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In the absence of the necessary valley topography, karst depressions are sometimes used to construct conventional impoundments in order to contain tailings. Leakage is a primary concern for such impoundments. The purpose of the current study was to determine the characteristics and barrier performance of laterite mantling karst depressions, using, as an example, the Wujiwatang (WJWT) tailings impoundment, located in the Gejiu mining area, southwestern China. The geotechnical-hydrogeological properties, geochemistry, mineral compositions, and particle shapes of the laterite were investigated by geotechnical techniques, chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results showed that the laterite contained poorly sorted particles that covered a wide spectrum of grain sizes (<5 mm to <50 nm), and was unexpectedly categorized as silty clay or silt with a high liquid limit. The continuous gradation and small D90 value helped the laterite achieve saturated hydraulic conductivities in the range of <10–6 cm/s required for impoundment liners. The laterite beneath the tailings impoundment was finer-grained and had a lower permeability than that of the laterite on the depression walls within the same depression. Geochemically and mineralogically, the laterite was classified as true laterite and its major mineralogical constituents were gibbsite and goethite with chlorite occurring in trace amounts. The laterite was dominated by subspherolitic–spherolitic cohesionless grains (concretions) made up of Al, Fe, Ti, and Mn oxides and hydroxides. The laterite did not have plasticity indices in the clay range. Fortunately, slopewash prior to tailings containment selectively transported the finer oxide concretions to the depression floor, creating a natural low-permeability barrier for the WJWT tailings impoundment. This is undoubtedly important for the planning and design of future karst depression-type tailings impoundments around the world. [ABSTRACT FROM AUTHOR]

The influence of mining activities on groundwater quality is a growing concern due to highly toxic metals in the tailings. Carbonate rocks are common in the surrounding rocks of ore deposits. But such mining districts generally do not have the conditions to construct traditional tailings impoundments due to the different degrees of karstification. This paper utilises field investigations, chemical analyses, and permeability tests, etc. to study the effect of tailings impoundments on the underlying karst water systems in the Gejiu world-class Sn-polymetallic mine located in a typical karst region in southern China, with samples collected from both karst springs deriving from the mining area and tailings porewater. Because of the abundance of sulphide minerals in the ores, acid mine drainage is expected to pose a high risk. However, the results indicate that the tailings porewater is moderately neutral and is characterized by the SO4–Ca–Mg hydrochemical type. This can be attributed to the substantial buffering capacity of carbonate minerals. Pollution elements in the tailings porewater mainly include SO42− and toxic metals including As, Cd, Mn, Pb, and Hg. The type of pollution factors and the degree of contamination are not consistent in the different tailings impoundments. The hydrochemical classification of four karst springs distributed in the south of the mining area is HCO3–Ca–Mg. The concentrations of SO42− and the toxic constituents in the springs are far below the national standards for drinking water. The spring water not being contaminated may be attributed to the operation mode of the tailings impoundments (peripheral discharge and reuse of ponded water), the residual clay between the tailings impoundments and the carbonate bedrocks and the sufficient buffering capacity of the underlying karst systems. The tailings disposal at the Gejiu tin mine within the natural karst depressions is able to provide a reference for the operation of karst mines in China and elsewhere. [ABSTRACT FROM AUTHOR]

Tailings impoundments can potentially collapse due to damage caused by earthquakes, which has frequently occurred around the world. This study takes the proposed valley type tailings impoundment in Yunnan as the research object to analyze the dynamic response behavior under earthquake action with both numerical simulation and physical model test (1:300). The results of both tests show that the dynamic response of the valley type tailings impoundment is characterized by 'medium stiffness effect', in other words, in a certain range, the 'softer' the unsaturated tailings sand is, the more energy it can dissipate, which leads the decrease of the value of the acceleration amplification factor. In addition, the peak acceleration of the monitoring points increases with the vertical elevation, which indicates that the 'elevation amplification effect' exists in the tailings impoundment dynamic response. The middle part of the outer side of the raised embankment reacts more sensitive than the crest, which is similar to the slope dynamic response. The starter dam reacts sensitively under the earthquake excitation, which should be given more attention during the seismic design. The dynamic response rules reflected by the numerical simulation are consistent with the results monitored on the physical model test, although there are some differences between their values. The dynamic response rules of the valley type tailings impoundment can provide basis for the design of the similar projects in this region. [ABSTRACT FROM AUTHOR]