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

[摘要] ENGLISH ABSTRACT: The town of Kleinzee, located in the Northern Cape, South Africa exists solely to mine alluvial diamondsfound 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 toincrease the water supply needed, the town installed an underground membrane across the BuffelsRiver approximately 5.5km upriver from the town. However, climatic conditions, long term copper anddiamond mining and poor groundwater management practices have combined to produce very poorquality groundwater within the Buffels River Valley. The purpose of this study is to look at the impactof the membrane on the quality of both the shallow groundwater system as well as the soils within theriver bed. To do this, 46 sites were selected for soil analysis starting below the membrane andcontinuing above the membrane upriver for a distance of approximately 5 km. Additionally, a further15 groundwater samples were collected at the end of the wet season in October when groundwaterwas available. Cation and anion analysis of the shallow groundwater and the saturated paste extractsshows significant peaks in SO42- and Mg2+ immediately above the membrane in the sediments inaddition to Na+ and Cl-, diminishing upstream away from the membrane. Cu2+ and Zn2+ did not showan elevated concentrations in the groundwater or sediments above the membrane as originallythought. Experiments on atacamite, a Cu2+-hydroxide, which forms naturally in the Spektakel soilswithin the Buffels River Valley, indicates that although generally stable at moderate pH, large rainevents may increase the solubility of atacamite resulting in its transport downstream. However, thesource of sulphate is probably linked to processing of Cu2+ ores further up the river valley. The transportmechanism of the groundwater salts and trace metals is via dissolution mobilization. The membraneis accumulating trace metals and salts in sediments behind the membrane and not in groundwaterfound behind the membrane. Thus accumulation is due principally to evaporative concentration.

[发布机构] Stellenbosch University