Alaska Gold Belt; Nelson-Lott Prospect, Juneau District, Juneau Borough, Alaska, USA
Location: This prospect is at an elevation of approximately 1,200 feet on the east valley wall at the head of Sheep Creek. It is near the center of the SE1/4 section 34, T. 41 S., R. 68 E. of the Copper River Meridian. The location is accurate.
Geology: The Alaska Gold Belt prospect was developed in 1915 after the Alaska Gold Belt Company acquired the nearby Sheridan prospect (JU213). Development work consisted of a 2,750-foot adit that is now (2001) caved. The adit was designed to be a prospecting tunnel and was diamond drilled at the face (Redman and others, 1989). The deposit consists of quartz veins in black phyllite, chlorite phyllite, and metagabbro (Wells and others, 1986). Silicified black phyllite and quartz veins that contain minor pyrite can be seen on the dump. U.S. Bureau of Mines samples of the silicified phyllite contained up to 7.4 ppm silver and samples of quartz veins contained up to 24 ppm gold. Historic gold values up to 34 ppm of gold are reported (Redman and others, 1989). This prospect iis 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).
Workings: The Alaska Gold Belt prospect was developed in 1915 after the Alaska Gold Belt Company acquired the nearby Sheridan prospect (JU213). Development work consisted of a 2,750-foot adit that is now (2001) caved. The adit was designed to be a prospecting tunnel and was diamond drilled at the face (Redman and others, 1989).
Age: 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).
Commodities (Major) - Ag, Au
Development Status: 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. Redman, E.C., Maas, K.M., Kurtak, J.M., and Miller, L.D., 1989, Bureau of Mines Mineral Investigations in the Juneau Mining District, Alaska, 1984-1988, Volume 2--Detailed mine, prospect, and mineral occurrence descriptions, Section D, Juneau Gold Belt Subarea: U.S. Bureau of Mines Special Publication, 424 p. Wells, D.E., Pittman, T.L., Brew, D.A. and Douglass, S.L., 1986, Map and description of the mineral deposits in the Juneau, Taku River, Atlin, and part of the Skagway quadrangles, Alaska: U.S. Geological Survey Open-File Report 85-717, 332 p., 1 sheet, scale 1:250,000.
| Pyrite|| Quartz|
2 entries listed. 2 valid minerals.
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Locality Updated: Alemão Mine, Padre Paraíso, Jequitinhonha valley, Minas Gerais, BrazilFrom Reynaldo Contreira, 8th Dec 2013 19:30:40