Industrial metals

Metals have played a major role not only in human survival but also in the high standard of living that most cultures enjoy today. Humans have developed an understanding of the geologic conditions under which minerals form in nature and have learned to prospect for and produce those minerals from which metals are derived. A use has been found for virtually every metallic element. In 2021, the world mined more than 181 tons of industrial metals. Experts believe that mining for industrial metals will remain an important industry during and after the world's transition to sustainable energy. Metals are needed to produce zero-emission vehicles and carbon-free energy, among other purposes.

Major Metals

For convenience, industrial metals may be divided into three groups: the major nonferrous metals, the ferroalloys, and the minor metals. The major nonferrous metals are aluminum, copper, tin, lead, and zinc. Copper has been used longer than any metal except gold. It occurs in at least 160 different minerals, of which chalcopyrite is the most abundant ore. The world’s most important source of copper is in large masses of granite rock known as porphyry copper bodies, which are found throughout the western United States but are especially numerous in southern Arizona. Hydrothermal solutions deposited copper-bearing minerals in openings and cracks throughout these masses, and later weathering concentrated the ores beneath the surface in amounts that could be recovered economically. Copper also occurs in sedimentary rocks. Such deposits account for more than one-fourth of the world’s copper reserves, with the best examples in the Zambian-Zairean copper belt of Africa. A future resource is the copper in manganese nodules that cover large portions of the ocean floor, especially in the North Pacific. Chile, the United States, and Canada, in that order, are the world’s leading producers of copper.

Like copper, tin has long been used by humans. The principal ore mineral of tin is the oxide cassiterite, “tinstone.” Primary tin-bearing deposits include granite pegmatites and hydrothermal veins. Much more important from a commercial standpoint, however, are secondary stream placer deposits. Although domestic mine production is negligible, the United States is the world’s leading producer of recycled tin. World leaders in the mining of tin are Malaysia, Brazil, Indonesia, Thailand, China, and Bolivia.

Zinc and lead now rank behind copper and aluminum as essential nonferrous (not containing iron) metals in modern industry. The most important geologic occurrences of lead and zinc are within stratified layers of metamorphic or carbonate rocks. The deposits at Ducktown, Tennessee, and Franklin, New Jersey, are in metamorphic rocks, while those in the upper Mississippi Valley, southeastern Missouri (the Viburnum Trend), and the Tri-State mineral district (Missouri-Oklahoma-Kansas) are found in carbonate rocks. This latter type of occurrence is now referred to as Mississippi Valley-type deposits. The principal ore minerals for lead and zinc are the sulfides galena and sphalerite (zinc blende), respectively. These minerals were probably emplaced in the host rocks by later hydrothermal solutions. The United States is a major producer of lead, with most coming from the Viburnum Trend of Missouri. Recycled lead is also very important in the United States, accounting for more production than mining. Other major lead-producing countries are Australia, Canada, Peru, and Mexico. Canada, Australia, Peru, Mexico, and the United States are among the world’s leading producers of zinc.

Aluminum is in a class by itself because it is not mined from hydrothermal deposits in rocks but from tropical soils. Deep weathering of aluminum-rich rocks, typically igneous rocks rich in feldspar, removes all soluble elements and leaves a residue containing mostly aluminum, iron, and silica. This ore is called bauxite.

Ferroalloys

The ferroalloys are a group of metals whose chief economic use is for alloying with iron in the production of carbon and various specialty steels. Manganese is the most important of the ferroalloys, and it occurs principally in sandstone deposits. Chemically precipitated nodules on the ocean floor contain up to 20 percent manganese and represent an important potential resource.

The elements chromium, nickel, titanium, vanadium, and cobalt most commonly occur in basic igneous rocks, such as gabbro. Examples of such deposits are the Stillwater complex of Montana and the Bushveld complex of South Africa. The Bushveld is the largest such body in the world and holds most of the world’s chromium reserves. Nickel ranks second in importance to manganese among the ferroalloys. The large igneous deposits at Sudbury, Ontario, Canada, have been the world’s major supplier. The most important economic occurrences of titanium are in secondary placer deposits, notably the rutile beach sands of Australia and the ilmenite sands of northern Florida. In addition to its occurrence in dark igneous rocks, vanadium is found as a weathering product in uranium-bearing sandstones such as those of the Colorado Plateau region of the United States. Vanadium is also produced from the residues of petroleum refining and the processing of phosphate rock. While the primary occurrence of cobalt is in dark igneous rocks, it also is produced from laterites and as a by-product of the sedimentary copper deposits of the African copper belt.

Molybdenum, tungsten, niobium, and tantalum occur commonly in quartz veins and granite pegmatites. Most molybdenum production comes from the very large, but low-grade, porphyry deposits at Climax, Colorado, and as a by-product of the porphyry copper deposits at Bingham Canyon, Utah. Production of the minerals scheelite and wolframite from quartz veins accounts for more than one-half of the world’s production of tungsten. Because of their rarity, there is no mining operation solely for the production of either niobium (also known as columbium) or tantalum. Both are always produced as by-products of the mining of other metals.

The United States is self-sufficient and a net exporter only with respect to molybdenum. It is almost totally dependent on foreign sources for manganese, chromium, nickel, cobalt, niobium, and tantalum, and to a lesser degree vanadium, tungsten, and titanium.

Minor Metals

There are a number of metallic elements that are rare in nature. Most of these have a primary origin in hydrothermal veins or granite pegmatites and are produced either from such deposits (antimony, cadmium, beryllium, bismuth, arsenic, lithium, cesium, rubidium, and mercury) or from placer deposits that resulted from the weathering and erosion of the pegmatites (zirconium, hafnium, thorium, and the rare-earth elements). The sole exception is magnesium, which is produced mostly from seawater and natural brines in wells and lakes, as at Great Salt Lake in Utah.

Most elements in this group are produced exclusively as byproducts of the mining and processing of other metals. Antimony, in the mineral stibnite, is closely associated with lead ores in Mississippi Valley-type deposits, and most antimony is produced as a by-product of the mining and processing of lead, copper, and silver ores. China is the world’s leading producer of antimony. Cadmium is a trace element that is similar to zinc and therefore substitutes for zinc in some minerals. All cadmium is produced from the mineral sphalerite as a byproduct of zinc production. Large but untapped potential resources of cadmium exist in the zinc-bearing coal deposits of the central United States. There are no specific ore minerals of bismuth, and virtually all production is from the processing of residues from lead smelting. Mercury, or quicksilver, is the only metal that is a liquid at ordinary temperatures. It is produced from the sulfide mineral cinnabar and is marketed in steel “flasks,” each flask containing 76 pounds of liquid mercury. The mines at Almaden, Spain, have been the leading producers. Magnesium is the lightest metal and is especially strong for its weight. It is an abundant metal, both in the earth’s crust and in seawater. Lithium, cesium, and rubidium are often classified as the rare alkali metals, the abundant alkali metals being sodium and potassium. Like magnesium, lithium is abundant enough in brines and evaporite deposits to be processed economically from these sources. Rare-earth elements, or lanthanide elements, are a group of chemically similar elements, of which cerium is the most abundant and widely used. Thorium is a heavy metal, the parent element of a series of radioactive decay products that end in a stable isotope of lead. It is not an abundant element, but it is widespread, occurring in veins, placers, and sedimentary rocks.

The United States is well endowed with some of these minor metals, including beryllium, lithium, magnesium, and rare-earth elements. In contrast, it must import virtually all of its supplies of antimony, cadmium, bismuth, mercury, arsenic, and rubidium, and one-half of its annual consumption of zirconium and thorium ores and products.

Exploration for Metals

It is a fair assumption that almost all the large and easily accessible metallic ore bodies have been discovered. The focus of the years ahead will be the detection of deposits in more remote localities, concealed deposits, or lower-grade deposits, as well as extending the useful life of existing deposits. While research provides more sophisticated tools, the basic exploration approach remains the same. Four main prospecting techniques are employed: geological, geochemical, geophysical, and direct.

Geological exploration generally involves plotting the locations of rock types, faults, folds, fractures, and areas of mineralization on base maps. Examples of deposits that have been discovered by simple surface exploration and mapping are as follows: chromite, which is resistant to weathering and “crops out”; manganese-bearing minerals, which oxidize to a black color; and molybdenite, with a characteristic silver color. Because ore minerals are known to be associated with rocks formed in certain geologic environments, the focus of study today is on understanding such associations as clues to locating mineral deposits.

Geochemical exploration consists of chemically analyzing soil, rock, stream, and vegetation samples. Concentrations of metallic elements in the surface environment are assumed to be representative of similar concentrations in the rocks below. Areas of low mineral potential can be eliminated, while targets for further study and testing can be outlined. In some instances, it is necessary to trace metals back through the surface environment to their points of origin. Research is being done not only on the movement and concentration of economically important metallic elements, but also on the elements that are often associated with them but that nature, for various reasons, can more easily move and concentrate. Cobalt, for example, is mobile, moving through rocks and sediments easily. It may be possible to trace this element back to its source and in the process locate other associated metals.

Geophysical techniques range from large-scale reconnaissance surveys to detailed local analysis. These techniques detect contrasts in physical properties between the ore bodies and the surrounding host rocks. Airborne magnetic and electromagnetic surveys are useful for rapid coverage of remote and inaccessible terrain, and of areas where ore bodies are covered by glacial sediments. Radiometric surveys can be used to detect concentrations of radioisotopes and have been effective in locating deposits of thorium, zirconium, and vanadium-bearing minerals. Other applications of geophysical techniques include seismic and gravity studies to determine the thickness of overburden, airborne infrared imagery to detect residual heat in igneous deposits, light reflectance of vegetation, side-looking radar, and aerial and satellite photography. In general, airborne reconnaissance techniques are followed by detailed geological, geochemical, or geophysical ground surveys.

The final stage in the exploration process is the direct stage. Here, a prospect is directly sampled by drill, pit, trench, or mine to determine its potential. This step is the most expensive. It is the purpose of geological, geochemical, and geophysical prospecting to narrow the possibilities, lower the odds, and thereby reduce the final cost by selecting the most promising prospects for direct sampling.

Uses of Major and Minor Metals

The great value of copper derives from its high thermal and electrical conductivity, corrosion resistance, ductility, and strength. It alloys easily, especially with zinc to form brass, and with tin and zinc to form bronze. Principal uses of tin are plating on cans and containers, in solder, in bronze, and with nickel in superconducting alloys. Restrictions on the use of lead in pipes and solder should cause an increase in tin consumption, as a lead replacement. Bottle and can deposit laws, enacted in a number of states, will increase the use of scrap (recycled) tin. The principal use of lead is in automobile batteries, but cable sheathing, type metal, and ammunition are other important applications. Zinc uses include galvanizing for iron and steel, die castings, and brass and bronze.

The minor metals have a variety of industrial applications, both as metals and in chemical compounds. Antimony is used primarily as a fire retardant, but it is also alloyed with lead for corrosion resistance and as a hardening agent. This last characteristic is important for military ordnance and cable sheathing. Cadmium is used in the electroplating of steel for corrosion resistance, in solar cells, and as an orange pigment. Beryllium is alloyed with aluminum and copper to provide strength and fatigue resistance, and is widely used in the aerospace industry. It is a “nonsparking” metal that can be used in electrical equipment. Oxides of beryllium are used in lasers and ceramics, and as refractories and insulators. The principal use of bismuth is in the pharmaceutical industry. It soothes digestive disorders and heals wounds. Salts of bismuth are widely used in cosmetics because of their smoothness. Bismuth metal lowers the melting points of alloys so that they will melt in a hot room. This allows them to be used in automatic water sprinkler systems and in safety plugs and fuses.

Mercury, because it is a liquid at room temperature, has applications in thermometers, electrical switches, fluorescent lights, and, with rubidium, in vapor lamps. It also is used in insecticides and fungicides, and has medical and dental applications. Because of its toxicity, such uses as thermometers are being phased out. Magnesium is alloyed in aircraft with aluminum to reduce weight and at the same time provide high rigidity and greater strength. The metal also burns at low temperature, which makes it suitable for flash bulbs, fireworks, flares, and incendiary bombs. The largest use of magnesium is in the oxide magnesia for refractory bricks. Arsenic is mostly used in chemical compounds as a wood preservative and in insecticides and herbicides. Lithium-based greases have wide applications in aircraft, the military, and the marine environment, as they retain their lubricating properties over a wide temperature range and are resistant to water and hardening. Lithium carbonate is used in medicine for treating certain mental disorders. Metallic lithium, as well as magnesium, is alloyed with aluminum for aerospace applications. In the future, however, the principal use of lithium will be in rechargeable batteries. Cesium is used in magnetohydrodynamic electric power generators, in photoelectric cells (automatic door openers), and in solar voltaic cells. Zirconium is used as a refractory in crucibles and brick, as an abrasive and polisher, and for jewelry (cubic zirconium). The rare-earth element cerium has applications in photography and as a “colorizer” in television tubes. Other rare-earth elements are increasingly important in solid-state electronics. Most of the thorium consumption in the United States is by the nuclear fuel industry.

Uses of Ferroalloys

As a group, ferroalloys occupy an economic status that is closely tied to that of steel. These elements impart to steel such properties as strength at high temperatures (especially titanium and molybdenum), making them vital for aerospace applications; hardness (tungsten and manganese), for use in armor plate, structural steel, and high-speed cutting tools; and resistance to corrosion (chromium and nickel), for plating. The most important of these elements is manganese, for which there is no substitute. It acts as a scavenger during smelting to remove oxygen and sulfur, and is alloyed with the steel for hardness.

The ferroalloys also find important applications in industry beyond their use in steel. Manganese is widely used in dry batteries, pigments, and fertilizers. Chromium is used in refractory brick for high-temperature furnaces. Molybdenum, nickel, and vanadium compounds are catalysts in a number of chemical processes, and molybdenum is used in industrial lubricants. Tungsten carbide is the hardest cutting and polishing agent after diamond, and metallic tungsten is commonly the filament in electric light bulbs. Titanium oxide is an important pigment. It is opaque and forms the whitest of all paints. Nickel is used in coinage, batteries, and insecticides, as well as for plating and catalysts. Cobalt is used in magnetic alloys and as a blue pigment in glass and ceramics. The radioisotope cobalt-60 has a number of medical applications. The rare ferroalloy tantalum is used for capacitors and rectifiers in the electronics industry.

Principal Terms

basic: a term to describe dark-colored, iron- and magnesium-rich igneous rocks that crystallize at high temperatures, such as basalt

by-product: a mineral or metal that is mined or produced in addition to the major metal of interest

granite: a light-colored, coarse-grained igneous rock that crystallizes at relatively low temperatures; it is rich in quartz, feldspar, and mica

hydrothermal solution: a watery fluid, rich in dissolved ions, that is the last stage in the crystallization of a magma

laterite: a deep red soil, rich in iron and aluminum oxides and formed by intense chemical weathering in a humid tropical climate

nodule: a chemically precipitated and spherical to irregularly shaped mass of rock

ore mineral: any mineral that can be mined and refined for its metal content at a profit

pegmatite: a very coarse-grained igneous rock that forms late in the crystallization of a magma; its overall composition is usually granitic, but it is also enriched in many rare elements and gem minerals

placer: a surface mineral deposit formed by the settling of heavy mineral particles from a water current, usually along a stream channel or a beach; gold, tin, and diamonds often occur in this manner

primary: a term to describe minerals that crystallize at the time that the enclosing rock is formed; hydrothermal vein minerals are examples

refractory: a term to describe minerals or manufactured materials that resist breakdown; most silicate minerals and furnace brick are examples

reserve: that part of the mineral resource base that can be extracted profitably with existing technology and under current economic conditions

resource: a naturally occurring substance, the form of which allows it to be extracted economically

secondary: a mineral formed later than the enclosing rock, either by metamorphism or by weathering and transport; placers are examples

vein: a mineral-filled fault or fracture in rock; veins represent late crystallization, most commonly in association with granite

Bibliography

Alloway, B. J. Heavy Metals in Soils. 2d ed. London: Blackie Academic and Professional, 1995.

Evans, Anthony M. An Introduction to Economic Geology and its Environmental Impact. Oxford: Blackwell Scientific Publications, 1997.

Gray, Theodore. The Elements: A Visual Exploration of Every Known Atom in the Universe. New York: Black Dog & Leventhal Publishers, 2009.

Halka, Monica, and Brian Nordstrom. Metals and Metalloids. New York: Facts on File, 2011.

Hutchison, Charles S. Economic Deposits and Their Tectonic Setting. New York: John Wiley & Sons, 1983.

Jensen, Mead L., and Alan M. Bateman. Economic Mineral Deposits. 3d. rev. ed. New York: John Wiley & Sons, 1981.

Jones, Adrian P., Frances Wall, and C. Terry Williams, eds. Rare Earth Minerals: Chemistry, Origin, and Ore Deposits. New York: Chapman and Hall, 1996.

Lamey, C. A. Metallic and Industrial Mineral Deposits. New York: McGraw-Hill, 1966.

Laznicka, Peter. Giant Metallic Deposits. 2d ed. Berlin: Springer-Verlag, 2010.

Lazzarino, Marco, Jeremy Berill, and Aleksandar Sevic. "The Importance of Distinguishing Between Precious and Industrial Metals When Investing in Mining Stocks." Resources Policy, vol. 78, Sept. 2022, doi.org/10.1016/j.resourpol.2022.102802. Accessed 25 July 2024.

Manthey, Ewa. "Industrial Metals Monthly: Dim Global Economic Growth Clouds Metal Outlook." Commodities, Food, & Agriculture, 9 Aug. 2023, think.ing.com/articles/industrial-metals-monthly-dim-global-economic-growth-clouds-metals-outlook/. Accessed 25 July 2024.

Salomons, Willem, Ulrich Feorstner, and Pavel Mader, eds. Heavy Metals: Problems and Solutions. New York: Springer-Verlag, 1995.

Totten, George E., and D. Scott MacKenzie, eds. Handbook of Aluminum. New York: Marcel Dekker, 2003.

‗‗‗‗‗‗‗‗‗‗. Mineral Commodity Summaries. Washington, D.C.: Government Printing Office, issued annually.

‗‗‗‗‗‗‗‗‗‗. Minerals Yearbook. Vol. 1, Metals and Minerals. Washington, DC: Government Printing Office, issued annually.

US Geological Survey. United States Mineral Resources. Professional Paper 820. Washington, D.C.: Government Printing Office, 1973.