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1. METHOD Airborne gamma-ray spectrometry (AGRS) measures the abundance of Potassium (K), Thorium (eTh) and Uranium (eU) in rocks and weathered materials by detecting gamma-rays emitted due to the natural radioelement decay of these elements. Potassium abundance is measured directly as gamma-rays are emitted when 40 K decays to Argon. Uranium and T...
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... gamma-ray spectrometry (AGRS) measures the abundance of Potassium (K), Thorium (eTh) and Uranium (eU) in rocks and weathered materials by detecting gamma-rays emitted due to the natural radioelement decay of these elements. Potassium abundance is measured directly as gamma-rays are emitted when K decays to Argon. Uranium and Thorium cannot be measured directly. Daughter nuclides generated during the decay of parent elements are measured, and the abundance of parent elements is inferred. Distinct emission peaks associated with 208 Tl and 214 Bi are used to calculate the concentration of Th and U (Figure 1). Therefore, U and Th are expressed in equivalent parts per million (eU and eTh). Airborne gamma-ray data is collected by either helicopter or aeroplane, typically between 60 to 100 metres flying height above the surface. Sodium-iodide scintillation crystals on the aircraft measure gamma-rays emanating from the surface. Photomultiplier tubes attached to the scintillation crystals record and amplify the gamma-ray induced signal (Minty, 1997). The spatial resolution of gamma-ray data largely depends on the line spacing of the airborne survey. Flight line spacing is usually a compromise between data resolution and acquisition costs. Regional airborne geophysical surveys ...
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In this work we present progress obtained in analysis airborne geophysical survey data for the north-central region of the state of Goias. It included both aeromagnetic and gamma spectrometric surveys.
Analysis of aeromagnetic data reveals the presence of a large number of magnetic lineaments, indicative of distinct structural features in subsoil l...
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... Hence, the need for its evaluation in global sustainable energy drive. Moreover, an acquired airborne radiometric data usually has a spectral resolution that depends largely on the line spacing of the survey design [6]. The choice of a flight line intervals is a product of a compromise between cost of acquiring the data and the data resolution [6]. ...
... Moreover, an acquired airborne radiometric data usually has a spectral resolution that depends largely on the line spacing of the survey design [6]. The choice of a flight line intervals is a product of a compromise between cost of acquiring the data and the data resolution [6]. Therefore, a higher resolution data requires a higher acquisition cost and vice-versa. ...
... Moreover, the basaltic rock units of the study area has an average value of 2.32 μW/m 3 which is higher than the 0.74 μW/ m 3 reported by [34] for the basic rocks of Norway (Table 3). The general observation of the RHP values when compared with other previous studies such as [2], and [6] who reported RHP values of granites and gneissic rocks (within northwest, and southwestern Nigeria) to be within a range of 0.40 μW⋅m − 3 to 2.34 μW⋅m − 3 and 1.10 μW⋅m − 3 to 1.50 μW⋅m − 3 respectively. This shows that the present result is within the range of their findings. ...
An estimate of the radiogenic heat production (RHP) across the different petrologic units of northeastern, Nigeria was previously not performed. Hence, their geothermal potentials are not widely known. However, an airborne radiometric data of equivalent uranium, (eU), equivalent thorium (eTh,) and percentage potassium (% K) acquired by Nigerian geological survey agency (NGSA) in the year 2009 was deployed in the evaluation of the RHP across the major petrologic outcrops of northeastern, Nigeria. The objective of this study is to estimate the quantity of RHP across the 13 petrologic units of the northeastern Nigerian terrain via the use of an empirical equation (RHP=ρ(0.0952Cu+0.0256CTh+0.0348Ck)). The petrologic units studied are; medium-coarse grained biotite-hornblende granites (OGe), porphyritic biotite-hornblende granites (OGp), banded gneiss (bG), charnokytes (Ch), ignimbrites (JYG), migmatites-gneiss (MG), basalts (bb), Gombe sandstones (GS), Pindiga Formation (PS), Yolde Formation (YL), Bima sandstones (BS), Keri-Keri Formation (KK), and alluvium (AL). Basic/preliminary processing such as; signal integration, signal validation, and examination of spurious data were applied prior to the RHP computation. The results of the heat production analysis performed show the range of RHP to be from 1.11μW/m3 to 3.35μW/m3 Hence, the maximum heat production value of 3.35μW/m3 was recorded along porphyritic biotite-hornblende granites (OGp) rock block, while the least value of 1.11μW/m3 was recorded over alluvium (AL) rock outcrops. Furthermore, the spatial distribution of the RHP values over the study location shows a gradual increase from the middle, low heat production (sedimentary zones) to the high heat producing areas (granitic and metamorphic zones) around eastern and western parts. The petrologic units arranged in order of decreasing magnitude of radiogenic heat generation are; OGp > MG > OGe/bG > bb > GS > Ch > JYG > BS > PS/YL > KK > AL. On a general note, the petrologic units studied were classified as low in terms of geothermal character based on comparison with other previous global RHP studies.
... Airborne geophysics based on gamma-ray spectrometry estimates the concentration of Potassium (K), Uranium (eU) and Thorium (eTh) at the earth's surface down to 30-45 cm [52][53][54][55]. These radioelements occur in widely varying concentrations in the rocks that form the earth's crust. ...
The Kelâat M'Gouna inlier (KM'G) is located in the Eastern Anti-Atlas of Morocco, north of the West African Craton (WAC). It offers outcrops of great lithological diversity and has a polycyclic tectonic history. Its bedrock bears traces of the Pan-African orogeny, and its Adoudou-Cambrian cover was affected by the Hercynian orogeny. Therefore, the KM'G inlier is a privileged geological region for a geo-structural study to evaluate its mining potential. In this study, high-resolution aeromagnetic and surface geological data were used to map the structural architecture of the inlier and determine its relationship to the spatial distribution of mineral deposits and showings. Several filters and operators such as Reduction to Pole (RTP), Upward Continuation (UC), Centre for Exploration Targeting (CET) and Tilt Derivative (TDR) were applied to the aeromagnetic data to reveal important magnetic signatures such as magnetic lineaments/domains in the study area. The TDR and UC subdivided the area into two magnetic morpho-structural domains: to the north, a domain dominated by negative anomalies (labeled NMA1, NMA2 and NMA3), which coincide with the Sidi Flah fault and the Azlag and Ibantarn granites; to the south, a domain dominated by positive anomalies (labeled PMA4 and PMA6) which are deeply rooted. CET and TDR have been applied to map structural complexity and depth estimation. Four main magnetic lineament trends were deduced (NE-SW, Sub E-W, NW-SE, and Sub N–S) with variable depths ranging from 45 to 2120 m. A thorough structural scheme was developed based on the CET and TDR outputs and surface geological data. This scheme shows that the main deposits and mineral occurrences are known from the KM’G geological map are in areas with high magnetic lineament density values. Thus, several potential mineralization zones in the study area have been delineated. These results should guide the exploration of possible metal deposits in the KM’G inlier.
... Gamma-ray spectrum showing the position of the K, Th, U and total count windows[16]. ...
... Airborne geophysics based on gamma-ray spectrometry estimates the concentration of Potassium (K), Uranium (eU) and Thorium (eTh) at the earth's surface down to 30-45 cm [52][53][54][55]. These radioelements occur in widely varying concentrations in the rocks that form the earth's crust. ...
The mapping of hydrothermal alteration zones associated with mineralization is of paramount importance in searching for metal deposits. For this purpose, targeting alteration zones by analyzing airborne geophysical and satellite imagery provides accurate and reliable results. In the Kelâat M’Gouna inlier, located in the Saghro Massif of the Moroccan Anti Atlas, natural gamma-ray spectrometry and ASTER satellite data were used to map hydrothermal alteration zones. Natural gamma-ray spectrometry data were processed to produce maps of Potassium (K in %), Uranium (eU in ppm), Thorium (eTh in ppm) and ratios of K/eTh and K/eU. In addition, four-band ratios were computed, on ASTER data, to map the distribution of clay minerals, phyllitic minerals, propylitic minerals, and iron oxides. The combined results obtained from geophysical and satellite data were further exploited by fuzzy logic modelling using the Geographic Information System (GIS) to generate a mineral prospectivity map. Seven hydrothermal alteration zones likely to be favorable for mineralization have been identified. They show a spatial correlation with (i) known surface prospects and mineral occurrences, (ii) the granite-encasing contact zone, and (iii) the fault zones (Sidi Flah and Tagmout faults). This research therefore provides important information on the prospecting of mineral potential in the study area.
... Gamma-ray spectrometry is widely used in geosciences, geochemical, environmental studies, mineral exploration and remote sensing (e.g., Galbraith and Saunders (1983); Harris (1989); Graham and Bonham-Carter (1993); Wilford et al. (1997); Maden and Akaryalı (2015); dos Santos Albuquerque et al. (2020)). Airborne gamma-ray spectrometry estimates the concentration of potassium (K), uranium (eU), and thorium (eTh) in the surface (rocks, soils, and weathered materials), by up to 30-45-cm deep (Dickson and Scott, 1997;Minty, 1997;Wilford, 2002;IAEA, 2003). The natural radiation is determined by the disintegration of potassium 40 ( 40 K), uranium 238 ( 238 U) and thorium 232 ( 232 Th) series. ...
... AGRI is often available as the result of mineral exploration studies and this source may do double duty to allow inference of soil and regolith properties as well as to help understand the soil-landscape process over the generally quite large area covered by the airborne survey. Wilford and Minty ( 2007) , in their review of the application of AGRI to soil survey, showed that AGRD generally relates to bedrock mineralogy and its weathering state as influenced by geomorphic stability and the climate of a region (Lacoste et al., 2011;Pickup and Marks, 2000;Pickup and Marks, 2001;Rawlins et al., 2007;Schuler et al., 2010;Tunstall, 2003 ;Wilford, 2002;Wilford et al., 1997). These are related to soil-forming factors such as parent material, climate and time. ...
Thailand has a long tradition of using detailed soil information in agriculture and watershed management. Agricultural extension workers locally named “ soil doctors ”, give advice on farm level on increasing agricultural production and combat land degradation. Unfortunately, detailed soil information is only available for the flat areas where most of the agriculture used to be concentrated, with conventional soil mapping methods based on the US Soil Taxonomy classification system. As more and more of the hilly and mountainous areas are being used there is now a distinct lack of detailed soil data for these services. Also the complexity of the services has increased, dealing with integrated watershed management, addressing sustainability and more complex forms of land degradation, soil conservation and infrastructure development.
The Thai government cannot afford to do a detailed soil survey for the entire country as it is prohibitively expensive. Large scale soil survey products are not adequate, either categorically or cartographically, and cannot be easily downscaled for detailed applications. This study investigates an alternative soil survey method, developing a framework as a standard or guidelines to implement soil survey projects efficiently based on digital soil mapping (DSM) techniques. The framework should cope with the generation, maintenance and use of digital soil map products to meet the increasing demand of soil data for multi- purpose use and also offering possibilities for the update of soil information. The purpose of this research, therefore, is to investigate DSM methods for fine- scale soil mapping. The specific objectives include: 1) an investigation of high- resolution DEM and digital terrain modelling techniques, 2) application of airborne gamma- ray imagery and 3) use of fuzzy logic for fine- scale soil mapping. The study was conducted in Lomsak, Phetchabun province in Thailand, an area characterized by a variable terrain (flat to mountainous) and a large variety in soil types.
Eight terrain attributes were computed from two DEM resolutions (original 5- m. and degraded to 10- m.) using three neighborhood sizes (5x5, 10x10 and 20x20 cells). These attributes and their standardized principal components were then used as predictive variables for soil series and properties using logistic and linear regression, respectively. The results show that DEM derivatives based on grid resolution alone are not sufficient in analyzing their applicability in soil mapping. The neighborhood size also becomes important. The application of high resolution DEM at 5 m resolution with neighborhood size of 10x10 pixels gave good result to help map soil series. Single terrain variables could only model about 20% of the variability in subsoil bulk density and pH, with no clear advantage to either resolution or window size. Principal components derived from 5- m DEM with 20x20 neighborhood size and 10- m DEM with 10x10 neighborhood size were moderately successful ( 20- 25% of variance explained) for these two properties. Probabilities of occurrence for two of three representative soil series were successfully modeled (area under ROC curve about 0.9) from the 5-m DEM with 10x10 neighborhood and 10- m DEM with 5x5 pixel of neighborhood. Predictive maps generally conformed to expert knowledge of experienced mappers, but showed large differences in detail among window sizes. No general conclusion can be drawn about appropriate resolution and window size; these must be investigated per- property or series. Further, relief alone is a poor predictor of soil properties in this landscape.
The relationship between gamma-ray data and geological units was examined with box- and- whisker plots, using rock and soil samples. Rock and soil sample classifications were compared with the gamma- ray image and to typical radioelement responses found in the literature. To interpret AGRI data in terms of regolith and soil genesis, we compared AGRI to two existing soil maps: geopedologic and soil series maps. First, the geopedologic map was split into four maps according to the geopedologic hierarchy: landscape, lithology, relief, and landform; at the latter ( lowest) level, soil units are also associated. Secondly, soil series and geopedologic soil units were used to examine the distribution of radioelement response to selected soil characteristics: parent material, texture, mineralogy, and thickness. The correlation in both soil maps was interpreted in terms of the radioelement changes during pedogenic and geomorphic process, based on a review of literature and supported by soil samples.
AGRI provided useful information in three forms (single signal, ratio, and so called ternary images enhanced with a hill shaded DEM) by relating these to lithology, material transport, and internal pedogenic processes. AGRI correlated well with the classes of the geopedologic map (1:50,000) at the two higher levels (landscape and lithology) but to a lesser degree at the two lower levels (relief and landform in geopedologic approach). In the mapping stage, AGRI showed deficiencies in the soil series map (1:50,000) made by conventional aerial photo analysis and limited field surveys, especially in inaccessible areas but also in low- relief terraces and flood plains, which provided a basis for future field sampling to correct these deficiencies. AGRI suggested new boundaries, differentiating topsoil properties and the presence of plinthite, despite its coarse resolution. Clustering of gamma ray and elevation data ( DEM) was carried out using fuzzy logic to generate various classification layers. Class labels were assigned to the one with the largest total inverse distance over the entire set of fuzzy classification bands. The result shows relatively higher classification accuracy for soil parent material differentiation (overall accuracy of 72%) as compared to the classification for soil types ( 67% ). Therefore, the result also shows that gamma- ray helps in determining lithology/parent material, weathering index and topsoil texture.
Soil series and topsoil texture mapping in a complex landscape has been carried out using fuzzy logic (SoLIM). An expert system is used whereby rule-based reasoning is applied for mapping soils in which the soil- landscape relationship is taken into account. The accuracies of the fuzzy logic derived soil map and that of conventional soil map are tested using a set of validation data. The results show that a soil series map generated by fuzzy logic has an overall accuracy of 67%, the highest accuracy is found in the Ct series ( 88 %) and the lowest in So series ( 57%). The results depend on the degree in which a series are related to a landscape position, and the broadness of the definition of the series. Regarding the topsoil texture, three texture classes give the highest accuracy (greater than 80%) are Silty Clay, Slightly Gravelly Clay Loam and Rock outcrops, while the lowest accuracy was found in Clay Loam (53% ). The overall accuracy is about 65%. The accuracy of the soil map prepared by the conventional method shows an overall accuracy of 13%. The results confirm that Fuzzy Logic is advantageous in providing detailed information about spatial variations and representing realistic spatial patterns in soil series and topsoil texture maps. It has also the potential for reducing inconsistency associated with the traditional soil mapping processes, and as mapping can be carried out with a relatively low density of soil samples it may also reduce costs.
Soil survey works in Thailand are the responsibility of the Land Development Department (LDD), Ministry of Agriculture & Cooperatives. Currently, there is an increased demand of soil information not only for farm level planning but also for addressing complex sustainability issues. LDD has adopted geo- information system (GIS) and remote sensing techniques (RS) for digitizing existing soil maps, map visualization and data retrieval, but the LDD has not yet implemented digital soil mapping (DSM) techniques. The research results can be used to support soil survey works in Thailand in developing guidelines and framework for digital soil mapping, also for soil mapping in complex sloping landscapes, based upon specific Thai needs and conditions.
... Typically, the main component of gamma-ray flux is contained within the upper 30 cm of the Earth's surface (Wilford 2002). The airborne gamma-ray spectrometry has specific three windows (channels) in order to record the radiation emitted by the radionuclides K 40 , U 238 and Th 232 (IAEA 2003). ...
Interpretation of remote sensing data for allocating of lithologic units and for mapping of radioactive zones, supplies a valuable utility to produce Potential Radioactivity Map for the uraniferous granite. The study applied a digital image processing technique including interpretation and manipulation of Geophysical Airborne gamma-ray spectrometry data and The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) sensor image data of Terra satellite over a case study well-known radioactive area of El-Missikat, El-Eridya and Kab Amiri areas in the Central Eastern Desert, Egypt. The possible forms of digital image manipulation are categorised into the following procedures: Minimum Noise Fraction (MNF) rotation, colour composite, band ratios, Principle Component Analysis (PCA), decorrelation stretching and Iterative Self-Organising Data Analysis Technique Algorithm (Isodata) unsupervised classification. Matched Filter (MF) classification was performed on the data to map a chosen well- known alteration mineral association with the uranium occurrences from USGS library. Each of these constructed images with the surveyed Airborne spectrometry data (equivalent uranium) has been given a suitable weight to be integrated using Geographic Information System (GIS) tools to delineate the most promising potential radioactive zones. Moreover, the other comparatively and quantitatively goal of the study was to evaluate the performance of various knowledge-driven mineral probability modelling.
... orthoclase and micas). As such, the variation at the spatial scales detected, reflects the accumulation in topographic lows, or at least lower parts of the landscape, where K rich clays have weathered from micas and K-feldspar from upslope positions and eroded into lower lying positions (Wilford et al., 1997). In contrast, we note that at no scales was there any significant regions of variation for 40 K in the second half of the transect (~1600 m to the end). ...
... AGRI is often available as the result of mineral exploration studies and this source may do double duty to allow inference of soil and regolith properties as well as to help understand the soil-landscape process over the generally quite large area covered by the airborne survey. Wilford and Minty (2007), in their review of the application of AGRI to soil survey, showed that AGRD generally relates to bedrock mineralogy and its weathering state as influenced by geomorphic stability and the climate of a region (Lacoste et al., 2011;Marks, 2000, 2001;Rawlins et al., 2007;Schuler et al., 2011;Tunstall, 2003;Wilford, 2002Wilford, , 2011Wilford et al., 1997). These are related to soilforming factors such as parent material, climate and time. ...
Airborne gamma-ray imagery (AGRI) provides coarse-resolution (approximately 400 × 400 m pixel) spatial information on gamma-ray emitting elements, i.e. potassium (K), thorium (Th) and uranium (U), in the upper half meter of the soil. These radioelements are a potential information source for soil mapping since their abundance is related to soil geochemistry, specifically the chemical composition of parent materials and their weathering products resulting from geomorphic and pedogenic processes.
The aim of this study was to evaluate the potential of AGRI for improving digital soil survey process in two phases: (1) a preliminary phase, where hypotheses of soil-landscape relationships are developed, and (2) a phase where soil map unit boundaries are placed or revised. The study also evaluated the match between AGRI and existing lithologic, geopedologic, and soil series maps. The study was conducted in a well-characterized complex soil landscape: the 560 km2 upper Pa Sak watershed in Petchaboon province, Thailand. The relationship between gamma-ray data and geological units was examined with box-and-whisker plots and confirmed by rock and soil samples. Rock and soil sample classifications were compared with the gamma-ray image and to typical radioelement responses found in the literature.
To interpret AGRI data in terms of regolith and soil genesis, we compared AGRI to two existing soil maps: geopedologic and soil series maps. First, the geopedologic map was split into four maps according to the geopedologic hierarchy: landscape, lithology, relief, and landform; at the latter (lowest) level, soil units are also associated. Secondly, soil series and geopedologic soil units were used to examine the distribution of radioelement response to selected soil characteristics: parent material, texture, mineralogy, and thickness. The interpretations from best correlation in both soil maps were described in terms of the radioelement changes during pedogenic and geomorphic processes, based on a review of literature and supported by soil samples.
In the hypotheses-generating stage, AGRI provided useful information in three forms (single signal, ratio, and ternary images enhanced with a hill shaded DEM) by relating these to lithology, material transport, and internal pedogenetic processes. AGRI correlated well with the classes of the geopedologic map (1:50,000) at the two higher levels (landscape and lithology) but to a lesser degree at the two lower levels (relief and landform in geopedologic approach). In the mapping stage, AGRI showed deficiencies in the soil series map (1:50,000) made by conventional aerial photo analysis and limited field surveys, especially in inaccessible areas but also in low-relief terraces and flood plains, which provided a basis for future field sampling to correct these deficiencies. AGRI suggested new boundaries, differentiating topsoil properties and the presence of plinthite, despite its coarse resolution.
Clustering of gamma ray and elevation data (DEM) was carried out using fuzzy logic to generate various classification layers. Final map was produced using total weighted inverse distance of all the classes in a 3 by 3 window. Class label was assigned to the one with the largest total inverse distance over the entire set of fuzzy classification bands. The result shows relatively higher classification accuracy for soil parent material differentiation (overall accuracy of 72%) as compared to the classification for soil types (67%).
... AGRI is often available as the result of mineral exploration studies and this source may do double duty to allow inference of soil and regolith properties as well as to help understand the soil-landscape process over the generally quite large area covered by the airborne survey. Wilford and Minty (2007), in their review of the application of AGRI to soil survey, showed that AGRD generally relates to bedrock mineralogy and its weathering state as influenced by geomorphic stability and the climate of a region (Lacoste et al., 2011;Marks, 2000, 2001;Rawlins et al., 2007;Schuler et al., 2011;Tunstall, 2003;Wilford, 2002Wilford, , 2011Wilford et al., 1997). These are related to soilforming factors such as parent material, climate and time. ...
