Unnamed Occurrence (ARDF - EA117; east of South Fork), Fortymile District, Southeast Fairbanks Borough, Alaska, USA

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Location: This occurrence is along a tractor trail on a ridge top at an elevation of about 3,050 feet about 2.9 miles east-southeast of the old town of Franklin. The occurrence is in section 4, T. 27 N., R. 19 E., of the Copper River Meridian. The location is accurate.
Geology: The rocks in the vicinity of this occurrence are interlayered Paleozoic, amphibolite-facies paragneiss, schist, amphibolite, orthogneiss, and minor marble (Werdon and others, 2001) that to the south have been intruded by small Jurassic plutons. Quartz-feldspar-white mica gneiss is iron-oxide stained and contains disseminated limonite cubes (pseudomorphs after pyrite?). Pyrite cubes approximately 1 millimeter in diameter occur within vuggy quartz veins. Many fractures are filled with limonite. An assay of this material contains 40 ppm arsenic, 444 ppm lead, and 136 ppm zinc (Werdon and others, 2000).
Age: Paleozoic or younger; possibly related to nearby Jurassic intrusions.
Alteration: Quartz-feldspar-white mica gneiss at the site is iron-oxide stained and contains disseminated limonite cubes (pseudomorphs after pyrite?).

Commodities (Major) - Pb, Zn; (Minor) - As
Development Status: None
Deposit Model: Distal Zn-Pb skarn?

References

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. Werdon, M.B., Szumigala, D.J., Newberry, R.J., Grady, J.C., and Munly, W.C., 2000, Major oxide, minor oxide, trace element, rare-earth element, and geochemical data from rocks collected in Eagle and Tanacross quadrangles, Alaska in 2000: Alaska Division of Geological and Geophysical Surveys Raw-Data File 2000-4, 27 p., 3 sheets, scale 1:63,360.

Mineral List

Limonite

Pyrite

Quartz

3 entries listed. 2 valid minerals.