Geochemistry of artificial groundwater recharge into the Kopoasfontein breccia pipe near Calvinia, Karoo
type: CreativeWork
description: Artificial groundwater recharge has been proposed as an innovative strategy for managing the scarce water supplies of the town of Calvinia, near the edge of the Karoo, South Africa. Surplus runoff water from the town dam or groundwater from boreholes in weathered shale aquifers would be injected into the Kopoasfontein breccia pipe, a roughly cylindrical body of fractured rock, 12 km east of the town. Subsurface water storage would then mjnjmjse evaporative losses, so that the injected water could be recovered when emergency water supplies are needed. Underground storage space for an estimated 70 000 m3 of water is available in the natural fractures and cavities of the breccia, but the unusual geochemistry of the breccia pipe system promises to be a controlling factor affecting the viability of the scheme. A geochemical investigation of the rocks from Kq,oasfontein and the various water sources has revealed substantial differences in composition, pH and redox status between the brcccia pipe, Karoo groundwater and surface water sys=m. Major rock types in the upper portion of the breccia pipe are baked, fragmented mudstoncs and shales, which have been subjected to hydrothermal alteration. Base cations in the rock are dominated by K, Mg and Na, but Ca concentrations are generally low. There is a trend of inaeasing Na and· decreasing K with depth over the upper 400 m of the brcccia pipe. The major mineral phases in the bulk rock are quartz, feldspar and clays from the illite, chlorite and kaolinite groups. Late stage secondary minerals have also been deposited in the brecciated shale environment by hydrothermal solutions. Quartz, calcite, chlorite and ~tal sulphide minerals (pyrite, pyrrhotite, chalcopyrite, galena) occur as vein minerals in the breccia and as coatings on the walls of fractures and cavities. Well-formed crystals of the subzeolite mineral, fluorapophyllite, line many of the breccia cavities. Toe hydrothermal minerals generally occur along the zones of wea…
abstract: Artificial groundwater recharge has been proposed as an innovative strategy for managing the scarce water supplies of the town of Calvinia, near the edge of the Karoo, South Africa. Surplus runoff water from the town dam or groundwater from boreholes in weathered shale aquifers would be injected into the Kopoasfontein breccia pipe, a roughly cylindrical body of fractured rock, 12 km east of the town. Subsurface water storage would then mjnjmjse evaporative losses, so that the injected water could be recovered when emergency water supplies are needed. Underground storage space for an estimated 70 000 m3 of water is available in the natural fractures and cavities of the breccia, but the unusual geochemistry of the breccia pipe system promises to be a controlling factor affecting the viability of the scheme. A geochemical investigation of the rocks from Kq,oasfontein and the various water sources has revealed substantial differences in composition, pH and redox status between the brcccia pipe, Karoo groundwater and surface water sys=m. Major rock types in the upper portion of the breccia pipe are baked, fragmented mudstoncs and shales, which have been subjected to hydrothermal alteration. Base cations in the rock are dominated by K, Mg and Na, but Ca concentrations are generally low. There is a trend of inaeasing Na and· decreasing K with depth over the upper 400 m of the brcccia pipe. The major mineral phases in the bulk rock are quartz, feldspar and clays from the illite, chlorite and kaolinite groups. Late stage secondary minerals have also been deposited in the brecciated shale environment by hydrothermal solutions. Quartz, calcite, chlorite and ~tal sulphide minerals (pyrite, pyrrhotite, chalcopyrite, galena) occur as vein minerals in the breccia and as coatings on the walls of fractures and cavities. Well-formed crystals of the subzeolite mineral, fluorapophyllite, line many of the breccia cavities. Toe hydrothermal minerals generally occur along the zones of wea…
author: Cave, Lisa Caryn
keywords: Geological Sciences
date published: 1999
date modified: 2026-07-22T22:22:51Z
provider: University of Cape Town
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Department of Geological Sciences

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property ID: Handle
value: http://hdl.handle.net/11427/40287