| Research Abstract |
The aim of our study was to establish the outline of Fe isotopic for modern and ancient sediments and rocks and to elucidate interactions between lithosphere/hydrosphere and biosphere based on these Fe isotopes. We have gained scientific results as follows.
(1)Major, trace and rare earth element contents were determined for sedimentary iron ores from the Gunma iron deposit. Preferential uptake of P,Sc,Cu, Mo, Ba, Th, and light REEs occurs in the iron ores (BIM ores) formed through biologically induced mineralization. Unique enrichment of these elements is a promising indicator of biomineralization for 〓〓cient sedimentary iron deposits (Kato et al.,2002, Resource Geology). The 57Fe/54Fe, 56Fe/54Fe and 57Fe/56Fe ratios for these iron deposits and meteoritic irons have been measured using a plasma mass spectrometry coupled with laser ablation sampling technique. Those of BIM ore are fractionated significantly, about 2〜7‰ for 57Fe/54Fe, 2〜5‰ for 56Fe/54Fe and 1〜3% for 57Fe/56Fe, indicating the mass-dependent fractionation feature with different degree of isotopic fractionation.
(2) There is also a large Fe isotope fractionation in the iron ores preserving numerous algal fossils, near Sasebo (Nagasaki).
(3) 3.46 Ga ferruginous cherls are interpreted to have been an in situ precipitate derived from a high-T hydrothermal solution emanating from a mid-oceanic ridge (Kato and Nakamura, 2003, Precambrian Research).
(4) In-situ Fe isotopic ratio measurements for solid samples have been carried out using laser ablation-multiple collector-inductively couples plasma mass spectrometry (LA-MS-ICP-MS). Using a dry plasma condition achieved by laser sample introduction technique, mass spectrometric interferences could be successfully reduced (Hirata and Ohno, 2001, JAAS).
|
