Vladimír Bouška

Quality parameters of lignite of the North Bohemian Basin in the Czech Republic in comparison with the world average lignite

Abstract Sulfur is considered to be the most harmful element in atmospheric emissions and fall-out which originate from coal combustion. Total sulfur content (Std) in lignites of the North Bohemian Basin (NBB) has a geometric mean of 1.61 wt.% at n=12 979, and is mostly influenced by the presence of iron disulfides. The distribution of sulfur and many trace elements is log normal. A non-uniform distribution of sulfur in lignite was found within the basin, with the lowest Std contents (i.e., not exceeding 1 wt.% S) confined to the eastern and southeastern margin of the NBB. Contents between 1 and 1.5 wt.% S are most common in lignites of the South-Central NBB. Lower sulfur contents were identified in the area of the Žatec delta and its northern extension. In contrast, high contents of sulfur in lignite (exceeding 1.5 wt.%) are found along the northern margin of the basin at the foot of the Krusne hory Mts and in the westernmost part of the NBB. Three genetically different types of iron disulfides occur in lignite of the NBB—synsedimentary (early diagenetic), diagenetic, and epigenetic. Among those forms, synsedimentary disulfides (mostly pyrite) appear to be most abundant. They form finely dispersed microscopic framboids or veinlets that commonly parallel the coal bedding. The other iron disulfide forms are much less abundant. Dissolved sulfate which was supplied to the NBB during the Miocene is likely to have been derived from sulfides of the Krusne hory Mts crystalline complex. This unit has an isotopic composition of sulfide sulfur varying between −1 and +5‰. Consequently, the sulfate supplying the NBB should exhibit slightly positive δ 34 S values. Syngenetic pyrites forming microframboids or veinlets in coal show δ 34 S values close to 0‰. These values are similar those of sulfur dioxide in gases of power stations burning NBB coal. This implies that no considerable shifts in sulfur isotopic composition occur during thermal oxidation of the dominant pyrite. Arsenic is positively correlated with sulfur (r2=+0.89). Its total content (Astd) is 20.53 ppm at n=9172.

Geochemical evidence for the origin of moldavites

Abstract Forty-eight moldavites and samples of rocks from the impact crater of Ries were analyzed using non-destructive neutron activation analysis. The following elements have been determined: La, Ce, Sm, Eu, Lu, Sc, Co, Cs, Hf and Th; and Rb and Cr in two moldavites. The darker moldavites, more common in Moravia, show higher contents of trace elements than those lighter in colour, from Southern Bohemia. Terrestrial igneous rocks cannot be regarded as a suitable source material, but terrestrial sandy to silty claystones show strong similarities in major and trace element abundances, and exhibit analogous inter-element variations to moldavites. The Tertiary claystones and sandstones which probably covered the Ries area before the impact, are a possible source rocks for moldavites.

Correlation of some physical and chemical properties of moldavites

Abstract Relations of chemical composition, trace-element content, specific gravity, index of refraction and microhardness of moldavites, selected according to colour from several localities, to the colour shade show that colour is a more important guide to their physical and chemical properties than locality. Seven samples selected according to colour from a small plot near Dukovany (Moravia) exhibit a wide range of properties.

On the original rock source of tektites

On the Kohler & Raaz diagram for rock analyses all projection points of tektites and impact glasses, except for the impact glass from Ries, lie inside the field of sedimentogenic rocks. (The Ries glass is just inside the boundary of magmatogenic rocks). This indicates that the majority of tektites derive from terrestrial sedimentogenic rocks. Possible exceptions are the Australian-Asian tektites, which may have originated from weathered rocks of granodioritic to granitic composition. In the authors opinion these are also the only tektites which might possibly have originated on the Moon.

Rare earth elements in tektites

Abstract Four moldavites and one sample each of an australite, billitonite, indochinite, philippinite, thailandite, Ivory Coast tektite, bediasite and a georgianite were analyzed using neutron activation analysis for La, Ce, Sm, Eu, Tb, Yb and Lu. The REE abundances resemble those of sedimentary rocks. Most of the tektites display a depletion of Eu, a characteristic feature of mature Phanerozoic continental sedimentary rocks. However, the Ivory Coast tektite and georgianite are relatively enriched in Eu, possibly due to the presence of plagioclase-rich source rocks.

Geology and stratigraphy of moldavite occurrences

Moldavites occur in the southwestern part of Czechoslovakia in two mutually not fully connected areas—in southern Bohemia and in southwestern Moravia. Moldavite occurrences can be divided into three groups: 1. 1. High-altitude gravels and sands (old terraces) 2. 2. Slope loams 3. 3. Alluvial deposits along present-day water courses To date I have no reliable evidence of a moldavite find in undisplaced eluvium. An explicit and safe age classification can be given only for the second and third type of occurrences. The slope loams belong to the Pleistocene, the young deposits along the present-day water courses mostly to the Holocene, less often to uppermost Pleistocene. The question of the age of the so-called high-altitude gravels has remained debatable and imprecisely formulated. There exists evidence showing that the moldavite-bearing gravels are younger than the Mydlovary series in southern Bohemia of Miocene age. The present research, however, shows that the moldavite-bearing gravels are also younger than the Ledenice series of Pliocene age. The stratigraphic conditions in Moravia are by no means simpler. We lack there even the determination of the age of the terraces and their systematic study in the drainage area of the Jihlava river. The explanation that the fall of moldavites took place in the period closely preceding the sedimentation of the high-altitude gravels or simultaneously with their sedimentation seems to be the most acceptable. It is towards the end of the Pliocene or in the Pleistocene.

Values of δ34S in iron disulphides of the North Bohemian Lignite Basin, Czech Republic

Abstract Three main, genetically different, types of iron disulphides occur in lignite of the North Bohemian Basin — synsedimentary, diagenetic and epigenetic. Among them the synsedimentary disulphide appears to be the most abundant. It forms fine dispersed microscopic framboids or veinlets mostly parallel with the coal bedding. This disulphide is mostly represented by pyrite. The other types are much less abundant. The epigenetic variety consists of large macroscopic clusters of crystals of marcasite twins or crystalline filling of fractures. The shift in sulphur isotopic composition between the original sulphate and the derived sulphides, which originated through bacterial reduction, may vary considerably depending on conditions, particularly on the open or closed nature of the system with respect to sulphate. The largest shifts in the isotopic composition between sulphate and sulphide sulphur are typical for an open system. Dissolved sulphate which supplied the North Bohemian Basin during the Miocene is likely to have been derived from weathered sulphides of the Krušné hory crystalline complex. This unit has isotopic compositions of sulphide sulphur varying between −1 and +5‰ and assuming no significant shifts in sulphur isotope compositions, the sulphate supplying the basin should exhibit a slightly positive δ34S value. Organic sulphur is thought to have played a much less important role. Synsedimentary pyrites, which form microframboids or veinlets in coal, show δ34S values close to 0‰. These values when compared with those of sulphur dioxide in gases exhaled by power stations burning lignite of the North Bohemian Basin indicate that they correspond to mean values for synsedimentary pyrite. This also implies that no considerable shifts in isotopic composition take place during thermal oxidation in power plants.

Electron microprobe analyses of two-colored moldavites

Abstract Teo-colored moldavites are very rare among Czechoslovakian tektites. Recently nine new two-colored moldavites were found in Southern Bohemia. Three of these were analyzed by electron microprobe. All the specimens are characterized on the basis of macroscopic and microscopic observations for: color and other optical properties; shape, bubble content; and number of lechatelierite grains. It is found that the variations in the color of the glass are the result of variations in chemical composition, especially in total iron content, Fe 2+ /Fe 3+ ratio, and, to a less extent, in MnO content. The sharpness of the contact between the differently colored areas indicates that the two-colored moldavites were at a high temperature for a short time only.

Double Moldavites in Southern Bohemia

Two noteworthy finds of moldavites were made in southern Bohemia. In both cases two moldavites are thrust into each other. The collision evidently took place during the flight of an inhomogeneous swarm of moldavites, still plastic but already displaying almost definite aerodynamic shapes. It is the first time such moldavites have been encountered, and the authors propose to designate them as double moldavites.