Combined investigations of fluid inclusions in opaque ore minerals by NIR/SWIR microscopy and microthermometry and synchrotron radiation X-ray fluorescence

An alternative IR microscopy system in the NIR (near infrared, up to 10 μm) and SWIR (short wavelength infrared, up to 1.4 μm) ranges has been developed for the study of opaque ore minerals. The system uses either IR LED or IR light bulb sources depending on the degree of opacity of the investigated minerals. This paper presents the methodology and the promising results obtained in studies of opaque ore minerals such as Ag minerals (pyrargyrite) from epithermal deposits and Nb-tantalates (columbite) from pegmatites. It also presents results on the internal features of hematites from Fe ore banded formations and tungstates from granite–greenstone belt deposits. The data obtained on fluid inclusions from pyrargyrite and hematite crystals have been integrated by complementary information from X-ray fluorescence analysis using synchrotron radiation (μ-SXRF) under conditions specifically designed for the study of opaque ore minerals.     

Composition and origin of fluids associated with lode gold deposits in a Mesoarchean greenstone belt (Warrawoona Syncline, Pilbara Craton, Western Australia) using synchrotron radiation X-ray fluorescence

Microthermometry and Raman spectroscopy techniques are routinely use to constrain ore-fluids δ¹⁸O and molar proportions of anhydrous gas species (CO₂, CH₄, N₂). However, these methods remain imprecise concerning the ore-fluids composition and source. Synchrotron radiation X-ray fluorescence allows access to major and trace element concentrations (Cl, Br and K, Ca, Fe, Cu, Zn, As, Rb, Sr) of single fluid inclusion. In this paper, we present the results of the combination of these routine and newly developed techniques in order to document the fluids composition and source associated with a Mesoarchaean lode gold deposit (Warrawoona Syncline, Western Australia). Fluid inclusion analyses show that quartz veins preserved records of three fluid inclusion populations. Early fluids inclusions, related to quartz veins precipitation, are characterized by a moderate to high Br/Cl ratio relative to modern seawater, CO₂ ± CH₄ ± N₂, low to moderate salinities and significant base metal (Fe, Cu, Zn) and metalloid (As) concentrations. Late fluid inclusions trapped in secondary aqueous fluid inclusions are divided into two populations with distinct compositions. The first population consists of moderately saline aqueous brines, with a Br/Cl ratio close to modern seawater and a low concentration of base metals and metalloids. The second population is a fluid of low to moderate salinity, with a low Br/Cl ratio relative to modern seawater and significant enrichment in Fe, Zn, Sr and Rb. These three fluid inclusion populations point to three contrasting sources: (1) a carbonic fluid of mixed metamorphic and magmatic origin associated with the gold-bearing quartz precipitation; (2) a secondary aqueous fluid with seawater affinity; and (3) a surface-derived secondary aqueous fluid modified through interaction with felsic lithologies, before being flushed into the syncline. Primary carbonic fluids present similar characteristics than those ascribed to Mesoarchaean lode gold deposits. This suggests similar mineralization processes for mid- and Mesoarchaean lode gold deposits despite contrasting fluid–rock interaction histories. However, in regard to the protracted history documented in the Warrawoona Syncline, we question the robustness of the epigenetic crustal continuum model, as ore-fluid characteristics equally support an epigenetic or a polyphased mineralization process.     

Pattern of minor element enrichment in columbites: A synchrotron radiation X-ray fluorescence (SRXRF) study

The pattern of minor elements incorporation in columbites from granitic pegmatites of Alto Ligonha, Mozambique, was disclosed on the basis of synchrotron radiation X-ray fluorescence (SRXRF) data. Major elements (Fe, Mn, Nb, Ta) were analyzed with an electron microprobe (EPMA).Minor and trace element contents display a common general trend pointing towards the preferential uptake of metals that minimize the stress induced in the host crystal structure by the non-commensurability of cations with distinct valences and ionic radii. The simultaneous incorporation of Ti, Zr, U, Pb, Y and W assures electrostatic equilibrium, being conditioned by the dominant presence of niobium, while Sc concentrates in solid solutions with low Nb / (Nb + Ta) ratios.     

Interpretation of heterogeneity effects in synchrotron X-ray fluorescence microprobe data

Heterogeneity effects often limit the accuracy of synchrotron X-ray fluorescence microprobe elemental analysis data to ± 30%. The difference in matrix mass absorption at Kα and Kβ fluorescence energies of a particular element can be exploited to yield information on the average depth-position of the element or account for heterogeneity effects. Using this technique, the heterogeneous distribution of Cu in a simple layered sample could be resolved to a 2 × 2 × 10 (x, y, z, where z is the depth coordinate) micrometer scale; a depth-resolution limit was determined for the first transition metal series and several other elements in calcite and iron oxide matrices. For complex heterogeneous systems, determination of average element depth may be computationally limited but the influence of heterogeneity on fluorescence data may still be assessed. We used this method to compare solid-state diffusion with sample heterogeneity across the Ni-serpentine/calcite boundary of a rock from Panoche Creek, California. We previously reported that Ni fluorescence data may indicate solid state diffusion; in fact, sample heterogeneity in the depth dimension can also explain the Ni fluorescence data. Depth heterogeneity in samples can lead to misinterpretation of synchrotron X-ray microprobe results unless care is taken to account for the influence of heterogeneity on fluorescence data.     

日本马氏贝珍珠化学组成的同步辐射X射线荧光光谱分析

采用同步辐射微区X射线荧光光谱技术,探测古铜色日本马氏贝珍珠剖面(珠核与珍珠层)的元素分布。测试结果表明,样品中主要含有Ca、Sr、Ba等3种碱土金属元素,Mn、Fe、Cu、Zn等4种3d过渡金属元素以及稀土元素,各元素在珍珠中表现出一定的空间分布规律:珠核表面稀土元素浓度最高,珍珠层和珠核的稀土元素浓度大致相当;Mn和Fe元素浓度自珠核浅表层向珠核表面有降低趋势;珍珠层内Mn和Fe元素浓度都出现大幅降低现象,且是在相同的圈层降低,显示其具有一定正相关性,推测二者大幅降低的圈层是平行层和棱柱层的分界,且Mn元素主要赋存于棱柱层;Ca与Sr、Ba元素的分布具有负相关性。     

Analysis of individual fluid inclusions using synchrotron X-ray fluorescence microprobe: progress toward calibration for trace elements

A critical problem for conducting quantitative analysis of individual fluid inclusions using Synchrotron X-Ray Fluorescence (SXRF) technique relates to the standardization and the calibration of the X-ray spectra. In this study, different approaches have been tested for calibration purposes: (a) the use of chlorine when Cl content can be estimated either from melting point depressions of undersaturated fluid inclusions or from saturation limits for halite-bearing fluid inclusions, (b) the use of calcium from synthetic fluid inclusions of known CaCl₂ content as an external standard. SXRF analysis was performed on individual fluid inclusions from the Chivor and Guali emerald deposits, Columbia. These well-known samples contain a single fluid inclusion population for which detailed crush-leach analyses are available, thus providing a relevant compositional reference frame. Concentration estimates were also compared to Particle Induced X-ray Emission (PIXE) analysis carried out independently on the same fluid inclusions.Results of the calibration tests indicate that major (Cl, K, Ca, Fe, Mn) and trace element (Cu, Zn, As, Br, Rb, Sr, Ba, Pb) concentration estimates can be performed without precise knowledge of the analytical volume and the inclusion’s 3D geometry. Although the standard deviation of the SXRF results can be relatively high depending on the calibration mode used, mean concentration estimates for most elements are in good agreement with PIXE and crush-leach analysis. Elemental distributions within single fluid inclusions were also established. Associated correlation diagrams argue for the homogeneous distribution of most elements in the fluid inclusion. In contrast, Br shows a bimodal distribution interpreted to reflect a significant enrichment of the vapor portion of the inclusion fluid.     

Study of laser heated iron using third generation synchrotron X-ray radiation facility with imaging plate at high pressures

Iron pressurized to 60 gigapascal (GPa) was heated with laser up to temperatures of over 2200 K. The structural changes were determined in-situ using third generation synchrotron X-ray source; the changes were recorded on an imaging plate with a monochromatic beam. The results strongly support the existence of a phase transformation of the hexagonal close-packed (hcp) structure to the new polymorph (β-phase of iron) at high pressure and temperature. We interpret the X-ray data as belonging to the double hexagonal close-packed (dhcp) structure distorted by stress due to laser heating. Received: 2 February 1998 / Accepted: 23 August 1998     

人体乳腺癌矿化的同步辐射研究

同步辐射具有常规光源不可比拟的优良性能,可用于微量生物矿化样品的物相、结构、形貌和成分研究。本文利用基于同步辐射光源的X射线粉末衍射(SR-XRD)、傅立叶变换红外光谱(SR-FTIR)、X射线荧光分析(SR-XRF)和X射线三维成像,对人体乳腺癌矿化进行了表征。研究表明,乳腺癌矿化的主要矿物物相为碳羟磷灰石,含有Sr、Zn等微量元素,其中砂粒体矿化具有独特的分层结构。研究结果为乳腺癌的病理研究和诊断提供了矿物学参考信息。     

Kinetic analysis of cation exchange in birnessite using time-resolved synchrotron X-ray diffraction

In this study, we applied time-resolved synchrotron X-ray diffraction (TRXRD) to develop kinetic models that test a proposed two-stage reaction pathway for cation exchange in birnessite. These represent the first rate equations calculated for cation exchange in layered manganates. Our previous work has shown that the substitution of K, Cs, and Ba for interlayer Na in synthetic triclinic birnessite induces measurable changes in unit-cell parameters. New kinetic modeling of this crystallographic data supports our previously postulated two-stage reaction pathway for cation exchange, and we can correlate the kinetic steps with changes in crystal structure. In addition, the initial rates of cation exchange, R (ų min⁻¹), were determined from changes in unit-cell volume to follow these rate laws: R = 1.75[]^0.56, R = 41.1[]^1.10, R = 1.15[]^0.50. Thus, the exchange rates for Na in triclinic birnessite decreased in the order: Cs ? K > Ba. These results are likely a function of hydration energy differences of the cations and the preference of the solution phase for the more readily hydrated cation.     

The opaque minerals of the ultramafic rocks of New Caledonia

The ultramafic rocks of New Caledonia contain a diversity of disseminated ore minerals in non-economic amounts. Eighteen opaque minerals are described herein with pentlandite, millerite and heazelwoodite most prominent. Several new or unusual mineralogical features are recorded. These include an eutectic intergrowth between pentlandite and primary chalcocite, reaction between pentlandite and chalcocite to form chalcopyrite and millerite, exsolution intergrowth between pentlandite and millerite, between pentlandite and mackinawite and between millerite and cubanite. In the formation of the garnieritic ores of New Caledonia some of the nickel would appear to have been derived from the breakdown of disseminated sulphides as well as from the nickel inherent in the silicate minerals of the ultramafic rocks.

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Résumé Les roches ultramafiques de la Nouvelle-Calédonie comportent une diversité de mineraux disséminés dans des quantités sous-économiques. Dix-huit minéraux opaques y sont décrites avec la proéminence de la pentlandite et la millerite. Quelques caractéristiques minéralogiques, nouvelles et exceptionelles, sont notées. Ceci comprend un enchevêtrement eutectique entre la pentlandite et la chalcopyrite primaire, une réaction entre la pentlandite et la chalcocite qui se changent en chalcopyrite et en millerite, un entredéveloppement par l'exsolution entre la pentlandite et la machinawite et entre la millérite et la cubanite. Il est établi que, pendant la formation du minérais garniéritique de la Nouvelle-Calédonie une part du nickel vient des sulphures disséminées de même que du nickel naissant dans les silicates des roches ultramafiques.

     

西华山钨矿床共生透明矿物与不透明矿物中流体包裹体的对比研究

西华山钨矿床是一个产于燕山期花岗岩中的大脉型钨矿床。笔者利用红外显微镜、冷热台及其他相关设备对矿床中的透明矿物(石英、绿柱石和萤石)与不透明矿物(黑钨矿、黄铁矿)中的流体包裹体进行了对比研究。结果显示,共生透明矿物与不透明矿物之间,在包裹体均一温度等特征上既可基本相同又可出现很大差异。一般来说,黑钨矿能有效地保存原生流体包裹体(t_h=300～420℃;晶洞中为220～290℃),仅有少量次生包裹体(t_h=160～280℃),而与之共生的石英中原生包裹体则几乎被破坏殆尽,现在所见到的包裹体绝大多数是次生的或是在较晚结晶时捕获的(t_h=130～270℃)。只有未经后期应力作用和流体改造的晶洞水晶及与其共生的黑钨矿,二者获得的结果才相同或相似。绿柱石中通常有大量的次生包裹体和原生包裹体。黑钨矿与绿柱石中硅酸盐熔融包裹体的出现,表明西华山钨矿床的成矿作用始于岩浆-热液过渡阶段,其初始成矿流体是一种岩浆-热液过渡性流体,尔后才演变成单一的热水溶液。笔者认为,在进行金属矿床流体包裹体研究时,应强调共生透明矿物与不透明矿物的对比研究,在进行对比研究时,详尽的基础地质研究和包裹体岩相学观察必不可少;当单独利用透明矿物包裹体资料对金属矿床进行地质解释时,需慎之又慎。     

热液矿床中不透明矿物的流体包裹体研究进展

脉石矿物中流体包裹体所提供的有关流体与成矿的物理化学条件不一定代表成矿时的实际流体和成矿条件,最好的办法是直接测定矿石矿物捕获的包裹体。红外显微镜的运用开拓了不透明矿物中流体包裹体研究的新领域。文章对红外显微镜工作的基本原理及设备做了简要的综述,重点介绍了不透明矿物中流体包裹体岩相学、显微测温以及成分分析研究,并举例说明了不透明矿物流体包裹体在W-Sn矿床以及其他矿床研究中的应用,最后指出了不透明矿物中流体包裹体研究尚且存在的问题、部分解决方法,并简单展望了其在中国的发展前景。     

X-ray spectra of iron atoms in minerals

The results of X-ray fluorescence Ka _1,2 and Kβ₁,β′-spectra of iron in 54 samples, including 23 minerals, are presented. Spectrum characteristics are mainly dependent on the environment of iron in the sample, the most susceptible parameter being the chemical shift δβ₁. For the compounds investigated δβ₁ varies between ?1.58 eV and +1.56 eV when referring to metallic iron. Chemical shifts of compounds with predominantly covalent bonds exhibit more negative values, compounds with metallic bonds nearly vanishing values and compounds with predominantly ionic bonds more positive values. The FeKβ₁,β′-group of lines is actually a superposition of three lines: the long-wave line β′ and two overlapping lines β ₁ ⁵ and β ₁ ⁷ of which the superposition is conventionally denoted as β₁. The relative intensity of β ₁ ⁵ increases with ionicity of the bond, while that of β ₁ ⁷ decreases. The effective charge of iron has been determined for a group of iron-bearing minerals.     

Some mineralogical applications of synchrotron radiation

Synchrotron radiation offers several advantages over the conventional X-ray sources, among which the most important are its high intensity, broad spectral range and natural collimation. Among the numerous techniques which have been recently developed we present a review of the results concerning more specifically mineralogical systems: X-ray absorption spectroscopy concerning high-resolution edge spectra and Extended X-ray absorption fine structure (EXAFS), X-ray diffraction under high P-high T conditions, small-angle scattering, X-ray microanalysis and X-ray topography. For each technique the basic principles are described together with the experimental devices used, before mineralogical examples are given. Two main applications may be pointed out: chemical and structural characterization of disordered systems and kinetic studies (phase transitions and evolution). Many other techniques (photoelectron spectroscopy, X-ray fluorescence analysis ...) which are actually under development as a result of the rapid increase of the use of storage rings are not covered in the present review but will possibly also be used in the near future in Earth Sciences.     

Heterogeneous shock-induced thermal radiation in minerals

A 500 channel optical imaging intensifying and spectral digital recording system is used to record the shock-induced radiation emitted from 406 to 821 nm from transparent minerals during the time interval that a shock wave propagates through the sample. Initial results obtained for single crystals of gypsum, calcite and halite in the 30 to 40 GPa (300 to 400 kbar) pressure range demonstrate greybody emission spectra corresponding to temperatures in the 3,000 to 4,000 K range and emissivities ranging from 0.003 to 0.02. In the case of gypsum and calcite, distinctive line spectra, are superimposed on the thermal radiation. The observed color temperatures are a factor of 2 to 10 greater than the Hugoniot temperature, calculable on the basis of continuum thermodynamics and equation of state models for the shock states achieved in the three minerals. These observed high temperatures are believed to be real. We conclude that we are detecting a large number of closed spaced high temperature shear-band regions immediately behind the shock front. A shear instability model, such as proposed independently by Grady (1977, 1980), Ananin et al. (1974), and Horie (1980), in which small zones of highly deforming and melted material are produced which are the source of the detected thermal radiation and have a fractional effective area approximately numerically equal to the measured emissivity, can be used to predict an effective emissivity of 0.0065 directly behind the shock front. If shear band instability arises from viscous flow processes, Grady's model and mineral thermal properties yield for the shocked mineral viscosities values in the range of 10⁹ to 10¹⁵ P immediately behind the shock front.     

2p X-ray absorption of titanium in minerals

Ti 2p X-ray absorption spectra for a series of minerals have been measured. Crystal field multiplet calculations can explain the spectral shape. The asymmetry of the e _g , peak is shown to be related to distortions of the Ti ^IV octahedron. It is found, theoretically as well as experimentally, that the absorption spectra are more sensitive to tetragonal distortions than to trigonal distortions. A number of silicate minerals and metamict minerals containing titanium are measured and Ti ^III has not been observed in any of these minerals. A comparison is made to the 1s X-ray absorption, and the potential of both for the study of minerals is discussed.     

白云鄂博REE—Fe—Nb矿床稀土氟碳酸盐矿物激光拉曼光谱特征及流体包裹体内稀土子矿物的鉴定

白云鄂博REE－Fe-Nb矿床典型稀土氟碳酸盐矿物都具有碳酸根离子最特征的拉曼振动频率，并普遍出现有氟化物的拉曼光谱振动峰。利用子矿物的激光拉曼峰特征，结合矿物晶形和扫描电镜能谱分析结果，可以确定这些矿物可能为氟碳铈矿和氟碳铈钡矿，说明初始成矿热液中极富含稀土元素，矿脉内多相包裹体中含稀土元素的子矿物是从被包裹体捕获的流体中结晶出来的，是真正的子矿物，激光拉曼光谱仪可以作为鉴定流体包裹体中未知子矿物的较为可靠手段之一。     

Quantification of mineral matter in the Argonne Premium Coals using interactive Rietveld-based X-ray diffraction

The mineral matter in the eight reference North American coal samples of the Argonne Premium Coal series has been investigated on a quantitative basis using X-ray diffraction (XRD) techniques. X-ray diffraction data obtained from electronic low-temperature (oxygen–plasma) ash (LTA) residues, from ashes produced by heating the coals in air at 370°C, and also from the raw coals themselves, were evaluated using an interactive data processing system ( ™) based on Rietveld interpretation methods. The results from the three types of material (LTA, 370°C ash and raw coal) were compared for each sample. This allowed the components present in the raw coals in crystalline form to be recognised separately from mineral artifacts produced, particularly in the low-rank coals, from interaction of organically associated elements (Ca, S, etc.) during the two ashing processes.After the allowance for the production of any artifacts, the quantitative mineral assemblages identified from XRD of the raw coals were found to be consistent, even for coals having a relatively low ash percentage (around 5%), with the results obtained from the respective mineral concentrates prepared by the ashing methods. The effects of heating the coal to 370°C could also be distinguished, relative to the raw coal or the LTA, through changes in components such as pyrite and the clay minerals.Although some areas of uncertainty exist, particularly with magnesium in the low-rank coals, the calculated chemical compositions of the coal ash derived from the mineral mixtures identified for each coal were also found to be consistent with the results of direct chemical analysis of the respective coal ash materials.     

Advances in energy-dispersive X-ray fluorescence

Recently, two new instruments for X-ray fluorescence analysis (XRF) with interesting features for geochemical applications came to the market. Both instruments were designed to improve the peak to background ratio, the principal factor limiting the sensitivity of XRF. Total reflection XRF (TXRF) was designed to analyse extremely small sample amounts. An instrument, using polarised X-rays (P-XRF) for excitation, is designed to reduce scattered background in spectra of bulk samples. The performance of both instruments was compared with conventional XRF-methods and ICP/MS. Results for GXR-1, GXR-2, GXR-3, GXR-4 and GXR-6 obtained with TXRF and P-XRF are in good agreement with literature data. The effective amount of sample, analysed by TXRF was 200 μg only and detection limits of ~ l μg/g were achieved. P-XRF shows considerable improved detection limits (0.25–0.5 μg/g) for bulk samples for elements with atomic numbers 42–51 (Mo-Sb) compared with conventional XRF-methods.