Determining rehabilitation effectiveness at the Otjikoto Gold Mine, Otjozondjupa Region, Namibia, using high-resolution NIR aerial imagery

Abstract

Mine rehabilitation is compulsory under the Namibian Environmental Management Act. B2Gold's Otjikoto gold mine complies by committing to rehabilitation of their waste-rock dumps and other disturbance features within their mining licence area in the Otjozondjupa Region. As the mine is in the early stages of operation and has committed to run-of-mine rehabilitation, there have been some rehabilitation attempts. Initial rehabilitation of an abandoned section of a district gravel road (D2808) and the western face of a waste rock dump (known as SP11) has been undertaken. Rehabilitation measures included ripping of the soil surface of the gravel road as well as covering the ripped soil surface and the waste rock dump slopes with stored topsoil removed from the first mining cut before it was excavated. We investigated the extent of vegetation establishment of these rehabilitation measures with the aid of high-resolution near infra-red aerial imagery coupled with ground-based observations on established plant biomass. It was evident that simple ripping of the road surface allowed limited establishment of grasses, which was greatly improved if the ripped surface was covered by stockpiled topsoil. Likewise, covering the waste rock dump with topsoil resulted in the natural establishment of various grasses, but also the leguminous shrubs Dichrostachys cinerea and Mundulea sericea. Erosion of the applied topsoil on the waste rock slope was, however, found to limit vegetation establishment. The natural establishment of both Dichrostachys cinerea and Mundulea sericea indicates a high potential for these species to be used for basic stabilisation of the slopes, possibly enabling colonisation by a variety of other species which we have listed. Several techniques published to aid the stabilisation of the slopes and establishment of vegetation cover were also reviewed and contextualised for Namibian conditions.