GEOPHYSICS

Geophysics

Geophysics is a science that applies the principles of physics to subsurface research using indirect measurements, usually performed on the surface of the terrain.

It is based on the investigation of the physical properties of rocks, being of extreme importance in the studies of structure of the interior composition of the planet. With the growing shortage of outcropping or of deposits shallow in beginning of the XX century, its development was necessary in order to map these deposits in subsurface, from natural or induced physical phenomena that manifest in it.

RAL innovates its Mineral Research market with the creation of the Geophysics Sector. The methods used are Magnetometry, Radiometry of airborne data (Recognition) and Eletroresistivity (Detail). In this way, it allows better understanding of the mineralized body in depth.

Magnetometry

The main purpose of magnetic surveys is to investigate the geology of an area based on anomalies of the Earth’s magnetic field, resulting from the magnetic properties of the subsurface rocks.  The rocks magnetize according to their magnetic susceptibility, which depends on the amount and mode of distribution of the ferromagnetic minerals present. The concentration of magnetic minerals produces local distortions in the Earth’s magnetic field, which can be illustrated by providing subsurface information.

Magnetometry is a widely used method in several areas of geosciences such as: mineral research, geotechnics, hydrogeology, structural analysis and others. The great use is due to the variation of magnetic susceptibility due to the existing discontinuities. Ideal for viewing zones of shear, these are usually associated with several mineralizations, in addition to showing zones of fractures and structures that are often essential for a better geological understanding of the target.

Eletrorresistivity

It is a technique of horizontal or vertical investigation, in one or several depths, approximately constant. The measurements are taken on the surface of the terrain through Laying of cable or Vertical Electrical Survey (SEV). The investigations carried out by the Laying of Cable are usually carried out along profiles and the results obtained are related to each other through a study in plan at a determined depth, or through sections with various depths of investigation even in 3D. The SEV geoelectric technique consists in the execution of a series of apparent resistivity measurements perfomed with an electrode arrangement in which a growing separation between emission and reception electrodes is promoted and is commonly recommended for the determination of the rock bottom, the layer thickness lithology and water level.

Thus, Electroresistance is a very suitable method to detect vertical or inclined geological contacts, mineralizations, dikes, fractures and / or failures and other bodies or structures that present as lateral heterogeneities of these parameters. It can also be used in the characterization of aquifers and deposits of sands and gravels, delineating their limits.