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As expensive as 3D seismic reflection surveys are, their high cost is justified by improved imaging of certain ore horizons in some of the Witwatersrand basin gold mines. The merged historical 3D seismic reflection data acquired for Kloof and South Deep mines forms an integral part of their Ventersdorp Contact Reef mine planning and development programme. The recent advances in 3D seismic technology have motivated the reprocessing and reinterpretation of the old data sets using the latest algorithms, therefore significantly increasing the signal-to-noise ratio of the data. In particular, the prestack time migration technique has provided better stratigraphic and structural imaging in complex faulted areas, such as the Witwatersrand basin, relative to older poststack migration methods. Interpretation tools such as seismic attributes have been used to identify a number of subtle geologic structures that have direct impact on ore resource evaluation. Other improvements include more accurate mapping of the depths, dip, and strike of the key seismic horizons and auriferous reefs, yielding a better understanding of the interrelationship between fault activity and reef distribution, and the relative chronology of tectonic events. The 3D seismic data, when integrated with underground mapping and borehole data, provide better imaging and modeling of critical major fault systems and zones of reef loss. Many faults resolve as multifault segments that bound unmined blocks leading to the discovery and delineation of resources in faulted areas of the mines.

Mineral deposits occur in different geological envi-ronments than oil and gas deposits, and are usually at very shallow depths (from surface outcrop, to hundreds of meters). Because of internal heterogeneities within most deposit types, extensive use of borehole sampling is required to satisfy resource and reserve reporting requirements. While borehole sampling can be designed to satisfy the geostatistical variability of a deposit, it is usually insufficient to adequately sample the structural continuity of deposits to a level required for accurate mine planning and production scheduling. For this reason, 2D and 3D seismic surveys are increasingly used in conjunction with borehole drilling and other geophysical methods such as aeromagnetic surveys to map the geological structure of known deposits. This paper will examine some challenges and results from Anglo American's use of seismic surveying in African coal and platinum deposits.

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