Katarzyna Górniak

The role of diagenesis in the formation of kaolinite raw materials in the Santonian sediments of the North-Sudetic Trough (Lower Silesia, Poland)

Abstract The Santonian sandy-clayey sediments of the North Sudetic Trough (Lower Silesia, Poland) are exploited as kaolinite raw materials. They are fluvial deposits, up to 500 m thick, showing distinct. differences in the mineral composition of the clay components of claystones and sandstones as well as in the nature of the constituent kaolinite. This diversification is connected with superposition of diagenetic and sedimentary processes. The claystones contain predominantly detrital-like kaolinite and up to 20% minerals of mica groups (illite, muscovite), whilst the clay materials of sandstones (particularly coarsest-grained) consist only of diagenetic kaolinite. The claystones are the products of redeposition of clay minerals formed under conditions of early diagenesis in pore spaces of sandstones from decomposing feldspars and micas. The differences in the mineral composition and the nature of kaolinite occurring in rocks showing various fabric enable selective exploitation of kaolinite raw materials at different quality.

Commercial bentonite from the Kopernica deposit (Tertiary, Slovakia): a petrographic and mineralogical approach

Abstract Commercial bentonite from the Kopernica deposit, Slovakia, is currently mined by the CERTECH Company, Poland, to produce materials intended for animal-care applications and other industrial purposes. The present study aimed to assess the mineralogical, petrographic and physicochemical characteristics of three bentonite varieties from Kopernica used by the company. The X-ray diffraction, optical microscopy, field emission scanning electron microscopy (FESEM), nuclear magnetic resonance, thermal analysis, infrared spectroscopy and chemical analyses showed that the main component of the rocks is montmorillonite with the average structural formula Ca0.31K0.08Na0.04(Al3.23Mg0.54Fe0.23)[(Si7.80Al0.20)O20](OH)4. In addition, opal-C/CT, biotite, potassium feldspar and plagioclase, quartz, clinoptilolite and kaolinite are present. Key information about the textural relationships between the mineral components identified was obtained from detailed thin-section petrography and FESEM studies. The rocks studied have fragmented, eutaxitic texture. They are composed of pumice fragments collapsed into lenticular masses (fiamme) which were strongly deformed and altered, though the shard structures were retained. The compressed glass shards were moulded around pyroclastic grains such as crystal fragments of quartz, biotite and zoned plagioclases, and clasts of volcanic rocks. Observations by FESEM showed that the axes of shards and the walls of the flattened vacuoles are outlined by the inward-growing microlites of silica (axiolitic texture), whilst the interiors of shards are altered to clay. Grain-size distribution, textural properties and microscope observations of grain-size fractions reveal that the Kopernica bentonite contains montmorillonite-opal aggregates difficult to disperse in water.

Bentonite from the Central Slovakia Volcanic Field – A Prospective Raw Material for Polish Industry

Abstract This paper summarizes information about recently worked bentonite deposits in Slovakia and presents the results of studies on bentonite from the Central Slovakia Volcanic Field (CSVF). The authors compared the mineralogy of commercial bentonites exploited in the Stara Kremnička (Jelšový potok), Kopernica, and Hliník nad Hronom deposits. X-ray diffraction (XRD), chemical analyses and microscopy showed that the main component is montmorillonite (37-88%), followed by opal C/CT (5-25%), clinoptilolite (up to 15%), feldspars (3-12%), quartz (up to 8%), biotite (2-5%), and kaolinite (up to 2%). The microscopic imaging provided information valuable for the technological assessment of bentonites, particularly the evaluation of mineralogy determined by XRD. The low variability of the mineral composition of commercial bentonites exploited in the western CSVF, together with the significant reserves and localization of deposits close to the Polish-Slovak state border prove that this raw material deserves more attention from Polish industry.