Raman Spectroscopy of Garnet—group Minerals

The Raman spectra of the natural end members of the garnet-group minerals,which include pyrope, almandine and spessarite of Fe-Al garnet series and grossularite ,andradite and uvarovite of Ca-Fe garnet series, have been strdied.Measured Raman spectra of these minerals are reasonably and qualitatively assigned to the internal modes, translational and rotatory modes of SiO4 tetrahedra, as well as the translational motion of bivalent cations in the X site.The stretch and rotatory A1g modes for the Fe-Al garnet series show obvious Raman shifts as compared with those for the Ca-Fe garnet series ,owing to the cations residing in the Xsite connected with SiO4 tetrahedra by sharing the two edges.The Raman shifts of all members within either of the series are attributed mainly to the properties of cations in the X site for the Fe-Al garnet series andin the Y site for the Ca-Fe garnet series.     

浅析如何完善地勘单位财务管理运行机制

目前国有地勘单位已逐步形成的以事业为主体,以市场化经营为重要补充的发展模式,在新的发展模式下,需要有与之相适应的财务管理运行机制。本文浅析了在财务管理方面所存在的主要问题,并提出了完善财务管理运行机制的建议。     

Observation of the oxidation of galena using Raman spectroscopy

Oxidation of galena (PbS) to oxysulfates, (PbO·PbSO₄, 3PbO·PbSO₄ and 4PbO·PbSO₄)_, has been observed using Raman spectroscopy. Peaks associated with the oxidation products have been assigned. The reaction appears to be a high temperature oxidation induced by the high laser (25 mW at 514.5 nm) power density at freshly cleaved galena surfaces. Damage to the galena surface was observed visually under the microscope. Moderate laser powers (5 mW at 514.5 nm) did not result in any damage. No Raman bands were observed or expected for freshly cleaved galena because it has the rock salt structure. Laser-induced production of these oxysulfates is dramatically different from high temperature methods previously employed. This procedure will permit easy identification of galena in complex mineral ore samples. Spontaneous air oxidation of freshly cleaved galena to oxides or polysulfides was not detected.     

Raman spectroscopy of ferritungstite: Experimental and model spectra

Raman spectra of ferritungstite are interpreted on the basis of model calculations. The presence of two broad vibrational bands in the spectral range 600–1000 cm^?1 is explained through the combination of two factors. Mainly, two principle bands in the spectral ranges 600–750 and 850–1000 cm^?1 are characteristic of the pyrochlore-type structure attained by ferritungstite and correspond to symmetric and asymmetric stretching of the W-O bonds, respectively. Also, broadening of the Raman lines results from structural disorder caused by the presence of iron atoms.     

Structure-composition relations and Raman spectroscopy of high-pressure sodium silicates

?-Na₂Si₂O₅, ζ-Na₂Si₂O₅, Na₂Si[Si₂O₇], and Na₆Si₃[Si₉O₂₇] have been synthesized using an MA6/8 superpress. Densification in high-pressure sodium silicates is effected largely by changes in packing. In the relaxed (1 bar) structures, cation polyhedra and thermal/displacement parameters are similar to those of low-pressure silicates, but the extra-framework cation positions are oversized. The two mixed ^[4]Si and ^[6]Si framework silicates of known structure (Na₂Si[Si₂O₇] and Na₆Si₃[Si₉O₂₇]) belong to the limited homologous series Na_2mSi_m[Si_n–mO_2n+m], with m<n. The structure-composition relationships of wadeite-type, A₂Ge₄O₉-type, and Na₆Si₃[Si₉O₂₇] silicates and germanates depend on T-O distance and size of the large extra-framework cation. Characteristic features of the SiO₄ tetrahedral units are present in micro-Raman spectra of mixed ^[4]Si and ^[6]Si framework silicates, but bands uniquely attributable to SiO₆ octahedra are weak or obscured. However, ^[6]Si has a profound indirect influence on the Raman spectra, resulting in intense and complex low-frequency bands, assigned to symmetric bending modes with coupled displacements at both bridging oxygens and nonbridging oxygens bonded to ^[6]Si, and a shift to higher frequency and reduction in intensity of the high-frequency bands assigned to symmetric ^[4]Si-O_nbr stretching vibrations. Raman spectroscopy does not appear to be a useful structural probe for small amounts of ^[6]Si in silicate glasses and melts.     

Using the DPFT approach to improve flash flood forecasting models

DPFT is a lumped approach for operational flash flood forecasting, based on the unit hydrograph. Using a multi-event alternating iterative algorithm, it identifies a robust and stable average transfer function and a consistent set of effective rainfall series associated with each event at the same time. This key ingredient allows an objective calibration of different loss functions, relating gauged precipitation and effective rainfall. A case study based on an operational French basin (545 km²) is presented. Three lumped production functions have been calibrated and compared. The results show that more elaborate models of loss functions must be proposed, and some possible directions for this are pointed out.     

Using the DPFT approach to improve flash flood forecasting models

DPFT is a lumped approach for operational flash flood forecasting, based on the unit hydrograph. Using a multi-event alternating iterative algorithm, it identifies a robust and stable average transfer function and a consistent set of effective rainfall series associated with each event at the same time. This key ingredient allows an objective calibration of different loss functions, relating gauged precipitation and effective rainfall. A case study based on an operational French basin (545 km²) is presented. Three lumped production functions have been calibrated and compared. The results show that more elaborate models of loss functions must be proposed, and some possible directions for this are pointed out.Presently at the Institut de Ciences de la Terra Jaume Almera, Apartat 30102, 08080 Barcelona, Spain.Presently at EDF-DTG. Service de Ressources en Eau, BP 4348, 31029 Toulouse Cedex, France.     

用先进文化的力量推动地质事业的发展

文化是一种传承,也是一种理念,先进文化更加体现时代气息并蕴含创新与发展的元素。孟宪来局长等撰写的这篇颇具新意的专论阐述了地质工作的文化属性,深刻揭示了行业文化与行业精神的弘扬对地质工作创新发展所起的重要推动作用。文化更是一种思想动力：用先进文化武装头脑,有助于人们从传统地质学走向“通学”的现代地质学,建立“跨文化”的概念,和谐共建“地球村”;有助于从理论和实践的角度领悟科学发展观的深层内涵,继而最大限度地从激发爱国主义精神、弘扬科学精神、倡导创新精神、守望奉献精神的层面重塑行业文化的精神脊梁。这是一篇贯穿科学文化与文化哲学思维的探究性文章,读者可以从中获得有益的启迪。[编者按]     

Raman spectroscopy and biomarker analysis reveal multiple carbon inputs to a Precambrian glacial sediment

Extractable biomarkers can help elucidate the environment and biota of ancient glaciations, although the method must be applied with care, as glacial sediments have a potential for incorporation of older detrital carbon. In Phanerozoic glacial sediments, the distinct elemental, molecular and isotopic compositions of the terrestrial and marine biomass allow discrimination between primary marine and redeposited terrestrial organic matter. However, as the Proterozoic biosphere was largely microbial and marine, biomarker and isotopic analyses are insufficient for distinguishing primary organic matter from secondary reworked organic matter. Here, we report the combined application of Raman spectroscopy and biomarker analysis to Precambrian glacial sediments, which, together, allows discrimination between mixed pools of organic carbon and provides a promising new approach for rapidly screening Precambrian sediments for immature organic matter amenable to biomarker analysis.     

Beryl-II,a high-pressure phase of beryl: Raman and luminescence spectroscopy to 16.4 GPa

The Raman and Cr³⁺ and V²⁺ luminescence spectra of beryl and emerald have been characterized up to 15.0 and 16.4 GPa, respectively. The Raman spectra show that an E _1g symmetry mode at 138 cm^?1 shifts negatively by ?4.57 (±0.55) cm^?1/GPa, and an extrapolation of the pressure dependence of this mode indicates that a soft-mode transition should occur near 12 GPa. Such a transition is in accord with prior theoretical results. Dramatic changes in Raman mode intensities and positions occur between 11.2 and 15.0 GPa. These changes are indicative of a phase transition that primarily involves tilting and mild distortion of the Si₆O₁₈ rings. New Raman modes are not observed in the high-pressure phase, which indicates that the local bonding environment is not altered dramatically across the transition (e.g., changes in coordination do not occur). Both sharp line and broadband luminescence are observed for both Cr³⁺ and V²⁺ in emerald under compression to 16.4 GPa. The R-lines of both Cr³⁺ and V²⁺ shift to lower energy (longer wavelength) under compression. Both R-lines of Cr³⁺ split at ~13.7 GPa, and the V²⁺ R₁ slope changes at this pressure and shifts more rapidly up to ~16.4 GPa. The Cr³⁺ R-line splitting and FWHM show more complex behavior, but also shift in behavior at ~13.7 GPa. These changes in the pressure dependency of the Cr³⁺ and V²⁺ R-lines and the changes in R-line splitting and FWHM at ~13.7 GPa further demonstrate that a phase transition occurs at this pressure, in good agreement with our Raman results. The high-pressure phase of beryl appears to have two Al sites that become more regular under compression. Hysteresis is not observed in our Raman or luminescence spectra on decompression, suggesting that this transition is second order in nature: The occurrence of a second-order transition near this pressure is also in accord with prior theoretical results. We speculate that the high-pressure phase (beryl-II) might be a mildly modulated structure, and/or that extensive twinning occurs across this transition.     

High-temperature Raman spectroscopy and quasi-harmonic lattice dynamic simulation of diopside

We investigated the lattice vibrational properties and lattice dynamical behaviour of diopside by combining laser micro-Raman spectroscopic measurements with quasi-harmonic lattice dynamic simulation using a transferable interatomic potential. We obtained polarized Raman spectra from a Fe-poor natural diopside and the temperature dependencies of the Raman modes to 1125?K from high-temperature Raman spectra of a Fe-poor and a Fe-rich natural diopside. The various modes display different temperature dependencies: from ?0.021?cm^?1/K to ?0.004?cm^?1/K. The temperature shift of low frequency modes is generally higher. A comparison of experimentally determined frequencies and symmetries of vibrational modes of the optical type (Raman and infrared) obtained in this and earlier studies with those calculated by us suggests that a consistent characterization of the vibrational properties was achieved. The good agreement between the experimental and simulated data on the temperature-dpendencies of the Raman modes (within 5%), crystal structure (2%), bulk modulus (5%), volume thermal expansivity (6%), and constant volume heat capacity (0.2%) testifies to the applicability of the transferable interatomic potential and the lattice dynamic model to predicting the vibrational, physical, and thermodynamic properties. The simulated properties from the lattice dynamic calculations are very similar to those obtained by molecular dynamic calculations with the same potential model.     

Raman spectroscopy of water tracer diffusion in zeolite single crystals

The water tracer diffusion in single crystals of natrolite, scolecite, mesolite, heulandite, and chabazite has been studied by Raman micro-spectroscopy. A model of water tracer diffusion is proposed. The H₂O, HDO, and D₂O molecule concentrations are calculated for a crystal of orthorhombic symmetry on deuteration of the initial H₂O-sample. A way is shown to find the diffusion coefficients, the constant of equilibrium, and the deuteron-proton exchange rate from experimental data. The water diffusion coefficients for natrolite placed in liquid D₂O appeared to be 1.5–2 times higher than those for a sample in vaporous D₂O. For natrolite at room temperature, 1.5–1.6 times higher water diffusion occurs along [001] than along [110].     

High-temperature X-ray diffraction and Raman spectroscopy of diopside and pseudowollastonite

Diopside (CaMgSi₂O₆) and pseudowollastonite (CaSiO₃) have been studied by X-ray powder diffraction and Raman spectroscopy up to their respective melting points. In agreement with previous unit-cell parameters determinations below 1100 K, thermal expansion of diopside along the a and c axis is much smaller than along the b axis. For pseudowollastonite, the axis expansivity increases slightly in the order b>a>c. For both minerals, the change in unit-cell angles is very small and there are no anomalous variations of the other unit-cell parameters near the melting point. With increasing temperatures, the main changes observed in the Raman spectra are strong increases of the linewidths for those bands which mainly represent Si−O−Si bending (near 600 cm⁻¹) or involve Ca−O or Mg−O stretching, in the range 270–500 cm⁻¹ for diopside, and 240–450 cm⁻¹ for pseudowollastonite. At temperatures near the onset of calorimetric premelting effects, this extensive band widening results in a broad Raman feature that can no longer be deconvoluted into its individual components. No significant changes affect the Si−O streching modes. For both diopside and pseudowollastonite, premelting appears to be associated with enhanced dynamics of the alkaline-earth elements. This conclusion contrasts markedly with that drawn for sodium metasilicate in which weaker bonding of sodium allows the silicate framework to distort and deform in such a way as to prefigure the silicate entities present in the melt. Received 16 July 1997 / Revised, accepted: 6 March 1998     

Coordination of Fe,Ga and Ge in high pressure glasses by Mössbauer,Raman and X-ray absorption spectroscopy,and geological implications

Mössbauer spectra of glasses of NaFeSi₃O₈ and 3NaAlSi₂O₆ · NaFeSiO₄ starting compositions consist of a dominant Fe³⁺ and subordinate Fe²⁺ quadrupole-split doublet, in agreement with previous work. Fe³⁺ is assigned to tetrahedral coordination. Pressure-induced coordination changes are not observed in the pressure range 1 bar to 30 kbar. A gradual increase in isomer shift of the Fe³⁺ doublet with increase in pressure is attributed to steric effects. Raman spectra of GeO₂, NaGaSi₃O₈ and NaGaSiO₄ glasses are dominated by network structure vibrations. There is no detectable change in the nearest-neighbor coordination of Ge⁴⁺ in GeO₂ from 1 bar to 14 kbar, of Ga³⁺ in NaGaSi₃O₈ from 1 bar to 28 kbar and of Ga³⁺ in NaGaSiO₄ from 1 bar to 25 kbar. However, some structural reorganization outside of the first coordination sphere occurs in the high pressure glasses.XANES and EXAFS spectra on powdered samples of 1 bar and 25 kbar NaGaSiO₄ glasses and crystalline NaGaSiO₄ were obtained from K edge absorption spectra at the Stanford Synchrotron Radiation Laboratory using a double crystal monochromator equipped with Si(220) crystals. The XANES spectra indicate that Ga³⁺ has a similar extended coordination geometry in both glasses. The EXAFS spectra reveal that Ga³⁺ is four-coordinated with oxygen in all three samples with a Ga³⁺-O distance of about 1.83 Å. The radial distribution functions of the two glasses are virtually identical. However, both XANES and EXAFS spectra indicate significant structural differences between crystalline NaGaSiO₄ (nepheline-type structure) and vitreous NaGaSiO₄ beyond the first coordination shell of Ga³⁺. Thus, X-ray absorption spectroscopy independently confirms the Raman results on the unchanged coordination of Ga³⁺ in NaGaSiO₄ glasses with pressures up to 25 kbar.Glass compositions were selected in anticipation that larger and/or lower charged cations would exhibit pressure-induced coordination changes at lower pressures than Al³⁺ and Si⁴⁺. The present null result suggests that the stabilizing features of open network structures in the liquid state (large entropy and minimized cation-cation repulsion) more than compensate for large molar volume in the pressure range accessible to experimentation. It appears that network structures in natural magmas should remain stable throughout the upper mantle. Consequently, the densities of magmas at high pressures which are calculated from compressibility data and the appropriate equation of state will be only slightly underestimated, due to the effect of minor structural changes beyond the first coordination sphere.     

利用小波阈值法提高地震勘探信号的信噪比

在地震勘探信号处理中,能否得到高信噪比的信号是正确解读实际勘探信号的关键。在实际勘探中,受到环境等因素的影响,检波器接收到的信号中夹杂着各种相干及随机噪声,降低接收信号的信噪比。鉴于传统傅里叶变换无法处理随机噪声,本工作提出利用改进的小波阈值法提高含随机噪声的信噪比,通过MATLAB仿真和勘探实验验证。建立仿真模型,比较了改进阈值函数与现有软、硬阈值法的去噪效果;信噪比和均方根误差结果显示,改进阈值函数去噪后的信噪比优于软和硬阈值函数的信噪比。利用地震雷克子波建立了地震正演模型,对比改进阈值函数处理前后的结果显示,改进阈值函数法能充分保留有用信号,有效地消减勘探信号中的随机噪声,可为勘探信号解释提供一种新的去噪方法。     

Contribution of long-term hydrothermal experiments for understanding the smectite-to-chlorite conversion in geological environments

The smectite-to-chlorite conversion is investigated through long-duration experiments (up to 9 years) conducted at 300 °C. The starting products were the Wyoming bentonite MX80 (79 % smectite), metallic iron and magnetite in contact with a Na–Ca chloride solution. The predominant minerals in the run products were an iron-rich chlorite (chamosite like) and interstratified clays interpreted to be chlorite/smectite and/or corrensite/smectite, accompanied by euhedral crystals of quartz, albite and zeolite. The formation of pure corrensite was not observed in the long-duration experiments. The conversion of smectite into chlorite over time appears to take place in several steps and through several successive mechanisms: a solid-state transformation, significant dissolution of the smectite and direct precipitation from the solution, which is over-saturated with respect to chlorite, allowing the formation of a chamosite-like mineral. The reaction mechanisms are confirmed by X-ray patterns and data obtained on the experimental solutions (pH, contents of Si, Mg, Na and Ca). Because of the availability of some nutrients in the solution, total dissolution of the starting smectite does not lead to 100 % crystallization of chlorite but to a mixture of two dominant clays: chamosite and interstratified chlorite/smectite and/or corrensite/smectite poor in smectite. The role of Fe/(Fe + Mg) in the experimental medium is highlighted by chemical data obtained on newly formed clay particles alongside previously published data. The newly formed iron-rich chlorite has the same composition as that predicted by the geothermometer for diagenetic to low-grade metamorphic conditions, and the quartz + Fe-chlorite + albite experimental assemblage in the 9-year experiment is close to that fixed by water–rock equilibrium.     

Raman spectroscopy, vibrational analysis, and heating of buergerite tourmaline

Polarized Raman spectra were collected for single crystal buergerite (NaFe₃Al₆(BO₃)₃Si₆O₁₈(O_0.92(OH)_0.08)₃F) from room temperature to near 1,375°C. Vibrational assignments to features in the room temperature spectra were determined by lattice dynamics calculations, where internal BO₃ motions dominate modes near 1,300 cm⁻¹, internal SiO₄ displacements dominate modes between 900 and 1,200 cm⁻¹, while less localized displacements within the isolated Si₆O₁₈ ring mix with motions within Na, Fe, Al, F, and BO₃ environments for fundamental modes below 780 cm⁻¹. At elevated temperatures, most buergerite Raman features broaden and shift to lower frequencies up to 900°C. Above this temperature, the lattice mode peaks evolve into broad bands, while OH stretch modes near 3,550 cm⁻¹ disappear. According to Raman spectroscopy, X-ray diffraction, differential thermal analysis, and scanning electron microscopy, buergerite undergoes a complex transition that starts near 700°C and extends over a 310°C interval, where initially, Al and Fe probably become disordered within the Y- and Z-sites, and most F and all OH are later liberated. A reversible crystal-to-amorphous transition is seen by Raman for buergerite fragments heated as high as 930°C. Buergerite becomes permanently altered when heated to temperatures greater than 930°C; after cooling to room temperature, these altered fragments are comprised of mullite and Fe-oxide crystals suspended in an amorphous borosilicate matrix.     

新疆塔里木盆地温宿凸起石油地质条件新认识

为了弄清塔里木盆地温宿凸起构造演化、油源条件及圈闭类型等关键地质问题,通过石油地质条件综合分析,结合样品测试分析,查清了温宿地区油气成藏的关键因素,提出了石油地质条件新认识。结果表明: 温宿凸起为一个继承性发育的古隆起,构造演化主要经历了4个发展阶段; 温宿凸起油气藏类型以构造-岩性型为主; 温宿凸起不发育烃源岩,但发育沟通拜城富烃凹陷的高效输导体系; 温宿凸起新近系吉迪克组油气藏类型以构造-岩性型为主; 油气的生成、运移、聚集主要发生在新近纪—第四纪,具有明显的晚期复式成藏特点; 优越的盖层条件是温宿吉迪克组油气藏形成的重要因素。