Hydrogeological study of geological features in the groundwater system of Tweefontein 360KT farm, Limpopo Province
Date
2018
Authors
Dalasile, Piwo-kuhle
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Abstract
A hydrogeological study was conducted to investigate the possible influence of geological structures on the groundwater flow (regime) and dynamics at the Tweefontein farm 360KT, near Steelpoort, Limpopo Province. The aim of the investigation was to understand the groundwater system, as well as to devise appropriate measures that promote proper groundwater resource management, which will allow for prediction and mitigation of possible groundwater ingress into underground workings. Field observations, cross sections, borehole data, chemical analyses and environmental stable isotopes were used to understand the influence of geological features on flow dynamics in Tweefontein farm.
Geological features, faults and dykes were found to enhance groundwater flow due to the presence of interconnected cross-cutting joints. Furthermore, weathering was also found to enhance groundwater flow within these structures. Calcrete and ferricrete within the weathered zone can act as a barrier or limit vertical flow of groundwater to the fractured zone, and this can enhance the formation of later flows which may contribute to formation of springs. There is no major ingress of groundwater into existing underground workings near a prominent NE-striking faulted shear zone that is partly overlain by a river. It can be postulated, based on the documentary evidence collected in this study that the inability of water to ingress underground workings overlain by rivers is attributed to depth, as well as the infilling within the prominent NE-striking geological features. Groundwater within the study area shows a Ca-Mg-HCO3-dominated water type indicative of fresh, shallow circulating groundwater. However, there also is a chloride-dominated facies showing the strong effect of evaporation within the shallow weathered zone aquifer. The enrichment in Ca and Mg ions may be attributed to weathering of ferromagnesian silicate minerals of the Bushveld Igneous Complex. Highly enriched stable isotope (δ2H and δ18O) signatures on surface-water and shallow groundwater suggest the presence of evaporation prior to infiltration. Water from mine fissures plot on the local meteoric water line suggesting direct and preferential recharge through geological structures during periods of rainfall in the summer and winter months. Groundwater in deep mine fissures shows a highly depleted isotopic signature compared to water in the shallow weathered aquifer, which suggests limited vertical hydraulic connection.
Description
A dissertation submitted in partial fulfillment for the degree of
Master of Science in Hydrogeology,
School of Geosciences, Faculty of Science, University of the Witwatersrand, Johannesburg, July 2018
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Citation
Dalasile, Piwo-kuhle (2018) Hydrogeological study of geological features in the groundwater system of Tweefontein 360KT farm, Limpopo province, University of the Witwatersrand, Johannesburg, https://hdl.handle.net/10539/26863