The historical development of the magnetic method in exploration

Abstract

The magnetic method, perhaps the oldest of geophysical exploration techniques, blossomed after the advent of airborne surveys in World War II. With improvements in instrumentation, navigation, and platform compensation, it is now possible to map the entire crustal section at a variety of scales, from strongly magnetic basement at regional scale to weakly magnetic sedimentary contacts at local scale. Methods of data filtering, display, and interpretation have also advanced, especially with the availability of low-cost, high-performance personal computers and color raster graphics. The magnetic method is the primary exploration tool in the search for minerals. In other arenas, the magnetic method has evolved from its sole use for mapping basement structure to include a wide range of new applications, such as locating intrasedimentary faults, defining subtle lithologic contacts, mapping salt domes in weakly magnetic sediments, and better defining targets through 3D inversion. These new applications have increased the method's utility in all realms of exploration — in the search for minerals, oil and gas, geothermal resources, and groundwater, and for a variety of other purposes such as natural hazards assessment, mapping impact structures, and engineering and environmental studies.

New techniques for estimation of source parameters: Applications to airborne gravity and pseudo-gravity gradient tensors

“…The aeromagnetic data can also be used in a variety of applications for example understanding tectonic settings, hydrocarbon exploration, modeling ground water and geothermal resources, mapping unexploded ordinances and environmental engineering. Nabighian et al (2005) gives an excellent overview on the developments of different types of magnetometers designed for ground, airborne, marine, space and borehole measurements. In general, types of magnetometers which have been used in airborne surveys are; 1-Fluxgate magnetometers: In fact, these instruments were the first instruments designed for airborne measurements.…”

“…They measure the intensity of the earth magnetic field. The main disadvantage of the proton-precession magnetometer is that in order to have a reasonable signal strength, a large amount of sensor liquid as well as a large coil are needed (Nabighian et al, 2005). Furthermore, the sampling rate is limited if a reasonable sensitivity is required.…”

“…3-Alkali vapor magnetometers: This type of magnetometer was first designed for laboratory measurements. Then, at about the same time as the proton-precession it was introduced to industry (Nabighian et al, 2005). Nowadays, Alkali vapor magnetometers are popular for airborne measurements.…”

“…They were mostly developed to estimate the depth to the source and thickness of sedimentary basins. Mapping basement structures was the preliminary application of gravity and magnetic data (Nabighian et al, 2005). These techniques were mainly based on curve matching, straight-slope, half-width amplitude and horizontal distance between various characteristic points.…”

Geophysical perspective on the structural interference zone along the Neoproterozoic Brasília and Ribeira fold belts in West Gondwana

“…The interpretation of the magnetic geophysical method has been reviewed in Blakely (1996) and Nabighian et al (2005b).These data are useful for deep crust magnetic structure observation, displayed for comparison to the features observed on geology, gravity and crustal thickness data. EMAG2 data are hosted in GMT (Wessel & Smith, 2013) software-compatible gridded surfaces for visualization.…”