Acid Mine Drainage Pollution at the Tharsis Mines (Iberian Pyrite Bel): A Serious Environmental and Socioeconomic Problem
Moreno González, Raúl; Olias, Manuel; Ruiz Cánovas, Carlos; Macías, Francisco
University of Huelva. Dpt. Earth Sciences, Spain
The Tharsis mines constitute the second most important exploitation of the Iberian Pyrite Belt, one of the richest regions in deposits of massive sulfides worldwide. This area have been mined, especially from the second half of the nineteenth century until the end of the twentieth century, to obtain copper and sulfuric acid, as well as gold and silver from gossans.
This paper presents the serious problems that exist in this zone, after the total cessation of mining activity in 2001, due to the generation of acid leachates with high levels of toxic metals, which produce the contamination of water courses of this area and downstream.
The total area affected by mining is of 394 ha, of which 244 ha are mine dumps (in some cases up to 80 m high with a high content of sulfides), 20 ha occupied by acid waters (the majority in flooded open-pits), etc. In 2016 a volume of 5.6 hm3 of acidic water was stored in pit lakes, of which 3.6 corresponded to the Filón Norte open-pit, in which the level of acidic water continues to rise. There are more than 30 sources of acid mine drainage (AMD) with discharges usually between 0.1 and 5 L/s, pH values lower than 3, electrical conductivity values ranging from 2.3 to 36 mS/cm and high concentrations of Fe (up to 103 g/L), Al (up to 8.1 g/L), As (up to 1.9 g/L), etc. The load of pollutants released from the mining area varies depending on the rainfall regime, reaching values of up to 7 ton/day of Fe, 1.9 ton/day of Al, 0.75 ton/day of Zn, etc.
The acid leachates generated produce the degradation of 115 km of water courses of the Meca and Oraque rivers, both belonging to the Odiel river basin. In addition, the Meca river basin is regulated by the Sancho reservoir (58 hm3 capacity), which have a pH close to 3.5 and significant concentrations of toxic elements, so the water must be treated before being used for the supply to an industrial facility. Other acidic leachates join the Oraque River, where a new reservoir of 246 hm3 of capacity is being built in the confluence with the Odiel river, which will store acidic waters if remediation measures are not taken. Finally, acidic leachates from the Tharsis mine also produce an important pollution in the Odiel River estuary.