History of Iron Accumulation in the Precambrian and Phanerozoic

Iron ores are mostly typical supergene mineralized rocks whose origins were controlled by various tectonic, paleogeographic, and biochemical factors. Mineralogical and petrographic analysis of iron ore types shows that the most widely spread and abundant Precambrian and Phanerozoic types are banded iron formations (BIF), oolitic hydrogoethite–chamosite–siderite (Lorraine type), and hematite and goethite–hydrogoethite weathering crusts (WC). The other types of the ores do not play any significant role in the resources, and their amount is at the level of the statistical error. The Earth’s history was associated with a clearly discernible evolution in the character of iron accumulation. The trend was pulsating, with several stages of ore accumulation. The accumulation of iron ores was confined to greenstone belts in the Archean, to protoplatforms in the Paleoproterozoic, to rift basins in the Neoproterozoic, and to platforms in the Phanerozoic. The Archean and Paleoproterozoic ores are BIF, the Neoproterozoic ones belong to the granular iron formation, and the Phanerozoic are the WC and oolitic formations. The mineralogical–petrographic types of ores also evolved with time. While hematite–magnetite ores are typical of the Archean and Paleoproterozoic; hematite ores are typical of the Neoproterozoic; and hematite, hydrohematite, goethite WC, and oolitic hematite–chamosite–siderite ores are characteristic of the Phanerozoic. The change in ore types was controlled by changes in the facies conditions and by metamorphic processes in the Precambrian.