Relationship of historical copper mining to the transport and accumulation of trace metals and salts in semi-arid environments : an example from Buffels River, Northern Cape, South Africa

Dunford, Alexander (2016-03)

Thesis (MSc)--Stellenbosch University, 2016.


ENGLISH ABSTRACT: The town of Kleinzee, located in the Northern Cape, South Africa exists solely to mine alluvial diamonds found in the Buffels River. Given the very low precipitation of the area (generally <150mm/yr) groundwater is the principal supply of domestic and industrial water to the town. In an effort to increase the water supply needed, the town installed an underground membrane across the Buffels River approximately 5.5km upriver from the town. However, climatic conditions, long term copper and diamond mining and poor groundwater management practices have combined to produce very poor quality groundwater within the Buffels River Valley. The purpose of this study is to look at the impact of the membrane on the quality of both the shallow groundwater system as well as the soils within the river bed. To do this, 46 sites were selected for soil analysis starting below the membrane and continuing above the membrane upriver for a distance of approximately 5 km. Additionally, a further 15 groundwater samples were collected at the end of the wet season in October when groundwater was available. Cation and anion analysis of the shallow groundwater and the saturated paste extracts shows significant peaks in SO4 2- and Mg2+ immediately above the membrane in the sediments in addition to Na+ and Cl-, diminishing upstream away from the membrane. Cu2+ and Zn2+ did not show an elevated concentrations in the groundwater or sediments above the membrane as originally thought. Experiments on atacamite, a Cu2+-hydroxide, which forms naturally in the Spektakel soils within the Buffels River Valley, indicates that although generally stable at moderate pH, large rain events may increase the solubility of atacamite resulting in its transport downstream. However, the source of sulphate is probably linked to processing of Cu2+ ores further up the river valley. The transport mechanism of the groundwater salts and trace metals is via dissolution mobilization. The membrane is accumulating trace metals and salts in sediments behind the membrane and not in groundwater found behind the membrane. Thus accumulation is due principally to evaporative concentration.

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