Treasury Hill; Gold Knob Mine, Juneau Mining District, Juneau, Alaska, USAi

Regional Level Types
Treasury Hill; Gold Knob Mine	Mine
Juneau Mining District	Mining District
Juneau	City Borough
Alaska	State
USA	Country

Location: This mine are at an elevation of 1,600 feet, between the headwaters of Waydelich Creek and Lake Creek . It is 2.5 miles southeast of Peterson Lake near the northeast corner of section 9, T. 40 S., R. 65 E. of the Copper River Meridian. The location is accurate.
Geology: The rocks in the area are black phyllite, graywacke, greenstone and greenschist (Knopf, 1912). A northwest-trending gabbro sill lies between a footwall of phyllite and a hanging wall of greenstone and greenschist. The sill is more than 200 feet thick and has been traced for over 2,000 feet along strike. The sill is cut by numerous quartz and calcite veins and stringers. Most of the quartz stringers are perpendicular to the strike of the sill but some are parallel. The quartz veins are up to 4.5 feet thick, average less than 2 feet thick, and contain disseminated arsenopyrite, pyrite, pyrrhotite, traces of galena, and native gold. The wallrocks adjacent to the veins are strongly altered and contain albite, chlorite, carbonate, sericite, and apatite. Arsenopyrite and pyrrhotite are concentrated along the margins of the veins (Knopf, 1912). The deposit was discovered in 1908 and prospected by numerous trenches and open cuts over a large area. Workings include the Gold Knob adit with 655 feet of workings, and two other adits. Approximately 300 ounces of gold was recovered in 1908 and 1909 by sluicing the soil overlying the exposures (Redman and others, 1989). The deposit was drilled in 1979 by Occidental Minerals and again in 1988 by FMC Corporation. U.S. Bureau of Mines samples contained up to 18.7 ppm gold (Redman and others, 1989). This mine 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 was discovered in 1908 and prospected by numerous trenches and open cuts over a large area. Workings include the Gold Knob adit with 655 feet of workings, and two other adits. The prospect was drilled in 1979 by Occidental Minerals and in 1988 by FMC Corporation.
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: Wallrocks adjacent to the veins are strongly altered and contain albite, chlorite, carbonate, sericite, and apatite.
Production: Approximately 300 ounces of gold was recovered in 1908 and 1909 by sluicing the soil overlying the quartz veins (Redman and others, 1989).

Commodities (Major) - Au; (Minor) - Pb
Development Status: Yes; small
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)

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Link to USGS - Alaska:	JU117

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References