Seasonal variations of Zn, Cu, As and Mo in arsenic-rich stream at the Mokrsko gold deposit, Czech Republic |
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| Authors: | Petr Drahota Martin Mihaljevi? Tomá? Grygar Jan Rohovec and Zdeněk Pertold |
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| Institution: | (1) Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic;(2) Geological Institute, Academy of Sciences of the Czech Republic, v.v.i., Rozvojov? 269, Suchdol, 165 00 Prague 6, Czech Republic;(3) Analytical Laboratory, Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, v.v.i., , 250 68 Řež, Czech Republic |
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| Abstract: | Monthly sampling of slightly alkaline arsenic-rich stream in the Mokrsko gold deposit revealed seasonal variations in dissolved
Zn, Cu, As and Mo. Concentrations of trace metal cations (Zn, Cu) increased as much as 330 and 178%, respectively, from minimum
mean values at autumn to maximum mean values at spring. In contrast, concentrations of trace element oxyanions (As, Mo) revealed
opposite seasonal pattern with increase to 189% (As) and 123% (Mo) during summer–autumn, indicating that in-stream biogeochemical
process(es) played the main role in controlling the seasonal variations of these trace elements. The trace elements were mainly
scavenged by low crystalline Mn oxyhydroxide and Fe oxyhydroxide (ferrihydrite). Results are consistent with sorption and
coprecipitation processes controlling seasonal variations of dissolved Zn and Cu, while As and Mo dynamics appear linked to
Mn redox reactions. The sorption processes and Mn redox processes are attributed to the changes of pH and oxic/anoxic conditions
on the surface of oxyhydroxides, respectively, which are themselves controlled by the balance between photosynthesis and respiration.
Under the geochemical conditions of the stream, inferred Mn redox reactions can only be explained by microbial activity. |
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