Frequency Domain Electromagnetic Surveys

Knowledge in the Field

Electromagnetic surveys are used to detect electrically conductive targets in moderately resistive host rocks or sediments. Frequency domain (FDEM) methods are used to provide rapid, generally shallow coverage while time domain methods (TDEM) are more commonly used on large, deep targets. While most deposit types may respond to EM methods, other sources of noise—graphite, conductive sediments, etc.—must also be considered when designing a survey.

High frequency horizontal loop (HLEM) surveys are a good kimberlite exploration tool for targets beneath lakes, but land-based targets may not respond well. High frequency HLEM is very useful in mapping structure in resistive environments where it provides information on the geometry and conductance of potential targets.  VLF-EM surveys are fast and relatively inexpensive but they rarely provide enough information to accurately assess a geophysical target. 

AGL Delivers

Aurora Geosciences offers a wide variety of EM surveys designed for a range of geological problems. VLF surveys, when combined with magnetics, provide an inexpensive first pass. Currently, we use Scintrex EDA VLF receivers for both conventional VLF and VLF-resistivity. For HLEM, we offer MaxMin I-9 / I-10 and SE-88 Genie systems. The former requires a reference cable but has an extremely broad operating spectrum and provides in-phase information, making it an excellent tool in assessing targets across the range of common resistivities. Genie does not require a reference cable but it behaves like a quadrature system, limiting it to relatively low conductance targets in resistive backgrounds.

Interpretation is provided with REVS, DigRes (when working with HEM data) and with proprietary software for MaxMin inversions. Output formats are tailored to the requirements of the surveys and include annotated stacked profiles, a variety of filtered contour maps and depth sections.