Black Chief Prospect, Juneau Mining District, Juneau, Alaska, USAi

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

Location: The Black Chief prospect is at an elevation of about 2,200 feet on the south wall of Cottrell Basin. It is in the NW1/4NE1/4 section 11, T. 38 S., R. 64 E. of the Copper River Meridian. The location is accurate within 1/4 mile.
Geology: The Black Chief prospect was discovered in 1906. It consists of a northwest-trending quartz stockwork zone in black phyllite and graphitic schist. The zone dips northeast and is up to 20 feet thick. The stockwork veins average approximately 1 inch thick and contain arsenopyrite, pyrite, and galena. A U.S. Bureau of Mines sample across a 2-foot width of the stockwork contained 16.7 ppm gold. Workings include a caved adit, a 320-foot adit, and an open cut (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).
Workings: Workings include a caved adit, a 320-foot adit, and an open cut.
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; (Minor) - Pb
Development Status: No
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)

Other Databases

Link to USGS - Alaska:	JU081

Other Regions, Features and Areas containing this locality

References