Unnamed Occurrence (ARDF - EA119; northwest of Purdy Mine), Fortymile District, Southeast Fairbanks Borough, Alaska, USA
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Geology: The rocks in the vicinity of this occurrence are predominantly granitic rocks of the Chicken pluton of Jurassic age (Werdon and others, 2001). Hornblende from the pluton gives a 40Ar/39Ar plateau age of 187.8 +/-0.9 Ma (Layer and others, 2002). The pluton is intruded by an undated, K-feldspar-porphyritic, biotite hornblende granite that is spatially associated with numerous aplite dikes (Werdon and others, 2001). The southern margin of this granite is brecciated and in high-angle fault contact with upper Paleozoic metasedimentary and metavolcanic rocks. The aplite dikes are commonly sericite-altered. A sample of a quartz-veined aplite dike with a weak iron-oxide stain contains 70 ppb gold, 1.4 ppm silver, 4 ppm bismuth, 74 ppm lead, and 50 ppm zinc (Szumigala and others, 2000).
Age: Jurassic or younger.
Alteration: Aplite dikes are commonly altered to sericite and are locally iron stained.
Commodities (Major) - Au
Development Status: None
Deposit Model: Plutonic-related gold.
Mineral List
2 entries listed. 2 valid minerals.
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References
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.
