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Hannover, Germany

Zeelmaekers E.,Catholic University of Leuven | Zeelmaekers E.,Royal Dutch Shell | Honty M.,Belgian Nuclear Research Center | Derkowski A.,Polish Academy of Sciences | And 6 more authors.
Clay Minerals | Year: 2015

The Boom Clay Formation of early Oligocene age, which occurs underground in northern Belgium, has been studied intensively for decades as a potential host rock for the disposal of nuclear waste. The goal of the present study is to determine a reference composition for the Boom Clay using both literature methods and methods developed during this work. The study was carried out on 20 samples, representative of the lithological variability of the formation. The bulk-rock composition was obtained by X-ray diffraction using a combined full-pattern summation and singlepeak quantification method. Siliciclastics vary from 27 to 72 wt.%, clay minerals with 25-71 wt.% micas, 0-4 wt.% carbonates, 2-4 wt.% accessory minerals (mainly pyrite and anatase) and 0.5-3.5 wt.% organic matter. This bulk-rock composition was validated independently by majorelement chemical analysis. The detailed composition of the clay-sized fraction was determined by modelling of the oriented X-ray diffraction patterns, using a larger sigma star (σ∗) value for discrete smectite than for the other clay minerals. The <2 μm clay mineralogy of the Boom Clay is qualitatively homogeneous; it contains 14-25 wt.% illite, 19-39 wt.% smectite, 19-42 wt.% randomly interstratified illite-smectite with about 65% illite layers, 5-12 wt.% kaolinite, 4-17 wt.% randomly interstratified kaolinite-smectite and 2-7 wt.% chloritic minerals (chlorite, "defective" chlorite and interstratified chlorite-smectite). All modelled clay mineral proportions were verified independently using major-element chemistry and cation exchange capacity measurements. Bulkrock and clay mineral analysis results were combined to obtain the overall detailed quantitative composition of the Boom Clay Formation. © 2015 Mineralogical Society.

Arguello G.L.,National University of Cordoba | Dohrmann R.,BGR LBEG | Sanabria J.A.,National University of Cordoba | Zahn E.,National University of Cordoba
Journal of South American Earth Sciences | Year: 2010

This paper deals with a loess profile located southeast of Córdoba (64° 05′ 30. W to 31°30′ S) that was dated in Beijing University using the OSL method according to Simple Aliquot Regeneration Protocol. This study provides some inferences regarding climatic and environmental features, such as transport agents and probable sources of the materials.The profile, located inside Llanura Pampeana, is approximately 6.80. m in depth and comprises ages between 22.4 ± 3.2 and 9.9 ± 0.3. ka. Throughout the profile, and for all grain sizes, major minerals are quartz and feldspar, with micas, and opaques as subordinates. Illite and chlorite appear as traces, though the last one was not confirmed in the finest fraction analysis. Calcite is abundant in the uppermost sample and decreases downwards. In the base of the profile, and in the clay fraction, XRD showed illite, swellable clay minerals (smectite. +. mixed layers) and kaolinite traces. It was concluded that the profile would have been derived from the accumulation of sediments, along several events very similar in transport conditions, even though there are some indications that about 21. ka BP, water availability was slightly smaller than for the rest of the profile. This change was also established in some other places, allowing some regional correlations. According to the analyzed data, about 19. ka BP, water availability again increased. © 2009 Elsevier Ltd.

Ufer K.,TU Bergakademie Freiberg | Kleeberg R.,TU Bergakademie Freiberg | Bergmann J.,Ludwig Renn Allee 14 | Dohrmann R.,BGR LBEG
Clays and Clay Minerals | Year: 2012

X-ray diffraction (XRD) of powdered materials is one of the most common methods used for structural characterization as well as for the quantification of mineral contents in mixtures. The application of the Rietveld method for that purpose requires structure models for each phase. The recursive calculation of structure factors was applied here to the Rietveld refinement of XRD powder patterns of illite-smectite (I-S) minerals. This approach allowed implementation of stacking disorder in structural models. Models for disordered stacking of cis-vacant and trans-vacant dioctahedral 2:1 layers as well as rotational disorder were combined with models for mixed layering of illitic and smectitic layers. The DIFFaX code was used to simulate non-basal (hk) reflections of illites with different degrees of disorder. Rietveld refinements of these simulated patterns were used to evaluate the application of this new approach. A model describing rotational disorder (n·120° and n·60° rotations) and mixed layering of cisvacant and trans-vacant dioctahedral layers was tested. Different starting parameters led to identical results within the ranges of standard deviations and confirmed the stability of the automatic refinement procedure. The influence on the refinement result of an incorrect choice of fixed parameters was demonstrated. The hk model was combined with models describing the basal reflections of disordered I-S and tested on measured data. A glauconitic mineral (Urkut, Hungary), an ordered I-S (ISCz-1, a special clay in the Source Clays Repository of The Clay Minerals Society), and a dioctahedral I-S (F4, Füze ́rradva ́ny, Hungary) were used as test substances. Parameters describing the mixed layering of illitic and smectitic layers were compared with the results from refinements of oriented mounts and showed good agreement. A pattern of a physical mixture of an I-S mineral and a turbostratically disordered smectite was analyzed in order to test the new approach for application in quantitative phase analysis. The quantitative Rietveld phase analysis results were found to be satisfactory.

Ufer K.,TU Bergakademie Freiberg | Kleeberg R.,TU Bergakademie Freiberg | Bergmann J.,Ludwig Renn Allee 14 | Dohrmann R.,BGR LBEG
Clays and Clay Minerals | Year: 2012

X-ray diffraction patterns of oriented mounts of clay minerals are often used in clay mineralogy for qualitative and quantitative purposes. Fequently occurring stacking defects, in particular, can be characterized by this technique. Modeling of these diffraction profiles has become an important tool in obtaining structural information about the nature of stacking order. Manual matching of calculated and observed patterns is time consuming and user dependent. Automatic refinement procedures are, therefore, desirable. An improved approach for the treatment of disordered layer structures within a Rietveld refinement is presented here. The recursive calculation of structure factors, similar to that of the simulation program DIFFaX, was introduced in the Rietveld code BGMN. Complete implementation is formulated within the interpreter language of the Rietveld code and is transparent as well as flexible. Such a method has opened the application of Rietveld refinement to patterns of oriented mounts where only basal reflections of stacking disordered structures were recorded. The DIFFaX code was used to simulate basal reflections of illite-smectite mixed layers (I-S) with different ratios of illitic and smectitic layers and with different degrees of long-range ordering (Reichweite). Rietveld refinements with these simulated patterns were used to evaluate the application of this new approach. Several I-S with different degrees of ordering were also chosen as tests for the refinement of basal reflections. The samples were prepared as standard airdried and ethylene glycol-solvated, oriented specimens. Realistic structural parameters were obtained for the composition and ordering of the I-S.

Siegesmund S.,University of Gottingen | Popp T.,Institute fur Gebirgsmechanik GmbH Leipzig | Kaufhold A.,University of Gottingen | Dohrmann R.,BGR LBEG | And 3 more authors.
Environmental Earth Sciences | Year: 2014

For the safe disposal of high-level radioactive waste, different host rocks are currently being considered. The favorable properties of clay are low permeability, some retention capacity concerning radionuclides, and the ability to self-seal cracks and fissures, e.g. by swelling or time-dependent compaction creep. In Switzerland, the Jurassic Opalinus Clay is envisaged as a potential host rock which-at Mont Terri-is subdivided into the sandy, shaly, and carbonate-rich facies, the latter being less abundant. For long-term safety assessments, the understanding of the relations of properties (e.g. mineralogical composition and microstructure) and performance (e.g. mechanical behavior) of clays and claystones is essential. In the case of the sandy Opalinus Clay, the mechanical strength increases with increasing carbonate content, because carbonates form the matrix. The mineralogical investigation of a set of sandy facies samples proved a significantly larger carbonate content (20-40 mass %) when compared to the shaly facies (10-20 mass %). The carbonates of the shaly Opalinus Clay, on the other hand, are mostly localized fossils aligned parallel to the bedding, acting as predetermined breaking points. Image analysis of SEM images of polished sections proved the determined microstructural differences. In addition, carbonate particles of the sandy facies are mostly isometric, whereas carbonate particles of the shaly facies cover a greater range of shapes. The mechanical tests were accompanied by investigations of the p- and s-wave velocities, which revealed that the anisotropy of the sandy facies is less pronounced than sedimentological analyses would suggest. The mechanical strength, which, for the first time, presents results of real triaxial tests of the sandy facies. The samples of the sandy facies exhibit a failure strength of σeff,B, approximately twice as high as was found for the shaly facies considering the deformation axis parallel to the bedding. Similar values were obtained when measuring perpendicularly to the bedding. © 2013 Springer-Verlag Berlin Heidelberg.

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