Cirque

Prospect, Active

Commodities and mineralogy

Main commodities Ag; As; Cu; Pb
Other commodities Au; Bi; Cd; Sb; Se; Sn; Te; W; Zn
Ore minerals boulangerite; chalcopyrite; galena; hessite; pyrite; sphalerite; stromeyerite; weibullite
Gangue minerals axinite; fluorite; quartz; tourmaline

Geographic location

Quadrangle map, 1:250,000-scale ID
Quadrangle map, 1:63,360-scale D-2
Latitude 62.8425
Longitude -156.9798
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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.

Geologic setting

Geologic description

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. An unnamed deposit 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 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 feet vertically. Szumigala (1993) placed the Cirque prospect in the center of a large mineralized area he called the 'south quartz zone'. Samples contained up to 21.0 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).
Systematic surface sampling and excellent exposure suggests an inferred resource of 190,000 tons of material with an average grade of 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).
In 2007, Alaska Ventures, Inc. (Bundtzen, 2008) staked 84 Alaska mining claims that covered much of the north-central Beaver Mountains and most of the high-grade copper-silver-gold(-tin) prospects and occurrences there. Four high-grade samples were analyzed that came from veinlets at the Cirque deposit. They contained 2.67 to 47.80 grams of silver per ton, 38.6 to 464 grams of bismuth per ton, and 0.47 to 88.1 grams of tellurium per ton. The high bismuth and tellurium values suggest silver-rich zones in the deposit and the minerals hessite (Ag2S) and weibullite (Pb6Bi8(S,Se)18) were identified in the samples by microprobe.
Geologic map unit (-156.982156837161, 62.8418416210128)
Mineral deposit model Sn-polymetallic veins (Cox and Singer, 1986; model 20b).
Mineral deposit model number 20b
Age of mineralization Undated; may be related to emplacement of the Beaver Mountains stock that has been dated at 70.3 Ma (Bundtzen and Laird, 1982).
Alteration of deposit Greisenization marked by tourmaline, quartz, and white mica in the mineralized zone, and by axinite in the wall rocks.

Production and reserves

Workings or exploration 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). In 2007, Alaska Ventures, Inc. (Bundtzen, 2008) staked 84 Alaska mining claims that covered much of the north-central Beaver Mountains and most of the high-grade copper-silver-gold(-tin) prospects and occurrences in the area, including the Cirque deposit.
Indication of production None
Reserve estimates The systematic surface sampling and excellent exposure suggests an inferred resource of 175,000 tonnes of material with an average grade of 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).

References

References

Reporters T.K. Bundtzen (Pacific Rim Geological Consulting, Inc.), M.L. Miller (U.S. Geological Survey); and C.C. Hawley (Hawley Resource Group); D.J. Grybeck (Port Ludlow, WA)
Last report date 6/5/2008