| Main commodities | Ag; Au |
|---|---|
| Other commodities | Pb; Zn |
| Ore minerals | arsenopyrite; galena; pyrite; sphalerite |
| Gangue minerals | quartz |
| Quadrangle map, 1:250,000-scale | JU |
|---|---|
| Quadrangle map, 1:63,360-scale | C-3 |
| Latitude | 58.5812 |
| Longitude | -134.7856 |
| Nearby scientific data | Find additional scientific data near this location |
| Location and accuracy | The Noonday prospect is at an elevation of approximately 2,400 feet on the southeast side of Yankee Basin. It is in the SE1/4NE1/4 section 14, T. 38 S., R. 64 E. of the Copper River Meridian. The location is accurate. |
Geologic descriptionThe Noonday prospect is in northwest-trending intercalated black phyllite, graphitic schist, and felsic phyllite (Knopf, 1912). The deposit consists of discontinuous quartz lenses and quartz-stringer lodes up to 6 feet thick in black phyllite. The quartz contains arsenopyrite, galena, pyrite, and sphalerite. This prospect together with the Puzzler (JU089), Julia (JU083), and Cascade (JU088) prospects are sometimes collectively referred to as the Julia group. The deposits were discovered before 1904. This prospect was developed by an 18-foot adit and 5 trenches. The area was drilled by Placid Oil in the early 1980s and by Houston Oil and Minerals in 1985. U.S. Bureau of Mines samples contained up to 50.3 ppm gold and 7.0 ppm silver (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 | (-134.787390503834, 58.5808751489502) |
|---|---|
| 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). |
| Workings or exploration | This prospect together with the Puzzler (JU089), Julia (JU083) and Cascade (JU088) prospects are sometimes collectively referred to as the Julia group. The deposits were discovered prior to 1904. This prospect was developed by an 18-foot adit and 5 trenches. The area was drilled by Placid Oil in the early 1980s and by Houston Oil and Minerals in 1985. |
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| Indication of production | None |
ReferencesGehrels, 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.
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| Reporters | J.C. Barnett and L.D. Miller (Juneau, Alaska ) |
|---|---|
| Last report date | 12/15/2001 |