The iron-formation mineral system, including the banded iron-formation-hosted and granular iron-formation-hosted varieties, represents the world's largest and highest grade iron ore districts and deposits.

Banded iron-formation (BIF), the precursor to low- and high-grade BIF-hosted iron ore, consists of Archean and Paleoproterozoic Algoma-type BIF (e.g. Serra Norte iron ore district in the Carajás Mineral Province), Proterozoic Lake Superior-type BIF (e.g. deposits in the Hamersley Province), and Neoproterozoic Rapitan-type BIF (e.g. the Urucum iron ore district) (see the review of the BIF-hosted iron mineral system by Hagemann et al., 2016).

Iron-formation ores include primary and enriched varieties. Primary magnetite-rich ores are generally lower grade (<40 wt% Fe_total) but have larger combined resources and reserves compared with enriched ores that have grades of 40 to 72 wt% Fe_total. Enriched ores include early hypogene (magnetite, crystalline hematite) and later supergene (goethite–hematite) ore types. Examples of primary and enriched iron-formation deposits are present in the Hamersley Basin, Pilbara Craton and Yilgarn Craton (Angerer et al., 2015; Hagemann et al., 2016; Hagemann et al., 2017).

Ore types that are not included in this system are the ooidal ironstones (channel iron deposits, also known as CID) or the detrital iron systems.

Key processes involved in the genesis of most BIF-hosted iron deposits include fluid flow along greenstone belt or basin-scale structures. Hydrothermal fluids ascend and descend along these structures and control hypogene alteration and mineralization – upgrading the iron content of BIF to iron ore. Supergene alteration and mineralization are the product of more recent cold meteoric water descent, preferentially along structures during the Cenozoic. At the depositional site, the transformation of protolith BIF to higher grade iron ore is controlled by: i) far field stress configuration, structural architecture and permeability at the time of upgrade from BIF to iron ore; ii) hypogene alteration processes caused by ascending deep fluids (largely magmatic or basinal brines) and descending ancient meteoric water; iii) supergene enrichment via weathering processes after uplift and exhumation.

1. SOURCE – of fertile primary BIFs

2. SOURCE – of secondary iron upgrade in BIF by fluids

3. PATHWAY – structural architecture – active pathway for delivery of fluids

4. EXHUMATION AND PRESERVATION – surficial modification and preservation – of BIF-hosted iron deposits

The Mineral SystemsTree is the graphical display of a mineral system analysis showing the link between critical/constituent processes and their recommended targeting features and GIS layers.

 Mineral System Tree: Iron formation

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Hagemann, SG, Angerer, T and Duuring, P 2017, Iron ore systems in Western Australia, in Australian ore deposits edited by GN Phillips: Australasian Institute of Mining and Metallurgy, Melbourne; Monograph, p. 59–62.

Hagemann, SG, Angerer, T, Duuring, P, Rosière, CA, Figueiredo e Silva, RC, Lobato, L, Hensler, AS and Walde, DHG 2016, BIF-hosted iron mineral system: A review: Ore Geology Reviews, v. 76, p. 317–359.

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Dalstra, H and Guedes, S 2004, Giant hydrothermal hematite deposits with Mg-Fe metasomatism: A comparison of the Carajás, Hamersley, and other iron ores: Economic Geology, v. 99, p. 1793–1800.

Duuring, P, Teitler, Y and Hagemann, SG 2017, Banded iron formation-hosted iron ore deposits of the Pilbara Craton, in Australian ore deposits edited by GN Phillips: Melbourne, Australasian Institute of Mining and Metallurgy, p. 345–350.

Duuring, P, Angerer, T and Hagemann, SG 2017, Iron ore deposits of the Yilgarn Craton, in Australian ore deposits edited by GN Phillips: Australasian Institute of Mining and Metallurgy, Melbourne, p. 181–184.

Figueiredo e Silva, RC, Hagemann, S, Lobato, LM, Rosière, CA, Banks, DA, Davidson, GJ, Vennemann, T and Hergt, J 2013, Hydrothermal fluid processes and evolution of the giant Serra Norte jaspilite-hosted iron ore deposits, Carajás Mineral Province, Brazil: Economic Geology, v. 108, p. 739–779.

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Mukhopadhyay, J, Gutzmer, J, Beukes, NJ and Hayashi, K-I 2008, Stratabound magnetite deposits from the eastern outcrop belt of the Archaean Iron Ore Group, Singhbhum craton, India: Applied Earth Science, v. 117, p. 175–186.

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Rosière, CA, Spier, CA, Rios, FJ and Suckau, VE 2008, The itabirites of the Quadrilátero Ferrîfero and related high-grade iron ore deposits: An overview: Reviews in Economic Geology, v. 15, p. 223–254.

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