Renaturing Gauteng's mining wastescapes?

Introduction

Globally, wastescapes, including mining-related wastescapes, are typically associated with abandoned territories, underutilised areas, previously polluted industrial sites, empty lands, waste management areas, and undefined spaces in between, are often found in isolated locations or the outskirts of metropolitan regions (Amenta and Timmeren, 2018; Weber, 2018). As a result, the location of mining wastescapes in Gauteng, bisecting Johannesburg and other urban centres, is atypical. This phenomenon arose due to the expansion of Johannesburg's urban landscape near the gold mines and the lax regulation of initial mining operations. Once mines became unprofitable, they were abandoned, and obligations to rehabilitate these spaces were only included in later years (Bobbins, 2013). Given the enormous volume of material produced by the deep mining of the area, a substantial part of Gauteng's core is marked by mine waste. As a result, many of these areas remain barren, long after the cessation of mining activity, leading to the underutilisation of large pieces of centrally-located land. However, some former mining areas have become renatured over time. Some have benefitted from deliberate rehabilitation processes such as soil replacement, landform reshaping, greening, and waste consolidation. Others have been transformed by natural processes of vegetation succession. Building on work in earlier maps (Bobbins and Trangoš, 2016 and Khanyile, 2016), this Map of the Month examines the distribution of mine waste and associated residual waste and analyses the presence of natural land cover on these sites.

Distribution of mining wastescapes in Gauteng

Map 1 displays the incidence of mining waste per square kilometre (km²) in Gauteng. According to Oelofse et al. (2010), the Witwatersrand mining belt has over 270 tailings, occupying an area of 400 km². The map indicates that areas of the province marked by mine waste and residue are not limited to the Witwatersrand mining region. There are also scattered occurrences of mine residue in the north and south of the province, following the dip of gold-bearing reefs and the exploration of other commodities (Bobbins and Trangos, 2018). However, the map also shows that areas across the mining belt, such as Benoni, Krugersdorp, Carletonville, areas north of Soweto, and areas south of Johannesburg city centre, are characterised by radioactive waste. This is because gold and uranium occur in the same geological environment, and uranium is extracted as a by-product and dumped into tailings without being recovered in most gold mining processes (Moshupya et al., 2022; Hecht, 2023).

Map 1: Presence of mine waste per km² in Gauteng.

The presence of different types of mine waste and residual waste

Map 2 depicts areas characterised by mine waste, including the residual waste from mining activities, where previously mined land has been extensively damaged and abandoned. This map shows the distribution of areas that are characterised by mine waste or a combination of types of mine waste and residual waste – evident in the number of waste types per km² (up to 4). Those areas that are shaded red have at least four of the following types of waste present in 1 km²: abandoned mines, mine residue, artificially flooded pits, and barren land. The co-presence of multiple types of mining and residual waste is particularly evident in Benoni, Springs, and Carletonville locations.

Map 2: Mining and related residual waste per km² in Gauteng.

Rehabilitation

Some forms of mine waste can be processed and converted to extract further value, although this carries risks of radioactivity and physical and chemical instability (Sibanda and Broadhurst, 2018; Slingerland et al., 2018; Council of Scientific and Industrial Research (CSIR), 2019). Based on the data from the Gauteng Department of Rural Development and Agriculture's (GDARD) Mine Residue Areas (2012), 157 of 374 mine residue areas are confirmed to be radioactive, covering an area of 220 km². Of the remaining mine residue sites, 18 are not radioactive, and the radioactivity of the others is not known. Radioactive dumps are sprayed with water to limit dust production. In other cases, they are reworked to reach the remaining gold or relocated, although uranium might be released in dust form during these processes.

Out of all the places where mine waste is found, only 25 km² is estimated to have the potential to be restored at a relatively modest cost (Bobbins, 2013). The rehabilitation usually entails revegetation, soil replacement, land reshaping, and waste relocation (Festin et al., 2019; Kengni and Nkosi, 2023). In some instances, the rehabilitated land has been used for the development of industrial and agricultural spaces. In other instances, the rehabilitated land has been converted into residential areas. For example, the outward expansion of Soweto and south of Germiston after the Mining Rights Act of 1967 (Mubiwa and Annegarn, 2013), and, more recently, Fleurhof (Mining Weekly, 2018). However, the reclamation of this land may result in protracted disturbances before it can be occupied by people (Sibanda and Broadhurst, 2018). Therefore, the existence of mining waste in this region gives rise to several problems, including issues of sustainability and community health.

Moreover, the abandonment of mines, some of which remain unsealed, poses safety problems in addition to the environmental and public health risks associated with mine tailings and slimes. Studies by Heath (2009), Mhlongo et al. (2019), and Mabaso (2023) have shown that abandoned mine shafts that are not adequately sealed off can provide an environment conducive to illicit mining operations, particularly in regions with significant levels of poverty and unemployment.

Consequently, there have been substantial efforts in recent years to restore some areas of land in Gauteng that have been affected by mining waste. However, a large number of mines are abandoned and are considered ownerless, and are not rehabilitated. Even in these cases, some transformation might have occurred due to natural processes of vegetation succession (Lubke, 2023). Based on GeoTerraImage's (GTI) 1990-2020 land use land cover change data (2020), 110 km² of land in Gauteng, previously designated for mining, has been converted to other land uses and cover in the past 30 years. A significant aspect of the province's rehabilitation and reclamation efforts involves the introduction of vegetation to mine dumps, considering the restricted suitability of some post-mined areas (Cook, 1971; Mining Weekly, 2015; Community Monitors, 2018). Map 3 depicts mined land that has been converted into other natural land uses and cover, such as vegetation and water bodies. Noting that while a single vegetation type may characterise some square kilometres (turquoise areas), others exhibit many vegetation types and waterbodies, particularly noticeable around the Witwatersrand mining belt (yellow to red areas).

Map 3: Post-mined areas in Gauteng that have been converted into natural land cover per km².

Given the profound impact of mining on the environment, the return of the biodiversity that once occurred on these lands is difficult. Slag material brought to the surface from great depths has little capacity to support plants and animals (Zou et al., 2019), and only some pioneer species can colonise the space. Some of these may be exotic and, therefore, of limited ecological value. However, they stabilise soil, sequester carbon, help begin the process of soil formation, help reduce erosion, and wind-born pollution experienced by surrounding neighbourhoods (Cook, 1971; Culwick et al., 2019; Naidoo et al., 2022). An interesting observation from the mapping indicates that much of the new vegetation is grassland, which is consistent with the general grassland biome of the region (Khanyile and Maree, 2017; Kgatla et al., 2022), although it is not possible to tell from this data whether this is anything more than a few pioneer species of grass.

This analysis offers one slice of data to understand the afterlives of Gauteng's mines. Some renaturing has occurred, in some cases, by both human-led and natural processes. A further area for spatial analysis is the distribution of abandoned mines and, therefore, not being actively managed.

Method

Gauteng's mining wastescapes were mapped using various data sources on mining-related activities across the province. These sources included data on abandoned mines (Council for Geosciences, 2012), mine waste and residues (including dumps, tailings, and slimes) (GDARD, 2012), and land use and cover change (GTI, 2020) datasets for identifying converted post-mined land. The land cover data was specifically used to extract the types of cover that former mined lands have been converted into. The data varied in scale and was aggregated into a grid cell of one square kilometre (km²) for a standardised analysis. The incidence of each form of mine waste, residual waste, or conversion of mining-related land use or cover was only counted once per km² basis (Map 2). For instance, the count of two mining residue sites per km² was considered a single occurrence, representing one sort of waste per km². An abandoned mine and mine residue area occurring in the same km² cell were treated as two distinct incidents, each representing a distinctive sort of waste within their respective square kilometre of occurrence.

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Suggested citation: Khanyile, S. (2024). Renaturing Gauteng's mining wastescapes? Map of the Month. Gauteng City-Region Observatory. February 2024. https://doi.org/10.36634/QUAU2712.

Edits and input: Dr Richard Ballard and Graeme Götz.

Map design: Jennifer Murray.