Editing Iron ore (section)

== Sources ==

{{Further|iron cycle}}
{{More citations needed|section|date=July 2021}}
Elemental iron is virtually absent on the [[Earth]]'s surface except as iron-nickel [[Alloy|alloys]] [[Meteoric iron|from meteorites]] and very rare forms of deep mantle [[xenolith]]s. Although iron is the fourth most abundant element in [[Earth's crust]], composing about 5% by weight,<ref>{{Cite book |last1=Murad |first1=Enver |title=Mossbauer Spectroscopy of Environmental Materials |last2=Cashion |first2=John |date=2011-06-28 |publisher=Springer Science & Business Media |isbn=9781441990402 |pages=159}}</ref> 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 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 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]], hematite, and [[pisolite|pisolitic]] ironstone deposits.

The origin of iron can be ultimately traced to its formation through nuclear fusion in stars, and most of the iron is thought to have originated in dying stars that are large enough to explode as [[supernova]]e.<ref>{{Cite journal |last1=Frey |first1=Perry A. |last2=Reed |first2=George H. |date=2012-09-21 |title=The Ubiquity of Iron |journal=ACS Chemical Biology |language=en |volume=7 |issue=9 |pages=1477–1481 |doi=10.1021/cb300323q |issn=1554-8929 |pmid=22845493}}</ref> The [[Internal structure of Earth|Earth's core]] is thought to consist mainly of iron, but this is inaccessible from the surface. Some [[iron meteorite]]s are thought to have originated from [[M-type asteroid|asteroids]] {{convert|1000|km|abbr=on}} in diameter or larger.<ref>{{Cite journal |last1=Goldstein |first1=J.I. |last2=Scott |first2=E.R.D. |last3=Chabot |first3=N.L. |date=2009 |title=Iron meteorites: Crystallization, thermal history, parent bodies, and origin |journal=Geochemistry |language=en |volume=69 |issue=4 |pages=293–325 |bibcode=2009ChEG...69..293G |doi=10.1016/j.chemer.2009.01.002}}</ref>

=== Banded iron formations ===
{{Main|Banded iron formation}}
[[File:Black-band ironstone (aka).jpg|thumb|Banded iron rock, estimated at being 2.1 billion years old]]
[[File:TaconitePellet.JPG|thumb|Processed [[taconite]] pellets with reddish surface oxidation used in [[steelmaking]] with a [[Quarter (United States coin)|U.S. quarter]] (diameter: {{Convert|24|mm|abbr=on|disp=sqbr}}) shown for scale]]
[[Banded iron formation]]s (BIFs) are [[sedimentary rock]]s 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 [[Metamorphism|metamorphosed]]. Banded iron formations may contain iron in [[Carbonate mineral|carbonates]] ([[siderite]] or [[ankerite]]) or [[Silicate mineral|silicates]] ([[minnesotaite]], [[greenalite]], or [[grunerite]]), but in those mined as iron ores, [[Oxide mineral|oxides]] ([[magnetite]] or [[hematite]]) are the principal iron mineral.<ref>Harry Klemic, Harold L. James, and G. Donald Eberlein, (1973) "Iron," in ''United States Mineral Resources'', US Geological Survey, Professional Paper 820, p.298-299.</ref> 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 [[Overburden|waste dump]]s, and 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.

=== Magnetite ores ===
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 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 dip|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 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]].<ref>{{Cite journal|last1=Troll|first1=Valentin R.|last2=Weis|first2=Franz A.|last3=Jonsson|first3=Erik|last4=Andersson|first4=Ulf B.|last5=Majidi|first5=Seyed Afshin|last6=Högdahl|first6=Karin|last7=Harris|first7=Chris|last8=Millet|first8=Marc-Alban|last9=Chinnasamy|first9=Sakthi Saravanan|last10=Kooijman|first10=Ellen|last11=Nilsson|first11=Katarina P.|date=2019-04-12|title=Global Fe–O isotope correlation reveals magmatic origin of Kiruna-type apatite-iron-oxide ores|journal=Nature Communications|language=en|volume=10|issue=1|page=1712|doi=10.1038/s41467-019-09244-4|pmid=30979878|pmc=6461606|bibcode=2019NatCo..10.1712T|issn=2041-1723|doi-access=free}}</ref> Magnetite-bearing banded iron formation 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 (hematite) ores===
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 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 ([[Clay mineral|clays]] within pisolites). Export-grade DSO ores are generally in the 62–64% Fe range.<ref>{{Cite journal|last1=Muwanguzi|first1=Abraham J. B.|last2=Karasev|first2=Andrey V.|last3=Byaruhanga|first3=Joseph K.|last4=Jönsson|first4=Pär G.|date=2012-12-03|title=Characterization of Chemical Composition and Microstructure of Natural Iron Ore from Muko Deposits|journal=ISRN Materials Science|language=en|volume=2012|pages=e174803|doi=10.5402/2012/174803|s2cid=56961299 |doi-access=free}}</ref>

===Magmatic magnetite ore deposits===
[[Granite]] and [[ultrapotassic]] [[igneous rock]]s were sometimes used to segregate [[magnetite]] crystals and form masses of magnetite suitable for economic concentration.<ref>{{Cite journal |last1=Jonsson |first1=Erik |last2=Troll |first2=Valentin R. |last3=Högdahl |first3=Karin |last4=Harris |first4=Chris |last5=Weis |first5=Franz |last6=Nilsson |first6=Katarina P. |last7=Skelton |first7=Alasdair |date=2013-04-10 |title=Magmatic origin of giant 'Kiruna-type' apatite-iron-oxide ores in Central Sweden |journal=Scientific Reports |language=en |volume=3 |issue=1 |page=1644 |doi=10.1038/srep01644 |pmid=23571605 |pmc=3622134 |bibcode=2013NatSR...3E1644J |issn=2045-2322 |doi-access=free}}</ref> A few iron ore deposits, notably in [[Chile]], are formed from [[volcanic]] flows containing significant accumulations of magnetite [[phenocryst]]s.<ref name="ChileIronOxideLava">{{cite journal |last1=Guijón |first1=R. |last2=Henríquez |first2=F. |last3=Naranjo |first3=J.A. | url=https://www.researchgate.net/publication/241044499 | title=Geological, Geographical and Legal Considerations for the Conservation of Unique Iron Oxide and Sulphur Flows at El Laco and Lastarria Volcanic Complexes, Central Andes, Northern Chile | journal=Geoheritage | year=2011 | volume=3 | issue=4 | pages=99–315 | doi=10.1007/s12371-011-0045-x|bibcode=2011Geohe...3..299G | s2cid=129179725 }}</ref>