Gaowa Naren1, Akane Miyazaki2*, Motoyuki Matsuo3, BAI Shuqin4, Kotaro Yonesu5, Yoshihiro Okaue1, and Takushi Yokoyama1*
1.Department of Chemistry, Faculty of Science, Kyushu University, Fukuoka 8128581, Japan;
2. Department of Chemical and Biological Sciences, Faculty of Science, Japan Women’s University, Tokyo 1128681, Japan;
3. Department of Chemistry, Graduate School of Arts and Sciences, University of Tokyo, Tokyo, Japan;
4. College of Environment and Resources, Inner Mongolia University, Hohhot 010021, China;
5. Department of Earth Resources Engineering, Faculty of Engineering, Kyushu University, Fukuoka 8190395, Japan
Abstract Five ferruginous deposit samples formed from neutral hot springs were analyzed to determine whether they consisted of a mixture of silica, hydrous iron oxide or iron silicate by differential thermal analysis (DTA), infrared (IR) spectroscopy, powder X-ray diffraction (XRD), and 57Fe Mössbauer spectroscopy. The Si/Fe atomic ratios of the deposits ranged from 0.25 to 0.45, and were smaller than those of hisingerite (1−2), but apparently close to those of siliceous ferrihydrite (0.25−0.5). Si was confirmed to be present as monomeric or oligomeric silicate from the Si-O stretching vibration frequencies on the IR spectra. Judging from the results of DTA, which minerals starting to produce after heating, and a relationship between Si-O stretching vibration frequency and Si/Fe atomic ratio proposed by Henmi et al. (1981), all the deposits in this study were concluded to be mixtures of various siliceous ferrihydrites with low and high Si/Fe atomic ratios. Moreover, by comparing the chemical properties of hot spring waters, the formation conditions of siliceous ferrihydrite were also discussed.
* Corresponding author, E-mail:yokoyamatakushi@chem.kyushu-univ.jp
CHINESE JOURNAL OF GEOCHEMISTRY Vol. 32, No. 1, 2013, page 27-34
© Science Press and Institute of Geochemistry, CAS and Springer-Verlag Berlin Heidelberg 2013
