Raman Microprobe Analysis Research Articles

The Giant Muruntau Gold Deposit: Geologic, Geochronologic, and Fluid Inclusion Constraints on Ore Genesis

We reinterpret the regional geologic setting of the giant Muruntau gold deposit and report new 40 Ar/ 39 Ar isotope age determinations and a laser Raman microprobe analysis of fluid inclusions. New 40 Ar/ 39 Ar isotope age determinations of hydrothermal sericite selvages to gold-stage quartz veins are in excellent agreement with older Rb-Sr dates on auriferous quartz veins. They suggest Triassic sericite formation at 245 and 220 Ma, some 30 m.y. later than subjacent felsic intrusions as defined by Rb-Sr data. These dates call into question the role of magmatic fluid, metal, and heat input. Indeed, the Rb-Sr pluton ages may be a reflection of hydrothermal activity rather than cooling from magmatic conditions. The Muruntau deposit is situated adjacent to a major rift, which has been periodically active from the Devonian to the Tertiary and has accumulated a substantial thickness of chemical, volcaniclastic, and clastic sediments, including red beds and evaporites. We infer that the Muruntau deposit is so large because of the presence of a major source of reduced sulfur in these nearby evaporitic sediments, via thermochemical sulfate reduction. Some support for the role of reduced sulfur is provided by the presence of detectable H2S in fluid inclusions from late-stage auriferous quartz veins. Reduced sulfur-rich fluids could have been focused into the depositional site along major northeast-trending structures, which have influenced rift-basin architecture as recently as the Jurassic. Oxidation could, therefore, be an important ore-precipitating mechanism. A change from early CH4- to later syngold CO2dominant fluid inclusions may be an indication of this process.

A fluid inclusion study of the Fosterville Mine: a turbidite-hosted gold field in the Western Lachlan Fold Belt, Victoria, Australia

Gold mineralisation at Fosterville occurs in association with disseminated arsenopyrite and pyrite adjacent to a complex series of quartz/carbonate veins along two NNW-trending fault zones. Quartz/carbonate veins, which have formed in dilational fractures within the sulphide ore zone, have δ 18O values between 16.0 and 17.6‰ and contain the following types of fluid inclusions: Type Ia two-phase, liquid-rich inclusions with less than 10 vol.% vapour and no detectable gases, Type Ib two-phase inclusions with approximately 10 vol.% CO 2-rich vapour, Type II CO 2-bearing inclusions with >30 vol.% vapour, and Type III liquid H 2O and liquid plus vapour CO 2 inclusions with variable H 2O/CO 2 ratios. Raman microprobe analysis showed that Types Ib, II and III contain CO 2 with variable amounts of N 2 and CH 4 in some inclusions. Type 1a, aqueous inclusions from Stage 4 of the paragenesis, have salinities ranging from 5 to 7 wt.% NaCl equivalent whereas the CO 2-bearing inclusions in the same stage, have average salinities around 3.5–4.0 wt.% NaCl equivalent. The CO 2-bearing inclusions exhibited two different types of homogenisation behaviour. Vapour-rich Type II and III inclusions either homogenised to vapour or showed near critical behaviour by gradual fading of the meniscus with homogenisation temperatures from 234 to 384°C and a mode at 270°C. Liquid-rich CO 2-bearing inclusions homogenised to the liquid phase with a bimodal distribution. The majority of inclusions homogenised between 243°C and 314°C with a mode around 270°C but a secondary mode occurs around 180°C. This mode corresponds fairly closely to the mode observed for the aqueous Type 1a inclusions at 170°C. The variable salinities, coexisting liquid- and vapour-rich inclusions, and the overlap of the homogenisation temperatures suggest that phase separation has occurred during vein formation and the resulting depth of mineralisation is estimated to be between 2.6 and 5.7 km. Gold precipitation resulted from the partitioning of H 2S into the vapour phase during fluid unmixing which was enhanced both by the decreasing pressure as fluid flowed from the faults and veins into the host rocks and by the addition of N 2 and CH 4. Comparisons with available fluid inclusion data for the Western Lachlan Fold Belt indicates that the Fosterville gold field formed at lower temperatures and at a higher crustal level than the quartz reef style of gold deposits in the Bendigo–Ballarat Zone. The fluids at Fosterville also contain greater amounts of N 2 and CH 4 suggesting that the mineralising fluids penetrated further into the host rocks and reacted either directly with carbonaceous matter or with reduced fluids contained within the host rocks.

Microstructural analysis of silicon carbide monofilaments.

In the development of monofilaments, a good understanding of the process/property relationships is essential. Transmission electron microscopy (TEM) is a powerful tool but too slow and expensive to be used routinely. Alternative, cheaper techniques have therefore been investigated. The microstructures of three SiC monofilaments (DERA Sigma SM1140+, Textron SCS-6 and Ultra-SCS) and some experimental samples were studied using a combination of TEM, electron microprobe analysis, Raman microprobe analysis, thermo-gravimetric analysis (TGA) and differential scanning calorimetry (DSC). It was found that the Raman technique was complementary to TEM and easily identified the presence of amorphous C and Si. These could not be seen by electron or X-ray diffraction techniques. DSC indicated the presence of free Si in the DERA Sigma SM1140+ monofilament by a distinctive peak at approximately 1400 degrees C. TGA showed the reaction of monofilament components with gaseous species. The Textron SCS-6 and Ultra species lost weight as C was oxidized to gaseous CO. By contrast, the Sigma monofilament gained weight from formation of SiO2 from the free Si. The separations of the transverse optical phonon peaks in the Raman spectra were correlated with the density of stacking faults in the SiC crystallites. This was similar in all monofilaments. Analysis of the polarization of the Raman scattering gave information on the orientation of crystallites. The crystallites in SM1140+ and SCS-6 were orientated predominantly with the <111> parallel to the radius. Preliminary interpretation of the polarized Raman scattering from Ultra-SCS indicated more than one orientation of crystallite. One possibility was a mixture of <111> and <110> directions parallel to the radius.

Corundum and zincian spinel from the Kakkonda geothermal system, Iwate Prefecture, northeastern Japan

Corundum and zincian spinel were found in a drill core of thermally metamorphosed rock at 2843 m in depth of the deep research well, WD-1, in the Kakkonda geothermal area, northeastern Japan. Corundum is surrounded by K-feldspar, and the occurrence suggests that corundum was formed by the decomposition of muscovite. Andalusite occurs in the same sample, without sillimanite. The petrography and previous works on phase relations between aluminous minerals suggest that corundum was formed at 600-700°C and 100 MPa at the peak of contact metamorphism. The ZnO content of spinel exceed 20 wt.%, and has a gahnitic composition. Zincian spinel is surrounded by K-feldspar as well as corundum, and it is assumed that spinel was formed by a similar reaction to the case of corundum. Two-phase vapor-rich and liquid-rich fluid inclusions occur in corundum, and they probably represent fluids formed at the metamorphic stage. A laser Raman microprobe analysis detected the presence of CO2, H2S and N2 in the fluid inclusions. The occurrence and analyses of the fluid inclusions indicate that the fluid produced during the thermal metamorphism at Kakkonda was low-salinity with gases and water.

Large areal extent of ultrahigh-pressure metamorphism in the Sulu ultrahigh-pressure terrane of East China: new implications from coesite and omphacite inclusions in zircon of granitic gneiss

Coesite and omphacite inclusions have been identified for the first time as minute inclusions in zircon from amphibolite-facies granitic orthogneiss in the Sulu ultrahigh-pressure (UHP) metamorphic terrane of eastern China by Raman spectroscopy and microprobe analyses. The occurrences of these minerals in the voluminous granitic gneiss of Sulu support a regional and pervasive UHP metamorphic event that predated regional amphibolitic retrogression. Taking into account the widespread discoveries of coesite in other lithologies, we thus conclude that a substantial crustal component in the Sulu UHP metamorphic terrane appears to have shared a common history of Triassic subduction to mantle depths and later exhumation.

Methane-rich fluid inclusions in the Proterozoic Zn–Pb–Ag deposit at Dugald River, NW Queensland: potential as an exploration guide

Calculated isochores, determined from microthermometry and laser Raman microprobe analysis, for CH 4 inclusions hosted in quartz grains from 3 different ore types in the Dugald River Zn–Pb–Ag deposit yield fluid trapping P–T conditions of 300–350°C and 0.8–2.3 kbar for post-depositional metamorphic conditions of sulfide mineralization. The consistent relationship between fluid composition and metamorphic grade of the host rocks suggests that CH 4 has been formed by reaction of graphite with aqueous fluids during metamorphic retrogression. Even though fluids responsible for mineralization are generally similar to those for barren quartz veins in chemistry and microthermometry, the substantial contents of CH 4 and CO 2 in the Dugald River lode inclusions contrast sharply with CO 2 alone in barren vein inclusions. The presence of CH 4-rich inclusions in the mineralization at Dugald River and other similar deposits, and their absence in the barren veins in a regional context, can be regarded as a possible exploration guide for defining target areas hosting mineralization of this style.

Semiconductor Thin Film Characterization Via Raman Microprobe Spectroscopy: Analysis At The Process Line

Raman Microprobe Spectroscopy has been used in research laboratories to model the growth of thin film silicide layers and the re-crystallization of α-silicon, however little progress has been made towards using these techniques as either at line or on line tools.At line and on line instrumental techniques such as ellipsometry and X-Ray Fluorescence have been used to characterize the physical properties of thin films in the semiconductor industry, which has lead to improvements in device yields. These techniques, however, do not provide the specificity to determine thin film phase changes which result in improved device performance, whereas Raman Microprobe Spectroscopy can monitor these changes.In order to perform at line or on line measurements, the spectrometer must be moved to the process line floor. The recent improvements in spectrometer design which has produced systems robust enough to endure high technology manufacturing environments will be briefly discussed. Two case studies of semiconductor process monitoring via Raman Microprobe analysis will be presented.

Ion beam modification of PES, PS and PVC polymers

MeV ions passing through polymer films modify their electrical and optical properties and these changes are related to changes in the chemical structures of the polymers. The effects of certain cross linking enhancers, such as sulfur and other pendant molecules, on the ion beam modification process were investigated. Stacked, thin films of polyethersulfone, polyvinyl chloride and polystyrene were bombarded with MeV helium ions and the induced changes in the chemical structure of the polymers were studied with Raman microprobe analysis and RBS combined with in situ residual gas analysis. FTIR spectroscopy was used to categorize the changes in the optical properties. The results were then compared with those from previously studied polyethylene and polyvinylidene chloride polymers.

A fluid inclusion study of syntectonic Zn-Pb-Ag mineralization at Dugald River, Northwest Queensland, Australia

Petrographic, microthermometric, and laser Raman microprobe analyses of fluid inclusions from the Zn-Pb-Ag sulfide deposit at Dugald River, northwest Queensland, indicate that fluids with a wide range of compositions in the CO 2 -CH 4 -H 2 O-NaCl system were involved in the formation of the deposit. Early primary inclusions are characterized by higher homogenization temperatures centered on 360 degrees C, an average salinity of 13 wt percent NaCl equiv, and they tend to be relatively CO 2 -rich. Such a fluid migrating through the thick sequence of the middle Proterozoic metasediments of the Corella Formation would acquire metals and reduced sulfur as well as CH 4 due to its interaction with the country rocks at deep levels. Ore deposition is interpreted to have resulted from Syntectonic boiling of CH 4 -rich volatile and aqueous chloride solutions, and consequent filling and replacement of brecciated and foliated black slate by metal-bearing hydrothermal fluids. The pressure and temperature conditions of mineralization show a narrow pressure range of 1.1 to 1.5 kbar and a wide temperature range of 315 degrees to

Occurrence and distribution of “moganite” in agate/chalcedony: a combined micro-Raman, Rietveld, and cathodoluminescence study

Agate/chalcedony samples of different origin were investigated by performing Raman, X-ray diffraction (using Rietveld refinement), and cathodoluminescence measurements. These analyses were performed to measure the content and spatial distribution of the silica polymorph moganite, which is considered to represent periodic Brazil-law twinning of α-quartz at the unit-cell scale in agate/chalcedonies. Homogeneous standard samples including the nearly α-quartz free moganite type material from Gran Canaria were analysed in order to compare results of the X-ray diffractometry and Raman spectroscopy techniques and to provide a calibration curve for the Raman results. However, due to the different length scales analysed by the two techniques, the “moganite content” in microcrystalline SiO2 samples measured by Raman spectroscopy (short-range order) was found to be considerably higher than the “moganite content” measured by X-ray diffractometry (long-range order). The difference is explained by the presence of moganite nanocrystals, nano-range moganite lamellae, and single Brazil-law twin-planes that are detected by vibrational spectroscopy but that are not large enough (in the sense of coherently scattering lattice domains) to be detected by X-ray diffractometry. High resolution Raman analysis provides a measure of the moganite content and its spatial variation in microcrystalline silica samples with a lateral resolution in the μm-range. Variations in the moganite-to-quartz ratio are revealed by varying intensity ratios of the main symmetric stretching-bending vibrations (A1 modes) of α-quartz (465 cm−1) and moganite (502 cm−1), respectively. Traces of Raman microprobe analyses perpendicular to the rhythmic zoning of agates revealed that the moganite-to-quartz ratio is often not uniform but shows a cyclic pattern that correlates with the observed cathodoluminescence pattern (colour and intensity). Data obtained from an agate sample from a fluorite deposit near Okorusu, Namibia and from a volcanic agate from Los Indios, Cuba were selected for detailed presentation. Variations of cathodoluminescence and Raman data between single bands in agates suggest alternating formation of fine-grained, highly defective chalcedony intergrown with moganite, and coarse-grained low-defect quartz. Multiple zones indicate dynamic internal growth during a self-organizational crystallization process from silica-rich fluids.

Structural changes in GaAs induced by ultrafast (fs) laser pulses

Ultrafast changes in the crystal structure of GaAs induced by intense femtosecond laser pulses are detected and investigated. Atomic force microscopy and Raman microprobe analysis of the laser-treated area show centrosymmetric (disordered) features which are different from the original zinc-blend structure of the GaAs lattice. The frozen-in structure shows evidence for a special heat transfer from the laser-induced crater to the boundary, namely the heat has been transferred ballistically by a high-density electron-hole plasma.

Effects of MeV ions on PE and PVDC

We studied the effects of 3.5 and 5.0 MeV alpha bombardment on polyethylene and polyvinylidene chloride, both of which have simple chemical structures. Using a thin polymer film stacking technique, we were able to map the effects of the MeV alpha particles in their track. The first layer of the thin polymer film stack experienced mostly the effects of the electronic energy deposited, and the last layer received mostly effects of the nuclear stopping. Using Raman microprobe analysis and by measuring the ratio of the formation of graphene structures (G-line) to the disordered (amorphous) carbon line (D-line), we were able to separate the severed bond effects at the end of the alpha particle tracks in the last polymer film layers from the effects of the electronic energy deposited in the first polymer film layers. The results are in agreement with our other measurements of each polymer film using FTIR, RBS and resistance measurements.

Extremely acid Permian lakes and ground waters in North America

Evaporites hosted by red beds (red shales and sandstones), some 275–265 million years old, extend over a large area of the North American mid-continent1. They were deposited in non-marine saline lakes, pans and mud-flats2, settings that are typically assumed to have been alkaline. Here we use laser Raman microprobe analyses of fluid inclusions trapped in halites from these Permian deposits to argue for the existence of highly acidic (pH <1) lakes and ground waters. These extremely acidic systems may have extended over an area of 200,000 km2. Modern analogues of such systems may be natural acid lake and groundwater systems (pH ∼2–4) in southern Australia3,4,5,6,7,8,9. Both the ancient and modern acid systems are characterized by closed drainage, arid climate, low acid-neutralizing capacity, and the oxidation of minerals such as pyrite to generate acidity. The discovery of widespread ancient acid lake and groundwater systems demands a re-evaluation of reconstructions of surface conditions of the past, and further investigations of the geochemistry and ecology of acid systems in general.

Raman microprobe analysis of strained polysilicon deposited layers

Microscopic strain distributions in varying thicknesses of polysilicon layers deposited as bridges over silicon substrates were determined by high resolution micro-Raman spectroscopy. In particular, we mapped the dependence of the first order Raman spectrum as a function of the position across polysilicon bridges (approximately 550 × 230 μm2), over tunnels etched in the silicon substrate. Shifts in Raman band frequencies as a function of position on the bridge structures were observed to be dependent upon the thickness of the membrane layer (between 1 and 3 μm) as well as the annealing conditions. Assuming a simplified uni-axial stress parallel to the surface, the effective tensile stress at the center of the bridge of thickness 2.5 μm is reduced by annealing from 2.5 GPa to 0.18 GPa.

Behavior of carbonate and magnesium ions in the initial crystallites at the early developmental stages of the rat calvaria

Analysis of the contents of calcium (Ca), magnesium (Mg), phosphate, and carbonate ions in the mineral phase of rat calvaria specimens obtained at different developmental stages indicated that the mineral at the newborn stage contained a negligible amount of carbonate, but a high content of Mg. There was no significant difference in Ca and phosphate (as PO4) contents between the newborn material and that from later stages. A relatively large amount of carbonate was detected in the calvaria from 6-day-old rats, in which only immature crystals were observed, thus indicating the beginning of apatite formation. Furthermore, using laser Raman microprobe analysis we confirmed that the Raman peak at 1120 cm-1 band, indicative of a Mg-CO3 compound, appeared at the 6-day stage. We also observed that the Raman peak at 988 cm-1 found in the samples from the newborn seemed to have shifted to 963-962 cm-1 in the case of those obtained from 6-day-old rats, a shift which suggests the conversion from the non-apatitic to the apatitic form. These results indicate that carbonate ions might facilitate the initiation of crystal development by converting the inhibitory Mg ion into its inactive form (Mg-carbonate compound).

Raman microprobe analysis of patterned Tl-2212 thin films

We have used MicroRaman spectroscopy to evaluate the effects of ion-milling on the exposed edges of patterned Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ (Tl-2212) lines. Raman microprobe has previously been used to evaluate oxygen loss at the edges of patterned YBCO lines. The results indicated that appreciable oxygen loss was caused by ion-milling under certain conditions. oxygen loss at the edges will decrease non-uniformly the effective width of the superconducting line. This can, in turn, impact the electrical characteristics of patterned devices. Using the 633 nm lined of a HeNe laser, we have measured the Raman spectrum scanning across patterned and unpatterned regions of several Tl-2212 films with a mapping stage. It is well known that the Raman peak at /spl ap/497 cm/sup -1/ corresponds to the Cu-O(2) stretching mode and is correlated with the superconducting transition temperature of the material. No appreciable variation in the center frequency of the Cu-O(2) peak was observed indicating thallium cuprate films are not degraded by our patterning process, even at the edges. Variations in the power handling of Tl-2212 co-planar lines, as determined by measurement of the Third Order Intercept, were not correlated with the Raman results.

Resolving the electronic and nuclear effects of MeV ions in polymers

The electronic and nuclear stopping effects produced by MeV ion bombardment in polyvinylidene chloride (PVDC) and polyethylene (PE) were separated by stacking thin films of the polymers. The resulting layered system consisting of each polymer was bombarded with 3.5 and 5.0 MeV alpha particles. A layered system was selected such that the first layers experienced most of the effects of the electronic energy deposited and the last layers received most of the effects of the nuclear stopping. The electrical conductance and the changes in the chemical structure were measured by direct resistivity measurements, Raman microprobe analysis and FTIR. Post-irradiation analyses of the films indicated differences in these properties in the various film layers which are attributed to the individual effects of the stopping powers in the polymer films.

Raman Study of the Chemical and Thermal Degradation of As-Received and Sol-Gel Embedded Nicalon and Hi-Nicalon SiC Fibres Used in Ceramic Matrix Composites

Raman microprobe analysis of Nicalon NLM 202 and Hi-Nicalon fibres as a function of thermal treatments in various atmospheres was carried out in order to understand the fibre evolution during the synthesis of composites and their use in combustion environments. Assignments are discussed and a description of the fibre structure on the nanoscale is proposed. A comparison is made between surface and core evolution of as-received fibres and of fibres used in the sol–gel route. The plateau observed between 1200 and 1600°C for Hi-Nicalon bands is consistent with a better thermal stability. © 1997 by John Wiley & Sons, Ltd.

Raman Study of the Chemical and Thermal Degradation of As‐Received and Sol–Gel Embedded Nicalon and Hi-Nicalon SiC Fibres Used in Ceramic Matrix Composites

Raman microprobe analysis of Nicalon NLM 202 and Hi-Nicalon fibres as a function of thermal treatments in various atmospheres was carried out in order to understand the fibre evolution during the synthesis of composites and their use in combustion environments. Assignments are discussed and a description of the fibre structure on the nanoscale is proposed. A comparison is made between surface and core evolution of as-received fibres and of fibres used in the sol–gel route. The plateau observed between 1200 and 1600°C for Hi-Nicalon bands is consistent with a better thermal stability. © 1997 by John Wiley & Sons, Ltd.

Nanosecond pulsed excimer laser machining of chemical vapour deposited diamond and highly oriented pyrolytic graphite: Part I An experimental investigation

A laser beam offers the benefits of high precision, contamination-free, high speed, and low bulk temperature for machining of chemically vapour deposited (CVD) diamond thin films that in turn enable ultrafine finishing of diamond coated cutting tool inserts and drills, and for finishing and drilling of diamond coated multichip module applications. In this work, laser hole drilling and polishing of CVD diamond (free-standing diamond and coated tool inserts) and HOPG (highly oriented pyrolytic graphite) using a 248 nm wavelength, 23 ns pulsed excimer laser were conducted. The threshold energy fluence required for ablation of diamond and graphite was nearly the same but the material removal rate rapidly increases with the energy fluence for the graphite compared to diamond. At an energy fluence of 10 J cm-2, the depth removed per pulse was 0.05 μm and 0.30 μm for diamond and graphite respectively. Raman microprobe analysis indicates that the laser machining induced the transformation of diamond to disordered forms of carbon in CVD diamond and some transformation of graphite to diamond in HOPG. The experimental data indicates that the transformation of diamond to graphite requires an energy input of 1.44 × 107 J per mole. For a given set of laser parameters, the depth per pulse was substantially higher for diamond coated tool inserts compared to the free-standing diamond. The surface roughness of CVD diamond was reduced by 0.25 μm per pulse at an energy fluence of 16 J cm-2