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Bear Mine, Juneau District, Juneau Borough, Alaska, USA

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Latitude & Longitude (WGS84): 58° 51' 40'' North , 135° 4' 48'' West
Latitude & Longitude (decimal): 58.8611111111, -135.08
 
Location: The Bear Mine is at an elevation of about 1,500 feet, about 2 miles east-northeast of Pt. Sherman on Lynn Canal and 1 mile southwest of Lions Head Mountain in the Kakuhan Range. It is in the SE1/4 section 4, T. 35 S., R. 62 E. of the Copper River Meridian. The location is accurate.
Geology: The Bear Mine is a quartz vein in Jualin Diorite. It strikes NW and dips 40-70 NE. It has been traced for 500 feet along strike and 350 feet vertically, and has an average width of 5 to 10 feet (Chris Croff, Placid Oil Co., oral commun., 1987; Redman and others, 1989). Placid Oil Co. drilled 4 core holes in 1984. A second vein, possibly the Savage (JU028), crops out uphill from the Bear vein. It was explored by Placid Oil Co. in 1982 and 1984 by 5 drill holes (Chris Croff, Placid Oil Co., oral commun., 1987) The veins are under control of Coeur Alaska and are in the Kensington Project area (see JU029). The Bear deposit was discovered in 1887 and was mined from 1895 to 1897. Workings include an 1,100-foot crosscut, a 200-foot raise, and 3 levels with 850 feet of drifts. A total of 800 ounces of gold was recovered from 5,900 tons of ore (Redman and others, 1989). The Bear mine is in the Berners Bay district at the north end of the Juneau Gold Belt. The district is characterized by a series of structurally-controlled, mesothermal, gold-bearing quartz veins. Most of the veins are in Early Cretaceous (105 Ma) Jualin Diorite, which intrudes Upper Triassic metabasalt. The Jualin Diorite is generally massive, jointed, blocky, quartz monzonite to quartz monzodiorite. Gold occurs in low-sulfide, quartz-carbonate veins that contain pyrite and tellurides; the veins are marked by distinctive ankeritic alteration zones. There are both extensional and shear veins that generally strike north to northwest and dip east. Discrete vein systems are defined by one or more through-going quartz veins, many of which are in shear zones. Levielle (1991) and Knopf (1911) describe other gangue minerals near vein margins including albite, chlorite, muscovite, and lesser tourmaline, rutile, and apatite. Hydrothermal alteration adjacent to the veins is characterized by reddish-brown ferroan dolomite (Miller and others, 1995). Other alteration includes sericitization of plagioclase, chloritization, sulfidization of mafic minerals, and albitization of feldspars (Leveille, 1991). Pyrite is the most abundant sulfide mineral, with lesser amounts of chalcopyrite, galena, sphalerite, arsenopyrite, and tetrahedrite. Gold occurs in the native state, in pyrite, and in various telluride minerals such as calaverite, hessite, and petzite (Leveille, 1991; Redman and others, 1989). The vein paragenesis consists of early quartz, carbonates, albite and pyrite, followed by deposition of base and precious metals. Gold, galena and the tellurides were the last to be deposited (Leveille, 1991). The age of hydrothermal muscovite from veins at Kensington Mine (JU029) varies from 53.4 Ma to 56.5 Ma (Miller and others, 1994). This coincides with the 55 Ma age of the other mesothermal gold vein deposits in the Juneau Gold Belt (Goldfarb and others, 1997).
Workings: The Bear deposit was discovered in 1887 and was mined from 1895 to 1897. Workings include an 1,100-foot crosscut, a 200-foot raise, and 3 levels with 850 feet of drifts. Placid Oil Co. drilled 4 core holes in 1984. A second vein, possibly the Savage (JU028), crops out uphill from the Bear vein. It was explored by Placid Oil Co. in 1982 and 1984 by 5 drill holes (Chris Croff, Placid Oil Co., oral commun., 1987) The veins are under control of Coeur Alaska and are in the Kensington Project area (see JU029).
Age: 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: 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: From 1895 to 1897, 800 ounces of gold were recovered from 5,900 tons of ore (Redman and others, 1989).

Commodities (Major) - Au; (Minor) - Ag, Cu, Pb, Zn
Development Status: Yes
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)

Mineral List



20 entries listed. 16 valid minerals.

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References

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. Knopf, Adolph, 1911, Geology of the Berners Bay region, Alaska: U.S. Geological Survey Bulletin 446, 58 p. 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. Redman, E.C., Maas, K.M., Kurtak, J.M., and Miller, L.D., 1989, Bureau of Mines Mineral Investigations in the Juneau Mining District, Alaska, 1984-1988, Volume 2--Detailed mine, prospect, and mineral occurrence descriptions, Section D, Juneau Gold Belt Subarea: U.S. Bureau of Mines Special Publication, 424 p.

 
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