St. Louis; Summit Prospect, Juneau Mining District, Juneau, Alaska, USAi

Regional Level Types
St. Louis; Summit Prospect	Prospect
Juneau Mining District	Mining District
Juneau	City Borough
Alaska	State
USA	Country

Location: The St. Louis prospect is at an elevation of approximately 1,300 feet, near the foot of the north-sloping ridge 1/4 mile south of lower Herbert Glacier. It is near the northwest corner of section 3, T. 39 S., R. 65 E. of the Copper River Meridian. The location is accurate.
Geology: The Summit and St. Louis are adjacent prospects that are described as a single prospect in this record. The deposit was discovered in 1889 and developed by a 22-foot shaft. It was explored by Houston Oil and Minerals in 1986 and by Echo Bay Mines in 1988 to 1992 (Redman and others, 1989). The deposit consists of two east-northeast-trending quartz veins in a shear zone that cuts the foliation of quartz-diorite gneiss. The veins vary from 0.7 foot to 4 feet thick, dip 75 southeast, and contain arsenopyrite, free gold and sparse galena. The wallrock, adjacent to the veins, exhibits potassic alteration (Redman and others, 1989). This deposit is one of the few south of the Berners Bay area in diorite gneiss rather than metamorphosed bedded rocks. U.S. Bureau of Mines samples contained up to 35.7 ppm gold, 3.1 ppm silver (Redman and others, 1989). 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 Summit and St. Louis are adjacent properties that are described as a single prospect in this record. The deposit was discovered in 1889 and developed by a 22-foot shaft. It was explored by Houston Oil and Minerals in 1986 and by Echo Bay Mines in 1988 to 1992 (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).
Alteration: Potassic alteration of the wallrock.

Commodities (Major) - Ag, 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:	JU099

Other Regions, Features and Areas containing this locality

References