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General Information

The third most abundant element in the earth’s crust, aluminum (Al) is, nevertheless, a relatively new metal to the human race. The commercial process allowing its recovery economically was not discovered until around the turn of the 20th century. Aluminum metal is silvery white, has a low specific gravity (2.69) and a low melting temperature. Except for iron and steel, aluminum is probably used for more purposes than any other metal. Its light weight – about one-third that of steel – and its strength when alloyed with other metals are two reasons for aluminum’s versatility. Other reasons are the ease with which the metal can be cast, machined, rolled, forged, extruded, and drawn. It has high electrical conductivity and significant resistance to atmospheric corrosion. Aluminum paint, beverage cans, baseball bats, high-voltage power lines, house siding, boats, and airplanes are just a few examples of aluminum metal's use.

Another advantage of aluminum is that it can be efficiently recycled. Whereas the extraction of new aluminum from bauxite consumes huge amounts of energy (this includes the energy consumed during mining, processing the ore, and land reclamation), aluminum metal reclaimed from used products requires only 5 percent as much energy. Much of the feedstock of the aluminum metal industry now consists of used beverage cans. In 1991, nearly 57 billion used aluminum cans were recycled in the United States.

Mineralogy and Processing of Arkansas Bauxite

bauxite.jpg (58488 bytes)
Pisolitic bauxite

The principal ore of aluminum is bauxite, a complex mixture of a number of aluminum hydroxides and hydrous aluminum oxides. The most common aluminum-bearing minerals in bauxite are gibbsite (AlOH3), boehmite (AlO(OH)), and diaspore (AlO(OH)). In the Arkansas deposits, diaspore has not been reported. Free quartz along with iron and titanium oxides are common components. Bauxite ranges in color from off-white to deep reddish brown, and structurally from a soft earthy material to a well-cemented rock. An easily recognizable oolitic (BB-sized concretions) to pisolitic (pea-sized concretions) grain texture characterizes many bauxite deposits, including those in Arkansas. Commercial bauxite usually has a minimum content of 50 to 55 percent alumina (Al2O3).

In the bauxite refining process, the aluminum-bearing minerals in bauxite are converted in a multiple-step process to alumina (Al2O3). Alumina can be smelted to form metallic aluminum or it can be used as the source of many other products, including refractory materials used to line high-temperature rotary kilns and metallurgical furnaces. In addition, alumina is a source of many chemicals used in the paper and ceramic industries, in petroleum refining, and in some water-purification processes. Other uses are for the production of synthetic corundum for the manufacture of abrasive stones and grinding wheels, as propants in the petroleum-production industry, and as an ingredient in deodorants, antacids, and some medicines.

Mining and Geology of Arkansas Bauxite

Many of the early-mined Arkansas bauxite deposits were exposed on the surface as outcrops or were beneath only a thin layer of sediments. Consequently, surface-mining methods were initially the most practical and economical. Before and during World War II, significant tonnages were mined underground. Some years after the war, surface operations resumed. Open-pit panel mining has been the normal surface method since the early 1960’s. A strip or block of bauxite is exposed, mined, and then another panel is exposed. The first panel is normally refilled with waste rock. Several panels may be open at the same time to supply the proper blend of ores to meet the mill specifications. In recent years, major reclamation programs have begun to restore not only the recently mined land, but much of the land that was disturbed before reclamation laws went into effect.

The Arkansas bauxite region covers about 275 square miles in the northern part of the West Gulf Coastal Plain and is divided into two mining districts. One area is in Pulaski County south and east of Little Rock and the other is in nearby Saline County, northeast and east of Benton. The bauxite is present mostly as sheet or blanket deposits in very close proximity to outcrops of the intrusive igneous rock, nepheline syenite. The deposits formed in early Tertiary time, developing as soils along the western edge of a shallow marine basin that occupied the Mississippi River Embayment. During that time, hills and knobs of syenite as islands were exposed to intense chemical weathering in a tropical or near-tropical environment (lateritic weathering). In the weathering process, leaching by rain, ground water, and perhaps by salt spray, decomposed the original igneous rock minerals (feldspar and nepheline), removed much of the silica, and concentrated the newly formed oxides and hydroxides of aluminum as the rock we term bauxite. These are residual deposits because they formed essentially in place (in situ paleo-soils). Many other deposits, generally smaller, consist of bauxite removed by erosion from its site of origin and redeposited nearby (transported deposits).

History of Discovery and Production

The aluminum industry has contributed significantly to the state's economy for many years. Bauxite was first mined in Arkansas as an ore of metallic aluminum in 1898, only 11 years after John C. Branner, State Geologist, first identified it in a sample from Pulaski County. Over the years, Arkansas industry has remained the major producer in the United States, providing about 90 percent of all domestic tonnage mined. As aluminum became more widely available, many new uses of the metal (and of the by-products of the aluminum industry) were discovered, and consumption increased rapidly. Tonnages of bauxite mined in Arkansas increased much more slowly than national consumption because larger deposits supplying higher grade bauxite were readily available in the Caribbean region. In the early stages of World War II, merchant freighters carrying bauxite to the United States suffered high losses to enemy submarines. It was imperative that foreign supplies be supplemented by increased domestic production. The tonnage of bauxite mined in Arkansas quickly increased many fold to meet wartime demands for aluminum, which was especially critical to the military aircraft industry. In 1943, more than 6 million long tons of bauxite were mined. Because of changing domestic and world economic market conditions, 1982 was the last year in which bauxite was mined in Arkansas for aluminum metal. Small tonnages continue to be mined and used in the production of a variety of alumina-based materials, including various chemicals, abrasives, and propants.

Certain references, listed in green below, are available from Publications.

Bramlette, M. N., 1936, Geology of the Arkansas bauxite region: Arkansas Geological Survey Information Circular 8, 68 p.
Canby, T. Y., 1978, Aluminum, the magic metal: National Geographic, v. 154, no. 2, p. 186-211.
Gordon, MacKenzie, Jr., Tracey, J. I., Jr., and Ellis, M. W., 1958, Geology of the Arkansas bauxite region: U. S. Geological Survey Professional Paper 299, 268 p.

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Antimony

Many minerals contain antimony (Sb), a soft white metal with a low melting point. However, stibnite and antimonial lead ores are the main sources of the metal. Stibnite (Sb2S3) and 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), a metallic luster, and often forms slender prismatic crystals that may have a curved habit. Stibiconite is an earthy yellow oxide formed by the weathering of stibnite.

Antimony 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, the rubber and patent-leather industries, paint pigments, enamelware glazes, and as fire-proof coatings on clothing.

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 deposits occurred as lenses or pockets of stibnite encased in nearly vertical quartz veins that cut steeply dipping, folded, and faulted beds of the Stanley Shale (Mississippian). The veins strike generally east-west. Sulfides of copper, zinc, iron, and bismuth may be locally associated with the antimony ores. Antimony was mined intermittently in Arkansas after its discovery in 1873. Mining activity peaked during World War I when metal prices were high. Some ore was recovered from shallow trenches excavated along the trend of the larger veins. 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. 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, were estimated by the U. S. Bureau of Mines at 5,390 tons.

Hall, R. B., 1940, Stibnite deposits of Sevier County, Arkansas: Evanston, Ill., Northwestern University, M. S. thesis, 102 p.
Hess, F. L., 1908, The Arkansas antimony deposits: U. S. Geological Survey Bulletin 340-D, p. 241-252.
Howard J. M., 1979, Antimony district of southwest Arkansas: Arkansas Geological Commission Information Circular 24, 29 p.
Pittenger, G. C., 1974, Geochemistry, geothermometry, and mineralogy of Cu, Pb, Zn, and Sb deposits, Sevier County, Arkansas: Fayetteville, University of Arkansas, M. S. thesis, 75 p.
Stearn, N. H., 1935, Stibnite in quartz: American Mineralogist, v. 20, no. 1, p. 59-62.

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Cobalt

Cobalt (Co) is a silvery gray metal which has a relatively high specific gravity (8.9), and is hard, ductile, malleable, and magnetic. Cobalt has diverse industrial and military applications. Its principal use is in super alloys for jet engine parts. Other important uses are in permanent magnets for electrical devices and as a binder for cutting and abrasive tools, such as diamond drill bits. Cobalt chemicals are used for catalysts in the petroleum and chemical industries, drying agents for paints, varnishes and inks, additives to ground coats for porcelain enamels, and as pigments for ceramics, paints, and plastics. Cobalt is rarely extracted from primary ores, but is recovered as a by-product. Most of the present Western World's demand is met by cobalt obtained as a by-product of copper production in the African countries of Zaire and Zambia. Small amounts are also recovered as by-products of platinum or nickel refining.

The United States is the largest consumer of cobalt, using about 30 percent of the world's production in 1991, yet there is no domestic production. Cobalt is considered a strategic and critical mineral because of its industrial and defense-related uses.

In 1983, sample analyses of more than 140 manganese-bearing sites in the Ouachita Mountains region indicated significant amounts (0.05 to 1.2 percent, combined) of cobalt, copper, lithium, and nickel in 40 percent of the deposits sampled. In 1992, the U. S. Bureau of Mines published two studies of the west-central Ouachita manganese district, both concerned with the extraction of manganese and other metals in these ores. In this area, manganese oxides, primarily the minerals cryptomelane (K(Mn4+,Mn2+)8O16) and psilomelane (massive hard manganese oxides), cement brecciated novaculite. Cobalt is concentrated in lithophorite ((Al, Li)Mn4+O2(OH)). Chemical analyses of initial concentrates gave values of 25 percent manganese and 0.17 percent cobalt. Magnetic separation yielded concentrates with up to 41 percent manganese and 0.22 percent cobalt with recoveries of 95 and 93 percent, respectively. No detailed resource evaluation has been done for the manganese district of the Ouachitas, despite several brief periods of active mining. Estimates of the district's manganese potential and, therefore, its potential for recoverable cobalt and other metals vary greatly, from 1 million short tons to over 6.4 million short tons.

O'Connor, W. K., White, J. C., and Turner, P. C., 1992, Carbothermic reduction and leaching of manganese ores from the west-central Arkansas district, in J. P. Hager, ed., Process Mineralogy, EPD Congress, The Minerals, Metals & Materials Society, p. 379-396.
O'Connor, W. K., White, J. C., and Turner, P. C., 1992, Geology and mineral processing of manganese deposits from the west-central Arkansas district: Mining Engineering, v. 44, p. 1361-1368.

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Copper

Copper (Cu), called the red metal, was one of the first metals used by man. This is because it is often present in nature as a native element (and therefore is easy to recognize) and because of unique properties which make it readily workable by primitive techniques. Copper is a soft metal with a relatively high specific gravity (8.9), and is highly ductile and malleable. Modern uses of copper are quite numerous, including electrical wiring, as a necessary metal in the alloys of brass, bronze, and nickel silver, self-lubricating bearings (copper powder), copper tubing, coinage, and copper sulfate (CuSO4), a compound which has many chemical applications. Copper sulfate usage in agriculture to prevent the growth of algae and fungi and as a source of essential trace copper in fertilizer and animal feeds has steadily increased over the years.

Copper is present in at least 19 minerals known in Arkansas. Most of these minerals are fairly scarce, but chalcopyrite (CuFeS2), malachite (Cu22+(CO3)(OH)), and native copper (Cu) are common enough to have encouraged some exploration. Copper mineralization is often present as a minor accessory mineral associated with lead and zinc deposits of the Ozark Plateaus and Ouachita Mountains. In the Ozarks, copper minerals, often associated with sphalerite ((Zn,Fe)S), are most frequently found near faults, flexures, and other structural irregularities in Paleozoic limestones and dolostones. In the Ouachita Mountains, small deposits of copper minerals are found in some quartz veins, usually in association with lead, zinc, or antimony mineralization.

All known deposits of copper minerals in Arkansas are small and uneconomic. In 1900, a small amount of copper was refined from malachite-bearing ore recovered from surface residuum at the Tomahawk mine in Searcy County. An occurrence of secondary copper minerals in Fulton County is sub-economic. Copper minerals associated with lead and zinc mineralization have not proven sufficiently abundant to develop, although the potential exists that copper could be recovered as a by-product from other mining activity.

McKnight, E. T., 1935, Zinc and lead deposits of northern Arkansas: U. S. Geological Survey Bulletin 853, 311 p.
Miser, H. D., and Purdue, A. H., 1929, Geology of the DeQueen and Caddo Gap quadrangles, Arkansas: U. S. Geological Survey Bulletin 808, 195 p.

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Gallium

Gallium (Ga) is a metal which does not form distinct minerals, but substitutes for aluminum in the structure of many aluminum-bearing minerals. Gallium arsenide (GaAs) is the principal compound used in light-emitting diodes, photodetectors, laser diodes, and solar cells. An important potential application incorporates gallium compounds in diodes in bar-code scanners used in grocery stores.

In 1937 V. M. Goldschmidt suggested that the extraction of gallium from alkali aluminate solutions in the Bayer aluminum process might be possible. In the 1940’s, chemists of the U.S. Geological Survey determined that gallium in Arkansas bauxite was enriched more than 4-fold over nepheline syenite, the parent rock of bauxite. The average content of gallium is 0.0086 percent (2.75 ounces per short ton). Gallium was recovered as a by-product of bauxite processing in Saline County from 1947 to 1983. Arkansas is one of two states where this metal has been produced. However, no recovery figures have been released.

Goldschmidt, V. M., 1937, The principles of distribution of chemical elements in minerals and rocks: Chemical Society of London Journal, pt. 1, p. 655-673.
Gordon, Mackenzie, Jr., and Murata, K. J., 1952, Minor elements in Arkansas bauxite: Economic Geology, v. 47, p. 169-179.
Gordon, Mackenzie, Jr., Tracey, J. I., Jr., and Ellis, M. W., 1958, Geology of the Arkansas bauxite region: U. S. Geological Survey Professional Paper 299, 268 p.

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Gold

No metal has gained attention throughout history as has gold. Gold (Au) was one of the earliest metals to be utilized due largely it exists as a native metal. It has unique properties which made it workable by early man. Its bright yellow metallic luster catches the eye. Gold is relatively soft, melts at a low heat, and may be hammered, cut, or drawn into fine wire. The metal has a very high specific gravity (19.3) which facilitates its recovery from ores. Gold has superior electrical conductivity and resistance to corrosion.

Worldwide, there are two types of gold deposits. In situ or lode deposits are disseminations of metallic gold in quartz veins, traces of gold contained in certain sulfide minerals, or extremely fine-grained particles dispersed in host rocks. Placer deposits form from weathering and erosion of rocks containing gold. Secondary gold concentrations result due to the metal's high specific gravity. Placer gold exists as fines, scales, flakes, grains, and nuggets. Native gold usually contains variable amounts of silver.

Gold is used several ways, but over half the world's yearly consumption is in jewelry and artwork. In jewelry, pure gold is alloyed with copper and silver to increase its hardness. Purity is expressed in carats; pure gold being 24 carats. Therefore, 14 carat gold used in jewelry contains 14 parts pure gold and 10 parts of other metals. Gold has emerged in the late 20th century as an essential industrial metal, used in computers, communication equipment, spacecraft, jet airplane engines, and many other applications. Gold is known for its use in jewelry, dental use, and for investment purposes (coins and bars).

In the early 1880’s, reports and rumors of gold finds in Arkansas prompted an investigation by the Arkansas Geological Survey. The results of the study were released in the Annual Report of the Arkansas Geological Survey for 1888 - Volume I. The conclusion was that no workable quantities of gold existed in the Ouachita Mountains region. In 1923, investigations by U. S. Geological Survey geologists in the vicinity of Hot Springs, Garland County, revealed sparse amounts of silver and gold in vein material associated with igneous dikes. In summary, no payable quantities of gold have been discovered in Arkansas.

Comstock, T. B., 1888, A preliminary examination of the geology of western-central Arkansas, with especial reference to gold and silver: Arkansas Geological Survey Annual Report for 1888, v. I, pt. 2, 320 p.
Purdue, A. H., and Miser, H. D., 1923, Description of the Hot Springs district, [Arkansas]: U. S. Geological Survey Atlas, Folio 215, 12 p.
Sick, G. P., 1984, North Mountain Mine – Gold?, in McFarland, J. D., III, and Bush, W. V., eds., Contributions to the geology of Arkansas, v. II: Arkansas Geological Commission Miscellaneous Publication 18-B, p. 115-117.

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Iron

When considering the entire composition of the earth, iron (Fe) is the most abundant element, but it only comprises approximately 6 percent of continental crust. Metallic iron is silvery-white, malleable, ductile, and may be readily magnetized. Elemental iron has a relatively high specific gravity (7.87) and high melting point. Iron is used primarily in the manufacture of iron and steel products. Also, substantial quantities of iron are consumed as paint pigments, in cement, in refractory materials as a fluxing agent used in smelting nonferrous metals, and as a constituent of some catalysts. Magnetic iron ore, magnetite, is used as shielding materials in nuclear power plants, heavy aggregate in concrete, and as a heavy-mineral medium in some metal refining mills.

The iron minerals present in Arkansas are the oxides – goethite (Fe3+O(OH)), limonite (hydrous iron oxides), hematite (Fe2O3), and magnetite (Fe2+Fe23+O4); the carbonates – siderite (Fe2+CO3) and ankerite (Ca(Fe2+,Mg,Mn)(CO3)2); and sulfides of iron – pyrite and marcasite (FeS2), and chalcopyrite (CuFeS2). Goethite is highly variable in habit and form, but is easily recognized when it forms lustrous grape-like masses having a radial internal structure and a brown streak when rubbed against unglazed porcelain. Limonite (essentially rust) varies in color from brown, black, or yellow. Hematite or "red iron ore" varies in color from shiny black to blackish red to brick red. Siderite may be highly variable in color, ranging from gray to yellow, green, white, or shades of reddish brown. Magnetite, which is black and has a metallic luster on a freshly broken surface, can be recognized by its magnetic properties. Pyrite, commonly called "fool’s gold", is extremely common, may be recognized by its brassy yellow metallic luster, brittleness, and is easily distinguished from native gold, which is quite malleable. Marcasite is known as white iron pyrite.

Iron minerals are common throughout Arkansas, but rarely are they in sufficient quantities to be of commercial value. In Carroll, Lawrence, Sharp, Fulton, and Randolph Counties, secondary deposits of limonite are associated with sandstone, chert, and dolostone formations of Paleozoic age. Deposits of iron-rich concretions are present near hilltops and are residual in nature. Individual deposits were calculated by the U. S. Bureau of Mines to contain 5,000 to 4,000,000 tons of iron ore with the majority probably containing less than 25,000 tons. Smaller deposits are also in Washington and Marion Counties. Past mining of these residual iron ores consisted of small-scale recovery of the harder surface-exposed material. In Hot Spring, Pulaski, Saline, and Cleveland Counties, magnetic iron ores are associated with igneous intrusions. In southern Arkansas, an iron ore-bearing area extends from northeastern Lafayette County northeast into southwest Nevada County. The iron-rich zones are in the Wilcox Group of Tertiary age and formed as concretions of residual limonite by the weathering of bedded siderite. The hilltops in this area have a potential tonnage of ferruginous material exceeding 100 million short tons with an average grade of 30 percent iron. Through 1965, approximately 120,000 tons of iron were produced from the Wilcox deposits, most being shipped to Lone Star Steel in east Texas. A small amount was used as an iron-rich supplement in dog food after 1965.

Two small pig-iron furnaces were operated in Arkansas before 1860; one in Carroll County and the other in Sharp County. About 3,500 tons of magnetite were mined from the central portion of Magnet Cove, Hot Spring County, in the early 1950’s. During the early 1960’s, iron ore was open-cut mined near Rosston in Nevada County. About 250 tons of iron ore were shipped in 1965, the last year of recorded production. In 1969, the U.S. Bureau of Mines calculated iron ore reserves in Arkansas to be 120 million long tons with an average grade of 30 percent iron. There has been no iron ore for smelting mined in the state since 1965. Currently, there are several iron and steel refineries in Arkansas, utilizing recycled steel and iron.


Erickson, R. L., and Blade, L. V., 1963, Geochemistry and petrology of the alkalic igneous complex at Magnet Cove, Arkansas: U. S. Geological Survey Professional Paper 425, 99 p.
Penrose, R. A. F., Jr., 1892, The iron deposits of Arkansas: Arkansas Geological Survey Annual Report for 1892, v. I, 153 p.

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Lithium

Lithium (Li) is the lightest of all the metals, having an atomic weight of 6.939 and a specific gravity of 0.534. The mineral spodumene (LiAlSi2O6), which is often present in extremely coarse-grained igneous rocks called pegmatites, is the most important commercial ore mineral of lithium. In the 1960’s, with the discovery of lithium in brines and in arid evaporative lakes and lake deposits (evaporites), new commercial sources of lithium became available. Lithium occurs in significant amounts in geothermal waters, oil-well brines, and as a trace element in a variety of rocks.

The most important lithium compounds produced commercially are lithium carbonate, lithium hydroxide, lithium chloride, lithium bromide, and butyllithium. The bulk of these compounds are consumed in the manufacture of ceramics, glass, and aluminum metal.   Recently, the applications of lithium in certain metallurgical and chemical industries have been rapidly expanding and diversifying. Because lithium is electrochemically active and has other unique properties, it has few substitutes. Highly purified lithium carbonate has been successfully used in chemotherapeutic treatment of manic depression. Two new applications which have significant potential are as absorption blankets in nuclear fusion reactors and as a component in high-energy, long shelf-life batteries.

The 3 lithium minerals that exist in Arkansas occur in the Ouachita Mountains. Cookeite (LiAl4(Si3Al)O10(OH)8) is in small hydrothermal quartz veins, most commonly filling fractures in the Jackfork Sandstone (Pennsylvanian) from Pulaski County westward through Saline and into Perry County. Taeniolite (KLiMg2 Si4O10F2) is present in smoky quartz veins in the recrystallized novaculite adjacent to the Magnet Cove intrusion (Cretaceous), Hot Spring County, and in a chalcedony-fluorite-pyrite vein in the "V" intrusive (Cretaceous age igneous dikes), Garland County. Lithiophorite ((Al, Li)Mn4+O2 (OH)) has been reported in the manganese deposits in Polk and Montgomery Counties, and as a late secondary mineral in quartz veins from many localities in the Ouachita Mountains. None of these minerals are considered economical sources of lithium.

The bromine-rich brines from wells in the Upper Jurassic Smackover Formation of Columbia County in southwestern Arkansas contain as much as 445 parts per million lithium. Lower values are reported in waters originating from some water wells and hot and cold springs scattered across Arkansas. Except for lithium's potential as a by-product from the bromine brines in the Smackover Formation, other concentrations of commercial potential are not known to exist in Arkansas.

Collins, A. G., 1974, Geochemistry of liquids, gases, and rocks from the Smackover Formation: U. S. Bureau of Mines Report of Investigations 7897, 84 p.
Kunasz, I. A., 1975, Lithium raw materials, in LeFond, S. J., ed., Industrial Minerals and Rocks, 4th ed.: American Institute of Mining, Metallurgical, and Petroleum Engineers, p. 791-803.
Miser, H. D., and Stevens, R. E., 1938, Taeniolite from Magnet Cove, Arkansas: American Mineralogist, v. 23, no. 2, p. 104-110.
Stone, C. G., and Milton, Charles, 1976, Lithium mineralization in Arkansas, in Vine, J. D., ed., Lithium resources and requirements by the Year 2000: U. S. Geological Survey Professional Paper 1005, p. 137-142.
Trout, M. L., 1974, Origin of bromide-rich brines in southern Arkansas: Columbia, University of Missouri, M. A. thesis, 79 p.

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Manganese

General Information
Manganese (Mn) is a gray-white to silvery metal with a moderate melting temperature and relatively high specific gravity (7.2 to 7.4). Manganese is added to iron along with other metals and carbon, to make steel. Manganese never occurs as the native metal in nature, but instead in some combination with other elements.

There are over 100 minerals known to contain manganese. The most important manganese ore minerals identified in Arkansas are psilomelane (massive hard manganese oxides), hausmannite (Mn2+Mn23+O4), pyrolusite (Mn4+ O2), wad (soft, massive manganese oxides), and braunite (Mn2+Mn63+SiO12). Other minerals such as manganite (Mn3+O(OH)), bementite (Mn82+Si6O15 (OH)10), and rhodochrosite (Mn2+CO3) have also been noted. Because of its sulfur-fixing, deoxidizing, and alloying properties, the principal use of manganese is in iron and steel manufacture. About 90 percent of the manganese consumed in the United States is in the form of an alloy known as ferromanganese, which is used in the manufacture of steel. Relatively small amounts of manganese and different manganese compounds are utilized in the manufacture of other metal alloys, animal feed, soil conditioners, dyes and paints, pharmaceuticals, dry-cell batteries, and as a coloring material in pottery, tile, and brick.

Arkansas Manganese Deposits
Commercially important manganese deposits are present in two principal regions in Arkansas – the Batesville district and the West-Central Arkansas district. Other areas of Arkansas have been prospected for manganese and, although mineralization exists, quantities are not economic. Mines in the Batesville district, which includes about 100 square miles located in northwestern Independence County, south-eastern Izard County, and northeastern Stone County, produced over 98 percent of the manganese ore shipped from Arkansas. The West-Central Arkansas district includes portions of Pulaski, Saline, Garland, Hot Spring, Montgomery, Pike, Howard, and Polk Counties.

The ores in the manganese deposits of the Batesville district are classified into 4 major types: manganiferous limestone, residual in situ clay, clay-talus residuum, and placer. Manganiferous limestone, mostly in the Early Mississippian St. Joe and Boone Formations, is the most abundant ore; but is usually low grade. Residual in situ clay and clay-talus residual ores are present as local deposits of irregular lumps, masses, and nodules, mainly in pockets of residual clay lying in depressions in the bedrock. These latter ore types are secondary residual minerals concentrated by the decomposition and replacement of some of the rocks of the Ferndale Limestone through Cason Shale (Ordovician) strata. Placer ores and deposits containing them are derived by the transportation of residual deposits and are usually mixed with sand and gravel.

History of Mining and Production
The Batesville district manganese deposits were mined intermittently from 1849 to the early 1880’s by both open-pit and subsurface methods. From 1881 to 1959, mining activity was almost continuous. Major production occurred in both World Wars, but the highest single-year production was during 1956 when more than 29,000 tons of manganese ore were extracted. The U. S. Bureau of Mines has calculated that almost 200 million long tons of ore containing 4 to 9 percent manganese still remain in the district. Deposits of manganese ore may be difficult to evaluate because they are generally small, scattered, methods utilizing geophysical techniques are not usually economically feasible, and normal methods of obtaining representative samples are not effective.

The west-central Arkansas manganese deposits are mainly oxides in veins, open pockets, and cement that binds breccias together in fractured zones in the Arkansas Novaculite (Devonian/Mississippian) and the Stanley Shale (Mississippian). The manganese mineralization in ore deposits ranges in thickness from a fraction of an inch to about 10 feet. The deposits, which contain a large amount of low-phosphate manganese in the aggregate, are usually small and discontinuous. Exploration in the district is incomplete. A few mines and prospects are well known and minor production by both open-pit and subsurface methods was recorded in the first half of the 20th century, but the cost of mining, modest quantities and low grade of ore has so far precluded significant development of these resources. Phosphate-free manganese ores from the west-central district were utilized during World War II to upgrade the more phosphate-rich ores of the Batesville district.

There has been no manganese ore mined in Arkansas since federal stockpile programs were stopped in 1959. The potential for manganese ore production will depend primarily on the growth rate of steel production and the availability of manganese ore from foreign sources.

Miser, H. D., 1917, Manganese deposits of the Caddo Gap and DeQueen quadrangles, Arkansas: U. S. Geological Survey Bulletin 660-C, p. 59-122.
Miser, H. D., 1922, Deposits of manganese ore in the Batesville district, Arkansas: U. S. Geological Survey Bulletin 734, 273 p.
Penrose, R. A. F., Jr., 1890, Manganese: Its uses, ores, and deposits: Arkansas Geological Survey Annual Report for 1890, v. I, 642 p.
Stroud, R. B., Kline, H. D., Brown, W. F., and Ryan, J. P., 1981, Manganese resources of the Batesville district, Arkansas: Arkansas Geological Commission Information Circular 27, 146 p.

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Mercury

General Information
Elemental mercury (Hg) is relatively scarce and is formed by the weathering or oxidation of several mercury-bearing minerals. The most important ore mineral is cinnabar (HgS). Elemental mercury is a liquid at normal temperatures, freezes at -38.4° C, and boils at 357° C. This liquid state at ordinary temperatures led to its early use in thermometers. It will dissolve finely divided gold (dust and flour) and can then be boiled off, leaving the gold behind. Consequently, it has been used for centuries to collect gold that would otherwise not be recoverable. Mercury is in most rock types in trace amounts.

Although mercury was widely used in the past for several applications, the market for products containing mercury steadily declined in the 1980’s because it was recognized to be toxic. It still has important uses in the chemical and electrical industries as well as in dental applications and measuring and control devices.

Geology of Arkansas Mercury Deposits
The mercury-bearing district in southwest Arkansas occupies an area 6 miles wide by 30 miles long extending from eastern Howard County through Pike County and into western Clark County. Surface rocks in the mercury district are sandstone, shale, and siltstone of the Mississippian and Pennsylvanian Systems (Paleozoic). These rocks are covered in the southern portions of the previously mentioned counties by Cretaceous clay, sand, gravel, and limestone beds. The Paleozoic rocks have been folded and faulted into steeply dipping, generally east-west trending ridges and valleys. Cinnabar and other primary minerals were deposited by aqueous solutions rising through the fractured Paleozoic rocks.

History of Mining and Production
Cinnabar, the principal ore mineral, was first discovered in southwestern Arkansas in 1930. Prospecting along the major trends of larger faults in the area was conducted by examination of outcrops, pitting, trenching, core drilling, and some geochemical sampling. Mining, by both surface and underground methods, began in 1931 and mercury was recovered yearly through 1944. Minor, but rich, placer cinnabar was recovered at the Parker Hill mill site in Pike County and added to the primary ore before roasting. Cinnabar was roasted in the presence of oxygen, to break the mineral down into free mercury vapor and sulfur dioxide. These gases were then cooled and the mercury condensed as a liquid and was recovered. Refining during this period yielded approximately 1,500 76-pound flasks. Mining has been negligible since 1946.

Branner, G. C., 1932, Cinnabar in southwestern Arkansas: Arkansas Geological Survey Information Circular 2, 51 p.
Clardy, B. F., and Bush, W. V., 1976, Mercury district of southwest Arkansas: Arkansas Geological Commission Information Circular 23, 57 p.
Gallager, David, 1942, Quicksilver deposits near the Little Missouri River, Pike County, Arkansas: U. S. Geological Survey Bulletin 936-H, p. 189-219.
Reed, J. C., and Wells, F. G., 1938, Geology and ore deposits of the southwestern Arkansas quicksilver district: U. S. Geological Survey Bulletin 886-C, 90 p.
Stone, C. G., Nix, J. F., and McFarland, J. D., 1995, A regional survey of the distribution of the mercury in the rocks of the Ouachita Mountains of Arkansas: Arkansas Geological Commission Information Circular 32, 25 p.

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Molybdenum

Molybdenum (Mo) is a refractory metal that is obtained primarily by processing the mineral molybdenite (MoS2). Molybdenite is soft, lead gray, has a metallic luster, a greasy feel, and produces a greenish streak when rubbed on unglazed porcelain. Molybdenite is an effective dry solid lubricant. Elemental molybdenum is a hard gray metal with a relatively high melting point (4,730° F.) and a high specific gravity (10.2). Molybdenum (moly) is used primarily as an alloying agent in iron and steel, where it enhances hardenability, strength, toughness, and resistance to wear and corrosion. Steels containing molybdenum are used in the transportation industry and as drill steel in deep oil and gas wells. Molybdenum is also used as a metal in numerous chemical applications, including fire retardants, catalysts, and pigments.

Molybdenite was identified at  Magnet Cove in Hot Spring County in 1939, where it is present in veins in a fractured igneous rock. The veins are composed mainly of orthoclase feldspar and pyrite, with minor amounts of quartz, fluorapatite, plagioclase feldspar, molybdenite, and brookite, and range in thickness from less than 0.5 inch to 5 feet. The Mo-Ti prospect, as this site was named, was explored by geophysical methods, trenching, and drilling. Molybdenum mineralization occurs in Baxter County where the lead molybdate -- wulfenite, is reported to be associated with galena, cerussite, and quartz. No molybdenum ore has been mined in Arkansas.

Erickson, R. L., and Blade, L. V., 1963, Geochemistry and petrology of the alkalic igneous complex at Magnet Cove, Arkansas: U. S. Geological Survey Professional Paper 425, 99 p.
Holbrook, D. F., 1948, Molybdenum in Magnet Cove, Arkansas: Arkansas Resources and Development Commission, Division of Geology Bulletin 12, 16 p.
McKnight, E. T., 1935, Zinc and lead deposits of northern Arkansas: U. S. Geological Survey Bulletin 853, 311 p.

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Nickel

Nickel (Ni) is the fifth most abundant element in the earth, but it is rare in crustal rocks. Elemental nickel is a silvery, hard, ductile metal with a moderately high melting temperature and a relatively high specific gravity (8.9). The main use of nickel is as an alloy in steel and cast iron. Nickel is vital to the stainless steel industry and played a key role in the 20th century in the development of the chemical and aerospace industries. It is used in nonferrous alloys, heat- and electricity-resistant alloys, and in plating. Nickel gives its alloys toughness, strength, corrosion resistance, and special electrical, thermal, and magnetic qualities.

Nickel-bearing deposits result from several geological processes. Lateritic nickel deposits form from weathering of certain silica-deficient igneous rocks rich in iron and magnesium, which concentrates nickel in the weathering product. Nickel sulfide accumulations result from the deposition of nickel minerals by hydrothermal (hot water) fluids. The most common nickel-bearing mineral known in Arkansas is millerite (NiS). Millerite has a metallic luster and a pale brass-yellow color with a greenish tinge and typically forms fine, hair-like masses.

The discovery of millerite in Arkansas was at the now abandoned Rabbit Foot mine, located within the northwestern city limits of Benton in Saline County. Millerite in cavities and crevices in a quartz vein hosted by black shale was exposed in a creek bed.   In 1887, 1,991 pounds of ore were sampled and assayed, showing 1.46 percent nickel and cobalt combined. Work began in 1887 and ended shortly thereafter. Today, the site is covered by stream alluvium. Three minor occurrences of millerite are in north Arkansas, two in Benton County and one in Izard County. Soapstone deposits in Saline County contain traces of nickel-bearing minerals. Investigations of manganese deposits in the Ouachita Mountains region of west-central Arkansas also revealed nickel in the manganese ores. Analyses of manganese ore concentrates indicated nickel in the range of 0.03 to 0.39 percent. Further evaluation of the manganese deposits and associated trace elements (cobalt, nickel, and lithium) is necessary to determine the economic potential of these deposits. No nickel mining occurred in Arkansas since the exploration work at the Rabbit Foot mine.

Comstock, T. B., 1888, A preliminary examination of the geology of western-central Arkansas, with especial reference to gold and silver: Arkansas Geological Survey Annual Report for 1888, v. I, pt. 2, 320 p.
O'Connor, W. K., White, J. C., and Turner, P. C., 1992, Geology and mineral processing of manganese deposits from the west-central Arkansas district: Mining Engineering, v. 44, p. 1361-1368.
Sterling, P. J., Stone, C. G., and Renfroe, C. A., 1962, An occurrence of violarite and millerite in calcite veins, Benton County, Arkansas: Economic Geology, v. 57, no. 3, p. 453-455.

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Niobium

Niobium (Cb), also called columbium, is a rare metal, which is steel gray, resistant to acids, and has a high melting point. Elemental niobium is a soft, ductile, malleable metal with a moderately high specific gravity (8.57). It is used mainly as an additive in stainless steel and imparts creep resistance and fatigue strength in light-weight high-temperature alloys. Niobium is critical because of its defense-related uses in aerospace, energy, and transportation industries.

Three areas of significant niobium mineralization occur in Arkansas: Magnet Cove in Hot Spring County, Potash Sulphur Springs in Garland County, and the bauxite deposits in Saline and Pulaski Counties. The first two locations are characterized by alkaline igneous intrusions and mineralized zones of contact metamorphism and the third by the concentration of titanium minerals in bauxite. In the Magnet Cove area, there are substantial deposits of titanium minerals, rutile and brookite (TiO2), and perovskite (CaTiO3). Rutile and brookite crystals contain an average of 2 percent and a maximum of 5 percent niobium. Perovskite may contain up to 9 percent niobium by analysis because niobium substitutes for titanium in the mineral's structure.  The U.S. Bureau of Mines calculated that 12 million pounds of niobium are present in the rutile-brookite deposits at Magnet Cove. The niobium of the Potash Sulphur Springs area is present as an essential element of the mineral pyrochlore ((Ca,Na)2Nb2O6(OH,F)). Soil samples analyzed from this area contained up to 0.9 percent niobium. Another possible source of niobium in Arkansas is in the processed bauxite waste material. Arkansas bauxite contains niobium from 0.02 to 0.1 percent and averages 0.05 percent. In 1954, the U. S. Bureau of Mines calculated that bauxite deposits and plant waste fines contained up to 150 million pounds of niobium metal.

Although niobium-bearing minerals have long been known to exist in the state, there has been no commercial recovery. If any sites enriched in titanium-bearing minerals become economic, niobium may be recovered as a by-product.

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Rare Earths

The rare earth metals are a family of 17 elements consisting of scandium, yttrium, and the lanthanum-group elements. The term "rare earths" is a misnomer, as some of these elements are not particularly rare and all of them are metals, not earths. The elements are similar in their chemical properties to aluminum. Among this group, however, are a few of the rarest elements known. Perhaps best known of the group are cerium and yttrium. Monazite sand, a by-product of heavy-mineral processing, is the most important mineral source of the rare-earth group.  Deposits of the minerals bastnaesite and xenotime are also important sources of certain rare earths.

The rare earths were once scientific curiosities, but modern methods of separation and new applications, particularly in the fields of atomic energy and metals research, make them commercially valuable. Rare earths are used as catalysts in automotive catalytic converters, as iron and steel additives, as ceramic and glass additives for their decolorizing properties, as light-emitting substances (phosphors), and as components in electronic devices, permanent magnets, light bulbs, and in various aspects of research. Common lighter flint contains a cerium compound.

Investigations by auger drilling in the central region of Magnet Cove, Hot Spring County, revealed up to 4.3 percent combined rare earths in analyzed samples. Selected hand samples of bastnaesite-(Ce) ((Ce,La)(CO3)F) / synchysite-(Ce) (Ca(Ce,La)(CO3)2F) mineralization contained over 30 percent combined lanthanides. The mineralization is present as secondary veins up to 4 inches thick in carbonatite, an igneous rock composed mostly of calcite. Rare earths also are known to be associated with several igneous intrusions in Pulaski, Saline, Cleveland, and Garland Counties.

Samples collected from Independence and Izard Counties specifically for their rare-earth content were submitted to the U.S. Geological Survey for rare-earth analysis. The basal phosphatic zones of the Cason Shale (Silurian-Ordovician), west of Batesville, were sampled and the analyses reported sub-economic values of rare earths. Although values are not high enough to be considered ore, should mining of the Cason phosphate deposits become economically feasible, rare earths might be recoverable as a by-product. There has been no mining of rare earths in the state.

Barwood, H. L., and Howard, J. M., 1990, Rare earth fluorcarbonates at Magnet Cove, Hot Spring County, Arkansas (abs.): Geological Society of America Abstracts with Programs, v. 22, no. 1, p. 2.
Erickson, R. L., and Blade, L. V., 1963, Geochemistry and petrology of the alkalic igneous complex at Magnet Cove, Arkansas: U. S. Geological Survey Professional Paper 425, 99 p.
Grosz, A. E., Meier, A. L., and Clardy, B. F., 1995, Rare earth elements in the Cason Shale of northern Arkansas: a geochemical reconnaissance: Howard, J. M., ed., Arkansas Geological Commission Information Circular 33, 13 p.

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Silver

Silver (Ag) has been an important metal since ancient times. Often present as a native element possessing readily workable properties of malleability, ductility, and sectility, silver was easily fashioned into ornaments, utensils, and coinage. Today silver has many important industrial uses, including photographic negative films and papers, photocopy paper, X-ray plates, and photographic off-set printing plates. All of these uses are dependent on the light-sensitive nature of silver halides. Metallic silver has applications in electrical and electronic products due to its high electrical and thermal conductivity. In fact, silver has the highest electrical and thermal conductivity of all the metals. Silver is also used in the manufacture of batteries for special applications, especially where reduced size and weight are important, as in hearing aids and in space craft. Silver is used decoratively in jewelry and sterling ware, usually as sterling silver (92.5 percent silver and 7.5 percent copper alloy). Due to their high cost, sterling silver tea sets have lost popularity recently. Silver solders have important applications in the jewelry, electronic, and air conditioning industries, due to silver solder's high strength. Silver is commonly used to create the reflective backing of mirrors, as catalysts, as one of the alloy metals in dental fillings, and for investment purposes as bars, coins, medallions, and commemorative objects.

Geologically, silver may form as a native metal in veins associated with bismuth, cobalt, and other silver-bearing minerals. Silver-bearing sulfides and sulfosalts may be associated with gold mineralization. However, the conditions under which silver mineralization is deposited are more diverse than those of gold.

All significant silver mineralization in Arkansas is associated with hydrothermal lead-, zinc-, and copper-bearing quartz veins scattered throughout the Ouachita Mountain region. The deposits are present mostly in small fracture-filling quartz veins which formed in tightly folded sedimentary rock of Paleozoic age. The deposits are present in rocks ranging from the Collier Shale to the Jackfork Sandstone (Cambrian to Pennsylvanian). The silver is usually associated with galena (PbS) or sphalerite ((Zn,Fe)S). Minor amounts of freibergite ((Ag,Cu,Fe)12(Sb,As)4S13) may be present.

The abandoned Kellogg mines in Pulaski County, a lead-, zinc-, copper-, silver-bearing deposit, were discovered in the early 1840’s and mined underground intermittently until 1927. The greatest period of activity was before the Civil War. In 1925, 3,118 troy ounces of silver were reported recovered from processing of galena concentrates. The silver was valued at $2,194. In 1926, mining activity recovered 70 short tons of silver-bearing lead concentrates, valued at about $6,000 (combined silver and lead value).
Prospecting of lead-, zinc-, copper-, and silver-bearing quartz veins occurred in the late 1800’s near the community of Silver in Montgomery County. Although no commercial mining took place, several tons of concentrates were processed for lead and silver as part of the exploration effort.

In the early 1980’s, company exploration programs for zinc deposits in Montgomery County involved drilling and examination of cores of the Womble Shale and Bigfork Chert (both Ordovician). The work revealed traces of silver and zinc mineralization. Analyses of selected Paleozoic shale units in the Arkansas Valley indicate that some lead-bearing shales also contain traces of silver. Only traces of silver have been reported by analytical work on the zinc, lead, and copper deposits of the Ozark region of northern Arkansas.

There are no deposits of silver in Arkansas known to be of commercial importance, although silver may be potentially recovered as a by-product should mining of lead-zinc ores of the Ouachita Mountain region become economically feasible.

Comstock, T. B., 1888, Report upon the geology of western-central Arkansas with special reference to gold and silver: Arkansas Geological Survey Annual Report for 1888, v. I, pt. 2, 320 p.
Konig, R. H., and Stone, C. G., 1977, Geology of abandoned Kellogg lead-zinc-silver-copper mines, Pulaski County, Arkansas, in Stone, C. G., ed., Symposium on the geology of the Ouachita Mountains, v. 2: Arkansas Geological Commission Miscellaneous Publication 14, p. 5-18.
Kurrus, A. W., III, 1980, Geochemistry, geothermometry, and mineralogy of quartz and base metal vein deposits, Montgomery County, Arkansas: Fayetteville, University of Arkansas, M. S. thesis, 84 p.

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Strontium

Strontium (Sr) is a soft, silvery, easily oxidized metallic element with a relatively low melting point and low specific gravity (2.54). The commercial strontium-bearing minerals are celestine (SrSO4), containing 56.4 percent strontium oxide, and strontianite (SrCO3), containing 70.1 percent strontium oxide. Of these two minerals, celestine (formerly called celestite) is the only one found with commercial potential in Arkansas. Celestine may form in association with rocks deposited by the evaporation of sea water (evaporites) or with igneous rocks.

Approximately 80 percent of all strontium is consumed in glass and ceramic manufacturing, primarily in television face-plate glass, and magnets for specialty applications. About 2 pounds of strontium oxide are in the face plate of the picture of every color television set, where it blocks X-ray radiation and improves the brilliance of the picture. Strontium-bearing magnets are used in small electric motors, loudspeakers, and in the magnetic closures of refrigerator doors. Strontium is also used in fireworks (imparts red color), tracer bullets, zinc-metal processing, paint pigments, desensitizing toothpaste, aluminum-parts manufacture, optical and piezoelectrical applications, fluorescent lights, and in analytical laboratories.

Celestine in Arkansas is associated with sedimentary evaporite deposits in the DeQueen Limestone of the Trinity Group (Cretaceous), which extends from the Little Missouri River in Pike County westward across Pike, Howard, and Sevier Counties and into Oklahoma. The best exposures of coarsely crystalline celestine are at the Certain Teed gypsum mine at Briar in Howard County and about 3 miles south of Dierks, Howard County.  South of Dierks, celestine is present as thin layers 25 to 35 feet above the base of the DeQueen Limestone. Two celestine beds have been investigated in this area. While the upper bed consists of lenses, the lower bed is continuous and averages 2 to 4 inches in thickness, but may be 6 inches thick in places. These celestine beds underlie at least 3 square miles and have an average thickness of 4 inches. The celestine is often intergrown with calcite.

Celestine was discovered in Arkansas in 1929 by U.S. Geological Survey geologists while mapping the southwest area of the state. In 1941, 1,500 pounds of celestine were collected and marketed by W. F. Hintze Company. During 1942 and 1943, a company conducted a prospecting and exploration project for celestine. The company dug test pits and drilled 750 test holes over 30 square miles of Howard County. Subsequently, 90 tons of celestine ore were mined by open-pit methods and shipped to Nacagdoches, Texas, for processing.

Currently, celestine mining in the United States is inactive due to our close proximity to Mexico, the world's largest strontium-mineral producer.

Dane, C. H., 1929, Upper Cretaceous formations of southwestern Arkansas: Arkansas Geological Survey Bulletin 1, 215 p.
Miser, H. D., and Purdue, A. H., 1929, Geology of the DeQueen and Caddo Gap quadrangles, Arkansas: U. S. Geological Survey Bulletin 808, 195 p.

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Tantalum

Tantalum (Ta) is a refractory, acid resistant, ductile and easily fabricated metal with a high melting temperature (2,996° Celsius). It is a good conductor of heat and electricity. Tantalum combines readily with other refractory metals, such as tungsten, to form alloys with high-temperature strength and stability.

The major use of metallic tantalum is in the manufacture of electronic components, mainly tantalum capacitors. Because of their long shelf life and reliability, these capacitors are used in computers, communication systems, and controls and instruments for aircraft, missiles, ships, and weapon systems. Tantalum is combined with cobalt, iron, and nickel in super-alloys for aerospace structures and jet engine parts. Tantalum is also combined with carbon as tantalum carbide and with other metals to use as metal-cutting tools, wear-resistant parts, and for boring tools.

Tantalum and niobium are chemically similar and are often present in similar geologic environments. Niobium may be 10 to 20 times more abundant than tantalum. The principal ore minerals are ferrotantalite (Fe2+ Ta2O6) and microlite-pyrochlore ((Ca,Na)2Ta2O6(O,OH,F)-(Ca,Na)2Nb2O6(OH,F)). Struverite ((Ti,Ta,Fe3+)3O6), which is recovered from tin-mining wastes, is another source.

There is potential for tantalum resources in Arkansas because niobium is present in the Cretaceous igneous rocks.  Although no evaluation or mining of tantalum in Arkansas has occurred, the recovery of this metal, along with niobium, would probably be as a byproduct of the mining of titanium-bearing minerals.

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Thorium

Thorium (Th) is a radioactive metallic element that, until the 1950’s, was known only by chemists and physicists. It is not abundant, but major supplies are in sands rich in monazite ((Ce,La, Nd,Th)PO4). Commercially, monazite is recovered as a by-product of the processing of titanium-bearing heavy-mineral sands. Thorium is used mainly for refractory applications, metal technology applications, ceramics, and welding rod coatings. Thorium was formerly used in all gasoline lantern mantles, but suitable substitutes are now used. Thorium had minor use as a nuclear fuel in a few foreign-based nuclear reactors.

Since thorium minerals are generally radioactive, several discoveries of thorium-bearing areas were made in the United States during uranium exploration in the early 1950’s.  In Arkansas, radioactive anomalies (see Uranium) were discovered in the Magnet Cove area in Hot Spring County. Samples of the anomalous material contained thorium rather than uranium. Another radioactively anomalous site is the Uebergang deposit in Saline County. Here, both thorium and uranium are in a quartz-feldspar rock. A select sample analyzed 0.019 percent uranium and 1.5 percent thorium. There has been no mining of thorium ores in Arkansas.

Erickson, R. L., and Blade, L. V., 1963, Geochemistry and petrology of the alkalic igneous complex at Magnet Cove, Arkansas: U. S. Geological Survey Professional Paper 425, 99 p.

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Titanium

Titanium (Ti) is a lightweight metal which was discovered in 1791 and is known for its corrosion resistance and high strength-to-weight ratio. Titanium comprises about 0.62 percent of the earth's crust and is present mainly in the minerals   rutile, brookite, anatase (all TiO2), leucoxene (fine-grained titanium oxides), ilmenite (Fe2+TiO3), perovskite (CaTiO3), and titanite (CaTiSiO5). In Arkansas, the most important ore minerals are rutile, brookite, and ilmenite. Rutile and brookite each have a specific gravity of over 4.0 and the same chemical formula, but differ in crystalline structure. Both are commonly black in Arkansas and occur as grains and crystals, water-worn pebbles and granules, or crystalline masses. Ilmenite is black with a metallic luster, and has a specific gravity of 4.7. It occurs as water-worn sand-sized grains.

Titanium is used mainly in the form of titanium dioxide, although the metal is also used as an alloy. Titanium dioxide's main use is as a white pigment in paint, paper, and plastics. Minor uses of titanium minerals include ceramics, chemicals, welding-rod coatings, heavy aggregate, and steel-furnace flux. Uses for titanium metal alloys include metal bone replacements for humans and parts for hearts, eye glasses frames, and as parts for aircraft, submarine engines, golf clubs, and electric generation plants. Titanium is classified as a strategically important metal.

Titanium-bearing minerals in Arkansas are in Pulaski, Saline, Hot Spring, Garland, Pike, Howard, Sevier, and Little River Counties, and in alluvial sands of the Arkansas River. Titanium-bearing minerals from Pulaski and Saline Counties are in intrusive bodies of nepheline syenite and deposits of bauxite. Ilmenite is also present in bauxite in both counties

Rutile, brookite, and perovskite occur at Magnet Cove, Hot Spring County. At Magnet Cove, two general types of rutile-brookite deposits are present: feldspar-carbonate-rutile veins in the intrusion and brookite-quartz veins in the altered Arkansas Novaculite contact zone adjacent to the intrusion.  Perovskite is associated with late-stage carbonate-rich piercing bodies in the intrusion's interior. Rutile was mined from open pits at Magnet Cove from 1932 to 1944, where about 5,400 tons of rutile concentrates were recovered. Investigations by the U. S. Bureau of Mines show that deposits in the Magnet Cove area contain 8 million tons of titanium-bearing material ranging from 4 to 8 percent TiO2. However, high trace element-content, particularly of niobium, has precluded any commercial development. High-level terrace deposits south of Magnet Cove contain well-rounded placer rutile, which ranges in grain size from sand to pebble gravel. This area had minor open-pit production during the 1930’s. In Garland County, sporadic titanium values were noted during vanadium mining at Potash Sulphur Springs, but none were recovered.

In Pike, Howard, Sevier, and Little River Counties, ilmenite is in the upper sandy part of the Cretaceous Tokio Formation. The Tokio Formation crops out near Arkadelphia, Clark County, and extends west to the Arkansas state line, north of Arkinda, Little River County. The largest deposits of ilmenite sands are located near Mineral Springs, Howard County. One deposit was surface-mined, but minimal ilmenite was recovered. Recent drilling investigations by the Arkansas Geological Commission have revealed that some 110,000 tons of TiO2 are within 50 feet of the surface. During 1939 and 1940, 12.8 short tons of ilmenite were recovered by processing of sand from the Arkansas River by a company in Yell County.  No ilmenite is mined in Arkansas today.

Calhoun, W. A., 1950, Titanium and iron minerals from black sands in bauxite: U. S. Bureau of Mines Report of Investigations 4621, 15 p.
Fryklund, V. C., Jr., Harner, R. S., and Kaiser, E. P., 1954, Niobium (columbium) and titanium at Magnet Cove and Potash Sulphur Springs, Arkansas: U. S. Geological Survey Bulletin 1015-B, p. 23-57.
Fryklund, V. C., Jr., and Holbrook, D. F., 1950, Titanium ore deposits of Hot Spring County, Arkansas: Arkansas Resources and Development Commission, Division of Geology Bulletin 16, 173 p.
Hanson, W. D., 1997, Heavy-mineral sands of the Tokio Formation in southwest Arkansas: Arkansas Geological Commission Information Circular 33, 39 p.
Holbrook, D. F., 1947, A brookite deposit in Hot Spring County, Arkansas: Arkansas Resources and Development Commission, Division of Geology Bulletin 11, 21 p.

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Uranium

Uranium (U) minerals are classified as primary and secondary. Primary uranium minerals are in the same physical state as when originally deposited and secondary uranium minerals are formed by chemical weathering of the primary minerals. The most commercially important primary mineral is pitchblende. Pitchblende, a massive form of uraninite (UO2), is not known in Arkansas. Secondary uranium minerals are normally brightly colored and may be in any type of rock. Carnotite (K2(UO2)2V2O8.3H2O), a canary-yellow mineral, is the most common. Both primary and secondary uranium minerals may be detected by their radioactivity, using Geiger counters or scintillometers. Some instruments will not distinguish between radiation emitted by uranium or by other radioactive materials. Therefore, a chemical assay of the radioactive substance is necessary to determine the amount of uranium.

With the advent of the "atomic age" in July, 1945, the search for uranium in the United States began. Prospecting was stimulated by exploration and discovery bonuses provided by Federal atomic energy legislative acts.

In Arkansas, several uranium anomalies were discovered during the 1950’s. Several localities yielded samples with 0.1 percent or more uranium oxide. At most localities the radioactive mineralization is secondary or related to organic matter. In most instances, the uranium-bearing minerals have not been identified.

The Potash Sulphur Springs igneous intrusion in Garland County is probably the best known and perhaps the first site where uranium was discovered in Arkansas. The mineralization is at the contact of the Cretaceous syenite complex with folded Paleozoic novaculite and shale beds. The U.S. Geological Survey identified the uranium-bearing mineral as pyrochlore ((Ca,Na)2Nb2O6(OH,F)), a primary mineral. Soil samples assaying up to 0.4 percent uranium were collected from this site.  The Rankin prospect in Pike County consists of radioactive carbonized wood fragments in the lower part of the Trinity Group (Cretaceous). The fragments range greatly in size, the smallest containing the most uranium. The highest assay obtained was 0.24 percent uranium oxide. The uranium mineralization is secondary, but the uranium-bearing minerals have not been identified. At the Chandler prospect in Garland County, uranium is present in gorceixite (BaAl3(PO4)(PO3OH)(OH)6), an uncommon mineral that coats the surface of narrow fractures in the novaculite. Samples of this mineral have as much as 0.35 percent uranium oxide.

The radioactive material at the Bear Hill prospect in Marion County is a bitumen sparsely scattered through an outcrop of Paleozoic black shale. Samples of the bitumen assayed up to 2.0 percent uranium oxide, although no uranium-bearing mineral has been identified. At the Runyan prospect, just north of Magnet Cove in Hot Spring County, radioactive material is present in narrow smoky quartz veins that fill fractures in the host rock, novaculite. Samples assaying as much as 0.14 percent uranium oxide were collected from this deposit, although the individual radioactive minerals are unknown. The Uebergang prospect in Saline County contains both thorium and uranium in a granite-like quartz-feldspar rock. A select sample contained 0.019 percent uranium. Individual uranium-bearing minerals have not been identified.

Although samples from Potash Sulphur Springs and the other prospects contain uranium-bearing minerals, no economically viable deposits have been discovered.

Erickson, R. L., and Blade, L. V., 1963, Geochemistry and petrology of the alkalic igneous complex at Magnet Cove, Arkansas: U. S. Geological Survey Professional Paper 425, 99 p.
Stroud, R. B., 1951, The areal distribution of radioactivity in the Potash Sulfur[sic] Springs complex: Fayetteville, University of Arkansas, M. S. thesis, 42 p.
Swanson, V. E., and Landis, E. R., 1962, Geology of a uranium-bearing black shale of Late Devonian age in north-central Arkansas: Arkansas Geological and Conservation Commission Information Circular 22, 16 p.

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Vanadium

Vanadium (V) is a metal with a moderate specific gravity (6.0) and a relatively high melting point (1710° C). Vanadium is often considered to be an uncommon element, but its abundance in the earth's crust is actually comparable to that of copper, nickel, and zinc. However, despite its abundance, it is one of the most expensive elements to recover. Ore values generally are 1.5 percent vanadium pentoxide. Vanadium pentoxide (V2O5) is the principal starting material for the manufacture of all vanadium compounds.

The steel industry consumes more than 80 percent of the world's output of vanadium. Vanadium combined with iron, termed ferro-vanadium alloy, is added to steel to increase strength and improve both toughness and ductility. Such high-strength steels are used in high-rise construction, bridges, large-diameter pipelines, and automobiles because of the weight savings. High quality vanadium-steel kitchen knives are prized for their ability to retain a sharp edge. Other uses of vanadium alloys and compounds include aerospace applications and catalysts.

By 1940, chemical analyses of rocks and minerals from the Magnet Cove area, Hot Spring County, indicated that commercial concentrations of vanadium be present. During uranium exploration in the early 1950’s, significant vanadium values were reported at Potash Sulphur Springs in Garland County by geologists and chemists from the University of Arkansas. Subsequent research centered on uranium and niobium, but also gathered data on vanadium. In 1962, Union Carbide Corporation initiated a systematic study of the Potash Sulphur Springs igneous complex and its adjacent contact metamorphic rocks, which resulted in the discovery of several ore-grade deposits and led to construction of the Wilson Springs processing mill in Garland County.

Vanadium deposits at Potash Sulphur Springs consist of highly altered sedimentary rocks, mainly the Arkansas Novaculite (Mississippian-Devonian) and altered igneous rocks in and adjacent to the contact metamorphic zone. These deposits were mined from open pits. The mineral suite is complex and includes several complex vanadium species, usually too fine-grained to identify in hand specimens. Vanadium ores may also include concentrations of titanium and niobium. The Christy vanadium deposit at Magnet Cove, Hot Spring County, was mined by open-pit methods and the ore processed at the Wilson Springs mill. The last production of V2O5 from Arkansas ores was in 1990. The vanadium contained in the Christy deposit formed in recrystallized and altered novaculite. Vanadium is contained mainly in vanadiferous goethite, with minor contribution from vanadium-bearing brookite.

Since production start-up, the Wilson Springs facility processed over 4.8 million short dry tons of approximately 1.2 percent V2O5-bearing ore. Concentrate from this facility was shipped to Marietta, Ohio, for conversion to "Carvan" vanadium (a ferro-vanadium alloy).

Evans, H. T., Jr., Nord, Gordon, Marinenko, John, and Milton, Charles, 1984, Straczekite, a new calcium barium potassium vanadate mineral from Wilson Springs, Arkansas: Mineralogical Magazine, v. 48, p. 289-293.
Flohr, M. J. K., 1994, Titanium, vanadium, and niobium mineralization and alkali metasomatism from the Magnet Cove complex, Arkansas: Economic Geology, v. 89, p. 105-130.
Hollingsworth, J. S., 1974, Geology of the Wilson Springs vanadium deposits, in Arkansas – Texas economic geology field trip: Arkansas Geological Commission Guidebook 74-1, p. 10-16.
Howard, J. M., and Owens, D. R., 1995, Minerals of the Wilson Springs vanadium mines, Potash Sulphur Springs, Arkansas: Rocks & Minerals, v. 70, p. 154-170.
Taylor, I. R., 1969, Union Carbide's twin-pit vanadium venture at Wilson Springs: Mining Engineering, v. 21, p. 82-85.

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Zinc & Lead

Zinc (Zn) is a bluish-white lustrous metal that is brittle at room temperature, but malleable when heated. It has a low melting point (419.5°C) and a moderately high specific gravity (7.13). Lead (Pb) is a soft, ductile, malleable, bluish-white metal with a low melting point (327.4°C) and a high specific gravity (11.3).   Zinc and lead minerals often occur together because, as elements, they have similar chemical behavior and combine with sulfur as primary minerals.

People have used zinc-bearing mineral compounds for more than 2,500 years. Only iron, aluminum, and copper are more used today. The main uses for metallic zinc are for galvanizing steel and iron, in making brass and other metal alloys, battery electrodes, sheet zinc, and as sacrificial metal to retard corrosion of ship hulls, pipelines, and other submerged or buried steelworks. Zinc compounds are ingredients in paints, rubber, chemical catalysts, fungus retardants, pharmaceuticals, electronic devices, and is the core of the U. S. penny.

Lead is easily recovered from its ore minerals. The mainl use of lead is in batteries. Lead oxides are added to glass, paint, ceramics, and other chemicals to impart special properties. Lead is alloyed with antimony, copper, and bismuth to make type metal. Compounds of lead, such as carbonate and acetate, are used in drugs.

The zinc minerals of commercial importance in Arkansas are sphalerite ((Zn,Fe)S) and smithsonite (ZnCO3). Sphalerite, contains 67.1 percent zinc, whereas smithsonite contains only 48 percent zinc. Sphalerite may contain small percentages of iron, manganese, or cadmium. Sphalerite is usually a shade of amber, has a resinous luster, and is transparent to translucent. Smithsonite is harder than sphalerite, has a glossy to pearly luster, usually is white to light brown, and is normally translucent. Some smithsonite with a striking yellow color and botryoidal habit is called "turkey fat" ore. Minor amounts of hemimorphite (Zn4Si2O7 (OH)2.H2O), were also mined in the north Arkansas zinc districts.

Galena (PbS) is the only lead mineral of commercial importance in Arkansas. Galena contains about 86 percent lead, is very heavy (density of 7.4-7.6), gray in color with a metallic luster, and is easily cleaved. Silver may be an impurity, and if appreciable, it can be a by-product. Galena frequently forms with sphalerite.

Zinc and lead ores are present in the north Arkansas district, which includes Boone, Marion, Newton, Searcy, and parts of Baxter, Stone, Independence, Sharp, and Lawrence Counties, and the mineral belt of west-central Arkansas extending through and including all or parts of Pulaski, Saline, Garland, Hot Spring, Montgomery, Polk, Howard, Pike, and Sevier Counties. The north Arkansas district has been the most important commercially with more than 350 mines and prospects. The zinc and lead minerals in north Arkansas are present in irregular bodies in limestone, dolostone, and/or chert beds of Paleozoic age, often associated with local structural incongruities. Deposits have been mined from the Cotter, Powell, and Everton Formations (Ordovician), and the Boone and Batesville Sandstone Formations (Mississippian). They were mined mostly by under-ground methods, although some high-grade pockets of carbonate ore were open-pit mined. In west-central Arkansas, the zinc and lead minerals are associated with quartz veins in folded Paleozoic sandstones, shales, and novaculite. The Stanley Shale, Jackfork Sandstone, and Arkansas Novaculite host lead- and zinc-bearing quartz veins. Essentially all lead and zinc mining in the Ouachita region was by underground methods.

Although zinc is more common, lead ore was recognized and developed first in the north Arkansas district because of its use for bullets. The presence of lead in this district was noted in 1818. Lead was mined locally before the Civil War, and 3 lead refining furnaces (smelters) were in operation during the Civil War at Lead Hill in Boone County.  Afterwards, lead deposits were worked intermittently through 1959 when mining ceased. The history of lead mining closely parallels that of zinc.

The earliest attempts to work north Arkansas zinc deposits were made in 1857 at Calamine, Sharp County, when a zinc smelter was placed in operation.  Zinc mining began in the counties farther west in 1899 and reached its peak during World War I. Since 1918, there has been only intermittent mining activity in the district, ending in 1962.

In west-central and central Arkansas, a few zinc and lead mines were worked. The Kellogg mine immediately north of North Little Rock in Pulaski County was operated sporadically from 1840 to 1940 and concentrates of lead, zinc, silver, and copper were shipped out of state to be refined. This mine is the deepest shaft mine in Arkansas, with an inclined shaft that followed an ore vein to a depth of 1,125 feet.  At Petty, 6 miles west of Gillham, Sevier County, several small lead and zinc mines were operated by the Confederate States Government in the early 1860’s. Between 1,000 and 1,500 tons were mined and 3 lead furnaces were in operation. In 1899, the same mines were reopened for several years. During the first two years, 1,140 tons of ore were removed. The district has been essentially inactive since the turn of the 20th century.

Approximately 27,000 short tons of zinc and lead concentrates were mined from north Arkansas and about 5,000 short tons from the west-central district. During the entire period of lead and zinc mining in Arkansas little ore was found by drilling.  The mines began on surface outcroppings of the ores in both regions of the state. Calculations indicate that 110,000 short tons (zinc-lead ores) of potential shallow resources remain. Significant potential exists in north Arkansas for the discovery of deep (>1,500 feet) deposits of lead and zinc as the southern extension of the New Viburnum lead district in southern Missouri.

Branner, J. C., 1892, The zinc and lead region of north Arkansas: Arkansas Geological Survey Annual Report for 1891, v. V, 395 p.
Konig, R. H., and Stone, C. G., 1977, Geology of abandoned Kellogg lead-zinc-silver-copper mines, Pulaski County, Arkansas, in Stone, C. G., ed., Symposium on the geology of the Ouachita Mountains, v. 2: Arkansas Geological Commission Miscellaneous Publication 14, p. 5-18.
McKnight, E. T., 1935, Zinc and lead deposits of northern Arkansas: U. S. Geological Survey Bulletin 853, 311 p.
Miser, H. D., and Purdue, A. H., 1929, Geology of the DeQueen and Caddo Gap quadrangles, Arkansas: U. S. Geological Survey Bulletin 808, 195 p.

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