The influence of tectonic setting on groundwater chemical composition in the Peshkopi gypsum karst area, Korab Mountains, Eastern Albania

Abstract

The diversity of groundwater chemistry in the Peshkopi gypsum karst area may be related to its setting within the tectonically active Korab Massif (Albania), as shown by field tests of temperature, pH, Eh and EC, and sampling of the waters for chemical analysis (both major and trace components) from cool brackish springs and mineralized thermal springs. The relationship between the chemical composition of the spring waters and of the reservoir rocks was elucidated by analysis of anhydrite-gypsum rocks and experimental dissolution of an anhydrite-gypsum sample. Statistical analysis was used in the processing of hydrochemical data. Comparison of analytical results from 2019 with earlier data indicates compositional stability of the groundwaters over time. Our results together with statistical analysis of the hydrochemical data support an earlier hypothesis of two systems of groundwater circulation within the anhydrite-gypsum deposits of the Peshkopi region. A shallow circulation system involves cold (10–14°C), mainly brackish SO₄-Ca waters with very low concentrations of Na⁺ and Cl^- ions, reflecting their formation in a sulphate rock environment that probably corresponds spatially with a gypsum layer formed by hydration of anhydrite in the near-surface zone. A deep circulation system conditioned, inter alia, by the presence of a large fault, brings to the surface water at up to 44°C, saturated with H₂S, mineralized, of the SO₄-Ca type with an increased content of Na, K, HCO₃, Cl, BO₃ and SiO₂. The chemical composition of these waters, regardless of the presence of large amounts of sulphates, is significantly different and suggests the influence of other factors on their formation, such as slow circulation, contact with flysch rocks in the fault zone and the mixing of deep and near-surface waters in the final part of their ascent to the surface.