The most popular model for quantitative interpretation of airborne EM data is the conductive half‐plane. This is a good shape for representing many long‐strike conductors, but a different model is needed for interpreting localized anomalies. A conductive sphere is an obvious choice. Although the mathematical solution has been available for decades and dozens of papers have been published on the subject, no sets of type curves or interpretation diagrams for this simple model and actual EM prospecting system are yet available in the open literature. For this paper, response profiles for an airborne EM system of “double dipole” type (coil axes in the direction of flight) have been computed from the mathematical solution using all necessary terms of the series. The anomaly profiles are of simple shape and it has been found that the profile half‐width has a constant relationship with the depth to the center of the sphere. The profile half‐widths along with the in‐phase and quadrature anomaly amplitudes allow a direct interpretation of depth, radius, and conductivity of the sphere. Where the sphere is also permeable, interpretation of the accompanying magnetic survey profile can allow this extra parameter to be taken into account. Finally, sample AEM profiles from the New Insco deposit are interpreted. True depth as obtained from drilling lies between the depth interpreted by two extreme models, viz., a sphere and a half‐plane.

The high-resolution reflection seismic technique is being used increasingly to address geologic exploration and engineering problems. There are, however, a number of problems in applying reflection seismic techniques in a crystalline rock environment. The reflection seismic data collected over a fractured crystalline rock environment are often characterized by low signal-to-noise ratios (SIN) and inconsistent reflection events. Thus it is important to develop data processing strategies and correlation schemes for the imaging of fracture zones in crystalline rocks. Two sets of very low SIN, high-resolution seismic data, previously collected by two different contractors in Pinawa, Canada, and the island of Aspo, Sweden, were reprocessed and analyzed, with special emphasis on the shallow reflection events occurring at depths as shallow as 60--100 m.The processing strategy included enhancing the signals hidden behind large-amplitude noise, including clipped ground roll. The pre-and poststack processing includes shot f-k filtering, residual statics, careful muting after NMO correction, energy balance, and coherency filtering. The final processed seismic sec-

Results from borehole geophysical logs, full waveform sonic logs, VSP and laboratory core sample measurements indicate that lithologic variations within the Sudbury Igneous Complex (SIC) and footwall rocks are the primary cause of reflections observed regionally on the multi‐channel seismic reflection profiles. The effects of macroscopic fracturing and low‐grade alteration on the seismic response are only important to a depth of ∼ 320 m. The major lithologic units of the SIC and footwall rocks in the North Range of the Sudbury structure have contrasting physical properties: Felsic norite and quartz‐gabbro have higher Vp (∼ 6300 m/s) than granophyre (∼ 6000 m/s) due to their higher pyroxene content and the presence of quartz rather than calcic plagioclase in the granophyre. Velocities are higher (Vp ∼ 6500 m/s) within the brecciated footwall rocks due to an overall increase in mafic mineral content. The contrasting velocities and densities of these units imply that the granophyre/quartz‐gabbro contact and the SIC/footwall transition can be mapped regionally using seismic reflection methods. Subunits within these units are also highly reflective, consistent with the nature of the seismic data, but are likely discontinuous laterally.

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