July 8, 2022
With the evolution of technologies provided by Mining 4.0 the use of remote sensing is becoming increasingly common in the mining sector, with applications in all phases of a mining project. Throughout this text, we will cover 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 industry. Want to find out more? Check out the full content below.
In general terms, remote sensing is a set of techniques for obtaining images from a distance, over the earth's surface, without there being any physical contact between the sensor and the surface being studied.
According to Filho et al. (2021), there are three levels of data acquisition:
In their operation, sensors capture the electromagnetic radiation (EMR) emitted by targets as a method of detecting and measuring their physical characteristics. EMR 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 remote sensing images, a target can be identified by detecting its spectral behaviour.
A practical example of this method in the geological context is the differentiation of rocks. Felsic minerals such as quartz, albite, feldspar and muscovite reflect REM relatively uniformly and have high reflectance. Consequently, igneous rocks with a felsic composition, including pegmatite and granite, will show greater reflectance intensity in satellite images.
The decrease in silica in the rock's composition and the increase in basic minerals such as biotite, olivine, pyroxenes and amphiboles mean that the intensity of the reflectance is lower. Therefore, ultrabasic or ultramafic rocks have low reflectance.
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, infrared (near, far and mid) and ultraviolet bands, among others.
Depending on the spectral behaviour 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 analysing geological and structural features.
With regard to mineral prospecting the presence of some elements on the surface can be a good indication of a mineralised region. In this context, the 400 to 1000 nm range is suitable for detecting minerals containing iron 3+ oxides/hydroxides, since these 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 haematite) can be better identified in the 450 nm, 650 nm and 850-950 nm spectral regions due to their high absorption rate. We call this association limonite. When limonite has a higher relative concentration of goethite in a given region, it can be a good indication of sulphide deposits.
Mineral deposits containing iron 3+ oxides/hydroxides include auriferous mineralisations related to hydrothermal alteration zones and deposits of massive sulphides of base metals (Cu, Ni, Cr, Zn). In both cases, limonite is present as a product of sulphide weathering (CRÓSTA, 1993).
This example demonstrates how remote sensing is useful in geological reconnaissance of the selected area during the mineral exploration process.
When the assets of a mining project cover large areas, satellite images, provided in high resolution, are the best way to monitor the area during the planning phase.
These high-resolution images also make it possible to identify uses, pits, tailings ponds, roads and accesses, administrative units and natural areas.
With regard to the environmental regularity of a mine, remote sensing makes it possible to obtain data related to changes in surface topography. This type of analysis, combined with elevation models generated from stereo satellite data, pinpoints potential areas of movement, helping to monitor dams, for example.
In addition, it is also possible to quantify environmental rehabilitation areas and document the changes generated by mining activity, which contributes directly to the mine closure plan.
In this topic, you can see some cases in which remote sensing has been applied in mining. These include RADAM - Brazil, gold prospecting in Pedra Branca and the sensemetrics company's sensor for monitoring dams.
The RADAM project, organised 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, using radar remote sensing and aerophotogrammetry. At the time, one of the technological advances was the use of side-looking airborne radar (SLAR), which made it possible to obtain images during the day, at night and in cloudy weather.
At first, in 1970, the focus was on surveying mineral resources in the Amazon. With the success of the survey, the work was expanded to the entire national territory. The platform used was a Caravelle aeroplane, 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 on a scale of 1:250,000 were produced and made available to the public.
Researchers from Institute of Geosciences of UNICAMP together with the Geological Survey of Brazil - CPRM have carried out a study analysing the efficiency of hyperspectral remote sensing, in which high-resolution sensors are used, for gold prospecting.
The research data was extracted from the central region of the state of Ceará, in the Pedra Branca gold deposits. This data was made available in material produced by CPRM between 2013 and 2014 and contains hyperspectral images of the area.
For analysis purposes, the work also determined the spectral behaviour 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 makes it easy to identify mineralogical trends related to mineralising events, which, when detected by satellite images based on their spectral signature, can be prospective guides.
In CREA - MG seminar in 2020, the North American company sensemetrics presented its new sensor that makes it possible to monitor any type of mining dam, including monitoring the stability of slopes and tailings piles, as well as environmental and structural monitoring, in addition to water management in the operation.
These examples highlight the advantages of using remote sensing techniques in various areas of mining. The trend is for more and more high-tech sensors to be used in the mining sector, from the mineral exploration phase to mine closure.
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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 characterisation of minerals of interest - mineral prospecting and its use in digital image processing. Simpósio Brasileiro de Sensoriamento Remoto, v. 7, n. 1993, p. 202-209, 1993.
Satellite remote sensing in the discovery of deposits. Available at: <https://agregadosonline.com.br/sensoriamento-remoto-via-satelite-jazidas/>
The importance of satellite images 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 for 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 monitoring and managing dams in real time. Available at: <https://agregadosonline.com.br/seminario-no-crea-mg-monitoramento-de-barragens/>
Brenda Costa Belchior Guimarães
Mining Engineering student at the Federal University of Minas Gerais and DMT intern.