Controls on the mineralogical and geochemical dispersion in soil and water around a tailing storage facility in the epithermal gold–silver mine in Central Kalimantan, Indonesia

Abstract

The mineralogical and geochemical parameters on soil, waste, and tailings are major components for water quality assessments because they dictate the behavior of the chemical composition and water–rock interactions. Arsenic and trace metal contamination occasionally occurs because of the oxidation of arsenic-rich minerals and hydrothermal alteration or because of anthropogenic influences, such as industrial mining activity. This study aimed to understand the characteristics of tailings, soils, surface water, and groundwater to evaluate the possible geochemical dispersion of metals employed in tailing storage facilities. A study site at the former epithermal Au–Ag mine in Central Kalimantan, Indonesia, was selected because it was suitable for investigating the geochemical behavior of trace metals in water and solid samples and their possible contribution to metal contamination in tropical regions. A detailed study of the tailings comparing mineralogical and geochemical analysis indicates that the presence of unaltered, intermediate, and oxidized zone within the tailings can be related to the sulfides alteration indices (SAI). These zones include an unoxidized zone in the submerged areas where sulfides, including pyrite with less sphalerite and galena, remain fresh. In the intermediate zone, pyrite starts to change to iron oxyhydroxide. The SAI parameters from the intermediate zone, extending 50 cm below the tailing surface, indicate that only a few grains of pyrite in this zone are weakly altered and are capped by a thin (<10 μm) iron oxyhydroxide. The oxidized zone is indicated by traces of remaining pyrite and iron oxyhydroxide as the primary mineral. Heavy metals and rare earth elements from tailings storage facilities were scavenged from the soil solutions by groundwater. The stable isotopes of oxygen, hydrogen, and dissolved rare earth elements (REEs) were used as natural tracers in systems affected by acid mine drainage. The results showed that stable isotope and rare earth elements data do not support contamination between the surface and groundwater. This study found that the oxidation of ferrous iron to ferric ion and precipitation of Fe-oxyhydroxides in soil and water has a close spatial relationship with rare earth elements, which are concentrated only in intermediate and oxide zones.