Magnetite isotopic data

Shackleton NJ, Hall MA, Line J, Gang S (1983) Carbon isotope data in core V19-30 confirm reduced carbon dioxide concentration in the ice age atmosphere. Nature 306 319-322 Shahar A, Young ED, Manning CE (2008) Equihbrium high-temperature Fe isotope fractionation between fayalite and magnetite an experimental calibration. Earth Planet Sci Lett 268 ... 

On the basis of the isotopic data obtained, the hypothesis of chemogenic deposition of cherty iron sediments of complex composition in sea basins seems to be most applicable. Only by such a process was it possible for compounds to form which already differed sharply in oxygen isotopic composition—oxides (goethite or hematite, magnetite) and carbonates (siderite, sideroplesite)—in the original iron sediment. 

In other districts, for instance in the KMA, reduction of oxide sediment to magnetite and siderite by organic matter probably was of great ore-forming importance (Plaksenko, 1966). Isotopic data on this district are still insufficient for definite conclusions in two out of three analyses (see Fig. 96) the S 0 of coexisting oxides are similar, and in one the magnetite oxygen is... 

The geochemical data given make no claim to completeness and do not give the whole idea of the distribution of elements between all the rock types and between the various coexisting minerals. However, the basic conclusion that the ore minerals, primarily magnetite, are of complex polygenetic origin is consistent with the physicochemical and isotopic data. 

Based on the experimental muscovite-water and quartz-water calibrations of O Neil and Taylor (1969) and Matsuhisa et al. (1979) with a straight line constrained to go through the origin. Based on natural quartz-biotite data where temperatures were determined by the Bottinga and Javoy (1973) calibrations of the feldspar-quartz, feldspar-muscovite or feldspar-magnetite isotope thermometers. 

Figure 13. Plot of lO lnaA-B values versus lOVT (T in K) for inter-mineral fractionation between magnetite-olivine, orthopyroxene-olivine, and clinopyroxene-olivine, and Fe metal-olivine as calculated from spectroscopic data by Polyakov and Mineev (2000), and as measured from natural samples by Zhu et al. (2002), Beard and Johnson (2004). Also shown is the Fe isotope fractionation factor between magnetite and Fe-silicates measured by Berger and von Blanckenburg (2001).

Comparing the data in Fig. 94, it can be suggested that the spread of of the ore minerals of Precambrian BIF was caused by substantial differences in the original oxygen isotopic composition, which makes it possible to use the results obtained to reconstruct the conditions of sedimentation and determine the composition of the iron sediments and the origin of the main ore mineral, magnetite. 

Figure 18. Plot of oxygen isotope fractionation factor between magnetite and water at low temperatures. Data sources Becker and Clayton (1976) and Rowe et al. (1994) - empirical-theoretical calculations Zheng (1995) -empirical increment method O Neil and Clayton (1964) - extrapolation of high-temperature experimental results to an analysis of magnetite teeth from marine chiton Blattner et al. (1983) -natural samples from active geothermal system in New Zealand Zhang et al. (1997) - extracellular magnetite...

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