Neutron-capture elements in halo,thick-disk,and thin-disk stars: Neodymium

We have derived the LTE neodymium abundances in 60 cool stars with metallicities [Fe/H] from 0.25 to ?1.71 by applying a synthetic-spectrum analysis to spectroscopic observations of NdII lines with a resolution of λ/Δλ?60 000 and signal-to-noise ratios of 100–200. We have improved the atomic parameters of NdII and blending lines by analyzing the corresponding line pro files in the solar spectrum. Neodymium is overabundant with respect to iron in halo stars, [Nd/Fe]=0.33±0.09, with the [Nd/Fe] ratio decreasing systematically with metallicity when [Fe/H]>?1. This reflects an onset of efficient iron production in type I supernovae during the formation of the thick disk. The [Nd/Ba] and [Nd/Eu] abundance ratios behave differently in halo, thick-disk, and thin-disk stars. The observed abundance ratios in halo stars, [Nd/Ba]=0.34±0.08 and [Nd/Eu]=?0.27±0.05, agree within the errors with the ratios of the elemental yields for the r-process. These results support the conclusion of other authors based on analyses of other elements that the r-process played the dominant role in the synthesis of heavy elements during the formation of the halo. The [Nd/Ba] and [Nd/Eu] ratios for thick-disk stars are almost independent of metallicity ([Nd/Ba]=0.28(±0.03)?0.01(±0.04) [Fe/H] and [Nd/Eu]=?0.13(±0.03)+0.05(±0.04) [Fe/H]) but are smaller in absolute value than the corresponding ratios for halo stars, suggesting that the synthesis of s-process nuclei started during the formation of the thick disk. The s-process is estimated to have contributed ?30% of the neodymium produced during this stage of the evolution of the Galaxy. The [Nd/Ba] ratio decreases abruptly by 0.17 dex in the transition from the thick to the thin disk. The systematic decrease of [Nd/Ba] and increase of [Nd/Eu] with increasing metallicity of thin-disk stars point toward a dominant role of the s-process in the synthesis of heavy elements during this epoch.     

1992 compilation of analytical data for rare-earth elements, scandium, yttrium, zirconium and hafnium in twenty-six GSJ reference samples

Abstract: Analytical data for fourteen rare-earth elements, scandium, yttrium, zirconium and hafnium, received by May 1992, have been compiled on twenty-six GSJ (Geological Survey of Japan) reference samples. Seventeen of them are 'Igneous rock series' and nine are "Sedimentary rock series". The reported data including personal communication were evaluated under the consideration on analytical methods and geochemical evidences. No significant difference has been observed between the values obtained by the different analytical methods. Based on the selected available data, 1992 compilation values were tabulated.     

Revised magnesium abundances in galactic halo and disk stars

A differential analysis of the magnesium abundances in 61 F-K dwarfs and subgiants with metallicities ?2.6<[Fe/H]<+0.2 is performed based on published observational data. Fundamental parameters for 36 stars are determined: T _eff from V-K and V-R; logg from HIPPARCOS parallaxes, and [Fe/H] and ξ_t from Fe II lines. The computations allow for non-LTE effects in the formation of the Mg I lines. For most of the stars, the standard errors in the Mg abundances do not exceed 0.07 dex. The metallicity dependence of [Mg/Fe] is analyzed. Magnesium shows a constant overabundance relative to Fe of 0.46±0.06 dex for metallicities ?2.6<[Fe/H] $\overline {[Mg/Fe]} = + 0.22 dex$ ) compared to the [Mg/Fe] values for other stars with similar [Fe/H].     

Anomalous rare earth element,yttrium and zirconium mobility associated with uranium mineralization

The mobility of REE, Y and Zr during the Variscan uranium mineralization event in high‐grade metasediments of the Bohemian Massif, Czech Republic has been investigated to understand their behaviour in alkaline hydrothermal alterations. The REE patterns together with high mobility of Y and Zr point to movement of REE, Y, Zr and U by highly mineralising, oxidising basinal fluids in the Permian. Their high mobility during the origin of an economically important uranium mineralization is supported by the occurrence of Y‐ and Zr‐rich coffinite.     

The motion of halo stars in dynamical numerical models of open clusters

Equations of motion containing a small parameter μ are derived for stars at the peripheries of open star clusters. The parameter μ is obtained for six numerical open-cluster models. The general analytical solution of these equations of motion for μ = 0 is found. An iterative method is used to derive the frequencies of the stellar motions for first-order expansions in μ of the solutions of the equations of motion for stars at the cluster periphery. Applications of the results are discussed.     

Rare earth elements and yttrium in lithotypes of Bulgarian coals

Rare earth element and yttrium abundances in vitrain, xylain, liptain, fusain and whole coal samples from Bulgarian coal deposits have been studied. Vitrain, xylain, and liptain are depleted, while fusain is enriched in REE and Y as compared to the whole coal samples from which they were selected. Chondrite-normalized patterns show relative enrichment of light (LREE) against heavy (HREE) rare earth elements, negative Eu anomaly, and positive Lu anomaly. The shale-normalized patterns of the lithotypes reveal an increase from LREE to HREE, while those of the whole coal samples and mineral interlayers are less fractionated. The petrographic composition of the coals is of secondary importance for the concentration of the REE and Y. The main factors are the source area and the input of dissolved REE and Y into the coal depositional sites.     

稀土元素及钇在东太平洋CC区深海泥中的富集特征与机制

东太平洋CC区深海泥具有高的REY(REE+Y)含量,理解其富集机制对于寻找深海稀土资源具有重要意义。本文对WPC1101站位的沉积物柱状样开展了沉积物类型、粒度、黏土矿物和元素组成分析,结合已有资料探讨研究区深海泥的稀土元素富集特征及其形成机制。研究区深海泥主要以远洋黏土和硅质生物组分为主,其∑REY范围主要为400~1 000 μg/g。深海泥北美页岩标准化后的REY配分模式具有显著的负Ce异常,指示富稀土深海泥中海相自生组分贡献较大。根据统计发现,研究区深海泥的∑REY与Al2O3、MnO、P2O5均具有良好的相关性,黏土组分、铁锰氧化物和磷酸盐对REY都有贡献。通过综合分析,提出研究区富稀土泥中高P含量是高∑REY重要的控制因素。     

Fractionation in the solar nebula: condensation of yttrium and the rare earth elements

The condensation of Y and the rare earth elements (REE) from the solar nebula may be controlled by thermodynamic equilibrium between gas and condensed solids. Highly fractionated REE patterns may result if condensates are removed from the gas before condensation is complete. It is found that the fractionation is not a smooth function of REE ionic radius but varies in an extremely irregular pattern. Both Yb and Eu are predicted to be extremely depleted in the early condensate without the requirement of condensation in the divalent state. The model is discussed with respect to a highly fractionated pattern observed by Tanaka and Masuda (Icarus19, 523–530 1973), in a pink Ca-Al-rich inclusion from the Allende meteorite and can account for the abundances of each REE determined. According to the model this inclusion represents a condensate from a previously fractionated gas rather than from a gas of solar composition. Before the condensation of this inclusion, an earlier condensate was formed and was removed from equilibrium with the gas.     

Partitioning of rare earth elements, yttrium, and some major elements among source rocks, liquid and vapor of Larderello-Travale geothermal field, Tuscany (Central Italy)

Rare earth elements (REE), yttrium and some major element concentrations have been measured in the high-enthalpy fluids (HEF) of several geothermal wells and the fluid′s source rocks in the Larderello-Travale area (Tuscany/Central Italy). The REE and Y abundances in the HEF range from 0.1 to about 10 pmol/kg and are slightly higher in the HEF originating from evaporite/carbonate sequences (Calcare Cavernoso) than in those from phyllites. The resulting REY distribution factors between HEF and source rocks, ^appKdsource-rockHEF defined as the ratios of REY/Ca in both phases, range from <0.01 to 0.03 and 0.03 to 0.1 for phyllites and evaporite-limestone sequences (Calcare Cavernoso), respectively. REE+Y are more retained by the source rocks than Ca. HEF show no inherited and, with exception of a small Y anomaly, no acquired anomalies. This indicates a static equilibrium between HEF and the source rocks. The absence of any Eu anomalies points to temperatures less than 250°C in the source region. The small negative Y anomalies are the result of Y depletion in the rock fractions taking part in the water-rock interaction.Due to depressurization of the HEF to about 120°C and 2 bars, a liquid and a vapor phase is produced, which were sampled for the determination of the REE+Y partitioning between the two phases. The apparent partition factors between vapor and liquid ^appDliquidvapor of REE+Y range between 0.05 to 0.2 and about 3 for HEF originating from the phyllites and evaporites/carbonates, respectively. Among all ionic species determined, only NH₄⁺ has an apparent partition factor ^appDliquidvapor above one. In general, REY partition more easily into the vapor phase than the earth alkaline and alkaline elements. No significant correlation of REE+Y in the vapor phase with any of the determined ionic species could be detected. This probably points to the dominant presence of ion pairing such as REY(OH)₃^o or REYO(OH)^o.     

Abundance and distribution of the rare-earth elements and yttrium in the rocks and minerals of the Oka carbonatite complex,Quebec

are-earth (REE) and yttrium abundances were determined, by an ion-exchange-X-ray fluorescence procedure, for whole-rock (14) and mineral (87) samples from the Oka carbonatite complex. Whole-rock and mineral data indicate a trend of total REE + Y enrichment, and relative enrichment in light REE, in the order: ultrafenites < ijolites < okaites. The sövites may show wide variations in total REE + Y concentrations, but relative REE abundance patterns will be similar. The greatest REE and Y concentrations occur in apatite, niocalite, perovskite and pyrochlore. Many of the minerals show europium anomalies (both positive and negative), and these are believed to be the result of closed system competition between the various minerals for divalent Eu. The partition coefficients for mineral pairs are quite variable, indicating that the Oka rocks were emplaced through a wide-range of physicochemical and/or nonequilibrium conditions. A reasonable model for the origin of the complex involves a limited partial melting of mantle material, emplacement of the melt in a magma chamber, crystallization of mafic minerals resulting in a residual liquid which produced ijolite and subsequently okaite, and crystallization of the carbonatites from a volatile-rich, possibly immiscible, phase.     

The aqueous geochemistry of the rare earth elements and yttrium. Part 7. REE,Th and U contents in thermal springs associated with the Idaho batholith

Concentrations of the rare earth elements (REE), Th and U have been determined in thermal waters emerging from a number of locations in and around the Idaho Batholith. Previous investigators have suggested that the source of heat for the geothermal systems studied is the radioactive decay of K, Th and U which are enriched in the rocks through which the fluids flow. Thus, knowledge of the behavior of REE, Th and U in these systems may contribute to a better understanding of the potential consequences of the interaction of hydrothermal fluids with deeply buried nuclear waste. Such studies may also lead to the possible use of REE as an exploration tool for geothermal resources. The thermal waters investigated may be characterized as near-neutral to slightly alkaline, dilute, NaHCO₃-dominated waters with relatively low temperatures of last equilibration with their reservoir rocks (<200°C). REE, Th and U concentrations were measured using Fe(OH)₃ coprecipitation, followed by ICP-MS, which yielded detection limits of 0.01–0.003 μg/l for each element, depending on the volume of fluid sample taken. The concentrations of REE, Th and U measured (from <0.1 up to a few μg/l) are 3–5 orders of magnitude less than chondritic, in agreement with concentrations of these elements measured in other similar continental geothermal systems. The REE exhibit light REE-enriched patterns when normalized to chondrite, but when normalized to NASC or local granites, they exhibit flat or slightly heavy REE-enriched trends. These findings indicate that the REE are either taken up in proportion to their relative concentrations in the source rocks, or that the heavy REE are preferentially mobilized. Concentrations of REE and Th are often higher in unfiltered, compared to filtered samples, indicating an important contribution of suspended particulates, whereas U is apparently truly dissolved. In some of the hot springs the REE concentrations exhibit marked temporal variations, which are greater than the variations observed in major element concentrations, alkalinity and temperature. There are also variations in the fluid concentrations of REE, Th and U related to general location within the study area which may be reflective of variations in the concentrations of these elements in the reservoir rocks at depth. Thermal waters in the southern and central parts of the field area all contain ∑REE concentrations exceeding 0.1 μg/l (up to as high as 3 μg/l), Th exceeding 0.2 μg/l and U generally <0.4 μg/l. In contrast, thermal waters from the northern area contain lower ∑REE (<0.6 μg/l) and Th (<0.1 μg/l), but higher U (>3.0 μg/l). Using experimentally measured and theoretically estimated thermodynamic data, the distribution of species for La, Ce and Nd have been calculated and also the solubility of pure, endmember (La, Ce, Nd) phosphate phases of the monazite structure in selected hot spring fluids. These calculations indicate that, at the emergence temperatures, CO²⁻₃ and OH⁻ complexes of the REE are the predominant species in the thermal waters, whereas at the deep-aquifer temperatures, OH complexes predominate. In these thermal waters, monazite solubility is strongly prograde with respect to temperature, with solubility often decreasing several orders of magnitude upon cooling from the deep-aquifer to the emergence temperature. At the surface temperature, calculated monazite solubilities are, within the uncertainty of the thermodynamic data, comparable to the REE concentrations measured in the filtered samples, whereas at the deep-aquifer temperature, monazite solubilities are generally several orders of magnitude higher than the REE concentrations measured in the filtered or unfiltered samples. Therefore, a tentative model is suggested in which the thermal fluids become saturated with respect to a monazite-like phase (or perhaps an amorphous or hydrated phosphate) upon ascent and cooling, followed by subsequent precipitation of that phase. The temporal variations in REE content can then be explained as a result of sampling variable mixtures of particulate matter and fluid and/or variable degrees of attainment of equilibrium between fluid and solid phosphate.     

Rare earth elements, yttrium and H, O, C, Sr, Nd and Pb isotope studies in mineral waters and corresponding rocks from NW-Bohemia, Czech Republic

The sparkling waters from the area of Kyselka near Karlovy Vary at the western slope of the Doupovske hory, Bohemia (Czech Republic), and CO₂-poor waters from two underground boreholes at Jachymov, Krusne hory, Bohemia, have been studied with the aim of characterizing the distribution of rare earth elements, yttrium, and H, O, C, Sr, Nd, Pb isotopes during the low-temperature alteration processes of the host rocks. Additionally, leaching experiments were performed at pH 3 on the granitic and basaltic host rocks from Kyselka and the granite of Jachymov. All REE patterns of the granite- and the basalt-derived waters from the Kyselka area are different from those of their source rocks and the leachates of the latter. This elucidates the inhomogeneous distribution of REE and Y among the solid phases in the altered magmatic rocks. The Eu and Ce anomalies in granite-derived waters are inherited, the Y anomaly is achieved by fluid migration. Yttrium is always preferentially leached by mineral waters, whereas Y/Ho ratios of rocks and their leachates are very similar. The REE abundances in waters from the wells in Jachymov are derived from rocks intensely leached and depleted in easily soluble REE-bearing minerals, whereas the granites and basalts from Kyselka still contain soluble, REE-bearing minerals. A comparison of REE/Ca patterns of the experimental leachates with those of the mineral waters elucidate the high retention of REE in rocks during water–rock interaction. In strongly altered rocks Sr isotope ratios of mineral waters and rocks differ widely, whereas the corresponding Nd isotope ratios are very similar. ²⁰⁷Pb/²⁰⁸Pb, ²⁰⁶Pb/²⁰⁸Pb and ²⁰⁶Pb/²⁰⁷Pb ratios in mineral waters are independent from U/Th ratios in the rocks. ²⁰⁶Pb/²⁰⁸Pb and ²⁰⁶Pb/²⁰⁷Pb are lower in mineral waters than in their source rocks and their leachates, which indicates that Pb is primarily derived from solid phases that do not contain significant contents of leachable U and Th. Thus, mineral waters, although CO₂ rich, only interact with surface films on minerals and not with the bulk of the minerals as in the leaching experiments.Calculation of mixing ratios of waters from the granitic and basaltic sources of the waters from the Kyselka area yield about 40% of water from the underlying granite in water recovered from the basalt, whereas the granite-derived water is mixed with only about 5% of the water from the basalt.     

A study of rare earth elements in the atmospheres of chemically peculiar stars. Pr III and Nd III lines

We determine the abundances of Pr and Nd in the atmospheres of magnetic and non-magnetic chemically peculiar stars from the lines of rare earth elements in the first and second ionization states. The computations for the magnetic stars take into account the influence of the magnetic field on line formation. We studied the influence of errors in the stellar-atmosphere parameters and the atomic parameters of the spectral lines on the accuracy of abundance determinations. Within the derived accuracy, ionization equilibrium is satisfied in the atmospheres of non-pulsating magnetic and non-magnetic stars (so that abundances derived separately from lines of first and second ions agree). For all the pulsating magnetic (roAp) stars studied, the abundances derived from lines of second ions are 1.0 to 1.7 dex higher than those derived from first ions. The violation of ionization equilibrium in the atmospheres of pulsating stars is probably due to, first, considerable enrichment of Pr and Nd in the uppermost atmospheric layers, and second, a higher location for the layer of enhanced elemental abundance in roAp stars than in non-pulsating stars. Two objects from the list of non-pulsating magnetic stars, HD 62140 and HD 115708, exhibit anomalies of their Pr and Nd lines characteristic of roAp stars. The differences in the rare earth anomalies for the pulsating and non-pulsating peculiar stars can be used as a selection criterion for candidate roAp stars.     

新疆哈巴河县托库孜巴依金矿床26号矿脉盲矿预测的构造叠加晕实用模式

根据新疆哈巴河县托库孜巴依金矿床的地质特征及成矿规律,对矿床的26号脉及主要围岩进行了系统采样和多元素分析,结合矿区地球化学背景确定了各元素的分带标准;通过对26号矿脉(体)的地球化学特征及构造叠加晕特征研究,总结出金矿(体)单一次成矿的原生晕轴向分带,对矿体不同成矿阶段形成的晕在空间上的叠加形态进行了识别,建立了矿体形成的构造叠加晕实用模式(包括成矿构造叠加晕模式、预测标志及分带标准),利用该实用模式对矿脉深部以及外围进行找矿预测,提出了找矿预测靶位。     

Transfers of titanium,zirconium, and hafnium in high-temperature solutions

At 500–600°C and 500–800 atm, in alkaline solutions, two mechanisms of the migrations of Ti, Zr, and Hf are experimentally indicated: a) in the absence of fluorine and other halogens, these metals migrate as titanates, zirconates, and hafnates of K and Na, the forms which are conducive to their dissipation but not deposition-accumulation in the rocks, within a wide range of temperature, as long as the pH of the solution remains alkaline; b) in the presence of fluorine, Ti, Zr, and Hf migrate as fluoride complexes (with Na and K) from which they may be liberated by hydrolysis and deposited at decreasing temperature, as the corresponding oxides.     

中国典型高温热田热水的锶同位素研究

滇藏地热带的热水大多是大气降水成因，大气降水沿断裂带向下渗透，随地温的增加而逐步升温，并不断地与深部岩石发生水岩相互作用，从造岩矿物中淋滤出锶组分。通过测定热水中的锶同位素组成，可以帮助确定热水的深部滞留环境，研究深、浅层热水的内在联系，区分出不同的水热循环系统。西藏羊八井热田深部由多期次花岗岩组成，岩性差别不大，而锶同位素差异比较明显。热田的深、浅层热水有着相似的^87Sr/^86Sr值，并且只与上新世花岗岩的锶同位素组成相接近，反映了深部热储的岩性特征。在热水从升流部位向排泄区运移时，浅层冷水、始新世火山岩和第四系砂砾岩对热水的锶同位素改造作用较小。云南腾冲热海热田是典型的有幔源岩浆囊作为热源的高温热田，热田由东、西两区组成，其气体和热水在化学组成上有一定的差异，^87Sr/^86Sr值也有明显的不同。因此，可以确定东、西两区的水热系统虽具有共同的热源，但两者之间的水力联系比较微弱，而且热水中的锶组分与热田内大面积出露的火山岩没有关联。     

Strontium and samarium diffusion in diopside

The volume chemical diffusion of trace amounts of Sr in diopside has been measured as a function of temperature (1100–1300°C), pressure (1 bar–20 kbar), crystallographic direction, and composition. Three experimental/analytical techniques were employed: radiotracer and sectioning; stable tracer and ion microprobe; and Rutherford back-scattering spectroscopy. Comparison of the three yielded excellent agreement. Both natural and synthetic single crystal samples were used with results in the natural diopside giving diffusivities approximately two orders of magnitude greater than those in the man-made crystals. Samarium diffusion in the synthetic crystals was also examined with the ion probe technique with results similar to Sr.Arrhenius relations for diffusion (D = D₀exp[?ΔH_a/RT]) were calculated for different pressures and analytical techniques, and activation volumes (gDV_a) were derived from the equation D = D' exp[?PΔV_a/ RT]. Values of ΔV_a were negative for Sr diffusion. An empirical relation describing the temperature and pressure dependence of D for Sr in the c direction of the synthetic samples is: D(P, T) = 1200 (cm²/sec) exp[?122 (Kcal/mol)/RT (°K)]exp[?P (bar)/(2.94T ? 4640)R]. The expression for D_Sr in the natural samples (c direction) at one atmosphere is: D(0, T) = 54 (cm²/sec) exp[?97 (Kcal/mol)/RT (°K)]. A single compensation trend for all the data was evident for all values of D₀ and ΔH_a in the synthetic crystals.A number of models of geologic processes were investigated in light of the present data. Closure temperatures (T_c) were calculated for examples of mineral-mineral age-dating and trace element geothermometry. High values of T_c indicate that pyroxenes record emplacement events and are generally not disturbed unless a fluid enters the system. Isotopic equilibration times were examined for lower crustal xenoliths and the mantle source region for MORB using the formula of Hofmann and Hart (1978). Equilibration was shown to be too fast for production of isotopic anomalies in MORB via disequilibrium melting. Also. reasonable residence times at lower crustal temperatures were shown to produce the mineralogical-scale isotopic homogeneity observed in a crustal xenolith from Kilbourne Hole, New Mexico.