The research paper presents detailed mineral and geochemical analysis of flysch rocks and gravel-stones in Dragonja river basin. Flysch rocks of researched area represent the surroundings and source of Sečovlje Salina sediments and coastal marine sediments, that contain high concentrations of Ni (nickel) and Cr (chromium). The optical microscopy has shown presence of opaque minerals which could be the potential carriers of heavy metals. X-ray powder diffraction (XRD) was used to determine mineral composition of the samples, in which quartz and calcite have the highest percentage in comparison to other minerals like dolomite, kaolinite, muscovite, microcline, albite, chlorite, illite, pyrite and hematite that have lower shares. High Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICP-MS) was used to identify major oxides and trace elements/heavy metals of samples. In all the samples SiO2 in CaO strongly dominate and are followed by Al2O3, Fe2O3, MgO, K2O, Na2O in TiO2. The analysis of heavy metals concentrations has shown the highest content of Ni and Cr. The highest ppm numbers of Ni and Cr are in weathered parts of rocks, which can be explained with isomorphic substitution of Ni and Cr ions. The results of SEM-EDS microscopy have shown that the sample DP9A has Cr-spinels which consequently represent the source of Cr and have confirmed the thesis of opaque minerals as potential sources of heavy metals. Because of very low contents of Ni in sample, Ni sources with SEM-EDS analysis couldn´t be identified. We predict that source of Ni is mineral pyrite, in which isomorphic substitution of Fe and Ni ions plays its part.
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