Trace elements distribution in stream sediments of an abandoned U mining site in the Eastern Carpathians, Romania, with particular focus on REEs
Introduction
Rare earth elements (REEs) and other trace elements present in many geological settings are assigned as useful chemical parameters to understand the geological and geochemical processes taking place in the Earth. Their insolubility and resistance to mobilization during geological processes such as weathering, diagenesis and metamorphism make them important tools for the geochemical characterization of the Earth (Mc Lennan and Taylor, 2012). Generally, REE are found in many minerals but only few of them, such as monazite and bastnaesite, are rich enough to be considered of economic interest (Neary and Highley, 1984). Immobile elements and REEs are usually concentrated in riverbed sediments and can be used as tracers for the sediments’ sources (Taylor and McLennan, 1985).
The REEs-rich mineralized carbonate-rich veins of the Eastern Carpathians’ Igneous Complex from Romania are referred to some extend as potential important REEs resources in Europe (Honour et al., 2018). Some mineralizations (Paltin type) in Valea Seaca and Argintaria-tributaries of the Barasau River are genetically related with some vein mineralizations from Ditrau Igneous Complex (Gyula, 1998; Ionescu, 2000). The age of the Paltin type mineralizations is Upper Jurassic- to Early Cretaceous and they are similar or at least close to the Ditrau Complex mineralizations (Ionescu, 2000). The area is charcaterised by rocks containing galena and chalcopyrite, sulphides and REE and uranium deposits (Ionescu, 2000).
Important mineral resources are found in the area, with special focus on the Uranium deposits (Tulghes-Grinties) located in mica schists and feldspathic quartzites from the Bretila Group (Bejenaru and Cioloboc, 1993). Geological surveys suggest the area as the largest uranium deposit in Romania with valuable economic potential (Tofan et al., 2016). A study published in 2020 reports for Tulghes-Grinties area reduced radiological hazard from naturally occurring radionuclides within riverbed sediments near uranium deposits (Sandu et al., 2020). Moreover, the fingerprint of serpentinite ultramafic rocks present in the Prisacani River represents a potential suitable tool for understanding the geological setting, as the geochemistry may differ based on the influence of some parameters such as the temperature of formation and the nature of primordial fluid. The geochemical composition of serpentinites is usually influenced by the geological settings especially due to the influences derived from their formation temperature and the nature of primordial fluid (Deschamps et al., 2013). Nevertheless, the source of the serpentinite has not yet been found.
The present work aims to document the geochemical and mineralogical characteristics of stream/riverbed sediments of the main left tributaries of the Bistricioara River (Primatar, Grintiesul Mare, Bradul, Prisacani, Barasau and Valea Seaca) in the Central Group of the Eastern Carpathians, i.e. Bistritei Mountains. Of special concern in the present work are rare earth elements (REE) and selected trace elements in terms of quantitative assessments and their origin sources.
Section snippets
Geological framework
The studied area is located in Bistricioara hydrographic basin and it lies within two geological units known as Crystalline–Mesozoic in the Center (or Median Dacides) and Carpathian flysch in the East (Fig. 1). The Eastern Carpathians are geomorphological segments of the European Alpine mountain belt, with a length of about 200 km, corresponding to a relatively young tectonic setting which was formed during the Miocene collision (Kräutner and Bindea, 1995).
The origins of the Carpathians
Sample preparation
A number of 40 stream sediments samples were collected in May 2019 from Bistricioara’s left-bank tributaries (Primatar – 8 samples, Grintiesul Mare – 8 samples, Valea Seaca – 6 sample, Basarau – 5 samples, Prisacani – 4 samples, Bradul – 4 samples, Bistricioara – 5 samples), the sector spanning between the villages of Capu Corbului and Grinties. The sampling network was established based on accessibility. Each composite sample was generated from at least five sampling points that covered
Trace elements
Data related to quantified values in the concentration of selected elements (Ti, V, Ni, Cu, Zn, Li, Be, Rb, Sr, Y, Sc, Zr, Nb, Sb, Ba, Ta, W, Th, U) are presented in Table 1 while for the identified REEs (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) concentration values are presented in Table 2. Both Table 1, Table 2 present individual data for each analysed stream sediment sample accompanied by minimum, maximum and mean for each set of samples.
Trace elements in stream riverbed sediments in comparison with the upper continental crust (UCC)
A better way of understanding the geogenic and anthropogenic contribution is to compare the variability on the concentrations of the identified elements to the average values from the upper continental crust (UCC) (Maftei et al., 2018). The geology of the Bistricioara basin predominantly consists of metamorphic rocks and, in a lesser proportion, of sedimentary rocks. A comparison between the trace elements composition of the Bistricioara and its tributaries and the average of upper continental
Conclusions
A significant number of rare earth elements (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb Lu) and other metals of potential interest (Ti, V, Cr, Co, Zn, Li, Be, Rb, Sr, Y, Sc, Zr, Nb, Sb, Ba, Ta, W, Pb, U, Ni, Cu, Mo, As, Th) were identified and quantified in water stream sediments collected from a geographical area with relevance to about 50 km2 in the neighborhood of an U mining site (Tulghes-Grinties) in the Eastern Carpathians, Romania.
The enrichment in trace elements, such as Pb and
CRediT authorship contribution statement
Data curation: Marius C. Sandu and Laurentiu V. Soroaga. Formal analysis: Marius C. Sandu, Laurentiu V. Soroaga, Ovidiu Chiscan, Gabriel O. Iancu, Cecilia Arsene and Romeo I. Olariu. Methodology: Marius C. Sandu, Laurentiu V. Soroaga and Ciprian Chelariu. Validation: Marius C. Sandu, Laurentiu V. Soroaga, Cecilia Arsene, Romeo I. Olariu. Writing - original draft: Marius C. Sandu, Laurentiu V. Soroaga, Sorin I. Balaban, Ciprian Chelariu, Gabriel O. Iancu and Romeo I. Olariu. Writing - review &
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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