Joyce-Jenson Prospect, Juneau Mining District, Juneau, Alaska, USAi

Regional Level Types
Joyce-Jenson Prospect	Prospect
Juneau Mining District	Mining District
Juneau	City Borough
Alaska	State
USA	Country

Location: The Joyce-Jenson prospect is at an elevation of about 2,200 feet on the northwest side of the ridge crest that is bounded on the north by Cowee Creek, on the northeast by Canyon Creek, and on the west by South Fork Cowee Creek. It is 1/4 mile northwest of Cottrell Basin, in the SW1/4NW1/4 section 2, T. 38 S., R. 64 E. of the Copper River Meridian. The location is accurate within 1/4 mile.
Geology: The Joyce-Jensen deposit was discovered in 1906. It is in phyllite and consists of a northwest-trending quartz vein that dips northeast and is up to 12 feet thick. The vein parallels the foliation of the phyllite and contains up to 5 percent sulfides in pods and stringers. The sulfides are arsenopyrite, pyrite, pyrrhotite, chalcopyrite, and galena (Knopf, 1912; Redman and others, 1989). U.S. Bureau of Mines samples contain up to 11.8 ppm gold. Workings include a 220-foot adit, a 10-foot adit, an open cut,and several trenches. The deposit was drilled 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).
Workings: Workings include a 220-foot adit, a 10-foot adit, an open cut, and several trenches. The deposit was drilled by Houston Oil and Minerals in 1985.
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) - Ag, Cu, Pb
Development Status: No
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)

Other Databases

Link to USGS - Alaska:	JU079

Other Regions, Features and Areas containing this locality

References