Zdeněk Losos

Geochemical behaviour and mineralogical transformations during spontaneous combustion of a coal waste pile in Oslavany, Czech Republic

Abstract Geochemical processes and mineralogical transformations in the spontaneously combusting coal waste pile of the Kukla mine in Oslavany, Czech Republic, were investigated. The aims of the study were: (1) the characterization of secondary minerals; and (2) determination of processes which influence the mobility of elements in the pile. The pile burned from the late 19th century until the 1990s and has acquired a zoned nature, with original black material in the core of the pile, red material produced by burning close to the pile slopes and grey and white efflorescent salts precipitated on the pile top and slopes. Several mineral assemblages have been identified including (1) primary minerals in the black material including bituminous coal to anthracite, micas, pyrite and goethite; (2) hematite, spinels and corundum in the red material produced by pyrometamorphism; and (3) hydrated sulphates of magnesium including hexahydrite, konyaite and picromerite in efflorescent precipitates on the slopes of the pile. A conceptual model of geochemical processes in the pile includes seasonal changes with mineral dissolution during the wet season and precipitation of efflorescent salt minerals during the dry season. Formation of secondary minerals such as hematite, which is resistant to weathering and immobilizes hydrolysable Fe, may have a positive environmental impact in the long term.

On the presence of OH defects in the zircon-type phosphate mineral xenotime, (Y,REE)PO4

Abstract The infrared (IR) spectra of gem-quality xenotime crystals containing considerable amounts of rare earth elements (REEs), are characterized by sharp and strongly pleochroic absorption bands in the 3650-3350 cm-1 region. In contrast, the spectra of partially metamict samples are dominated by a broad band centered at around 3450 cm-1. Xenotime presents the interesting case of a nominally anhydrous mineral, where the OH stretching frequency region of weakly hydrogen-bonded OH groups is overlapped by absorption bands due to low-energetic f-f electron transitions of REEs, especially of dysprosium. In polarized spectra measured parallel to the c-axis, Dy shows a prominent sharp band at 3519 cm-1. The assignment of the REE bands is based on the polarized IR spectra of REE doped xenotime single crystals, which have been synthesized by the flux method. A single band at 3480 cm-1, strongly polarized perpendicular to the c-axis, is assigned to the stretching vibration of an OH group. Deuteration experiments performed at 950 °C prove the assignment of this band and the presence of additional structural OH groups, appearing at annealing temperatures above 500 °C. Models of the OH point defect incorporation into the crystal structure of xenotime can be derived on the basis of fully occupied cation sites and under the assumption of Y- and P-site vacancies. The water content of the gem-quality samples ranges from 5 to 10 wt ppm and for the partially metamict samples from 370 wt ppm to 1.7 wt% H2O.

Rare hydrated Mg-carbonates-hydroxides assemblage ofserpentinite fissures in Hrubšice, western Moravia (CzechRepublic): a genetic model of its formation

Low-temperature fissure Mg- (Fe-) hydrocarbonate mineralization was found in the Hrubsiceserpentinite body, Moravian Moldanubicum. It is formed by rare minerals (hydromagnesite, artinite, brugnatellite, coalingite), followed by aragonite, brucite, dolomite and calcite. Two main stages of crystallization have been recognised. The old stage of mineralization was relatively Fe-rich, with brugnatellite, coalingite and Fe-bearing brucite. The younger, more extensive Mg-rich stage, produced artinite and various morphological types of hydromagnesite. The youngest minerals of fissures are calcite, dolomite and aragonite. Mineral assemblages have formed from low-temperature solutions, which were enriched in Mg2+, at pH ~ 9, with relatively low Al activity, low fugacity of CO2 and temperature lower than 44 oC.

Kinoshitalite with a high magnesium content in sulphide-rich marbles from the Rožná uranium deposit, Western Moravia, Czech Republic

Ba-micas including magnesian kinoshitalite (XMg more than 0.99) were found in sulphide-rich dolomite marbles at the Rožna uranium deposit, Moldanubicum, Czech Republic. The Ba-micas (phlogopite with Ba > 0.280 apfu and kinoshitalite with Ba from 0.869 to 1.244 apfu) are Mn, Fe and Ti-poor in comparison to other Ba-micas described up to date. The main substitution mechanism in Ba-micas is (Ba2+,Ca2+) (Al3+) (K+,Na+)-1 Si4+-1. Relatively high content of Mn in silicates and carbonates from the host marble is in contrast to the chemistry of Ba-micas. Barium and manganese show distinct behaviour during metamorphism. Manganese and iron were probably partitioned to metamorphic sphalerite and pyrrhotite relative to (Mn, Fe)-poor Ba-micas. Barium concentrated in mica minerals and the system was evidently Ba-depleted in late stages.

Polarized FTIR spectroscopic examination on hydroxylation in the minerals of the wolframite group, (Fe,Mn,Mg)[W,(Nb,Ta)][O,(OH)] 4

Abstract Polarized FTIR spectroscopic measurements of 11 natural wolframite single crystals from different occurrences revealed the common presence of structurally bound OH groups in their crystal lattice, with potential influence on the properties of thisse geologically and technologically important group of compounds. Despite differences in the appearance of the OH absorption pattern, dependent among other on the end-member ratio, two types of “intrinsic” OH defects could be discerned from detailed studies of the pleochroic behavior of the absorption bands both at 80 K and room temperature. The accompanying chemical analyses by the electron microprobe helped to clearly identify the substitution trend W6+ + O2– ↔ (Nb,Ta)5+ + OH– as the prevailing hydrogen incorporation mechanism into wolframite. The assignment of the observed IR absorption phenomena to hydrous defects was confirmed by the results of deuteration experiments and the negligible contribution of included impurities to the FTIR spectra in the OH absorption region. The results obtained in this study of natural wolframite crystals can be used to detect and analyze hydrous defects in synthetic technologically important tungstates.