The lease area of the Atomic Energy of Canada Limited Underground Research Laboratory covers 3.8 km2 and is located 2.5 km north of the south contact of the Lac du Bonnet Batholith. A shaft to 255 m and 130 boreholes up to 1100 m deep expose the third dimension.The underlying granite is largely of two types: (i) pink porphyritic, which may be biotite rich, gneissic, and (or) xenolithic; and (ii) grey homogeneous and equigranular. Composition layering, including xenolith-rich zones, outlines domes along an antiform trending north-northeast through the western part of the lease area. The southeast-dipping flank underlies the eastern half of the site, including the shaft. Axes of folding trend 065 °and 140°. Homogeneous grey granite, being relatively fresh and unfractured, is associated with a magnetic field that is about 100 nT higher and with a resistivity that is up to 5000 Ω∙m higher than those of other units. A pattern of highs in the magnetic field, caused by the high magnetite content of some xenoliths, can be used to map the antiform.Three thrust faults that dip 10–30° east-southeast are partly controlled by the compositional layering. Anomalies in the very low frequency electromagnetic (VLF-EM) field occur at the surface projections of faults. One fault has been mapped at depth by a high-resolution seismic reflection survey. A suite of downhole geophysical methods, including cross-hole seismic, has been used to map discontinuities in boreholes.Subvertical penetrative foliations and pegmatitic dykes are part of the late crystallization fabric, providing (with filled fractures) a continuous deformation history in response to north- to northeast-trending compressive stress.

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-

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An analytical solution for simple one‐dimensional geometry establishes the basic theory of the movement of [Formula: see text] (radon) in overburden, involving diffusion and convection. The computer‐adapted finite‐difference method is then used to determine radon concentrations for the following more complex configurations: a two‐dimensional source, a vertical fault, a three‐dimensional source, and multilayered overburden. The key parameters are the radon concentration at the source, the diffusion coefficient of the overburden, and the geometry. This analysis indicates that if diffusion is the only transport process considered, the maximum depth at which uranium mineralization can be detected by the usual types of field equipment is limited to a few tens of meters. However, if convective transfer is also considered, radon attenuation is significantly decreased, e.g., by as much as a factor of 800 for a one‐dimensional configuration considered. It appears that an upward velocity component for the movement of radon, or geochemical dispersion of uranium and radium, are needed for long‐distance detection of uranium mineralization.

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