Title - Deep Uranium Exploration with Transient AMT. Mapping basement conductors and sandstone alteration in the Virgin River Area.

Overview – Transient AMT (TAMT) can be used to map basement conductors at depths exceeding 1 km opening up the entire Athabasca basin for exploration. Conductive alteration in the sandstone can also be well mapped as can “structure” (disturbed sandstone) up dip from deeper faults. The magnetic field tipper is essential in mapping both the basement conductors and the shallow sandstone structure while the impedance best maps alteration features. However, as the response is dominantly one of current channelling, basement conductors need to suitably isolated from other conductive structure in order to be resolved.

Title – Delineating Resistive Paleochannels with Transient Audio Magnetotellurics: Implications for Oil/Gas Exploration.

Overview – Transient AMT (TAMT) can be used to map shallow resistive paleochannels, real data from southern Manitoba is presented. In the context of oil/gas exploration in North-western Alberta, a minimum channel depth of 100 m is required in order to distinguish a wet channel from a hydrocarbon charged channel. The TM mode impedance shows the largest anomalous response.

Title – Results of a Transient Magnetotelluric Survey on line WAS-4. Comparison with UTEM III, DC Resistivity and Gravity data.

Overview - Our Transient AMT (TAMT) data locates the graphitic Saskatoon Lake conductor at approximately 700 m depth at station 24W. A second weaker conductor at slightly more shallow depth is seen further to the east. Within the sandstone, a wide alteration zone is revealed over the Saskatoon Lake conductor, based on the high frequency TM mode impedance and the tipper (5 to 30 kHz), the eastern edge of the alteration zone is steeply dipping while the western edge is much more gradational. Due to the high frequency of the observed anomaly, the source of this feature is interpreted to lie at less than 200 m depth. Interpretation of moving loop UTEM III data places the Saskatoon Lake conductor at station 23W at 800 m depth. The small discrepancy in the station location is reasonable given that the UTEM III data is best coupled to vertical structure while the TAMT data also responds to the shallow dipping graphitic lithology that lies at greater depth. Interpretation of the gravity low centered on about 22W places a wedge like structure with a sharp eastern edge and a shallow dipping western edge, at less than 150 m depth. This agrees very well with the interpretation of the TAMT data above. DC resistivity data collected on the line used a moving Schlumberger array designed to profile at a depth of 200 to 300 m. Strangely, the DC resistivity data does not respond to the conductive alteration wedge as does the TAMT and gravity data, while a resistivity low is indicated further to the east, possibly associated with the weak eastern conductor seen on the TAMT data.

Title – Transient Magnetotelluric Imaging of a Buried Valley.

Overview – A Transient AMT (TAMT) survey was conducted over a buried valley system in southern Manitoba in November, 2001. Data was collected on nearly the same line as occupied previously by the Saskatchewan Research Council with an EM-47. Our TAMT data resolved structure nearly as shallow as the EM-47 ( approximately 5 m vs. 10 m) but also about 6 times deeper ( approximately 60 m vs. 400 m). In good agreement with the EM-47 data, our TAMT data finds the channel to be approximately 1 km wide. Drift thickness mapping studies in the area done by the GSC indicate a maximum thickness of 82 m, in good agreement, we place the channel bottom at 70 to 80 m depth. By comparison, the EM-47 data was not able to penetrate deeply enough to resolve the bottom of the channel although it was able to better able to image the drift/shale interface at approximately 15 m depth. This is a result of the AMT dead band which limits the model resolution in the 15 m to 35 m depth range.

Title - Natural Source Transient EM.

Overview – Theoretical analysis of our Adaptive Polarization Stacking (APS) algorithm, designed to work specifically with linearly polarized transient data. We show that given typical polarization characteristics of transient data, our APS algorithm has a higher order bias convergence than conventional Remote-Reference (RR) and Least Squares (LS) methods and requires a minimum number of channels for essentially unbiased estimation of the impedance tensor (4 Ch) or tipper (3 Ch). As opposed to RR, we don’t assume a circularly polarized source field, we don’t assume infinite sample size and we make no assumptions about the statistical properties of the noise. Our APS algorithm is therefore more appropriately connected to the raw data and returns earth response curves and error bars that properly reflect the polarization properties, the SNR and sample size of the data. This results in good quality inversions free from artifacts that can be caused from bad (overly small) error bars.