Geo-environmental and physical risk associated with the derelict and ownerless gold mines from Transvaal- Drakensberg and Barberton Greenstone Belt Gold Fields, Mpumalanga Province, South Africa

Abstract

Historically mines had poor reputation for addressing environmental and safety concerns during mining and at mine closure as a result historic mining areas are left with large open pits, unsealed shafts filled with water and scattered waste spoils and tailings. The current research formed part of the larger national project that focused on assessing environmental and physical risks associated with derelict and ownerless mines of all commodities. Gold mines from two geological units namely; the Barberton Greenstone Belt and the Transvaal Drakensberg Gold Field were selected for the study as a regional approach in risk ranking derelict mines from these gold fields for prioritization of rehabilitation. The primary aim of this study was to identify and compare the potential environmental, public safety and health hazards posed by the derelict and ownerless mines of the Barberton Greenstone Belt to that of the Transvaal Drakensberg Gold Field. This aim was achieved through geochemical assessment of water, soils, tailings dump and waste rock dumps in both mine sites and surrounding ecosystems and assessment of illegal mining and assessment of geology of the mining areas. A field investigation which involved identifying observable physical, potentially hazardous mine infrastructure, such as adits, shafts, pits, waste rock dumps, tailings dumps, degree of erosion and mine buildings and environmental hazards on site was employed to achieve the objectives of the study. Samples collected were analysed onsite and some were sent to the Council for Geoscience laboratory. Water samples were collected for onsite analyses (pH & EC) and laboratory analyses (ion chromatography and ICP-MS). Soil samples were collected for on-site analysis using the handheld XRF analyser. Tailings samples were collected for laboratory analyses (XRF, XRD, ABA & ICP-MS) and handheld XRF analysis. Waste rock samples were collected for laboratory analyses (XRF , XRD, ABA & ICP-MS). Derelict mines from the Transvaal Drakensberg gold fields presents a high risk for contamination of water. This was concluded through the observation of measurable erosion gullies of tailings dumps and PHEs in tailings dumps which are likely to generate acid mine drainage. The high rainfall and proximity of the derelict mines of the Transvaal Drakensberg Gold Field to major rivers was identified as a major environmental concern. Mines from the Barberton Greenstone Belt are likely to generate alkaline drainage due to the presence of buffer minerals within their tailings materials. The presence of faults and joints in the surrounding geology of Bourke's Luck Gold Field of Transvaal Drakensberg Gold Field present a high risk for contamination of ground water. Bonanza and Golden Snake mine of the Barberton Greenstone Belt are also characterised by series of faults and joints which also provide pathway for percolation of plumes to contaminate groundwater. Mines closer to human settlements such as Bonanza mine in the Barberton Greenstone Belt were ranked as highest in case of public safety and health. High concentration of PHEs in surrounding soil in the area are most likely to cause health problems to locals at proximity to the mine, therefore further medical studies are required to validate this hypothesis. Open shafts in all visited sites were documented as high safety risk to locals with Bonanza Mine presenting the worse-case due to its proximity to Sheba community, therefore requiring immediate sealing. High level of illegal mining in the Transvaal Drakensberg gold field presents a high risk of environmental degradation and public safety. An immediate intervention to curb illegal activities in the old mine workings is required for the safety of the public and surrounding agroecosystems.