Jualin Mine, Juneau District, Juneau Borough, Alaska, USA
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Geology: The Jualin Mine is in Jualin Diorite in a shear zone 400 to 600 feet wide; the shear zone has a strike length of nearly 15,000 feet, and extends from the Jualin Mine area to the Ophir prospect (JU026). The veins in the shear zone generally strike N 35 W and dip 50-75 NE. The ore zones pinch and swell along strike to as much as 40 feet thick. The orebodes in the Jualin deposit consist of ore shoots that exhibit a strong southeast rake (Barnett and others, 1989). Noteworthy veins at the Jualin deposit include the Empire vein, East vein, number 1, 2, 3, 3E and 4 veins, Production was from relatively high grade individual veins. The number 1 vein averages 7 feet thick and varies from 0.53 to 0.73 ounce of gold per ton gold; the number 2 vein averages 3 feet thick and contains from 0.73 to 0.12 ounce of gold per ton; and the number 3 vein averages 5 feet thick with an average grade of 0.48 ounce of gold per ton (Redman and others, 1989). The Berners Bay district features two general types of veins (Miller et al., 1995): network (stockwork) veins which generally contain 0.1 to 0.25 ounce of gold per ton, as at Kensington mine (JU029); and individual veins that contain 0.5 ounce or more of gold per ton; as at the Jualin mine. Historically, the gold has been produced from the individual veins. The current (2001) reserves of the Jualin mine are 1,069,400 tons of ore with an average grade of 0.349 ounce of gold per ton (Woollett, 1990). The Jualin 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: Workings at the Jualin Mine include over 15,000 feet of workings on 5 levels; two inclined shafts, one 220 deep and the other 160 feet deep; a 310-foot main shaft; a 150-foot shaft; and the 5, 000-foot Berners Tunnel (Redman and others, 1989). A 5.5-mile access road was completed from tidewater to the mine site in July, 1988 (Barnett, 1989). Core drilling as of the end of 1991 totaled 82,337 feet in 126 holes (Bundtzen and others, 1991). Coeur Alaska acquired the rights to the Jualin Mine area from International Curator Resources Ltd. in 1995 (Swainbank and others, 1995).
Age: Hydrothermal muscovite from veins in the Jualin Mine gives ages of from 53.2 Ma to 55.5 Ma (Miller and others, 1994). This coincides with the 55 Ma age of the mesothermal gold-quartz-vein deposits in the rest of the Juneau Gold Belt (Goldfarb and others, 1997).
Alteration: Hydrothermal alteration adjacent to individual 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). The quartz carbonate stockworks in the Jualin vein system feature three zones of alteration within and adjacent to the stockworks: 1) an inner zone of intense carbonate-sericite alteration; 2) an intermediate zone of mottled, dark-green diorite marked by cataclastic fabric and increased chlorite +/- sericite; and 3) an outer zone of equigranular diorite with abundant epidote, and locally, potassium feldspar (Barnett and others, 1989).
Production: The Jualin deposit was discovered in 1895 and the mine commenced production in 1896 when a 10-stamp mill was in operation. In 1914, the first semi-diesel generators in Alaska were installed. Between 1895 and 1929 the mine produced 37,913 ounces of gold from 74,624 tons of ore. Milling recovered 85-90% of the gold; 85% of the gold was free-milling and the remaining 15% was combined with sulfides (Redman and others, 1989).
Reserves: Current (2001) reserves are 1,069,400 tons of ore that averages 0.349 ounce of gold per ton (Woolett, 1990).
Commodities (Major) - Au; (Minor) - Cu, Pb, Zn
Development Status: Yes
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)
20 entries listed. 16 valid minerals.
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Barnett, J.C., 1989, Jualin gold project, 1988 progress report, Berners Bay District: Unpublished report for International Curator Resources, Ltd., 75 p. Barnett, J.C., Vandel, J.C., Monks, J.I., and Johnson, G.S., 1989, Jualin gold project, 1989 progress report: Unpublished report for Placer Dome U.S., Inc., 75 p. Bundtzen, T.K., Swainbank, R.C., Wood, J.E., Clough, A.H., 1991, Alaska's Mineral Industry 1991: Alaska Division of Geological & Geophysical Surveys, Special Report 46, 89 p. Cheney, E.S., 1981, Geology of the Jualin gold property, Berners Bay district of the Juneau Gold Belt: Unpublished report for B-T Enterprises, Seattle, Wash. 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., 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., Clough, A.H., Henning, M.W., and Hansen E.W., 1995, Alaska's mineral industry 1994: Alaska Division of Geological and Geophysical Surveys Special Report 49, 77 p. Woollett, G.N., 1990, Jualin Project: Unpublished report for International Curator International Resources, Ltd., Denver, Colo., 13 p.