Photon Factory Activity Report 2005 #23 Part B (2006)
Applied Science

9A, 12C/2004G334

Determination of the Eu(II)/Eu(III) ratios in minerals by
X-ray absorption near-edge structure (XANES) andits application to hydrothermal deposits
Yoshio TAKAHASHI1*, German R. KOLONIN,2 Galina P. SHIRONOSOVA,3Irina I. KUPRIYANOVA,3 and Hiroshi SHIMIZU11Dept. Earth and Planetary Systems Science, Hiroshima University, Hiroshima 739-8526, Japan
2
Institute of Mineralogy and Petrography, SB RAS, Prosp. Koptyuga 3, Novosibirsk, 630090, Russia
3Fedorovskii All-Russia Research Institute of Mineral Resources, Staromonetnyi per. 31, Moscow,119017, Russia

244

Users' Report

spectra is clearly different in each Eu(II) and Eu(III)species, as exemplified in the Fig. 1. Despite thisambiguity, the method was applied to Eu in naturalhydrothermal apatites (Eu = 39 and 64 ppm) andfluocerite (Eu = 282 ppm). The relation between theEu(II)/Eu(III) ratio in these hydrothermal minerals, andthe distribution coefficients of Eu(II) and Eu(III) werediscussed, taking into account Eu anomalies in their REE
patterns.
It is considered that by combining theEu(II)/Eu(III) ratios determined by XANES and thedegree of Eu anomaly in REE patterns, we can provide
new information on the distribution of Eu(II) and Eu(III)in various geochemical studies.
References[1]Y. Takahashi et al., Min. Mag. 69 (2005) 177-188.
* ytakaha@hiroshima-u.ac.jp

Normalized absorption

Abundances of rare earth elements (REE) haveprovided useful information for characterizing various
geochemical samples such as rocks, minerals, and water
samples, with the purpose of estimating the source
materials of the sample and environment where thesample was formed. Among various features involved in
REE patterns (= relative abundances of REE normalized
by proper reference materials), an anomalous abundanceof Eu, called Eu anomaly, can be used as an indicator ofredox conditions, origin of the materials, and REE
fractionation during crystallization differentiation. The
Eu anomaly is presumably caused by the formation ofEu(II) in reducing environment, which induces thefractionation of Eu from other trivalent REEs. The extentofEu
anomalyisoften
expressedas*
1/2
1/2
EuN/EuN =EuN/{(SmN) (GdN) }, where N indicatesnormalized abundances. Although there have been many
*studies discussing Eu anomaly with the EuN/EuN ratio
assuming the presence of Eu(II), few studies haveidentified Eu(II) in rocks and minerals. X-ray absorption
near-edge structure (XANES) is a promising tool for thespeciation of trace elements, which was employed in thisstudy to determine Eu(II)/Eu(III) ratios in apatite andfluocerite in hydrothermal vein deposits, Malyshevskoe
and Katuginskoe deposites, respectively, in Russia. It is
expected that the Eu(II)/Eu(III) ratio determined for theminerals can be used to estimate the Eu(II)/Eu(III) ratio inhydrothermal solutions where the minerals have formed,
which in turn can be used to estimate fO2 in thehydrothermal solution, based on the relationship between
the Eu(II)/Eu(III) ratio and fO2.
Europium LIII-edge XANES was measured insynchrotron radiation facilities in both BL-12C of Photon
Factory (PF) in KEK, Tsukuba, Japan. The fluorescence
yield was measured using a 19-element Ge semiconductor
detector (SSD).
It was found that the Eu(II)/Eu(III) ratios in minerals
can be determined based on the peak area ratio of whitelines, resonance peak, in normalized XANES spectra forEu(II) and Eu(III) species. For precise determination ofthe Eu(II)/Eu(III) ratios, however, it was revealed that thetransition probabilities for each individual Eu(II) andEu(III) species in the system must be quantified, because
we found that the peak area in normalized XANES

EuSO4

EuS

EuCl3
Eu2(SO4)3
Eu2O3-40-30-20-10010Energy (eV)2030

40Fig. 1. Europium LIII-edge XANES spectra for variousEu(III) and Eu(II) species: Eu2O3, Eu2(SO4)3, EuCl3, EuS
and EuSO4.