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| Traditional gold mining |
Minerals are defined as naturally occurring solids found in the earth that are composed of matter other than plants or animals. Ore is a naturally occurring source of minerals, such as a rock. A mineral can be composed from one element, such as diamond, which contains only carbon, or several elements, such as quartz, which contains silicon and oxygen. An element is a substance that cannot be divided by ordinary chemical means.
Even ice is considered a mineral. Minerals are found everywhere on Earth, from the bottom of the ocean to the highest mountains. Mineral deposits are frequently located underground, and thus they must be mined. South Africa and Russia hold the largest amount of minerals in the world. Minerals are vital to people’s lives, and many of these minerals are critical to countries’ industries and economies.
The United States is relatively poor in critical minerals, including platinum, cobalt, and gold, but there are sand deposits of titanium ore in Florida and the Pacific Northwest. In the central United States, minerals that contain lead and gallium (used in computer chips) are abundant, and iron ore is found in the states near the Great Lakes. Most of the diamonds are mined in Africa, as is gold, although gold is found in many other locations as well.
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Importance of minerals
Minerals are essential in every aspect of life for humans. Humans need to ingest minerals in order for our bodies to function normally. Most of these required minerals come from the foods people eat. Gold and silver have been valued by civilization since ancient times.
Metals became useful for purposes other than money during the Bronze Age, when weapons and tools could be made from metal as people became more educated with how to process the minerals and extract (remove) metals. As metals were not evenly dispersed around the globe, the more powerful nations became that way through military might from weapons made from metal.
Mineral reserves are of great importance in the marketplace and it is not uncommon to stockpile (save) certain metals extracted from mineral ores. Because large mineral deposits are located in regions of the world that are, at times, politically and economically unstable, the supply of critical minerals is not guaranteed. The United States stockpiles metals such as platinum, palladium, cobalt, chromium, manganese, and vanadium.
These metals are used in the high-technology industries and the military. Chromium, for instance, is used to produce stainless steel. Vanadium is used, along with aluminum, to make forms of titanium that are resistant to fracture (breaking), enabling the manufacture of jet planes that can withstand extreme conditions.
Platinum is used in removing the impurities from oil. Palladium is used in the exhaust systems of automobiles to reduce the amount of pollutants. It is advantageous for a highly-industrialized country such as the United States to have these resources at hand, and to purchase reserves when prices are low.
Water-laid ores and minerals
The formation of mineral deposits always involves water. Water is part of the chemical processes of mineral formation and also changes the mineral content of rocks by dissolving certain elements in the ore and transporting them elsewhere. Heat is another ingredient in the formation of many mineral deposits.
Hydrothermal deposits. Many metal-bearing ores are found in veins (cracks in rock filled with minerals) that cut through surrounding rock. In these cases, very hot water reacted with elements and other minerals in the rock, and burst through the layers of rock where there was a weakness. These mineral deposits are called hydrothermal deposits.
Hydrothermal deposits form gold, silver, and the platinum-group metals, which are commonly found in veins. The metals themselves are hosted in a vein that is often quartz. Miners follow the vein, extract the ore, and remove the host rock to extract the metals contained within. Mining minerals from veins is an expensive process that is seldom used today.
When hot water flows through porous rock (rock with many small holes), the rock can become a host to a kind of deposit known as porphyry. The host rock containing a porphyry deposit is filled with small veins of (usually) quartz that contain the minerals. Although the mineral content is low, porphyry deposits are large, and most of the copper that is mined comes from these unique deposits. Fool’s gold (iron sulfide) is often found in porphyry deposits as well.
Elements in the water that is in contact with the magma, along with the rock through which the water travels on its way to the surface, determine the kinds of minerals found in volcanogenic deposits. For the most part, lead and iron ore are found in volcanogenic deposits, along with smaller amounts of cadmium, antimony, and copper.
On the floor of the ocean, the same kinds of deposits can form where magma seeps through a crack in the seabed. These features are called black smokers, because the iron-rich magma makes the plume appear like black smoke. The mineral deposits collect near the smoker until the hole becomes plugged or the magma is diverted elsewhere.
Mining for minerals
The process of mining for minerals begins after a mineral deposit has been identified. The common types of mines used to excavate minerals are open-pit mines, strip mines, and stope and adit mines.
- Open-pit mines: These mines are large craters dug into the earth to extract ore that is near the surface. Open pit mines are usually associated with porphyry deposits, and minerals such as galena (which contains lead), chalcopyrite (which contains copper), and sphalerite (which contains zinc) are commonly mined at open pits. The open pit is excavated using very powerful and large earth-moving equipment, and processing of the ore (crushing, grinding, partial refinement) is often done near the open pit. Open pits are less environmentally friendly than conventional mines because any native vegetation in the area is lost, and abandoned open pit mines eventually pool waters that are frequently contaminated. Open-pit mines are used for copper in Arizona.
- Strip mines: These mines are large swaths dug through ore-rich zones (common for coal). Most mines are located below the surface of the Earth, and require drilling shafts to enable workers to reach the ore below and transport it to the surface. Strip mines are used for coal in many states and other areas where the ore is buried deeply, as in Montana, where platinum and palladium ore is extracted (removed).
- Stope and adit mines: These mines are bored into the ground. Shafts are bored vertically, and horizontal offshoots (adits) from the shafts that lead into ore-containing portions of the subsurface are dug. Large mining vehicles that crush the rock move along veins of ore, and this byproduct is transported to the surface by rail or cable lifts. Temperatures in conventional mines are high, and the conditions are dangerous—cave-ins occur often—so safety measures are very strict. The shafts and other structures are reinforced with concrete or metal supports.
Other ore and mineral deposits
Placer deposits are concentrated metals that have been transported to streambeds (the channel through which the stream runs) or beaches. The most famous placer deposits are gold nuggets, although silver is sometimes found as well. Placer metals must be resistant to water, or they would dissolve again.
The usual way to extract the placer deposits is to scoop sediment (particles of rock, clay, or silt) from the stream and sift it, leaving the larger rock behind and making the gold easier to spot. California, Alaska, Oregon, and Idaho have all had significant placer deposits of gold.
Evaporite deposits form by evaporation. As waters that contain dissolved mineral species evaporate, the minerals remain in solid form. Minerals found in evaporites include potassium chloride, sodium chloride (halite or table salt), calcium sulfate (gypsum), barium sulfate (barite), and potassium nitrate (saltpeter). Most of these deposits are near the surface and are scooped from the ground with large earth-moving equipment.
Gypsum is used to make sheetrock, which is used to construct the walls of homes and buildings. It is fire-retardant and easily cast into shapes. Barium sulfate is used as drilling mud in oil-producing wells because it is very dense, and prevents oil gushers from erupting as the drill is lowered. Barium itself has use in medicine. Saltpeter is used as an ingredient in gunpowder and fertilizers.
In the oceans, concentrations of dissolved mineral ingredients are very high. Evaporites of the chloride type are most common, and they occur in areas where seawater collects in shallow areas that are confined. Thus, a pool of salt-rich water forms, evaporation speeds up the process, and salt deposits result. Another widespread mineral formed in marine environments is limestone, or calcium carbonate.
This mineral is formed in the same way as the chloride salts, but also includes another source, organisms whose skeletons are made from calcium carbonate. These organisms die and collect on the sea floor, where they add to the content of calcium carbonate. Limestone is used in constructing buildings and as an ingredient in concrete.
