The Almadén district is the largest mercury concentration in the world, with a total content of about 250 000 t of mercury, nearly one third of the known total mercury resources of the Earth. Mercury has been exploited since the Celtic and Roman times, with peak production during the Renaissance and between 1939–1945. The district is hosted by a Paleozoic synclinorium overlying Precambrian rocks. The Paleozoic sequence comprises epicontinental quartz arenite rocks, including black shales and quartzites. Diatremes, alkaline lavas of different composition, and late tholeiitic diabases account for the Ordovician to Devonian magmatism. The tectonic setting of this complex suite corresponds to the intraplate type. The mercury deposits of Almadén can be classified into two main types: type 1, early stratiform type ores characterized by cinnabar deposition on the lower Silurian quartzites (Criadero quartzite; e.g. the Almadén and El Entredicho deposits), and type 2, late discordant orebodies (e.g. Las Cuevas), largely hosted or related to diatremes (the `frailesca rocks') of alkaline basaltic composition. In type 1 cinnabar was deposited during diagenesis, in relation to hydrothermal circulation driven by magmatic activity. Type 2 include a variety of deposits having in common the discordant character of the orebodies (e.g. veins, stockworks, massive replacements), and their wide dispersion along the stratigraphic column, i.e. from Lower Silurian (e.g. Nueva Concepción) to Upper Devonian (e.g. Corchuelo).

Authors and Affiliations

1. Minas de Almadén y Arrayanes S.A., Almadén (Ciudad Real), Spain, , , , , , ES

   A. Hernández

2. Université du Québec à Montréal, Département des Sciences de la Terre, CP 8888, suc. Centre Ville, Montréal (QUE) H3C 3P8, Canada, , , , , , CA

   M. Jébrak

3. Departamento de Ingeniería Geológica y Minera, Escuela Universitaria Politécnica de Almadén, Universidad de Castilla La Mancha, Plaza M. Meca 1, 13400 Almadén, Spain E-mail: phiguera@igem-al.uclm.es, , , , , , ES

   P. Higueras

4. Departamento de Cristalografía y Mineralogía, Facultad de Ciencias Geológicas, Universidad Complutense, 28040 Madrid, Spain, , , , , , ES

   R. Oyarzun

5. Departamento de Geología, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile, , , , , , CL

   D. Morata

6. Departamento de Geôciencias, Universidad de Lisboa, Campo Grande, Ed. C5, 5°. 1700 Lisboa, Portugal, , , , , , PT

   J. Munhá

Received: 23 October 1998 / Accepted: 4 January 1999

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