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Sunday, September 22, 2019

Mining engineering

From Wikipedia, the free encyclopedia

Surface coal mine with haul truck in foreground
 
Mining engineering is an engineering discipline that applies science and technology to the extraction of minerals from the earth. Mining engineering is associated with many other disciplines, such as mineral processing, Exploration, Excavation, geology, and metallurgy, geotechnical engineering and surveying. A mining engineer may manage any phase of mining operations – from exploration and discovery of the mineral resource, through feasibility study, mine design, development of plans, production and operations to mine closure

With the process of Mineral extraction, some amount of waste and uneconomic material are generated which are the primary source of pollution in the vicinity of mines. Mining activities by their nature cause a disturbance of the natural environment in and around which the minerals are located. Mining engineers must therefore be concerned not only with the production and processing of mineral commodities, but also with the mitigation of damage to the environment both during and after mining as a result of the change in the mining area. Such Industries go through stringent laws to control the pollution and damage caused to the environment and are periodically governed by the concerned departments.

History of mining engineering

From prehistoric times to the present, mining has played a significant role in the existence of the human race. Since the beginning of civilization people have used stone and ceramics and, later, metals found on or close to the Earth's surface. These were used to manufacture early tools and weapons. For example, high quality flint found in northern France and southern England were used to set fire and break rock. Flint mines have been found in chalk areas where seams of the stone were followed underground by shafts and galleries. The oldest known mine on archaeological record is the "Lion Cave" in Swaziland. At this site, which radiocarbon dating indicates to be about 43,000 years old, paleolithic humans mined mineral hematite, which contained iron and was ground to produce the red pigment ochre.

The ancient Romans were innovators of mining engineering. They developed large scale mining methods, such as the use of large volumes of water brought to the minehead by numerous aqueducts for hydraulic mining. The exposed rock was then attacked by fire-setting where fires were used to heat the rock, which would be quenched with a stream of water. The thermal shock cracked the rock, enabling it to be removed. In some mines the Romans utilized water-powered machinery such as reverse overshot water-wheels. These were used extensively in the copper mines at Rio Tinto in Spain, where one sequence comprised 16 such wheels arranged in pairs, lifting water about 80 feet (24 m).

Black powder was first used in mining in Banská Štiavnica, Kingdom of Hungary (present-day Slovakia) in 1627. This allowed blasting of rock and earth to loosen and reveal ore veins, which was much faster than fire-setting. The Industrial Revolution saw further advances in mining technologies, including improved explosives and steam-powered pumps, lifts, and drills as long as they remained safe.

Education

Colorado School of Mines
 
There are many ways to become a Mining Engineer but all include a university or college degree. Primarily, training includes a Bachelor of Engineering (B.Eng. or B.E.), Bachelor of Science (B.Sc. or B.S.), Bachelor of Technology (B.Tech.) or Bachelor of Applied Science (B.A.Sc.) in Mining Engineering. Depending on the country and jurisdiction, to be licensed as a mining engineer a Master's degree; Master of Engineering (M.Eng.), Master of Science (M.Sc or M.S.) or Master of Applied Science (M.A.Sc.) maybe required. There are also mining engineers who have come from other disciplines e.g. from engineering fields like Mechanical Engineering, Civil Engineering, Electrical Engineering, Geomatics Engineering, Environmental Engineering or from science fields like Geology, Geophysics, Physics, Geomatics, Earth Science, Mathematics, However, this path requires taking a graduate degree such as M.Eng, M.S., M.Sc. or M.A.Sc. in Mining Engineering after graduating from a different quantitative undergraduate program in order to be qualified as a mining engineer. 

The fundamental subjects of mining engineering study usually include:
In the United States, about 14 universities offer B.S. degree in mining and/or mineral engineering. The top rated universities include Colorado School of Mines, Pennsylvania State University, Virginia Tech, the University of Kentucky, the University of Arizona, South Dakota School of Mines and Technology etc. A complete list can be accessed from smenet.org. Most of these universities offer M.S. and Ph.D. degrees too. 

In Canada, McGill University offers both undergraduate (B.Sc. or B.Eng.) and graduate (M.Sc. or M.S.) degrees in Mining Engineering. and the University of British Columbia in Vancouver offers a Bachelor of Applied Science (B.A.Sc.) in Mining Engineering and also graduate degrees (M.A.Sc. or M.Eng and Ph.D.) in Mining Engineering.

In Europe most programs are integrated (B.S. plus M.S. into one) after the Bologna Process and take 5 years to complete. In Portugal, the University of Porto offers a M.Eng. in Mining and Geo-Environmental Engineering and in Spain the Technical University of Madrid offers degrees in Mining Engineering with tracks in Mining Technology, Mining Operations, Fuels and Explosives, Metallurgy.

In South Africa, leading institutions include the University of Pretoria, offering a 4-year Bachelor of Engineering (B.Eng in Mining Engineering) as well as post-graduate studies in various specialty fields such as rock engineering and numerical modelling, explosives engineering, ventilation engineering, underground mining methods and mine design; and the University of the Witwatersrand offering a 4-year Bachelor of Science in Engineering (B.Sc.(Eng.)) in Mining Engineering as well as graduate programs (M.Sc.(Eng.) and Ph.D.) in Mining Engineering.

Some Mining Engineers go on to pursue Doctorate degree programs such as Doctor of Philosophy (Ph.D., DPhil), Doctor of Engineering (D.Eng., Eng.D.) these programs involve a very significant original research component and are usually seen as entry points into Academia.

Salary and statistics

Mining salaries are usually determined by the level of skill required, where the position is, and what kind of organization the engineer is working for. When comparing salaries from one region to another, cost of living and other factors need to be taken into consideration. 

Mining engineers in India earn relatively high salaries in comparison to many other professions, with an average salary of $15,250. However, in comparison to mining engineer salaries in other regions, such as Canada, the United States, Australia and the United Kingdom, Indian salaries are low. In the United States, there are an estimated 6,150 employed mining engineers, with a mean yearly salary of U.S. $103,710.

Pre-mining

The Prospector by N. C. Wyeth, 1906
 
Mineral exploration is the process of finding ores (commercially viable concentrations of minerals) to mine. Mineral exploration is a much more intensive, organized and professional form of mineral prospecting and, though it frequently uses the services of prospecting, the process of mineral exploration on the whole is much more involved. 

The foremost stage of mining starts with the process of finding and exploration of the mineral deposit. In the initial process of mineral exploration, however, the role of geologists and surveyors is prominent in the pre-feasibility study of the future mining operation. Mineral exploration and estimation of reserve through various prospecting methods are done to determine the method and type of mining in addition to profitability condition.

Mineral discovery

Once a mineral discovery has been made, and has been determined to be of sufficient economic quality to mine, mining engineers will then work on developing a plan to mine this effectively and efficiently.

The discovery can be made from research of mineral maps, academic geological reports or local, state, and national geological reports. Other sources of information include property assays, and local word of mouth. Mineral research usually include the sampling and analysis of sediments, soil and drill-core. Soil sampling and analysis is one of the most popular mineral exploration tools. Common tools include satellite and airborne photographs or aiborne geophysics, including magnetometric and gamma-spectrometric maps. Unless the mineral exploration is done on public property, the owners of the property may play a significant role in the exploration process, and may be the original discoverer of the mineral deposit.

Mineral determination

After a prospective mineral is located, the mining geologist and/or mining engineer then determines the ore properties. This may involve chemical analysis of the ore to determine the composition of the sample. Once the mineral properties are identified, the next step is determining the quantity of the ore. This involves determining the extent of the deposit as well as the purity of the ore. The geologist drills additional core samples to find the limits of the deposit or seam and calculates the quantity of valuable material present in the deposit.

Feasibility study

Once the mineral identification and reserve amount is reasonably determined, the next step is to determine the feasibility of recovering the mineral deposit. A preliminary study shortly after the discovery of the deposit examines the market conditions such as the supply and demand of the mineral, the amount of ore needed to be moved to recover a certain quantity of that mineral as well as analysis of the cost associated with the operation. This pre-feasibility study determines whether the mining project is likely to be profitable; if it is then a more in-depth analysis of the deposit is undertaken. After the full extent of the ore body is known and has been examined by engineers, the feasibility study examines the cost of initial capital investment, methods of extraction, the cost of operation, an estimated length of time to payback, the gross revenue and net profit margin, any possible resale price of the land, the total life of the reserve, the total value of the reserve, investment in future projects, and the property owner or owners' contract. In addition, environmental impact, reclamation, possible legal ramifications and all government permitting are considered. These steps of analysis determine whether the mine company should proceed with the extraction of the minerals or whether the project should be abandoned. The mining company may decide to sell the rights to the reserve to a third party rather than develop it themselves, or the decision to proceed with extraction may be postponed indefinitely until market conditions become favorable.

Mining operation

Mining engineers working in an established mine may work as an engineer for operations improvement, further mineral exploration, and operation capitalization by determining where in the mine to add equipment and personnel. The engineer may also work in supervision and management, or as an equipment and mineral salesperson. In addition to engineering and operations, the mining engineer may work as an environmental, health and safety manager or design engineer.

The act of mining required different methods of extraction depending on the mineralogy, geology, and location of the resources. Characteristics such as mineral hardness, the mineral stratification, and access to that mineral will determine the method of extraction.

Generally, mining is either done from the surface or underground. Mining can also occur with both surface and underground operations taking place on the same reserve. Mining activity varies as to what method is employed to remove the mineral.

Surface mining

Surface mining comprises 90% of the world's mineral tonnage output. Also called open pit mining, surface mining is removing minerals in formations that are at or near the surface. Ore retrieval is done by material removal from the land in its natural state. Surface mining often alters the land characteristics, shape, topography, and geological make-up.

Surface mining involves quarrying which is excavating minerals by means of machinery such as cutting, cleaving, and breaking. Explosives are usually used to facilitate breakage. Hard rocks such as limestone, sand, gravel, and slate are generally quarried into a series of benches.

Strip mining is done on softer minerals such as clays and phosphate are removed through use of mechanical shovels, track dozers, and front end loaders. Softer Coal seams can also be extracted this way. 

With placer mining, minerals can also be removed from the bottoms of lakes, rivers, streams, and even the ocean by dredge mining. In addition, in-situ mining can be done from the surface using dissolving agents on the ore body and retrieving the ore via pumping. The pumped material is then set to leach for further processing. Hydraulic mining is utilized in forms of water jets to wash away either overburden or the ore itself.

Mining process

Blasting:
 
Explosives are used to break up a rock formation and aid in the collection of ore in a process called blasting. Blasting utilizes the heat and immense pressure of the detonated explosives to shatter and fracture a rock mass. The type of explosives used in mining are high explosives which vary in composition and performance properties. The mining engineer is responsible for the selection and proper placement of these explosives, in order to maximize efficiency and safety. Blasting occurs in many phases of the mining process, such as development of infrastructure as well as production of the ore. 

Leaching:
 
Leaching is the loss or extraction of certain materials from a carrier into a liquid (usually, but not always a solvent). Mostly used in rare-earth metals extraction.

Flotation:
 
Flotation (also spelled floatation) involves phenomena related to the relative buoyancy of minerals. It is the most widely used metal separate method. 

Electrostatic separation:
 
Separating minerals by electro-characteristic differences.

Gravity separation:
 
Gravity separation is an industrial method of separating two components, either a suspension, or dry granular mixture where separating the components with gravity is sufficiently practical.

Magnetic separation:
 
Magnetic separation is a process in which magnetically susceptible material is extracted from a mixture using a magnetic force.

Hydraulic separation:
 
Hydraulic separation is a process that using the density difference to separate minerals. Before hydraulic separation, minerals were crushed into uniform size; because minerals have uniform size and different density will have different settling velocities in water, and that can be used to separate target minerals.

Mining health and safety

Legal attention to Mining Health and Safety began in the late 19th century and in the subsequent 20th century progressed to a comprehensive and stringent codification of enforcement and mandatory health and safety regulation. A mining engineer in whatever role they occupy must follow all federal, state, and local mine safety laws.

United States

The United States Congress, through the passage of the Federal Mine Safety and Health Act of 1977, known as the Miner's Act, created the Mine Safety and Health Administration (MSHA) under the US Department of Labor.

This comprehensive Act provides miners with rights against retaliation for reporting violations, consolidated regulation of coal mines with metallic and nonmetallic mines, and created the independent Federal Mine Safety and Health Review Commission to review MSHA's reported violations.

The Act as codified in Code of Federal Regulations § 30 (CFR § 30) covers all miners at an active mine. When a mining engineer works at an active mine he or she is subject to the same rights, violations, mandatory health and safety regulations, and mandatory training as any other worker at the mine. The mining engineer can be legally identified as a "miner."

The Act establishes the rights of miners. The miner may report at any time a hazardous condition and request an inspection. The miners may elect a miners' representative to participate during an inspection, pre-inspection meeting, and post-inspection conference. The miners and miners' representative shall be paid for their time during all inspections and investigations.

Mining and the environment

United States

Land reclamation is regulated for surface and underground mines according to the Surface Mining Control and Reclamation Act of 1977. The law creates as a part of the Department of Interior, the Bureau of Surface Mining (OSM). OSM states on their website, “OSM is charged with balancing the nation’s need for continued domestic coal production with protection of the environment.” 

The law requires that states set up their own Reclamation Departments and legislate laws related to reclamation for coal mining operations. The states may impose additional regulations and regulate other minerals in addition to coal for land reclamation.

Saturday, September 21, 2019

Ore genesis

From Wikipedia, the free encyclopedia
 
High-grade gold ore from the Harvard Mine, Jamestown, California, a wide quartz-gold vein in California's Mother Lode. Specimen is 3.2 cm (1.3 in) wide.
 
Various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore-genesis theories vary depending on the mineral or commodity examined.

Ore-genesis theories generally involve three components: source, transport or conduit, and trap. (This also applies to the petroleum industry: petroleum geologists originated this analysis.)
  • Source is required because metal must come from somewhere, and be liberated by some process.
  • Transport is required first to move the metal-bearing fluids or solid minerals into their current position, and refers to the act of physically moving the metal, as well as to chemical or physical phenomenon which encourage movement.
  • Trapping is required to concentrate the metal via some physical, chemical, or geological mechanism into a concentration which forms mineable ore.
The biggest deposits form when the source is large, the transport mechanism is efficient, and the trap is active and ready at the right time.

Ore genesis processes

Endogenous

Magmatic processes

  • Fractional crystallization: separates ore and non-ore minerals according to their crystallization temperature. As early crystallizing minerals form from magma, they incorporate certain elements, some of which are metals. These crystals may settle onto the bottom of the intrusion, concentrating ore minerals there. Chromite and magnetite are ore minerals that form in this way.
  • Liquid immiscibility: sulfide ores containing copper, nickel, or platinum may form from this process. As a magma changes, parts of it may separate from the main body of magma. Two liquids that will not mix are called immiscible; oil and water are an example. In magmas, sulfides may separate and sink below the silicate-rich part of the intrusion or be injected into the rock surrounding it. These deposits are found in mafic and ultramafic rocks.

Hydrothermal processes

These processes are the physicochemical phenomena and reactions caused by movement of hydrothermal water within the crust, often as a consequence of magmatic intrusion or tectonic upheavals. The foundations of hydrothermal processes are the source-transport-trap mechanism.

Sources of hydrothermal solutions include seawater and meteoric water circulating through fractured rock, formational brines (water trapped within sediments at deposition), and metamorphic fluids created by dehydration of hydrous minerals during metamorphism

Metal sources may include a plethora of rocks. However most metals of economic importance are carried as trace elements within rock-forming minerals, and so may be liberated by hydrothermal processes. This happens because of:
  • incompatibility of the metal with its host mineral, for example zinc in calcite, which favours aqueous fluids in contact with the host mineral during diagenesis.
  • solubility of the host mineral within nascent hydrothermal solutions in the source rocks, for example mineral salts (halite), carbonates (cerussite), phosphates (monazite and thorianite), and sulfates (barite)
  • elevated temperatures causing decomposition reactions of minerals
Transport by hydrothermal solutions usually requires a salt or other soluble species which can form a metal-bearing complex. These metal-bearing complexes facilitate transport of metals within aqueous solutions, generally as hydroxides, but also by processes similar to chelation

This process is especially well understood in gold metallogeny where various thiosulfate, chloride, and other gold-carrying chemical complexes (notably tellurium-chloride/sulfate or antimony-chloride/sulfate). The majority of metal deposits formed by hydrothermal processes include sulfide minerals, indicating sulfur is an important metal-carrying complex. 

Sulfide deposition:
 
Sulfide deposition within the trap zone occurs when metal-carrying sulfate, sulfide, or other complexes become chemically unstable due to one or more of the following processes;
  • falling temperature, which renders the complex unstable or metal insoluble
  • loss of pressure, which has the same effect
  • reaction with chemically reactive wall rocks, usually of reduced oxidation state, such as iron-bearing rocks, mafic or ultramafic rocks, or carbonate rocks
  • degassing of the hydrothermal fluid into a gas and water system, or boiling, which alters the metal carrying capacity of the solution and even destroys metal-carrying chemical complexes
Metal can also precipitate when temperature and pressure or oxidation state favour different ionic complexes in the water, for instance the change from sulfide to sulfate, oxygen fugacity, exchange of metals between sulfide and chloride complexes, et cetera.

Metamorphic processes

Lateral secretion:

Ore deposits formed by lateral secretion are formed by metamorphic reactions during shearing, which liberate mineral constituents such as quartz, sulfides, gold, carbonates, and oxides from deforming rocks, and focus these constituents into zones of reduced pressure or dilation such as faults. This may occur without much hydrothermal fluid flow, and this is typical of podiform chromite deposits.

Metamorphic processes also control many physical processes which form the source of hydrothermal fluids, outlined above.

Sedimentary or surficial processes (exogenous)

Surficial processes are the physical and chemical phenomena which cause concentration of ore material within the regolith, generally by the action of the environment. This includes placer deposits, laterite deposits, and residual or eluvial deposits. The physical processes of ore deposit formation in the surficial realm include;
  • erosion
  • deposition by sedimentary processes, including winnowing, density separation (e.g.; gold placers)
  • weathering via oxidation or chemical attack of a rock, either liberating rock fragments or creating chemically deposited clays, laterites, or supergene enrichment
  • Deposition in low-energy environments in beach environments

Classification of ore deposits

Classification of hydrothermal ore deposits is also achieved by classifying according to the temperature of formation, which roughly also correlates with particular mineralising fluids, mineral associations and structural styles. This scheme, proposed by Waldemar Lindgren (1933) classified hydrothermal deposits as hypothermal, mesothermal, epithermal, and telethermal.
  • Hypothermal hydrothermal rocks and minerals ore deposits are formed at great depth under conditions of high temperature.
  • Mesothermal mineral deposits are formed at moderate temperature and pressure, in and along fissures or other openings in rocks, by deposition at intermediate depths, from hydrothermal fluids.
  • Epithermal mineral ore deposits are formed at low temperatures (50-200 °C) near the Earth's surface (<1500 and="" breccias="" fill="" m="" span="" stockworks.="" that="" veins="">
  • Telethermal mineral ore deposit are formed at shallow depth and relatively low temperatures, with little or no wall-rock alteration, presumably far from the source of hydrothermal solutions.
Ore deposits are usually classified by ore formation processes and geological setting. For example, sedimentary exhalative deposits (SEDEX), are a class of ore deposit formed on the sea floor (sedimentary) by exhalation of brines into seawater (exhalative), causing chemical precipitation of ore minerals when the brine cools, mixes with sea water, and loses its metal carrying capacity. 

Ore deposits rarely fit neatly into the categories in which geologists wish to place them. Many may be formed by one or more of the basic genesis processes above, creating ambiguous classifications and much argument and conjecture. Often ore deposits are classified after examples of their type, for instance Broken Hill type lead-zinc-silver deposits or Carlin–type gold deposits.

Genesis of common ores

As they require the conjunction of specific environmental conditions to form, particular mineral deposit types tend to occupy specific geodynamic niches, therefore, this page has been organised by metal commodity. It is also possible to organise theories the other way, namely according to geological criteria of formation. Often ores of the same metal can be formed by multiple processes, and this is described here under each metal or metal complex.

Iron

Iron ores are overwhelmingly derived from ancient sediments known as banded iron formations (BIFs). These sediments are composed of iron oxide minerals deposited on the sea floor. Particular environmental conditions are needed to transport enough iron in sea water to form these deposits, such as acidic and oxygen-poor atmospheres within the Proterozoic Era.

Often, more recent weathering is required to convert the usual magnetite minerals into more easily processed hematite. Some iron deposits within the Pilbara of Western Australia are placer deposits, formed by accumulation of hematite gravels called pisolites which form channel-iron deposits. These are preferred because they are cheap to mine.

Lead zinc silver

Lead-zinc deposits are generally accompanied by silver, hosted within the lead sulfide mineral galena or within the zinc sulfide mineral sphalerite.

Lead and zinc deposits are formed by discharge of deep sedimentary brine onto the sea floor (termed sedimentary exhalative or SEDEX), or by replacement of limestone, in skarn deposits, some associated with submarine volcanoes (called volcanogenic massive sulfide ore deposits or VMS), or in the aureole of subvolcanic intrusions of granite. The vast majority of SEDEX lead and zinc deposits are Proterozoic in age, although there are significant Jurassic examples in Canada and Alaska. 

The carbonate replacement type deposit is exemplified by the Mississippi valley type (MVT) ore deposits. MVT and similar styles occur by replacement and degradation of carbonate sequences by hydrocarbons, which are thought important for transporting lead.

Gold

High-grade (bonanza) gold ore, brecciated quartz-adularia rhyolite. Native gold (Au) occurs in this rock as colloform bands, partially replaces breccia clasts, and is also disseminated in the matrix. Published research indicates that Sleeper Mine rocks represent an ancient epithermal gold deposit (hot springs gold deposit), formed by volcanism during Basin & Range extensional tectonics. Sleeper Mine, Humboldt County, Nevada.
 
Gold deposits are formed via a very wide variety of geological processes. Deposits are classified as primary, alluvial or placer deposits, or residual or laterite deposits. Often a deposit will contain a mixture of all three types of ore.

Plate tectonics is the underlying mechanism for generating gold deposits. The majority of primary gold deposits fall into two main categories: lode gold deposits or intrusion-related deposits. 

Lode gold deposits are generally high-grade, thin, vein and fault hosted. They are primarily made up of quartz veins also known as lodes or reefs, which contain either native gold or gold sulfides and tellurides. Lode gold deposits are usually hosted in basalt or in sediments known as turbidite, although when in faults, they may occupy intrusive igneous rocks such as granite

Lode-gold deposits are intimately associated with orogeny and other plate collision events within geologic history. It is thought that most lode gold deposits are sourced from metamorphic rocks by the dehydration of basalt during metamorphism. The gold is transported up faults by hydrothermal waters and deposited when the water cools too much to retain gold in solution. 

Intrusive related gold (Lang & Baker, 2001) is generally hosted in granites, porphyry, or rarely dikes. Intrusive related gold usually also contains copper, and is often associated with tin and tungsten, and rarely molybdenum, antimony, and uranium. Intrusive-related gold deposits rely on gold existing in the fluids associated with the magma (White, 2001), and the inevitable discharge of these hydrothermal fluids into the wall-rocks (Lowenstern, 2001). Skarn deposits are another manifestation of intrusive-related deposits. 

Placer deposits are sourced from pre-existing gold deposits and are secondary deposits. Placer deposits are formed by alluvial processes within rivers and streams, and on beaches. Placer gold deposits form via gravity, with the density of gold causing it to sink into trap sites within the river bed, or where water velocity drops, such as bends in rivers and behind boulders. Often placer deposits are found within sedimentary rocks and can be billions of years old, for instance the Witwatersrand deposits in South Africa. Sedimentary placer deposits are known as 'leads' or 'deep leads'. 

Placer deposits are often worked by fossicking, and panning for gold is a popular pastime.

Laterite gold deposits are formed from pre-existing gold deposits (including some placer deposits) during prolonged weathering of the bedrock. Gold is deposited within iron oxides in the weathered rock or regolith, and may be further enriched by reworking by erosion. Some laterite deposits are formed by wind erosion of the bedrock leaving a residuum of native gold metal at surface.

A bacterium, Cupriavidus metallidurans plays a vital role in the formation of gold nuggets, by precipitating metallic gold from a solution of gold (III) tetrachloride, a compound highly toxic to most other microorganisms. Similarly, Delftia acidovorans can form gold nuggets.

Platinum

Platinum and palladium are precious metals generally found in ultramafic rocks. The source of platinum and palladium deposits is ultramafic rocks which have enough sulfur to form a sulfide mineral while the magma is still liquid. This sulfide mineral (usually pentlandite, pyrite, chalcopyrite, or pyrrhotite) gains platinum by mixing with the bulk of the magma because platinum is chalcophile and is concentrated in sulfides. Alternatively, platinum occurs in association with chromite either within the chromite mineral itself or within sulfides associated with it.

Sulfide phases only form in ultramafic magmas when the magma reaches sulfur saturation. This is generally thought to be nearly impossible by pure fractional crystallisation, so other processes are usually required in ore genesis models to explain sulfur saturation. These include contamination of the magma with crustal material, especially sulfur-rich wall-rocks or sediments; magma mixing; volatile gain or loss.

Often platinum is associated with nickel, copper, chromium, and cobalt deposits.

Nickel

Nickel deposits are generally found in two forms, either as sulfide or laterite.

Sulfide type nickel deposits are formed in essentially the same manner as platinum deposits. Nickel is a chalcophile element which prefers sulfides, so an ultramafic or mafic rock which has a sulfide phase in the magma may form nickel sulfides. The best nickel deposits are formed where sulfide accumulates in the base of lava tubes or volcanic flows — especially komatiite lavas. 

Komatiitic nickel-copper sulfide deposits are considered to be formed by a mixture of sulfide segregation, immiscibility, and thermal erosion of sulfidic sediments. The sediments are considered to be necessary to promote sulfur saturation.

Some subvolcanic sills in the Thompson Belt of Canada host nickel sulfide deposits formed by deposition of sulfides near the feeder vent. Sulfide was accumulated near the vent due to the loss of magma velocity at the vent interface. The massive Voisey's Bay nickel deposit is considered to have formed via a similar process. 

The process of forming nickel laterite deposits is essentially similar to the formation of gold laterite deposits, except that ultramafic or mafic rocks are required. Generally nickel laterites require very large olivine-bearing ultramafic intrusions. Minerals formed in laterite nickel deposits include gibbsite.

Copper

Copper is found in association with many other metals and deposit styles. Commonly, copper is either formed within sedimentary rocks, or associated with igneous rocks. 

The world's major copper deposits are formed within the granitic porphyry copper style. Copper is enriched by processes during crystallisation of the granite and forms as chalcopyrite — a sulfide mineral, which is carried up with the granite. 

Sometimes granites erupt to surface as volcanoes, and copper mineralisation forms during this phase when the granite and volcanic rocks cool via hydrothermal circulation

Sedimentary copper forms within ocean basins in sedimentary rocks. Generally this forms by brine from deeply buried sediments discharging into the deep sea, and precipitating copper and often lead and zinc sulfides directly onto the sea floor. This is then buried by further sediment. This is a process similar to SEDEX zinc and lead, although some carbonate-hosted examples exist.

Often copper is associated with gold, lead, zinc, and nickel deposits.

Uranium

Five cylinder-like bodies on a flat surface: four in a group and one separate.
Citrobacter species can have concentrations of uranium in their bodies 300 times higher than in the surrounding environment.
 
Uranium deposits are usually sourced from radioactive granites, where certain minerals such as monazite are leached during hydrothermal activity or during circulation of groundwater. The uranium is brought into solution by acidic conditions and is deposited when this acidity is neutralised. Generally this occurs in certain carbon-bearing sediments, within an unconformity in sedimentary strata. The majority of the world's nuclear power is sourced from uranium in such deposits. 

Uranium is also found in nearly all coal at several parts per million, and in all granites. Radon is a common problem during mining of uranium as it is a radioactive gas. 

Uranium is also found associated with certain igneous rocks, such as granite and porphyry. The Olympic Dam deposit in Australia is an example of this type of uranium deposit. It contains 70% of Australia's share of 40% of the known global low-cost recoverable uranium inventory.

Titanium and zirconium

Mineral sands are the predominant type of titanium, zirconium, and thorium deposit. They are formed by accumulation of such heavy minerals within beach systems, and are a type of placer deposits. The minerals which contain titanium are ilmenite, rutile, and leucoxene, zirconium is contained within zircon, and thorium is generally contained within monazite. These minerals are sourced from primarily granite bedrock by erosion and transported to the sea by rivers where they accumulate within beach sands. Rarely, but importantly, gold, tin, and platinum deposits can form in beach placer deposits.

Tin, tungsten, and molybdenum

These three metals generally form in a certain type of granite, via a similar mechanism to intrusive-related gold and copper. They are considered together because the process of forming these deposits is essentially the same. Skarn type mineralisation related to these granites is a very important type of tin, tungsten, and molybdenum deposit. Skarn deposits form by reaction of mineralised fluids from the granite reacting with wall rocks such as limestone. Skarn mineralisation is also important in lead, zinc, copper, gold, and occasionally uranium mineralisation. 

Greisen granite is another related tin-molybdenum and topaz mineralisation style.

Rare earth elements, niobium, tantalum, lithium

The overwhelming majority of rare earth elements, tantalum, and lithium are found within pegmatite. Ore genesis theories for these ores are wide and varied, but most involve metamorphism and igneous activity. Lithium is present as spodumene or lepidolite within pegmatite. 

Carbonatite intrusions are an important source of these elements. Ore minerals are essentially part of the unusual mineralogy of carbonatite.

Phosphate

Phosphate is used in fertilisers. Immense quantities of phosphate rock or phosphorite occur in sedimentary shelf deposits, ranging in age from the Proterozoic to currently forming environments. Phosphate deposits are thought to be sourced from the skeletons of dead sea creatures which accumulated on the seafloor. Similar to iron ore deposits and oil, particular conditions in the ocean and environment are thought to have contributed to these deposits within the geological past.

Phosphate deposits are also formed from alkaline igneous rocks such as nepheline syenites, carbonatites, and associated rock types. The phosphate is, in this case, contained within magmatic apatite, monazite, or other rare-earth phosphates.

Vanadium

Tunicates such as this bluebell tunicate contain vanadium as vanabin.
 
Due to the presence of vanabins, concentration of vanadium found in the blood cells of Ascidia gemmata belonging to the suborder Phlebobranchia is 10,000,000 times higher than that in the surrounding seawater. A similar biological process might have played a role in the formation of vanadium ores. Vanadium is also present in fossil fuel deposits such as crude oil, coal, oil shale, and oil sands. In crude oil, concentrations up to 1200 ppm have been reported.

Ore

From Wikipedia, the free encyclopedia

Manganese ore – psilomelane (size: 6.7 × 5.8 × 5.1 cm)
 
Lead ore – galena and anglesite (size: 4.8 × 4.0 × 3.0 cm)
 
Gold ore (size: 7.5 × 6.1 × 4.1 cm)
 
Cart for carrying ore from a mine on display at the Historic Archive and Museum of Mining in Pachuca, Mexico
 
An ore is a natural occurrence of rock or sediment that contains sufficient minerals with economically important elements, typically metals, that can be economically extracted from the deposit. The ores are extracted at a profit from the earth through mining; they are then refined (often via smelting) to extract the valuable element or elements. 

The ore grade, or concentration of an ore mineral or metal, as well as its form of occurrence, will directly affect the costs associated with mining the ore. The cost of extraction must thus be weighed against the metal value contained in the rock to determine what ore can be processed and what ore is of too low a grade to be worth mining. Metal ores are generally oxides, sulfides, silicates, or native metals (such as native copper) that are not commonly concentrated in the Earth's crust, or noble metals (not usually forming compounds) such as gold. The ores must be processed to extract the elements of interest from the waste rock and from the ore minerals. Ore bodies are formed by a variety of geological processes. The process of ore formation is called ore genesis.

Ore deposits

An ore deposit is an accumulation of ore. This is distinct from a mineral resource as defined by the mineral resource classification criteria. An ore deposit is one occurrence of a particular ore type. Most ore deposits are named according to their location (for example, the Witwatersrand, South Africa), or after a discoverer (e.g. the Kambalda nickel shoots are named after drillers), or after some whimsy, a historical figure, a prominent person, something from mythology (phoenix, kraken, serepentleopard, etc.) or the code name of the resource company which found it (e.g. MKD-5 was the in-house name for the Mount Keith nickel sulphide deposit).

Classification

Ore deposits are classified according to various criteria developed via the study of economic geology, or ore genesis. The classifications below are typical.

Hydrothermal epigenetic deposits

Granite related hydrothermal

Magmatic deposits

Volcanic-related deposits

A cross-section of a typical Volcanic hosted massive sulfide|volcanogenic massive sulfide (VMS) ore deposit

Metamorphically reworked deposits

Carbonatite-alkaline igneous related

Sedimentary deposits

Magnified view of banded iron formation specimen from Upper Michigan. Scale bar is 5.0 mm.

Sedimentary hydrothermal deposits

Astrobleme-related ores

Extraction

Some ore deposits in the world
 
Some additional ore deposits in the world

The basic extraction of ore deposits follows these steps:
  1. Prospecting or exploration to find and then define the extent and value of ore where it is located ("ore body")
  2. Conduct resource estimation to mathematically estimate the size and grade of the deposit
  3. Conduct a pre-feasibility study to determine the theoretical economics of the ore deposit. This identifies, early on, whether further investment in estimation and engineering studies is warranted and identifies key risks and areas for further work.
  4. Conduct a feasibility study to evaluate the financial viability, technical and financial risks and robustness of the project and make a decision as whether to develop or walk away from a proposed mine project. This includes mine planning to evaluate the economically recoverable portion of the deposit, the metallurgy and ore recoverability, marketability and payability of the ore concentrates, engineering, milling and infrastructure costs, finance and equity requirements and a cradle to grave analysis of the possible mine, from the initial excavation all the way through to reclamation.
  5. Development to create access to an ore body and building of mine plant and equipment
  6. The operation of the mine in an active sense
  7. Reclamation to make land where a mine had been suitable for future use

Trade

Ores (metals) are traded internationally and comprise a sizeable portion of international trade in raw materials both in value and volume. This is because the worldwide distribution of ores is unequal and dislocated from locations of peak demand and from smelting infrastructure. 

Most base metals (copper, lead, zinc, nickel) are traded internationally on the London Metal Exchange, with smaller stockpiles and metals exchanges monitored by the COMEX and NYMEX exchanges in the United States and the Shanghai Futures Exchange in China. 

Iron ore is traded between customer and producer, though various benchmark prices are set quarterly between the major mining conglomerates and the major consumers, and this sets the stage for smaller participants. 

Other, lesser, commodities do not have international clearing houses and benchmark prices, with most prices negotiated between suppliers and customers one-on-one. This generally makes determining the price of ores of this nature opaque and difficult. Such metals include lithium, niobium-tantalum, bismuth, antimony and rare earths. Most of these commodities are also dominated by one or two major suppliers with >60% of the world's reserves. The London Metal Exchange aims to add uranium to its list of metals on warrant.

The World Bank reports that China was the top importer of ores and metals in 2005 followed by the US and Japan.

Equality (mathematics)

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