Rehabilitation ofAbandoned open Excavation forBeneficial use of the pit Lake at Nyala Magnesite Mine

Abstract

Abandoned surface mine excavations can be a major environmental, social and/or human health<br />problem for the mining industry as well as for the community living nearby. This problem is exacerbated by the<br />rapidly growing population encroaching on areas of historic mined lands. The aim of this studywas to assess the<br />safety status of the historic Nyala Mine excavation with the purpose of coming up with rehabilitation options that<br />promote the beneficial use of the pit lake. The study involved characterisation of the abandoned excavation<br />through field description,modelling of both the geometry of the pit and the flow of surface runoff in to the pit, and<br />chemical analysis of the pit lake water. A survey of the pit landscape showed pit walls of up to 22m high with a<br />slope angle ranging from 10° to 30°. The pit was found to be accumulating runoff water from high grounds along<br />the northern part of the excavation. Pit water was found to be alkaline (pH ±9.6), with F- (±1.1 ppm), Cl-<br />(±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.