The primary objective of seismic exploration in a hard rock environment is the detection of heterogeneities such as fracture zones, small-scale geobodies, intrusions, and steeply dipping structures that are often associated with mineral deposits. Prospecting in such environments using seismic-reflection methods is more challenging than in sedimentary settings due to lack of continuous reflector beds and predominance of steeply dipping hard rock formations. The heterogeneities and “fractal” aspect of hard rock geologic environment produce considerable scattering of the seismic energy in the form of diffracted waves. These scatterers can be traced back to irregular and often “sharp-shaped” mineral bodies, magmatic intrusions, faults, and complex and heterogeneous shear zones. Due to the natural lack of reflectors and abundant number of diffractors, there are only a few case studies of diffraction imaging in hard rock environments. There are almost no theoretical models or field examples of diffraction imaging in prestack domain. We have filled this gap by applying a 3D prestack diffraction imaging method to image point diffractors. We calculated the diffractivity by computing the semblance of seismic data along diffraction traveltime curves in the prestack domain. The performance of the method is evaluated on a synthetic case and a field seismic data set collected over the Kevitsa mineral deposit in northern Finland. The high-resolution results obtained by the application of prestack diffraction imaging suggest that diffractivity is a robust attribute that can be used in addition to other seismic attributes for the interpretation of seismic data in hard rock environment.

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SUMMARYA 3D high-resolution reflection seismic data were acquired to investigate its utilisation for exploration of typically excessively complex IOCG deposits in Hillside, South Australia. Full 3D pre-stack imaging produced results where seismic character well resembled different rock types. Further assessment of the value provided by seismic data required borehole calibration. Unfortunately only core samples were available. These information were enriched by utilising a specific gravity voxet that was extracted from the Rex supplied database. Core sample tests (velocity) and specific gravity information were utilised during the process of volumetric interpretation. We show that faults extracted from variance attribute correlate with the faults extracted using guided-tracking method. However, petrophysical data shows that the boundaries between gabbro and metasediments may not generate acoustic impedance contrast to be clearly detected by seismic reflection method. The tops to the main rock formations however are mappable in depth slices and agree very well with magnetic data. Further work involves correlation of seismic interpretation with the geological cross sections and lithological logs collected from the site.

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