Green Monster

Mine, Active

Commodities and mineralogy

Main commodities Ag; Cu; Epidote; Fe
Other commodities Au
Ore minerals chalcopyrite; galena; magnetite; molybdenite; pyrite; pyrrhotite
Gangue minerals albite; epidote; garnet; hornblende; quartz

Geographic location

Quadrangle map, 1:250,000-scale CR
Quadrangle map, 1:63,360-scale A-2
Latitude 55.24571
Longitude -132.54868
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Green Monster Mine is at an elevation of about 2,500 feet, about 0.2 mile east of Lake Josephine and about 0.4 mile west-northwest of the southeast corner of section 30, T. 76 S., R. 85 E.

Geologic setting

Geologic description

The Green Monster Mine was located in 1900 and most of the early work was done prior to WW I (Brooks, 1902; Wright and Wright, 1908; Wright, 1915; Wedow and others, 1953; Herreid and others 1978; Maas and others, 1991, 1995). The early workings consisted of two 65-foot adits and several trenches and open pits on 14 fourteen patented claims. The deposits are in hornfels and albite-quartz-epidote-garnet-hornblende skarn developed from late Proterozoic or Cambrian marble of the Wales Group. The metamorphic rocks are bordered on the west by a Cretaceous granodiorite stock and on the east by a smaller stock of epidotized, Cretaceous gabbro and diorite. The deposits explored before WW I are mainly irregular masses of chalcopyrite and magnetite in skarn, and chalcopyrite in irregular quartz veins and masses associated with steeply-dipping faults. Galena, pyrrhotite, pyrite, and molybdenite are locally present. Brooks (1902) reports gold assays of up to $8-$10 per ton in high grade samples (gold at $20.67 per ounce). Maas and others (1991) collected several samples that contained up to 6.93 percent copper, 40.2 parts per million silver, and 1,868 parts per billion gold, and noted that there is significant tonnage of copper ore in sight.
For several decades, there has been substantial production of epidote crystals from a small open pit several hundred feet southeast of the old adits. The epidote from this locality is widely known and specimens of it are found in museums and private collections throughout the world (Leavens and Thomssen, 1977). The mine is closed to private collection and as of 2004 is being mined by Doug Toland.
Geologic map unit (-132.550345035979, 55.2453559549422)
Mineral deposit model Copper skarn (Cox and Singer, 1986; model 18b).
Mineral deposit model number 18b
Age of mineralization The deposit is between two Cretaceous granitic bodies, one or both of which is probably the source of the metals and of the skarn and hornfels host rocks.
Alteration of deposit The deposits are associated with skarn and hornfels developed in marble near Cretaceous granitic bodies to the west and east.

Production and reserves

Workings or exploration The Green Monster deposit was discovered in 1900 and most of the early work was done prior to WW I. The early workings consisted of two 65-foot adits and several trenches and open pits on 14 fourteen patented claims. For several decades, there has been substantial production of epidote crystals from a small open pit several hundred feet southeast of the old adits. The epidote from this locality is widely known and specimens of it are found in museums and private collections throughout the world (Leavens and Thomssen, 1977). The mine is closed to private collection and as of 2004 is being mined by Doug Toland.
Indication of production Yes; small
Reserve estimates There are no published ore reserves. There is every indication, however, that world-class epidote crystals will continue to be mined indefinitely on a small scale from this deposit.
Production notes
Epidote crystals have been produced for at least the last 20 years by
Doug Toland. The quantity is unknown but the production is probably substantial on the scale of the mineralogical trade. This locality is known as the source for some of the finest known examples of epidote crystals; they are featured in collections and museums throughout the world and many have been sold for large sums.

References

MRDS Number A010085

References

Leavens, P.B., and Thomssen, R.W., 1977, Famous mineral localities: Prince of Wales Island, Alaska: Mineralogical Record, v. 8, no. 1, p. 4-12.
Roppel, Patricia, 1991, Fortunes from the earth: Manhattan, Kansas, Sunflower University Press, 139 p.
Reporters D.J. Grybeck (Applied Geology)
Last report date 5/1/2004