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129-466: Hematite occurs naturally in black to steel or silver-gray, brown to reddish-brown, or red colors. It is mined as an important ore mineral of iron . It is electrically conductive. Hematite varieties include kidney ore , martite ( pseudomorphs after magnetite ), iron rose and specularite ( specular hematite). While these forms vary, they all have a rust-red streak. Hematite is not only harder than pure iron, but also much more brittle . Maghemite

258-464: A Fermi gas . For these materials one contribution to the magnetic response comes from the interaction between the electron spins and the magnetic field known as Pauli paramagnetism. For a small magnetic field H {\displaystyle \mathbf {H} } , the additional energy per electron from the interaction between an electron spin and the magnetic field is given by: where μ 0 {\displaystyle \mu _{0}}

387-526: A band structure picture as arising from the incomplete filling of energy bands. In an ordinary nonmagnetic conductor the conduction band is identical for both spin-up and spin-down electrons. When a magnetic field is applied, the conduction band splits apart into a spin-up and a spin-down band due to the difference in magnetic potential energy for spin-up and spin-down electrons. Since the Fermi level must be identical for both bands, this means that there will be

516-714: A torque being provided on the magnetic moments by an applied field, which tries to align the dipoles parallel to the applied field. However, the true origins of the alignment can only be understood via the quantum-mechanical properties of spin and angular momentum . If there is sufficient energy exchange between neighbouring dipoles, they will interact, and may spontaneously align or anti-align and form magnetic domains, resulting in ferromagnetism (permanent magnets) or antiferromagnetism , respectively. Paramagnetic behavior can also be observed in ferromagnetic materials that are above their Curie temperature , and in antiferromagnets above their Néel temperature . At these temperatures,

645-508: A Curie type law but with exceptionally large values for the Curie constants. These materials are known as superparamagnets . They are characterized by a strong ferromagnetic or ferrimagnetic type of coupling into domains of a limited size that behave independently from one another. The bulk properties of such a system resembles that of a paramagnet, but on a microscopic level they are ordered. The materials do show an ordering temperature above which

774-465: A concern as well, and where enforced, modern practices have significantly improved safety in mines. Unregulated, poorly regulated or illegal mining , especially in developing economies , frequently contributes to local human rights violations and environmental conflicts . Mining can also perpetuate political instability through resource conflicts . Since the beginning of civilization, people have used stone , clay and, later, metals found close to

903-539: A decrease in temperature at 260 K (−13 °C) is caused by a change in the anisotropy which causes the moments to align along the c axis. In this configuration, spin canting does not reduce the energy. The magnetic properties of bulk hematite differ from their nanoscale counterparts. For example, the Morin transition temperature of hematite decreases with a decrease in the particle size. The suppression of this transition has been observed in hematite nanoparticles and

1032-399: A diamagnetic response of opposite sign. Strictly speaking Li is a mixed system therefore, although admittedly the diamagnetic component is weak and often neglected. In the case of heavier elements the diamagnetic contribution becomes more important and in the case of metallic gold it dominates the properties. The element hydrogen is virtually never called 'paramagnetic' because the monatomic gas

1161-512: A ferromagnet and a 'paramagnet'. The word paramagnet now merely refers to the linear response of the system to an applied field, the temperature dependence of which requires an amended version of Curie's law, known as the Curie–Weiss law : This amended law includes a term θ that describes the exchange interaction that is present albeit overcome by thermal motion. The sign of θ depends on whether ferro- or antiferromagnetic interactions dominate and it

1290-2973: A few K , M J g J μ B H / k B T ≪ 1 {\displaystyle M_{J}g_{J}\mu _{\mathrm {B} }H/k_{\mathrm {B} }T\ll 1} , and we can apply the approximation e M J g J μ B H / k B T ≃ 1 + M J g J μ B H / k B T {\displaystyle e^{M_{J}g_{J}\mu _{\mathrm {B} }H/k_{\mathrm {B} }T\;}\simeq 1+M_{J}g_{J}\mu _{\mathrm {B} }H/k_{\mathrm {B} }T\;} : m ¯ = ∑ M J = − J J M J g J μ B e M J g J μ B H / k B T ∑ M J = − J J e M J g J μ B H / k B T ≃ g J μ B ∑ M J = − J J M J ( 1 + M J g J μ B H / k B T ) ∑ M J = − J J ( 1 + M J g J μ B H / k B T ) = g J 2 μ B 2 H k B T ∑ − J J M J 2 ∑ M J = − J J ( 1 ) , {\displaystyle {\bar {m}}={\frac {\sum \limits _{M_{J}=-J}^{J}{M_{J}g_{J}\mu _{\mathrm {B} }e^{M_{J}g_{J}\mu _{\mathrm {B} }H/k_{\mathrm {B} }T\;}}}{\sum \limits _{M_{J}=-J}^{J}e^{M_{J}g_{J}\mu _{\mathrm {B} }H/k_{\mathrm {B} }T\;}}}\simeq g_{J}\mu _{\mathrm {B} }{\frac {\sum \limits _{M_{J}=-J}^{J}M_{J}\left(1+M_{J}g_{J}\mu _{\mathrm {B} }H/k_{\mathrm {B} }T\;\right)}{\sum \limits _{M_{J}=-J}^{J}\left(1+M_{J}g_{J}\mu _{\mathrm {B} }H/k_{\mathrm {B} }T\;\right)}}={\frac {g_{J}^{2}\mu _{\mathrm {B} }^{2}H}{k_{\mathrm {B} }T}}{\frac {\sum \limits _{-J}^{J}M_{J}^{2}}{\sum \limits _{M_{J}=-J}^{J}{(1)}}},} which yields: m ¯ = g J 2 μ B 2 H 3 k B T J ( J + 1 ) . {\displaystyle {\bar {m}}={\frac {g_{J}^{2}\mu _{\mathrm {B} }^{2}H}{3k_{\mathrm {B} }T}}J(J+1).} The bulk magnetization

1419-472: A gas of electrons is not the full picture as the magnetic susceptibility coming from the ions has to be included. Additionally, these formulas may break down for confined systems that differ from the bulk, like quantum dots , or for high fields, as demonstrated in the De Haas-Van Alphen effect . Pauli paramagnetism is named after the physicist Wolfgang Pauli . Before Pauli's theory, the lack of

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1548-493: A good example. Even in the frozen solid it contains di-radical molecules resulting in paramagnetic behavior. The unpaired spins reside in orbitals derived from oxygen p wave functions, but the overlap is limited to the one neighbor in the O 2 molecules. The distances to other oxygen atoms in the lattice remain too large to lead to delocalization and the magnetic moments remain unpaired. The Bohr–Van Leeuwen theorem proves that there cannot be any diamagnetism or paramagnetism in

1677-636: A hopper and a shaking screen or trommel which frees the desired minerals from the waste gravel. The minerals are then concentrated using sluices or jigs. Large drills are used to sink shafts, excavate stopes, and obtain samples for analysis. Trams are used to transport miners, minerals and waste. Lifts carry miners into and out of mines, and move rock and ore out, and machinery in and out, of underground mines. Huge trucks, shovels and cranes are employed in surface mining to move large quantities of overburden and ore. Processing plants use large crushers, mills, reactors, roasters and other equipment to consolidate

1806-883: A mass of actual rock. Both types of ore deposit, placer or lode, are mined by both surface and underground methods. Some mining, including much of the rare earth elements and uranium mining , is done by less-common methods, such as in-situ leaching : this technique involves digging neither at the surface nor underground. The extraction of target minerals by this technique requires that they be soluble, e.g., potash , potassium chloride , sodium chloride , sodium sulfate , which dissolve in water. Some minerals, such as copper minerals and uranium oxide , require acid or carbonate solutions to dissolve. Explosives in Mining Explosives have been used in surface mining and sub-surface mining to blast out rock and ore intended for processing. The most common explosive used in mining

1935-426: A mining operation. Once the analysis determines a given ore body is worth recovering, development begins to create access to the ore body. The mine buildings and processing plants are built, and any necessary equipment is obtained. The operation of the mine to recover the ore begins and continues as long as the company operating the mine finds it economical to do so. Once all the ore that the mine can produce profitably

2064-503: A more sustainable future, the demand for metals is set to skyrocket. Between 2022 and 2050, an estimated 7 billion metric tons of metals will need to be extracted. Steel will account for the largest portion of this total at 5 billion tons, followed by aluminum at 950 million tons, copper at 650 million tons, graphite at 170 million tons, nickel at 100 million tons, and other metals. Notably, the energy expenditure required to extract these metals will soon surpass that of coal mining, highlighting

2193-519: A net paramagnetic response over a broad temperature range. They do not follow a Curie type law as function of temperature however; often they are more or less temperature independent. This type of behavior is of an itinerant nature and better called Pauli-paramagnetism, but it is not unusual to see, for example, the metal aluminium called a "paramagnet", even though interactions are strong enough to give this element very good electrical conductivity. Some materials show induced magnetic behavior that follows

2322-604: A paramagnetic ion with noninteracting magnetic moments with angular momentum J , the Curie constant is related to the individual ions' magnetic moments, C = n 3 k B μ e f f 2  where  μ e f f = g J μ B J ( J + 1 ) . {\displaystyle C={\frac {n}{3k_{\mathrm {B} }}}\mu _{\mathrm {eff} }^{2}{\text{ where }}\mu _{\mathrm {eff} }=g_{J}\mu _{\mathrm {B} }{\sqrt {J(J+1)}}.} where n

2451-417: A purely classical system. The paramagnetic response has then two possible quantum origins, either coming from permanent magnetic moments of the ions or from the spatial motion of the conduction electrons inside the material. Both descriptions are given below. For low levels of magnetization, the magnetization of paramagnets follows what is known as Curie's law , at least approximately. This law indicates that

2580-484: A sensitive analytical balance to detect the effect and modern measurements on paramagnetic materials are often conducted with a SQUID magnetometer . Paramagnetism is due to the presence of unpaired electrons in the material, so most atoms with incompletely filled atomic orbitals are paramagnetic, although exceptions such as copper exist. Due to their spin , unpaired electrons have a magnetic dipole moment and act like tiny magnets. An external magnetic field causes

2709-523: A small surplus of the type of spin in the band that moved downwards. This effect is a weak form of paramagnetism known as Pauli paramagnetism . The effect always competes with a diamagnetic response of opposite sign due to all the core electrons of the atoms. Stronger forms of magnetism usually require localized rather than itinerant electrons. However, in some cases a band structure can result in which there are two delocalized sub-bands with states of opposite spins that have different energies. If one subband

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2838-544: A strong Curie paramagnetism in metals was an open problem as the leading Drude model could not account for this contribution without the use of quantum statistics . Pauli paramagnetism and Landau diamagnetism are essentially applications of the spin and the free electron model , the first is due to intrinsic spin of electrons; the second is due to their orbital motion. Materials that are called "paramagnets" are most often those that exhibit, at least over an appreciable temperature range, magnetic susceptibilities that adhere to

2967-408: A strong inducement to extract these metals or to lease the deposits and collect royalties from mine operators. English, German , and Dutch capital combined to finance extraction and refining . Hundreds of German technicians and skilled workers were brought over; in 1642 a colony of 4,000 foreigners was mining and smelting copper at Keswick in the northwestern mountains. Use of water power in

3096-425: A two-line ferrihydrite precursor prepared from solution. Hematite exhibited temperature-dependent magnetic coercivity values ranging from 289 to 5,027 oersteds (23–400 kA/m). The origin of these high coercivity values has been interpreted as a consequence of the subparticle structure induced by the different particle and crystallite size growth rates at increasing annealing temperature. These differences in

3225-399: A weak magnetism. This is why s- and p-type metals are typically either Pauli-paramagnetic or as in the case of gold even diamagnetic. In the latter case the diamagnetic contribution from the closed shell inner electrons simply wins over the weak paramagnetic term of the almost free electrons. Stronger magnetic effects are typically only observed when d or f electrons are involved. Particularly

3354-515: A wider sense includes extraction of any non-renewable resource such as petroleum , natural gas , or even water . Modern mining processes involve prospecting for ore bodies, analysis of the profit potential of a proposed mine, extraction of the desired materials, and final reclamation or restoration of the land after the mine is closed. Mining materials are often obtained from ore bodies, lodes , veins , seams , reefs , or placer deposits . The exploitation of these deposits for raw materials

3483-651: Is ammonium nitrate . Between 1870 and 1920, in Queensland Australia, an increase in mining accidents lead to more safety measures surrounding the use of explosives for mining. In the United States of America, between 1990 and 1999, about 22.3 billion kilograms of explosives were used in mining quarrying and other industries; Moreover " coal mining used 66.4%, nonmetal mining and quarrying 13.5%, metal mining 10.4%, construction 7.1%, and all other users 2.6%". Artisanal and small-scale mining (ASM)

3612-399: Is a generalization as it pertains to materials with an extended lattice rather than a molecular structure. Molecular structure can also lead to localization of electrons. Although there are usually energetic reasons why a molecular structure results such that it does not exhibit partly filled orbitals (i.e. unpaired spins), some non-closed shell moieties do occur in nature. Molecular oxygen is

3741-811: Is a blanket term for a type of subsistence mining involving a miner who may or may not be officially employed by a mining company but works independently, mining minerals using their own resources, usually by hand. While there is no completely coherent definition for ASM, artisanal mining generally includes miners who are not officially employed by a mining company and use their own resources to mine. As such, they are part of an informal economy . ASM also includes, in small-scale mining, enterprises or individuals that employ workers for mining, but who generally still use similar manually-intensive methods as artisanal miners (such as working with hand tools). In addition, ASM can be characterized as distinct from large-scale mining (LSM) by less efficient extraction of pure minerals from

3870-424: Is a clay that is colored by varying amounts of hematite, varying between 20% and 70%. Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite ( Fe 2 O 3  ·  H 2 O ). The principal use of ochre is for tinting with a permanent color. Use of the red chalk of this iron-oxide mineral in writing, drawing, and decoration is among the earliest in human history. To date,

3999-594: Is a pigment used in traditional Swedish house paints. Originally, it was made from tailings of the Falu mine. The spectral signature of hematite was seen on the planet Mars by the infrared spectrometer on the NASA Mars Global Surveyor and 2001 Mars Odyssey spacecraft in orbit around Mars. The mineral was seen in abundance at two sites on the planet, the Terra Meridiani site, near

Hematite - Misplaced Pages Continue

4128-540: Is a polymorph of hematite (γ- Fe 2 O 3 ) with the same chemical formula, but with a spinel structure like magnetite. Large deposits of hematite are found in banded iron formations . Gray hematite is typically found in places that have still, standing water, or mineral hot springs , such as those in Yellowstone National Park in North America . The mineral may precipitate in

4257-468: Is attributed to the presence of impurities, water molecules and defects in the crystals lattice. Hematite is part of a complex solid solution oxyhydroxide system having various contents of H2O (water), hydroxyl groups and vacancy substitutions that affect the mineral's magnetic and crystal chemical properties. Two other end-members are referred to as protohematite and hydrohematite. Enhanced magnetic coercivities for hematite have been achieved by dry-heating

4386-420: Is close to zero this does not mean that there are no interactions, just that the aligning ferro- and the anti-aligning antiferromagnetic ones cancel. An additional complication is that the interactions are often different in different directions of the crystalline lattice ( anisotropy ), leading to complicated magnetic structures once ordered. Randomness of the structure also applies to the many metals that show

4515-506: Is dependent on investment, labor, energy, refining, and transportation cost. Mining operations can create a negative environmental impact, both during the mining activity and after the mine has closed. Hence, most of the world's nations have passed regulations to decrease the impact; however, the outsized role of mining in generating business for often rural, remote or economically depressed communities means that governments often fail to fully enforce such regulations. Work safety has long been

4644-492: Is derived from the Greek word for blood, αἷμα (haima) , due to the red coloration found in some varieties of hematite. The color of hematite is often used as a pigment . The English name of the stone is derived from Middle French hématite pierre , which was taken from Latin lapis haematites c. the 15th century, which originated from Ancient Greek αἱματίτης λίθος ( haimatitēs lithos , "blood-red stone"). Ochre

4773-400: Is diamagnetic; if it has unpaired electrons, then the substance is paramagnetic. Unlike ferromagnets , paramagnets do not retain any magnetization in the absence of an externally applied magnetic field because thermal motion randomizes the spin orientations. (Some paramagnetic materials retain spin disorder even at absolute zero , meaning they are paramagnetic in the ground state , i.e. in

4902-476: Is done by removing surface vegetation, dirt, and bedrock to reach buried ore deposits. Techniques of surface mining include: open-pit mining , which is the recovery of materials from an open pit in the ground; quarrying , identical to open-pit mining except that it refers to sand, stone and clay; strip mining , which consists of stripping surface layers off to reveal ore underneath; and mountaintop removal , commonly associated with coal mining, which involves taking

5031-452: Is incorporated into radiation shielding. As with other iron ores, it often is a component of ship ballasts because of its density and economy. In the coal industry, it can be formed into a high specific density solution, to help separate coal powder from impurities. Mining Mining is the extraction of valuable geological materials and minerals from the surface of the Earth . Mining

5160-613: Is mining upward, creating a sloping underground room, long wall mining , which is grinding a long ore surface underground, and room and pillar mining, which is removing ore from rooms while leaving pillars in place to support the roof of the room. Room and pillar mining often leads to retreat mining , in which supporting pillars are removed as miners retreat, allowing the room to cave in, thereby loosening more ore. Additional sub-surface mining methods include hard rock mining , bore hole mining, drift and fill mining, long hole slope mining, sub level caving, and block caving . Heavy machinery

5289-484: Is much more common, and produces, for example, 85% of minerals (excluding petroleum and natural gas) in the United States, including 98% of metallic ores. Targets are divided into two general categories of materials: placer deposits , consisting of valuable minerals contained within river gravels, beach sands, and other unconsolidated materials ; and lode deposits , where valuable minerals are found in veins, in layers, or in mineral grains generally distributed throughout

Hematite - Misplaced Pages Continue

5418-479: Is non-linear and much stronger, so that it is easily observed, for instance, in the attraction between a refrigerator magnet and the iron of the refrigerator itself. Constituent atoms or molecules of paramagnetic materials have permanent magnetic moments ( dipoles ), even in the absence of an applied field. The permanent moment generally is due to the spin of unpaired electrons in atomic or molecular electron orbitals (see Magnetic moment ). In pure paramagnetism,

5547-413: Is not of immediate interest to the miner. The total movement of ore and waste constitutes the mining process. Often more waste than ore is mined during the life of a mine, depending on the nature and location of the ore body. Waste removal and placement is a major cost to the mining operator, so a detailed characterization of the waste material forms an essential part of the geological exploration program for

5676-460: Is not uncommon to call such materials 'paramagnets', when referring to their paramagnetic behavior above their Curie or Néel-points, particularly if such temperatures are very low or have never been properly measured. Even for iron it is not uncommon to say that iron becomes a paramagnet above its relatively high Curie-point. In that case the Curie-point is seen as a phase transition between

5805-441: Is preferentially filled over the other, one can have itinerant ferromagnetic order. This situation usually only occurs in relatively narrow (d-)bands, which are poorly delocalized. Generally, strong delocalization in a solid due to large overlap with neighboring wave functions means that there will be a large Fermi velocity ; this means that the number of electrons in a band is less sensitive to shifts in that band's energy, implying

5934-584: Is recovered, reclamation can begin, to make the land used by the mine suitable for future use. Technical and economic challenges notwithstanding, successful mine development must also address human factors. Working conditions are paramount to success, especially with regard to exposures to dusts, radiation, noise, explosives hazards, and vibration, as well as illumination standards. Mining today increasingly must address environmental and community impacts, including psychological and sociological dimensions. Thus, mining educator Frank T. M. White (1909–1971), broadened

6063-451: Is required to obtain most materials that cannot be grown through agricultural processes , or feasibly created artificially in a laboratory or factory. Ores recovered by mining include metals , coal , oil shale , gemstones , limestone , chalk , dimension stone , rock salt , potash , gravel , and clay . The ore must be a rock or mineral that contains valuable constituent, can be extracted or mined and sold for profit. Mining in

6192-413: Is seldom exactly zero, except in the dilute, isolated cases mentioned above. Obviously, the paramagnetic Curie–Weiss description above T N or T C is a rather different interpretation of the word "paramagnet" as it does not imply the absence of interactions, but rather that the magnetic structure is random in the absence of an external field at these sufficiently high temperatures. Even if θ

6321-453: Is stable only at extremely high temperature; H atoms combine to form molecular H 2 and in so doing, the magnetic moments are lost ( quenched ), because of the spins pair. Hydrogen is therefore diamagnetic and the same holds true for many other elements. Although the electronic configuration of the individual atoms (and ions) of most elements contain unpaired spins, they are not necessarily paramagnetic, because at ambient temperature quenching

6450-644: Is the vacuum permeability , μ e {\displaystyle {\boldsymbol {\mu }}_{e}} is the electron magnetic moment , μ B {\displaystyle \mu _{\rm {B}}} is the Bohr magneton , ℏ {\displaystyle \hbar } is the reduced Planck constant, and the g-factor cancels with the spin S = ± ℏ / 2 {\displaystyle \mathbf {S} =\pm \hbar /2} . The ± {\displaystyle \pm } indicates that

6579-461: Is the z -component of the magnetic moment for each Zeeman level, so μ M J = M J g J μ B − μ B {\displaystyle \mu _{M_{J}}=M_{J}g_{J}\mu _{\mathrm {B} }-\mu _{\mathrm {B} }} is called the Bohr magneton and g J is the Landé g-factor , which reduces to

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6708-656: Is the largest producer of diamonds in Africa, with an estimated 12 million carats in 2019. Other types of mining reserves in Africa include cobalt , bauxite , iron ore , coal, and copper . Gold and coal mining started in Australia and New Zealand in the 19th century. Nickel has become important in the economy of New Caledonia . In Fiji , in 1934, the Emperor Gold Mining Company Ltd. established operations at Vatukoula , followed in 1935 by

6837-468: Is the number of unpaired electrons . In other transition metal complexes this yields a useful, if somewhat cruder, estimate. When Curie constant is null, second order effects that couple the ground state with the excited states can also lead to a paramagnetic susceptibility independent of the temperature, known as Van Vleck susceptibility . For some alkali metals and noble metals, conduction electrons are weakly interacting and delocalized in space forming

6966-493: Is the number of atoms per unit volume. The parameter μ eff is interpreted as the effective magnetic moment per paramagnetic ion. If one uses a classical treatment with molecular magnetic moments represented as discrete magnetic dipoles, μ , a Curie Law expression of the same form will emerge with μ appearing in place of μ eff . Curie's Law can be derived by considering a substance with noninteracting magnetic moments with angular momentum J . If orbital contributions to

7095-1032: Is then M = n m ¯ = n 3 k B T [ g J 2 J ( J + 1 ) μ B 2 ] H , {\displaystyle M=n{\bar {m}}={\frac {n}{3k_{\mathrm {B} }T}}\left[g_{J}^{2}J(J+1)\mu _{\mathrm {B} }^{2}\right]H,} and the susceptibility is given by χ = ∂ M m ∂ H = n 3 k B T μ e f f 2  ; and  μ e f f = g J J ( J + 1 ) μ B . {\displaystyle \chi ={\frac {\partial M_{\rm {m}}}{\partial H}}={\frac {n}{3k_{\rm {B}}T}}\mu _{\mathrm {eff} }^{2}{\text{ ; and }}\mu _{\mathrm {eff} }=g_{J}{\sqrt {J(J+1)}}\mu _{\mathrm {B} }.} When orbital angular momentum contributions to

7224-423: Is to conduct a feasibility study to evaluate the financial viability, the technical and financial risks, and the robustness of the project. This is when the mining company makes the decision whether to develop the mine or to walk away from the project. This includes mine planning to evaluate the economically recoverable portion of the deposit, the metallurgy and ore recoverability, marketability and payability of

7353-419: Is used in mining to explore and develop sites, to remove and stockpile overburden, to break and remove rocks of various hardness and toughness, to process the ore, and to carry out reclamation projects after the mine is closed. Bulldozers, drills, explosives and trucks are all necessary for excavating the land. In the case of placer mining , unconsolidated gravel, or alluvium , is fed into machinery consisting of

7482-439: Is valid under the commonly encountered conditions of low magnetization ( μ B H ≲ k B T ), but does not apply in the high-field/low-temperature regime where saturation of magnetization occurs ( μ B H ≳ k B T ) and magnetic dipoles are all aligned with the applied field. When the dipoles are aligned, increasing the external field will not increase the total magnetization since there can be no further alignment. For

7611-399: Is very much the rule rather than the exception. The quenching tendency is weakest for f-electrons because f (especially 4 f ) orbitals are radially contracted and they overlap only weakly with orbitals on adjacent atoms. Consequently, the lanthanide elements with incompletely filled 4f-orbitals are paramagnetic or magnetically ordered. Thus, condensed phase paramagnets are only possible if

7740-477: The Opportunity rover showed a significant amount of hematite, much of it in the form of small " Martian spherules " that were informally named "blueberries" by the science team. Analysis indicates that these spherules are apparently concretions formed from a water solution. "Knowing just how the hematite on Mars was formed will help us characterize the past environment and determine whether that environment

7869-416: The dipoles do not interact with one another and are randomly oriented in the absence of an external field due to thermal agitation, resulting in zero net magnetic moment. When a magnetic field is applied, the dipoles will tend to align with the applied field, resulting in a net magnetic moment in the direction of the applied field. In the classical description, this alignment can be understood to occur due to

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7998-470: The Greek author Diodorus Siculus , who mentions fire-setting as one method used to break down the hard rock holding the gold . One of the complexes is shown in one of the earliest known mining maps. The miners crushed the ore and ground it to a fine powder before washing the powder for the gold dust known as the dry and wet attachment processes. Mining in Europe has a very long history. Examples include

8127-585: The Morin transition at 250 K (−23 °C), and a canted antiferromagnet or weakly ferromagnetic above the Morin transition and below its Néel temperature at 948 K (675 °C), above which it is paramagnetic . The magnetic structure of α-hematite was the subject of considerable discussion and debate during the 1950s, as it appeared to be ferromagnetic with a Curie temperature of approximately 1,000 K (730 °C), but with an extremely small magnetic moment (0.002  Bohr magnetons ). Adding to

8256-525: The Upper Rhine . Rich deposits of hematite have been found on the island of Elba that have been mined since the time of the Etruscans . Underground hematite mining is classified as carcinogenic hazard to humans. Hematite shows only a very feeble response to a magnetic field . Unlike magnetite, it is not noticeably attracted to an ordinary magnet. Hematite is an antiferromagnetic material below

8385-517: The argentiferous galena in the mines of Cartagena ( Cartago Nova ), Linares ( Castulo ), Plasenzuela and Azuaga , among many others. Spain was one of the most important mining regions, but all regions of the Roman Empire were exploited. In Great Britain the natives had mined minerals for millennia , but after the Roman conquest , the scale of the operations increased dramatically, as

8514-836: The greenstone of the Langdale axe industry based in the English Lake District . The oldest-known mine on archaeological record is the Ngwenya Mine in Eswatini (Swaziland) , which radiocarbon dating shows to be about 43,000 years old. At this site Paleolithic humans mined hematite to make the red pigment ochre . Mines of a similar age in Hungary are believed to be sites where Neanderthals may have mined flint for weapons and tools. Ancient Egyptians mined malachite at Maadi . At first, Egyptians used

8643-509: The 21st century begins, a globalized mining industry of large multinational corporations has arisen. Peak minerals and environmental impacts have also become a concern. Different elements, particularly rare-earth minerals , have begun to increase in demand as a result of new technologies. In 2023, 8.5 billion metric tons of coal were extracted from the Earth's crust. However, as the global economy transitions away from fossil fuels and toward

8772-680: The 7th century to the 14th century. Gold was often traded to Mediterranean economies that demanded gold and could supply salt , even though much of Africa was abundant with salt due to the mines and resources in the Sahara desert . The trading of gold for salt was mostly used to promote trade between the different economies. Since the Great Trek in the 19th century, after, gold and diamond mining in Southern Africa has had major political and economic impacts. The Democratic Republic of Congo

8901-545: The Curie or Curie–Weiss laws. In principle any system that contains atoms, ions, or molecules with unpaired spins can be called a paramagnet, but the interactions between them need to be carefully considered. The narrowest definition would be: a system with unpaired spins that do not interact with each other. In this narrowest sense, the only pure paramagnet is a dilute gas of monatomic hydrogen atoms. Each atom has one non-interacting unpaired electron. A gas of lithium atoms already possess two paired core electrons that produce

9030-524: The Earth's surface. These were used to make early tools and weapons; for example, high quality flint found in northern France , southern England and Poland was used to create flint tools . Flint mines have been found in chalk areas where seams of the stone were followed underground by shafts and galleries. The mines at Grimes Graves and Krzemionki are especially famous, and like most other flint mines, are Neolithic in origin (c. 4000–3000 BC). Other hard rocks mined or collected for axes included

9159-675: The French crown to operate mines in 1733, becoming "the first practical miner on Lake Superior"; seven years later, mining was halted by an outbreak between Sioux and Chippewa tribes. Mining in the United States became widespread in the 19th century, and the United States Congress passed the General Mining Act of 1872 to encourage mining of federal lands. As with the California Gold Rush in

9288-643: The Loloma Gold Mines, N.L., and then by Fiji Mines Development Ltd. (aka Dolphin Mines Ltd.). These developments ushered in a “mining boom”, with gold production rising more than a hundred-fold, from 931.4 oz in 1934 to 107,788.5 oz in 1939, an order of magnitude then comparable to the combined output of New Zealand and Australia's eastern states. During prehistoric times, early Americans mined large amounts of copper along Lake Superior 's Keweenaw Peninsula and in nearby Isle Royale ; metallic copper

9417-722: The Martian equator at 0° longitude, and the Aram Chaos site near the Valles Marineris . Several other sites also showed hematite, such as Aureum Chaos . Because terrestrial hematite is typically a mineral formed in aqueous environments or by aqueous alteration, this detection was scientifically interesting enough that the second of the two Mars Exploration Rovers was sent to a site in the Terra Meridiani region designated Meridiani Planum . In-situ investigations by

9546-481: The Romans needed Britannia 's resources, especially gold , silver , tin , and lead . Roman techniques were not limited to surface mining. They followed the ore veins underground once opencast mining was no longer feasible. At Dolaucothi they stoped out the veins and drove adits through bare rock to drain the stopes. The same adits were also used to ventilate the workings, especially important when fire-setting

9675-598: The Spanish to pulverize ore after being mined. This device was powered by animals and used the same principles used for grain threshing . Much of the knowledge of medieval mining techniques comes from books such as Biringuccio 's De la pirotechnia and probably most importantly from Georg Agricola 's De re metallica (1556). These books detail many different mining methods used in German and Saxon mines. A prime issue in medieval mines, which Agricola explains in detail,

9804-756: The Umm el-Sawwan site; gypsum was used to make funerary items for private tombs. Other minerals mined in Egypt from the Old Kingdom (2649-2134 BC) until the Roman Period (30 BC-AD 395) including granite , sandstone , limestone , basalt , travertine , gneiss , galena , and amethyst . Mining in Egypt occurred in the earliest dynasties. The gold mines of Nubia were among the largest and most extensive of any in Ancient Egypt. These mines are described by

9933-408: The absence of thermal motion.) Thus the total magnetization drops to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency. The attraction experienced by ferromagnetic materials

10062-476: The available thermal energy simply overcomes the interaction energy between the spins. In general, paramagnetic effects are quite small: the magnetic susceptibility is of the order of 10 to 10 for most paramagnets, but may be as high as 10 for synthetic paramagnets such as ferrofluids . (SI units) In conductive materials, the electrons are delocalized , that is, they travel through the solid more or less as free electrons . Conductivity can be understood in

10191-519: The basis for red, purple, and brown iron-oxide pigments, as well as being an important component of ochre, sienna, and umber pigments. The main producer of hematite for the pigment industry is India, followed distantly by Spain. As mentioned earlier, hematite is an important mineral for iron ore. The physical properties of hematite are also employed in the areas of medical equipment, shipping industries, and coal production. Having high density and capable as an effective barrier against X-ray passage, it often

10320-528: The bright green malachite stones for ornamentations and pottery . Later, between 2613 and 2494 BC, large building projects required expeditions abroad to the area of Wadi Maghareh in order to secure minerals and other resources not available in Egypt itself. Quarries for turquoise and copper were also found at Wadi Hammamat , Tura , Aswan and various other Nubian sites on the Sinai Peninsula and at Timna . Quarries for gypsum were found at

10449-417: The cutter-head is progressively launched further into the coal seam. High wall mining can produce thousands of tons of coal in contour-strip operations with narrow benches, previously mined areas, trench mine applications and steep-dip seams. Sub-surface mining consists of digging tunnels or shafts into the earth to reach buried ore deposits. Ore, for processing, and waste rock, for disposal, are brought to

10578-427: The direction opposite to that of the applied magnetic field. Paramagnetic materials include most chemical elements and some compounds ; they have a relative magnetic permeability slightly greater than 1 (i.e., a small positive magnetic susceptibility ) and hence are attracted to magnetic fields. The magnetic moment induced by the applied field is linear in the field strength and rather weak. It typically requires

10707-579: The earliest known human use of the powdery mineral is 164,000 years ago by the inhabitants of the Pinnacle Point caves in what now is South Africa, possibly for social purposes. Hematite residues are also found in graves from 80,000 years ago. Near Rydno in Poland and Lovas in Hungary red chalk mines have been found that are from 5000 BC, belonging to the Linear Pottery culture at

10836-401: The electrons' spins to align parallel to the field, causing a net attraction. Paramagnetic materials include aluminium , oxygen , titanium , and iron oxide (FeO). Therefore, a simple rule of thumb is used in chemistry to determine whether a particle (atom, ion, or molecule) is paramagnetic or diamagnetic: if all electrons in the particle are paired, then the substance made of this particle

10965-496: The eras. In Roman times, the pigment obtained by finely grinding hematite was known as sil atticum . Other names for the mineral when used in painting include colcotar and caput mortuum . In Spanish, it is called almagre or almagra , from the Arabic al-maghrah , red earth, which passed into English and Portuguese. Other ancient names for the pigment include ochra hispanica , sil atticum antiquorum , and Spanish brown . It forms

11094-698: The focus to the “total environment of mining”, including reference to community development around mining, and how mining is portrayed to an urban society, which depends on the industry, although seemingly unaware of this dependency. He stated, “[I]n the past, mining engineers have not been called upon to study the psychological, sociological and personal problems of their own industry – aspects that nowadays are assuming tremendous importance. The mining engineer must rapidly expand his knowledge and his influence into these newer fields.” Mining techniques can be divided into two common excavation types: surface mining and sub-surface (underground) mining . Today, surface mining

11223-487: The form of water mills was extensive. The water mills were employed in crushing ore, raising ore from shafts, and ventilating galleries by powering giant bellows . Black powder was first used in mining in Selmecbánya , Kingdom of Hungary (now Banská Štiavnica , Slovakia) in 1627. Black powder allowed blasting of rock and earth to loosen and reveal ore veins. Blasting was much faster than fire-setting and allowed

11352-532: The free-electron g-factor, g S when  J  =  S . (in this treatment, we assume that the x - and y -components of the magnetization, averaged over all molecules, cancel out because the field applied along the z -axis leave them randomly oriented.) The energy of each Zeeman level is E M J = − M J g J μ B H {\displaystyle E_{M_{J}}=-M_{J}g_{J}\mu _{\mathrm {B} }H} . For temperatures over

11481-400: The growing importance of sustainable metal extraction practices. The process of mining from discovery of an ore body through extraction of minerals and finally to returning the land to its natural state consists of several distinct steps. The first is discovery of the ore body, which is carried out through prospecting or exploration to find and then define the extent, location and value of

11610-608: The growth rates are translated into a progressive development of a subparticle structure at the nanoscale (super small). At lower temperatures (350–600 °C), single particles crystallize. However, at higher temperatures (600–1000 °C), the growth of crystalline aggregates, and a subparticle structure is favored. Hematite is present in the waste tailings of iron mines . A recently developed process, magnetation , uses magnets to glean waste hematite from old mine tailings in Minnesota 's vast Mesabi Range iron district. Falu red

11739-410: The interactions of the spins that lead either to quenching or to ordering are kept at bay by structural isolation of the magnetic centers. There are two classes of materials for which this holds: As stated above, many materials that contain d- or f-elements do retain unquenched spins. Salts of such elements often show paramagnetic behavior but at low enough temperatures the magnetic moments may order. It

11868-452: The latter are usually strongly localized. Moreover, the size of the magnetic moment on a lanthanide atom can be quite large as it can carry up to 7 unpaired electrons in the case of gadolinium (III) (hence its use in MRI ). The high magnetic moments associated with lanthanides is one reason why superstrong magnets are typically based on elements like neodymium or samarium . The above picture

11997-439: The magnetic field can be written as: with n e {\displaystyle n_{e}} the total free-electrons density and g ( E F ) {\displaystyle g(E_{\mathrm {F} })} the electronic density of states (number of states per energy per volume) at the Fermi energy E F {\displaystyle E_{\mathrm {F} }} . In this approximation

12126-406: The magnetic moment are negligible (a common case), then in what follows J = S . If we apply a magnetic field along what we choose to call the z -axis, the energy levels of each paramagnetic center will experience Zeeman splitting of its energy levels, each with a z -component labeled by M J (or just M S for the spin-only magnetic case). Applying semiclassical Boltzmann statistics ,

12255-655: The magnetic moment are small, as occurs for most organic radicals or for octahedral transition metal complexes with d or high-spin d configurations, the effective magnetic moment takes the form ( with g-factor g e = 2.0023... ≈ 2), μ e f f ≃ 2 S ( S + 1 ) μ B = N u ( N u + 2 ) μ B , {\displaystyle \mu _{\mathrm {eff} }\simeq 2{\sqrt {S(S+1)}}\mu _{\mathrm {B} }={\sqrt {N_{\rm {u}}(N_{\rm {u}}+2)}}\mu _{\mathrm {B} },} where N u

12384-436: The magnetization is given as the magnetic moment of one electron times the difference in densities: which yields a positive paramagnetic susceptibility independent of temperature: The Pauli paramagnetic susceptibility is a macroscopic effect and has to be contrasted with Landau diamagnetic susceptibility which is equal to minus one third of Pauli's and also comes from delocalized electrons. The Pauli susceptibility comes from

12513-1526: The magnetization of such a substance is n m ¯ = n ∑ M J = − J J μ M J e − E M J / k B T ∑ M J = − J J e − E M J / k B T = n ∑ M J = − J J M J g J μ B e M J g J μ B H / k B T ∑ M J = − J J e M J g J μ B H / k B T . {\displaystyle n{\bar {m}}={\frac {n\sum \limits _{M_{J}=-J}^{J}{\mu _{M_{J}}e^{{-E_{M_{J}}}/{k_{\mathrm {B} }T}\;}}}{\sum \limits _{M_{J}=-J}^{J}{e^{{-E_{M_{J}}}/{k_{\mathrm {B} }T}\;}}}}={\frac {n\sum \limits _{M_{J}=-J}^{J}{M_{J}g_{J}\mu _{\mathrm {B} }e^{{M_{J}g_{J}\mu _{\mathrm {B} }H}/{k_{\mathrm {B} }T}\;}}}{\sum \limits _{M_{J}=-J}^{J}{e^{{M_{J}g_{J}\mu _{\mathrm {B} }H}/{k_{\mathrm {B} }T}\;}}}}.} Where μ M J {\displaystyle \mu _{M_{J}}}

12642-535: The metals due to the difficulties of transporting them, but the copper was eventually traded throughout the continent along major river routes. In the early colonial history of the Americas, "native gold and silver was quickly expropriated and sent back to Spain in fleets of gold- and silver-laden galleons", the gold and silver originating mostly from mines in Central and South America. Turquoise dated at 700 AD

12771-768: The mid-19th century, mining for minerals and precious metals, along with ranching , became a driving factor in the U.S. Westward Expansion to the Pacific coast. With the exploration of the West, mining camps sprang up and "expressed a distinctive spirit, an enduring legacy to the new nation"; Gold Rushers would experience the same problems as the Land Rushers of the transient West that preceded them. Aided by railroads, many people traveled West for work opportunities in mining. Western cities such as Denver and Sacramento originated as mining towns. When new areas were explored, it

12900-497: The mid-sixteenth century. On the continent, mineral deposits belonged to the crown, and this regalian right was stoutly maintained. But in England, royal mining rights were restricted to gold and silver (of which England had virtually no deposits) by a judicial decision of 1568 and a law in 1688. England had iron , zinc , copper , lead , and tin ores. Landlords who owned the base metals and coal under their estates then had

13029-432: The minehead, where the water was stored in large reservoirs and tanks. When a full tank was opened, the flood of water sluiced away the overburden to expose the bedrock underneath and any gold-bearing veins. The rock was then worked by fire-setting to heat the rock, which would be quenched with a stream of water. The resulting thermal shock cracked the rock, enabling it to be removed by further streams of water from

13158-454: The mineral-rich material and extract the desired compounds and metals from the ore. Paramagnetic Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field , and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, diamagnetic materials are repelled by magnetic fields and form induced magnetic fields in

13287-431: The mining of previously impenetrable metals and ores. In 1762, one of the world's first mining academies was established in the same town there. The widespread adoption of agricultural innovations such as the iron plowshare , as well as the growing use of metal as a building material, was also a driving force in the tremendous growth of the iron industry during this period. Inventions like the arrastra were often used by

13416-405: The ore body. This leads to a mathematical resource estimation to estimate the size and grade of the deposit. This estimation is used to 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. The next step

13545-462: The ore concentrates, engineering concerns, milling and infrastructure costs, finance and equity requirements, and an analysis of the proposed mine from the initial excavation all the way through to reclamation. The proportion of a deposit that is economically recoverable is dependent on the enrichment factor of the ore in the area. To gain access to the mineral deposit within an area it is often necessary to mine through or remove waste material which

13674-442: The ore, lower wages, decreased occupational safety, benefits, and health standards for miners, and a lack of environmental protection measures. Artisanal miners often undertake the activity of mining seasonally. For example, crops are planted in the rainy season , and mining is pursued in the dry season . However, they also frequently travel to mining areas and work year-round. There are four broad types of ASM: Surface mining

13803-570: The overhead tanks. The Roman miners used similar methods to work cassiterite deposits in Cornwall and lead ore in the Pennines . Sluicing methods were developed by the Romans in Spain in 25 AD to exploit large alluvial gold deposits, the largest site being at Las Medulas , where seven long aqueducts tapped local rivers and sluiced the deposits. The Romans also exploited the silver present in

13932-431: The remaining part of a coal seam previously exploited by other surface-mining techniques has too much overburden to be removed but can still be profitably exploited from the side of the artificial cliff made by previous mining. A typical cycle alternates sumping, which undercuts the seam, and shearing, which raises and lowers the cutter-head boom to cut the entire height of the coal seam. As the coal recovery cycle continues,

14061-446: The shafts could no longer be pumped dry with the available technology. Although an increased use of banknotes , credit and copper coins during this period did decrease the value of, and dependence on, precious metals , gold and silver still remained vital to the story of medieval mining. Due to differences in the social structure of society, the increasing extraction of mineral deposits spread from central Europe to England in

14190-598: The sign is positive (negative) when the electron spin component in the direction of H {\displaystyle \mathbf {H} } is parallel (antiparallel) to the magnetic field. For low temperatures with respect to the Fermi temperature T F {\displaystyle T_{\rm {F}}} (around 10 kelvins for metals), the number density of electrons n ↑ {\displaystyle n_{\uparrow }} ( n ↓ {\displaystyle n_{\downarrow }} ) pointing parallel (antiparallel) to

14319-567: The silver mines of Laurium , which helped support the Greek city state of Athens . Although they had over 20,000 slaves working them, their technology was essentially identical to their Bronze Age predecessors. At other mines, such as on the island of Thassos , marble was quarried by the Parians after they arrived in the 7th century BC. The marble was shipped away and was later found by archaeologists to have been used in buildings including

14448-554: The spin interaction with the magnetic field while the Landau susceptibility comes from the spatial motion of the electrons and it is independent of the spin. In doped semiconductors the ratio between Landau's and Pauli's susceptibilities changes as the effective mass of the charge carriers m ∗ {\displaystyle m^{*}} can differ from the electron mass m e {\displaystyle m_{e}} . The magnetic response calculated for

14577-474: The surface through the tunnels and shafts. Sub-surface mining can be classified by the type of access shafts used, and the extraction method or the technique used to reach the mineral deposit. Drift mining uses horizontal access tunnels, slope mining uses diagonally sloping access shafts, and shaft mining uses vertical access shafts. Mining in hard and soft rock formations requires different techniques. Other methods include shrinkage stope mining , which

14706-404: The surprise was a transition with a decrease in temperature at around 260 K (−13 °C) to a phase with no net magnetic moment. It was shown that the system is essentially antiferromagnetic, but that the low symmetry of the cation sites allows spin–orbit coupling to cause canting of the moments when they are in the plane perpendicular to the c axis. The disappearance of the moment with

14835-434: The susceptibility, χ {\displaystyle \chi } , of paramagnetic materials is inversely proportional to their temperature, i.e. that materials become more magnetic at lower temperatures. The mathematical expression is: M = χ H = C T H {\displaystyle \mathbf {M} =\chi \mathbf {H} ={\frac {C}{T}}\mathbf {H} } where: Curie's law

14964-602: The tomb of Amphipolis. Philip II of Macedon , the father of Alexander the Great , captured the gold mines of Mount Pangeo in 357 BC to fund his military campaigns. He also captured gold mines in Thrace for minting coinage, eventually producing 26 tons per year. However, it was the Romans who developed large-scale mining methods, especially the use of large volumes of water brought to the minehead by numerous aqueducts . The water

15093-448: The top of a mountain off to reach ore deposits at depth. Most placer deposits, because they are shallowly buried, are mined by surface methods. Finally, landfill mining involves sites where landfills are excavated and processed. Landfill mining has been thought of as a long-term solution to methane emissions and local pollution. High wall mining, which evolved from auger mining, is another form of surface mining. In high wall mining,

15222-628: The top slats. Many examples of such devices have been found in old Roman mines and some examples are now preserved in the British Museum and the National Museum of Wales . Mining as an industry underwent dramatic changes in medieval Europe . The mining industry in the early Middle Ages was mainly focused on the extraction of copper and iron . Other precious metals were also used, mainly for gilding or coinage. Initially, many metals were obtained through open-pit mining , and ore

15351-498: The water and collect in layers at the bottom of the lake, spring, or other standing water. Hematite can also occur in the absence of water, usually as the result of volcanic activity. Clay -sized hematite crystals also may occur as a secondary mineral formed by weathering processes in soil , and along with other iron oxides or oxyhydroxides such as goethite , which is responsible for the red color of many tropical , ancient, or otherwise highly weathered soils. The name hematite

15480-469: The world's gold, followed by the establishment of large mines such as the Mount Morgan Mine , which ran for nearly a hundred years, Broken Hill ore deposit (one of the largest zinc-lead ore deposits), and the iron ore mines at Iron Knob . After declines in production, another boom in mining occurred in the 1960s. In the early 21st century, Australia remains a major world mineral producer. As

15609-474: The world, which was increasingly demanding copper for electrical and household goods. Canada's mining industry grew more slowly than did the United States due to limitations in transportation, capital, and U.S. competition; Ontario was the major producer of the early 20th century with nickel, copper, and gold. Meanwhile, Australia experienced the Australian gold rushes and by the 1850s was producing 40% of

15738-606: Was favorable for life". Hematite is often shaped into beads, tumbling stones, and other jewellery components. Hematite was once used as mourning jewelry. Certain types of hematite- or iron-oxide-rich clay, especially Armenian bole , have been used in gilding . Hematite is also used in art such as in the creation of intaglio engraved gems . Hematine is a synthetic material sold as magnetic hematite . Hematite has been sourced to make pigments since earlier origins of human pictorial depictions, such as on cave linings and other surfaces, and has been employed continually in artwork through

15867-628: Was mined in pre-Columbian America; in the Cerillos Mining District in New Mexico , an estimate of "about 15,000 tons of rock had been removed from Mt. Chalchihuitl using stone tools before 1700." In 1727 Louis Denys (Denis) (1675–1741), sieur de La Ronde – brother of Simon-Pierre Denys de Bonaventure and the son-in-law of René Chartier – took command of Fort La Pointe at Chequamegon Bay ; where natives informed him of an island of copper. La Ronde obtained permission from

15996-576: Was primarily extracted from shallow depths, rather than through deep mine shafts. Around the 14th century , the growing use of weapons , armour , stirrups , and horseshoes greatly increased the demand for iron. Medieval knights , for example, were often laden with up to 100 pounds (45 kg) of plate or chain link armour in addition to swords , lances and other weapons. The overwhelming dependency on iron for military purposes spurred iron production and extraction processes. The silver crisis of 1465 occurred when all mines had reached depths at which

16125-406: Was still present near the surface in colonial times. Indigenous peoples used Lake Superior copper from at least 5,000 years ago; copper tools, arrowheads, and other artifacts that were part of an extensive native trade-network have been discovered. In addition, obsidian , flint , and other minerals were mined, worked, and traded. Early French explorers who encountered the sites made no use of

16254-411: Was the removal of water from mining shafts. As miners dug deeper to access new veins, flooding became a very real obstacle. The mining industry became dramatically more efficient and prosperous with the invention of mechanically- and animal-driven pumps. Iron metallurgy in Africa dates back over four thousand years. Gold became an important commodity for Africa during the trans-Saharan gold trade from

16383-403: Was used for a variety of purposes, including removing overburden and rock debris, called hydraulic mining , as well as washing comminuted , or crushed, ores and driving simple machinery. The Romans used hydraulic mining methods on a large scale to prospect for the veins of ore, especially using a now-obsolete form of mining known as hushing . They built numerous aqueducts to supply water to

16512-465: Was used. At other parts of the site, they penetrated the water table and dewatered the mines using several kinds of machines, especially 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, and lifting water about 24 metres (79 ft). They were worked as treadmills with miners standing on

16641-539: Was usually the gold ( placer and then lode ) and then silver that were taken into possession and extracted first. Other metals would often wait for railroads or canals, as coarse gold dust and nuggets do not require smelting and are easy to identify and transport. In the early 20th century, the gold and silver rush to the western United States also stimulated mining for coal as well as base metals such as copper, lead, and iron. Areas in modern Montana, Utah, Arizona, and later Alaska became predominant suppliers of copper to

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