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Fractionation of REE along the Gessencreek


dani

Institution

Institute of Earth Sciences
Applied Geology
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Daniela Sporleder

 

 

The former mining area Ronneburg is in the state of post flooding since 1997. Groundwater level was pumped and thus decreased to 220 m a.s.l. in mining days (Geletneky, 2002). Thus an unsaturated zone formed. Nowadays with no reasonable alternative for remediation, the groundwater level is naturally rising (240 m a.s.l.). Caused by the orographic situation and former drillings in Gessental, groundwater exceeds the underground and seeps aboveground into an isolated part of Gessenbach forming reddish precipitates (figure 1). Gessenbach was predicted to be one of the main discharge areas of the mine waters in the post flooding period (Merten et al., 2005). Several students from FSU Jena investigated hydrogeology (Jörn Geletneky, Stefan Senitz) and microbiology (Jana Sitte, Eva Maria Burkhardt, Maria Fabisch) in this interesting and evolving area.

Oxidation of sulfide minerals, especially pyrite (FeS2), occurs when water (groundwater) and oxygen (unsaturated zone) react with sulfide minerals (host rock). This results in acid mine drainage (AMD). In Gessental, slightly acidic (pH 4.8 – 7.3) and slightly oxidizing (redox potential 200-460mV) seepage water reaches the surface. The water shows a high heavy metal load (electrical conductivity up to 5240 µS/cm), in particular Fe (up to 260 mg/l), as well as Rare Earth Elements (REE).

The REE are 15 (14 stable) elements from La to Lu which are used to study processes after normalization with a suitable standard (here: PAAS: Post Archean Australian Shale (Taylor & McLennan, 1985)). Because of different abundances of even and odd atomic numbers (Oddo-Harkins-Rule) the normalization is necessary. REE are separated in light (LREE: La-Nd), middle (MREE: Sm-Dy) and heavy (HREE: Ho-Lu) REE. Fractionation of REE for abiotic as well as biotic reasons will be investigated.  Because the REE concentration is strictly depending on pH, elevated concentrations are found in AMD influenced habitats like Gessental. Here, diverse seepage waters stream into the isolated part of Gessenbach. Although they are only few meters in distance, hydrochemistry as well as REE pattern differ a lot. Several reactions and processes are worth considering, for example host rock, origin of the water and other abiotic and biotic reasons (Figure 2).

This work aims to give answers about which reactions do fractionate the REE in the AMD impacted area Gessental. First of all, hydrogeochemical analysis is focused. If required, the REE in water are enriched (Shabani et al. 1992). Mineralogy of precipitates is determined with X-ray-diffraction (XRD). For tree ring samples, dendroanalytic as well as total digestion will be used. For fungi and algae other methods will be applied.

Daniela

Figure 1 Area of seepage water with reddish iron precipitates in Gessental

Daniela 1

 

 

Figure 2 Scheme of isolated Gessenbach and REE fractionation by biotic and abiotic reactions

 

 
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