engleski

Clay minerals and heavy metal distributions in overbank sediments of the historical mining region, Žumberak, Croatia

Five overbank sediment profiles were sampled along the course of the Gradna stream to its mouth in the river Sava. Gradna with its tributaries Ludvić and Lipovečka Gradna drain a historical base metal mining area of Žumberak in northwest Croatia. Chemical analyses were carried out on the <125 mm fraction, while mineralogical analyses were performed on the <125 mm fraction, as well as on <2 mm fraction. The profiles contain a record of both, natural geochemical patterns and those showing the mining impact on the fluvial geochemical environment. The heavy metal concentrations highly exceed the background values (parentheses refer to enrichment factors as compared with background values): mercury (132), barium (19), copper (29), lead (4), cobalt (2,5) and zinc (2). The sediments contain following mineral phases: quartz, dolomite, calcite, feldspar, goethite, illitic material, chlorite and well-crystallized and disordered kaolinite. In the upper part of the profiles traces of smectite also occur. Gypsum, pyrite and siderite are also present in some samples. The variability in the amount of dolomite and calcite is expressed in their increase downstream, while the amount of heavy metals, phyllosilicates, feldspars and Fe and Mn oxides and hydroxides decreases toward the Gradna stream mouth. Correlation between Pb, Zn, Co, Ni and the content of phyllosilicates (in <125 mm fraction) indicates that these heavy metals were probably hydromorphicaly dispersed and adsorbed on phyllosilicates and scavenged by Fe-hydroxides. The lack of correlation between Hg, Cu and Ba and the phyllosilicates indicates to a physical weathering mechanism and transport.

overbank sediments; clay minerals; heavy metals; historical mining

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