Abstract
The mining industry has been associated with environmental pollution throughout the ages. Old abandoned mines are of particular concern due to the lack of remediation and monitoring of the pollution. The abandoned Edendale Lead Mine in Tshwane, South Africa, was in operation from the 1980’s until 1938 and mined primarily galena for the lead content, although some silver was also recovered in the early years. The mine was decommissioned before environmental legislation in South Africa, namely the National Environmental Management Act 107 of 1998 and the Minerals and Petroleum Resources Development Act 28 of 2002, required the mitigation of environmental impacts associated with mining. Consequently, the environmental effects of Edendale Lead Mine have not been determined. This study is aimed at establishing the source, extent and magnitude of environmental pollution associated with metal contamination from mining operations in the area. Such investigation is of particular interest as there are two schools in the area, namely the Edendale Primary and High School, and the mine site is located immediately adjacent to the Edendalespruit. Furthermore, there are numerous farms and some private residences in the area that rely on borehole water that may potentially be polluted.
The ore at Edendale Lead Mine was mined from a hydrothermal deposit, with irregularly disseminated argentiferous galena being the only ore mineral of importance. Two mineralisation stages can be recognised from material available on waste rock dumps, i.e. an intensely fragmented and strongly silicified breccia and a carbonate-dominated breccia with minor pyrite. The galena is restricted to the first mineralisation stage.
Water and solid samples were collected from the mine site and from the surrounding area. Through ion chromatography, Inductively Coupled Plasma - Optical Emission Spectrometry (ICP-OES) and Inductively Coupled Plasma - Mass Spectrometry (ICP-MS) analysis, the water of the area is found to be of good quality according to the South African Department of Water Affairs and Forestry Domestic Water Guidelines. The main concern is the presence of hazardous concentrations of lead in the Edendalespruit below the old plant site and in a pit near shaft one; determined to be from the abundance of relatively soluble anglesite (PbSO4) and susannite/leadhillite (Pb4(SO4)(CO3)2(OH)2) in the slag heap and the waste rock dump.
Solid samples were mineralogically and chemically analysed using X-Ray Powder Diffraction (XRD) and X-Ray Fluorescence Spectrometry (XRF), which determined the soil to be enriched in lead, zinc, and copper. The lead, zinc and copper are from secondary minerals of galena, sphalerite and chalcopyrite, respectively.
Metal mobility and availability was found to be limited through high soil pH conditions, which encourage metal-carbonate precipitation reactions and absorption by iron oxides and hydroxides. However, the high concentrations of lead in the soil are of considerable concern due to its toxicity and the number of people at risk, namely at the Edendale Primary and High Schools as well as users of the Edendalespruit and local ground water sources. The soil lead levels exceed the European Union target and intervention standards, therefore, requiring immediate mitigation and remediation measures. Recommendations for remediation and prevention measures may include the removal of the slag heap at the old mine site and the use of phytoremediation.
Prof. J.M. Huizenga
Prof. J. Gutzmer
Mr. H. Coetzee