Spatial distribution of acid mine drainage indexes in diferente water environments

Abstract

The Iberian Pyrite Belt is one of the largest metallogenic province in the world. The characteristics of this region have a reflection on the existence of Acidic Mine Drainage (AMD) discharged into the river network affecting the water quality. A several number of surface and groundwaters in the Iberian Pyrite Belt (south of Portugal) was collected in different water environments. Mine water is highly acid with medium-high to extreme metal contents, while surface and groundwater are neutral with low metal contents. Mine waters are the most contaminated with a maximum EC value (27570 µS/cm) and SO4 2- (80691 mg/L), As (141 mg/L), Cu (1445 mg/L), Fe (41023 mg/L), Zn (841 mg/L) contents. A numerical index of acid mine drainage (AMDI) has been calculated. The group of mine water environment had a mean AMDI of 20.0 reflecting a little or no dilution of direct mine water drainage. River network could be indicated as an affected river downstream mine drainage (AMDI 80.2), while groundwater (AMDI 92.2) is uncontaminated by AMD. The groundwater composition will be strongly controlled by natural geochemical processes, from the geology of the ore deposits and water rock interaction.