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Ophir; Hartford; Chilkat; Selkirk; Acropolis Prospect, Juneau District, Juneau Borough, Alaska, USA

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Location: The Ophir Mine is at an elevation of about 1,450 feet, 2 miles northeast of Pt. Sherman on Lynn Canal and 1 mile west-southwest of Lions Head Mountain in the Kakuhan Range. The Ophir Mine is marked on the Juneau D-4 topographic map. It is approximately 3/4 mile northwest of the Kensington mine (JU029), in the NE1/4 section 5, T. 35 S., R. 62 E. of the Copper River Meridian. The location is accurate.
Geology: The Ophir Mine (as it is commonly called but has no production) consists of several quartz veins and associated quartz-vein stockworks in Jualin Diorite. The Ophir deposit was discovered in 1887. Workings consist of a 350-foot adit with 250 feet of drifts, a 125-foot adit with a 75-foot crosscut, and a 75-foot inclined shaft (Redman and others, 1989). The Ophir workings explored at least 5 principal quartz veins, named the Hartford, Ophir, Chilkat, Selkirk, and Acropolis (Kensington Mines, 1914). The Ophir prospect is in the Kensington project area, that in 2001 was controlled by Coeur Alaska. It 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 Ophir deposit was discovered in 1887. Workings consist of a 350-foot adit with 250 feet of drifts, a 125-foot adit with a 75-foot crosscut and a 75-foot inclined shaft (Redman and others, 1989). The deposit has been extensively explored by Placid Oil Co. and Echo Bay Mines-Coeur Alaska, and in 2001 is controlled by Coeur Alaska.
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: No recorded production.
Reserves: The Kensington project area (see JU029), as defined by Coeur-Alaska, includes the Kensington (JU029), Ophir, Mexican (JU028), Horrible (JU027), and other veins, that collectively contain over 1.96 million ounces of proven and probable gold (Bundtzen and others, 1996).

Commodities (Major) - Au; (Minor) - Ag, Cu, Pb, Zn
Development Status: Undetermined.
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

Bundtzen, T.K., Swainbank, R.C., Clough, A.H., Henning, M.W., and Charlie, K.M., 1996, Alaska's mineral industry, 1995: Alaska Division of Geological and Geophysical Surveys Special Report 50, 72 p. Coeur d'Alene Mines Corporation, 2001, Corporate website: http://www.ceour.com; accessed August 2002 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. Kensington Mines Company, 1902-1914, Miscellaneous reports and data in connection with Kensington Mines Company, Berners Bay, Alaska: Alaska Territorial Department of Mines, Miscellaneous Report MR 112-02, 112 p. Knopf, Adolph, 1911, Geology of the Berners Bay region, Alaska: U.S. Geological Survey Bulletin 446, 58 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., Gehrels, G,E., and Snee, L.W., 1994, Genetic links among fluid cycling, vein formation, regional deformation, and plutonism in the Juneau gold belt, southeastern Alaska: Geology, v. 22, p. 203-206 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. Swainbank, R.C., Bundtzen, T.K., and Wood, J.E., 1991, Alaska's mineral industry, 1990: Alaska Division of Geological and Geophysical Surveys Special Report 45, 78 p.

 
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