Abstract
Recent progress in the use of geophysical exploration techniques for unconformity-related uranium deposits within permafrost terrain in the northeastern part of the Thelon basin, Northwest Territories, Canada, is summarized using exploration case histories. These exploration techniques have attempted to use the unique physical and petrological propertiesof altered rocks that accompany uranium mineralization.
Altered rocks are detectable as low resistivity anomalies by airborne resistivity and ground VLF-resistivity surveying, and the influence of thin surficial thawed zones on the responses are minimal except for the ground underneath large lakes. Gravity surveys are very effective for detecting low density zones associated with alteration and mineralization provided that the overburden is uniform in thickness (or the actual thickness is known), and a low density alteration zone is relatively shallow and/or large enough to produce a recognizable anomaly.
A geophysical model can be established to link the physical properties of various alteration zones. Resistivity can be significantly decreased in the early stages of alteration (or relatively weak alteration) by hydrolysis of feldspar (sericitization). However, it is not the hydrolysis of feldspar that is responsible for the significant change of density that is typical of inner part of alteration zones, but rather the dissolution of quartz followed by replacement by water. This suggests that an influx of a considerable volume of hydrothermal solutions has contributed to promote desilication, and that the mineralization must be related to this influx of solution, which can be inferred by the close spatial relationship between desilication and uranium mineralization.
