Mine site rehabilitation — are we reinventing the wrong wheel?

Abstract

Mine site rehabilitation generally aims to produce a safe, stable and non polluting post-mining landscape that serves some agreed post-mining land use. Historically, the presumed post-mining land use has generally driven the rehabilitation process, often regardless of whether the adopted land use matches the pre-mining land use or is achievable. This dictates the flattening of the mine waste landform and the choice of surface cover applied. In the past, the adopted post-mining land use has often been grazing, which dictates that steep (usually angle of repose) mine waste slopes be flattened substantially, and that the surface be topsoiled and grassed. The tops of surface dumps and tailings surfaces often require reshaping to enhance surface drainage or water management prior to capping, topsoiling and grassing. The outer slopes of waste dumps and tailings storage facilities are generally flattened to allow access for equipment, topsoiling and grassing, possibly with the aim of allowing grazing. Even where grazing is not to be the post-mining land use, slope flattening, topsoiling, and grassing are often adopted. Whether or not grazing is the adopted post-mining land use, it may not be utilised, and a grass cover may be difficult to establish and even more difficult to sustain. Further, the limited extent to which steep mine waste slopes can be flattened generally results in slope angles that are still too steep for grazing use, and are prone to erosion, particularly if covered with topsoil and the grass cover is inadequate. This historical approach to mine site rehabilitation has led to repeated failures of flattened, topsoiled and grassed steep mine waste slopes and of regraded, capped, topsoiled and grassed dump tops and tailings. Increasingly, the establishment and sustainability of ecological functionality is seen as the key to achieving a safe, stable, and non-polluting post-mining landscape. Hence, it is argued that ecological function should be the preferred driver of mine site rehabilitation over the post-mining land use, since it better addresses the accepted rehabilitation aims. The paper presents a history of the conventional approach to mine site rehabilitation governed by slope flattening, topsoiling and grass covers, illustrated with global examples of mine site rehabilitation failures due to the adoption of those practices. These include examples from gold mining in Johannesburg, surface coal mining in Australia, and metalliferous mining in Australia, and focusses on the rehabilitation of steep mine slopes in tailings, spoil or waste rock.