Open pit flooding as a post-closure option: a geochemical approach

[摘要] English: Australasian, European, Canadian and American geo-environmental specialistshave long been involved with pit lake studies in the physical processes anddynamics as well as the geochemical aspects of these mitigation methods andevents. The use of pit flooding as an environmental post-closure option hashowever been studied and used to a limited extent in Southern Africa and Africa toa whole, with some recorded cases mostly being by accident rather than aplanned mitigation. This document is a written paper on a hydrogeochemicalinvestigation on the feasibility of flooding an open pit platinum mine in theBushveld Igneous Complex as a post-closure mitigation option.Various data sets and sources were compiled and processed and served as inputdata into a hydrogeochemical model of the expected impacts on the conceptualmeromictic pit lake environment. Weathering and speciation models allowed theevaluation of the current system with thermodynamic and chemical reactionprocesses leading to the hydrochemical composition of the groundwater as weobserve it in the field. Furthermore transient mixing simulations betweengroundwater, surface water and rain water was allowed to occur under variousreducing and evaporative conditions. The modelled lake chemistry was thenevaluated against recreational, agricultural and domestic water use standards toinvestigate the feasibility of the lake to be used post-closure.Final recommendations and mitigation methods were proposed with the floodingof the open pit as a post-closure option declared feasible. A final deliverable ofthe study was a system thinking and modelling template for hydrogeochemicalmodelling in various scenarios to guide other scientist through the process ofmodelling fluid-rock, fluid-waste and fluid-fluid interaction.

[发布机构] University of the Free State