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Cirque Prospect, Iditarod District, Yukon-Koyukuk Borough, Alaska, USA

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Location: The Cirque prospect is on the west-facing, steep headwall of a cirque at the head of a fork of Billy Goat Creek. The prospect is at an elevation of about 3,000 feet about 0.5 mile south-southwest of the center of section 21, T. 32 N., R 41 W., of the Seward Meridian. The location is accurate.
Geology: The Cirque prospect consists of a series of parallel, tourmaline-axinite- quartz-sulfide fracture fillings and breccia bodies in monzonite and quartz syenite of the Beaver Mountains stock. The major fractures strike N75E and dip steeply to vertically; they are discontinuously exposed for about 2 miles. The unnamed deposit at about a mile to the northeast may be an easterly extension of this mineralized zone. The Cirque prospect is one of the best-exposed lode deposits in the Iditarod quadrangle. The most extensive zone of mineralization lies along the side of a steep cirque headwall where nearly massive chalcopyrite-tourmaline pods up to 6 feet wide are exposed for almost 65 feet along strike. Lesser amounts of galena, pyrite, sphalerite, and bismuth-antimony sulfosalts, including boulangerite and stromeyerite, are found in a gangue of tourmaline, fluorite, and quartz. Axinite alteration is conspicuous in the walls of the deposit. Excellent exposures allow for a three dimensional estimate of the size of the main zone; it is about 500 feet long, 10 feet thick, and extends for about 800 vertically. Szumigala (1993) placed the Cirque prospect in the center of a large mineralized area called the 'south quartz zone' mineralized area. Samples contained up to 21.00 percent copper, 1,108 parts per million (ppm) silver, 1,400 parts per billion (ppb) gold, more than 2,000 ppm arsenic, 570 ppm bismuth, 60 ppm cadmium, more than 2.00 percent lead, 0.70 percent antimony, 200 ppm tin, 100 ppm tungsten, and 0.50 percent zinc (Bundtzen and Laird, 1982; Bundtzen and Miller, 1997; McGimsey and others, 1988; Miller, Bundtzen, and Gray, 2005). The systematic surface sampling and excellent exposure suggests an inferred resource of 190,000 tons of material with 3.50 percent copper and 445 ppm silver in the main mineralized zone at the Cirque prospect (Bundtzen and Miller, 1997; Miller, Bundtzen, and Gray, 2005).
Workings: Several groups have conducted surface sampling at the Cirque prospect. The U.S. Geological Survey and Alaska Division of Geological and Geophysical Surveys sampled the prospect between 1981 and 1986. Anaconda Minerals sampled the property in 1981. Noranda Exploration sampled the prospect in 1983 (John Dunbier, oral communication, 1983). Battle Mountain Mining Company sampled the prospect in 1990 (Szumigala, 1993).
Age: Undated; may be related to emplacement of the Beaver Mountains stock that has been dated at 70.3 Ma (Bundtzen and Laird, 1982).
Alteration: Greisen developed with tourmaline, quartz, and white mica in the mineralized zone, with axinite on the walls.
Reserves: The systematic surface sampling and excellent exposure suggests an inferred resource of 175,000 tonnes of material with 3.50 percent copper and 445 ppm silver for the main mineralized zone at the Cirque prospect (Bundtzen and Miller, 1997; Miller, Bundtzen, and Gray, 2005).

Commodities (Major) - Ag, As, Cu, Pb; (Minor) - Au, Bi, Cd, Sb, Sn, W, Zn
Development Status: None
Deposit Model: Sn-polymetallic veins (Cox and Singer, 1986; model 20b).

Mineral List



10 entries listed. 8 valid minerals.

The above list contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

Bundtzen, T.K., and Laird, G.M., 1982, Geologic map of the Iditarod D-2 and eastern D-3 quadrangles, Alaska: Alaska Division of Geological and Geophysical Surveys Geologic Report 72, 1 sheet, scale 1:63,360. McGimsey, R.G., Miller, M.L., and Arbogast, B.F., 1988, Paper version of analytical results, and sample locality map for rock samples from the Iditarod quadrangle, Alaska: U.S. Geological Survey Open-File Report 88-421-A, 110 p., 1 sheet, scale 1:250,000. Miller, M.L., Bundtzen, T.K., and Gray, J.E., 2005, Mineral resource assessment of the Iditarod quadrangle, west-central Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-2219-B, scale 1:250,000, pamphlet. Szumigala, D.J., 1993, Gold mineralization related to Cretaceous-Tertiary magmatism in the Kuskokwim Mountains of west-central and southwestern Alaska: Los Angeles, University of California Ph.D. dissertation, 300 p.

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