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Field Investigation Techniques for Potentially Contaminated Sites
Published in Kofi Asante-Duah, Management of Contaminated Site Problems, 2019
Two basic types of magnetometers are commonly used in the investigation of contaminated site problems—viz., fluxgate and proton devices. In a fluxgate magnetometer, the sensor consists of an iron core that undergoes changes in magnetic saturation in response to variations in the earth’s magnetic field. Differences in saturation are proportional to field-strength variations, which are detected as electronic signals, amplified, and recorded. Two fluxgate elements can be mounted together to form a gradiometer, which measures the gradient of a directional component of the earth’s magnetic field. In a proton magnetometer, an excitation voltage is applied to a coil around a container filled with a proton-rich fluid such as kerosene. The field produced reorients the protons in the fluid, allowing for measurement of a nuclear precession frequency, which is proportional to the strength of the field. Proton magnetometers measure the earth’s total field intensity and are not sensitive to orientation.
Gravity and magnetic data processing further constrained inversion for 3D modelling and tonnage calculation
Published in Applied Earth Science, 2020
Saâd Soulaimani, Saïd Chakiri, Ahmed Manar, Ayoub Soulaimani, Abdelhalim Miftah, Mustapha Boujamaoui
In 1968, an airborne geophysical survey using INPUT electromagnetic and magnetometric methods was conducted by Geoterrex on the Guemassa Paleozoic massif. This survey showed that several magnetic anomalies had no associated conductive bedrock anomalies, most probably because magnetic bodies are too deep. At that time, these magnetic anomalies were not selected for ground follow up (Bellott et al. 1991). Only in the early 1980s was their potential interest considered. As soon as massive mineralisation was found in drillhole HSl, systematic detailed magnetic and gravity surveys were carried out by the Ministry’s Directorate of Geology (Hathouti 1990). Total magnetic field and gravity were measured every 25 m on north–south profiles 200 m apart, except in the central part of the survey area where the line spacing was reduced to 100 m (Figure 4). Along with the geophysical surveys, three drillholes were completed (Bellott et al. 1991). The area extension is 3.2 km long and 1.6 km wide. In total, 1089 gravity stations and 1210 magnetic stations were measured (Figure 4). The data acquisition was carried out by Lacoste & Romberg gravimeters and Geometries proton magnetometer, with a resolution of 0.01 mgal and 1 nT.