Groundhog

Mine, Inactive

Alternative names

Perseverance
Alaska Gastineau
Alaska Juneau

Commodities and mineralogy

Main commodities Ag; Au; Pb
Other commodities Cu; Zn
Ore minerals arsenopyrite; bismuth; bismuthinite; chalcopyrite; electrum; galena; gold; joseite; pyrite; pyrrhotite; sphalerite; tetrahedrite
Gangue minerals ankerite; quartz

Geographic location

Quadrangle map, 1:250,000-scale JU
Quadrangle map, 1:63,360-scale B-2
Latitude 58.2963
Longitude -134.3355
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mine is at an elevation of 2,700 feet at the head of Icy Gulch. It is 3 miles southeast of Mt. Juneau and 1/2 mile northeast of Gastineau Peak, near the center of the SW1/4 section 20, T. 41 S., R. 68 E. of the Copper River Meridian. The location is accurate. Descriptions of the Alaska-Juneau mine (JU165) commonly include the Groundhog Mine.

Geologic setting

Geologic description

The Groundhog mine is often considered part of the Perseverance Mine (JU168) which is in turn often considered part of the Alaska-Juneau Mine (JU165). The surface over the Groundhog Mine was placer-mined prior to 1888, and lode mining began in 1889. The mine was consolidated with the Perseverance Mine (JU168) in 1911. The total recorded production from the Groundhog mine is 900 tons of ore. Gold recovery from placer operations is not documented but several thousand dollars of gold (at $20.67 per ounce) were probably produced (Redman and others, 1989). There are 3 adits, placer workings and 8 open cuts. The Groundhog mine was explored extensively by Echo Bay Mines between 1986 and 1997 (Redman and others, 1989).
The Groundhog deposit represents the upper portion of the Perseverance orebody of the Alaska-Juneau mine, and consists of a system of sulfide-bearing, auriferous, quartz-ankerite veins in the structurally lowest portion of the Perseverance Slate, an Upper Triassic unit of carbonaceous and graphitic quartz-sericite phyllite, schist, and black slate, with minor carbonaceous limestone and numerous sill-like lenses of amphibolite or metagabbro (Miller and others, 1992; Light and others, 1989). The vein system extends for more than 6 kilometers along strike, 700 meters in vertical extent , and is confined to the lowest 100 meters of the Perseverance Slate. The system comprises numerous veins, veinlets, stringers and stockworks; individual veins range from a few centimeters to over 1 meter thick. The veins are 95 percent quartz with subordinate ankerite, pyrrhotite, galena, sphalerite, electrum, arsenopyrite, pyrite, and native gold. Approximately 90 percent of the gold is free-milling (Light and others, 1989; Twenhofel, 1952).
The Groundhog 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 (-134.33726705082, 58.2959730627339)
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 Alteration consists of hydrothermal biotite, ferroan dolomite, and sericite; chlorite and albite partly replace amphibolite (Miller and others, 1992). The alteration has been traced with decreasing intensity as much as 1 kilometer from the Alaska-Juneau mine. Inward from its periphery, magnetite, then ilmenite and magnetite, are replaced by pyrrhotite (Miller and others, 1992; Newberry and Brew, 1987).

Production and reserves

Workings or exploration The surface over the Groundhog Mine was placer-mined prior to 1888, and lode mining began in 1889. The mine was consolidated with the Perseverance Mine (JU168) in 1911. There are 3 adits, placer workings, and 8 open cuts. The Groundhog Mine was explored extensively by Echo Bay Mines between 1986 and 1997.
Indication of production Yes; small
Reserve estimates Assuming a sublevel caving mining model, Echo Bay Mines Ltd. calculated an indicated and inferred resource for the Alaska-Juneau Mine--including the Groundhog Mine--of 89 million tons of ore that contain 0.05 ounce of gold per ton.
Production notes The total recorded production from the Groundhog Mine is 900 tons of ore. Gold and silver recovery is not documented. Gold recovery from the placer operations is not documented but several thousand dollars in gold (at $20.67 per ounce) was probably produced.

References

MRDS Number A012039

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., Barton, C.C., Fredericksen, R.S., and Bressler, J.R., 1992, Structural evolution of the Alaska-Juneau lode gold deposit, southeastern Alaska: Canadian Journal of Earth Sciences, v. 29, p. 865-878.
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