Rehabilitation of Abandoned open Excavation for Beneficial use of the pit Lake at Nyala Magnesite Mine

Abandoned surface mine excavations can be a major environmental, social and/or human health problem for the mining industry as well as for the community living nearby. This problem is exacerbated by the rapidly growing population encroaching on areas of historic mined lands. The aim of this studywas to assess the safety status of the historic Nyala Mine excavation with the purpose of coming up with rehabilitation options that promote the beneficial use of the pit lake. The study involved characterisation of the abandoned excavation through field description,modelling of both the geometry of the pit and the flow of surface runoff in to the pit, and chemical analysis of the pit lake water. A survey of the pit landscape showed pit walls of up to 22m high with a slope angle ranging from 10° to 30°. The pit was found to be accumulating runoff water from high grounds along the 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.