Aurora Borealis

Mine, Active

Alternative names

Morningstar

Commodities and mineralogy

Main commodities Au
Other commodities Pb
Ore minerals arsenopyrite; galena; pyrite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale C-3
Latitude 58.5929
Longitude -134.8632
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mine is at an elevation of about 1,200 feet between Bessie Creek and South Fork Cowee Creek. It is 1/4 mile northeast of the Bessie mine (JU085), in the SW1/4 section 9, T. 38 S., R. 64 E. of the Copper River Meridian. The location is accurate.

Geologic setting

Geologic description

The Aurora Borealis Mine, also known as the Morning Star, was discovered in 1896. It consists of a northeast-trending quartz vein and quartz stringer lode that dips 20 NW. The vein is in northerly-striking, west-dipping black phyllite near the contact with metamorphosed volcanic conglomerate. The vein mostly follows a shear zone in the phyllite and varies from a few inches to 3.6 feet thick; it commonly branches into numerous quartz veinlets and stringers. The quartz contains up to 2 percent pyrite and arsenopyrite, with minor galena. The sulfides are concentrated near the vein margins (Barnett, 1988; Redman and others, 1989). A U.S. Bureau of Mines sample of the quartz vein contained up to 4.1 ppm gold over 2.7-foot width, and a sample of metavolcanic rock contained 11.3 ppm gold (Redman and others, 1989). In 1988, Monument Resources panel-sampled the entire 200-foot length of the vein exposed in one adit. The weighted average of their assays was 0.163 ounce of gold per ton over 200 feet. Included in that average was a 50-foot zone that had a weighted average of 0.431 ounce of gold per ton (Barnett, 1988). There are 4 adits and 1,400 feet of underground workings. The mine is estimated to have produced 150 ounces of gold prior to 1913, which is half of the combined production of the Aurora Borealis and the Bessie mine (JU085) (Redman and others, 1989). The U.S. Bureau of Mines estimates that the Aurora Borealis deposit contains a resource of 3,500 tons of ore that average 0.1 ounce of gold per ton. The area was explored by Noranda in 1981 and by Monument Resources in 1988. Monument Resources drilled 5 holes on the Bessie (JU085) and the Aurora Borealis properties in 1988. The holes intersected 2 narrow veins, each assaying more than 1.1 ounces of gold per ton (Barnett, 1988).
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 (-134.864991964389, 58.592575606444)
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 There are 4 adits and 1,400 feet of underground workings. The mine area was explored by Noranda in 1981 and by Monument Resources in 1988. Monument Resources drilled 5 holes on the Bessie (JU085) and the Aurora Borealis properties in 1988 (Barnett, 1988; Redman and others, 1989; Roehm, 1936).
Indication of production Yes; small
Reserve estimates The U.S. Bureau of Mines estimates that the Aurora Borealis deposit contains a resource of 3,500 tons of ore that average 0.1 ounce of gold per ton.
Production notes The mine is estimated to have produced 150 ounces of gold prior to 1913, half of the combined production of the Aurora Borealis and the Bessie mine (JU085) (Redman and others, 1989).

References

MRDS Number A012073

References

Barnett, J.C., 1988, 1988 Summary report, Bessie gold project: Unpublished report for Monument Resources, Ltd., 35 p.
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