Highway Copper; Bruce Occurrence, Fortymile District, Southeast Fairbanks Borough, Alaska, USA

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Location: The adit of the Highway Copper prospect is located below the Taylor Highway, about 1.5 miles east of the town of Chicken, Alaska. The adit is in the SE1/4 section 33, T. 27 N., R. 18 E. of the Copper River Meridian. The location is accurate. This prospect is locality 14 of Cobb (1972 [MF-393]), locality 8 of Eberlein and others (1977), and locality 82 of Burleigh and Lear (1994).
Geology: The Highway Copper lode deposit is in upper Paleozoic greenschist-facies unit of mainly hornblende metagabbro and metadiabase; these rocks are in high-angle fault contact with faulted slivers of foliated granitic rocks of the Taylor Mountain batholith of Triassic age (Werdon and others, 2001). Earlier reports simply referred to the host rocks as greenstone (Saunders, 1957; Smith, 1968). The greenstone exhibits epidote-chlorite-calcite alteration, and it is faulted, brecciated, and quartz-veined in the prospect area. Multiple generations of quartz veins are commonly present. Pyrite occurs in the quartz veins and as disseminated grains in surrounding host rocks. Other sulfides include chalcopyrite, sphalerite, and tetrahedrite(?); secondary malachite is also present (Burleigh and Lear, 1994). The greenstone is locally cut by granitic and pegmatitic dikes. Sericite from an altered quartz monzonite dike at the prospect gives an interpreted model age of 193.9 Ma (Layer and others, 2002). This suggests the deposit may be related to Jurassic intrusions in the area. The Highway Copper prospect is interpreted to be a pluton-related, copper-gold prospect. Assays of mineralized samples contain as much as 31 ounces of silver per ton, 2,160 ppb gold, 2,150 ppm arsenic, 36 ppm bismuth, 4,450 ppm copper, 37 ppm molybdenum, 1.47 percent lead, 3,260 ppm antimony, 18.5 ppm tellurium, and 5,852 ppm zinc (Burleigh and Lear, 1994; U.S. Bureau of Mines, 1995). Smith (1968) noted that silver(?) occurs in veinlets; samples of mineralized float contain 0.02 ounce of gold, 0.68 ounce of silver per ton, 0.1 percent copper, 0.2 percent lead, and 0.3 percent zinc (Smith, 1968). The Highway Copper prospect was explored in the 1960's and 1970's (Eberlein and others, 1977) and was reexamined by the U.S. Bureau of Mines in the mid-1990's (Burleigh and Lear, 1994).
Workings: The Highway Copper prospect was explored in the 1960's and 1970's (Eberlein and others, 1977) and was reexamined by the U.S. Bureau of Mines in the mid-1990's (Burleigh and Lear, 1994).
Age: Sericite from an altered quartz monzonite dike at the prospect gives an interpreted model age of 193.9 Ma (Layer and others, 2002). This suggests the deposit may be related to Jurassic intrusions in the area.
Alteration: The greenstone host rock is altered to epidote, chlorite, and calcite; it is faulted, brecciated, and quartz-veined.

Commodities (Major) - Ag, Au, Cu; (Minor) - As, Bi, Mo, Pb, Sb, Te, Zn
Development Status: Undetermined.
Deposit Model: Pluton-related Cu-Au deposit.

References

Burleigh, R.E., Fechner, S.A., and Lear, K.G., 1994, Preliminary results of the mineral resource evaluation of the Bureau of Land Management Black River and Fortymile River planning units: U.S. Bureau of Mines Open-File Report 48-94, 117 p. Cobb, E.H., 1972, Metallic mineral resources map of the Eagle quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-393, 1:250,000 scale, 1 sheet. Eberlein, G.D., Chapman, R.M., Foster, H.L., and Gassaway, J.S., 1977, Map and table describing known metalliferous and selected nonmetalliferous mineral deposits in central Alaska: U.S. Geological Survey Open-File Report 77-168-D, 132 p., 1 sheet, scale 1:1,000,000. 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] 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. U.S. Bureau of Mines, 1995, Final report of the mineral resource evaluation of the Bureau of Land Management Black River and Fortymile River Subunits: U.S. Bureau of Mines Open-File Report 79-95, 226 p. 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.

Mineral List

Calcite Chalcopyrite

Malachite Pyrite

Quartz Sphalerite

Tetrahedrite

7 entries listed. 7 valid minerals.