Hydrological characterization of acidic pit lakes in the Tharsis mines (Iberian Pyrite Belt): the evolution of flood levels and future trends

Abstract

Opencast mining operations frequently lead to the creation of large voids that become anthropogenic lakes when the water table recovers. In the case of coal, and especially sulfide mining, the stored water is of an acidic nature with significant concentrations of toxic metals and, therefore, a high pollutant potential. The present work analyzes the status of four acidic mine pit lakes in the Tharsis mines, which is the second most important mine district in the Iberian Pyrite Belt (IPB), after the Río Tinto mines. The accumulation of huge volumes of acidic and metal-rich waters (5.2 Mm3) in these pit lakes poses a serious environmental concern; approximately 9,000 tons of Fe, 1,000 tons of Al and Zn, and large amounts of other toxic metals are currently stored in the pit lakes. The water level in Sierra Bullones and Filón Norte, the largest lakes, shows an average rise of approximately 2.8 m/yr, which would lead to an overflow by 2051 if the trend continues. However, the increase in the evaporation rate that is expected as a result of the larger surface area during flooding episodes would induce a hydrological equilibrium before reaching the overflow level, leading to the formation of a terminal lake. On the other hand, the water level in Filón Centro and Filón Sur Pit Lakes remain approximately stable. The methodology used in the present work may be of interest to be applied in abandoned opencast mining areas in other regions worldwide.