Big Boulder Creek Occurrence, Skagway District, Juneau District, Haines Borough, Alaska, USA
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Geology: Wright (1904 [B 225 and B 236]) cites the presence of placer gold in Boulder Creek stream gravels but doubts that there are sufficient quantities to warrant mining. Still and others (1984) noted that gold was found in stream gravels and boulders that included argillite float and that porphyritic andesite float was present at the mouth of the canyon just above the the alluvial fan near the Haines Highway. Winkler and MacKevett (1970) collected several bedrock samples, MK 13A, MK 13D-1, and MK 13E, along Boulder Creek below the 1,000 foot elevation. Their description of MK 13A mentions an altered fault zone with quartz pods. The descriptions of MK 13D-1 and MK 13E mention quartz stringers. Sample MK 13A contained 1,500 ppm barium, 300 ppm lanthanum, 500 ppm niobium, 20 ppm tin, 200 ppm yttrium, and greater than 9,999 ppm zirconium. The description by MacKevett and others (1974) of an altered fault zone on Big Boulder Creek mentions fragmented pegmatitic material and apparently refers to the site sampled by MK 13A. Bedded rocks within the Big Boulder Creek drainage area are variably metamorphosed, metasediments and metavolcanics of the Cheetdeekahyu Group of Redman and others (1985). North of the Klehini River, the metamorphic grade and average grain size of these rocks increases to the north and northeast towards Four Winds Mountain. These rocks have been included in the Four Winds metamorphic complex (Forbes and others, 1987; Gilbert and others, 1987). They are of probable Devonian or Late Triassic age (Gilbert and others, 1987).
Workings: Worked by hand methods in early 1900's, but no production is documented.
Age: Quaternary placer.
Production: Probably minor, at best.
Commodities (Major) - Au; (Minor) - Ag
Development Status: No
Deposit Model: Quaternary Au placer (Cox and Singer, 1986; model 39a).
Mineral List
2 entries listed. 2 valid minerals.
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References
Berg, H.C., 1984, Regional geologic summary, metallogenesis, and mineral resources of southeastern Alaska: U.S. Geological Survey Open-file Report 84-572, 298 p., 1 plate, scale 1:600,000. Forbes, R.B., Gilbert, W.G., and Redman, E.C., 1987, The Four Winds Complex; a newly recognized Paleozoic metamorphic terrane in southeastern Alaska [abs.]: Geological Society of America, Abstracts with Program, v. 19, no. 6, p. 378. Gilbert, W.G., Burns, L.E., Redman, E.C., and Forbes, R.B., 1987, Preliminary bedrock geology and geochemistry of the Skagway B-3 quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Report of Investigations 87-2, 2 sheets, scale 1:36,200. MacKevett, E.M., Jr., Robertson, E.C., and Winkler, G.R., 1974, Geology of the Skagway B-3 and B-4 quadrangles, southern Alaska: U.S. Geological Survey Professional Paper 832, 33 p., 1 plate. Redman, E.C., Gilbert, W.G., Jones, B.K., Rosenkrans, D.S., and Hickok, B.D., 1985, Preliminary bedrock-geologic map of the Skagway B-4 quadrangle: Alaska Division of Geological and Geophysical Surveys Report of Investigations 85-6, 1 sheet, scale 1:40,000. Still, J.C., Weir, K.R., Gilbert, W.G., and Redman, E.C., 1984, Stream-sediment, float, and bedrock sampling in the Porcupine mining area, southeast Alaska: U.S. Bureau of Mines Open-File Report 173-84, 16 p., 1 sheet. Winkler, G.R., and MacKevett, E.M., Jr., 1970, Analyses of bedrock and stream-sediment samples from the Haines-Porcupine region, southeastern Alaska: U.S. Geological Survey Open-File Report 369, 91 p., 1 sheet, scale 1:125,000. Wright, C.W., 1904, The Porcupine placer district, Alaska: U.S. Geological Survey Bulletin 236, 35 p. Wright, C.W., 1904, The Porcupine placer mining district, Alaska in Emmons, S.F., and Hayes, C.W., eds., Contributions to economic geology 1903: U.S. Geological Survey Bulletin 225, p. 60-63.
