DighemII airborne electromagnetic/resistivity/magnetic VLF survey of the Chalk River research area, Ontario

A DIGHEMII airborne electromagnetic/resistivity/magnetic VLF survey was carried out over the Chalk River research area in early 1979, along north-south and east-west flight lines spaced approximately 100 m apart. The Results indicate that the geological environment in the survey area is relatively resistive with typical apparent ground resistivity values ranging from about 2,000 Ω · m to more than 4,000 Ω · m. Several lower resistivity zones were detected, which were associated with numerous weak but identifiable EM anomalies (conductance values lower than 10 S) that are believed to reflect geological features of concern to the Nuclear Fuel Waste Management Program, e.g., faults or fracture zones. Three identified prominent zones showed good correlation with the VLF-EM and magnetic data sets. The first group of EM anomalies, correlating with apparent resistivities as low as 200 Ω · m is confined to Maskinonge Lake. It appears to reflect the combined effects of near-surface conduction (e.g., conductive lake-bottom sediments) and of a geological structure. The strike of the geological structure within this zone is close to north-south in the central part of the lake, and about N15 degrees E in its northern part. The second group of EM anomalies crosses the southern end of Maskinonge Lake and is structurally complex. It is associated with 500 to 700 Ω · m resistivities and well-defined VLF anomalies. The third group striking north-south and occurring in the eastern part of the survey area is characterized by a narrow low-resistivity zone and a well-defined VLF anomaly. Numerous other EM, resistivity, magnetic and VLF trends occur with strikes close to 10 to 20 degrees, 45 degrees, 80 degrees, 90 to 120 degrees, and 140 to 160 degrees. All of these show good correlation with ground VLF and surface fracture analysis data