Mineralogical and geochemical properties of a water dam receiving historical AMD contamination by sulfide tailings in Riotinto mine SW Spain

Abstract

The present study was performed in the Marismillas water dam, in the Iberian Pyrite Belt, SW Spain. This reservoir receives water from the Tinto River, known by its historical high levels of contamination by AMD. Additionally to soluble pollutants, sulfates and metals in the form of particulate matter have been transported for decades. Consequently, today, Marismillas is clogged by the accumulation of sulfide-rich material from the RioTinto mines. An integrated sampling campaign was accomplished with the following objectives: i) to characterize the input waters; ii) to reveal horizons for preferential accumulation of metals, and iii) to propose a model of the clogging process. The samples were collected in three drill cores, from the surface to the bottom. Geochemical and mineralogical analyses were performed each 10 cm. The results indicate high average concentrations of metals and metaloids (Cu, Zn, Pb, and As > 1200 ppm). A strong accumulation of these elements (> 2000 ppm) was detected at depth 1-2 m. Geochemical trends indicate strong correlation between major elements mobilized from the source materials (sulfides and felsic host rocks). So, Fe and Al, as well as Cu and Zn are clearly associated in the sediments. Regarding mineralogy, in addition to clay minerals, the finest fraction (<2µm) is dominated by jarosite and goethite. Therefore, combining geochemistry and mineralogy allowed mapping the properties of dam, identifying major mineralogical hosts of environmental, but also economic relevant elements, such as REE.