Ebner

Mine, Inactive

Commodities and mineralogy

Main commodities Ag; Au
Other commodities Cu
Ore minerals chalcopyrite; gold; pyrite; pyrrhotite
Gangue minerals ankerite; quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale B-2
Latitude 58.3107
Longitude -134.3749
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Ebner Mine is at an elevation of approximately 700 feet, on the southeast side of Gold Creek. It is 1.2 mile southeast of Mt. Juneau and immediately south of Ebner Falls. It is near the center of the SE1/4 section 13, T. 41 S., R. 67 E. of the Copper River Meridian. The location is accurate. References to the Alaska Juneau mine (JU165) commonly include the Ebner Mine (JU149), the Groundhog Mine (JU169), the Sheep Creek Tunnel (JU177), and the Perseverance Mine (JU168).

Geologic setting

Geologic description

The deposit at the Ebner Mine was discovered in 1880. The mine was developed by nearly 11,000 feet of underground workings including the 3,500-foot Ebner Tunnel which was rehabilitated by Echo Bay Mines in 1987. The mine produced an estimated 32,000 ounces of gold and over 1,000 ounces of silver between 1889 and 1907, and 165,750 tons of ore with an average of 0.1 ounce gold per ton between 1925 and 1930. There was some gold production prior to 1898 but accurate production records are not available. The mine was acquired by the Alaska-Juneau Mining Co. in 1923. It currently (2001) is referred to as the Ebner orebody and represents the northern extension of the Alaska-Juneau Mine (JU165). The Ebner orebody was explored extensively by Echo Bay Mines in the late-1980s and 1990s. The U.S. Bureau of Mines has estimated that it contains a reserve of 300,000 tons of ore with an average of 0.07 ounce of gold per ton (Redman and others, 1989). The Ebner mine and the Alaska-Juneau mine are in the structurally lowest portion of the Perseverance Slate, a Upper Triassic unit that consists of quartz-sericite phyllite, schist, and black slate with minor carbonaceous limestone and numerous sill-like lenses of amphibolite or metagabbro (Miller and others, 1992; Light and others, 1989). The deposit is a system of quartz veins more than 6 kilometers in strike length, and 700 meters in vertical extent. The quartz-vein system is restricted to the lower 100 meters of the Perseverance Slate. The quartz-vein system is made up of numerous veins, veinlets, stringers and stockworks; individual veins vary from a few centimeters to over 1 meter thick. The Ebner veins are 95 percent quartz, with subsidiary ankerite, pyrrhotite, pyrite, chalcopyrite, and native gold. Approximately 90 percent of the gold is free-milling (Light and others, 1989). Hydrothermal alteration associated with the emplacement of the quartz veins formed biotite, ferroan dolomite and sericite as well as some chlorite and albite in the amphibolite. The alteration has been traced with decreasing intensity as much as 1 kilometer from the Alaska-Juneau mine. Inward from its periphery, magnetite, then ilmenite and magnetite, are replaced by pyrrhotite (Miller and others, 1992; Newberry and Brew, 1988).
This mine is in the Juneau Gold Belt, which consists of more than 200 gold-quartz vein deposits that have produced nearly 7 million ounces of gold. These gold-bearing mesothermal quartz vein systems form a 160-km-long by 5- to 8-km-wide zone along the western margin of the Coast Mountains. The vein systems are in or near shear zones adjacent to west-verging, mid-Cretaceous thrust faults. The veins are hosted by diverse, variably metamorphosed, sedimentary, volcanic, and intrusive rocks. From the Coast Mountains batholith westward, the host rocks include mixed metasedimentary and metavolcanic sequences of Carboniferous and older, Permian and Triassic, and Jurassic-Cretaceous age. The sequences are juxtaposed along mid-Cretaceous thrust faults (Miller and others, 1994). The sequences are intruded by mid-Cretaceous to middle Eocene plutons, mainly diorite, tonalite, granodiorite, quartz monzonite, and granite. Sheetlike tonalite plutons emplaced just east of the Juneau Gold Belt and undeformed granite and granodiorite bodies that are emplaced farther to the east are between 55 and 48 Ma (Gehrels and others, 1991). The structural grain of the belt is defined by northwest-striking, moderately to steeply northeast-dipping, penetrative foliation that developed between Cretaceous and Eocene time (Miller and others, 1994). The majority of the veins in the Juneau Gold Belt strike northwest. Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997).
Geologic map unit (-134.376668748975, 58.3103732171442)
Mineral deposit model Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Isotopic dates indicate that the auriferous veins in the Juneau Gold Belt formed between 56 and 55 Ma (Miller and others, 1994; Goldfarb and others, 1997).
Alteration of deposit Hydrothermal alteration associated with the emplacement of the quartz veins formed biotite, ferroan dolomite and sericite, as well as some chlorite and albite in the amphibolite. The alteration has been traced with decreasing intensity as much as 1 kilometer from the Alaska-Juneau mine. Inward from its periphery, magnetite, then ilmenite and magnetite, are replaced by pyrrhotite (Miller and others, 1992; Newberry and Brew, 1987).

Production and reserves

Workings or exploration The deposit at the Ebner Mine is now part of the Alaska-Juneau Mine (JU165) system and was discovered in 1880. The mine was developed by nearly 11,000 feet of underground workings including the 3,500-foot Ebner Tunnel, which was rehabilitated by Echo Bay Mines in 1987. The mine was acquired by the Alaska-Juneau Mining Co. in 1923. It currently (2001) is referred to as the Ebner Orebody and represents the northern extension of the Alaska-Juneau Mine (JU165). The Ebner Orebody was explored extensively by Echo Bay Mines in the late-1980s and 1990s.
Indication of production Yes; medium
Reserve estimates The U.S. Bureau of Mines has estimated that this orebody contains a reserve of 300,000 tons of ore with an average of 0.07 ounce of gold per ton.
Production notes The Ebner mine produced an estimated 32,000 ounces of gold and over 1,000 ounces of silver between 1889 and 1907, and 165,750 tons of ore with an average grade of 0.1 ounce of gold per ton between 1925 and 1930. There was some gold production prior to 1898 but accurate production records are not available.

Additional comments

References to the Alaska-Juneau mine commonly include the Ebner Mine (JU149), the Groundhog Mine (JU169), the Sheep Creek Tunnel (JU177), and the Perseverance Mine (JU168).

References

MRDS Number A012043

References

Gehrels, G.E., McClelland, W.C., Samson, S.D., and Patchett, P.J., 1991, U-Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska: Canadian Journal of Earth Sciences, v. 28, no. 8, p.1285-1300.
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.
Miller, L.D., Barton, C.C., Fredericksen, R.S., and Bressler, J.R., 1992, Structural evolution of the Alaska-Juneau lode gold deposit, southeastern Alaska: Canadian Journal of Earth Sciences, v. 29, p. 865-878.
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
Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska )
Last report date 12/15/2001