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Cameron; Chicken West; Opal Prospect, Fortymile District, Southeast Fairbanks Borough, Alaska, USA

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Location: The Cameron prospect is about 2 miles west of Chicken. It is at an elevation of about 1,900 feet on the north wall of the Mosquito Fork in the SW1/4 section 36, T. 27 N, R. 17 E., of the Copper River Meridian.
Geology: The rocks in the vicinity of the Cameron prospect consist predominantly of granodiorite, quartz monzodiorite, tonalite, and quartz diorite of the Taylor Mountain batholith (Foster, 1976; Werdon and others, 2001). Sphene from the batholith gives a uranium-lead age of 214 Ma (Aleinikoff and others, 1981); this is interpreted to represent the age of intrusion. The batholith has undergone an early Jurassic heating and deformation event. It is cut by porphyritic hornblende quartz diorite dikes, one of which has a 40Ar/39Ar hornblende plateau age of 197.5 Ma (Layer and others, 2002). Minor Paleozoic phyllite, metatuffs, and greenstone are also present in the area. The batholith and the schists have been offset by high-angle faults, and intruded by Tertiary gabbro (Werdon and others, 2001). Tertiary sandstone, conglomerate, and tuff are locally present, and Quaternary alluvium, colluvium, and terrace deposits are extensive in the Mosquito Fork drainage. The Cameron prospect is a weathered, 6-foot-thick mineralized zone that consists of clayey material and many fragments of vein quartz (Prindle, 1905). Rock sample assays contain 0.36 to 0.58 ounce of gold per ton and 0.10 ounce of silver per ton. The original host rock probably was a quartz diorite or granodiorite. Smith (1968) observed flour gold in a lode deposit about 200 feet above the river, and he probably was referring to this occurrence (Cobb, 1977 [OFR 77-845]).
Age: Triassic or younger.
Alteration: Clay alteration of plutonic host rock.

Commodities (Major) - Ag, Au
Development Status: None
Deposit Model: Gold in quartz along a fault zone; possibly a pluton-hosted lode gold deposit re

Mineral List



3 entries listed. 2 valid minerals.

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References

Aleinikoff, J.N., Dusel-Bacon, Cynthia, and Foster, H.L., 1981, Geochronologic studies in the Yukon-Tanana Upland, east-central Alaska, in Albert, N.R., and Hudson, T., eds., The United States Geological Survey in Alaska--Accomplishments during 1979, U.S. Geological Survey Circular C-823-B, p. 34-37. Cobb, E.H., 1977, Summary of references to mineral occurrences in the Eagle quadrangle, Alaska: U.S. Geological Survey Open-File Report 77-845, 122 p. Foster, H.L., 1976, Geologic map of the Eagle quadrangle, Alaska: U.S. Geological Survey Miscellaneous Investigations Series, Map 922, 1 sheet, scale 1:250,000. Layer, P.W., Drake, J., and Szumigala, D.J., 2002, 40Ar/39Ar dates for mineralization and igneous and metamorphic rocks in a portion of the Fortymile mining district, Eagle quadrangle, Alaska: Alaska Division of Geological and Geophysical Surveys Preliminary Interpretive Report. [In preparation in 2002] Prindle, L.M., 1905, The gold placers of the Fortymile, Birch Creek, and Fairbanks regions, Alaska: U.S. Geological Survey Bulletin 251, 89 p. Smith, W.H., 1968, Geochemical investigation of a portion of the Fortymile district, Alaska: Alaska Division of Mines and Minerals Geochemical Report 16, 17 p. Wasserberg, G.J., Eberlein, G.D., and Lanphere, M.A., 1963, Age of Birch Creek Schist and some batholithic intrusion in Alaska [abs.]: Geological Society of America Special Paper 73, p. 258-259. Werdon, M.B., Newberry, R.J., and Szumigala, D.J., 2001, Bedrock geologic map of the Eagle A-2 quadrangle, Fortymile mining district, Alaska: Alaska Division of Geological and Geophysical Surveys Preliminary Interpretive Report 2001-3b, 1sheet, scale 1:63,360.

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