Author's personal copy The acidic mine pit lakes of the Iberian Pyrite Belt: An approach to their physical limnology and hydrogeochemistry Javier Sa ´nchez Espan ˜a * , Enrique Lo ´ pez Pamo, Esther Santofimia Pastor, Marta Diez Ercilla Direccio ´ n de Recursos Minerales y Geoambiente, Instituto Geolo ´ gico y Minero de Espan ˜a (IGME), Rios Rosas, 23, 28003 Madrid, Spain Received 7 August 2006; accepted 27 December 2007 Editorial handling by B. Kimball Available online 13 February 2008 Abstract This study examines some relevant limnological and hydrogeochemical characteristics of 22 mine pit lakes of the Iberian Pyrite Belt (IPB). The studied pit lakes include some of the largest and historically most important mines of the IPB (including Corta Atalaya and Cerro Colorado in Riotinto, Filo ´n Norte, Filo ´n Centro and Filo ´n Sur in Tharsis, Aznalco ´l- lar, or San Telmo) and many other of minor size. As a whole, these lakes constitute, at present, a large volume of highly acidic and metal-polluted water. Some of these pit lakes are very recent (e.g., Corta Atalaya, 2.5 a; Los Frailes, 6 a) and present a continuous hydrological and geochemical evolution, although many others were abandoned decades ago and show nearly constant water volume. Depth profiles obtained in several pit lakes (e.g., San Telmo, Confesionarios, Cueva de la Mora, Concepcio ´ n) indicate that many of them have developed meromixis and show, at present, a permanent thermal and chemical stratification with a well defined chemocline separating an anoxic, Fe(II)-rich monimolimnion, and a well mixed, oxygenated and Fe(III)-rich mixolimnion. In the upper layer, the bacterial oxidation of Fe(II) competes with pho- toreductive processes which take place in the surface water, thus provoking diel cycles of Fe(II) concentration. The observed water chemistry reflects the oxidation and dissolution of pyrite and other sulphides and gangue aluminosilicates from the country rock. The pit lakes of the IPB cover a wide range of water compositions, from circumneutral and relatively low-metal (e.g., Los Frailes, pH 7.2, 0.07 mg/L Fe, 3.8 mg/L Mn, 30 mg/L Zn), to extremely acidic and metal (loid)-rich (e.g., Corta Atalaya, pH 1.2, 36.7 g/L Fe, 6.7 g/L Zn, 1.3 g/L Cu, 159 mg/L As). Most pit lakes, however, are comprised within the pH range of 2.2–3.6 and appear to be strongly buffered by the hydrolysis and precipitation of Fe(III) in the form of schwertmannite, which forms colloids that can sorb trace elements from the aqueous phase. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction and scope The intensive mining carried out in the Iberian Pyrite Belt (IPB) has left a legacy of mine pits with considerable size. Good examples of such pit size are those of Corta Atalaya-Riotinto (1200 m long  900 m wide  360 m high), Aznalco ´ llar 0883-2927/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.apgeochem.2007.12.036 * Corresponding author. Tel.: +34 913 495740; fax: +34 913 495834. E-mail address: j.sanchez@igme.es (J. Sa ´nchez Espan ˜ a). Available online at www.sciencedirect.com Applied Geochemistry 23 (2008) 1260–1287 www.elsevier.com/locate/apgeochem Applied Geochemistry