Precambrian banded iron formations

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... 

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-... 

Rapid embedding in silica is particularly favourable for the good preservation of the organic matter, and this was surely the case with the well-preserved microstructures. But there is much indication from the thin section petrography that the Precambrian banded iron-formations were primarily deposited as carbonates (Lougheed, 1983)The origin of the embedding chert has been a major problem,... 

Mel nik, Y. P. Precambrian Banded Iron-Formations, Amsterdam, Oxford, New York, Elsevier Sci. P.C. 1982... 

Data are from Saito et al. (1984) unless otherwise noted. Noble gas amounts are in cm3STPg 1 and are representative values. ( ) Markov et al. (1990) magnetites were separated from Precambrian banded iron formation (BIF) in Russia. 

In the precambrian (or on present day Mars), the absence, of an ozone layer allowed solar UV radiation with energies as high as 40,000 cm"1 (0.25 microns). Photoreduction transitions via the Fe(3d) to Fe(4s) transition may have been very significant. The photochemical oxidation of Fe2+, and the precipitation of FeOOH, may be the origin of the extensive precambrian banded iron formations (38-40). Moreover, the photooxidation of Fe2 may have reduced C02 to organic molecules (37.41) ... 

Precambrian banded iron-formations, their distribution and their age, spatial, and genetic relationships... 

Alexandrov, E.A., 1973. The Precambrian banded iron-formations of the Soviet Union. Econ. Geol., 68 ... 

Banerji, A.K., 1977. On the Precambrian banded iron-formations and the manganese ores of the Singhbhum Region, Eastern India, Econ. Geol., 72 90-98. 

Drever, J.I., 1974, Geochemical model for the origin of Precambrian banded iron formations. Bull. Geol. Soc. Am., 85 1099-1106. 

Holland, H.D., 1973. The Oceans a possible source of iron-formations. Econ. Geol., 68 1169-1172. Hough, J.L., 1958. Fresh-water environment of deposition of Precambrian banded iron formations. J. Sediment. Petrol. 28 414-430. 

PRECAMBRIAN BANDED IRON-FORMATIONS Physicochemical Conditions of Formation... 

The problem of the formation of the Precambrian banded iron-formations (BIF), repeatedly the subject of discussion, continues to be pressing. The present interest in it is explained not only by the ever-increasing importance of iron cherts as economic ores, but also by the special position they occupy in the geologic history of the Earth. 

Melnik Y. P. (1982) Precambrian Banded Iron Formation Physiochemical Conditions of Formation. Elsevier, Amsterdam, p. 310. 

Konhauser K. O., Hamade T., Raiswell R., Morris R. C., Ferris F. G., Southam G., and Canfield D. E. (2002) Could bacteria have formed the Precambrian banded iron formations Geology 30(12), 1079-1082. 

The Precambrian banded iron formations are huge, flat accumulations, ( V 500 km across and V 500 m thick) mainly of silica and iron minerals arranged in bands, present in the Precambrian cores of all continents They are the world s main ore of iron. The consensus is that they formed by precipitation out of shallow water bodies at earth s surface temperatures, and that somehow their origin appears to be tied to the composition and evolution of the earth s early atmosphere. Beyond this, everything else is controversial How did such extreme chemical winnowing take place over whole basins up to hundreds of kilometers across ... 

Jones, F,T, 1952, American Mineralogist 37, pp, 578-587. Mel nik, Y.P. 1982, Precambrian banded iron formations. Developments in Precambrian Geology 5, Amsterdam, Elsevier,... 

---