SRK South Africa was recently appointed to assist one of the older gold mines in the Witwatersrand Basin develop a closure strategy, particularly focussed on post closure water management of the water expected to rewater the underground workings. As the operation is in a region of dolomite with the aquifers associated with the host rock being a potentially valuable resource in a water-scarce country, SRK was required to develop a closure solution that would limit potential post- closure impacts on this resource.
We were able to demonstrate that although the orebody and surrounding rock had the potential to generate acid rock drainage and metal leaching, the relatively rapid rewatering of the workings would limit acid production and associated metal and salt formation. As the workings rewatered and the water table intersected the dolomite geology, the inherent neutralising potential of the geology and the rapid water movement through the aquifer would limit potential geochemical impacts to a very narrow radius around the shaft collars.
We were able to geochemically demonstrate that because the impact was limited and rapidly dissipated in the surrounding aquifer, no specific post-closure measures were required to maintain a water level below the dolomite aquifer. Our ability to demonstrate that no postclosure water management was required translates into a potential cost saving of hundred of millions of Rands to the company as there is no longer a closure requirement to abstract and treat water.
