No abstract

Telluric and magnetotelluric surveys utilizing natural 8‐hz electromagnetic fields have detected resistivity variations associated with some proven sulfide deposits. From an operational point of view the telluric method is preferred to magnetotellurics. Either method, however, can detect a conducting dike, providing that its width is greater than its depth of burial. For surveys where the telluric field is measured in a direction perpendicular to the strike of the conductor, theoretical profiles derived from two‐dimensional conductivity structures agree well with the field results. For this polarization, it is thus possible to use a general model as an aid to the interpretation of survey data.

No abstract

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.

Self potential measurements, both in drill holes and on surface, have been made in and around sulphide mineralization. Similar measurements were carried out on small scale laboratory models. The potential and current configurations around theoretical sulphide bodies are also described. Results of the model and field work seem to verify, in a qualitative manner, the electrochemical mechanism of spontaneous polarization proposed by Sato and Mooney. Possible causes are suggested for the abnormally large surface anomalies frequently found in the field.