Mayfield

Mine, Probably inactive

Alternative names

Alaska Mayfield

Commodities and mineralogy

Main commodities Au
Other commodities Cu; Pb; Zn
Ore minerals arsenopyrite; chalcopyrite; galena; gold; pyrite; sphalerite
Gangue minerals carbonate minerals; chlorite; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale VA
Quadrangle map, 1:63,360-scale A-8
Latitude 61.1591
Longitude -146.8304
Nearby scientific data Find additional scientific data near this location
Location and accuracy This mine is one-half mile northwest of the northwest end of Lake No. 1 along the east side of Columbia Glacier. It is at an elevation of about 3,000 feet in the SW1/4 section 22, T. 8 S., R. 9 W., of the Copper River Meridian. This mine is probably located to within one-quarter mile. It is locality 7 of Cobb and Matson (1972) and locality 4 of Winkler and others (1981 [OFR 80-892-B]).

Geologic setting

Geologic description

Discontinuous gold-bearing quartz veins and lenses occur along a northwest-trending zone that cuts metaflysch of the Valdez Group (Johnson, 1915). The zone dips to the north and can be traced on the surface for several hundred feet. The quartz veins contain gold, pyrite, chalcopyrite, galena, sphalerite, and arsenopyrite. One of the larger veins was from 1 to 10 feet wide and 200 feet long (Jansons and others, 1984). These veins were explored and developed by at least two adits and more than 600 feet of underground workings (Cobb, 1979 [OFR 79-1241]; Jansons and others, 1984). The veins were located in 1911, and development work and/or production was reported intermittently to 1938 (Cobb, 1979 [OFR 79-1241]), but the total production is only 13 ounces of gold and 2 ounces of silver (Jansons and others, 1984). The U.S. Bureau of Mines collected nine chip samples from the area that contained 0.03 to 70 ppm gold and 0.1 to 25.2 ppm silver; a grab sample contained 52 ppm gold and 22.5 ppm silver. Jansons and others (1984) identified inferred reserves of 600 tons of material that contain 9.54 ppm gold and 3.4 ppm silver.
These veins are probably similar to other gold-bearing quartz veins cutting metaflysch of the Valdez Group in the southern Valdez quadrangle. Data summarized by Goldfarb and others (1997) show that gold-bearing quartz veins in the Valdez Group commonly contain pyrite, arsenopyrite, carbonate minerals, chlorite, and white mica and formed from water-rich fluids with 5 to 15 mole percent CO2 and significant amounts of CH4, N2, and H2S. The vein-forming fluid salinities were less than 8 percent, vein formation temperatures ranged from 225 to 375 degrees centigrade, and emplacement depths varied from 3 to 10 kilometers. The vein-forming fluids were produced by metamorphic devolatilization reactions. Radiometric dating indicates that the veins formed from 57 to 49 Ma (Goldfarb and others, 1997, p. 171) when deep parts of the accreted Valdez Group flysch underwent high-grade metamorphism and partial melting (Hudson, 1994).
Geologic map unit (-146.832470675156, 61.1585704531569)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Radiometric dating indicates that the gold-bearing quartz veins in the Valdez Group formed from 57 to 49 Ma (Goldfarb and others, 1997, p. 171), when deep parts of the accreted Valdez Group flysch underwent high-grade metamorphism and partial melting (Hudson, 1994).
Alteration of deposit Country rocks to gold-bearing quartz veins in Valdez Group metaflysch can be variably silicified, carbonitized, and sericitized (Goldfarb and others, 1997).

Production and reserves

Workings or exploration These veins were explored and developed by at least two adits and more than 600 feet of underground workings (Cobb, 1979 [OFR 79-1241]; Jansons and others, 1984).
Indication of production Yes; small
Production notes These deposits were located in 1911 and development work and/or production were reported intermittently to 1938 (Cobb, 1979 [OFR 79-1241]), but total reported production is only 13 ounces of gold and 2 ounces of silver (Jansons and others, 1984).

References

MRDS Number A011443

References

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.
Hudson, T.L., 1994, Crustal melting events in Alaska, in Plafker, G., and Berg, H. C., eds., The Geology of Alaska: Geological Society of America, DNAG, The Geology of North America, Vol. G-1, p. 657-670.
Reporters Travis L. Hudson
Last report date 12/14/2001