HORRIFIC CONSEQUENCES Bafokeng mine, the Saaiplass mine and Merriespruit mine are the most well-known, documented tailings dam failures in South Africa
Photo by: Reuters
A detailed review of the literature on issues related to mine residue disposal facilities (MRDFs) and an evaluation of information from local historical cases of tailings dam failures have been conducted by the Council for Geoscience (CGS).
CGS senior scientist and engineering geo- logist Sifiso Ngubelanga says the current practice across various mining regions in South Africa with regard to the design, planning of opera- tions, management and decommissioning of tailing dams was also reviewed during the study.
“About 147 cases of tailings dam failures worldwide have been recorded over the past 100 years. This is a problem that is also prevalent in South Africa,” he adds.
Ngubelanga points out that the Bafokeng mine (in 1974), in the North West, the Saaiplass mine (in 1993) and Merriespruit mine (in 1994), both in the Free State, are the most well-known, docu- mented tailings dam failures in South Africa, which resulted in the loss of lives and in signi- ficant destruction of private property.
He says that, owing on these tailings dam failure events, the Department of Mineral Resources (DMR) is undertaking various studies on mine water management, including the sustainable disposal of mine residues.
Ngubelanga notes that the Barbeton and Pilgrim’s Rest mining areas, in Mpumalanga, have been identified as the starting point for site observations and an initial assessment of their current conditions has started.
He explains that this study aims to find ways to improve tailings slurry disposal options, with particular focus on geotechnical and stabi- lity aspects and the overall aim being developing a “checklist” for the DMR to use in the licensing and monitoring of tailings dam operations.
Additionally, Ngubelanga says that, according to available literature on mine residues, the activity status, construction method, slurry disposal method and operational systems generally determine the overall stability of tailings facilities.
“Based on our observations at visited MRDFs throughout the country, it is evident that upstream construction methods, such as paddock disposal options and wet operational systems, are commonly used for the operational life cycle of the MRDFs,” he states.
Further, Ngubelanga notes that a literature review on mine residues indicates that more MRDFs failure incidents worldwide have occurred in active dams where upstream construction methods have been used.
However, he points out that, statistically, the most common causes of failure are related to weather or climate conditions, such as unusual rain or heavy storms, which differ from one region to another and may be followed by seismic liquefaction.
In water-surplus (high rainfall) or seismically active regions, the centreline or downstream construction method is preferred, as this is considered less susceptible to failure.
Ngubelanga highlights that South Africa is geographically a water-deficient country charac- terised by low seismicity where the upstream construction method is preferred for the impoundment of MRDFs.
He comments that a total of 27 tailings dams (active, inactive and abandoned) were identified during site visits to various mining areas in South Africa. “Only six of these tailings dams are currently active, meaning there is slurry depo- sition. The rest are inactive, currently being remined or have been abandoned, with upstream construction and paddock slurry disposal methods being the most common operational systems at these sites.”
The general conclusions reached by this pre- liminary analysis indicate that all the investigated MRDFs are geotechnically stable.
“However, there is an urgent need for a comprehensive decision-support system to enforce regulations regarding monitoring, life-cycle operation, management and decommissioning processes for tailings facilities.
“This initiative should also be supported by research to address knowledge gaps regarding tailings facilities. It should also be supported by research to overcome knowledge gaps regarding the engineering behaviour of ‘soillike’ tailings materials,” Ngubelanga concludes.