Using impacts of deep-level mining to research karst hydrology—a Darcy-based approach to predict the future of dried-up dolomitic springs in the Far West Rand goldfield (South Africa). Part 1: a conceptual model of recharge and inter-compartmental flow

Some of the world’s deepest goldmines are located in the Far West Rand (FWR) goldfield operating below of up to 1.2-km-thick dolomites hosting some of the largest karst aquifers in South Africa. Associated impacts include the dewatering of the overlying karst aquifers as well as linking previously disconnected compartments by mining through aquicludes (dykes). The focus of the study is on predicting groundwater balances in re-watered aquifers after mining ceases as this will determine whether or not associated karst springs that dried-up due to dewatering will ever flow again. Critically revisiting, Swart et al. (Environ Geol 44:751–770, 2003a) who predict that all springs will flow again, this study uses significantly larger data sets and modified assumptions to increase the robustness of findings as the question is crucial for post-closure development. As a first of two papers, this part develops a conceptual model on the mega-compartment concept that predicts a flat water table across all linked compartments that would leave the springs dry. The model identifies the ratio between inflowing surface water (recharge) and underground water losses to downstream compartments via mined-through dykes (‘inter-compartmental groundwater flow’, IGF) as a key factor governing the elevation of the post-mining water table, creating the base for part 2, where the IGF and the post-mining water tables are determined using unique large data sets that have not been evaluated before.     

Environmental impact of gold tailings and the long-term implications for remediation and mine closure——The Far West Rand goldfield, South Africa

Commercial gold mining of the Witwatersrand Supergroup in the Far West Rand goldfields of South Africa started early in the previous century and produced U as a by-product. Grades of up to 1000 mg/kg, was achieved between 1952 and 1991. Before and after this period large amounts of U brought to the surface as part of the gold ore-material were deposited as solid-water-mixtures （sludge） on slimes dams. Tailings of gold mines in the Witwatersrand basin therefore contain elevated levels of radioactive and chemo-toxic heavy metals. Mining for gold occurs at great depths below the Transvaal Supergroup dolomite. The inflow of water from the overlying dolomite aquifers resulted in substantial volumes being pumped continuously from the mine void to prevent flooding. Since large-scale dewatering of the dolomite compartments was allowed for mining, extensive sinkhole formation occurred. Between 1960 and 2000, these sinkholes and other subsidence features were back：filled as part of rehabilitation program, using a mixture of mine tailings and cement. Many of the gold mines are reaching the end of their economic viability and will close down in the next few years. Dewatering of the dolomite water compartments will come to an end resulting in a gradual rise in the water table. The uncontrolled rise of the water table to pre-mining levels will not only result in further land degradation due to renewed ground instability but also may also lead to uncontrolled pollution and acid mine drainage imminent from slimes filled sinkholes and cavities Furthermore, gold tailings facilities were placed on well-drained dolomite, resulting in seepage of dissolved U from tailing deposits into the dolomitic aquifer. The majority of the studies into mining-related pollution conducted thus far focused either on point-discharges of mining effluents into surface streams or on erosion of tailing particles from slime dams as contamination sources. This paper investigates the magnitude of land degradation and pollution potential of the sinkholes filled by tailings and cement. A combination of LIDAR and Aerial magnetic and radiometric techniques are used to localize sinkholes, structures such as dykes and faults along which polluted water will be transported from slimes and tailings into the aquifer.     

Environmental impact of gold tailings and the long-term implications for remediation and mine closure—The Far West Rand goldfield, South Africa

Commercial gold mining of the Witwatersrand Supergroup in the Far West Rand goldfields of South Africa started early in the previous century and produced U as a by-product. Grades of up to 1000 mg/kg, was achieved between 1952 and 1991. Before and after t…