Hydrogeochemistry and distribution of potentially toxic elements in a metallogenic province – The Iberian Pyrite Belt, Portugal

¹ ICT, Institute of Earth Sciences, Pole of the University of Minho, 4710 Braga, Portugal
² Departamento de Geologia, UTAD, Vila Real; GeoBioTec., Universidade de Aveiro
³ ICT, Institute of Earth Sciences, University of Évora, 7000 Évora, Portugal
⁴ Centro de Recursos Naturais e Ambiente), Universidade de Lisboa, 1049 Lisbon, Portugal

^* Corresponding author: teresav@dct.uminho.pt

Abstract

Contamination by acid drainage is an environmental problem in mineralized regions, especially in the surroundings of sulphide mines. The water rock interaction process involves the oxidative dissolution of sulphides, naturally or by mining activity, that generates acidity which, in turn, produces sulfate, and water pollution by sulphide-hosted metals. The particular geology of the Iberian Pyrite Belt (IPB) in the southwestern Iberian Peninsula creates the ideal conditions for such water contamination. Different water types were sampled at 28 locations across the entire IBP metallogenetic province. Anions, metals, and arsenic were analysed to assess the influence of acid drainage. The results demonstrate the sulfate nature of waters in the vicinity of mines. Other types of water in the IPB region are mainly mixed chloride and bicarbonate (river and groundwater) and mixed and sodium-bicarbonate (lakes) types. Water quality assessment indicated strong contamination of surface waters that are directly influenced by mine wastes. There is the additional concern that some lakes and groundwaters exhibit concentrations of potentially toxic elements (e.g. Al, As) that are above the regulatory limits established by the European Commission Water Framework Directive.