Spatial Water Interaction In Radium/Uranium Mines – A Portuguese Case study
Antunes, Margarida Horta (1); Teixeira, Rui (2); Neiva, Ana Margarida (3); Albuquerque, Teresa (4); Valente, Teresa (3); Santos, António (3)
1: ICT, University of Minho, Portugal; 2: CEMUC, University of Trás-os-Montes and Alto Douro, Portugal; 3: GEOBIOTEC, Department of Earth Sciences, University of Coimbra, Portugal; 4: Instituto Politécnico de Castelo Branco, QRural/IPCB, CEF/University of
The extraction of radioactive ore produces tailings, large volumes of contaminated waste rocks and heap-leach residues accumulated in the dumps at mine sites. In Portugal, about 60 radioactive ore deposits were extracted, between 1908 and 2001, from the production of radium and uranium. These mines were abandoned and local areas were studied to assess the influence of environmental radioactivity and potentially toxic elements in the public health.
The abandoned Picoto radium mine area is located close to Vilar Seco village (Viseu, central Portugal). The mineralization occurs mainly in quartz veins, which intersect a Variscan medium- to coarse-grained porphyritic two-mica granite. The quartz veins contain torbernite, meta-torbernite and uranophane, and some U-bearing minerals, such as chlorite and Fe- and Mn-hydroxides. Pyrite is also present. The torbernite, meta-torbernite, Fe- and Mn-hydroxides are also disseminated along weathering zones, filling microfractures and between grain boundaries in the granite, but anatase may also occur in granite samples affected by episyenitization.
The mine was exploited in open pits and underground. A first radium exploitation was carried out between 1917-21, in two open pit mines located at NE of the Cagavaio River. The largest open pit mine is approximately 160 m long, 7-10 m wide and has a maximum slope of 7 m. At a later stage, from 1950-53, the exploitation was reactivated, in underground galleries with about 150 m long, to produce uranium. This mine was closed in 1953 and never has been restored. Therefore, a local growing area was developed, mainly for vineyards and agricultural products of domestic consumption.
Three dumps retained the waste from the mine exploitation and contain about 35 000 tonnes of material slightly covered by vegetation but was not restored yet. The mine is in a soft slope area with altitudes ranging from 360 and 380 m, included in the Cagavaio river catchment, with a dominant NE-SW drainage.
A total of ten surface water and groundwater samples were collected in the study area. Most water samples have pH values ranging from 3.6 to 6.5 and are poorly mineralized (EC=45-224 µS/cm; TDS=17-150 mg/L). However, some waters are contaminated with NO2-, Fe, Mn, 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/uranium mine and human activities developed in the area. The drainage waters must be controlled within a temporal and spatial monitorization.