Treasury Hill

Mine, Inactive

Alternative names

Gold Knob

Commodities and mineralogy

Main commodities Au
Other commodities Pb
Ore minerals arsenopyrite; galena; gold; pyrite; pyrrhotite
Gangue minerals calcite; quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale B-3
Latitude 58.4227
Longitude -134.6754
Nearby scientific data Find additional scientific data near this location
Location and accuracy 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.

Geologic setting

Geologic description

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).
Geologic map unit (-134.677186791049, 58.4223724047238)
Mineral deposit model Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization 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 of deposit Wallrocks adjacent to the veins are strongly altered and contain albite, chlorite, carbonate, sericite, and apatite.

Production and reserves

Workings or exploration 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.
Indication of production Yes; small
Production notes Approximately 300 ounces of gold was recovered in 1908 and 1909 by sluicing the soil overlying the quartz veins (Redman and others, 1989).

References

MRDS Number A012013

References

Gehrels, G.E., McClelland, W.C., Samson, S.D., and Patchett, P.J., 1991, U-Pb geochronology of detrital zircons from a continental margin assemblage in the northern Coast Mountains, southeastern Alaska: Canadian Journal of Earth Sciences, v. 28, no. 8, p.1285-1300.
Goldfarb, R.J., Miller, L.D., Leach, D.L., and Snee, L.W, 1997, Gold deposits in metamorphic rocks in Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 151-190.
Miller, L.D., Goldfarb, R.J., Gehrels, G,E., and Snee, L.W., 1994, Genetic links among fluid cycling, vein formation, regional deformation, and plutonism in the Juneau gold belt, southeastern Alaska: Geology, v. 22, p. 203-206.
Reporters J.C. Barnett and L.D. Miller (Juneau, Alaska )
Last report date 12/15/2001