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Banded iron formation from the Barberton Greenstone Belt, South Africa. A typical banded iron formation consists of repeated, thin layers (a few millimeters to a few centimeters in thickness) of silver to black iron oxides, either magnetite (Fe 3 O 4) or hematite (Fe 2 O 3), alternating with bands of iron-poor chert, often red in color, of similar thickness.
The Gunflint Iron Formation is a banded iron formation, composed predominantly of dense chert and slate layers interbedded with ankerite carbonate layers. The chert layers can be subdivided into black layers (containing organic material and pyrite), red layers (containing hematite), and green layers (containing siderite). [5]
These iron compounds precipitated from the sea water in varying proportions with chert, producing banded-iron formations. [9] Banded-iron formations occur in several ranges around the margins of this basin, five of which contained sufficient concentrations of iron to be economically mined. [2] These banded-iron formations have been one of the ...
Iron formations can be divided into subdivisions known as: banded iron formations (BIFs) and granular iron formations (GIFs). [3] The above classification scheme is the most commonly used and accepted, though sometimes an older system is used which divides iron-rich sedimentary rocks into three categories: bog iron deposits, ironstones, and ...
Jasper is the main component in the silica-rich parts of banded iron formations (BIFs) which indicate low, but present, amounts of dissolved oxygen in the water such as during the Great Oxidation Event or snowball earths. [16] The red bands are microcrystalline red chert, also called jasper.
The iron deposit is a banded iron formation of the Early Proterozoic Animikie Group. [2] [3] The Gunflint Iron Formation is overlain by "brecciated and complexly deformed iron formations", which in turn is overlain by ejecta from the "Sudbury meteorite impact event." This Sudbury Impact Layer is overlain by the Rove Formation.
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The range is one of the oldest mountain ranges on Earth and primarily consists of ancient rock formations, including banded iron formations (BIFs), that are about 2.5 billion years old. The Pilbara Craton, which underlies the Hamersley Range, dates back to around 3.4 billion years, but the range itself is younger than that.