Geophysics is used to define science which is destined to study the physical phenomenons that take place on Earth, which can be caught and analyzed through geophysical equipments and explored by qualified personnel. A variety of geophysical techniques allow us at present to capture phenomenons or features of the ground measured.
For it, we use two methods to detect them. The active methods allow us to obtain information by applying an external element to the soil, whether it be by means of seismic, electrical or electromagnetic polls. The passive elements, do not apply any type of external action and include the MAGNETO-TELURICOS, seismic or gravimeter as well as others.
The antennas of the geo-radar GPR are also available in 20 and 25 MHz, with a depth of 30 and 40 meters for the mining industry.
In the exploration of the mining field, the exploration technologies most used are the MAGNETOMETRY, the air GRAVIMETRY and the seismic 3D. Though none determine the presence of minerals, the first one leads us to areas with strong magnetic fields (mineralization of rocks without being able to distinguishing the minerals that there are). The second one determines the density of the area.
The seismic one is in charge of establishing the different layers of the Earth by spotting the acoustic waves. We can determine the type of rocks depending on the density and the capacity of acoustic response which these can generate.
In this article we aim to show a new methodology of work using geophysical exploration as an only treatment of electromagnetic waves in different frequencies, all of them located between the microwaves (106 Hz) and the distant infrared (1012 Hz).
By means of remote sensing, HETEROGENETIES can be located at large distances. The variations of absorption, reflection and emission of certain electromagnetic waves on the surface of the planet are good examples of them. This way, direct images are obtained or records that give place, once processed, to images, profiles and maps. There are four types of remote sensing: Spatial Photography (visible Light), remote sensing visible in a multi-spectral way (several wave lengths, separately), thermal remote sensing or thermographic (Infrared), as well as GRASS RADAR (issued and reflected radar waves)
In terms of infrared waves, the ‘Band 1’ or blue is created to penetrate bodies made of water and it is useful for the mapping of coasts, to differentiate between soil and vegetation, as well as classifying between different woodlands, also to distinguish the different types of rocks in the terrestrial surface. The ‘Band 2’ or green allows us to differentiate the different types of rock and the presence of LIMONITE. The ‘Band 3’ or red also helps us to differentiate the different types of rock and the presence ofLIMONITE. The ‘Band 4’ (nearby infrared) determines the content of the biomass for the delimitation of water bodies and the classification of the rocks.
On the other hand, the ‘Band 5’ or infrared, indicates the content of dampness in the vegetation and the soil, as well as to distinguish between snow and clouds. The ‘Band 6’ or thermal Infrared is useful in analyzing the stress of the vegetation, the determination of the dampness of the soil and the thermal mapping. The ‘Band 7’ or infrared way show great potential for the discrimination of rocks and the hydrothermal mapping. It measures the quantity of hydroxides and the water absorption.
Range of radiations
Every atom can issue or absorb electromagnetic radiation, even though only in some frequencies that are of their own features of each one of the different chemical elements. If we issue radiation to a certain element, at the same time, it issues radiation in certain frequencies defined as spectrum of emission or range of radiation.
The same element, when it receives electromagnetic radiation it absorbs it selectively, precisely in the same ones in which it issues it. This is its absorption spectrum. Here we see Kirchhoff’s Law fulfilled, which indicates that all elements absorb radiation in the same lengths of wave in which they issue it. The spectra of absorption and of emission turn out to be, the negative form of one and other.
The spectrum of the issued electromagnetic radiation is its spectrum of emission. There are bodies that issue more than the infrared band, for example, and other bodies that not so much. The bodies absorb selectively the radiation issued from others, fact that allows us to determine what element it refers to. For what concerns the microwave spectrum, the frequency of wave emission is the one that will determine the resolution and depth of scope of the wave. What concerns the antennas of major frequency (between 800 and 250 Mhz) they do not allow us to come to depths below 10 meters, but in exchange they offer an excellent resolution.
In reference to the extensive exploration, the air radar M2 allows it to be installed in helicopters or planes and to include big extensions of surface and depth in relatively little time with the aim to determine the zones of major interest.
This is a sophisticated equipment of passive Radar M2 that registers electromagnetic waves proceeding from the terrestrial bark and that allows us to locate more important zones with presence of HETEROGENETIES. The anomalies can relate to geological structures of the emission of the subsoil, absorption or reflection of a certain frequency of wave. The results can be determined by a presence or absence of the above mentioned frequencies by means of technologies of spectral analysis.
For intensive exploration, the terrestrial radar equipment (GPR) it allows us to carry out in detail a characterization of the geological superficial stratigraphic of the subsoil, once the air equipment has determined the significant points.
The GPR test run is an active test of electromagnetic reflection that allows us to obtain information of the terrestrial subsoil across the emission, spread and previously received of the electromagnetic pulses. In the mining industry there is a habit of said process being used to conduct the scaling of material, to determine zones of rock fracture, etc.
With regards to the practical cases of location of minerals, the presentation of the results are normally carried out through a presentation of the plans with the zones with a high presence of anomalies with the desired characteristics. These are two-dimensional (a vector with the direction of the anomaly and estimated depth) and three-dimensional (a flat surface and the estimated depth).
The work of exploration for the location of new sources of mineral requires/needs new technological and sustainable advances that will allow it to improve the productivity with the minimal environmental impact. This fact must carry a necessary reduction of costs and improvement the findings of the above mentioned sources, be these of water, hydrocarbons or minerals, eliminating as many possible uncertainties.
The geophysical exploration with the equipments M2 and GPR allow us to carry out a detailed exploration of the subsoil with the purpose of exploring extensive areas with a great resolution and of maximizing the possibilities of success.