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In the abandoned Mortórios uranium mine area there are quartz veins containing wolframite and sulphides and basic rock dykes with torbernite and autunite cutting a porphyritic granite. The basic rock dykes were exploited and produced about 27 t of U3O8, from 1982 to 1988. There are an open pit lake and nine dumps. Surface water and groundwater are contaminated in U, As, Cd, Cr, Cu, Fe, Mn, Ni and Pb. Stream sediments are contaminated in U, As, Th and W, which are adsorbed by smectite, kaolinite and iron- and aluminium- oxy-hydroxides. The maximum U concentrations are of 1268 μg/L in the open pit lake, 100 μg/L in surface water, 103 μg/L in groundwater and 81.5 mg/kg in stream sediments all downstream of the open pit lake and dumps. Further downstream the U concentration in water decreases, due to the high mobility of U (VI), but the U concentration in stream sediments increases. Calcium uranyl carbonate dominates in the open pit lake, but uranyl carbonate complexes dominate in surface water and groundwater. The maximum As concentrations are 56.0 μg/L in the open pit lake, 63.4 μg/L in the surface water and 66.7 μg/L in the groundwater, both downstream of the open pit lake and dumps. The arsenic occurs as As (V). The Mortórios area is compared with two other areas exploited from open pits, all located in the uranium-bearing Beira area of central Portugal. Vale de Abrutiga produced 90 t of U3O8 between 1982 and 1989 and Mondego Sul produced 75 t of U3O8 from 1987 to 1991. The two mines consist of quartz veins containing sulphides, saleeite and meta-saleeite at Vale de Abrutiga and with sulphides, autunite, torbernite, meta-uranocircite and meta-saleeite at Mondego Sul cutting the Schist-graywacke Complex. The mine area of Vale de Abrutiga with the highest exploitation of U3O8 has strongly acidic to slight alkaline water, which is the most contaminated. Mortórios with the lowest exploitation presents a higher contamination of slightly acidic to alkaline water than that of acidic to alkaline water from Mondego Sul, but the former has As (V), whereas the latter has As (III), which is toxic. The stream sediments from Mortórios present the lowest contamination, except for Th that has a higher median value than that from Vale de Abrutiga. Stream sediments from Mondego Sul have higher U, Th, Pb and lower Co, Cr, Cu and Zn median values than those of Vale de Abrutiga.

This work focuses on the study of water–sediment interaction around abandoned uranium mines with open-pit lakes and mine dumps. Nineteen water and eleven stream sediment samples were collected in the abandoned Barrôco D. Frango mine, central Portugal. The trace element distribution was compared with other abandoned uranium mines in Portugal and worldwide. Generally, U, Th, and As contents in the open-pit water are high and similar to those of downstream water, suggesting its influence on aquatic systems. In abandoned mines with small to medium U exploitation, the stream sediments are moderately to heavily contaminated with U, Th and As, being U and As the most important contaminants, confirmed by their partition coefficients. A moderate to considerable potential ecological risk (34–79) was found around the abandoned Barrôco D. Frango mine area, mainly due to As contents in stream sediments. Water and stream sediments from abandoned U mines worldwide have U levels of up to 436 μg/L and 5024 mg/kg, respectively, while those from Barrôco D. Frango have 37.3 μg/L and 189 mg/kg, respectively. However, the longer the distance from the Barrôco D. Frango open-pit lake and mine dump, the higher U, Th and As contents in stream sediments, which is a warning indicator. Cluster heat maps of the water composition from four abandoned uranium mine areas show that Mondego Sul and Barrôco D. Frango mines are the most geochemically similar. Results show that stream sediments should be included in water quality management and future remediation plans of abandoned uranium mines.