GROUND WATER AND MINING IN THE BUSHVELD COMPLEX

摘要

Water Geosciences Consulting completed a number of groundwater projects for mining companies operating in the Bushveld Complex. The mines are extracting the PGE minerals, which comprise Platinum, Palladium, Rhodium and Gold, together with base metals Copper and Nickel. This article focuses on the description of the aquifer systems associated with the Bushveld Complex's mafic and ultramafic rocks and attempts to characterise the shallow groundwater as well as mine fissure inflows within different geographical settings. The general aquifer model for the Bushveld Complex comprises a perched, shallow aquifer in the weathered zone underlain by a deeper, semi-confined fractured bedrock aquifer. The weathered aquifer system,, as well as the upper portions of the underlying fractured bedrock aquifer, are partially dewatered in the vicinity of mining operations. Groundwater inflow rates into shallow mining operations within the weathered aquifer vary significantly depending on the structural setting within which the mines are located. Mine fissure (i.e. groundwater) inflow rates into deeper mining operations are highly variable spatially and can be due to leakage from the shallow weathered aquifer, to inflows along distinct fracture systems tapping into both local and distant sources or to a mixture of these sources. Mine fissure inflow rates were retrieved from existing mine plans to identify locations of significant historical and recent inflows. The identification of distinct structural regimes/settings for water-bearing fissures enables the prediction thereof and allow for early intervention measures (e.g. sealing of fissures, altering mine production programmes, etc.). Mine fissure inflows are predominantly associated with small-scale faults and minor jointing rather than large-scale regional faults, that were found to be comparatively dry. Groundwater samples from boreholes as well as the mine fissure inflows were analysed for macro- and trace elements, stable isotopes as well as for radio-active isotopes such as tritium (~3H) and carbon-14.