Soil geochemistry and manganese contamination risk in the abandoned mining area - Eastern Carpathians

The investigated area belongs to the Mn metamorphosed ore chain along the Bistriţa Mountains in Eastern Carpathians. Over time, mining waste accumulated and underwent physico-chemical changes. A particular situation of sampling area consists of ore-roasting furnace tailings, abandoned without extensive reclamation. The study included the control soil and Technosol associated with tailings. XRD and XRF methods were applied for mineralogical and geochemical characterization of the two soil categories. The rare minerals of Mn (sonolite, hodgkinsonite, bustamite, braunite, ardenite, nimite and pyrosmalite) were identified. Pedogenetic effects were reflected by the presence of clay minerals (illite-montmorillonite; chlorite-montmorilonite; montmorillonite). The geochemical indices and mass balance were applied for soil maturity degree evaluation. The average CIA (76.60) and MIA (70.29) in control soil and CIA (73.12) and MIA (67.79) respectively for Technosol denoted that the soil achieved an intermediate to advance state of evolution. Mass balance also inferred these weathering state of soil due to the depletion of Ca > Mg > Na > K. The compositional peculiarity was determined by Mn high abundance (averages of: 1,894 mg/kg in control soil; 23,421 mg/kg in Technosol). The Mn risk of contamination in Technosol evaluated by the means of metal enrichment index (MEI) was very high (10.28-21.71),but the ecological risk (E_i) was low (< 40). The quality of control soil in relation with Mn enrichment did not require any monitoring program. Only Technosol could induce ecological risk over time.