Srovnani koncentraci Hg ve vybranych horninach CHKO Brdy v tepelsko-barrandienske oblasti

The Brdy Protected Landscape Area is built of geologically heterogeneous units with numerous rock types which locally show signs of hydrothermal alterations. This study was carried out as an additional investigation to the mapping of local forest humic soils contaminated by Hg. Results of the survey did not exactly correspond to the so far known history of Hg pollution in the area, and therefore a possible influence of bedrock with naturally elevated Hg contents was studied. Samples from seventeen lithological types, which are characteristic of the Brdy Protected Landscape Area, were analyzed (Table 1, Fig. 1). Both inorganic and organic carbon and sulfur were analyzed using a carbon/sulfur analyzer Eltra CS 530, whereas mercury was analyzed by means of AMA 254, a single-purpose atomic absorption spectrometer. The highest concentrations of Hg were detected in Carboniferous sedimentary rocks of the Mirošov Basin rich in organic carbon, for example a black coal from Záborčí with Hg content of 9 347 ppb or carbon-rich siltstone with concentration of 1 339 ppb Hg. Ore samples with sulfides showed also high contents of Hg such as an oolitic Fe-ore from the locality of Jedová hora contained 1 017 ppb Hg, and a lens of hydrothermal ore consisting mostly of limonite and hematite confined to Carboniferous quartzite (Žák et al. 2014) at Přední Záběhlá showed 757 ppb Hg. Ordovician period in the Prague Basin is characterized by higher concentrations of Hg in volcanic rocks and related volcanoclastic sediments (Sattran et al. 1978). Concentrations of Hg in diabase from Jedová hora (4 158 ppb) and quartzite from the Felbabka locality (100 ppb) obviously support data mentioned above. A conglomerate of supposedly Cambrian age found at Jezevčí skála (Havlíček et al. 1986) also revealed high content of Hg (1 540 ppb). As Cambrian conglomerates from other localities of the area do not exhibit elevated Hg contents, the origin of high Hg in the Jezevčí skála conglomerates remains unclear; it may be related to some processes taking place during the Ordovician. Unusually high is also the Hg content in a sample of schist to greywacke of Neoproterozoic age (up to 4 194 ppb) which is likely to be connected with basic volcanic material contained in the sample. Another sample with remarkably high content of Hg is a Carboniferous arkose from the Záborčí Hill at Mirošov (778 ppb) that could be explained by higher content of Hg derived from eroded underlying coal bed, or due to secondary dissemination of sulfidic mineralization in the Mirošov Basin (Pešek et al. 2001). The results of this study indicate Hg to be related to Ordovician or even Neoproterozoic basic volcanism. However, in order to prove this assumption and to come to more reliable conclusions some more sampling and more detailed investigation should be carried out in future.

References

Ambrož, F. (1865): Geologische Studien aus der Gegend von Padrť. - Jb. K.-Kön. geol. Reichsanst. 15, 215-228.

Beuge, P. (1976): Zur Geochemie des Quecksilbers in Magmatiten und Einzelmineralen. - Freiberg Forsch.-H. 313, 1-62.

Havlíček, V., red. (1986): Geologická mapa České republiky 1 : 50 000 s Vysvětlivkami, list 12-34 Hořovice. - Čes. geol. služba. Praha.

Cháb, J. (1993): General problems of the TB (Teplá-Barrandian) Precambrian, Bohemian Massif, the Czech Republic. - Věst. Čes. geol. Úst. 68, 1-6.

Chlupáč, I. - Brzobohatý, R. - Kovanda, J. - Stráník, Z. (2011): Geologická minulost České republiky. - 436 str. Academia. Praha.

Maucher, A. (1965): Die Antimon-Wolfram-Quecksilber formation und ihre beziehungen zu magmatismus und geotektonik. - Freiberg Forsch.-H. 186, 173-188.

Michlová, N. (2016): Tektono-sedimentární vývoj plzeňské pánve a její ložiskově-geologická charakteristika. Bakalář. práce, 33 str., 4 příl. - MS Úst. geol. paleont. Přírodověd. fak. Univ. Karl. Praha.

Pešek, J. - Holub, V. - Jaroš, J. - Malý, L. - Martínek, K. - Prouza, V. - Spudil, J. - Tásler, R. (2001): Geologie a ložiska svrchnopaleozoických limnických pánví České republiky. - 243 str. Čes. geol. úst. Praha.

Sattran, V. - Maňour, J. - Odehnal, L. - Pták, J. - Zima, L. (1978): Regionální prognózy Hg-zrudnění v Českém masívu. - 137 str. Ústř. úst. geol. Praha.

Velebil, D. (2014): Příspěvek k poznání chemismu rtuťových tetraedritů: lokality Jedová hora (Česko), Rudňany, Rožňava, Nižná Slaná, Slovinky (Slovensko), Maškara (Bosna a Hercegovina). - Bull. mineral.-petrol. Odd. Nár. Muz. 22/1, 131-143.

Waldhausrová, J. (1997): Proterozoic volcanic geochemistry and mineral chemistry: A contribution to the Barrandian Upper Proterozoic stratigraphy (Bohemian Massif, Czech Republic. - Krystalinikum 23, 151-180.

Yudovich, Y. E. - Ketris, M. P. (2005): Mercury in coal: a review Part 1 Geochemistry. - Int. J. Coal Geol. 62, 107-134.View article

Žák, K. - Svojtka, M. - Breiter, K. - Ackerman, L. - Zachariáš, J. - Pašava, J. - Veselovský, F. - Litochleb, J. - Ďurišová, J. - Haluzová, E. (2014): Padrť Stock (Teplá-Barrandian Unit, Bohemian Massif): petrology, geochemistry, U-Pb zircon dating of granodiorite, and Re-Os age and origin of related molybdenite mineralization. - J. Geosci. 59, 351-366.View article