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In 1886, an Australian prospector named George Harrison discovered gold in the Main Reef Conglomerates on the farm Langlaagte, which now falls within the present day City of Johannesburg. Since then, hundreds of mine residue deposits (MRDs) have been built across the Witwatersrand Basin. By the mid-1970s, gold recovery processes had improved sufficiently to also allow residual gold from old MRDs to be recovered at a profit. This resulted in dump reprocessing operations and the clearing of soils previously covered by MRDs (`footprints’). Estimates put the area of MRDs and ‘footprints’ at between 400 and 500 km2, comprising some 6 billion t of tailings (Chevrel et al., 2003), containing approximately 430000 t of low-grade uranium (Winde et al., 2004) and 30 million t of sulphur (Witkowski and Weiersbye, 1998). Historically, mining companies often located MRDs in sensitive areas and employed no pollution control. Acid mine drainage (AMD) is associated with Witwatersrand gold mines and MRDs (Maree et al., 1996), and contamination from gold mining has been identified many kilometres downstream from the original sources (Naiker et al., 2003). An argument on the environmental merit of dump reprocessing is that this provides opportunity to relocate residues to more appropriate and better contained sites. However, there is also evidence that reprocessing exacerbates contamination though exposure of previously anaerobic tailings to air and water (Tutu et al., 2005). With the curtailing of mining activities and clearing of land previously covered by MRDs, there comes a demand to use this land for residential, agricultural or industrial purposes. In South Africa, the right to an environment not harmful to a person’s health and wellbeing, and the right to the protection of the environment are basic constitutional human rights (s24 of the Constitution of the Republic of South Africa 108 of 1996). Thus there is a need to understand the extent and types of contamination, and the potential risks associated with different land-uses not only on mining land after closure, but on other affected land. Baseline environmental conditions were rarely established prior to commencing with mining operations and subsequent dump reprocessing. In order for such operations to achieve mine closure it is necessary that they obtain agreement with Government regarding the limits of their liabilities, which could originate from up to 120 years of mining by numerous companies, many of which no longer exist. Historical aerial photographs and satellite-based earth observation systems are powerful tools that have been used to establish culpability (such as in the case of the failure of the Merriespruit slimes dam), but also have the potential to demonstrate absence of liability via mapping of historical contamination that pre-dates current mining operations. The aim of this study is to determine the adequacy of historical aerial photographs and satellite thematic imagery (TERRA satellite ASTER images), integrated with geographic information systems (GIS)-based metadata, for visualising historical contamination emanating from MRDs in a representative semi-arid gold and uranium-mining region (the East Rand of Johannesburg). This aim is of value in establishing standardized tools for mapping mine impacts, in order to focus environmental cleanup, demonstrate compliance, and assist in closure planning. Mine Closure 2006 ― Andy Fourie and Mark Tibbett (eds) © 2006 Australian Centre for Geomechanics, Perth, ISBN 0-9756756-6-4 Mine Closure 2006, Perth, Australia 667

A GIS-Based History of Gold Mine Residue Deposits and Risk Assessment of Post-Mining Land-Uses on the Witwatersrand Basin, South Africa