Mountain Top

Mine, Probably inactive

Commodities and mineralogy

Main commodities Hg
Other commodities Ag; As; Au; Co; Cr; Sb
Ore minerals cinnabar; pyrite; stibnite
Gangue minerals carbonate; quartz

Geographic location

Quadrangle map, 1:250,000-scale SM
Quadrangle map, 1:63,360-scale B-6
Latitude 61.3957
Longitude -157.96285
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Mountain Top Mine is on a small plateau about 4.2 mile east-northeast of Chineekluk Mountain. It is at an elevation of about 1400 feet, about 0.6 mile northwest of the center of sec. 18, T. 15 N., R. 48 W., of the Seward Meridian. The location is accurate. The mine is locality 34 of Miller and others (1989).

Geologic setting

Geologic description

The rocks in the vicinity of the Mountain Top Mine consists of thermally altered, olivine basalt that overlies (?) sandstone and siltstone of the Upper Cretaceous, Kuskokwim Group (Cady and others, 1955; Sorg and Estlund, 1972). The basalt is interpreted to be a large dike by Sorg and Estlund (1972); a flow by Reifenstuhl and others (1984) and by the reporters of this record (T.K. Bundtzen and M.L. Miller, unpublished field data, 1988).
A series of four, en echelon, high-angle faults cut the olivine basalt; the faults strike about N 50 W, and dip about 80 NE (T.K. Bundtzen and M.L. Miller, unpublished prospect map, 1988). The faults are filled with cinnabar, pyrite, and minor stibnite, in a gangue that consists of carbonate minerals and euhedral crystals of quartz. The individual ore zones range from 120 to 190 feet long and 4 to 18 inches thick.
Sorg and Estlund (1972) reported that small amounts of liquid hydrocarbon accompany the cinnabar; they also identified dickite and buddingtonite in the mineralized zones. Their mineralized grab samples contained up to 2.00 percent mercury, 1,500 parts per million (ppm) chromium, 100 ppm cobalt, 1,500 ppm arsenic, and 1.5 ppm silver. The high chromium and cobalt probably reflect high background values in the mafic host rocks. Up to 300 parts per billion gold were identified in cinnabar-rich zones (Robinson, 1984 [RI 84-11]). From 1982-1986, about 165 flasks (about 12,540 pounds) of mercury were produced from the Mountain Top Mine (Bundtzen and others, 1987; Miller and others, 1989).
Geologic map unit (-157.965200097963, 61.3949934074384)
Mineral deposit model Silica-carbonate mercury? (Cox and Singer, 1986; model 27c).
Mineral deposit model number 27c?
Age of mineralization Undated, although the nearby Fairview prospect (ARDF SM019) has a 40Ar/39Ar age of 72.6 Ma (Gray, Gent, and others, 1997).
Alteration of deposit Mafic dikes are altered to dickite and buddingtonite.

Production and reserves

Workings or exploration James R. Wylie discovered the Mountain Top deposit in 1968 after panning cinnabar to its hardrock source. J. R. Wylie subsequently explored the deposit with an auger drill and a bulldozer. In 1970, the U.S. Bureau of Mines drilled seven core holes on the property, the deepest of which was 50 feet. Sorg and Estlund (1972) published a detailed geologic map of the property in 1971. The reporters of this record made a geologic sketch of the property in 1988 (T.K. Bundtzen and M.L. Miller, unpublished. data). In 1988, a D-6 bulldozer, a small ball mill, a jig plant, and a retort furnace were on the mine site.
Indication of production Yes; small
Reserve estimates According to Sorg and Estlund (1972), there were 200 flasks of mercury 'in sight' in 1971.
Production notes From 1982 to 1986, about 165 flasks of mercury were produced from the Mountain Top Mine (Bundtzen and others, 1987; Miller and others, 1989).


MRDS Number A013448


Bundtzen, T.K., Cox, B.C., and Veach, N.C., 1987, Heavy mineral provenance studies in the Iditarod and Innoko districts, western Alaska: Process Mineralogy VII, The Metallurgical Society, p. 221-246.
Gray, J.E., Gent, C.A., Snee, L.W., and Wilson, F.H., 1997, Epithermal mercury-antimony and gold-bearing vein lodes of southwest Alaska, in Goldfarb, R.J., and Miller, L.D., eds., Mineral Deposits of Alaska: Economic Geology Monograph 9, p. 287-305.
Wells, J.T., and Ghiorso, M.S., 1988, Rock alteration, mercury transport, and metal deposition at Sulphur Bank, California: Economic Geology, vol. 83, p. 606-618.
White, D. E., and Robinson, C. E., 1962, Sulphur Bank, California, a major hot spring quicksilver deposit, in Engel, A.E.J., James, H.L., and Leonard, B.F., eds., Petrologic studies: A volume in honor of A.F. Buddington: Boulder, Colorado, Geological Society of America p. 397-428.
Reporters T.K. Bundtzen (Pacific Rim Geological Consulting, Inc.) and M.L. Miller (U.S. Geological Survey)
Last report date 5/3/2003