Near-surface characterization and delineation of water conduits at South Deep Gold Mine, South Africa

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Abstract. Velocity models of the shallow (a few hundreds of meters) geology are hardly retrieved from deep seismic reflection exploration data, despite their importance in near-surface characterization, improving seismic mapping resolution at depth, and constraining deeper geological models. In this work, we compute the near-surface shear wave velocity model in the vicinity of South Deep Gold Mine, using surface waves present in the 2D and 3D deep seismic reflection data acquired at the mine. The obtained near-surface model is then used to (1) characterize the near-surface and (2) better constrain possible water conduits (faults, fracture zones and dykes) mapped at mining levels, that enable the migration of water from overlying formations to the mining levels, and (3) constrain the timing of faults and dykes activity in the vicinity of the mine. The analysis is carried-out on reflection seismic data acquired for deep mineral exploration, where the acquisition parameters were not optimized for surface wave techniques, thus the reciprocity principle is used to improve the data density, coverage, and near-surface mapping resolution. The lithostructural information retrieved from the produced pseudo-2D and -3D shear wave velocity models are consistent with information obtained from available borehole data and published records in the study area. Integrating the produced near-surface shear wave velocity model with a legacy 2003 P-wave seismic reflection cube, mine mapping and drilling information enabled the investigation of the structural linkage between the near-surface groundwater aquifers and deep mining levels (~ 3 km depth). The faults and dykes mapped at the mining level intersect and cross the near-surface aquifers, thus making these structures possible conduits for water migration to the deep mining levels. The findings of this research illustrate the advantages of integrating shallow and deep subsurface information to constrain the timing of geological structures and mitigate the risks associated with water ingress to the mining levels. The final model produced can be used for future mine development, improving safety and production, and for extending the Life of Mine (LoM).

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