Evolution of moisture in tailings dams located in arid climates. Case study: Castaño Viejo mine, San Juan, Argentina

Abstract

This paper presents the results obtained in geotechnical exploration campaigns carried out in mining tailings dams resulting from the extraction process of lead, zinc and copper. The studied dams have been abandoned for more than half a century and are located in the Andes Mountains, San Juan, Argentina, an area characterized by water deficit regimens. The observation of degrees of saturation, which is surprisingly high in the internal zones of the tailings dams, led to a long-term field experiment (plot test) to investigate the observed behaviour. Based on the results of the plots test, we have concluded that stratigraphy controls the evolution of the water stored with the tailings. Clay and silty layers develop high degrees of saturation due to the capillary barrier effect, whilst the interlayers of sand dry up to a residual saturation condition. This situation inhibits the capillary rise and the diffusion of vapour, thus isolating the interior of the tailings from the atmosphere. It was observed that the depth of the active layer is 10 to 35 cm for evaporation and 35 to 75 cm for infiltration in the plot experiment. Such asymmetry determines a net flow of water into the system, which is consistent with the generation and conservation of a high degree of saturation within the tailings.