The oxidation states of Fe within olivine, orthopyroxene, clinopyroxene, and spinel in a spinel lherzolite xenolith from the Tariat Depression, Mongolia were investigated using ⁵⁷Fe Mössbauer spectroscopy to evaluate the redox condition of the upper mantle from which the Tariat spinel lherzolite xenolith was derived. The purity of separated minerals for the Mössbauer spectroscopic analysis was examined using X-ray powder diffraction, Raman spectroscopy, and transmission electron microscopy. Average Fo and Fe contents of olivine at the core part of the xenolith are 89.9(4) mol % and 0.195(3) atoms per formula unit, respectively. The Fe³⁺/ΣFe values of the olivine, orthopyroxene, clinopyroxene, and spinel, determined by Mössbauer spectroscopic analysis, are 0.027(2), 0.15(1), 0.26(3), and 0.34(5), respectively. The Mössbauer spectrum of olivine consists of two doublets assigned to Fe²⁺ at the octahedral sites and one doublet, with I.S. of 0.40(2) mm/s and Q.S. of 0.69(3) mm/s assigned to Fe³⁺ at the octahedral site. Since the Tariat spinel lherzolite xenolith in this study shows no evidence of metasomatism or thermal alteration, the existence of a small amount of Fe³⁺ in olivine and the fairly high Fe³⁺ contents of clinopyroxene, orthopyroxene, and spinel imply that the upper mantle under the Tariat area was in a rather oxidized condition.

The abundance and distribution of rare-earth elements (REE) within fish debris from the Japanese Exclusive Economic Zone around Minami-Torishima Island have been investigated to determine the host materials of REE in the REE-rich deep-sea mud. The study was performed using REE-extraction experiments, field emission electron probe microanalysis (FE-EPMA), transmission electron microscopy with an energy-dispersive X-ray spectrometer (TEM-EDX), laser-induced breakdown spectroscopy (LIBS), Fourier-transform infrared (FTIR) spectroscopy and X-ray absorption near edge structure (XANES) analysis. The EPMA data indicate that the amount of REE in the apatite in the teeth is less than that in the bone debris. According to TEM-EDX analysis, yttrium (Y) is contained in the rod-like apatite crystals in the bone debris, but not in the long rod-like apatite crystals of the teeth. Analyses by LIBS and EPMA indicate that Y-rich bone debris is also rich in C. The FTIR spectroscopic analysis indicates the presence of carbonate groups within the Y-rich apatite structure. Moreover, the results of the XANES analysis and REE-extraction experiments indicate that Y occurs within the crystal structure of C-bearing apatite in the bone debris. These results suggest that the REE within C-bearing apatite in the fish debris from the Minami-Torishima REE-rich deep-sea mud substitute for Ca in apatite via an ionic exchange reaction, probably Ca ² ⁺ + P⁵⁺ ↔ REE ³ ⁺ + C⁴⁺.