Antimony (Sb) is a hard, brittle, silver-white metal with a relatively high specific gravity (6.69) and a relatively low melting temperature. Antimony is a constituent in some alloys. The presence of this metal hardens the alloy, lowers the melting point, and decreases contraction during solidification. The metal’s main use is to impart stiffness and hardness to lead alloys. Antimony compounds are used in medicines, paint pigments, enamelware glazes, and as fireproof coatings on clothing. They are also used in the rubber and patent-leather industries.
Many minerals contain antimony; however, stibnite and antimonial lead ores are the main sources of the metal. Stibnite (Sb2S3) and its alteration oxide, stibiconite (Sb3+Sb25+O6(OH)), were the only minerals mined in Arkansas for this metal. Stibnite is steel-gray, has a relatively high specific gravity (4.6), and has a metallic luster. It often forms slender prismatic crystals that may have a curved habit. Stibiconite is an earthy yellow oxide formed by the weathering of stibnite. Antimony sulfide mineralization is encased within quartz veins and was formed under relatively low temperature conditions for vein mineralization.
Ore-bearing quartz veins cut steeply dipped, folded, and faulted beds of the Stanley Shale (Mississippian). The veins strike generally east-west. Sulfides of copper, zinc, iron, and bismuth have been reported locally associated with the antimony ores. Veins are traceable on the surface for 1.5 to two miles, but the veins pinch and swell within short distances, causing the ore minerals to vary from a feather edge to several feet thick in lenses and pods. Such unpredictability of ore requires expensive exploration to delineate significant deposits. Little to no exploration was ever done of the deposits during active mining.
Mining of antimony ore has been limited to northern Sevier County, although some stibnite is also present in Pike County, associated with cinnabar (HgS). Mined ore deposits occurred as lenses or pockets of stibnite encased in nearly vertical quartz veins. Antimony mining took place intermittently in Arkansas after the metal’s discovery in 1873. Smelting attempts were made first in 1887 but were unsuccessful. The first commercial production was recorded in 1889. Mining activity peaked during World War I when metal prices were high, and sporadic efforts to continue mining ended in 1924 due to the low price of the metal. Initially, some oxide ore was recovered from shallow trenches excavated along the trend of the larger veins, and at depth, sulfide mineralization was encountered. Underground mining consisted of sinking shafts or driving horizontal entrances (adits) into surface-exposed ore bodies, driving crosscuts through the veins, and tunneling along the strike of the veins into adjacent ore bodies. There was no exploratory drilling program. The only ore reserves noted were those exposed on the ore face during mining. Significant water flows were encountered during mining from the mining faces and cross veins of quartz that were encountered, causing the added expense of keeping the underground mines open. Ores produced from the mines were not concentrated, except by hand labor in a process called hand cobbing; therefore, only high-grade ores were mined. Ores were shipped by wagon to nearby rail facilities and then to out-of-state smelters. The potential resource of the district is estimated by the U.S. Bureau of Mines at about 5,000 tons of concentrates. Total production of antimony concentrates through 1947, the last year of mining, was estimated by the U.S. Bureau of Mines at 5,390 tons valued at $230,000.
Known ore bodies were essentially depleted. In the event that they need to be mined because of a national emergency, some low-grade ores still exist on the larger mine sites, remnants of the hand cobbing of high-grade ores. These materials would have to be shipped, as any construction of a mill depends on the discovery and blocking out of significant ore reserves.
For additional information:
Hall, R. B. “Stibnite Deposits of Sevier County, Arkansas.” MS thesis, Northwestern University, 1940.
Hess, F. L. “The Arkansas Antimony Deposits.” U.S. Geological Survey Bulletin 340-D, pp. 241–252. Washington DC: U.S. Geological Survey, 1908.
Howard J. M. “Antimony District of Southwest Arkansas.” Arkansas Geological Commission Information Circular 24. Little Rock: Arkansas Geological Commission, 1979.
Pittenger, G. C. “Geochemistry, Geothermometry, and Mineralogy of Cu, Pb, Zn, and Sb Deposits, Sevier County, Arkansas.” MS thesis, University of Arkansas, 1974.
Stearn, N. H. “Stibnite in Quartz.” American Mineralogist 20.1 (1935): 59–62.
Stroud, R. B., R. H. Arndt, F. B. Fulkerson, and W. G. Diamond. Mineral Resources and Industries of Arkansas. U.S. Bureau of Mines Bulletin 645. Washington DC: U.S. Department of the Interior, 1969.
J. Michael Howard
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