rehabilitation ofabandoned open excavation forbeneficial use of the pit lake at nyala magnesite mine

abandoned surface mine excavations can be a major environmental, social and/or human healthproblem for the mining industry as well as for the community living nearby. this problem is exacerbated by therapidly growing population encroaching on areas of historic mined lands. the aim of this studywas to assess thesafety status of the historic nyala mine excavation with the purpose of coming up with rehabilitation options thatpromote the beneficial use of the pit lake. the study involved characterisation of the abandoned excavationthrough field description,modelling of both the geometry of the pit and the flow of surface runoff in to the pit, andchemical analysis of the pit lake water. a survey of the pit landscape showed pit walls of up to 22m high with aslope angle ranging from 10° to 30°. the pit was found to be accumulating runoff water from high grounds alongthe northern part of the excavation. pit water was found to be alkaline (ph ±9.6), with f- (±1.1 ppm), cl-(±169.6 ppm),mg2+ (±67.85 ppm) andk+ (±87.16 ppm) concentrations that were all above the standards permissible for domestic use. this study demonstrated that beside backfilling of oldmines excavations; rehabilitation techniques that transform lifeless landscapes into prosperous ones, with beneficial end uses can be considered.