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Prague, Czech Republic

Kubouskova S.,Masaryk University | Krmicek L.,Geologicky Ustav AV CR | Pokorny R.,J.E. Purkyne University in Usti nad Labem
Geoscience Research Reports

The coal mining in the Faroe Islands continued throughout the whole of 20th century. Adits were driven to extract coal at localities where coal beds of the Prestfjall Formation are exposed on the surface. In addition to the extracted Prestfjall Fm. there also exist coal-bearing strata confined to the older Beinisv0r6 Fm. Currently, there is only one mine (New Prestfjall Mine) in operation where the coal is of high quality, similar to anthracite, due to the contact metamorphism of coal beds with basalt lava flows. Xylitic type of coal was of ten found in other deposits. The majority of abandoned coal mines lie in the north part of the Suóuroy Island. Old adits and other mine workings are mostly burried under basalt block slides or other slope deformations, and also overgrown by vegetation. Some of them are still accessible, but are relatively unstable. The size of coal waste dumps and wrecks of mining equipment indicate the scope of mining operations in the past. Some abandoned mines, including that one in operation, have problems with the draining groundwater. On the other hand, there can be observed some coal seams and lenses in sedimentary sequences near the coastline, but were not systematically extracted due to their small thickness, poor quality and difficult access. Coal samples were collected in the majority of observed coal deposits and analyzed using X-ray fluorescence method. Geochemical character of analyzed samples allows to distiguish coal of the Beinisvøro Fm. from that confined to the Prestfjall Fm. Coal from the locality of Rókhagi was formed within the local limnic basins, however we can not exclude a fluvial-related origin for the other coal profiles. Source

Bella P.,Catholic University in Ruzomberok | Bosak P.,Geologicky Ustav AV CR | Bosak P.,Institute za Raziskovanje Krasa | Pruner P.,Geologicky Ustav AV CR | Hercman H.,Polish Academy of Sciences
Geograficky Casopis

Geological and geomorphological research in the Belianska Cave conducted during the last decade has gradually revealed its complicated multi-phased genesis especially during the pre-Quaternary period. The origins and evolutionary phases of the cave were formulated on the basis of detailed studies of the geological structures, cave morphology, composition and dating of sediments. The primary phreatic morphology with voluminous cupolas was sculptured by the deep phreatic waters ascending along a steep fault between the central and the edge of the eastern parts of the Belianske Tatry Mts. Fine-grained cave sediments as residues from dissolved carbonate rocks can be dated to ca 4.18-6.15 Ma. Some morphogenetic features of the cave give evidence of the hydrographical connection with the evolution of landforms in the eastern part of the Belianske Tatry Mts. and the adjacent area. On the basis of relicts of planation surfaces, the cave morphology and dating of cave sediments the multiple-phased development of the Biela River Valley in relation to the development of the subhorizontal epiphreatic passages in the upper (Pontian?) and the lower parts (Upper Pliocene, Lower Pleistocene) of the Belianska Cave were reconstructed. Source

Breiter K.,Geologicky Ustav AV CR | Vasinova Galiova M.,Masaryk University | Korbelova Z.,Geologicky Ustav AV CR | Vankova M.,Masaryk University | Kanicky V.,Masaryk University
Geoscience Research Reports

Elements Ga, In, and Tl of the 3rd group of the Periodic table belong in the Earth's crust among those that are rather scarce, and remain scattered forming only a few rare minerals. Although all three elements are interesting in terms of modern technologies, their behaviour in magmatic processes is known only insufficiently (Table 1). Approximately 25% of the world's known reserves of In are associated with highly fractionated granites (Schwarz-Schampera - Herzig 2002), so we decided to analyze the content of In and accompanying Ga and Tl in different types of Variscan granitoids of the Bohemian Massif and their rock-forming minerals to define trends in behavior of these elements during the magmatic differentiation. Typical bulk-rock samples of peraluminous granites from the Moldanubicum and the western Erzgebirge, calc-alkaline granitoids of the Central Bohemian pluton, K, Mg-rich melagranitoids (durbachites) of the Třebíč pluton and anorogenic granites from the central and eastern Erzgebirge were analyzed using ICP-MS in ACME laboratories in Vancouver. The contents of Ga, In, and Tl in trioctahedral micas and feldspars were determined by LA-ICP-MS at the Department of Chemistry, Masaryk University, Brno. The contents of Ga, In, and Tl in bulk-rocks are shown in the Table 2, and in Fig. 1. The contents of Ga in granites are generally in a range of 15-30 ppm, with maxima in the strongly fractionated rocks up to 55 ppm. The contents of In are usually lower than 0.1 ppm, in fractionated granites about 0.2 ppm, max. up to 0.55 ppm In. The Tl-contents are commonly in a range of <1-6 ppm, in fractionated rocks 6-10 ppm, max. up to 14 ppm. Vertical profile through the intrusion of rare-metal granite at Cínovec/Zinnwald along the borehole CS-1 illustrates the increase in the content of all the observed elements in the upper part of the cupola (Fig. 1). The content of In reaches its maximum of 0.35 ppm in a single analyzed sample of quartz-zinnwaldite greisen at a depth of 154 m. The distribution of Tl is less regular, because due to the crystal-chemical similarities between Tl and K it is strongly influenced by the variability of K-feldspar content along the drilling profile. The contents of all three elements are always higher in mica than in coexisting feldspars (Table 3). Gallium reached 60 ppm in feldspars and 170 ppm in micas from strongly peraluminous rocks. Thallium may be enriched up to 55 ppm in K-feldspar and up to 70 ppm in mica. Indium was detected only in micas ranging from 0.2 to 0.8 ppm, with maximum in a greisen from Cínovec. Our tentative study proved accumulation of Ga, In, and Tl in the late facies of strongly fractionated granitic systems in the Erzgebirge. These contents are similar in both the strongly peraluminous S-type granites (Nejdek pluton, Podlesí) and subaluminous A-type granites (Zinnwald). We conclude, that the contents of Ga, In, and Tl are governed by the degree of magma fractionation, and not by its geotectonic-geochemical affiliation. Source

Prouza V.,Ceska geologicka sluzba | Coubal M.,Geologicky Ustav AV CR | Adamovic J.,Geologicky Ustav AV CR
Geoscience Research Reports

This contribution presents a modern look at the architecture of the Hronov-Poříčí Fault (HPF), a major post-Variscan structure within the Elbe Fault Zone in the NE part of the Bohemian Massif. Geology has been relatively well documented by galleries excavated in the 19th century and by boreholes and test pits in the 1960s, and reviewed by several field trips within the present study. The main fault plane of the HPF dips NE at 60-80° and has the character of a reverse fault. The hangingwall block exposes Carboniferous sediments (Westphalian to Stephanian) with coal seams, dipping NE at steep to medium angles. The footwall block generally exposes Permian (Cisuralian, Guadalupian) sediments and volcanics. A 0.2-2 km broad synclinal structure in the footwall block, known as the Hronov-Poříčí Graben, is elongated parallel to the fault and filled with Upper Permian (Lopingian), Tri-assic and Upper Cretaceous sediments. Both limbs of this structure show tectonic dips of max. 60-80°. The fault core is several tens of centimetres, max. a few metres thick, being dominated by tectonic clay and fractured wallrock. The inner part of the fault damage zone has a width of hundreds of metres, but only tens of metres in the SE segment of the fault (Hronov area), showing crushing, mylonitization and brecciation. The outer part of the zone with slickensides and intensive jointing reaches max. 1 km from the main fault. The drag zone is 2km wide in the footwall block, where reverse drag passes to normal drag in the immediate fault proximity, thereby forming the "Hronov-Poříčí Graben". In the hangingwall block, reverse drag continues to the SW limb of the Police Syncline (width 10 km). The complex structure of the HPF and the extreme width of the drag zone suggest that the fault has a polyphase kinematic history controlled by transpression. Its architecture can be most readily described as bulldozer-style deformation resulting from steep reverse faulting combined with subhorizontal compression. Source

Zak K.,Geologicky Ustav AV CR | Svojtka M.,Geologicky Ustav AV CR | Breiter K.,Geologicky Ustav AV CR | Durisova J.,Geologicky Ustav AV CR | And 2 more authors.
Geoscience Research Reports

The Bohutín Stock is one of several small isolated intrusions occurring in the northern surroundings of the Variscan Central Bohemian PlutonicComplex (Bohemian Massif, Czech Republic). The stock with surface outcrop area of about 3.6 sq. km is known thanks to intensive underground mining of the Bohutín Ag-Pb Zn-Sb vein-type deposit (1841-1979) down to 1350 m below the surface. The Bohutín Stock is a petrographically variable body with quartz diorite or tonalite as the most widespread rock type. More basic diorite to gabbrodiorite enclaves as well as rocks of granodiorite to granite composition (trondhjemite) also occur in the stock. Earlier conventional K-Ar ages of the Bohutín Stock indicated Silurian to Early Devonian age of the intrusion (440-400 Ma) which was rather controversial, since the formation of majority of the Central Bohemian PlutonicComplex covers a period between 354 ± 4 and 337 ± 1 Ma. One later Ar-Ar age determination on amphibole from a gabbrodiorite enclave had excess argon with plateau age of 348.5 ± 0.5 Ma. To solve this controversy, the main intrusive rock type of Bohutín Stock, quartz diorite, was dated by zircon U-Pb method using laser ablation ICP-MS. The dated sample was collected at a depth of 1199 m below the surface. Representative cathodoluminescence images of the dated zircon grains are shown in Fig. 1 and U-Pb concordia diagram for zircons from Bohutín in Fig. 2. Studied quartz diorite from the deeper part of the Bohutín Stock is homogeneous equigranular fine-grained rock composed of (in descending order) subhedral zoned plagioclase (labradorite→oli-goclase), actinolitic amphibole, anhedral biotite, quartz, and K-feld-spar. For chemical composition of studied sample see Table 1. The obtained U-Pb zircon concordant age of 344.2 ± 0.6 Ma (for data of individual zircon grains see Table 2) is close to the age of zircons from granodiorite of the nearby Padr͖ Stock (342.8 ± 1.1 Ma). Both small intrusions therefore probably intruded in the same phase of structural evolution of the complex boundary zone between Moldanubian Unit and Bohemicum. Their age is within the age range of the main intrusive masses of the Central Bohemian Plutonic Complex. Source

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