Abstract: This paper describes the processes leading to uranium distribution in the groundwater of five boreholes near a restored uranium mine (dug in granite), and the environmental impact of restoration work in the discharge area. The groundwater uranium content varied from \textless1 μg/L in reduced water far from the area of influence of the uranium ore-containing dyke, to 104 μg/L in a borehole hydraulically connected to the mine. These values, however, fail to reflect a chemical equilibrium between the water and the pure mineral phases. A model for the mobilization of uranium in this groundwater is therefore proposed. This involves the percolation of oxidized waters through the fractured granite, leading to the oxidation of pyrite and arsenopyrite and the precipitation of iron oxyhydroxides. This in turn leads to the dissolution of the primary pitchblende and, subsequently, the release of U(VI) species to the groundwater. These U(VI) species are retained by iron hydroxides. Secondary uranium species are eventually formed as reducing conditions are re-established due to water–rock interactions.

Abstract: We present a first paragenetic study of the Wuyier, Wuyisan, Wuyiyi and Shihongtan sandstone-hosted roll-front uranium deposits, northwest China. The mineralization is hosted by Lower–Middle Jurassic coarse- to medium-grained sandstones, which are dark-gray to black due to a mixture of ore minerals and carbonaceous debris. The sandstone is alluvial fan-braided river facies. Minerals associated with these deposits can be broadly categorized as detrital, authigenic, and ore-stage mineralization. Ore minerals consist of uraninite and coffinite. This is the first noted occurrence of coffinite in this type of deposit in China. Sulfide minerals associated with the uranium minerals are pyrite, marcasite, and less commonly, sphalerite and galena. The sulfide minerals are largely in textural equilibrium with the uranium minerals. However, these sulfide minerals occasionally appear to predate, as well as postdate, the uranium minerals. This implies that there are multiple generations of sulfides associated with these deposits. The ore minerals occur interstitially between fossilized wood cells in the sandstones as well as replace fossilized wood and biotite. The deposits are generally low-grade. Primary uranium minerals associated with the low-grade deposits are generally too small, ranging from 0.2 to 0.3 μm in diameter, to be observed by optical microscopy and are only observed by electron microscopy. Mineral paragenesis and textures indicate that these deposits formed under low temperature (30–50 °C) conditions.

Abstract: In Southern Africa elevated nitrate concentrations are observed in mostly uninhabited semi-arid areas. In the Kalahari of Botswana groundwater locally exhibits concentrations up to 600mg/l. It is assumed, that nitrate found in the groundwater originates mainly from nitrogen input and transformations in the soils. Our investigations in the Kalahari between Serowe and Orapa show that cattle raising is an important source for enhanced nitrate concentrations in the soils (Arenosols). But also in termite mounds very high nitrate stocks were found, and under natural vegetation (acacia trees and shrubs) nitrate concentrations were mostly unexpectedly high. This nitrate enrichment in the soils poses a serious threat to the groundwater quality. However, calculated soil water age distributions in the unsaturated zone clearly show that today’s nitrate pollution of the groundwater below the investigation area could originate from natural sources, but cannot be caused by the current land use for cattle raising.

Abstract: Demonstration des Potentials der Nitrat-Isotopenanalytik für die Strategieentwicklung der Sanierung Nitrat-belasteter Brunnen