Banded iron formation

Commonly termed BIFs by geologists, they are iron-rich rocks almost always of Precambrian age, predominantly associated with the great oxygenation event (GOE) about 2.3-2.8 billion years ago. It typically consists of repeated, thin iron oxide layers (a few mm to a few cm in thickness) but may be banded from a microscopic to a metre scale. The oxide bands are dark grey to to black magnetite (Fe₃O₄) or hematite (Fe₂O₃), alternating with bands of iron-poor shales and cherts, usually red in color, of similar thickness, or iron rich silicates and carbonates, including siderite, ankerite, riebeckite, stilpnomelane, minnesotaite, etc. They provide our major source of iron ore, usually after upgrading by various hypogene and supergene processes.

Types of Banded Iron Formations

BIFs Types Formation Age Tectonic Settings Rock Assemblages Significant Deposits/Regions Algoma Archean and Paleoproterozoic Intracraton rifts or volcanic arcs settings Greywacke; fine-grained volcanic (clastic) rocks Archean Yilgarn and Pilbara deposits Superior Neoarchean and Paleoproterozoic Passive continental margin Sedimentary formations; such as carbonate rocks; quartz sandstones; and black shales Hamersley and the Transvaal deposits in Australia and South Africa Rapitan Early Neoproterozoic Rifted basin Glaciogenic lithologies such as diamictites and dropstone layers Urucum in the Mato Grosso State; Brazil; and Rapitan in the Northwest Territories of Canada

Yin et al (2023)