MERCURY PARTITIONING IN THE WATER COLUMN OF EL ENTREDICHO OPEN-PIT (ALMADÉN, SPAIN)

The Almadén mercury (Hg) mining district (Ciudad Real, central Spain) is located within the largest geochemical anomaly of this element in the world. The district includes a series of deposits that comprise a variety of structural and textural styles sharing a simple paragenesis, where a dominant cinnabar mineralization is associated with other accessory minerals but in very low proportions to be considered the deposits as monomineral. An intensive mining activity has been developed during more than 2000 years, leaving an important number of decommissioned mines and liabilities scattered in the area. Among the several sites of exploitation, El Entredicho (Fig. 1) is the most peculiar since it is an unusual open-pit mine which was in operation only for Hg extraction. It is the second mine in importance within the district which produced 290,000 flask of Hg in nineteen years of exploitation. As a consequence of the mine operations, a big hole was created (87,500 m2 of surface and 72 m of depth) which was restored by flooding with waters from the near Valdeazogues River in 1998. Today, this open-pit only receives waters from runoff without other inputs from ground or surface waters. Due to this unusual environmental setting, water column has evolved in isolation during the last seventeen years making this artificial lake a unique laboratory for investigating mercury biogeochemical processes in an isolated freshwater environment. This research focuses on a preliminary characterization of Hg abundance and fractionation in the water column of El Entredicho open-pit to understand the effects of physical and biogeochemical factors on the distribution of Hg species