Foster Prospect, Juneau Mining District, Juneau, Alaska, USAi

Regional Level Types
Foster Prospect	Prospect
Juneau Mining District	Mining District
Juneau	City Borough
Alaska	State
USA	Country

Location: The Foster prospect is at an elevation of approximately 200 feet on the northwest bank of Kowee Creek on Douglas Island, immediately west of West Juneau. It is in the SE1/4SW1/4 section 22, T. 41 S., R. 67 E. of the Copper River Meridian. The location is accurate.
Geology: The Foster prospect was discovered before 1900 and has 4 adits (Redman and others, 1989). The deposit consists of several, thin, concordant, quartz veins in black phyllite. The veins contain pyrite. U.S. Bureau of Mines samples did not contain significant metal values (Redman and others, 1989). The country rocks are Upper Jurassic or Cretaceous marine argillite and graywacke, interbedded with andesite or basalt (Brew and Ford, 1985). The bedded rocks are regionally metamorphosed to prehnite-pumpellyite or greenschist grade, and cut by diorite or gabbro dikes and sills. 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).
Workings: The deposit at the Foster prospect was discovered before 1900 and has 4 adits (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) - Au ?
Development Status: None

Other Databases

Link to USGS - Alaska:	JU186

Other Regions, Features and Areas containing this locality

References