Investigation of the Metal Contamination in the Upper Olifants Primary Catchment by Using Stream Sediment Geochemistry, Witbank Coalfield, South Africa

Abstract

The Olifants primary catchment area, consists of nine sub-catchments marked from B1 to B9, extends over the border between South Africa and Mozambique, and has a total area of approximately 87,000 km². The B1 catchment, where most of the mining activities surround the major towns of Witbank (Emalahleni) and Middleburg, in turn straddles the provinces of Mpumalanga and Limpopo. Although industrial and agricultural activities are also important, the contribution of contamination from the mining activities within the catchment is significant as the result of intense mining activities of various mineral commodities such as coal and from ferrochrome processing plants located in Emalahleni and Middleburg towns with in the catchment area and yet not fully quantified. This paper investigates the severity of the mining impacts on the water resources and the ecosystem of the Olifants primary catchment area and in particular, the upper reaches of the catchment. The paper discusses the results of research which focused on deciphering the severity and the sources water contamination, and on how to minimise the dispersion of these metals into the streams, and on the relationship of the water quality and metal loadings on the sediments. Stream sediment and water samples have been collected and analysed. The sediments were analysed by Simultaneous X-ray Fluorescence and Inductively Coupled Plasma-Mass Spectrometry techniques for metal loadings. The areas were marked by anomalous level determined at 50th percentile threshold of Fe, Mn, Ni, Cr, Co, V, Pb in Emalahleni and Al, Fe, Mn, Cr, As, Zn, Pb and U in Middleburg. The ICP-MS and IC analytical techniques were used in the assessment of water quality data. From the stream sediments regional geochemistry at catchment level and for this investigation, the sediments that were found marked by high levels of Na, K, Mg, Al, Ca, Mn, and Fe signature can be attributed to the coal mines as a probable source. Whereas the sediment quality of the areas like Emalahleni and Middleburg towns, where mining of coal (with many abandoned mines) and ferrochrome processing is happening simultaneously, there are anomalous level of Cr, Ni, V and As, which is a signature of the Bushveld PGE mines material. The SO₄ ²⁻ concentration of above 500 mg/kg on the water quality, which has exceeded the Department of Water Affairs water quality guideline for domestic and industrial use, is an evidence for contamination. The approach adopted herein suggests that the stream sediment and water quality data can be used in characterizing or fingerprinting impacted areas.