Banded iron formation

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. 

Becker RH, Clayton RN (1976) Oxygen isotope study of a Precambrian banded iron-formation. Hamersley Range, Western Australia. Geochim Cosmochim Acta 40 1153-1165 Beard BL, Johnson CM (2004) Fe isotope variations in the modem and ancient earth and other planetary bodies. Rev Mineral Geochem 55 319-357... 

Figure 2. Co-variation of Fe/ "Fe and Fe/ "Fe ratios of individual layers from Banded Iron Formations, modified from Johnson et al. (2003a). The horizontal axis shows isotopic compositions in 5 Fe (bottom) and Fe (top), and the vertical axis shows values in d Fe (left) and s Fe (right). Point A has a d Fe of +1.00%o, which corresponds to an s Fe value of +15.0. Figure illustrates the multiple ways in which the same Fe isotope composition may be reported when isotopic variations are due to mass-dependent processes. See text for discussion.

Figure 21. Plot of the measured 6 Fe value of pairs of magnetite and siderite layers from Banded Iron Formations. Data from Johnson et al. (2003a) and C. Johnson and B. Beard unpublished.

Ewers WE (1983) Chemical factors in the deposition and diagenesis of banded iron-formation. In Iron Formations Facts and Problems. Trendall AF, Morris RC (eds) Elsevier, Amsterdam, p 491-512 Fantle MS, DePaolo DJ (2002) The isotopic composition of continental iron and implications for the global Fe cycle. EOS Trans Am Geophys Union 83 V22B-1234... 

Figure 19. Iron isotope fractionations between magnetite and Fe carbonates from adjacent bands in Banded Iron Formations (Johnson et al. 2004a), compared to Fe(II)aq sources and Fe pathways inferred from the Fe isotope fractionations given in Table 3. values are as measured, and the scales for...

Baur ME, Hayes JM, Studley SA, Walter MR (1985) Millimeter-scale variations of stable isotope abundances in carbonates from banded iron-formations in the Hamersley Group of Western Australia. Econ Geol 80 270-282... 

Harder EC (1919) Iron-depositing bacteria and their geologic relations. US Geol Surv Prof Pap 113 Hartman H (1984) The evolution of photosynthesis and microbial mats a speculation on banded iron formations. In Microbial Mats Stromatolites. Cohen Y, Castenholz RW, Halvorson HO (eds) Alan Liss Pub, New York, p 451-453... 

Johnson CM, Skulan JL, Beard BL, Sun H, Nealson KH, Braterman PS (2002) Isotopic fractionation between Pe(III) and Ee(II) in aqueous solutions. Earth Planet Sci Lett 195 141-153 Johnson CM, Beard BL, Beukes NJ, Klein C, O Leary JM (2003) Ancient geochemical cycling in the Earth as inferred from Ee isotope studies of banded iron formations from the Transvaal Craton. Contrib Mineral Petrol 144 523-547... 

Kaufman AJ (1996) Geochemical and mineralogic effects of contact metamorphism on banded iron-formation an example from the Transvaal Basin, South Africa. Precam Res 79 171-194... 

Nealson KH, Myers CR (1990) Iron reduction by bacteria a potential role in the genesis of banded iron formations. Amer Jour Sci 290A 35-45... 

Although under chemolithoautotrophic growth conditions, cell densities of only 3-5 x 10 cells per milliliter were observed, the specific rate of Fe(III) reduced per cell unit was about 10 times faster than what had been published for any other Fe(lll) reducer. This strengthens the hypothesis that microbially mediated Fe(III) reduction by obligately anaerobic thermophiles could have been an important process on early Earth, when elevated temperatures were predominant (Baross 1998 Kashefi and Lovley 2000), which includes the involvement in the formation of specific Banded Iron Formations. In light of the properties of the above Fe(lll) reducers, the theories on the origin and biogeochemistry of Banded Iron Formations should be revisited. 

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. 

Fig. 3. Indicators of redox variations in the Earth s hydrosphere and atmosphere. Dominance of CH4 H2 defined from anomalies, H2 from anomalies and C02 SO2 from banded iron formations. Data from Canfield (2005), Holland (2005), Melezhik ef al. (2005).

As predicted from the nuciear size effect on the distribution of uranium isotopes, Steriing et al. (2007) and Weyer et al. (2008) report a totai variation of 1.5 %o in the 238 j/2S5 j pg jQg decreasing in the order from biack shaies > basaits, > seawater, > banded iron formations (BiFs). The biack shaies reflect preferentiai reduction by organic matter of U from seawater. 

Geochemistry of auriferous banded iron formation, northeastern Saharan metacraton, Egypt... 

Keywords Owienat, Archean, Early Proterozoic, Banded Iron Formation, felsic granulites... 

El Shimi, K.A. Soliman, A.A. 2002. Gold mineralization associated the banded iron formation in the central Eastern Desert of Egypt first record. Annals of the Geological Survey, Egypt, 25, 281-299. 

Khattab, M.M, et at. 2002. Al Oweinat Banded Iron Formation (SW Egypt) distribution and related gold mineralization. Annals of Geological Survey, Egypt, 25, 343-364... 

Keywords Woodstock, Manganese, Banded Iron Formations, Plymouth Deposit. 

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