Spatial surface and groundwater interaction in an abandoned radium-bearing mine (Guarda, Central Portugal)

The abandoned Alto da Várzea radium mine exploited quartz veins containing ore minerals and U-bearing minerals, such as autunite and torbernite. The area is located on a Variscan two-mica granite that intruded the schist–greywacke complex. The mine was exploited underground from 1911-22 and was closed down in 1946. This mine was not restored and actually a commercial area is deployed.A total of ten surface water and groundwater samples were collected in the study area between 2008/09. Most water samples have pH values ranging from 4.3 to 6.8 and are poorly mineralized (EC=41-186 μ S/cm; TDS=33-172 mg/L). However, the waters are contaminated with NO2-, Mn, Cu, As and U and must not be used for human consumption and some of them in agricultural activities. The water contamination is mainly associated with the old radium mine and human activities developed in the area.