Abandoned tailings deposits, acid drainage and alluvial sediments geochemistry, in the arid Elqui River Basin, north-central Chile.

Two major pollutant sources exist in the Elqui river basin: acid drainage from Andean epithermal El Indio Au-Ag-As mining district and nearby hydrothermal alteration zones; and diffuse sediment dispersion from abandoned tailings deposits in usually dry creeks in the western belt of the basin. This work analyses the contribution of both sources to current metal contents of the fine-grained sediments of the rivers and creeks of the Elqui basin, including a group of chemical elements and data analysis techniques not considered in previous works carried out in the area. Analysis of active sediments, in permanent contact with surface water, in the main channel and tributaries of the river reveals that both pollutant sources contribute to their exceptionally high Cu contents (0.1-0.2% in the -60 mesh fraction). However, As pollution (0.03%) is mainly derived from the El Indio district. Potentially toxic heavy metals, notably Cd, Pb, Hg and Mo, are present in low concentrations and do not present major threats to ecology or human health. Nevertheless, ongoing erosion of abandoned tailings deposits may result in soil contamination and thus be detrimental to the export-oriented agriculture of the Elqui basin. Consequentially, remediation of that source should be prioritised.
Two major pollutant sources exist in the Elqui river basin: acid drainage from Andean epithermal El Indio Au-Ag-As mining district and nearby hydrothermal alteration zones; and diffuse sediment dispersion from abandoned tailings deposits in usually dry creeks in the western belt of the basin. This work analyses the contribution of both sources to current metal contents of the fine-grained sediments of the rivers and creeks of the Elqui basin, including a group of chemical elements and data analysis techniques not considered in previous works carried out in the area. Analysis of active sediments, in permanent contact with surface water, in the main channel and tributaries of the river reveals that both pollutant sources contribute to their exceptionally high Cu contents (0.1-0.2% in the -60 mesh fraction). However, As pollution (0.03%) is mainly derived from the El Indio district. Potentially toxic heavy metals, notably Cd, Pb, Hg and Mo, are present in low concentrations and do not present major threats to ecology or human health. Nevertheless, ongoing erosion of abandoned tailings deposits may result in soil contamination and thus be detrimental to the export-oriented agriculture of the Elqui basin. Consequentially, remediation of that source should be prioritised.