Horizontal-loop electromagnetic signature of a buried dike, Al Quweira area, southwest Jordan

During 1999, horizontal-loop electromagnetic (HLEM) measurements were made over a buried dike in the Al Quweira area, southwest Jordan, using the APEX MAX MIN III instrument, as part of a mineral exploration project. The obje ctives of the study were (i) to evaluate the resolution of the HLEM techniq ue in field work in detecting and locating anomalies caused by vein-like bo dies, and (ii) to assess the capability of HLEM surveys for detecting targe ts in other locations throughout our geophysical survey programme. In-phase and quadrature anomalies were recorded with 50 m and 100 m coil separation s and multiple frequencies across the strike of the buried dike. Data recor ded at 43 locations, spaced 10 m apart along the survey line, were interpre ted quantitatively. For a 50 m separation, corresponding to shallow depths of investigation, the results do not show any recognizable response from th e buried dike. The HLEM data were modelled using a three-layer structure in order to estimate the thickness of the weathering layer along the survey l ine. Conversely, data obtained with a 100 m separation, corresponding to mo derate depths of investigation, reveal significant anomalies from the burie d dike at high frequencies. A phasor or vector diagram was used to calculat e the response parameter, depth and dip of the buried dike.