1:30pm - 1:45pm
µ-EDXRF based classification of chromites. A quick approach for testing hand specimen and drill cores.
Chromites from ophiolites and layered intrusions show a wide variety in Cr#, Mg# and Cr/Fe ratios. These ratios provide information on the genesis of the chromite deposits e.g. the place of formation.
By means of µ-EDXRF this information can be obtained in a very quick way from cut hand specimen.
Unfortunately, chromites show a number of very intensive diffraction signals due to the polychromatic beam of the µ-EDXRF system, which even after calculating the minimum of two detectors has still some influence on the chemistry of a single chromite grain.
To reduce this problem, chromite aggregates were segmented and for each individual grain, the shapes were used to calculate the mean spectra for both of the detectors (D1/D2), the minimum (min) of both, the mean, the detector minus minimum of both (D1/2-min) to localize the position of the diffraction signals in the spectrum.
All individual grain D1 and D2 spectra are plotted against each other to detect those grains showing a minimum of diffraction, to reduce the diffraction impact on the chemical signal.
Assuming that the chemical pattern of chromite grains within a texturally homogeneous sample should not be to extreme regarding Cr# and Mg# those grains of minimum D1/D2 deviation were selected to represent the chromite chemistry. Validation is done by microprobe analysis.
In a second step these “pure” pattern of selected samples referring to individual tectonic levels of an ophiolite are used as endmembers for hyperspectral classification of chromite of various samples into individual groups/tectonic levels.
1:45pm - 2:00pm
X-ray absorption spectroscopy study of Mn reference compounds for the identification and quantification of Mn species in soils
1Soil Mineralogy Group, Institute of Mineralogy, Gottfried Wilhelm Leibniz University Hannover, Callinstr. 3, D-30167 Hannover, Germany; 2Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, D-30655 Hannover, Germany
Chemical reactivity, mobility, and bioavailability of manganese (Mn) in the environment depend crucially on its speciation. Despite the broad application of X-ray absorption spectroscopy (XAS) to environmental samples, studies covering the identification and quantification of Mn species in soils are surprisingly scarce. In this study, we analyzed 32 organic and inorganic Mn reference compounds by Mn K-edge (6,539 eV) XAS to assess the potential of XAS to differentiate various Mn coordination environments in soils. X-ray absorption near-edge structure (XANES) spectra of reference compounds were evaluated for the oxidation state of Mn using linear combination fit analysis. Results of this analysis were validated by redox titrations. The average local coordination environment (<5 Å) of Mn was analyzed by shell-fitting of extended X-ray absorption fine structure (EXAFS) spectra. Based on spectroscopic data and statistical data analysis, Mn reference compounds were grouped into physically and/or chemically meaningful clusters with diagnostic spectral features. Our results show that XANES spectroscopy can accurately determine the average oxidation state of Mn within 0.12 valence units. EXAFS spectroscopy is capable of differentiating at least three major Mn species groups, which include Mn(III/IV) manganates, Mn(III) oxyhydroxides and organic Mn(III) compounds. Using this information, we elucidated the oxidation state and local coordination environment of Mn in Cambisols, Luvisols, and a Stagnosol (L, O, A, B, and C horizons). Our talk will highlight the capabilities and limitations of XAS in analyzing Mn speciation of bulk soils and provide a guide for scientists exploring the biogeochemical Mn cycle in soil environments.
2:00pm - 2:15pm
Large-scale quantification of Li in spodumene pegmatite using Laser Induced Breakdown Spectroscopy
Bundesanstalt für Geowissenschaften und Rohstoffe, Germany
Spatially detailed surface analysis of geological samples and drill cores offers insight into element and mineral distributions on large scales, an important information in ore exploration processes.
Laser Induced Breakdown Spectroscopy (LIBS) is an uprising technology that allows fast in-situ geochemical measurements directly on a sample surface under atmospheric conditions. Since nearly no sample preparation is needed, the technology is suitable for spatially-resolved measurements on large samples such as drill cores. LIBS also allows the detection of light elements like Li, an important element due to the increasing amounts needed for battery production of all kinds. Nevertheless, interpreting LIBS data is challenging, since various physical and chemical matrix effects do not allow a straightforward analysis of heterogeneous material. Especially quantification remains problematic.
We used a LIBS drill core scanner (Nd:YAG Q-switched 20Hz 1064nm laser and a high-resolution 285-964nm Echelle spectrometer) for 1D profile measurements of 10 consecutive drill core meters from the Rapasaari Li-deposit in Finland. The deposit covers Li-bearing spodumene and muscovite pegmatite, from which five large samples were measured with high resolution in 2D, as well. Small-scale ICP-MS mappings were used as pixel-matched quantitative reference measurements of Li concentrations. They were successfully co-registrated with the LIBS measurements, which enabled matrix-matched quantification using chemometric quantification models.
2:15pm - 2:30pm
Systematic analysis of precision, long-term stability and data processing of MC-ICP-MS 230Th/U-dating of secondary carbonates
Institute for Environmental Physics, Heidelberg University, Germany
MC-ICP-MS has become the clearly dominant technology in 230Th/U-dating over the last 20 years. The ongoing increase in measurement performance allows for ε-precision by now (Andersen et al., 2004; Cheng et al., 2013) and enabled the production of a large amount of datasets and insights covering a broad range of fields. Despite this large database, systematic studies on the impact of individual corrections on the raw data, long-term instrumental stability and on data processing routines are still sparse.
We present the measurement and data analysis protocols developed and applied at the Institute for Environmental Physics at Heidelberg University and examine the contribution of individual corrections, such as tailing and hydride correction, to the total uncertainties of the atomic ratios 230Th/238U and 234U/238U and of the ages for this procedure. As demonstration examples, three different speleothem samples of different U and Th concentrations and ages were chosen. This puts specific quantitative constraints on general findings as the dominance of tailing correction.
Long-term instrumental stability is examined by compiling a multi-year dataset of (230Th/238U) and (234U/238U) for the Harwell-Uraninite 1 (HU-1) reference material of more than thousand measurements which is then used for the recalibration of the inhouse 229Th, 233U and 236U spike. Lastly, we present a Python-based GUI for the combined evaluation of mass-spectrometric data and age determination that offers high flexibility with regard to the variation of input constants, such as the initial (230Th/232Th) used for detritus correction.