Comet

Mine, Active

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Cu; Pb; Zn
Ore minerals chalcopyrite; galena; gold; pyrite; sphalerite
Gangue minerals calcite; chlorite; ferroan dolomite; quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale D-4
Latitude 58.8552
Longitude -135.0723
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Comet Mine is at an elevation of about 2,300 feet, about 3 miles east of Pt. Sherman on Lynn Canal and 1.5 miles south-southwest of Lions Head Mountain in the Kakuhan Range. The mine is marked on the Juneau D-4 topographic map. It is in the NE1/4 section 9, T. 35 S., R. 62 E. of the Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

Note: Beginning in the 1990s, this and other old mines and prospects in the vicinity were consolidated by Coeur-Alaska into a single property (Birak, 2006). They have carried out major new drilling and underground exploration that better defines the mineralization, largely blurs the geologic distinction among the old deposits, and extends the ore bodies greatly. They have developed a coherent modern interpretation of the mineralization as a single deposit which Coeur-Alaska intends to mine as a unit. This deposit is described separately in ARDF as the Kensington (Coeur-Alaska) deposit (JU261). For geologic reference purposes and for their historic value, the pre-Coeur-Alaska data for this and the other old mines and prospects that Coeur-Alaska consolidated are retained in ARDF.
The deposit at the Comet Mine consists of 2 principal quartz veins about 50 ft apart that strike north and dip 70E. The largest vein is 300-500 feet long; it averages 2 to 3 feet wide at the surface and is up to 9 feet thick in underground exposures. The vein is truncated to the north by a large, left-lateral fault; to the south it crosses a diorite-phyllite contact, where it splits and ends. The veins contain pyrite, chalcopyrite, galena and free gold (Redman and others, 1989).
The Comet Mine is the largest gold producer in the Berners Bay region; it produced 22,485 ounces of gold from 51,463 tons of ore between 1894 and 1900. The deposit was discovered in the 1880s and tunneling began in 1891. A 20-stamp mill was in place by 1892 and production began in 1894. The mine has 9,000 feet of workings on 9 levels, 5 adits, and 1 open stope.
Geologic map unit (-135.074116545726, 58.8548709426433)
Mineral deposit model Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a).
Mineral deposit model number 36a
Age of mineralization The age of mineralization in the Berners Bay district is about 55 Ma, the same as the other mesothermal gold-quartz-vein deposits in the Juneau Gold Belt (Goldfarb and others, 1997).
Alteration of deposit Hydrothermal alteration adjacent to the veins is characterized by reddish-brown ferroan dolomite alteration (Miller and others, 1995). Other alteration includes sericitization of plagioclase, chloritization and sulfidization of mafic minerals, and albitization of feldspars (Leveille, 1991).

Production and reserves

Workings or exploration The Comet deposit was discovered in the 1880s and tunneling began in 1891. A 20-stamp mill was in place by 1892 and production began in 1894. The mine has 9,000 feet of workings on 9 levels, 5 adits and 1 open stope. Placid Oil Co. drilled several core holes in 1981.
Indication of production Yes; small
Production notes The Comet Mine is the largest gold producer in the Berners Bay region producing 22,485 ounces of gold from 51,463 tons of ore between 1894 and 1900. The deposit was discovered in the 1880s and tunneling began in 1891. A 20-stamp mill was in place by 1892 and production began in 1894.

References

MRDS Number A012103

References

Birak, D.J., 2006, Kensington gold project: Unpublished Technical Report for Cour d'Alene Mines, 116 p. (posted on www/.sedar.com, April 20, 2006).
Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Kucinski, R., Porterfield, J., and Croff, C., 1985, Kensington Project summary report - 1985: Unpublished report for Placid Oil Co., 27 p.
Leveille, R.A., 1991, Geology and gold deposits of the Jualin mine area, Berners Bay district, southeastern Alaska: Fairbanks, University of Alaska, M.S. thesis, 200 p.
Miller, L.D., Goldfarb, R.J., Snee, L.W., Gent, C.A., and Kirkham, R.A., 1995, Structural geology, age, and mechanisms of gold vein formation at the Kensington and Jualin deposits, Berners Bay district, southeast Alaska: Economic Geology, v. 90, p. 343-368.
Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska ); D.J. Grybeck (Port Ludlow, WA)
Last report date 6/5/2008