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Kaolin deposits in the Seto-Tono district, central Japan, were formed by intense kaolinization of lacustrine arkose sediments deposited in small and shallow inland lakes in the late Miocene. Based on mineralogical and stable isotopic (Fe, C, N) studies of Motoyama kaolin deposit in the Seto area, we concluded that it was formed by microbial nitrification and acidification of lacustrine sediments underneath an inland lake. Small amounts of Fe–Ti oxides and Fe-hydroxide in the kaolin clay indicated that iron was oxidized and leached during the kaolinization. The field occurrences indicate that leached ferric iron precipitated on the bottom of the kaolin deposit as limonite crusts, and their significantly fractionated Fe isotope compositions suggest the involvement of microbial activity. The C/N ratios of most of the kaolin clay are distinctly higher than those of modern lacustrine sediment. Although, the possibility of a low-temperature hydrothermal origin of the kaolin deposit cannot be completely ruled out, it is more likely that acidification by dilute nitric acid formed from plant-derived ammonia could have caused the kaolinization, Fe oxidation and leaching. The nitrate-dependent microbial Fe oxidation is consistent with dilute nitric acid being the predominant oxidant.

Lead is a toxic metal, and its characterization in contaminated soils is crucial to the success of a remediation, especially for the soil washing, one of most commonly used technologies. In this study, we propose a convenient approach that combines sedimentary hydro-classification with semi-quantitative powder X-ray diffraction analysis for characterizing the Pb-bearing minerals in soils. The approach was applied to two samples (YYm and YYu-1) collected from a closed Cu–Pb–Zn mine in the Tohoku region of Japan. The samples were taken from adjacent areas but had different appearances (YYm was a gray soil and YYu-1 was a creamy colored soil). The coarser YYm fractions had higher Pb contents than the finer YYm fractions, but the finer YYu-1 fractions (diameters

The Benjamin River apatite prospect in northern New Brunswick, Canada, is hosted by the Late Silurian Dickie Brook plutonic complex, which is made up of intrusive units represented by monzogranite, diorite and gabbro. The IOA ores, composed mainly of apatite, augite, and magnetite at Benjamin River form pegmatitic pods and lenses in the host igneous rocks, the largest of which is 100 m long and 10–20 m wide in the diorite and gabbro units. In this study, 28 IOA ore and rock samples were collected from the diorite and gabbro units. Mineralogical observations show that the apatite–augite–magnetite ores are variable in the amounts of apatite, augite, and magnetite and are associated with minor amounts of epidote-group minerals (allanite, REE-rich epidote and epidte) and trace amounts of albite, titanite, ilmenite, titanomagnetite, pyrite, chlorite, calcite, and quartz. Apatite and augite grains contain small anhydrite inclusions. This suggests that the magma that crystallized apatite and augite had high oxygen fugacity. In back scattered electron (BSE) images, apatite grains in the ores have two zones of different appearance: (i) primary REE-rich zone; and (ii) porous REE-poor zone. The porous REE-poor zones mainly appear in rims and/or inside of the apatite grains, in addition to the presence of apatite grains which totally consist of a porous REE-poor apatite. This porous REE-poor apatite is characterized by low REE (

The Na Son deposit is a small-scale Pb–ZnPb–Zn–Ag deposit in northeast Vietnam and consists of biotite–chlorite schist, reddish altered rocks, quartz veins and syenite. The biotite–chlorite schist is intruded by syenite. Reddish altered rocks occur as an alteration halo between the biotite–allanite-bearing quartz veins and the biotite–chlorite schist. Allanite occurs in the biotite–allanite-bearing quartz veins and in the proximal reddish altered rocks. Rare earth element (REE) fluorocarbonate minerals occur along fractures or at rim of allanite crystals. The later horizontal aggregates of sulfide veins and veinlets cut the earlier reddish altered rocks. The earlier Pb–Zn veins consist of a large amount of galena and lesser amounts of sphalerite, pyrite and molybdenite. The later Cu veins cutting the Pb–Zn veins include chalcopyrite and lesser amounts of tetrahedrite and pyrite. The occurrences of two-phase H2O–CO2 fluid inclusions in quartz from biotite–allanite-bearing quartz veins and REE-bearing fluorocarbonate minerals in allanite suggest the presence of CO2 and F in the hydrothermal fluid. The oxygen isotopic ratios of the reddish altered rocks, biotite–chlorite schist, and syenite range from +13.9 to +14.9 ‰, +11.5 to +13.3 ‰, and +10.1 to +11.6 ‰, respectively. Assuming an isotopic equilibrium between quartz (+14.6 to +15.8 ‰) and biotite (+8.6 ‰) in the biotite–allanite-bearing quartz vein, formation temperature was estimated to be 400°C. At 400°C, δ18O values of the hydrothermal fluid in equilibrium with quartz and biotite range from +10.5 to +11.7 ‰. These δ18O values are consistent with fluid that is derived from metamorphism. Assuming an isotopic equilibrium between galena (+1.5 to +1.7 ‰) and chalcopyrite (+3.4 ‰), the formation temperature was estimated to be approximately 300°C. The formation temperature of the Na Son deposit decreased with the progress of mineralization. Based on the geological data, occurrence of REE-bearing minerals and oxygen isotopic ratios, the REE mineralization is thought to result from interaction between biotite–chlorite schist and REE-, CO2- and F-bearing metamorphic fluid at 400°C under a rock-dominant condition.

The Khaldzan Burgedei peralkaline complex is one of the potential rare metal (Zr&ndash, Nb&ndash, REE) deposits in Mongolia. The complex consists mainly of quartz syenite and granite, and zircon is the most common accessory mineral in the rocks. Based on texture and mineral paragenesis, zircon is classified into three types. Type-I zircons in the quartz syenite and granite are generally isolated and euhedral to subhedral, 25&ndash, 100 &mu, m in size, enclosed by albite, K-feldspar, and quartz. Type-II zircons occur as subhedral to euhedral 20&ndash, 150 &mu, m grains, with quartz, and fluorite in the metasomatized zone in the quartz syenite as well as an upper part of the granite near the contact with the quartz syenite. These zircons contain porous core parts (Type-I) or remnants of corroded xenotime-(Y) and synchysite-(Ce). Type-III zircons are observed in the hydrothermally altered zone in quartz syenite and pegmatite. These zircons are anhedral, fine-grained, 10&ndash, 30 &mu, m in size, and occur in amphibole pseudomorphs which were replaced by quartz, fluorite, chlorite, and hematite. Laser Raman spectra show that Type-I and Type-II zircons contain high amounts of water. Among these, three types of zircons, Type-II zircons are most enriched in REE, Nb, and Th. The texture and composition of the three types of zircons indicate that Type-I, Type-II, and Type-III zircons are magmatic, metasomatic and late hydrothermal in origin, respectively, and they experienced remobilization and recrystallization during the transition from a magmatic to a hydrothermal system.

Zircon (ZrSiO4) from Naegi and Ohro granitic pegmatites, Japan and from Saigon alkali basalt, Vietnam, were mineralogically characterized by inductively couples plasma mass spectrometry (ICP-MS), electron-microprobe analysis (EMPA), X-ray powder diffraction, micro-Raman spectroscopy and leaching experiment. The powder XRD and Raman spectra analyses show that the degree of metamictization increases in the following order: Saigon (crystalline), Ohro (partly metamict) and Naegi zircons (fully metamict). Quantitative analytical results by the EMPA indicate that the Naegi and Ohro zircon samples contain a large amount of REE2O3, while REE2O3 contents in Saigon zircon are below detection limit. The leaching experiments using a solvent 1 M-HCl for the present zircons under the condition at a room temperature to 250 °C and retention time of 30 h resulted in about 100%, 50% and 1% recoveries of REE from the Naegi, Ohro and Saigon zircons, respectively. Leaching experiments for the Naegi zircon at different temperatures and retention time 30 h, showed that a significant amount of REE was leached out at the temperature above 150 °C, although REE were hard to be leached at a room temperature (about 25 °C). Therefore, both low crystallinity of zircon and higher leaching temperature are requisite for effective leaching of REE from zircon.

The crystal chemistry of volcanic allanites from both the Youngest Toba Tuff (YTT), Sumatra, Indonesia and SK100 volcanic ash beds (SK100-VAB), Niigata, Japan has been examined by electron microprobe analysis (EMPA), Fourier-transform infrared spectroscopic analysis (FTIR), and single-crystal structure analysis. In the FTIR study, based on the Diamond ATR accessory, YTT and SK100- VAB allanites were observed to have different OH contents, respectively: the former has 0.64 wt% H2O (OH: 0.40 apfu.), while the latter has 1.65 wt% H2O (OH: 1.00 apfu.). The crystal structures of these two allanites have been refined to individual R indices (3.64 and 4.25) based on 1350 observed reflections (, Fo, > 4sig, ) measured using a single-crystal diffractometer with MoKα X-radiation. The OH-poor YTT allanite has a shorter b axis, a longer c axis, and larger β value than the relatively OH-rich SK100-VAB one. The bond valence sums of O4 (accepter oxygen for H atom) and O10 (donor oxygen for H atom) are 1.962 and 1.709 v.u. for YTT allanite (valence sum: 3.671 v.u.) and 1.754 and 1.271 v.u. for SK100-VAB one (valence sum: 3.025 v.u.). The difference from the ideal total bond valence value (4.00 v.u.) of O4 and O10 in YTT allanite (0.33 v.u.) is smaller than that in SK100-VAB (0.98 v.u.). These difference values are also broadly consistent with the corresponding differences in OH content between the YTT (OH: 0.40 apfu.) and SK100-VAB allanites (OH: 1.00 apfu.) determined by FTIR- ATR. Chemical analyses, FTIR-ATR and crystal structure refinement of YTT and SK100-VAB allanites yielded the following crystal chemical formula: YTT: (Ca0.83Mn2+ 0.06Fe2+ 0.11)(La0.24Ce0.32Pr0.04Nd0.11Sm0.02Th0.04Ca0.21)(Al0.73Fe3+ 0.19Ti0.08)(Al0.89Fe3+ 0.11)(Fe2+ 0.22Fe3+ 0.62Mg0.16)(SiO4)Si2O7O1.6(OH)0.4, SK100-VAB: (Ca0.81Fe2+ 0.13Mn2+ 0.06)(La0.22Ce0.34Pr0.05Nd0.13Sm0.02Th0.02Ca0.22)(Al0.76Fe3+ 0.19Ti0.05)Al1.00(Fe2+ 0.73Fe3+ 0.17Mg0.10)(Si0.96Al0.04O4)Si2O7O(OH). Therefore, it is concluded that welding of the Youngest Toba Tuff caused the following post-crystallization changes to occur in YTT allanite: oxidation of Fe2+ to Fe3+, release of H2, and the concomitant replacement of OH− by O2−. These oxidation and dehydrogenation processes advanced during the welding to thereby produce oxyallanite. Oxyallanite had been reported only in laboratory studies where it was produced by heating natural allanite. Our report on natural oxyallanite suggests that it may be present in other welded silicic volcanic rocks as well.

Euhedral dissakisites from Trimouns dolomite mine, France, is compositionally zoned. Back-scattered electron (BSE) images reveal that each of the described dissakisite crystals has three distinct compositional zones: normal zoned core (Mg-rich), oscillatory zoned middle (Ca–Al-rich) and homogeneous rim (Fe–ΣREE-rich). The latter zone with Fe2+ > Mg corresponds to allanite-(Ce). Dissakisite-(Ce) also displays pronounced zoning in Fe/Mg which may suggest that the temperature of crystallization continuously decreased from core to rim. Despite a systematic increase in Fe/Mg of the dissakisite with an allanite rim, there is no monotonic decrease in the REE zoning: the normal zoned core and homogeneous rim are rich in La, Ce and Pr, but the relatively REE-poor oscillatory zoned middle is relatively abundant in Y, Sm and Gd. Discontinuous variation in REE content of the dissakisite, with the allanite rim may indicate a localized change in either the relative concentration of various ligands or pH of the crystallizing fluid. Observations under the polarizing microscope confirm that the different zones have simultaneous extinction. These chemical and optical observations suggest that epitaxial crystallization of dissakisite, from Trimouns, passes through three formation stages. The ternary Fe2+–Mg2+–(Al + Fe)3+ diagram illustrates that in general dissakisite can be classified into two groups, (Al + Fe)3+-rich and an Mg-rich; dissakisite from Trimouns belongs to the former group. Chondrite-normalized REE patterns of dissakisites from Trimouns are similar to those of allanites formed by hydrothermal fluids. In conclusion, it is clear from the above two geochemical characteristics that dissakisites from Trimouns are of (Al + Fe)3+-type, and were derived from hydrothermal fluids.

Earth Evolution Sciences, Life and Environmental Sciences, University of Tsukuba, �-�-� Tennodai, Tsukuba ��5-8572, Japan Geological Survey of Japan, AIST, �-�-� Higashi, Tsukuba ��5-8567, Japan Chemical Analysis Division, Research Facility Center for Science and Technology, University of Tsukuba, �-�-� Tennodai, Tsukuba ��5-8572, Japan Center for Tsukuba Advanced Research Alliance, University of Tsukuba, �-�-� Tennodai, Tsukuba ��5-8572, Japan

Allanites from the Japanese island arc are not necessarily the same as those from other countries of the world. The study of minerals occurring in the Japanese islands context is integrated into “island arc mineralogy”, which concerns the following space-time continuum: (1) the present island arc, (2) the post-Paleozoic rocks, (3) subduction-related magmatism, (4) volcanic front, (5) tectonic discontinuities, and (6) an abundant variety of minerals, their paucity and characteristic accessory minerals. “Island arc mineralogy” of allanites from Japan is functionally related to (1), (2), (3) and (6). This paper focuses on tectonic setting (intracontinental settings,island arcs, and continental margin), formation age and a variety of host rock types containing allanite, crystal chemisry of REE-rich epidote group minerals, particularly allanite, and geochemical role of their chemical composition, crystal structure and mineral inclusion.

Dissakisites from Trimouns dolomite mine, France, have two kinds of single crystals: chemical-zoned and homogeneous types. Back-scattered electron microprobe (BSE) images of these dissakisites reveal both Ca–Al rich dark zones and Fe-ΣREE rich bright zones. Crystal structures of three dark and two bright zones in a chemical-zoned dissakisite and of a homogeneous zone in unzoned dissakisite were refined to individual R indices (about 3.0–5.0%) based on 1,400 observed [|F 0| > 4σF 0] reflections measured with MoKα X-radiation using the single crystal diffractometer. The differences in brightness between their BSE images arise from those in coupled substitutions of the elements occupying A2 and M3 sites. The main reason for these differences is that ten-coordinated A2 polyhedra and M3 octahedra are directly linked through their shared edge, which creates a great potential for making this coupled substitution. This zoning indicates that formation of the whole zoned crystal, where each zone could be grown steadily with its crystallographic axes mutually parallel to each other, may be identified as autoepitaxy.

The oxidation of Feto Fe, the release of H2, and the concomitant replacement of OH by O would produce an oxy-equivalent of allanite (CaREEAl2FeSi3O11O(OH)) (Dollase 1973). The reaction Fe + OH↔Fe+ O+ 1/2H2 is formally equivalent to the oxy-reaction observed in other hydrous Fe -bearing silicate minerals, such as mica and amphiboles (e.g., Hogg & Meads 1975; Ferrow 1987). However, occurrence of oxyallanite (CaREEAl2FeSi3O11O(O)) in natural environment has never been reported. The purpose of the preset study is to discuss occurrence of natural oxyallanite. Chemical compositions and crystal structures of the allanites from two rhyolitic rocks--(1) Youngest welded tuff from Toba (YTT), Sumatra, Indonesia and (2) volcanic ash from SK100 (SK100-VAB), Niigata, Japan--were determined by electron microprobe analysis and single crystal diffractometer, respectively. Despite the close similarity, in chemical composition, between YTT allalnites and SK100 ones, their unit-cell parameters are distinct from each other. The former have shorter b axis and longer c axis and larger β value in comparison with cell parameters of the latter. FT-IR analysis shows that YTT allanites have both the smaller OH-absorption band area and the shift of its bands to higher wavenumbers as compared to SK100 ones. Welding of the ash flow tuff including the allanites preformed in Youngest Toba welded tuff would cause them to undergo oxidations, dehydration and replacement. The sequential reaction would result in producing the present YTT allanite, namely oxyallanite. Although oxyallanite was only obtained by heating the natural allanite (e.g., Armbruster et al. 2006), this study first reports that oxyallanite may commonly occur in welded rocks at high temperatures.