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119-411: Iron-rich sedimentary rocks have economic uses as iron ores . Iron deposits have been located on all major continents with the exception of Antarctica . They are a major source of iron and are mined for commercial use. The main iron ores are from the oxide group consisting of hematite , goethite , and magnetite . The carbonate siderite is also typically mined. A productive belt of iron formations

238-535: A continental shelf . This classification has been more widely accepted, but the failure to appreciate that it is strictly based on the characteristics of the depositional basin and not the lithology of the BIF itself has led to confusion, and some geologists have advocated for its abandonment. However, the classification into Algoma versus Lake Superior types continues to be used. Banded iron formations are almost exclusively Precambrian in age, with most deposits dating to

357-445: A photic zone inhabited by cyanobacteria that had evolved the capacity to carry out oxygen-producing photosynthesis, but which had not yet evolved enzymes (such as superoxide dismutase ) for living in an oxygenated environment. Such organisms would have been protected from their own oxygen waste through its rapid removal via the reservoir of reduced ferrous iron, Fe(II), in the early ocean. The oxygen released by photosynthesis oxidized

476-434: A tsunami at least 1,000 m (3,300 ft) high at the point of impact, and 100 m (330 ft) high about 3,000 km (1,900 mi) away. It has been suggested that the immense waves and large underwater landslides triggered by the impact caused the mixing of a previously stratified ocean, oxygenated the deep ocean, and ended BIF deposition shortly after the impact. Although Cloud argued that microbial activity

595-516: A 33% to 40% recovery of magnetite by weight, to produce a concentrate grading in excess of 64% iron by weight. The typical magnetite iron ore concentrate has less than 0.1% phosphorus , 3–7% silica , and less than 3% aluminium . As of 2019, magnetite iron ore is mined in Minnesota and Michigan in the United States , eastern Canada , and northern Sweden . Magnetite-bearing banded iron formation

714-510: A Snowball Earth state the continents, and possibly seas at low latitudes, were subject to a severe ice age circa 750 to 580 Ma that nearly or totally depleted free oxygen. Dissolved iron then accumulated in the oxygen-poor oceans (possibly from seafloor hydrothermal vents). Following the thawing of the Earth, the seas became oxygenated once more causing the precipitation of the iron. Banded iron formations of this period are predominantly associated with

833-684: A benchmark to be followed by the rest of the industry. Singapore Mercantile Exchange (SMX) has launched the world's first global iron ore futures contract, based on the Metal Bulletin Iron Ore Index (MBIOI) which uses daily price data from a broad spectrum of industry participants and independent Chinese steel consultancy and data provider Shanghai Steelhome's widespread contact base of steel producers and iron ore traders across China. The futures contract has seen monthly volumes over 1,500,000 t (1,500,000 long tons; 1,700,000 short tons) after eight months of trading. This move follows

952-859: A blast furnace more efficient. Others are added because they make the iron more fluid, harder, or give it some other desirable quality. The choice of ore, fuel, and flux determines how the slag behaves and the operational characteristics of the iron produced. Ideally, iron ore contains only iron and oxygen. In reality, this is rarely the case. Typically, iron ore contains a host of elements which are often unwanted in modern steel. Banded iron formation Banded iron formations ( BIFs ; also called banded ironstone formations ) are distinctive units of sedimentary rock consisting of alternating layers of iron oxides and iron-poor chert . They can be up to several hundred meters in thickness and extend laterally for several hundred kilometers. Almost all of these formations are of Precambrian age and are thought to record

1071-505: A factor of 50 under conditions of low oxygen. Oxygenic photosynthesis is not the only biogenic mechanism for deposition of banded iron formations. Some geochemists have suggested that banded iron formations could form by direct oxidation of iron by microbial anoxygenic phototrophs . The concentrations of phosphorus and trace metals in BIFs are consistent with precipitation through the activities of iron-oxidizing bacteria. Iron isotope ratios in

1190-657: A few centimeters thick. Many of the chert mesobands contain microbands of iron oxides that are less than a millimeter thick, while the iron mesobands are relatively featureless. BIFs tend to be extremely hard, tough, and dense, making them highly resistant to erosion, and they show fine details of stratification over great distances, suggesting they were deposited in a very low-energy environment; that is, in relatively deep water, undisturbed by wave motion or currents. BIFs only rarely interfinger with other rock types, tending to form sharply bounded discrete units that never grade laterally into other rock types. Banded iron formations of

1309-441: A fossil may sometimes be referred to as degree of pyritization (DOP). Magnetite and hematite are opaque under the microscope under transmitted light. Under reflected light, magnetite shows up as metallic and a silver or black color. Hematite will be a more reddish-yellow color. Pyrite is seen as opaque, a yellow-gold color, and metallic. Chamosite is an olive-green color in thin section that readily oxidizes to limonite. When it

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1428-447: A higher energy depositional environment , in shallower water disturbed by wave motions. However, they otherwise resemble other banded iron formations. The great majority of banded iron formations are Archean or Paleoproterozoic in age. However, a small number of BIFs are Neoproterozoic in age, and are frequently, if not universally, associated with glacial deposits, often containing glacial dropstones . They also tend to show

1547-721: A higher level of oxidation, with hematite prevailing over magnetite, and they typically contain a small amount of phosphate, about 1% by mass. Mesobanding is often poor to nonexistent and soft-sediment deformation structures are common. This suggests very rapid deposition. However, like the granular iron formations of the Great Lakes, the Neoproterozoic occurrences are widely described as banded iron formations. Banded iron formations are distinct from most Phanerozoic ironstones . Ironstones are relatively rare and are thought to have been deposited in marine anoxic events , in which

1666-534: A hydrous silica gel. The conversion of iron hydroxide and silica gels to banded iron formation is an example of diagenesis , the conversion of sediments into solid rock. There is evidence that banded iron formations formed from sediments with nearly the same chemical composition as is found in the BIFs today. The BIFs of the Hamersley Range show great chemical homogeneity and lateral uniformity, with no indication of any precursor rock that might have been altered to

1785-430: A key element of most theories of deposition. The few formations deposited after 1,800  Ma may point to intermittent low levels of free atmospheric oxygen, while the small peak at 750  million years ago may be associated with the hypothetical Snowball Earth. The microbands within chert layers are most likely varves produced by annual variations in oxygen production. Diurnal microbanding would require

1904-439: A marine environment. Oxide-facies are precipitated under the most oxidizing conditions. Silicate- and carbonate-facies are precipitated under intermediate redox conditions. Sulfide-facies are precipitated under the most reducing conditions. There is a lack of iron-rich sedimentary rocks in shallow waters which leads to the conclusion that the depositional environment ranges from the continental shelf and upper continental slope to

2023-613: A mode of formation does not require a global anoxic ocean, but is consistent with either a Snowball Earth or Slushball Earth model. Banded iron formations provide most of the iron ore presently mined. More than 60% of global iron reserves are in the form of banded iron formation, most of which can be found in Australia, Brazil, Canada, India, Russia, South Africa, Ukraine, and the United States. Different mining districts coined their own names for BIFs. The term "banded iron formation"

2142-568: A much larger spectrum of iron minerals, have more reduced facies, and are more abundant. BIFs are divided into type categories based on the characteristics related to the nature of their formation and unique physical and chemical properties. Some categories of banded iron formations are the Rapitan type , the Algoma type , and the Superior type . Rapitan types are associated with the glaciogenic sequences of

2261-472: A peculiar kind of Precambrian evaporite . Other proposed abiogenic processes include radiolysis by the radioactive isotope of potassium , K, or annual turnover of basin water combined with upwelling of iron-rich water in a stratified ocean. Another abiogenic mechanism is photooxidation of iron by sunlight. Laboratory experiments suggest that this could produce a sufficiently high deposition rate under likely conditions of pH and sunlight. However, if

2380-424: A premium price. Due to the high density of hematite relative to associated silicate gangue, hematite beneficiation usually involves a combination of beneficiation techniques. One method relies on passing the finely-crushed ore over a slurry containing magnetite or other agent such as ferrosilicon which increases its density. When the density of the slurry is properly calibrated, the hematite will sink and

2499-408: A process that did not produce great quantities of biomass, so that little carbon was present to reduce hematite to magnetite. However, it is possible that BIF was altered from carbonate rock or from hydrothermal mud during late stages of diagenesis. A 2018 study found no evidence that magnetite in BIF formed by decarbonization, and suggests that it formed from thermal decomposition of siderite via

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2618-453: A relatively low-grade ore, they are also inexpensive to collect, as they do not have to be mined. Because of this, companies such as Magnetation have started reclamation projects where they use iron ore tailings as a source of metallic iron. The two main methods of recycling iron from iron ore tailings are magnetizing roasting and direct reduction. Magnetizing roasting uses temperatures between 700 and 900 °C (1,292 and 1,652 °F) for

2737-600: A source of iron ore. Prior to the industrial revolution, most iron was obtained from widely-available goethite or bog ore , for example, during the American Revolution and the Napoleonic Wars . Historically, much of the iron ore utilized by industrialized societies has been mined from predominantly hematite deposits with grades of around 70% Fe. These deposits are commonly referred to as "direct shipping ores" or "natural ores". Increasing iron ore demand, coupled with

2856-597: A switch to index-based quarterly pricing by the world's three largest iron ore miners— Vale , Rio Tinto , and BHP —in early 2010, breaking a 40-year tradition of benchmark annual pricing. Iron is the most abundant element on earth but not in the crust. The extent of the accessible iron ore reserves is not known, though Lester Brown of the Worldwatch Institute suggested in 2006 that iron ore could run out within 64 years (that is, by 2070), based on 2% growth in demand per year. Geoscience Australia calculates that

2975-800: A thickness of 60 meters (200 feet). Other examples of early Archean BIFs are found in the Abitibi greenstone belts , the greenstone belts of the Yilgarn and Pilbara cratons , the Baltic shield , and the cratons of the Amazon , north China , and south and west Africa. The most extensive banded iron formations belong to what A.F. Trendall calls the Great Gondwana BIFs. These are late Archean in age and are not associated with greenstone belts. They are relatively undeformed and form extensive topographic plateaus, such as

3094-492: A thin layer on the ocean floor. Each band is similar to a varve , resulting from cyclic variations in oxygen production. Banded iron formations were first discovered in northern Michigan in 1844. Banded iron formations account for more than 60% of global iron reserves and provide most of the iron ore presently mined. Most formations can be found in Australia , Brazil , Canada , India , Russia , South Africa , Ukraine , and

3213-418: A time of under 1 hour to produce an iron concentrate (Fe 3 O 4 ) to be used for iron smelting. For magnetizing roasting, it is important to have a reducing atmosphere to prevent oxidization and the formation of Fe 2 O 3 because it is harder to separate as it is less magnetic. Direct reduction uses hotter temperatures of over 1,000 °C (1,830 °F) and longer times of 2–5 hours. Direct reduction

3332-485: A twofold division of BIFs into an Algoma type and a Lake Superior type, based on the character of the depositional basin. Algoma BIFs are found in relatively small basins in association with greywackes and other volcanic rocks and are assumed to be associated with volcanic centers. Lake Superior BIFs are found in larger basins in association with black shales, quartzites , and dolomites , with relatively minor tuffs or other volcanic rocks, and are assumed to have formed on

3451-655: A typically titanium -bearing magnetite, often with vanadium . These ores form a niche market, with specialty smelters used to recover the iron, titanium, and vanadium. These ores are beneficiated essentially similarly to banded iron formation ores, but usually are more easily upgraded via crushing and screening . The typical titanomagnetite concentrate grades 57% Fe, 12% Ti, and 0.5% V 2 O 5 . For every one ton of iron ore concentrate produced, approximately 2.5–3.0 tons of iron ore tailings will be discharged. Statistics show that there are 130 million tons of iron ore tailings discharged every year. If, for example,

3570-632: A value of $ 2.3 billion. 46% of Canada's iron ore comes from the Iron Ore Company of Canada mine, in Labrador City , Newfoundland , with secondary sources including the Mary River Mine in Nunavut . According to the U.S. Geological Survey's 2021 Report on iron ore, India is estimated to produce 59,000,000 t (58,000,000 long tons; 65,000,000 short tons) of iron ore in 2020, placing it as

3689-429: A very high rate of deposition of 2 meters per year or 5 km/Ma. Estimates of deposition rate based on various models of deposition and sensitive high-resolution ion microprobe (SHRIMP) estimates of the age of associated tuff beds suggest a deposition rate in typical BIFs of 19 to 270 m/Ma, which are consistent either with annual varves or rhythmites produced by tidal cycles. Preston Cloud proposed that mesobanding

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3808-724: A way to classify iron formations because it is a common component in many types of rocks. They are well banded and the banding can be anywhere from a few millimeters to tens of meters thick. The layers have very distinct banded successions that are made up of iron rich layers that alternate with layers of chert. Iron formations are often associates with dolomite , quartz-rich sandstone, and black shale . They sometimes grade locally into chert or dolomite. They can have many different textures that resemble limestone. Some of these textures are micritic, pelleted, intraclastic, peloidal, oolitic , pisolitic , and stromatolitic . In low-grade iron formations, there are different dominant minerals dependent on

3927-511: Is a high-volume, low-margin business, as the value of iron is significantly lower than base metals. It is highly capital intensive, and requires significant investment in infrastructure such as rail in order to transport the ore from the mine to a freight ship. For these reasons, iron ore production is concentrated in the hands of a few major players. World production averages 2,000,000,000 t (2.0 × 10 long tons; 2.2 × 10 short tons) of raw ore annually. The world's largest producer of iron ore

4046-428: Is expected to rise by a CAGR of 2% between 2023 and 2027, and industry analyst Fitch Solutions forecasted in 2021 that Brazil's annual production will reach 592,000,000 t (583,000,000 long tons; 653,000,000 short tons) by 2030. In 2017, Canadian iron ore mines produced 49,000,000 t (48,000,000 long tons; 54,000,000 short tons) of iron ore in concentrate pellets and 13.6 million tons of crude steel. Of

4165-510: Is followed by Japan and Korea, which consume a significant amount of raw iron ore and metallurgical coal . In 2006, China produced 588,000,000 t (579,000,000 long tons; 648,000,000 short tons) of iron ore, with an annual growth of 38%. Over the last 40 years, iron ore prices have been decided in closed-door negotiations between the small handful of miners and steelmakers which dominate both spot and contract markets. Until 2006, prices were determined in annual benchmark negotiations between

4284-530: Is in the iron ranges around Lake Superior . These iron ranges occur in Minnesota and Michigan, which combined accounted for 93% of the usable iron ore produced in the United States in 2014. Seven of the nine operational open pit mines in the United States are located in Minnesota as well as two of the three tailings reclamation operations. The other two active open pit mines were located in Michigan . In 2016, one of

4403-524: Is known as an iron range. The accepted classification scheme for iron-rich sedimentary rocks is to divide them into two sections: ironstones and iron formations Ironstones consist of 15% iron or more in composition. This is necessary for the rock to even be considered an iron-rich sedimentary rock. Generally, they are from the Phanerozoic which means that they range in age from the present to 540 million years ago. They can contain iron minerals from

4522-642: Is mined extensively in Brazil as of 2019, which exports significant quantities to Asia , and there is a nascent and large magnetite iron ore industry in Australia . Direct-shipping iron ore (DSO) deposits (typically composed of hematite ) are currently exploited on all continents except Antarctica , with the largest intensity in South America , Australia, and Asia. Most large hematite iron ore deposits are sourced from altered banded iron formations and (rarely) igneous accumulations. DSO deposits are typically rarer than

4641-411: Is more precisely defined as chemically precipitated sedimentary rock containing greater than 15% iron . However, most BIFs have a higher content of iron, typically around 30% by mass, so that roughly half the rock is iron oxides and the other half is silica. The iron in BIFs is divided roughly equally between the more oxidized ferric form, Fe(III), and the more reduced ferrous form, Fe(II), so that

4760-433: Is often made from this process and is a major source of iron in sediments. However, once it is deposited it must be dehydrated in order to come to an equilibrium with hematite. The dehydration reaction is: Pyritization is discriminatory. It rarely happens to soft tissue organisms and aragonitic fossils are more susceptible to it than calcite fossils. It commonly takes place in marine depositional environments where there

4879-421: Is organic material. The process is caused by sulfate reduction which replaces carbonate skeletons (or shells) with pyrite (FeS 2 ). It generally does not preserve detail and the pyrite forms within the structure as many microcrystals. In freshwater environments, siderite will replace carbonate shells instead of pyrite due to the low amounts of sulfate. The amount of pyritization that has taken place within

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4998-425: Is oxidation by anaerobic denitrifying bacteria . This requires that nitrogen fixation by microorganisms is also active. The lack of organic carbon in banded iron formation argues against microbial control of BIF deposition. On the other hand, there is fossil evidence for abundant photosynthesizing cyanobacteria at the start of BIF deposition and of hydrocarbon markers in shales within banded iron formation of

5117-706: Is partially or fully oxidized to limonite, the green color becomes a yellowish-brown. Limonite is opaque under the microscope as well. Chamosite is an iron silicate and it has a birefringence of almost zero. Siderite is an iron carbonate and it has a very high birefringence. The thin sections often reveal marine fauna within oolitic ironstones. In older samples, the ooids may be squished and have hooked tails on either end due to compaction. Iron ore Iron ores are rocks and minerals from which metallic iron can be economically extracted. The ores are usually rich in iron oxides and vary in color from dark grey, bright yellow, or deep purple to rusty red. The iron

5236-456: Is the raw material used to make pig iron , which is one of the main raw materials to make steel —98% of the mined iron ore is used to make steel. In 2011 the Financial Times quoted Christopher LaFemina, mining analyst at Barclays Capital, saying that iron ore is "more integral to the global economy than any other commodity, except perhaps oil ". Metallic iron is virtually unknown on

5355-476: Is the Brazilian mining corporation Vale , followed by Australian companies Rio Tinto Group and BHP . A further Australian supplier, Fortescue Metals Group Ltd, has helped bring Australia's production to first in the world. The seaborne trade in iron ore—that is, iron ore to be shipped to other countries—was 849,000,000 t (836,000,000 long tons; 936,000,000 short tons) in 2004. Australia and Brazil dominate

5474-425: Is used to produce sponge iron (Fe) to be used for steel-making. Direct reduction requires more energy, as the temperatures are higher and the time is longer and it requires more reducing agent than magnetizing roasting. Lower-grade sources of iron ore generally require beneficiation , using techniques like crushing, milling , gravity or heavy media separation , screening, and silica froth flotation to improve

5593-409: Is used which divides iron-rich sedimentary rocks into three categories: bog iron deposits , ironstones , and iron formations . A bog-iron deposit is iron that formed in a bog or swamp through the process of oxidation . Banded iron formations (BIFs) were originally chemical muds and contain well developed thin lamination. They are able to have this lamination due to the lack of burrowers in

5712-467: Is usually found in the form of magnetite ( Fe 3 O 4 , 72.4% Fe), hematite ( Fe 2 O 3 , 69.9% Fe), goethite ( FeO(OH) , 62.9% Fe), limonite ( FeO(OH)·n(H 2 O) , 55% Fe), or siderite ( FeCO 3 , 48.2% Fe). Ores containing very high quantities of hematite or magnetite, typically greater than about 60% iron, are known as natural ore or direct shipping ore , and can be fed directly into iron-making blast furnaces . Iron ore

5831-968: The Archean and Early Proterozoic. The type is distinctive as the hydrothermal-input has notably less influence on this formation's Rare Earth Element (REE) chemistry than other formations during this time period. Algoma types are small lenticular iron deposits that are associated with volcanic rocks and turbidites . Iron content in this class type rarely exceeds 10 tons. They range in thickness from 10–100 meters. Deposition occurs in island arc / back arc basins and intracratonic rift zones. Superior types are large, thick, extensive iron deposits across stable shelves and in broad basins . Total iron content in this class type exceeds 10 tons. They can extend to over 10 kilometers. Deposition occurs in relatively shallow marine conditions under transgressing seas. Granular iron formations (GIFs) were originally well-sorted chemical sands. They lack even, continuous bedding that takes

5950-878: The Chichester Range , the Hamersley Range and Koolyanobbing , Western Australia . Other types of ore are coming to the fore recently, such as oxidised ferruginous hardcaps, for instance laterite iron ore deposits near Lake Argyle in Western Australia. The total recoverable reserves of iron ore in India are about 9,602,000,000 t (9.450 × 10 long tons; 1.0584 × 10 short tons) of hematite and 3,408,000,000 t (3.354 × 10 long tons; 3.757 × 10 short tons) of magnetite . Chhattisgarh , Madhya Pradesh , Karnataka , Jharkhand , Odisha , Goa , Maharashtra , Andhra Pradesh , Kerala , Rajasthan , and Tamil Nadu are

6069-598: The Earth 's surface except as iron-nickel alloys from meteorites and very rare forms of deep mantle xenoliths . Although iron is the fourth-most abundant element in the Earth's crust , composing about 5%, the vast majority is bound in silicate or, more rarely, carbonate minerals, and smelting pure iron from these minerals would require a prohibitive amount of energy. Therefore, all sources of iron used by human industry exploit comparatively rarer iron oxide minerals, primarily hematite . Prehistoric societies used laterite as

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6188-821: The Great Lakes region and the Frere Formation of western Australia are somewhat different in character and are sometimes described as granular iron formations or GIFs . Their iron sediments are granular to oolitic in character, forming discrete grains about a millimeter in diameter, and they lack microbanding in their chert mesobands. They also show more irregular mesobanding, with indications of ripples and other sedimentary structures , and their mesobands cannot be traced out any great distance. Though they form well-defined, discrete units, these are commonly interbedded with coarse to medium-grained epiclastic sediments (sediments formed by weathering of rock). These features suggest

6307-697: The Hamersley Range . The banded iron formations here were deposited from 2470 to 2450 Ma and are the thickest and most extensive in the world, with a maximum thickness in excess of 900 meters (3,000 feet). Similar BIFs are found in the Carajás Formation of the Amazon craton, the Cauê Itabirite of the São Francisco craton , the Kuruman Iron Formation and Penge Iron Formation of South Africa, and

6426-929: The Mulaingiri Formation of India . Paleoproterozoic banded iron formations are found in the Iron Range and other parts of the Canadian Shield . The Iron Range is a group of four major deposits: the Mesabi Range , the Vermilion Range , the Gunflint Range , and the Cuyuna Range . All are part of the Animikie Group and were deposited between 2500 and 1800 Ma. These BIFs are predominantly granular iron formations. Neoproterozoic banded iron formations include

6545-555: The Pilbara region of Western Australia is approximately 844,000,000 t (831,000,000 long tons; 930,000,000 short tons) per year and rising. Gavin Mudd ( RMIT University ) and Jonathon Law ( CSIRO ) expect it to be gone within 30–50 years and 56 years, respectively. These 2010 estimates require ongoing review to take into account shifting demand for lower-grade iron ore and improving mining and recovery techniques (allowing deeper mining below

6664-563: The Sturtian glaciation . An alternative mechanism for banded iron formations in the Snowball Earth era suggests the iron was deposited from metal-rich brines in the vicinity of hydrothermally active rift zones due to glacially-driven thermal overturn. The limited extent of these BIFs compared with the associated glacial deposits, their association with volcanic formations, and variation in thickness and facies favor this hypothesis. Such

6783-491: The United States . A typical banded iron formation consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides , either magnetite (Fe 3 O 4 ) or hematite (Fe 2 O 3 ), alternating with bands of iron-poor chert , often red in color, of similar thickness. A single banded iron formation can be up to several hundred meters in thickness and extend laterally for several hundred kilometers. Banded iron formation

6902-412: The abyssal plain . (The diagram does not have the abyssal plain labeled, but this would be located to the far right of the diagram at the bottom of the ocean). Ferrous and ferric iron are components in many minerals, especially within sandstones. Fe is in clay , carbonates, sulfides, and is even within feldspars in small amounts. Fe is in oxides, hydrous, anhydrous, and in glauconites . Commonly,

7021-452: The oxygenation of the Earth's oceans . Some of the Earth's oldest rock formations, which formed about 3,700  million years ago ( Ma ), are associated with banded iron formations. Banded iron formations are thought to have formed in sea water as the result of oxygen production by photosynthetic cyanobacteria . The oxygen combined with dissolved iron in Earth's oceans to form insoluble iron oxides, which precipitated out, forming

7140-407: The silicate mineral fragments will float and can be removed. Iron is the world's most commonly used metal—steel, of which iron ore is the key ingredient, represents almost 95% of all metal used per year. It is used primarily in structures, ships, automobiles, and machinery. Iron-rich rocks are common worldwide, but ore-grade commercial mining operations are dominated by the countries listed in

7259-420: The 13,600,000 t (13,400,000 long tons; 15,000,000 short tons) of steel 7,000,000 t (6,900,000 long tons; 7,700,000 short tons) was exported, and 43,100,000 t (42,400,000 long tons; 47,500,000 short tons) of iron ore was exported at a value of $ 4.6 billion. Of the iron ore exported, 38.5% of the volume was iron ore pellets with a value of $ 2.3 billion, and 61.5% was iron ore concentrates with

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7378-680: The 62–64% Fe range. Granite and ultrapotassic igneous rocks were sometimes used to segregate magnetite crystals and form masses of magnetite suitable for economic concentration. A few iron ore deposits, notably in Chile , are formed from volcanic flows containing significant accumulations of magnetite phenocrysts . Chilean magnetite iron ore deposits within the Atacama Desert have also formed alluvial accumulations of magnetite in streams leading from these volcanic formations. Some magnetite skarn and hydrothermal deposits have been worked in

7497-579: The Archean. These older BIFs tend to show a positive europium anomaly consistent with a hydrothermal source of iron. By contrast, Lake Superior-type banded iron formations primarily formed during the Paleoproterozoic era, and lack the europium anomalies of the older Algoma-type BIFs, suggesting a much greater input of iron weathered from continents. The absence of hydrogen sulfide in anoxic ocean water can be explained either by reduced sulfur flux into

7616-454: The Fe(II) to ferric iron, Fe(III), which precipitated out of the sea water as insoluble iron oxides that settled to the ocean floor. Cloud suggested that banding resulted from fluctuations in the population of cyanobacteria due to free radical damage by oxygen. This also explained the relatively limited extent of early Archean deposits. The great peak in BIF deposition at the end of the Archean

7735-514: The Great Oxygenation Event. Prior to 2.45 billion years ago, the high degree of mass-independent fractionation of sulfur (MIF-S) indicates an extremely oxygen-poor atmosphere. The peak of banded iron formation deposition coincides with the disappearance of the MIF-S signal, which is interpreted as the permanent appearance of oxygen in the atmosphere between 2.41 and 2.35 billion years ago. This

7854-481: The Pilbara craton. The carbon that is present in banded iron formations is enriched in the light isotope, C, an indicator of a biological origin. If a substantial part of the original iron oxides was in the form of hematite, then any carbon in the sediments might have been oxidized by the decarbonization reaction: Trendall and J.G. Blockley proposed, but later rejected, the hypothesis that banded iron formation might be

7973-570: The Precambrian world, they have been intensively studied by geologists. Banded iron formations are found worldwide, in every continental shield of every continent. The oldest BIFs are associated with greenstone belts and include the BIFs of the Isua Greenstone Belt , the oldest known, which have an estimated age of 3700 to 3800 Ma. The Temagami banded iron deposits formed over a 50-million-year period, from 2736 to 2687 Ma, and reached

8092-443: The Precambrian. BIFs show regular alternating layers that are rich in iron and chert that range in thickness from a few millimeters to a few centimeters. The formation can continue uninterrupted for tens to hundreds of meters stratigraphically. These formations can contain sedimentary structures like cross-bedding , graded bedding , load casts , ripple marks , mud cracks , and erosion channels. In comparison to GIFs, BIFs contain

8211-429: The United States is estimated to have accounted for 2% of the world's iron ore output. In the United States there are twelve iron ore mines, with nine being open pit mines and three being reclamation operations. There were also ten pelletizing plants, nine concentration plants, two direct-reduced iron (DRI) plants, and one iron nugget plant that were operating in 2014. In the United States the majority of iron ore mining

8330-613: The Urucum in Brazil, Rapitan in the Yukon , and the Damara Belt in southern Africa. They are relatively limited in size, with horizontal extents not more than a few tens of kilometers and thicknesses not more than about 10 meters (33 feet). These are widely thought to have been deposited under unusual anoxic oceanic conditions associated with the " Snowball Earth ." Banded iron formation provided some of

8449-424: The availability of reduced iron on time scales of decades. In the case of granular iron formations, the mesobands are attributed to winnowing of sediments in shallow water, in which wave action tended to segregate particles of different size and composition. For banded iron formations to be deposited, several preconditions must be met. There must be an ample source of reduced iron that can circulate freely into

8568-411: The concentration of the ore and remove impurities. The results, high-quality fine ore powders, are known as fines. Magnetite is magnetic , and hence easily separated from the gangue minerals and capable of producing a high-grade concentrate with very low levels of impurities. The grain size of the magnetite and its degree of commingling with the silica groundmass determine the grind size to which

8687-533: The country's " economic demonstrated resources " of iron currently amount to 24 gigatonnes , or 24,000,000,000 t (2.4 × 10 long tons; 2.6 × 10 short tons). Another estimate places Australia's reserves of iron ore at 52,000,000,000 t (5.1 × 10 long tons; 5.7 × 10 short tons), or 30% of the world's estimated 170,000,000,000 t (1.7 × 10 long tons; 1.9 × 10 short tons), of which Western Australia accounts for 28,000,000,000 t (2.8 × 10 long tons; 3.1 × 10 short tons). The current production rate from

8806-533: The current composition. This suggests that, other than dehydration and decarbonization of the original ferric hydroxide and silica gels, diagenesis likely left the composition unaltered and consisted of crystallization of the original gels. Decarbonization may account for the lack of carbon and preponderance of magnetite in older banded iron formations. The relatively high content of hematite in Neoproterozoic BIFs suggests they were deposited very quickly and via

8925-417: The deep ocean became sufficiently oxygenated at that time to end transport of reduced iron. Heinrich Holland argues that the absence of manganese deposits during the pause between Paleoproterozoic and Neoproterozoic BIFs is evidence that the deep ocean had become at least slightly oxygenated. The "Canfield ocean" model proposes that, to the contrary, the deep ocean became euxinic and transport of reduced iron

9044-472: The deep ocean or a lack of dissimilatory sulfate reduction (DSR), the process by which microorganisms use sulfate in place of oxygen for respiration. The product of DSR is hydrogen sulfide, which readily precipitates iron out of solution as pyrite. The requirement of an anoxic, but not euxinic, deep ocean for deposition of banded iron formation suggests two models to explain the end of BIF deposition 1.8 billion years ago. The "Holland ocean" model proposes that

9163-584: The depletion of high-grade hematite ores in the United States, led after World War II to the development of lower-grade iron ore sources, principally the use of magnetite and taconite . Iron ore mining methods vary by the type of ore being mined. There are four main types of iron ore deposits worked currently, depending on the mineralogy and geology of the ore deposits. These are magnetite, titanomagnetite , massive hematite, and pisolitic ironstone deposits. The origin of iron can be ultimately traced to its formation through nuclear fusion in stars, and most of

9282-412: The deposition basin. Plausible sources of iron include hydrothermal vents along mid-ocean ridges, windblown dust, rivers, glacial ice, and seepage from continental margins. The importance of various sources of reduced iron has likely changed dramatically across geologic time. This is reflected in the division of BIFs into Algoma and Lake Superior-type deposits. Algoma-type BIFs formed primarily in

9401-551: The depositional basin became depleted in free oxygen . They are composed of iron silicates and oxides without appreciable chert but with significant phosphorus content, which is lacking in BIFs. No classification scheme for banded iron formations has gained complete acceptance. In 1954, Harold Lloyd James advocated a classification based on four lithological facies (oxide, carbonate, silicate, and sulfide) assumed to represent different depths of deposition, but this speculative model did not hold up. In 1980, Gordon A. Gross advocated

9520-518: The different types of facies . The dominant minerals in the oxide facies are magnetite and hematite. The dominant minerals in the silicate facies are greenalite , minnesotaite , and glauconite . The dominant mineral in the carbonate facies is siderite. The dominant mineral in the sulfide facies is pyrite . Most iron formations are deformed or metamorphosed simply due to their incredibly old age, but they still retain their unique distinctive chemical composition; even at high metamorphic grades. The higher

9639-492: The first evidence for the timing of the Great Oxidation Event , 2,400 Ma. With his 1968 paper on the early atmosphere and oceans of the Earth, Preston Cloud established the general framework that has been widely, if not universally, accepted for understanding the deposition of BIFs. Cloud postulated that banded iron formations were a consequence of anoxic, iron-rich waters from the deep ocean welling up into

9758-552: The following groups: oxides , carbonates , and silicates . Some examples of minerals in iron-rich rocks containing oxides are limonite , hematite, and magnetite. An example of a mineral in iron-rich rock containing carbonates is siderite and an example of minerals in an iron-rich rock containing silicate is chamosite . They are often interbedded with limestones , shales , and fine-grained sandstones . They are typically nonbanded, however they can be very coarsely banded on occasion. They are hard and non- cherty . The components of

9877-508: The form of discontinuous layers. Discontinuous layers likely represent bedforms that were generated by storm waves and currents. Any layers that are thicker than a few meters and are uninterrupted, are rare for GIFs. They contain sand-sized clasts and a finer grained matrix , and generally belong to the oxide or silicate mineral facies. There are four facies types associated with iron-rich sedimentary rocks: oxide-, silicate-, carbonate-, and sulfide-facies. These facies correspond to water depth in

9996-606: The fossils are partly or entirely replaced by iron minerals. A good example of this is pyritization . They are smaller in size and less likely to be deformed or metamorphosed than iron formations. The term iron ball is occasionally used to describe an ironstone nodule . Iron formations must be at least 15% iron in composition, just like ironstones and all iron-rich sedimentary rocks. However, iron formations are mainly Precambrian in age which means that they are 4600 to 590 million years old. They are much older than ironstones. They tend to be cherty, though chert can not be used as

10115-442: The gangue is separated during the beneficiation process and is removed as tailings . Taconite tailings are mostly the mineral quartz , which is chemically inert. This material is stored in large, regulated water settling ponds. The key parameters for magnetite ore being economic are the crystallinity of the magnetite, the grade of the iron within the banded iron formation host rock, and the contaminant elements which exist within

10234-450: The grade, the more metamorphosed it is. Low grade rocks may only be compacted while high grade rocks often can not be identified. They often contain a mixture of banded iron formations and granular iron formations. Iron formations can be divided into subdivisions known as: banded iron formations (BIFs) and granular iron formations (GIFs). The above classification scheme is the most commonly used and accepted, though sometimes an older system

10353-789: The groundwater table). Brazil is the second-largest producer of iron ore after Australia, accounting for 16% of the world's iron ore production. After a somewhat sluggish production volume 2010-2020, partly due to the Mariana dam disaster in 2015 and the Brumadinho dam disaster in 2019, which halted the production at the two involved mines, production has increased steadily since 2021, when Brazil produced 431,000,000 t (424,000,000 long tons; 475,000,000 short tons). In 2022 it increased to 435,000,000 t (428,000,000 long tons; 480,000,000 short tons) and in 2023 to 440,000,000 t (430,000,000 long tons; 490,000,000 short tons). The Brazilian production

10472-450: The iron and carbon smelting must be kept in an oxygen-deficient (reducing) state to promote the burning of carbon to produce CO and not CO 2 . The inclusion of even small amounts of some elements can have profound effects on the behavioral characteristics of a batch of iron or the operation of a smelter. These effects can be both good and bad, some catastrophically bad. Some chemicals are deliberately added, such as flux, which makes

10591-442: The iron came from a shallow hydrothermal source, other laboratory experiments suggest that precipitation of ferrous iron as carbonates or silicates could seriously compete with photooxidation. Regardless of the precise mechanism of oxidation, the oxidation of ferrous to ferric iron likely caused the iron to precipitate out as a ferric hydroxide gel. Similarly, the silica component of the banded iron formations likely precipitated as

10710-413: The iron from the oxygen, a stronger elemental bond must be presented to attach to the oxygen. Carbon is used because the strength of a carbon-oxygen bond is greater than that of the iron-oxygen bond at high temperatures. Thus, the iron ore must be powdered and mixed with coke , to be burnt in the smelting process. Carbon monoxide is the primary ingredient of chemically stripping oxygen from iron. Thus,

10829-889: The iron is thought to have originated in dying stars that are large enough to explode as supernovae . The Earth's core is thought to consist mainly of iron, but this is inaccessible from the surface. Some iron meteorites are thought to have originated from asteroids 1,000 km (620 mi) in diameter or larger. Banded iron formations (BIFs) are sedimentary rocks containing more than 15% iron composed predominantly of thinly-bedded iron minerals and silica (as quartz ). Banded iron formations occur exclusively in Precambrian rocks, and are commonly weakly-to-intensely metamorphosed . Banded iron formations may contain iron in carbonates ( siderite or ankerite ) or silicates ( minnesotaite , greenalite , or grunerite ), but in those mined as iron ores, oxides ( magnetite or hematite ) are

10948-554: The late Archean (2800–2500 Ma) with a secondary peak of deposition in the Orosirian period of the Paleoproterozoic (1850 Ma). Minor amounts were deposited in the early Archean and in the Neoproterozoic (750 Ma). The youngest known banded iron formation is an Early Cambrian formation in western China. Because the processes by which BIFs are formed appear to be restricted to early geologic time, and may reflect unique conditions of

11067-441: The late Archean peak of BIF deposition was spread out over tens of millions of years, rather than taking place in a very short interval of time following the evolution of oxygen-coping mechanisms. However, his general concepts continue to shape thinking about the origins of banded iron formations. In particular, the concept of the upwelling of deep ocean water, rich in reduced iron, into an oxygenated surface layer poor in iron remains

11186-423: The magnetite concentrate. The size and strip ratio of most magnetite resources is irrelevant, as a banded iron formation can be hundreds of meters thick, extend hundreds of kilometers along strike , and can easily come to more than three billion or more tonnes of contained ore. The typical grade of iron at which a magnetite-bearing banded iron formation becomes economic is roughly 25% iron, which can generally yield

11305-476: The magnetite-bearing BIF or other rocks which form its main source, or protolith rock, but are considerably cheaper to mine and process as they require less beneficiation due to the higher iron content. However, DSO ores can contain significantly higher concentrations of penalty elements, typically being higher in phosphorus, water content (especially pisolite sedimentary accumulations), and aluminium ( clays within pisolites). Export-grade DSO ores are generally in

11424-399: The main iron ore producers ( BHP Billiton , Rio Tinto , and Vale S.A. ) and Japanese importers. In 2006, Chinese company Baosteel began handling negotiations for the importer side. The Chinese government replaced Baosteel with China Iron and Steel Association as lead negotiator in 2009. Traditionally, the first deal reached between these the major producers and the major importers sets

11543-410: The mine tailings contain an average of approximately 11% iron, there would be approximately 1.41 million tons of iron wasted annually. These tailings are also high in other useful metals such as copper , nickel , and cobalt , and they can be used for road-building materials like pavement and filler and building materials such as cement, low-grade glass, and wall materials. While tailings are

11662-592: The oldest banded iron formations (3700-3800 Ma), at Isua, Greenland, are best explained by assuming extremely low oxygen levels (<0.001% of modern O 2 levels in the photic zone) and anoxygenic photosynthetic oxidation of Fe(II): This requires that dissimilatory iron reduction, the biological process in which microorganisms substitute Fe(III) for oxygen in respiration, was not yet widespread. By contrast, Lake Superior-type banded iron formations show iron isotope ratios that suggest that dissimilatory iron reduction expanded greatly during this period. An alternate route

11781-504: The past as high-grade iron ore deposits requiring little beneficiation . There are several granite-associated deposits of this nature in Malaysia and Indonesia . Other sources of magnetite iron ore include metamorphic accumulations of massive magnetite ore such as at Savage River , Tasmania , formed by shearing of ophiolite ultramafics . Another, minor, source of iron ores are magmatic accumulations in layered intrusions which contain

11900-451: The presence of iron is determined to be within a rock due to certain colorations from oxidation. Oxidation is the loss of electrons from an element. Oxidation can occur from bacteria or by chemical oxidation. This often happens when ferrous ions come into contact with water (due to dissolved oxygen within surface waters) and a water-mineral reaction occurs. The formula for the oxidation/reduction of iron is: The formula works for oxidation to

12019-473: The principal Indian producers of iron ore. World consumption of iron ore grows 10% per year on average with the main consumers being China, Japan, Korea, the United States, and the European Union. China is currently the largest consumer of iron ore, which translates to be the world's largest steel producing country. It is also the largest importer, buying 52% of the seaborne trade in iron ore in 2004. China

12138-474: The principal iron mineral. Banded iron formations are known as taconite within North America. The mining involves moving tremendous amounts of ore and waste. The waste comes in two forms: non-ore bedrock in the mine ( overburden or interburden locally known as mullock), and unwanted minerals, which are an intrinsic part of the ore rock itself ( gangue ). The mullock is mined and piled in waste dumps , and

12257-429: The quartz is left behind when the resultant powder is passed under a magnetic separator. Generally, most magnetite banded iron formation deposits must be ground to between 32 and 45 μm (0.0013 and 0.0018 in) in order to produce a low-silica magnetite concentrate. Magnetite concentrate grades are generally in excess of 70% iron by weight and usually are low in phosphorus, aluminium, titanium, and silica and demand

12376-587: The ratio Fe(III)/Fe(II+III) typically varies from 0.3 to 0.6. This indicates a predominance of magnetite, in which the ratio is 0.67, over hematite, for which the ratio is 1. In addition to the iron oxides (hematite and magnetite), the iron sediment may contain the iron-rich carbonates siderite and ankerite , or the iron-rich silicates minnesotaite and greenalite . Most BIFs are chemically simple, containing little but iron oxides, silica, and minor carbonate, though some contain significant calcium and magnesium, up to 9% and 6.7% as oxides respectively. When used in

12495-500: The reaction The iron may have originally precipitated as greenalite and other iron silicates. Macrobanding is then interpreted as a product of compaction of the original iron silicate mud. This produced siderite-rich bands that served as pathways for fluid flow and formation of magnetite. The peak of deposition of banded iron formations in the late Archean, and the end of deposition in the Orosirian, have been interpreted as markers for

12614-570: The right or reduction to the left. Fe is the ferrous form of iron. This form of iron gives up electrons easily and is a mild reducing agent. These compounds are more soluble because they are more mobile. Fe is the ferric form of iron. This form of iron is very stable structurally because its valence electron shell is half filled. Laterization is a soil forming process that occurs in warm and moist climates under broadleaf evergreen forests. Soils formed by laterization tend to be highly weathered with high iron and aluminium oxide content. Goethite

12733-407: The rock must be comminuted to enable efficient magnetic separation to provide a high-purity magnetite concentrate. This determines the energy inputs required to run a milling operation. Mining of banded iron formations involves coarse crushing and screening, followed by rough crushing and fine grinding to comminute the ore to the point where the crystallized magnetite and quartz are fine enough that

12852-435: The rock range in size from sand to mud, but do not contain a lot of silica . They are also more aluminous. They are not laminated and sometimes contain ooids . Ooids can be a distinct characteristic though they are not normally a main component of ironstones. Within ironstones, ooids are made up of iron silicates and/or iron oxides and sometimes occur in alternating laminae. They normally contain fossil debris and sometimes

12971-446: The seaborne trade, with 72% of the market. BHP, Rio and Vale control 66% of this market between them. In Australia , iron ore is won from three main sources: pisolite " channel iron deposit " ore derived by mechanical erosion of primary banded-iron formations and accumulated in alluvial channels such as at Pannawonica, Western Australia ; and the dominant metasomatically altered banded iron formation -related ores such as at Newman ,

13090-459: The seventh largest global center of iron ore production, behind Australia, Brazil, China, India, Russia, and South Africa. Producers of iron ore in Ukraine include Ferrexpo , Metinvest , and ArcelorMittal Kryvyi Rih . In 2014, mines in the United States produced 57,500,000 t (56,600,000 long tons; 63,400,000 short tons) of iron ore with an estimated value of $ 5.1 billion. Iron mining in

13209-451: The seventh-largest global center of iron ore production, behind Australia, Brazil, China, Russia, South Africa, and Ukraine. India's iron ore production in 2023 was 285,000,000 metric tonnes and was the fourth largest producer in the world. According to the U.S. Geological Survey's 2021 Report on iron ore, Ukraine is estimated to have produced 62,000,000 t (61,000,000 long tons; 68,000,000 short tons) of iron ore in 2020, placing it as

13328-528: The singular, the term banded iron formation refers to the sedimentary lithology just described. The plural form, banded iron formations, is used informally to refer to stratigraphic units that consist primarily of banded iron formation. A well-preserved banded iron formation typically consists of macrobands several meters thick that are separated by thin shale beds. The macrobands in turn are composed of characteristic alternating layers of chert and iron oxides, called mesobands , that are several millimeters to

13447-401: The table aside. The major constraint to economics for iron ore deposits is not necessarily the grade or size of the deposits, because it is not particularly hard to geologically prove enough tonnage of the rocks exist. The main constraint is the position of the iron ore relative to market, the cost of rail infrastructure to get it to market, and the energy cost required to do so. Mining iron ore

13566-589: The two mines shut down. There have also been iron ore mines in Utah and Alabama ; however, the last iron ore mine in Utah shut down in 2014 and the last iron ore mine in Alabama shut down in 1975. Iron ores consist of oxygen and iron atoms bonded together into molecules. To convert it to metallic iron, it must be smelted or sent through a direct reduction process to remove the oxygen. Oxygen-iron bonds are strong, and to remove

13685-529: Was a key process in the deposition of banded iron formation, the role of oxygenic versus anoxygenic photosynthesis continues to be debated, and nonbiogenic processes have also been proposed. Cloud's original hypothesis was that ferrous iron was oxidized in a straightforward manner by molecular oxygen present in the water: The oxygen comes from the photosynthetic activities of cyanobacteria. Oxidation of ferrous iron may have been hastened by aerobic iron-oxidizing bacteria, which can increase rates of oxidation by

13804-406: Was a result of self-poisoning by early cyanobacteria as the supply of reduced iron was periodically depleted. Mesobanding has also been interpreted as a secondary structure, not present in the sediments as originally laid down, but produced during compaction of the sediments. Another theory is that mesobands are primary structures resulting from pulses of activity along mid-ocean ridges that change

13923-565: Was accompanied by the development of a stratified ocean with a deep anoxic layer and a shallow oxidized layer. The end of deposition of BIF at 1.85 billion years ago is attributed to the oxidation of the deep ocean. Until 1992 it was assumed that the rare, later (younger) banded iron deposits represented unusual conditions where oxygen was depleted locally. Iron-rich waters would then form in isolation and subsequently come into contact with oxygenated water. The Snowball Earth hypothesis provided an alternative explanation for these younger deposits. In

14042-472: Was blocked by precipitation as pyrite. Banded iron formations in northern Minnesota are overlain by a thick layer of ejecta from the Sudbury Basin impact. An asteroid (estimated at 10 km (6.2 mi) across) impacted into waters about 1,000 m (3,300 ft) deep 1.849 billion years ago, coincident with the pause in BIF deposition. Computer models suggest that the impact would have generated

14161-432: Was thought to be the result of the evolution of mechanisms for living with oxygen. This ended self-poisoning and produced a population explosion in the cyanobacteria that rapidly depleted the remaining supply of reduced iron and ended most BIF deposition. Oxygen then began to accumulate in the atmosphere. Some details of Cloud's original model were abandoned. For example, improved dating of Precambrian strata has shown that

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