Zakladni charakterizace dulnich vod lozisek Celina a Mokrsko

The Josef adit was driven during a mineral exploration project in search for gold in the Psí hory gold district in Central Bohemia in the 1980s. Two gold deposits were discovered in this area named after nearby villages of Čelina and Mokrsko. This area is built of two main geological units - the Jílové Zone consisting of a volcano-sedimentary complex of Neoproterozoic age, mainly composed of acid and intermediate volcanic rocks, tuffaceous shales and greywackes, and an amphibole-biotite granodiorite body of Variscan age belonging to the Central Bohemian Plutonic Complex. The low grade gold mineralization is disseminated in densely spaced quartz veins together with low amount of sulfides (pyrite, arsenopyrite, pyrrhotite). Recently, the Centre of Experimental Geotechnics of Faculty of Civil Engineering of the Czech Technical University in Prague established in the Josef adit an underground laboratory to carry out a range of experiments oriented on in-situ tests and measurements of underground structures or geotechnics in general including possible nuclear waste disposal site in relation to migration of groundwater or use of bentonite barriers and other tests. The groundwater chemistry is one of the main parameters which can strongly influence this kind of experiments, but no general groundwater chemistry was studied in this area as yet. One-year lasting groundwater monitoring, split into three quarterly sampling campaigns, was based on eleven monitoring and sampling sites. Six of them were in granodiorite, and the remaining five were located in the Jílové Zone. Some parameters such as pH, electric conductivity (EC), total dissolved solids (TDS) and temperature (T) were measured on site, while concentrations of Ca²⁺, Mg²⁺, K⁺, and SO₄^2? were determined in the laboratory shortly after collection of samples. The results showed that the host rocks played the major role in chemical composition of groundwater. There is no direct evidence that ground waters are affected by experiments and ongoing activities (salt solution influx, water pumping, construction works, etc). The only exception is the DOPAS experiment during which the grouting mixture was used in the construction which devaluated the measurements of potassium concentration. Based on chemical composition, two main types of groundwater can be distinguished. Both of them are classified as moderately mineralized waters. The first type is represented by water collected in the Jílové Zone showing pH close to neutral (7.85), higher TDS (369 mg/l), almost identical calcium and magnesium concentrations (43.5 and 51.5 mg/l), and higher content of sulfates (128 mg/l), which is likely to be due the oxidation of sulfides. The second type is a water from granodiorite which is slightly alkaline with pH corresponding to 8.18, with lower TDS content (307 mg/l), and showing significantly higher content of calcium relative to magnesium (59.9 and 24.7 mg/l, respectively), and lower concentration of sulfates (97.8 mg/l).

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