Paper 7

Three-dimensional (3-D) seismic exploration is a geophysical technique that has undergone rapid growth and development in the petroleum industry. It is a mature technology that has the potential to provide accurate volumetric images of the subsurface for interpreting the structural and stratigraphic framework of ore deposits. Under favourable circumstances, 3-D seismic methods can also provide direct delineation capabilities for large, deep-seated ore bodies. The 3-D seismic method involves the acquisition of seismic data on an areal grid. Processing and interpretation techniques exploit the dense subsurface sampling provided by the 3-D data volume. Some modifications to standard practice are required, in view of the complex scattering and weak reflectivity that characterizes seismic data from crystalline terranes. Critical steps in the processing sequence are those used to correct for variable near-surface conditions, attenuate noise, and re-position (migrate) reflections into their true subsurface configuration. Interpretation of the data is typically carried out on a computer workstation, using specialized software that permits efficient horizon picking, display of the data in vertical and time-slice orientation, and volume visualization. For massive sulfide exploration, recognition and characterization of scattering anomalies in the unmigrated data volume is one of the key challenges for interpretation of the data. Recent published tests of this technique in South Africa and Canada indicate a promising outlook for 3-D seismics in mineral exploration, as the search for new ore deposits pushes to greater depths and the need for improved deep-imaging methods for surface exploration becomes increasingly important.