Three‐dimensional inversion of transient magnetotelluric data at Pasfield Lake, Saskatchewan

A transient audio magnetotelluric (TAMT) survey was carried out in the Athabasca Basin of northern Saskatchewan as part of a uranium exploration program at Pasfield Lake. Inspection of the TAMT data revealed a complex structural setting near the line extremities with a large conductive uplifted block in central portions of the lines. Two-dimensional (2D) inversion was helpful but failed to fit the data satisfactorily in the structurally more complex areas. The results of 2.5D inversion (three-dimensional inversion on a single 2D profile) will be presented and compared to the original 2D inversions and known drilling. The 2.5D inversions show a much better fit to the measured data, returning models in good agreement with drill core defined lithology. Additionally, three-dimensional (3D) inversion of airborne total field magnetic and airborne gravity gradient data was performed and clearly corroborates the presence of an uplifted basement under Pasfield Lake. It would seem that the most likely source mechanisms to explain the Pasfield geophysical data and drill core to date are an explosive event in the form of a meteorite impact or a volcanic intrusive.