With the evolution of technologies provided by Mining 4.0, the use of remote sensing is increasingly constant in the mining sector, with applications in all phases that a mining enterprise encompasses. Throughout this text we will address the concept and operation of remote sensing, how it can be used in mining and some cases that demonstrate the effectiveness of this technology in the field. Want to know more? Check out the full content below.
Remote Sensing
In general terms, remote sensing is a set of techniques for obtaining images at a distance, over the earth's surface, without physical contact between the sensor and the surface studied.
According to Filho et al. (2021), there are three levels of data collection, namely:
- laboratory level, in which small portions of the object are analyzed by means of radiometers and spectroradiometers;
- aircraft level, using remotely controlled vehicles, such as RPA's and UAVs;
- orbital level, in which the sensors are attached to satellites orbiting the Earth.
In their operation, the sensors capture the electromagnetic radiation (REM) emitted by the targets as a method of detection and measurement of their physical characteristics. REM is energy, in the form of light, heat and others, propagating at the speed of light.
Each object on the Earth's surface has a relative intensity with which it emits, reflects and absorbs electromagnetic radiation, which defines its spectral signature. In the process of obtaining images by remote sensing, the identification of a target can be done by detecting its spectral behavior.
A practical example of this method in the geological context is rock differentiation. Felsic minerals, such as quartz, albite, feldspar, and muscovite, reflect REM relatively uniformly and exhibit high reflectance. Consequently, igneous rocks of felsic composition, including pegmatite and granite, will show greater reflectance intensity in satellite images.
The decrease in silica in the composition of the rock and the increase in basic minerals, such as biotite, olivine, pyroxenes and amphiboles, make the intensity of reflectance lower. Therefore, ultrabasic or ultramafic rocks have low reflectance.
Applications in Mineral Prospecting
Electromagnetic radiation can be divided into intervals according to the wavelength and frequency of radiation, forming the Electromagnetic Spectrum , divided into spectral regions, such as the visible band, infrared (near, far, medium), ultraviolet, among others.
Depending on the spectral behavior of the object on the surface, i.e. the intensity of reflectance at different wavelengths, different bands of a sensor can be used. The band of a satellite sensor that comprises the near-infrared wavelength, for example, is useful for analyzing geological and structural features.
Remote sensing and identification of geological features, such as drainages, faults and fractures. Source: https://www.srk.com/pt/servicos/sensoriamento-remoto-e-geofisica
Regarding mineral prospecting, the presence of some elements on the surface can be a good indicator of a mineralized region. In this context, the range of 400 to 1000 nm is indicated for the detection of minerals containing iron oxides/hydroxides 3+ since they have a higher level of absorption in this wavelength range, more intensely in the ultraviolet region.
In particular, the association of iron-rich minerals (goethite and hematite) can be better identified in the spectral regions 450 nm, 650 nm and in the range 850-950 nm due to their high absorption rate. This association is called limonite. When limonite has a higher relative concentration of goethite in a given region, it can be a good indicator of sulfide deposits.
Among the mineral deposits containing iron oxides/hydroxides 3+ are gold mineralizations related to hydrothermal alteration zones and massive sulfide deposits of base metals (Cu, Ni, Cr, Zn). In both cases, limonite is present as a sulfide weathering product. (CRÓSTA, 1993)
This example demonstrates how remote sensing is useful in geological reconnaissance of the selected area during the mineral exploration process.
Remote Sensing in the Monitoring of Mine Operations
When the assets of a mining enterprise reach extensive areas, satellite images, provided in high resolution, are the best means to monitor the area in the planning phase.
These high-resolution images also allow the identification of uses, pits, tailings basins, roads and accesses, administrative units and natural areas.
Regarding the environmental regularity of a mine, remote sensing makes it possible to obtain data related to the change in surface topography. This type of analysis, combined with elevation models generated from stereo satellite data, points out potential areas of movement, helping in the monitoring of dams, for example.
In addition, it is also possible to quantify the areas of environmental rehabilitation and document the changes generated by the mining activity, which directly contributes to the mine closure plan.
Remote Sensing and Mining Cases
In this topic, you can check out some cases in which remote sensing was applied in mining. Among them are RADAM – Brazil, gold prospecting in Pedra Branca and the sensor of the company sensemetrics for monitoring dams.
RADAM – BRAZIL
The RADAM project, organized by the Ministry of Mines and Energy with the help of the former National Department of Mineral Production (DNPM), was a pioneer in the research of natural resources in Brazil, with the use of remote sensing by radar image and aerial photogrammetry. At the time, one of the technological advances was the use of side-looking airborne radar (SLAR) that allowed the acquisition of daytime, night, and cloudy weather images.
At first, in 1970, the focus was to collect data on mineral resources in the Amazon. With the success of the research, the work was expanded to the entire national territory. To this end, the platform used was a Caravelle aircraft, with an average altitude of 11 km and an average speed of 690 km/h. The imaging system was the GEMS (Goodyear Mapping System 1000), operating in the X band (wavelengths close to 3 cm and frequency between 8 and 12.5 GHz).
As a result, 550 radar mosaics covering the entire country at a scale of 1:250,000 were produced and made available to the public.
UNICAMP and CPRM Study – Efficiency of hyperspectral remote sensing for gold prospecting.
Researchers from the Institute of Geosciences of UNICAMP, together with the Geological Survey of Brazil – CPRM, developed a research that analyzes the efficiency of hyperspectral remote sensing, in which high-resolution sensors are used for gold prospecting.
The data for the research were extracted from the central region of the state of Ceará, in the gold deposits of Pedra Branca. These data were made available in material produced by CPRM, between 2013 and 2014, and contain hyperspectral images of the area.
For analysis, the work also determined the spectral behavior of the mineralogical composition of the Pedra Branca deposit.
Finally, the researchers concluded that the use of hyperspectral remote sensing is extremely useful for prospecting gold deposits. This is because this technique provides ease of identification of mineralogical trends related to mineralizing events, which, when detected by satellite images based on their spectral signature, can be prospective guides.
Sensemetrics sensor – Dam monitoring
At a seminar at CREA – MG, in 2020, the North American company sensemetrics presented its new sensor that enables the monitoring of any type of mining dam, including the monitoring of the stability of slopes and tailings piles, as well as environmental and structural monitoring, in addition to water management in the operation.
Dam monitoring through remote sensing. Source: agregadosonline.com.br/seminario-no-crea-mg-monitoramento-de-barragens/
These examples highlight the advantages of using techniques encompassed by remote sensing in various areas of mining. The trend is for more and more high-tech sensors to be used in the mineral sector, from the mineral research phase to the closure of the mine.
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References
ALMEIDA FILHO, Raimundo. Orbital remote sensing applied to mineral prospecting in the tin provinces of Goiás and Rondônia: a methodological contribution. 1984. Doctoral Thesis. University of São Paulo.
PARANHOS FILHO, A.C. et al. Geotechnologies for environmental applications. Maringá, PR: Uniedusul, 2021.
ARAÚJO, Marcelo Henrique Siqueira de. Fundamentals of geoprocessing applied to mining / Marcelo Henrique Siqueira de Araújo. Cruz das Almas, BA: UFRB, 2017.
CRÓSTA, ÁLVARO PENTEADO. Spectral characterization of minerals of mineral interest-prospecting and their use in digital image processing. Brazilian Symposium on Remote Sensing, v. 7, n. 1993, p. 202-209, 1993.
Remote sensing via satellite in the discovery of deposits. Available at: <https://agregadosonline.com.br/sensoriamento-remoto-via-satelite-jazidas/>
The importance of satellite imagery for mining. Available at: <https://www.codexremote.com.br/blogcodex/qual-a-importancia-das-imagens-de-satelite-para-mineracao/>
RADAM-D. Available at: <https://www.cprm.gov.br/publique/Geologia/Sensoriamento-Remoto-e-Geofisica/RADAM-D-628.html>
IG study adds new knowledge to gold prospecting. Available at: <https://www.unicamp.br/unicamp/noticias/2019/05/03/estudo-do-ig-agrega-novos-conhecimentos-para-prospeccao-aurifera>
Seminar at CREA/MG will focus on the importance of real-time dam monitoring and management. Available at: <https://agregadosonline.com.br/seminario-no-crea-mg-monitoramento-de-barragens/>