- Key People:
- Per Teodor Cleve
mineral deposit
-
What is a mineral deposit?
A mineral deposit is an unusually high concentration of a mineral aggregate. Prospectors seek mineral deposits, which are localized rock masses that form through specific geological processes. These deposits contain ore minerals and gangue, which are valuable and valueless minerals, respectively. The value of a mineral deposit increases with the concentration of ore minerals. Deposits have been located in continental rocks, though some lie beneath the ocean.
Whether a mineral deposit is economic to mine depends on factors affecting mining, processing, and transport, including deposit shape, depth, location, political stability, and market prices. Industries' ever-growing demand for mineral resources makes their location crucial to modern society.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How do mineral deposits form in the Earth?
Mineral deposits form through various geological processes in different environments. The four main categories of mineral formation are:
-
Igneous (Magmatic) Minerals crystallize from a melt. Certain magmas contain water. As the magma cools, anhydrous minerals crystallize, leaving a water-rich residue. Rare elements concentrate in this residue, potentially forming rare-metal pegmatites, which are coarse-grained igneous rocks enriched in rare elements.
-
Sedimentary Minerals result from sedimentation, using materials from weathered or eroded rocks. Detrital minerals survive weathering and are transported as clasts to the depositional site. Authigenic minerals form in place due to geochemical processes.
-
Metamorphic New minerals form as temperature and/or pressure changes existing rock types. The number of minerals present in a metamorphic rock is limited by thermodynamics. Metasomatism, diffusion across a chemical boundary, can lead to unique rock compositions and economic deposits.
-
Hydrothermal Minerals precipitate chemically from hot solutions within the Earth, often along fracture zones. These solutions, frequently brines, dissolve and transport minerals, depositing them in openings or replacing existing rocks.
5 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
-
What are some common types of mineral deposits?
Mineral deposits arise from concentrating agents that transport and precipitate ore minerals. Common types include:
-
Hydrothermal deposits Concentrations of metallic minerals form as solids precipitate from hot, mineral-laden water. The hot water dissolves and transports minerals through openings in rocks, depositing them in cavities or replacing the rocks themselves.
-
Placer deposits Natural concentrations of heavy minerals occur due to gravity acting on moving particles. Heavy, stable minerals freed by weathering are washed into streams, concentrating in stream, beach, and residual gravels.
-
Pegmatite deposits Rare-metal pegmatites are small, coarse-grained igneous bodies enriched in rare elements like lithium, beryllium, and niobium. They form from water-rich residual magma and provide a significant source of these elements.
-
Stratiform deposits Confined within specific strata, these deposits resemble sedimentary rocks. Hydrothermal solutions move through porous aquifers, depositing ore minerals in overlying shales.
-
Chemical sediment deposits These comprise iron or manganese compounds formed by precipitation from lake or seawater. The mineral constituents are transported in solution and then precipitate to form a sediment because of a chemical reaction.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
-
Why are mineral deposits important to people and industries?
Mineral deposits are vital to people and industries because they are the source of mineral resources that support industrial development and modern civilization. They provide raw materials for a wide range of industries, including construction, manufacturing, and energy production. Mineral deposits also contain valuable metals like copper, zinc, nickel, and gold, as well as nonmetallic minerals like limestone and gypsum. The work of economic geologists is crucial to modern society because continued industrial development is heavily dependent on mineral resources.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How are mineral deposits located and extracted?
Prospecting is the search for economically exploitable mineral deposits. Prospectors search for anomalies using geological, geophysical, and geochemical tools. Aerial and satellite imagery helps to examine large areas, looking for differences in geologic structure, rock, soil, and vegetation.
Once a discovery is made, the deposit's characteristics, like size, shape, orientation, and mineral quality, are determined. Exploration techniques include excavating trenches, driving drifts, and drilling probe holes to collect samples. Core samples are logged to determine the rock and mineral types present.
Surface mining techniques, such as open-pit mining, strip mining, and quarrying, extract mineral production. Evaluation and design involve drilling probe holes and creating a block model to determine ore reserves. Economic factors are applied to create an economic block model, and techniques like the floating cone technique determine which blocks should be included in the final pit.
3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What environmental impacts can result from mining mineral deposits?
Mining mineral deposits can lead to deforestation, as tropical forests are cleared to access mineral deposits, and wood is used for ore processing. Mining activities can cause slope erosion and siltation of streams. Harmful metals and toxic elements may be released into streams and groundwater, which affects the health of plants and animals. Additionally, the mercury used in gold extraction pollutes waterways, rendering fish inedible. Though stricter environmental laws have reduced damage from mining in developed countries since the 1970s, severe damage continues in many developing countries.
4 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
mineral deposit, aggregate of a mineral in an unusually high concentration.
About half of the known chemical elements possess some metallic properties. The term metal, however, is reserved for those chemical elements that possess two or more of the characteristic physical properties of metals (opacity, ductility, malleability, fusibility) and are also good conductors of heat and electricity. Approximately 40 metals are made available through the mining and smelting of the minerals in which they occur.
Certain kinds of mineral can be smelted more readily than others; these are commonly referred to as ore minerals. Ore minerals tend to be concentrated in small, localized rock masses that form as a result of special geologic processes, and such local concentrations are called mineral deposits. Mineral deposits are what prospectors seek. The terms ore mineral and mineral deposit were originally applied only to minerals and deposits from which metals are recovered, but present usage includes a few nonmetallic minerals, such as barite and fluorite, that are found in the same kinds of deposit as metallic minerals.
" height="20" alt="HEW Logo">
No deposit consists entirely of a single ore mineral. There are always admixtures of valueless minerals, collectively called gangue. The more concentrated an ore mineral, the more valuable the mineral deposit. For every mineral deposit there is a set of conditions, such as the level of concentration and the size of the deposit, that must be reached if the deposit is to be worked at a profit. A mineral deposit that is sufficiently rich to be worked at a profit is called an ore deposit, and in an ore deposit the assemblage of ore minerals plus gangue is called the ore.
All ore deposits are mineral deposits, but the reverse is not true. Ore deposit is an economic term, while mineral deposit is a geologic term. Whether a given mineral deposit is also an ore deposit depends on many factors other than the level of concentration and the size of the deposit; all factors that affect the mining, processing, and transporting of the ore must be considered as well. Among such factors are the shape of a deposit, its depth below the surface, its geographic remoteness, access to transportation, the political stability of the region, and market factors such as the price of the metal in world trade and the costs of borrowing the money needed to develop a mine. Because market factors change continually, a given mineral deposit may sometimes be an ore deposit, but at other times it may be uneconomic and hence not an ore deposit.
Mineral deposits have been found both in rocks that lie beneath the oceans and in rocks that form the continents, although the only deposits that actually have been mined are in the continental rocks. (The mining of ocean deposits lies in the future.) The continental crust averages 35–40 kilometres (20–25 miles) in thickness, and below the crust lies the mantle. Mineral deposits may occur in the mantle, but with present technology it is not possible to discover them.
Geochemically abundant and scarce metals
Metals used in industrial and technological applications can be divided into two classes on the basis of their abundance in Earth’s crust. The geochemically abundant metals, of which there are five (aluminum, iron, magnesium, manganese, and titanium), constitute more than 0.1 percent by weight of Earth’s crust, while the geochemically scarce metals, which embrace all other metals (including such familiar ones as copper, lead, zinc, gold, and silver), constitute less than 0.1 percent. In almost every rock, at least tiny amounts of all metals can be detected by sensitive chemical analysis. However, there are important differences in the way the abundant and scarce metals occur in common rocks. Geochemically abundant metals tend to be present as essential constituents in minerals. For example, basalt, a common igneous rock, consists largely of the minerals olivine and pyroxene (both magnesium-iron silicates), feldspar (sodium-calcium-aluminum silicate), and ilmenite (iron-titanium oxide). Careful chemical analysis of a basalt will reveal the presence of most of the geochemically scarce metals too, but no amount of searching will reveal minerals in which one or more of the scarce metals is an essential constituent.
The trusted destination for professionals, college students, and lifelong learners.
SUBSCRIBE
Geochemically scarce metals rarely form minerals in common rocks. Instead, they are carried in the structures of common rock-forming minerals (most of them silicates) through the process of atomic substitution. This process involves the random replacement of an atom in a mineral by a foreign atom of similar ionic radius and valence, without changing the atomic packing of the host mineral. Atoms of copper, zinc, and nickel, for example, can substitute for iron and magnesium atoms in olivine and pyroxene. However, since substitution of foreign atoms produces strains in an atomic packing, there are limits to this process, as determined by temperature, pressure, and various chemical parameters. Indeed, the substitution limits for most scarce metals in common silicate minerals are low—in many cases only a few hundred substituting atoms for every million host atoms—but even these limits are rarely exceeded in common rocks.
One important consequence that derives from the way abundant and scarce metals occur in common rocks is that ore minerals of abundant metals can be found in many common rocks, while ore minerals of scarce metals can be found only where some special, restricted geologic process has formed localized enrichments that exceed the limits of atomic substitution.
Ore minerals
Two factors determine whether a given mineral is suitable to be an ore mineral. The first is the ease with which a mineral can be separated from the gangue and concentrated for smelting. Concentrating processes, which are based on the physical properties of the mineral, include magnetic separation, gravity separation, and flotation. The second factor is smelting—that is, releasing the metal from the other elements to which it is chemically bonded in the mineral. Smelting processes are discussed below, but of primary importance in this consideration of the suitability of an ore mineral is the amount of energy needed to break the chemical bonds and release the metal. In general, less energy is needed to smelt sulfide, oxide, or hydroxide minerals than is required to smelt a silicate mineral. For this reason, few silicate minerals are ore minerals. Because the great bulk of Earth’s crust (about 95 percent) is composed of silicate minerals, sulfide, oxide, and hydroxide ore minerals are at best only minor constituents of Earth’s crust—and in many cases they are very rare constituents.
The preferred ore minerals of both geochemically abundant and geochemically scarce metals are native metals, sulfides, oxides, hydroxides, or carbonates. In a few cases, silicate minerals have to be used as ore minerals because the metals either do not form more desirable minerals or form desirable minerals that rarely occur in large deposits.