Julia

Prospect, Inactive

Commodities and mineralogy

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

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale C-3
Latitude 58.5936
Longitude -134.7933
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Julia prospect is at an elevation of about 2,200 feet, on the divide between Yankee Basin and Cottrell Basin. It is about 0.1 mile east of the center of section 11, T. 38 S., R. 64 E. of the Copper River Meridian. The location is accurate within 1/4 mile.

Geologic setting

Geologic description

The Julia prospect is in northwest-trending intercalated black phyllite, graphitic schist, and felsic phyllite. The deposit consists of discontinuous quartz lenses and quartz stringer-veins in black phyllite. The quartz contains arsenopyrite, galena, pyrite, and scorodite (Redman and others, 1989). U.S. Bureau of Mines samples contain up to 20.2 ppm gold and 12.0 ppm silver (Redman and others, 1989). This prospect, together with the Noonday (JU090), Puzzler (JU089), and Cascade (JU088) prospects, is sometimes collectively referred to as the Julia group. The deposits were discovered before 1904. The Julia prospect was developed by an 8-foot adit, several open cuts, and some trenches. The area was drilled by Placid Oil in the early 1980s and by Houston Oil and Minerals in 1985 (Redman and others, 1989).
This prospect is in the Juneau Gold Belt, which consists of more than 200 auriferous 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 (-134.795090139707, 58.593275713109)
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 is an 18-foot adit, an 8-foot adit, an inclined shaft, and several open cuts and trenches. The deposit was drilled by Placid Oil in the early 1980s and by Houston Oil and Minerals in 1985.
Indication of production None

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