The estimation of the peak metamorphic temperature by Raman spectroscopy of carbonaceous material (RSCM) is influenced by several bias sources grouped in measuring conditions, spectral processing and ...sample heterogeneity. The measuring conditions (selected excitation wavelength) and the operator bias during spectral processing have a pronounced impact on the temperature estimate and thus on the comparability and portability of thermometric data obtained by RSCM. Several calibration lines of RSCM geothermometers are published already, but no standardised approach exists. Samples of carbonaceous material bearing metasediments with well‐established metamorphic conditions of the central and western Alps compile a reference series. By applying an automated, iterative and randomised curve‐fitting approach, a consistent and user input‐independent RSCM geothermometer is presented, which covers peak metamorphic temperatures from ca. 160 to 600 °C. The method is hardware independent because the measuring conditions bias is excluded by the use of the reference series and the automated curve‐fitting approach reduces the spectral processing bias effectively, increasing the method's comparability and portability. By distributing the reference series and the automated curve‐fitting software, a laboratory will be able to derive a laboratory specific calibration line for the RSCM geothermometer.
Key Points
Based on a novel evaluation scheme and a reference series a standardized methodology to RSCM geothermometry is presented.
The Scaled Total Area (STA)‐RSCM approach will increase the comparability of RSCM geothermometric data.
The STA‐RSCM approach provides a continuous geothermometer from ca. 160 to 600 °C
At the northwestern margin of the Gurktal Alps (Eastern Alps), Eoalpine (Cretaceous) thrusting of carbonaceous material (CM) bearing metasediments formed a very low- to low-grade metamorphic nappe ...stack above higher-grade metamorphic basement nappes. Sedimentary burial as well as progressive metamorphism transformed the enclosed CM to anthracite, metaanthracite and semigraphite. In a kinematically well-constrained section at the northwestern frontal margin of the nappe stack, this transformation has been investigated by vitrinite reflectance measurements and Raman spectroscopy of carbonaceous materials (RSCM). Automated, interactive fitting of Raman spectra estimates the metamorphic peak temperatures in a complete section through the upper part of the Upper Austroalpine unit. A RSCM trend indicates a temperature profile of ca. 250–600 °C. The top part of the gradient is reconstructed by one-dimensional thermal modeling. The certainty of ca. ± 25 °C at a confidence level of 0.9 resembles the data variability within a sample location. Due to the large calibration range, the method is able to reconstruct a thermal crustal profile in space and time. The study highlights the versatility of RSCM, which characterizes almost 250 Ma of a complex and polyphase tectonic history. RSCM data characterize the Variscan metamorphic grade in nappes now imbricated in the Eoalpine nappe stack. They additionally constrain a numerical model which emphasizes the significance of an increased thermal gradient in a continental margin towards the western Neotethyan ocean during Permo-Triassic lithospheric extension. It finally characterizes the Eoalpine metamorphic gradient during nappe stacking and a significant metamorphic jump related to exhumation and normal faulting.
The growth conditions of natural graphite crystals are conventionally estimated by the application of petrological methods on the host rocks. As Raman Spectroscopy records detailed information on the ...microstructure of a carbon-material, this method is applied empirically to graphite from the southern margin of the Bohemian Massif to investigate the correlation between microstructure and metamorphic peak conditions directly, characterizing an economically important geomaterial. Automated fitting of the second-order Raman-spectrum of graphite assesses the strongly asymmetrical S2-band at ca. 2700 cm−1 by a shape parameter, characterizing the microstructural state of graphite. Applying this concept, a confident parameter (S2-shape) estimates the peak metamorphic temperature of natural graphite crystals between 600 °C and 800 °C. The application in the southern Bohemian Massif maps metamorphic peak temperatures related to Variscan tectonics. Comparing the microstructure of large crystals from graphite seams with tiny crystals dispersed in the rock matrix, there is evidence that small graphite particles are not influenced by a late-stage overprint.
•The shape of the second order Raman band estimates graphitization temperatures.•The formation temperatures of graphite from the Variscan belt are estimated directly.•A graphite ore is more temperature-sensitive than dispersed graphite grains.
Raman spectroscopy of carbonaceous material (RSCM) is frequently used to determine metamorphic peak temperatures from the structural order of carbonaceous material enclosed in metasediments. This ...method provides a quick, robust and relatively cheap geothermometer. However, the comparability of the RSCM parameter is low as there are at least three major sources of biasing factors. These sources are the spectral curve‐fitting procedure, the sample characteristics itself and the experimental design including the used Raman system. To assess the impacts of the biasing factors on RSCM, a series of experiments was performed. The experiments showed that curve‐fitting is strongly influenced by individual operator‐bias and the degrees of freedom in the model, implying the need for a standardised curve‐fitting procedure. Due to the diversity of components (optics, light detection device, gratings, etc.) and their combinations within the Raman systems, different Raman instruments generally give differing results. Consequently, to estimate comparable metamorphic temperatures from RSCM data, every Raman instrument needs its own calibration. This demands a reference material series that covers the entire temperature calibration range. Although sample heterogeneity will still induce some variation, a reference material series combined with standardised curve‐fitting procedures will significantly increase the overall comparability of RSCM data from different laboratories.
La spectroscopie Raman du matériel carboné (RSCM) est fréquemment utilisée pour déterminer les températures des pics métamorphiques à partir de l'organisation structurale du matériau carboné des métasédiments. Cette méthode fournit un géothermomètre rapide, robuste et relativement peu onéreux. Toutefois, la comparabilité du paramètre RSCM est faible car il y a au moins trois grandes sources de biais. Ces sources sont la procédure d'ajustement de la courbe spectrale, les caractéristiques de l'échantillon lui‐même et la conception expérimentale, y compris le système Raman utilisé. Pour évaluer les impacts des facteurs de biais sur la RSCM, une série d'expériences a été effectuée. Les expériences ont montré que la procédure d'ajustement de la courbe spectrale est fortement influencée par les biais de l'opérateur et les degrés de liberté du modèle, ce qui implique la nécessité d'une procédure d'ajustement de type courbe standardisée. En raison de la diversité des composants (optique, dispositif de détection de la lumière, grilles, etc.) et leurs combinaisons au sein des systèmes Raman, différents instruments Raman donnent généralement des résultats différents. Par conséquent, pour estimer des températures métamorphiques comparables à partir des données RSCM, chaque instrument Raman a besoin de son propre étalonnage. Cela exige l'utilisation d'une série de matériaux de référence qui couvre toute la gamme d'étalonnage de la température. Bien que l'hétérogénéité des échantillons induise encore une certaine variation, une série de matériaux de référence combinée avec des procédures d'ajustement de courbes standardisées permettra d'accroître considérablement la comparabilité globale des données de RSCM provenant de différents laboratoires.
Raman spectroscopy traces the microstructural evolution of carbonaceous matter (CM) during artificial heating. Thermo-chemical reactivity and strength of blast furnace coke at 1100 °C is dependent on ...the graphitization state of the feed coke. A standard coke reactivity index (CRI) sample is composed of lumps, showing a high microstructural variability. The frequency distribution of the D-STA parameter estimated by the “Interactive Fitting of Raman Spectra” (IFORS) software suggests a positive correlation between degree of CM organization and CRI. Samples from the tuyere region of an operating blast furnace evidence graphitization of CM at temperatures higher than 1900 °C. IFORS parameters, calibrated by x-ray diffraction-based lattice dimensions and transmission electron microscopy data constrain a temperature gradient decreasing from the raceway to the deadman zone. The gradient controls a continuous variation of the petrographic coke texture. As an application, the IFORS method is able to map the graphitization zones in the hearth of a working blast furnace.
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•“Interactive Fitting of Raman Spectra” on carbonaceous matter provides spectral parameters to trace the structural evolution of coke within the entire blast furnace.•Coke reactivity is dependent on the graphitization state of the feed coke.•Within the tuyere zone of a blast furnace, the textural coke composition is correlated to its microstructural state, controlled by a temperature gradient towards the tuyere openings.
Metallurgical coke should be resistant to mechanical, thermal, and chemical influences. This resistance is related to the structural order of the organic constituents. Raman microspectroscopy of ...carbonaceous matter (RSCM) is demonstrated as a promising tool to investigate this property. Variations of the microstructure among samples with different quality parameters are detected by analyzing the Raman spectra collected on their individual coke lumps. Three basic types of Raman spectra are discriminated. Their predominance in a bulk sample predicts roughly the coke quality, estimated by an ISO standardized test. To investigate the structural behavior of coke in a blast furnace, several samples have been treated under typical gas atmospheres of the blast furnace process (carbon dioxide, nitrogen) at temperatures between 850°C and 1100°C for 120min. RSCM data measured on the treated lumps evidence a progressive transformation of poorly ordered organic microstructure towards a higher structural order.
•Three basic types of Raman spectra are discriminated in coke.•Raman microspectroscopy predicts roughly the coke quality.•Poorly ordered coke microstructure is transformed towards a higher order.
Conventional (anthracite, calcined petroleum coke, and coke) and non-conventional (biochar, and biocokes (3 wt.% torrefied wood, and 3 wt.% petroleum coke + 3 wt.% charcoal)) carbon-bearing sources ...have been studied for their use in electric arc furnace (EAF)-based steel production. Commonly, for the use of carbon sources in EAFs, one of the important properties is the content of fixed carbon, the release of volatiles as well as the elemental composition of inorganics. The properties of six carbon sources were analyzed by determining the proximate analysis, X-ray fluorescence analysis (XRF), coke reactivity index (CRI), and strength after reaction with CO2 (CSR), Brunauer–Emmett–Teller (BET) specific surface area and Barrett–Joyner–Halenda (BJH) pore size and volume analysis, ash chemical analysis, optical and scanning microscopy, Raman spectroscopy and X-ray diffraction (XRD) analysis. The results indicate biocoke as a promising option to replace conventional carbon-bearing sources. In the sample set, the fixed carbon, volatiles, and ash content of the biocokes were similar despite the total difference in additives. Additionally, the use of additives did not significantly affect the biocoke reactivity indices, but slightly decreased the strength after the reaction with CO2. Carbon-bearing sources have been characterized in terms of their structural properties. XRD analysis revealed that the amount of disordered carbon increased in the order: coke < calcined petroleum coke ~ biocoke (3 wt.% torrefied wood) < biocoke (3 wt.% petroleum coke + 3 wt.% charcoal) < biochar. The results obtained on the physical, chemical, and structural properties of carbon sources are the basis for further research on the behavior of slag foaming.
The Carnic Alps (eastern Southern Alps) provide a classical area to study polyphase very-low- to low-grade metamorphism within the Variscan belt of Europe. Temperature indicators collected during the ...past three decades map the general metamorphic structure of a mountain chain affected by three major tectonic events (Variscan and Alpine thrusting, Oligocene transpression). Thermometric data obtained by Raman Spectroscopy of carbonaceous material (RSCM) described in this study extend the already published database, provide a map of metamorphic isotherms, and are interpreted in the view of current tectonic concepts. The RSCM temperatures of this study describe a gradient between ca. 460 °C in the tectonically deepest segments, bordered by the Periadriatic Fault System, and temperatures of ca. 200 °C in Permian- Triassic boundary strata of the Gartnerkofel-1 core. Mapped isotherms indicate three domains with different thermal histories, characterized by Variscan imbrication of an accretionary wedge, Permo-Mesozoic burial, and Oligocene contact metamorphism.
General P-T reconstruction of the conditions prevailing in the formation of epizonal gold deposits within Latimojong Metamorphic Complex, Indonesia, using combination of different mineralogical and ...geochemical techniques (i.e. Raman spectroscopy on carbonaceous material, electron microprobe analysis on chlorite and mica, fluid inclusion microthermometry and crush leach on bulk samples).
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•Epizonal gold mineralization was identified in the Awak Mas District, Indonesia.•The estimated trapping conditions of the gold are 180–250 °C and ca. 0.84–1.3 kbar.•Isothermal decompression mobilized large volumes of fluids leading to mineralization.•Accretionary complex may have contributed as host/as a driver of fluid generation.•Gold mineralization is not related to Neogene magmatism.
The gold deposits within the Latimojong Metamorphic Complex of Sulawesi, Indonesia, including Awak Mas and Salu Bulo, are estimated to host 50 tonnes Au with an average grade of 1.41 g/t. They are located within the metamorphic basement consisting of pumpellyite- to greenschist-facies metasedimentary and metavolcanic rocks, where gold precipitated in quartz veins that fill north-south striking normal faults and extensional fractures. The mineral assemblage is dominated by pyrite, chalcopyrite, galena, minor tetrahedrite-tennantite and sphalerite; gold is electrum with a low silver content (Au:Ag ratio of 8.5 to 9.1). Albite, dolomite-ankerite, siderite, chlorite, and white mica are the main alteration minerals. Quartz, albite and carbonate veins hosting H2O-bearing fluid inclusions with minor aqueous-carbonic phases (CO2 ± N2) were detected (mole fraction <0.15). Raman microspectroscopy, microthermometry, and crush leach analysis of gold-bearing quartz veins and associated host rocks provide evidence for processes resembling those described for epizonal gold mineralization. The gold bearing fluids have salinities between 1.4 and 7.3 eq. mass% NaCl and were trapped in quartz at about 180–250 °C and <1.27 kbar, corresponding to depths less than 5 km. Trapping conditions of barren veins are about 190–390 °C and <1.15 kbar with salinities ranging from 2.2 and 6.1 eq. mass% NaCl. Halogen and alkali ratios (Na/Cl/Br/I) from crush leach analyses correspond to deposits originating from metamorphic fluids with a strong albitization signature during ore formation. Isothermal decompression during the retrogression stage mobilized large volumes of fluids, leading to significant gold mineralization within the Awak Mas District.
Raman spectroscopy on carbonaceous matter reconstructs the progressive path of graphitization during granulite facies metamorphism in the Variscan collisional belt of the southern Bohemian Massif. In ...this area, heating to 650–750 °C gradually altered the graphite microstructure, attributed to a metamorphic field gradient. Late low-pressure and high-temperature metamorphism at temperatures above 800 °C as well as advective heat transport due to rising granulite diapirs improved the graphite lattice ordering significantly. Numerical parameters derived from the Raman spectra of carbonaceous matter, in particular the G-band width and the S2-band dispersion map metamorphic field gradients in high-grade metamorphic terrains.
•Raman spectroscopy effectively maps high-grade metamorphic field gradients.•Lattice-ordering of graphite is correlated to peak-metamorphic temperatures.•Graphite of the Bohemian Massif was gradually formed by Variscan metamorphism.
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