Caracterización ambiental de estructuras mineras en la Faja Pirítica Ibérica como soporte metodológico de gestión territorial

Abstract

The Iberian Pyrite Belt (IPB) is one of the most exploited regions in the world since ancient times as a result of the interest produced by its massive sulfide deposits. This intense mining activity throughout the metallogenic province has resulted in the pollution of the fluvial network by acid mine drainage (AMD). Nowadays, there are a multitude of mining structures that constitute sources of aquatic pollution, mobilizing large amounts of acidity, sulfates and metals into the watercourses. The main goal of this thesis is the environmental c haracterization of the different types of mining structures associated with sulfide exploitation in the Spanish sector of the IPB. For this purpose, a diversity of tools and techniques were implemented in order to establish a methodological support for lan d management, applicable to a scenario that is still only partially known. A novel point of this work addresses the detailed mapping and quantification of all mining structures in the IPB, differentiating between waste dumps, open pits, tailing dams and mi ning facilities, by means of field campaigns and digital photogrammetric support. Furthermore, the hydrochemical characterization of AMD - generating sources has also been carried out to each mining group present in the IPB, where waste dumps are the main so urce of contamination. Thus, a sampling campaign was performed in the rainy season. This was a critical condition for the production of leachate in all mining areas, including small dumps where leaching occurs only briefly after rain. Samples were also col lected downstream, in the main watercourse, which represents the global temporary receiving system. Therefore, sampling has been carried out in nine sub - watersheds that were defined under the scope of this work for the Spanish sector of the IPB: Trimpancho , Malagó n, Cobica, Meca, Oraque, Olivargas, Odiel, Tinto, and Guadiamar. First, the contamination level of the leachates produced in each mine waste dump has been assessed. By using the model proposed by Grande (2011), and according to the Council Directiv e 98/83/EC for water quality, weighting values for pollution have been determined. Similarly, the same method was applied to evaluate the contamination degree of the receiving watercourse. Then, the obtained results have provided the basis for the defini tion of an index that assesses each mining group’s capacity to cause contamination by AMD (ICAMD). Such an index represents one of the main contributions of this thesis, as a global index formulated for AMD - affected systems. Subsequently, ICAMD allowed to elaborate a risk map for the entire metallogenic province that reflects the potential degree of fluvial contamination by AMD of each mining group. So, this work has produced easy access and visualization tools for land management, which are made availab le for potential users. Resumen viii In summary, the IPB has undergone a major transformation of the territory by the intense and prolonged mining activity, showing over 4800 hectares of affected land. Almost a hundred of sulfide mines with their persistent structures are responsible for this change. Waste dumps are the main focus of environmental impact, representing approximately 60% of the degraded land, followed by tailings dams, open pits and, finally, mining facilities. At the watershed level, the Odiel and the Ti nto rivers are the largest areas occupied by waste dumps in the IPB. The Odiel watershed contains about 50% of the area occupied by waste dumps, while the Tinto comprises 32%, excluding Cobre las Cruces and Aguas Teñidas. These two mines cause no pollution by AMD as they are in operation and, consequently, forced to comply with current regulations regarding discharges into public channels. Likewise, the watersheds of both rivers receive the highest amounts of contaminant load in the IPB. In what concerns t he level of contamination, all the sampled effluents show signs of strong pollution, occasionally, mitigated by the sampling circumstances, during the rainy period. The metals that most often exceed the levels established by regulations are iron and cadmiu m (98% of cases). Qualitatively, the most affected channels are Trimpancho, Cobica, Meca, Odiel, and Tinto. The description of the index of contamination capacity by AMD along with the risk map allow to visualize how the river network in the IPB is affect ed since the beginning of its watercourses (from north to south), and how it collects leachates from numerous mines whose waste dumps generate extraordinary levels of contamination by AMD, originating an unique scenario in the world. The information obtained in this study will be useful for future mining projects in the IPB, especially in the context of copper demand in emerging countries. Furthermore, the methodology is transferable to any other area with similar problems that are not only associated with sulfide mining but also with other types of mining - environmental interaction.