Last Chance

Mine, Inactive

Alternative names

Caribou

Commodities and mineralogy

Main commodities Sb
Other commodities Ag; Au; Mo; Pb; Zn
Ore minerals gold; jamesonite; pyrite; pyrrhotite; sphalerite; stibiconite; stibnite
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale MM
Quadrangle map, 1:63,360-scale C-2
Latitude 63.6061
Longitude -150.8139
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Last Chance (sometimes called Caribou) mine is about at the center of the N1/2 NE1/4 of section 22, T. 15 S., R. 17 W., Fairbanks Meridian. The location is accurate within 300 feet. The mine is location 24 of Cobb (1972 [MF 366]), 21 of MacKevett and Holloway (1977), L of Hawley and Associates (1978), 63b of Bundtzen (1981), and 61 of Thornsberry, McKee, and Salisbury (1984).

Geologic setting

Geologic description

The country rock at the Last Chance mine is strongly-deformed, biotite- amphibolite schist of the upper Precambrian Birch Creek Schist (Bundtzen, 1981; Thornsberry, McKee, and Salisbury, 1984, fig. K-2). The deposit consists of a fault-controlled, mineralized quartz vein that strikes about N 30 E and dips 50-70 NW. The strike of the vein is approximately parallel to the strike of the schist hostrock, but the vein dips NW and the schist dips SE.
The vein is 2 to 6 feet thick. Stibnite is the main ore mineral; it occurs in massive form and in elongate crystals mixed with nearly euhedral quartz crystals (Prindle, 1907; Capps, 1919; Bundtzen, Smith, and Tosdal, 1976). Parts of the vein are composed of nearly massive quartz. The stibnite is accompanied by small amounts of pyrite, pyrrhotite, jamesonite, and probably sphalerite. Some of the stibnite is oxidized to stibiconite. The maximum antimony content in samples of the vein is about 26 percent, but the coarse, massive stibnite probably contains more than 50 percent antimony. More than 70 tons of the high-grade stibnite ore has been mined (Cobb, 1980 [OFR 80-363]; Bundtzen, Smith, and Tosdal, 1976).
The stibnite ore is weakly auriferous. Prindle (1907) reported that samples assayed as much as 0.12 ounce of gold and 4 ounces of silver per ton, and Hawley and Associates (1978) reported assays of as much as 0.14 ounce of gold per ton. Free gold has been reported; it probably occurs in quartz-rich parts of the vein, inasmuch as high-grade antimony ores generally contain little gold. Thornsberry, McKee, and Salisbury (1984, location 61, v. 2) reported about 100 ppm molybdenum in several samples and as much as 600 ppm zinc. The molybdenum mineral is unknown; the zinc probably is in small amounts of sphalerite.
Geologic map unit (-150.816190134155, 63.6055968741726)
Mineral deposit model Simple stibnite deposit (Cox and Singer, 1986; model 27d).
Mineral deposit model number 27d
Age of mineralization The deposit is assumed to be Eocene (see record MM091).
Alteration of deposit Local oxidation of stibnite.

Production and reserves

Workings or exploration The deposit was discovered in 1905 (Prindle, 1907; Brooks, 1916), and developed by open cuts, shallow shafts, and short adits. The shafts were flooded when the prospect was visited by Capps in 1916 (Capps, 1919). The mine operated on a small scale in 1968-1970, 1973-74, and 1984.
Indication of production Yes; small
Production notes Twelve 12 tons of high-grade stibnite ore reportedly was mined in about 1905. The ore was not shipped, because high antimony prices during the Russo-Japanese War fell abruptly at the end of the hostilities (Wells, 1933, p. 353-354). Buntzen, Smith, and Tosdal (1976) reported a total of 74,360 pounds of antimony recovered from 71.5 tons of ore before 1974. Thornsberry, McKee, and Salisbury (1984) reported a total production of about 70 tons of ore. There were 15 to 30 tons of ore stockpiled at the site in 1983.

Additional comments

Abundant stibnite occurs in the Caribou Creek placer deposit, just below the Last Chance mine. The property is in Denali National Park and Preserve.

References

MRDS Number A011227

References

Bundtzen, T.K., 1981, Geology and mineral deposits of the Kantishna Hills, Mt. McKinley quadrangle, Alaska: M. S. Thesis, University of Alaska, College, Alaska, 238 p.
Reporters C.C. Hawley
Last report date 5/2/2001