The Hiendelaencina district in Spain was the most important silver producer in Europe during 1844–1925. At the end of the 20th century, with mines having closed, some waste rock dumps were reprocessed, and the sludge from the flotation process was stored in two tailings ponds. When this activity ceased, the residues began to be eroded and disperse. In this study, the state of degradation of both deposits was evaluated using historical mapping and light detection and ranging (LiDAR) data, incorporated into a Geographic Information System. In the aerial images (1946–2018), mine tailings and their main erosive and sedimentary forms were mapped. Geoforms linked to hydrological (channels, gullies, alluvial cones), wind (eolian mantles), hydric–gravitational (colluvium) and anthropic (motorbike tracks) processes which move sludge into the surrounding areas were identified. A net loss of 8849 m3 of sludge, a release of 10.3 t of potentially polluting substances and a high erosion rate of 346 t/ha*year were calculated based on LiDAR data from 2009 and 2014. The ponds show a current high degree of erosion that could increase due to both human activity and the growing frequency of drought and torrential rain periods if stabilization measures are not undertaken.

More than twenty years after the last mining operations were completed in the Hiendelaencina Mining District, it is necessary to carry out a geochemical characterisation of the tailings stored in two contiguous mine ponds. Both have significant amounts of quartz, siderite, barite and muscovite and show significant contents of As, Ba, Pb, Sb and Zn. The tailings show alkaline pH and low electrical conductivity values, which support the visual observation that rules out acid drainage into the environment. The comparison of the National Topographic Map of 1954 with LiDAR data from 2014 has allowed estimating the volume of abandoned waste. Based on the volume of slurry and its average density, the total tonnage of pollutants has been estimated at 279 ± 9 t stored in Pond North and 466 ± 11 t stored in Pond South. Although these are significant quantities that pose a risk to the environment and nearby populations, they are lower than those present in other Spanish districts, such as the Iberian Pyrite Belt or Cartagena-La Unión. The combined use of LiDAR data, aerial imagery and geochemical methods has proven to be very useful for the estimation of the volume of pollutants stored in mine ponds.