Straight Creek Springs Occurrence, McGrath District, Yukon-Koyukuk Borough, Alaska, USA
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Location: Straight Creek Springs (more than a dozen distinct springs are known) are located on the west limit of Straight Creek valley just down stream from the Chip Loy deposit (MG032). The springs occur at an elevation of 2,800 feet (853 m) in the W1/2 sec. 15, T. 24 N., R. 28 W., of the Seward Meridian. The coordinates are in the center of the spring system. The reporter visited the site in 1998.
Geology: Straight Creek Springs consist of a very distinctive, north-south trending, 400-meter-long line of more than a dozen active springs, each containing conspicuous coatings and replacements of brilliant orange limonite and light gray, bleached, silicrete crusts up to 3 centimeters thick. The conspicuous orange-light gray colored springs occur immediately below the contact between the black shale-rich section of the Ordovician-Lower Silurian, Post River Formation and the mid to Late Silurian Terra Cotta Mountains Sandstone, both of lower Paleozoic age (Churkin and Carter, 1996; Bundtzen, Harris, and Gilbert, 1997). The springs may indicate a concealed mineralized source in the black shale section. Herreid (1968) and T.K. Bundtzen and G.M. Laird (written communications, 1998) report that samples of silicrete-limonite material from two of the springs contain up to 125 ppm copper, 270 ppm zinc, 400 ppm nickel, and 10 ppm molybdenum.
Workings: The Straight Creek Springs were first described by Herreid (1968). Herreid (1968) and T.K. Bundtzen and G.M. Laird (written communication, 1998) report that samples of silicrete-limonite material from three of the springs contain up to 125 ppm copper, 270 ppm zinc, 400 ppm nickel, and 10 ppm molydenum.
Age: Quaternary.
Alteration: Silicrete-limonite.
Reserves: None.
Commodities (Major) - Cu, Ni, Zn; (Minor) - Mo
Development Status: No
Deposit Model: Unknown; anomalous values are apparently derived from Ordovician-Silurian black
Mineral List
1 entry listed.
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References
Bundtzen, T.K., Harris, E.E., and Gilbert, W.G., 1997, Geologic Map of the eastern McGrath quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 97-14, 34 p., 1 sheet, scale 1:125,000. Churkin, Michael, Jr., and Carter, Claire, 1996, Stratigraphy, structure, and graptolites of an Ordovician and Silurian sequence in the Terra Cotta Mountains, Alaska Range, Alaska: U.S. Geological Survey Professional Paper 1555, 84 p., 4 plates. Herreid, G.H., 1968, Geological and geochemical investigations southwest of Farewell, Alaska: Alaska Division of Mines and Geology Geologic Report 26, 24 p., 1 sheet, scale 1:75,000.
