site represents an approximately 1.5-mile-long area of placer mining that includes upper Deep Creek and the lower parts of its tributaries, Innesvale Gulch and Hokeley Gulch (Thomas, 1957). For this record, the site is at the junction of Deep Creek and Hokeley Gulch, in the northwest quarter of section 27, T. 3 N., R. 17 W., of the Fairbanks Meridian. The location is accurate. The site corresponds to location 26 of Cobb (1972, 1977), and roughly to U.S. Bureau of Land Management MAS number 0020480003.|
The placer mines on Deep Creek and its tributaries are part of a group of cassiterite- and gold-bearing placer deposits known as the Tofty tin belt, a 12-mile-long area 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 placer deposits on Deep Creek and its tributaries stretch for more than a mile along the trace of an east-northeast-striking thrust fault. The bulk of the mining, from 1913 until at least 1941, appears to have been on benches about 1/4 of a mile south of the present channel of Deep Creek (Wayland, 1961). Although most of the gold was in gravel on the bedrock surface, gold and cassiterite ('tin') were also identified in overlying lenses of gravel. The cassiterite occurs chiefly as well-rounded to subangular particles that range in size from microscopic to several inches across. The larger sizes often are accompanied by vein quartz and tourmaline, as well as by fragments of sedimentary country rock. The smaller sizes generally are free of impurities (Thomas,1957). Other minerals identified in placer concentrates include aeschynite, chromite, columbite, ellsworthite, ilmenite, magnetite, monazite, picotite, pyrite, rutile, scheelite, an unknown silver mineral, and zircon (Waters, 1934; Thomas, 1957; Cobb, 1977). A gold grain analyzed by electron microprobe contained a tiny inclusion of native nickel (Newberry and Clautice, 1997).
The area of placer deposits has been divided into two sections, known locally as the Hokeley Gulch section (the western portion), and the Innesvale Gulch section (the eastern portion). The Hokeley Gulch placers were discovered in 1913 by Adolph Bock, and the first mining was reported by Eakin (1915). The shafts in the pay zone are 130 feet deep, with 6 to 8 feet of gravels lying on bedrock (Eakin, 1915). The gravels consist of angular phyllite, sandstone, and quartz boulders, along with minor quartz-tourmaline rock, chromite, and coarse-grained biotite granite. The gold is smooth and fine, suggesting that it is well traveled (Wayland, 1961).
The Innesvale Gulch section was initially mined in 1918, when Bock, Handson and Albrecht did much of the work. One of the claims worked in 1931 was visited by Mertie (1934), who noted that the occurrence of the gold and cassiterite differs from that in the Hokeley Gulch section, in that the depth to bedrock is only about 65 feet, and the gravels are 5 to 6 feet thick. Irregularities in the bedrock surface trapped the cassiterite and gold. The gravels are similar in composition to those in the Hokeley Gulch section, but lack granite and include a small amount of metadiorite (Wayland, 1961).Through 1956, production from the Deep Creek placers was 7,684 ounces of gold, 653 ounces of silver, and 64,200 pounds of cassiterite concentrate (Thomas, 1957). Barton (1962) reported that the placer tailings contained 0.1 to 5.0 percent niobium, and Kauffman and Holt (1965) published analyses of concentrates that showed 1 to 5 percent zircon. At least one sample of the concentrates below Hokeley Gulch contained 10 percent chromite (Cobb, 1973).
|Geologic map unit||(-150.988683626599, 65.0614409250623)|
|Mineral deposit model||Placer Au(-Sn) (Cox and Singer, 1986; model 39a).|
|Mineral deposit model number||39a|
|Age of mineralization||Quaternary.|
|Workings or exploration||The Hokeley Gulch placers were discovered in 1913 by Adolph Bock, and were worked through 1916. The shafts in the pay zone are 130 feet deep, with 6 to 8 feet of gravels lying on bedrock (Eakin, 1915). The Innesvale Gulch placers were initially mined in 1918. One of the claims worked in 1931 was visited by Mertie (1934), who noted that the occurrence of the gold and cassiterite differs from that in the Hokeley Gulch placers, in that the depth to bedrock is only about 65 feet, and the gravels are 5 to 6 feet thick.|
|Indication of production||Yes; small|
|Production notes||Thomas (1957) reported that 6,864 ounces of gold, 653 ounces of silver, and 64,200 pounds of cassiterite concentrate (60 percent tin) were produced from Deep Creek through 1956.|
Additional commentsThe stream gradient of Deep Creek is 50 to 100 feet per mile.
Barton, W.R., 1962, Columbium and tantalum, a materials survey: U.S. Bureau of Mines Information Circular 8120, 110 p.
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.
Eakin, H.M., 1915, Mining in the Hot Springs District: U.S. Geological Survey Bulletin 622, p. 239-245.
Kauffman, A.J., Jr., and Holt, D.C., 1965, Zircon: a review. with emphasis on west coast resources and markets: U.S. Bureau of Mines Information Circular 8268, 76 p.
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.
Newberry, R.J. and Clautice, K.H., 1997, Compositions of placer gold in the Rampart-Eureka-Manley-Tofty area, eastern Tanana and western Livengood quadrangles, central Interior Alaska, determined by electron microprobe analysis: Alaska Division of Geological and Geophysical Surveys Public Data File 97-49, 49 p.
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.
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.
Waters, A.E., 1934, Placer concentrates of the Rampart and Hot Springs district: U.S. Geological Survey Bulletin 844-D, p. 163-246.
|Reporters||G.E. Graham (ADGGS), D.J. Szumigala (ADGGS)|
|Last report date||2/14/2004|