Ascension

Mine, Inactive

Alternative names

Ibex

Commodities and mineralogy

Main commodities Ag; Au; Pb; Zn
Other commodities Cu
Ore minerals chalcopyrite; galena; gold; pyrrhotite; silver; sphalerite; tetrahedrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale B-1
Latitude 58.2852
Longitude -134.3147
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mine is at an elevation of approximately 2,600 feet on the north side of Sheep Creek. It is 1/2 mile southwest of Sheep Mountain and 1/2 mile east of Roberts Peak, just south of the center of the boundary between sections 28 and 29, T. 41 S., R. 68 E. of the Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

The Ascension (Ibex) Mine was discovered in 1887 and was developed by 4 adits. An estimated 800 tons of ore was mined but production records are not available. The deposit consists of three boudinaged, concordant, quartz veins near the contact between black phyllite and green phyllite (Redman and others, 1989). The veins are up to 300 feet long, 1.5 feet thick, and contain chalcopyrite, galena, native gold, native silver, pyrrhotite, sphalerite, and tetrahedrite. The U.S. Bureau of Mines has estimated an inferred resource of 10,000 tons of ore with 3.44 ounces of silver and 0.01 ounce of gold per ton, with an average mining width of 3.0 feet (Redman and others, 1989). Their samples of the veins contained up to 354.6 ppm silver, 0.7 ppm gold, 0.54 percent lead, and 0.47 percent zinc. They also collected a 300-pound metallurgical sample that contained 382 ppm silver and 6.2 ppm gold. Cyanide amenability tests recovered 63.7 percent of the gold but only 1.1 percent of the silver (Redman and others, 1989).
This prospect 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 zone 160 km long by 5 to 8 km wide 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 (-134.316466063023, 58.2848728854433)
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).

Production and reserves

Workings or exploration The deposit at the Ascension (Ibex) Mine was discovered in 1887 and was developed by 4 adits.
Indication of production Yes; small
Reserve estimates The U.S. Bureau of Mines has estimated an inferred resource of 10,000 tons of ore that contain 3.44 ounces of silver and 0.01 ounce of gold per ton, with an average mining width of 3.0 feet (Redman and others, 1989).
Production notes An estimated 800 tons of ore was mined but production figures are not available.

References

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., 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