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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.

Using the Rock Canyon Creek carbonate-hosted rare earth element (REE)–F–Ba deposit as an example, we demonstrate the need for verifying inherited geochemical data prior to reinterpretation. Inherited La, Ce, Nd and Sm data obtained by pressed pellet X-ray fluorescence (XRF), and La and Y data obtained by aqua regia digestion inductively coupled plasma atomic emission spectroscopy (ICP-AES) for more than 300 drill-core samples were analysed in 2009 and were subsequently compared to sample subsets re-analysed using lithium metaborate-tetraborate (LMB) fusion ICP mass spectroscopy (ICP-MS), Na2O2 fusion ICP-MS, and LMB fusion-XRF. We determine that LMB ICP-MS and Na2O2 ICP-MS accurately determined REE concentrations in control reference materials (CRM) SY-2 and SY-4, and provided precision of about 10%. Fusion-XRF was precise for La, Ce and Nd at concentrations greater than ten times the lower detection limit; however, accuracy of this method was not established because REE concentrations in SY-4 were below the lower detection limit. Analysis of the sample subset revealed substantial discrepancies for Ce concentrations determined by pressed pellet XRF in comparison to those determined by other methods due to Ba spectral interference. Samarium, present in lower concentrations than other REE that were determined, was consistently underestimated by XRF methods relative to ICP-MS methods. This may be the result of Sm concentrations approaching the lower detection limits of XRF methods, elemental interference or inadequate background corrections. Aqua regia dissolution results, reporting only for La and Y, are underestimated relative to the other methods. We highlight the importance of selecting the most appropriate analytical method and reference materials for determining the REE content of mineralized rock which may be several orders of magnitude higher than that of typical host rock.

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

Monazite [(Ce, La, Th) PO4], a common accessory mineral in low-Ca felsic rocks and a wide range of metamorphic rocks, is suitable for in situ U–Pb dating, rare earth element (REE) geochemistry, and Nd isotope tracer studies. To link monazite composition with igneous petrogenesis and differentiation, we carried out comprehensive LA-ICP-MS measurements of REE-Th-U abundances and Sm-Nd isotope ratios in monazites from magnetite-series (oxidized type) and ilmenite-series (reduced type) granitic rocks across the Japan arc. The data revealed systematic differences in monazite composition between magnetite-series and ilmenite-series samples, and between pegmatites and granites. In ilmenite-series granitic rocks, monazites from pegmatites showed larger negative Eu anomalies, lower light-REE/middle-REE ratios, and higher middle-REE/heavy-REE ratios than those from granites. These geochemical variations were attributed to significant fractional crystallization of feldspars, monazite, xenotime, and garnet during differentiation in relatively reduced peraluminous granitic magmas. In contrast, there was no remarkable difference in the REE fractionation pattern between magnetite-series pegmatites and granites. Furthermore, the magnitudes of the negative Eu anomalies in the magnetite-series monazites were smaller than those observed in the ilmenite-series samples. These features were interpreted to reflect the suppression of monazite, xenotime, and garnet fractionation and limited Eu incorporation into fractionating feldspars in relatively oxidized and non-peraluminous magmas. In addition, our data demonstrated intra-grain variations in REE-Th-U compositions in a monazite from the Masaki ilmenite-series pegmatite, despite its homogenous Nd isotope composition. These variations suggest that the core and rim of the grain crystallized from distinct magmas that were generated from similar crustal rocks, but were differentiated under different conditions. A comparison of the present data with previously reported data indicates that igneous monazites from granitic rocks are distinct from a wide range of metamorphic monazites in REE-Th-U composition, especially due to their larger negative Eu anomalies. This finding highlights the potential utility of monazite REE-Th-U systematics as a provenance indicator for detrital monazites.

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.

Apatite, which is used in the production of phosphorus fertilizers, contains small amounts of rare earth elements (REEs; 0.1–1%). Apatite deposits occur all over the world and thus have the potential to be a secure source of REEs. We investigated a method for recovery of REEs from an apatite sample; specifically, REEs were leached from the sample with an H2SO4 solution, the acid that is most commonly used for fertilizer production. At high H2SO4 concentrations, most of the REEs in the solution were lost to precipitation as insoluble gypsum (CaSO4·2H2O). However, at H2SO4 concentrations of

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.

The Blockspruit fluorite prospect, located in North West State of the Republic of South Africa, occurs within an actinolite rock zone that was emplaced into the Kenkelbos-type granite of Proterozoic age. There are a large number of termite mounds in the prospect. For geochemical prospecting for rare earth elements (REEs), in total, 200 samples of termite mound material were collected from actinolite rock and granite zones in the prospect. Geochemical analyses of these termite mound materials were conducted by two methods: portable X-ray fluorescence (XRF) spectrometry and inductively coupled plasma-mass spectrometry (ICP-MS). Comparison of the two methods broadly indicates positive correlations of REEs (La, Ce, Pr, Nd, and Y), in particular Y and La having a strong correlation. As the result of modal abundance analyses, the actinolite rock at surface mainly consists of ferro-actinolite (89.89 wt%) and includes xenotime (0.26 wt%) and monazite (0.21 wt%) grains as REE minerals. Termite mound materials from actinolite rock also contain xenotime (0.27 wt%) and monazite (0.41 wt%) grains. In addition, termite mound materials from the actinolite rock zone have high hematite and Fe silicate contents compared to those from granite zone. These relationships suggest that REE minerals in termite mound materials originate form actinolite rock. Geochemical anomaly maps of Y, La, and Fe concentrations drawn based on the result of the portable XRF analyses show that high concentrations of these elements trend from SW to NE which broadly correspond to occurrences of actinolite body. These results indicate that termite mounds are an effective tool for REE geochemical prospection in the study area for both light REEs and Y, but a more detailed survey is required to establish the distribution of the actinolite rock body.

The crystal chemistry of anorthite with low content of albite (An92.0 Ab3.4), part of a rapidly cooled anorthite megacryst occurring in 1940 ejecta from Miyake-jima volcano, Japan, has been investigated using a single-crystal X-ray diffractometer and an electron microprobe analyzer with wavelength dispersive X-ray spectroscopy (EMPA-WDS). The structure was refined in space group P1̅ and cell parameters, a=8.182(6) Å, b=12.883(4) Å, c=7.092(4) Å, α=93.19(4)°, β=115.91°(4), γ=91.18°(4). The final weighted R-factor is 3.77% for 1549 reflections. Averaged T-O distances are 1.681 Å for T1(0), 1.674 Å for T1(m), 1.677 Å for T2(0) and 1.680 Å for T2(m), indicating Al occupancies of 0.501, 0.453, 0.472, and 0.496, respectively. These results suggest that the Al/Si-distribution in the tetrahedral framework is highly disordered (QOD=0.06), which results in bisection of the c-period in Al/Si ordered anorthites (c∼14 Å). Chemical composition of the refined crystal obtained by EMPA-WDS is (Ca0.93 Na0.03 Fe0.02□0.01)(Mg0.01 Al1.94 Si2.05)O8. The extra-framework site-populations consist of the following two: (1) A(000) site occupied by Ca (86%), Na (8%), Fe2+ (4%) and □(2%), and (2) A(zi0) site by Ca (100%). The Al/Si tetrahedral framework is hence pseudo-face-centered in symmetry (C1ʩ so that both extra-framework cations and their defects appear to reduce the symmetry of the overall structure to P1ʮ Although the Al/Si disordered anorthite can be interpreted as a metastable phase, the observed chemical non-stoichiometry may stabilize such a metastable structure by introducing minor -Si4+-O-Si4+- bonds into the tetrahedral framework and anti-phase-boundary.

We have conducted geochemical and mineralogical investigations of the rare earth and yttrium (REY)-rich mud from the Minami-Torishima area in the Pacific in order to clarify the concentration of REY and their host-phase in the mud. X-ray diffraction analysis shows that the mud is mainly composed of phillipsite, fluorapatite, quartz, albite, illite and montmorillonite. Whole-rock CaO, P2O5 and total REY contents of the mud are positively correlated. Relative abundance of apatite is also positively correlated to P2O5 and total REY contents. These correlations suggest that apatite is the main host of the P2O5 and REY in the mud. We make in situ compositional analyses of constituent minerals in the REY mud. The results show that the apatite is abundant in REY (9300–32,000 ppm) and is characterized by a negative Ce anomaly and enrichment in heavy rare-earth elements. This abundance and composition of REY of the mud is similar those of fish debris apatites. In contrast, phillipsite is less abundant in REY (60–170 ppm). Therefore we conclude that the main REY host phase of the mud is apatite.

The two drill holes, which penetrated sub-horizontal rare earth element (REE) ore units at the Nechalacho REE in the Proterozoic Thor Lake syenite, Canada, were studied in order to clarify the enrichment mechanism of the high-field-strength elements (HFSE: Zr, Nb and REE). The REE ore units occur in the albitized and potassic altered miaskitic syenite. Zircon is the most common REE mineral in the REE ore units, and is divided into five types as follows: Type-1 zircon occurs as discrete grains in phlogopite, and has a chemical character similar to igneous zircon. Type-2 zircon consists of a porous HREE-rich core and LREE–Nb–F-rich rim. Enrichment of F in the rim of type-2 zircon suggests that F was related to the enrichment of HFSE. The core of type-2 zircon is regarded to be magmatic and the rim to be hydrothermal in origin. Type-3 zircon is characterized by euhedral to anhedral crystals, which occur in a complex intergrowth with REE fluorocarbonates. Type-3 zircon has high REE, Nb and F contents. Type-4 zircon consists of porous-core and -rim, but their chemical compositions are similar to each other. This zircon is a subhedral crystal rimmed by fergusonite. Type-5 zircon is characterized by smaller, porous and subhedral to anhedral crystals. The interstices between small zircon grains are filled by fergusonite. Type-4 and type-5 zircon grains have low REE, Nb and F contents. Type-1 zircon is only included in one unit, which is less hydrothermally altered and mineralized. Type-2 and type-3 zircon grains mainly occur in the shallow units, while those of type-4 and type-5 are found in the deep units. The deep units have high HFSE contents and strongly altered mineral textures (type-4 and type-5) compared to the shallow units. Occurrences of these five types of zircon are different according to the depth and degree of the hydrothermal alteration by solutions rich in F and CO3, which permit a model for the evolution of the zircon crystallization in the Nechalacho REE deposit as follows: (i) type-1 (discrete magmatic zircon) is formed in miaskitic syenite. (ii) LREE–Nb–F-rich hydrothermal zircon formed around HREE-rich magmatic zircon (type-2). (iii) type-3 zircon crystallized through the F and CO3-rich hydrothermal alteration of type-2 zircon which formed the complex intergrowth with REE fluorocarbonates; (iv) the CO3-rich hydrothermal fluid corroded type-3, forming REE–Nb-poor zircon (type-4). Niobium and REE were no longer stable in the zircon structure and crystallized as fergusonite around the REE–Nb-leached zircon (type-4); (v) type-5 zircon is formed by the more CO3-rich hydrothermal alteration of type-4 zircon, suggested by the fact that type-4 and type-5 zircon grains are often included in ankerite. Type-3 to type-5 zircon grains at the Nechalacho REE deposit were continuously formed by leaching and/or dissolution of type-2 zircon in the presence of F- and/or CO3-rich hydrothermal fluid. These mineral associations indicate that three representative hydrothermal stages were present and related to HFSE enrichment in the Nechalacho REE deposit: (i) F-rich hydrothermal stage caused the crystallization of REE–Nb-rich zircon (type-2 rim and type-3), with abundant formation of phlogopite and fluorite; (ii) F- and CO3-rich hydrothermal stage led to the replacement of a part of REE–Nb–F-rich zircon by REE fluorocarbonate; and (iii) CO3-rich hydrothermal stage resulted in crystallization of the REE–Nb–F-poor zircon and fergusonite, with ankerite. REE and Nb in hydrothermal fluid at the Nechalacho REE deposit were finally concentrated into fergusonite by way of REE–Nb–F-rich zircon in the hydrothermally altered units.

Electron-microprobe analyses were carried out on monazite from magnetite-series and ilmenite-series granitic rocks in Japan. All of the samples examined consist of monazite-(Ce), except for a unique case of monazite-(Sm) in the Shimo-ono ilmenite-series granitic pegmatite. The observed variations in their chemical composition are largely explained by the huttonite exchange [(Th + U) 4+ ↔Si 4+ ], and subordinately by the cheralite exchange [(Th + U) 4+ ↔2Ca 2+ ]. However, there are differences in the degree of contribution of the two exchanges between monazite grains from magnetite-series and ilmenite-series granitic rocks. The cheralite exchange is more important for monazite grains in ilmenite-series granitic rocks than for those in magnetite-series granitic rocks. Monazite grains in Japanese granitic rocks of these two series characteristically have a low cheralite component compared to those in S-type granites from various regions in the world, but chemical characteristics of ilmenite-series granitic rocks are more similar to S-type granitic rocks than those of the magnetite-series. The monazite grains of the Japanese granitic rocks show a continuous decrease in the slope of chondrite-normalized REE patterns from magnetite-series granites [(La/Sm)cn: 6.22–7.50] to ilmenite-series granitic pegmatite [(La/Sm)cn: 0.09–1.88] through magnetite-series granitic pegmatite [(La/Sm)cn: 2.25–3.70] and ilmenite-series granites [(La/Sm)cn: 2.13–4.56]. Thus, the REE compositions of the monazites reflect the degree of fractionation from granites to granitic pegmatites in both series. The same trend is confirmed by the (La/Nd)cn value, resulting in a positive correlation between (La/Nd)cn and (La/Sm)cn values of monazite from Japanese granitic rocks. Because the whole rock REE compositions of the magnetite-series and ilmenite-series granites show higher and lower (La/Sm)cn-(La/Nd)cn values, respectively, which are identical to the values of the respective granites-series monazites, we conclude that the chemical compositions (especially REE compositions) of monazite reflect the types (magnetite-series or ilmenite-series) and the degree of differentiation (granite or granitic pegmatite) of the granitic rocks in the subduction-related magmatic arcs.

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.

Zircon from granitic rocks, Japan is classified into two major types; based on the minor element content determined by electron microprobe, a heavy rare earth element (HREE)-U-Thpoor (Type I) and a HREE-U-Th-rich (Type 2). Zircons characteristically occurring in common granites of type-1 are relatively poor in HREE including Y and Sc, up to 2.72 wt% HREE2O3; up to 0.44 wt% ThO2; up to 2.10 wt% UO2, while zircons characteristically occurring in granitic pegmatites of type-2 are much richer in HREE including Y and Sc, up to 18.99 wt% HREE2O3; up to 11.09 wt% UO2; and up to 6.58 wt% ThO2 However, analyses showing a significantly high amount of REE+Y almost certainly represent altered zircon and/or accidental analysis of inclusions (Hoskin & Schaltegger 2003). Only crystal structure of zircon free of inclusions and zoning (type-2; Takenouchi granitic pegmatite) was refined to R = 4.3 % and for the first time has been confirmed that zircons of type-2 exist as a single-crystal phase in nature. .

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.

Recent increase of the demand for rare earth elements (REEs), especially dysprosium and terbium used in the permanent magnet industry is modifying a concept of the REE mineralogy and resources. This is amplified by the REE supply restrictions outside of China. Exploration has been extended worldwide to secure the supply of REEs, especially the heavy ones. In recent years, various attempts are made to produce heavy rare earth elements (HREEs) from unconventional sources, such as peralkaline igneous rocks, which have not been regarded as a REE source. Therefore, this paper reviews the potential sources of REEs, especially HREEs (ion-adsorption types and apatite deposits), which are regarded as the most critical group of elements for the future green technologies.

We have investigated allanite phenocrysts and the apatite and zircon inclusions they contain from three localities: (1) SK100 ash beds, Niigata, Japan, (2) the youngest Toba Tuff (YTT), Sumatra, Indonesia, and (3) the Bishop Tuff (BST) in eastern California, to gather geochemical inferences about the magmas from which these phases crystallized using an electron microprobe. Back-scattered electron (BSE) images reveal the presence of euhedral crystals of apatite (5–30 μm) and zircon (5–20 μm) incorporated into euhedral phenocrysts of allanite. Textural evidence suggests that apatite, zircon and allanite crystallized in that order. Furthermore, the chondrite-normalized REE pattern of apatite inclusions in these allanite phenocrysts resembles that of apatite in syenites and unfractionated carbonatites. This characteristic suggests that apatite inclusions crystallized from relatively alkaline magmas rich in REE, CO32− and PO43−. Such a magmatic signature could perhaps represent that of a boundary-layer melt. In addition, the F/Cl and Mn/Fe values of the apatite inclusions imply that the relative SiO2 contents of such magmas increase in order SK100 → YTT → BST. Variations in Y and Hf contents and Zr/Hf value among the zircon inclusions also show that they crystallized from mafic (SK100), intermediate (YTT), and felsic (BST) magmas. The host rocks are similar to magnetiteseries granites from Japan, according to two characteristics of the allanite: (1) appreciable amounts of Mg (0.078–0.165 apfu ) and Ti (0.057–0.137 apfu ) and (2) chondrite-normalized REE pattern. The petrogenetic processes envisaged for crystallization of allanite phenocrysts and their apatite and zircon inclusions can explain differences in (1) the REE pattern between allanite and apatite, (2) variations in minor elements among allanite, apatite and zircon, and (3) occurrences of minerals associated with the allanite phenocrysts.

The isotopic compositions of Sr and Nd were analyzed for sixteen samples of allanite-(Ce) from Mesozoic–Cenozoic granitic rocks in Japan (11 samples of an Mn-rich type, and five samples of an Mn-poor type). The Mn-rich allanite-(Ce) crystals have an initial 87Sr/86Sr value in the range 0.70811–0.71398 and an initial 143Nd/144Nd value in the range 0.512148–0.512471, whereas for crystals of Mn-poor allanite-(Ce), the analogous intervals are 0.70499–0.70704 and 0.512547–0.512606. There is a negative correlation between 87Sr/86Sr and 143Nd/144Nd values. The trend of these isotopic data for Mn-rich and Mn-poor allanite-(Ce) is parallel to that for ilmenite- and magnetite-series granitic rocks from Japan, respectively. This parallelism suggests that the genesis of these two groups of allanite-(Ce) is related to that of ilmenite-series and magnetite-series granitic rocks. The characteristics of allanite-(Ce) can shed light on the petrogenesis of granitic rocks.

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.

Nous avons caracterise avec une microsonde electronique la composition chimique de vingt-deux echantillons d'allanite-(Ce) provenant de roches granitiques au Japon. Les images formees par les electrons retrodiffuses montrent que l'allanite-(Ce) est homogene ou zonee de facon oscillatoire, normale ou irreguliere. Treize echantillons font preuve de quantites importantes de Mn (0.14-0.59 apfu). Les cristaux riches en Mn sont plus longs (2-6 cm) que les cristaux a plus faible teneur en Mn (0.5-2 cm). Ces deux groupes d'allanite-(Ce) different considerablement dans leurs spectres de terres rares normalises par rapport a une chondrite. L'allanite-(Ce) a faible teneur en Mn est relativement enrichie en terres rares legeres (TRL), comme c'est generalement le cas dans l'allanite des roches ignee, tandis que l'allanite-(Ce) riche en Mn montre un enrichissement dans les terres rares moyennes (TRM). La relation entre les deux groupes se decrit par une substitution couplee: Mn 2+ (TRM, TR lourdes) 3+ ⇄ Ca 2+ + TRL 3+ . La presence d'allanite-(Ce) manganifere dans les granites de l'arc insulaire japonais, de meme que les indices de mineraux du groupe de l'epidote riches en Mn et en terres rares dans les gisements de manganese, semblent temoigner d'un lien avec les phenomenes de subduction. Les roches granitiques contenant l'allanite-(Ce) pauvre en Mn font partie de la serie de roches granitiques a magnetite, tandis que les roches granitiques contenant l'allanite-(Ce) riche en Mn correspondent a la serie a ilmenite, et se seraient formees de magmas enrichis en composants volatils. C'est donc dire que la teneur de l'allanite-(Ce) en M serait un indicateur de l'origine des roches granitiques.

The crystal structure of allanite from granitic pegmatite, the Daibosatsu Pass, Yamanashi, Japan, has been refined under the constraint of chemical composition determined by electron microprobe analysis of rare earth elements. Back-scattered-electron images and X-ray element maps of the allanites show that each of their crystal grains has chemically homogeneous distribution of major elements. A typical formula for the chemistry is: (Ca0.920☐0.080)Σ1.000(La0.238Ce0.443Pr0.048Nd0.100Sm0.019Th0.042Mn0.008☐0.102)Σ1.000(Al0.607Fe0.3173+Ti0.076)Σ1.000(Al1.000)(Fe0.5432+Fe0.3653+Mn0.055Mg0.037)Σ1.000(SiO4)(Si2O7)O(OH).The crystal structure of allanite, monoclinic, a 8.905 (1), b 5.7606 (5), c 10.123 (1) Å, β 114.78°(1), space group P21/m, Z = 2, has been refined to an unweighted R factor of 3.46% for 1459 observed reflections. Although the H atom position was not determined on the Difference-Fourier map, inspection of the bond valence sums demonstrates that the H atom is uniquely located at the O10 atom and involved in a hydrogen bond to O4. A systematic examination as to crystal chemistry of allanites suggests that the isolated SiO4 tetrahedron has the largest distortion of three kinds of the tetrahedron containing Si2O7 groups in the allanite structure. This observation is common to the epidote group minerals, while the larger distortion of A2 sites caused by occupancy by REE in allanites contrasts with the smaller one of A sites in other epidote group minerals. In the allanite groups the bond angles between the O10–H bond and hydrogen bond H···O4 are found to range from 170 to 180°.Compilation of the chemical compositions of the title allanite and the others from granitic rocks, Japan, which reveals Th-incorporation as the coupled substitution of 3Th4+ + ☐ (vacancy) ⇌ 4REE3+, provides an explanation for the observation that higher Th concentrations characterize allanites from the island arcs. The ternary Al2O3-Fe2O3-ΣREE diagram illustrates that allanites are grouped, according to their origins, into three classes suggestive of tectonic backgrounds for the crystallization localities; (1) intracontinental, (2) island arc and (3) continental margin.

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.