Iron ore deposits occur in a large genetic variety. Two factors of iron concentration are especially prominent– redox changes and the metal’s high solubility in reduced saline fluids. The first controls the giant mass of iron in sedimentary depos its, such as Precambrian banded iron formations. Elevated salinity is a common theme in iron concentrations as diverse as iron oxide-copper-gold, skarn, hydrothermal-metasomatic siderite and high-grade haematite ore deposits. Scientific and economic significance suggests the following genetic tabulation:
- orthomagmatic iron ore deposits (intrusive and extrusive; mafic and felsic, alkaline, carbonatitic);
- contact-metasomatic and iron skarn ore deposits;
- magmatic-hydrothermal, epigenetic massive and vein deposits, including an apatite-iron oxide subclass;
- hydrothermal-metasomatic siderite stocks in carbonates (diagenetic or metamorphogenic);
- volcanogenic-exhalative and sedimentary hydrothermal (sedex) deposits; . residual, lateritic deposits;
- supergene infiltration “channel” ore deposits;
- terrestrial-sedimentary iron deposits (bog ore, karst iron ore, alluvial magnetite placers);
- marine-sedimentary and associated supergene enrichment iron ore deposits (magnetite BIF, BIF-derived martite-goethite ore, ironstones, oolitic iron ore, detrital iron ore, coastal placers);
- high-grade haematite ore deposits replacing banded iron formations (pre-enrichment by diagenetic-hydrothermal processes, final supergene enrichment).
Source: Economic Geology, principles and practice by Walter L. POHL.
