Banded iron formation, sedimentary

By far the most important ores of iron come from Precambrian banded iron formations (BIF), which are essentially chemical sediments of alternating siliceous and iron-rich bands. The most notable occurrences are those at Hamersley in Australia, Lake Superior in USA and Canada, Transvaal in South Africa, and Bihar and Karnataka in India. The important manganese deposits of the world are associated with sedimentary deposits the manganese nodules on the ocean floor are also chemically precipitated from solutions. Phosphorites, the main source of phosphates, are special types of sedimentary deposits formed under marine conditions. Bedded iron sulfide deposits are formed by sulfate reducing bacteria in sedimentary environments. Similarly uranium-vanadium in sandstone-type uranium deposits and stratiform lead and zinc concentrations associated with carbonate rocks owe their origin to syngenetic chemical precipitation. 

Klein C. and Bricker O. P. (1977). Some aspects of the sedimentary and diagenetic environment of Proterozoic banded iron formation. Econ. Geol, 72 1457-1470. 

During conversion of goethite to hematite only small fractionation effects seem to occur, because most of the oxygen remains in the solid (Yapp 1987). Thus, in principle it should be possible to reconstruct the sedimentary environment of iron oxides from Precambrian banded iron formations (BIF). By analyzing the least metamorphosed BlFs, Hoefs (1992) concluded, however, that the situation is not so simple. Infiltration of external fluids during diagenesis and/or low temperature metamor-... 

Hoefs J (1970) Kohlenstoff-und Sauerstoff-Isotopenuntersuchungen an Karbonatkonkretionen und umgebendem Gestein. Contrib Miner Petrol 27 66-79 Hoefs J (1992) The stable isotope composition of sedimentary iron oxides with special reference to Banded Iron Formations. In Isotopic signatures and sedimentary records. Lecture Notes in Earth Sci 43 199-213, Springer Verlag, Berlin... 

Hydrothermal- sedimentary hypogene banded Mt, Hm Greenstone belts banded iron formations Algona... 

Relationship of volcanic and sedimentary processes in the formation of the banded iron-formations... 

Iron formation, the sedimentary rock characterized by the association of chert and megaquartz with silicate, carbonate, and iron oxide minerals, is one of the most distinctive Precambrian sedimentary rocks. These rocks, which reached their peak in abundance during the Paleoproterozoic (Figure 2) (James, 1983 Isley, 1995), consist of both banded iron formations (BIFs) and granular (arenitic) iron formations (GIFs) and... 

Figure 8 Archean distribution of banded iron formations, with short reoccurrence associated with widespread glaciation in the Neoproterozoic, and the Proterozoic and Phanerozoic distribution of sedimentary rocks containing ferric-iron cements (red beds). The end of banded iron formation and beginning of red bed deposition at —2.2 Ga has been taken as evidence for a major oxygenation event in Earth s atmosphere.

Domain I, located in the NE of the greenstone belt was identified as a low-strain domain by Appel et al. (1998). This domain is dominated by mafic volcanic rocks, cherts and banded iron formation, and contains well-preserved, primary igneous and sedimentary features. Measured isotopic ages are between 3742 49Ma (Sm-Nd whole-rock, chloritic schists) and 3697 70 Ma (Pb-Pb whole-rock, banded iron formation) (Moorbath Kamber 1998 Frei et al, 1999). Moorbath Kamber (1998) suggested that their Sm-Nd isochron may represent the depositional age of this part of the Isua succession, whereas Frei et al. (1999) proposed that their Pb-Pb... 

Similarly, banded iron formation (BIF), a sedimentary rock produced by chemical precipitation, is extremely rare in the Phanerozoic but common in the Archaean and Proterozoic record. Explaining its origin in terms of the atmospheric or ocean chemistry of the early Earth is an important part of recovering the history of early Earth. This is discussed in Chapter 5 (Section 5.4.3.2). 

Konhauser, K.O. (2000) Hydrothermal bacterial biomineralization Potential modern-day analogues for banded iron-formations, in Marine Authigenesis From global to microbial (eds C.R. Glenn, L. Prevot-Lucas and J. Lucas), SEPM Publication No. 66, Society for Sedimentary Geology, Tulsa, OK, pp. 133-145. 

Figure 12-4 will now be discussed in more detail. The record of reduced carbon in sedimentary rocks and the associated, 3C/I2C isotope shift date back to the oldest deposits of 3.5 Gyr ago, and even further if one makes allowance for the metamorphic alterations of the still older Isua formation (see Fig. 11-2). The biological origin of the isotope shift has been convincingly demonstrated, as reviewed by Schidlowski et al (1983). The implication that life had been in full swing 3.5 billion yr ago is supported by several lines of fossil evidence stromatolites, microfossils, and banded iron formations.

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