Mine, Inactive

Commodities and mineralogy

Main commodities Ag; Au; Cu
Other commodities As; Co; Mo
Ore minerals chalcopyrite; gold; magnetite; pyrite
Gangue minerals calcite; epidote; quartz

Geographic location

Quadrangle map, 1:250,000-scale MC
Quadrangle map, 1:63,360-scale C-8
Latitude 61.5522
Longitude -143.7873
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mine is on the east valley wall of the Kuskulana River, 500 to 2,000 feet southwest of Berg Creek. The site is shown as a mine symbol on the McCarthy C-8 quadrangle (1995 edition), about 500 feet southwest of Berg Creek. It is at an elevation of about 2,750 feet , 4,000 feet north of elevation 5050. The mine is in the NW1/4 of section 4, T. 4 S., R. 9 E. of the Copper River Meridian. This is localities 107 and 108 of MacKevett (1976) and locality 36 of MacKevett and others (1978). Cobb and MacKevett (1980) included this mine under the name 'Berg Cr.'.

Geologic setting

Geologic description

The Midas mine has lower workings in Jurassic plutonic rocks and Triassic Chitistone Limestone and upper workings in the Triassic Nizina Limestone (MacKevett and others, 1978). The limestone is adjacent to a Jurassic granodiorite and quartz diorite pluton and is contact metamorphosed. The contact is very irregular and alternating intrusive rocks and limestone were encountered in the underground workings (Moffit and Mertie, 1923). The mine was explored by several adits, raises, winzes, and drifts (Moffit and Mertie, 1923, fig. 8).
At the lower and main workings of the mine, gold-bearing quartz-calcite veins, and magnetite and epidote skarn with irregularly distributed pyrite and chalcopyrite occur in Triassic Chitistone Limestone (Moffit and Mertie, 1923; Van Alstine and Black, 1946; MacKevett, 1976). The principal vein deposit is in granodiorite (Moffit and Mertie, 1923). It strikes N70E and dips 45S. It is a banded quartz-calcite vein with pyrite and chalcopyrite. A sample of vein material contained 8 parts per million (ppm) gold, 10 ppm silver, 1,000 ppm copper, and 20 ppm molybdenum (MacKevett, 1976). A sample of skarn from the lower workings contained 0.6 ppm gold, 1.5 ppm silver, 20,000 ppm copper, and 500 ppm cobalt.
At the upper workings, disseminations and small masses of magnetite, pyrite, and chalcopyrite occur in quartz veins and skarn bodies in metamorphosed Triassic Nizina Limestone. A sample of the vein material contained more than 10,000 parts per million arsenic.
Geologic map unit (-143.78938514052, 61.5517391503871)
Mineral deposit model Polymetallic vein; Cu? skarn (Cox and Singer, 1986; model 22c; 18b?).
Mineral deposit model number 22c, 18b?
Age of mineralization Probably Jurassic based on the age of the pluton associated with the deposit.
Alteration of deposit Calc-silicate replacement of limestone. The plutonic rocks are altered along the veins but the type of alteration is not described.

Production and reserves

Workings or exploration The mine was explored by several adits, raises, winzes, and drifts (Moffit and Mertie, 1923, fig. 8).
Indication of production Yes; small

Additional comments

The locality is in the Wrangell-Saint Elias National Park and Preserve.