Unnamed Occurrences (ARDF - EA110; midpoint of Ingle Creek), Fortymile District, Southeast Fairbanks Borough, Alaska, USA
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Geology: The rocks in the vicinity of Ingle Creek are primarily upper Paleozoic greenschist-facies metasedimentary and metavolcanic rocks that have been intruded by granitic rocks that are either related to the Taylor Mountain batholith of Triassic age to the south or the Chicken pluton of Jurassic age to the north (Werdon and others, 2001). These units have been cut by numerous high-angle faults. In the lower part of Ingle Creek, Tertiary gabbro is overlain by tuffaceous material and sparse shale. Quaternary colluvium and alluvium are present in the lower valley. There are two sites located about 1,700 feet apart that are included as part of this unnamed occurrence. At the southwestern site, greenstone with a fine-grained gabbroic texture exhibits chlorite-epidote alteration and is cut by veins of pyrite, quartz, calcite, and chalcopyrite. A select sample of one vein assayed 35 ppb gold and 603 ppm copper (Szumigala and others, 2000). At the northeastern site, many rock types are juxtaposed by many high-angle to moderately dipping faults; the rocks include upper Paleozoic greenstone; hypabyssal, feldspar porphyry dikes(?) of probable Jurassic age; highly foliated granitic plutonic rocks that are probably part of the Taylor Mountain batholith; and unfoliated dikes and plugs of Tertiary gabbro (M.B. Werdon, unpub. field mapping, 1999). A 5-foot-wide, highly silicified zone is present along the fault contact between a foliated granitic pluton and a hypabyssal porphyritic felsic rock. The silicified zone is light gray, and contains abundant epidote, pyrite, sprays of chlorite, and calcite occurs along joint surfaces. An assay from this zone contains 30 ppb gold and 197 ppm molybdenum (Szumigala and others, 2000).
Commodities (Major) - Au, Cu
Development Status: None
Mineral List
6 entries listed. 5 valid minerals.
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References
Szumigala, D.J., Newberry, R.J., Werdon, M.B., Finseth, B.A., Pinney, D.S., and Flynn, R.L., 2000, Major-oxide, minor-oxide, trace-element, and geochemical data from rocks collected in a portion of the Fortymile mining district, Alaska, in 1999: Alaska Division of Geological and Geophysical Surveys Raw-Data File 2000-1, 24 p., 2 sheets, scale 1:63,360. 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.
