The classic model for the formation of iron deposits suggested that the Fe (II) from the Earth's core was oxidized by the oxygen produced by cyanobacteria (blue - green algae). (sciencedaily.com)
The Soudan Mine opened in 1884 atop one of the richest iron deposits in the world — hard hematite, about 65 percent pure. (discovermagazine.com)
Although no written records exist of the early history of the Phalaborwa district, archaeologists and geologists agree that it was once an area of intense volcanic activity; resulting in rich iron deposits. (travelground.com)