Development of a computer-based advisory system for a selection of appropriate rehabilitation strategies for designated abandoned mine sites in Limpopo Province of South Africa

Abstract

South Africa has many abandoned mines which seriously affect the environment and the livelihood of the host communities. The lack of in-depth knowledge of the problems of these mines, limited resources for their rehabilitation, lack of clearly assigned responsibilities for rehabilitation, and the absence of criteria and standards of rehabilitation have led to the use of inappropriate strategies to rehabilitate abandoned mines. The main objective of this research was to develop a computer-based advisory system for selecting suitable rehabilitation strategies for designated abandoned mines. The research methodology involved characterization of the selected abandoned mine sites, devising methods for prioritization of mine features for rehabilitation, development of three expert systems that provide guidance on different aspects of rehabilitation of abandoned mines, and development of a framework for estimation of costs of rehabilitation of abandoned mines. The first part of this research involved development of methods for characterization and prioritization of abandoned mine entries and tailings dumps as well as selection of strategies for rehabilitation. These methods were written in an expert system shell to create expert systems (ESs) for ranking of abandoned mine entries and tailings dumps for rehabilitation. The study also used semi-quantitative methods such as SWOT (Strength, Weaknesses, Opportunities, and Threats) analysis as well as the Quantitative Strategic Planning Matrix (QSPM) technique and Multi-Criteria Decision-Making (MCDM) methods such as Analytic Hierarchy Process (AHP) and Pugh Matrix to evaluate different strategies for their suitability to deal with the issues of abandoned mines. Based on the current situation of abandoned mines in the study area, a framework for estimation of costs of rehabilitation of abandoned mines was developed by taking into consideration direct cost and other key cost estimates which were previously disregarded. The method for ranking the problems of abandoned mine entries was developed based on information collected during preliminary assessment of the mine entries while that of ranking the abandoned mine tailings was based on the potential of the dumps to pollute the surrounding environment and the landscape and the visual impact they present. These approaches are relatively less data demanding than the current tools used for rehabilitation of abandoned mines. Thus, these methods have the advantage of being suitable for use in developing countries where there are many abandoned mines but limited resources for their rehabilitation. The application of these methods at selected abandoned mines in Giyani and Musina areas showed that mine shafts had moderate physical and environmental hazards. The risks of people and animals falling into the shafts and the problems of ground movement around the shafts were identified as the major concerns. Strategies that provide long-term or permanent closure of the abandoned mine shafts were identified as the most suitable options. These include backfilling of the shafts, use of concrete plugs to seal the shafts, use of blast closure and injection/inclusion strategies. The results of the study showed that tailings dumps in the study area have the potential to pollute the environment with toxic materials such as Cd, As, Ni, Pb, Zn and Cu. Based on the determined mean pollution index, dispersion index and the index of landscape and visual impact of the tailing dumps in the study area it was found that rehabilitation of these mines is likely to require moderate efforts. The priority of rehabilitation of these mines should be in the following decreasing order: Fumani Gold Mine Tailings, Klein Letaba Gold Mine Tailings, Nyala Magnesite Mine Tailings (A), Nyala Magnesite Mine Tailings (B), Louis Moore Gold Mine Tailings, and Mesina Copper Mine Tailings. The description of the hazards and evaluation of the strategies for dealing with the problems of abandoned surface mine excavations and other structures demonstrated that repurposing of these features should be considered before application of traditional rehabilitation methods. The rule-based expert systems that provide guidance on the rehabilitation of abandoned mines were developed. The fact that these expert systems are web-based make them easily accessible for use in different parts of the world. Based on this, the characterization, prioritization and selection of strategies for rehabilitation of abandoned mines can be conducted in different regions following the same procedures and methods as described in this thesis. The framework which was developed for estimation of the costs of abandoned mines rehabilitation emphasized the need for inclusion of critical indirect costs in the estimation process to reduce elements in the risks of under estimation.