Banded ironstone

De Duve (and other authors) consider the source to be iron, which as Fe2+ provides one electron per Fe atom when subject to solar UV irradiation. The Fe3+ generated can be precipitated from solution with Fe2+ as a mixed oxide (FeO Fe2C>3 = FesOzt). This is found today in the form of black-band ironstone, an ore which is between 1.5 and 3.5 billion years old and was produced by interaction of Fe2+ with oxygen produced by light-converting bacteria. (The figure of 3.5 billion years is, however, not accepted by some scientists see Sect. 10.1). 

Harington, J.S. and Cilliers, J.J. le R., 1963. A possible origin of the primitive oils and amino acids isolated from amphibole asbestos and banded ironstone. Geochim. Cosmochim. Acta, 27 411-418. Harrison, C.G.D. and Peterson, M.N.A.-, 1965. A magnetic mineral from the Indian Ocean. Am. Mineral. 50 704-712. 

Schidlowski, M Eichmann, R. and Fiebiger, W., 1976. Isotopic fractionation between organic carbon and carbonate carbon in Precambrian banded ironstone series from Brazil. Neues Jahrb. Mineral. Monatsh., 8 344-353. 

Reliance Fm, Belingwe belt, Zimbabwe. About 6.5 mm across photo. Olivine crystals set in fine grained to once-glassy groundmass. For details see Nisbet et al. (1987). Photo W. E. Cameron, (b) Alternating iron-rich and carbon-rich shales. White bands are chert this lithology is transitional to banded ironstone. Approximately, 20 cm across picture. Belingwe belt, Zimbabwe. 

Eu anomalies are characteristic of sediments from fluids of hydrothermal systems that involve the breakdown of plagioclase. The ubiquitous positive Eu anomaly in Archaean and early Proterozoic banded ironstones is consistent with the chemical models (Drever 1974 Holland... 

The model of Fig. 7 is derived in part from the sedimentological facies (Nisbet et al. 1993 Hunter et at. 1998) and in part from the depositional chemistry of banded ironstones (e.g. Drever 1974). In a world where total biological productivity may have been roughly comparable with... 

Curtis, C.D., Pearson, M.J. 8l Somogyi, V.A. (1975) Mineralogy, chemistry, and origin of a concretionary siderite sheet (clay-ironstone band) in the Westphalian of Yorkshire. Miner. Mag., 40, 385-393. 

One clue to oxygen levels during this period is to be found in the very same iron formations that overlie the shales of the Hamersley Range. Massive sedimentary iron formations were deposited here and around the world in alternating bands of red or black ironstone (haematite and magnetite, respectively), and sediment, typically flint or quartz. The individual bands range in depth from millimetres to metres, while the formations themselves can be up to 600 metres [approximately 2000 feet] thick. Most of these formations were deposited between 2.6 and 1.8 billion years ago, but sporadic outcrops range in age from 3.8 billion to 800 million years. 

If this was the case, the banding of ironstones with flint or quartz could have been produced by seasonal influences, such as higher rates of photosynthesis (and therefore oxygen production) in the summer than in the winter, or seasonal upwellings according to climatic variations. The seasonal fluctuations in iron deposition would have been set against a... 

Ironing. A fault that may arise during the firing of decorated ware having cobalt blue bands, etc. the band appears dull and may have a reddish scum caused by the crystallization of cobalt silicate. Ironstone China. See mason s... 

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