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Fe Isotope Fractionation Mechanisms and its Application in Geoscience Field
Author(s) -
CAO Rui,
SONG Xuebing,
TAN Qian
Publication year - 2014
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.12384_1
Subject(s) - library science , citation , computer science , geochemistry , history , geology
The Fe isotope of hematite precipitate during Fe(III)aq hydrolysis at 98°C in 1–100 days had significant change. Fe isotopic fractionation coefficient (αFe(III)aq-hematite) between Fe(III)aq and hematite was −1.00132 (Skulan et al., 2002). Wiesli et al. (2004) studied the Fe isotopic fractionation during the process from Fe(II)aq to FeCO3 precipitate at 20°C. There was no isotopic fractionation effect between Fe(II)aq and FeCO3 in the experiment of quick precipitation. On the contrary, the isotope enrichment coefficient between FeCO3 and Fe(II)aq was −0.48‰ in the experiment of slow precipitation. Inorganic reaction, such as the change of oxidationreductions conditions could result in variation of valence of element and the coordination number, and Fe isotope fractionation (Yu et al., 2001). Leaching experiments of ion exchange resins showed that the solution leached at early stage riched Fe and lacked Fe at late stage. This experiment indicated inorganic reaction could result in notable isotope fractionation without bacteria (Anbar, 2008). Rouxel et al. (2004) found δFe of pyrite was −0.2‰ to −0.5‰ precipitated under the high temperature condition (>300°C) and that was −1‰ to −2‰ under 100–300°C. The result indicated the δFe of precipitated pyrite gradually decreased with decreasing of temperature. Fe enrichment coefficient between Fe(II)aq and remnants was 0.5‰ –1.3‰ in the process of water-rock leaching reaction; altered mineral, such as smectite and chlorite had priority to getting heavy Fe isotope ( Rouxel et al., 2003). Fe widely distributed in nature, and may participate in biochemical reaction. Bio-organic process involves multiple reaction steps, such as bio-filtration membrane and enzyme catalysis, and therefore biological process can trigger remarkable Fe isotope fractionation (Yu et al., 2001). The δFe value of tint stratum was about 0.91‰, that of dark stratum was about −0.34‰ in the research on iron sedimentary formation in the Proterozoic strata. Reduction reaction of bacteria was responsible for the difference of δFe value. However, the difference between red stratum and black stratum was quite small in the Archeozoic strata, that showed there wasn’t bacteria reduction reaction during the iron sedimentary formation (Beard, 1999).