Unnamed Occurrence (ARDF - EA126; Walker Fork), Fortymile District, Southeast Fairbanks Borough, Alaska, USA
Location: This occurrence is located at water level at the apex of a sharp bend of the Walker Fork of the Fortymile River in section 28, T. 27 N., R. 19 E., of the Copper River Meridian. The location is accurate.
Geology: This occurrence is in a hornblende-biotite granodiorite of the Walker Fork pluton. Biotite from the pluton gives a 40Ar/39Ar plateau age of 99.0 +/- 0.5 Ma (Layer and others, 2002). The pluton is left-laterally offset about one-half mile by a northeast-trending high-angle fault (Werdon and others, 2001). A prominent circular magnetic low along the fault is present in airborne geophysical survey data (Alaska Division of Geological and Geophysical Surveys and others, 1999). The magnetic low corresponds to an area of extensive shearing. The granodiorite is partially altered to chlorite, clay, and calcite. Altered granodiorite that is cut by limonite and quartz veins with ankerite(?) and calcite contains as much as 55 ppb gold (Szumigala and others, 2000).
Age: Associated with a fault that offsets the Walker Fork pluton of Cretaceous age.
Alteration: The granodiorite is partially altered to chlorite, clay, and calcite.
Commodities (Major) - Au
Development Status: None
Deposit Model: Shear zone-hosted lode gold.
ReferencesAlaska Division of Geological and Geophysical Surveys, Geoterrex-Dighem, and Stevens Exploration Management Corporation, 1999, CD-ROM containing profile and gridded data and section lines of 1997 geophysical survey data for part of the Fortymile mining district, Alaska, southern Eagle and northern Tanacross quadrangles: Alaska Division of Geological and Geophysical Surveys Public-Data File 99-9, 2 CD-ROMs. 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] 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.
| Ankerite ?|
| 'Chlorite Group'|
5 entries listed. 3 valid minerals.
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Locality Updated: High Rake (Bow Rake), Great Longstone, Derbyshire, England, UKFrom Knut Edvard Larsen, 7th Dec 2013 13:49:34