Integration of 3D reflection seismics and magnetic data for deep platinum mine planning and risk mitigation: a case study from Bushveld Complex, South Africa

Abstract

Loss-of-ground due to slumping, faulting or replacement of mineral horizons are common problems during mining in the Bushveld Complex, South Africa. Integrating high-resolution aeromagnetic and 3D reflection seismic data to delineate geological features allows for efficient mine planning and risk reduction. We use high-resolution seismic data from the western Bushveld Complex to image slump structures, iron-rich ultramafic pegmatoids (IRUPs), faults, dykes and diapirs that impact the economic horizons (UG-2). The seismic data are able to resolve faults with throws as small as ~10 m. These data reveal a slump structure in the north of the survey area, extending ~5 km along strike and causing up to 1 km of vertical displacement. This region is characterised by strong magnetic anomalies that are interpreted to be associated with IRUPs, as there were no boreholes drilled in this region. The structure is bounded on several sides by faults and IRUPs. Another feature that is better imaged using seismic data is a large-scale fault mapped on surface (locally known as the Chaneng structure). On seismic data, this structure is imaged as a complex fault network in the west of the study area and a region of material flow in the east. Seismic data also show good mapping resolution of dykes due to their close association with faults, which cause displacements on economic horizons. The seismic data are also characterised by disrupted seismic amplitude zones associated with a diapir (~6 km in diameter), which is linked with the upwelling of basement rocks during the emplacement of the complex. This diapir displaces the economic UG-2 horizon at the mining levels by ~0.05 s two-way traveltime or 175 m. This information could be used for future mining planning and design to assess and mitigate the risks posed by these features during mining activities.