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Data Acquisition <br />EM -31 MK2 <br />The FDEM data were acquired using an EM -31 <br />MK2 terrain conductivity meter (inset photo left) <br />produced by Geonics Limited. An FDEM <br />instrument consists of a transmitter coil which <br />generates a primary electromagnetic field at a <br />specified frequency separated by some distance <br />from a receiver coil which measures the response <br />(secondary) of the electromagnetic field <br />generated by the interaction of the subsurface <br />materials to the primary field (see Figure 3). <br />Frequency -Domain EM (FDEM) <br />1 Receiver 1 Transmitter <br />Rx Tx <br />Data Logger <br />Primary <br />Magnetic <br />I Field <br />Eddy Currents <br />;. <br />Figure 3. Conceptual model of the FDEM method. <br />The secondary response detected in the receiver coil is generated by electrical currents, called eddy <br />currents, induced in the subsurface materials by the fluctuating magnetic field generated in the <br />transmitter coil. FDEM instruments allow for simultaneous measurements of both in-phase (to the <br />primary field) and quadrature (orthogonal out-of-phase) components of the secondary magnetic field <br />generated in the receiver coil. The quadrature component is most sensitive to electrical conductivity, <br />Project No. 6422A 3 Geophysical Report <br />