Publisher © Czech Geological Survey, ISSN: 2336-5757 (online), 0514-8057 (print)

Contents of Hg in various rocks of the Brdy Protected Landscape Area, Teplá-Barrandian unit, Czech Republic

 

Michal Roll, Karel Žák, Tereza Nováková, Tomáš Navrátil

Geoscience Research Reports 51, 2018, pages 47–51
Map sheets: Hořovice (12-34)

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Published online: 15 June 2018

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Abstract

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.
 

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