Sediment characterization of an artificial reservoir impacted by mining activity in the Almadén mercury district (Spain)

Los sedimentos del embalse Castilseras, ubicado aguas abajo en el río Valdeazogues en el distrito de Almadén, se recogieron para evaluar los contenidos en mercurio totales asociados con las aportaciones de sedimentos del río que provienen de las minas clausuradas. Se ha determinado el contenido en mercurio total así como otras propiedades físico-químicas de estos sedimentos. Los resultados muestran que el contenido en mercurio es elevado, y que se relaciona con el de los materiales de la zona, relacionados con la minería. Los sedimentos presentan un nivel de acidez significativo, son moderadamente salinos y tienen un tamaño de grano predominantemente limoso. El análisis estadístico indica que las concentraciones de mercurio están positivamente correlacionadas con el porcentaje en limo de las muestras. De los resultados obtenidos se puede concluir que el contenido en mercurio se va diluyendo aguas abajo del embalse y que éste está relacionado con la actividad minera, convirtiendo a Castilseras en uno de los embalses con mayor contenido en mercurio del mundo.Sediments from the Castilseras reservoir, located downstream of the Valdeazogues River in the Almadén mercury district were collected to assess the total mercury content associated with river sediment input from several decommissioned mines. A geochemical characterization, including the determination of total mercury content, were investigated using different physical and chemical techniques. The results obtained suggested that sediments are slightly acidic and characterized by high mercury, related to mining activities. In addition, sediments showed a silty texture and the electrical conductivity results showed moderate salinity, related to acid mine drainage (AMD) processes. The multivariate statistical analysis suggested that mercury content is positively correlated with the silt fraction in collected samples. In regard to the obtained results, we can conclude that Castilseras is one of the reservoirs with the highest mercury concentration, as a result of mining activities carried out in the zone. In this reservoir, the mercury content is diluted downstreamDepto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEpu

Geochemical Assessment of Mineral Resource Potential in a Hg-Sb-Pb-Zn Mining Area: The Almadén and Guadalmez Synclines (South-Central Spain)

The geochemical data from surface soils are often neglected or questioned when prospecting for ore deposits within active mining districts due to the “background noise” produced by anthropogenic pollution derived from mining activity. Large datasets on a national and international scale offer interesting possibilities to discover prospective zones. In the present work, data from the Geochemical Atlas of Castilla–La Mancha were treated in an area with an intense history of mining Hg, Pb, Zn, and Sb: the Almadén and Guadalmez synclines and the Alcudia Valley. The sampling grid was densified to adapt it to the scale of the main geological formations, and a cluster analysis was carried out to establish the relationships between the variables and a factor analysis to distinguish between geogenic and metallogenic factors. The results showed very high concentrations of some elements of prospective interest in local background areas: Hg (51 mg kg−1), Pb (1190 mg kg−1), and Sb (45 mg kg−1), with high variation coefficients. Cluster analysis unveiled a relationship between most of the local ore-forming metals (As, Sb, Hg, Pb, and Ag) with a clear correlation between Hg and organic matter, suggesting a notable contribution of Hg in soil. The factor analysis highlighted five factors, three geogenic and two ore-forming elements. Despite Hg being the main candidate to form a separate factor, its aerial deposition and a large number of outliers in the Almadén syncline contributed to integrating the element into a geogenic factor. Instead, factors F4 (Pb and Zn) and F5 (As and Sb) delimited the prospective areas in both synclines far from the known and the exploited mines. Some of these areas coincided with discovered mineralized zones, specifically in the area SE of a derelict Sb mine, confirming the usefulness of these datasets and statistical tools in areas with recent mining activity