1 Introduction

Gabal Umm Tinassib and its surrounding area are situated in the northwestern region of the Arabian-Nubian Shield (ANS) within Egypt's North Eastern Desert. It lies between latitudes 28° 18′ 1.89″ N & 28° 47′ 1.82″ N and longitudes 32° 16′ 47.05″ E & 33° 7′ 29.78″ E (Fig. 1). This region encompasses a diverse range of basement and sedimentary rocks dating from the Precambrian to the Quaternary. Various wadis (dry valleys) filled with Quaternary sediments traverse these rock exposures (Fig. 1). The study area holds significant importance due to its abundance of hydrocarbon and mineral resources. It primarily consists of granitic rocks displaying indications of high radioactive mineralization detected through airborne radiometric surveys.

Fig. 1
figure 1

Geologic map of Gabal Umm Tinassib and its surrounding area, North Eastern Desert, Egypt. (Reproduced after [9]), with a location map (inset)

Full size image

Extensive geological, petrographic, and geochemical studies have been conducted in this area and its surrounding [2, 3, 25, 28]. The current work focuses on integrating RS and AGS methods to locate uranium zones and alteration anomaly zones while elucidating the relationship between high concentrations of radioelements and altered mineralization zones.

RS sensors gather information about the Earth's surface from various distances by measuring the emission or reflection of electromagnetic spectrum radiations across the microwave, thermal-infrared, near-infrared, and visible portions. The resultant data is categorized into two types: (1) details concerning the composition of surface materials and (2) indirect spatial information regarding the surface layout, including the distribution of surface materials, geological structures, and landforms.

AGS is a crucial method in geological mapping because it measures the chemical variation of radioactive elements such as K, U, and Th. This data greatly contributes to analyzing each lithological unit [12] and ultimately aids in identifying structures that bound lithological units. AGS stands out as the most cost-effective geophysical method for reconnaissance relatively unexplored or inaccessible areas. Typically, AGS data are utilized to identify surface phenomena, particularly in mineral exploration, focusing on minerals exhibiting considerable radiometric anomalies.

RS and AGS data are utilized in mineral prospecting and geological mapping. These methods have proven successful in detecting alteration minerals such as kaolinite, chlorite, hematite, illite, and sericite, crucial for identifying radioactive mineralization and hydrothermal alterations [11, 15,16,17,18, 20, 24]. Additionally, they aid in delineating and identifying various flood hazards, landforms, and structural lineaments for environmental mapping. Alteration anomalous zones in uranium and pathfinder elements, accompanied by minerals such as clay, kaolinite, illite, and chlorite, create haloes within the rocks that aid in the exploration of subsurface deposits [4, 5, 10].

2 Geologic setting

The geological understanding of the research area (Fig. 1) is derived from a 1:500,000 scale geological map of Benisuef, Egypt [9]. Numerous authors have contributed to the study of this area (e.g., [6, 14, 23, 30, 31]).

The Precambrian rocks encompass a sequence ranging from calk-alkaline foliated quartzdiorite to granodioritic compositions (older granites), calk-alkaline deformed granites (younger granites), Dokhan Volcanics, and Tertiary volcanics. These basement complexes dominate the surface exposures, primarily emerging in the central and southern parts of the study region, forming a segment of the northwestern ANS.

The sedimentary rocks span various ages from Paleozoic to Quaternary. They overlay the Precambrian basement rocks with substantial successions represented, in ascending order, by Araba, Samr el-Qa, Malha, Wadi Qena, Galala, Um Omeiyid, Hawashiya, Rakhiyat, Sudr, Esna, Rimth, Thebes formations, and Mokattam Group. These formations are covered by Miocene and Pliocene sediments as well as Quaternary sediments (Wadi sediments).

The Quaternary sediments, the most recent observed in the area, comprise undifferentiated recent coastal sediments, raised beaches, alluvial fans, wadi sediments, sand, gravel, and small coastal segments of Sabkha sediments rich in clay, silt, and evaporates. These sediments dominate the eastern region and blanket the primary wadis, including Wadi Hawashiya, Wadi Umm Rabul, Wadi Umm Arta, Wadi el-Dakhal, and Wadi Abu Rimth.

The study area is marked by numerous wadis (dry valleys) that drain toward the Red Sea, following NE–SW and E–W directions, in alignment with the major faults. Tectonically, the pattern of the basement rocks in the research area reflects the cumulative effects of successive earth movements since the Precambrian times. The geologic map of the area under investigation (Fig. 1) reveals four major sets of structural lineaments trending mainly in the NE–SW, NNE–SSW, NNW–SSE and E–W directions, alongside minor sets having the NW–SE, ENE–WSW, and N–S trends.

3 Materials and methodology

3.1 RS data processing

The Landsat 8 (OLI) data, obtained from USGS, underwent several processing steps using the ENVI software. The processing of RS data primarily aimed to facilitate the creation of geological maps and the characterization of uraniferous granite along with its associated alteration zones. Various outputs were generated using ArcGIS software, encompassing the selection of FCC (5, 6, 7 in RGB) derived from OIF, PCA (PC3, PC2, and PC1), (PC4, PC2, and PC1), ratio (6/7, 5/6, 4/2), ratio (6/7, 6/2, (4/5) * (6/5)), band ratio image (6/7), band ratios (6/7, 6/5, and 5 in RGB), and the CEM techniques. These outputs were integrated to detect the boundaries between outcropping rocks and identify alteration zones.

OIF technique, employed for band selection to determine the most suitable band triplets, was computed using the equation developed by [7, 8]:

$$ {\text{OIF}} = \frac{{{\text{Si}} + {\text{Sj}} + {\text{Sk}}}}{{({\text{Ri}},{\text{J}}) + ({\text{Ri}},{\text{k}}) + ({\text{Rj}},{\text{k}})}} $$
(1)

where Si, Sj, and Sk = Standard deviation for bands i, j, k; respectively. Ri, j, Ri, k and Rj, k = The correlation coefficients between two of the three bands being evaluated.

PCA techniques involve combining multispectral datasets to generate new enhanced data that minimize redundancy in spectral reflectance within the data bands [27].

Pour et al. [26] highlighted that the band ratio technique typically enhances the spectral outcomes of alteration minerals within alteration areas, leveraging their distinct absorption features at specific wavelengths. Accordingly, selecting appropriate ratios in the band ratio technique facilitates accurate differentiation between iron oxides and OH-bearing minerals, resulting in an RGB composite image tailored to meet the study's objectives.

Farrand and Harsanyi [19] explained that the CEM technique suppresses other output features (unidentified background) while amplifying the target spectrum output. This technique effectively maps alteration zones using the spectral analysis of alteration minerals, reducing the extensive field trips needed to identify alteration zones.

3.2 AGS data processing

The research area is considered a region of Egypt's North Eastern Desert and has been surveyed using AGS. The survey was carried out by the Aero-Service Division of the Western Geophysical Company. It utilized parallel traverse flight lines oriented at 45° and 225° from true north, spanning a northeastern to southwest direction. Tie lines were spaced ten kilometers apart and angled northwest to southeast with azimuths of 135° and 315°. The flying lines were set at intervals of 1.5 km. The survey maintained an average terrain clearance elevation of 120 m and an average flying speed ranging between 220 and 315 km/h [1].

The AGS data was processed using the Geosoft [21] Oasis Montaj program. Various maps were generated to display the distribution of TC, K%, eU, eTh, as well as the ratios (eU/eTh, eTh/K, & eU/K), alongside ternary composite images. A statistical analysis was performed on the AGS data for each geological unit within the study area. This involved calculating the minimum (Min), maximum (Max), arithmetic mean (X), standard deviation (SD), and coefficient of variability (CoV% = (S.D./X) * 100) for these statistical investigations.

Additionally, the alteration F-parameter for each rock unit was estimated. To delineate the spectrum of alteration across different rock units, Efimov [13] introduced a three-elemental effective parameter. F-parameter values are below 1.2 for unaltered rocks and exceed 1.2 for altered rocks. The F-parameter was computed by Gnojek and Prichystal [22] using the equation:

$$ \begin{aligned} F\left( \% \right) = &\; \frac{eU}{{eTh/K}} = \frac{K}{eTh/eU} \\ = &\; K*\left( {eU/etH} \right) \\ \end{aligned} $$
(2)

4 Interpretation of RS and AGS data

4.1 RS data

4.1.1 FCC

A set of three bands is essential to create a color image using band combinations. However, Landsat 8 (OLI) datasets encompass seven spectral bands, offering a wide range of potential three-band pairings. The latest version of Ilwis software was employed to identify optimal combinations that feature the most informative bands while minimizing information redundancy, thus enhancing the intended objectives (Fig. 2a). The selection of the optimal combination for lithological differentiation was based on the most significant value determined from the OIF ranking (Table 1).

Fig. 2
figure 2

a Landsat-8 FCC image, band (5, 6, 7), b False colour (PC3, PC2, and PC1) composite map, c False colour (PC4, PC2, and PC1) composite map, Gabal Umm Tinassib and its surrounding area, North Eastern Desert, Egypt

Full size image
Table 1 OIF index highest ranking of Landsat bands
Full size table

4.1.2 PCA

Analysis of the eigenvector matrix (Table 2) from Landsat 8 (OLI) data indicates that (PC3, PC2, and PC1) (Fig. 2b) and (PC4, PC2, and PC1) (Fig. 2c) contain valuable information with the highest variance. These components were utilized to elucidate rock connections and geological characteristics within the study area.

Table 2 Eigenvector matrix and loadings of principal component analysis
Full size table

4.1.3 Band ratio

Two primary color ratio composites, (6/7, 5/6, 4/2) and (6/7, 6/2, (4/5) * (6/5)), are identified as the most effective composites for discriminating lithological contacts (Fig. 3a–b). The rock units successfully delineated through these ratios include younger granite, older granite, Dokhan volcanic rocks, sedimentary rock, and Quaternary and Wadi sediments.

Fig. 3
figure 3

Landsat- band ratio a 6/7, 5/6, 4/2, b 6/7, 6/2, 4/5 * 6/5, c 6/7 in white tones, d 6/7, 6/5, and 5 in RGB spots the alteration zones, Gabal Umm Tinassib and its surrounding area, North Eastern Desert, Egypt

Full size image

The implementation of band ratio 6/7 reveals OH-bearing clay minerals in bright tones (Fig. 3c) over basement rocks. Bright tones representing band ratios 6/7, 6/5, and 5 were utilized to generate FCC image, illustrating an alteration map of the research area. Hydrothermal alteration areas are indicated in reddish, yellow, and bright green colors over the basement rocks (Fig. 3d).

4.1.4 CEM technique

The CEM technique was employed to delineate sites of mineral alterations within the research region, utilizing various colors (Fig. 4). These minerals encompass goethite, chlorite, calcite, sericite, montmorillonite, jarosite, hematite, epidote, and kaolinite. The spectral responses of these minerals have been extracted from the USGS spectral library and integrated into the ENVI version 5.3 software.

Fig. 4
figure 4

Constrained energy minimization (CEM) technique reflects the distribution of nine alteration minerals, Gabal Umm Tinassib and its surrounding area, North Eastern Desert, Egypt

Full size image

The presence of multiple mineral alterations in specific locations might indicate the degree of alteration intensity. Consequently, these locations are more likely to be mineralized. The CEM image (Fig. 4) highlights specific locations exhibiting several mineral alterations, suggesting a higher probability of radioactive minerals within the basement rocks of the study area. These alteration zones coincide with the contact zones between the basement complex and sediments. They also align along specific trends of the structural lineaments primarily trending in the NNW-SSE, NNE-SSW and E-W directions.

4.2 AGS data

4.2.1 Qualitative interpretation

  1. (A)

    TC and radio-element maps

The TC and individual K, eU, and eTh radioelement maps (Fig. 5a–d) exhibit higher radiation levels at their centers compared to their surrounding areas. The recorded radioactivity varies significantly between rock types and even within the same rock type. This variation in radiation levels serves as an indicator for identifying lithological contacts.

Fig. 5
figure 5

a Total-count (TC in Ur), b Potassium (K in %), c Equivalent uranium (eU in ppm), d Equivalent thorium (eTh in ppm) contour maps, Gabal Umm Tinassib and its surrounding area, North Eastern Desert, Egypt. [1]

Full size image

Upon examination of the TC, K%, eU, and eTh maps (Fig. 5a–d), three distinct radiation levels are apparent and described as follows:

The lowest level ranges from 1.3 to 6.1 Ur for TC, 0.2–2.2% for K, < 2.1 ppm for eU, and < 5.7 ppm for eTh. These values are primarily observed in the northern, northwestern, southwestern, and eastern parts, corresponding to undifferentiated upper Cretaceous sediments, the Malha Formation, Sudr Formation, Abu Rimth Formation, Quaternary sediments, and formations like Galala, Wadi Qena, Samr el-Qa, and Araba.

The intermediate level ranges from 6.1 to 8.8 Ur for TC, 2.2–2.7% for K, 2.1–3.2 ppm for eU, and 5.7–9 ppm for eTh. These readings are found in the central, southern, southeastern, and eastern parts, associated with older granites, Pliocene sediments, and Quaternary sediments.

The highest level varies from 8.8 to 19.3 Ur for TC, 2.7–3.6% for K, 3.2–11.1 ppm for eU, and 9–30 ppm for eTh. This level is represented by younger granites and Miocene sediments. The elevated values in the Miocene sediments might be due to the influence of adjacent granitic rocks.

  1. (B)

    Radiometric ratio maps

The eU/eTh ratio map illustrates low eU/eTh values (< 0.4) over the younger granites situated at the center of the map around Gabal Umm Tinassib and Wadi Umm Arta (Fig. 6a). Both eU and eTh maps exhibit nearly equal high values at this location, except in specific areas where eU content surpasses eTh (Fig. 5c–d). Furthermore, the eU/eTh ratio map indicates elevated values (> 0.7) in the northern and western sections (Fig. 6a), despite the overall low values of eU and eTh. These values correspond to the Abu Rimth Formation, undifferentiated upper Cretaceous sediments, Quaternary sediments, and the Galala Formation due to uranium's higher mobility compared to thorium. Intermediate eU/eTh ratios (ranging from 0.4 to 0.7) are also prevalent in the northern and western regions of the map (Fig. 6a).

Fig. 6
figure 6

a eU/eTh, b eU/K, c eTh/K ratio contour maps, Gabal Umm Tinassib and its surrounding area, North Eastern Desert, Egypt

Full size image

The eU/K ratio map (Fig. 6b) reveals three levels. The first level (low) spans values from 0.7 to 1.2, the second level (intermediate) ranges from 1.2 to 3.0, and the third level (high) varies from 3.0 to over 8.0. These levels align with their respective locations on the eU/eTh map, except for Gabal Umm Tinassib and its surrounding area, which display moderate values.

The eTh/K ratio (refer to Fig. 6c) showcases low eTh/K values (< 3.5) in the southeastern part, coinciding with Quaternary and Wadi sediments. Meanwhile, the highest values (> 5.6) are recorded over the Abu Rimth Formation, Quaternary sediments, undifferentiated upper Cretaceous sediments, and the Galala Formation.

  1. (C)

    Ternary (composite) image maps

The composite radioelement image (Fig. 7a) blends eU (blue), eTh (green), and K (red) data, displaying a significant spatial relationship with observed geological units. Sedimentary rocks in the north and west exhibit darker colors compared to eastern units, suggesting lower K, eU, and eTh contents. Bright colors (indicative of high values) correlate with younger granites and surrounding wadi sediments at the map's center.

Fig. 7
figure 7

a Radio-element, b Equivalent uranium, c Equivalent Thorium, d Potassium composite images, Gabal Umm Tinassib and its surrounding area, North Eastern Desert, Egypt

Full size image

The eU composite image (Fig. 7b) provides valuable insights into locating anomalous uranium concentration zones. This map integrates eU (red) with eU/eTh (green) and eU/K (blue). Bright white areas denote unusual uranium zones with high eU/K and eU/eTh ratios, displaying turquoise colors. Pink areas highlight high eU values in contrast to low eU/K and eU/eTh values, mainly associated with younger granites and adjacent wadi sediments. Dark regions (indicating low eU values) are primarily linked to Quaternary sediments.

The eTh composite image (Fig. 7c) illustrates the distribution and enrichment of eTh patches. Bright pink indicates eTh-enriched areas relative to K and eU, mainly associated with younger and older granites in the central and southern regions. High eTh relative to K predominates in all sedimentary cover in the northern and western regions. Elevated eTh relative to eU exists in Quaternary and wadi sediments in the eastern and southern regions.

The K composite image (Fig. 7d) demonstrates the general distribution of K contents. White areas represent high anomalies in K concentrations, mostly prevalent in granitic rocks and Quaternary sediments. Dark colors indicate low K values associated with sedimentary cover in the northern and western parts of the map (Fig. 7d).

4.2.2 Quantitative interpretation

A statistical analysis of the AGS data was performed to outline the distribution of TC, K, eU, and eTh. Table 3 presents the Min, Max, X, S.D., and CoV% values, serving to establish the normality of each rock unit. A rock unit is considered to have a normal distribution if its CoV% less than 100% [29].

  1. (A)

    Precambrian basement rocks

Table 3 Summary of the statistical treatments of gamma-ray spectrometric data for the rock units of Gabal umm Tinassib and its surrounding area, North Eastern Desert, Egypt
Full size table

These rocks exhibit a CoV% less than 100% for TC, K%, eU, and eTh, indicating a normal distribution. Among the basement rocks in the research area, Tertiary volcanics show the highest CoV% values for radiation parameters (TC, K%, eU, and eTh) of 21.09, 61.11, 28.03, and 39.16, respectively, indicating the lowest homogeneity. Conversely, younger granites display CoV% values of 16.40, 13.29, 26.20, and 20.88 for TC, K%, eU, and eTh, respectively, denoting higher homogeneity.

Table 3 highlights a diverse range of eU values for older granites (ranging from 0.7 to 11.65 ppm) and younger granites (ranging from 0.83 to 7.75 ppm). The relatively higher values observed in older granites could be attributed to the intrusion of acidic dykes and veins. These intrusions, often characterized by their narrow width, and have been missed or inaccurately mapped due to the scale of the map.

  1. (B)

    Sedimentary rocks


Paleozoic rocks

Only two rock units, the Araba and Samr el-Qa Formations, exhibit a CoV% of less than 100%, indicating a normal distribution for these units. The Araba Formation displays the highest uranium concentrations, ranging from 0.99 to 6.67 ppm, with a mean of 2.31 ppm and a CoV of 38.96%. K values vary from 0.01 to 3.4% (mean of 1.37% and CoV of 64.23%), while eTh values range from 2.35 to 25.63 ppm, averaging at 7.26 ppm with a CoV of 44.21%.


Mesozoic rocks

With a CoV% of less than 100% for most rock units, their distribution is considered normal, except for the Malha Formation, which displays a K value of 105.06%. Sudr Formation records high uranium concentrations, with eU values ranging between 0.28 and 4.07 ppm, averaging at 1.76 ppm and a CoV of 28.98%. K values range from 0.09 to 2.45%, averaging at 0.3% with a CoV of 80%. eTh values vary from 0.29 to 7.8 ppm, averaging at 1.66 ppm with a CoV of 53.61%.


Cenozoic rocks

The CoV% for these rocks is less than 100%, signifying their normal distribution, except the K-value for the Miocene sediments, which have CoV value of 113.75%. The K values recorded within certain sedimentary rock units, such as the Malha Formation, are associated with their proximity to granitic rocks. Radioactivity in Wadi sediments increases along two sections adjacent to the younger granites. This rise is attributed to uranium leaching from the surrounding rock unit, showcasing large radioactive anomalies at the wadi mouth. eU values range from 0.45 to 7.35 ppm, averaging at 2.21 ppm with a CoV of 45.70%, while K values vary from 0.01 to 3.36% with a CoV of 58.86%. Additionally, eTh values fluctuate from 0.34 to 18.96 ppm, with an average of 5.72 ppm and a CoV of 62.58%.

  1. (C)

    Alteration F-parameter

The F-parameter map (Fig. 8) highlights areas within the magenta contour line, exhibiting F-parameter values greater than 1.2, suggesting potential alteration zones primarily over younger and older granites.

Fig. 8
figure 8

Alteration F-parameter contour map, Gabal Umm Tinassib and its surrounding area, North Eastern Desert, Egypt

Full size image

An integrated map (Fig. 9) combines CEM and F-parameter techniques to delineate alteration zones, facilitating the identification of areas with significant mineralization. This combined approach validates high-priority mineralization zones, confirming zones identified by both techniques as high priorities. The identified significant alteration and mineralization zones align in the NNW–SSE, NE–SW, NW–SE and E–W directions. Among these trends, The NNW–SSE and NE–SW structural lineaments are regarded as the most crucial in the study area from the perspective Remote Sensing (RS) and Airborne Gamma-ray Spectrometric (AGS).

Fig. 9
figure 9

The integration map illustrates the high priority of mineralization based on CEM and the alteration F-parameter, Gabal Umm Tinassib and its surrounding area, North Eastern Desert, Egypt

Full size image

5 Conclusions

The analysis of Remote Sensing (RS) and airborne gamma-ray spectrometric (AGS) data in this study yielded insightful conclusions. Employing False Color Composite (FCC) with the best three bands from Optimum Index Factor (OIF), Principal Component Analysis (PCA) for extracting two highly informative datasets, and employing two band ratios facilitated accurate geologic mapping. The application of these band ratios notably revealed identical alteration locations on both younger and older granite basement rocks, while the Constrained Energy Mineralization (CEM) technique effectively pinpointed alterations across these strata.

High radioelement concentrations correlated significantly with outcrops of younger and older granites. In contrast, the lowest values were consistently observed over undifferentiated upper Cretaceous sediments, such as the Abu Rimth Formation, Galala Formation, and specific sections of Quaternary sediments. The composite eU image clearly depicted zones with high eU anomalies, appearing as bright white spots, that are identified as potential exploration areas for subsequent geochemical and ground geophysical studies. Statistical findings showcased a wide range of radioactivity in the region, with TC values ranging from 1.3 to 19.3 Ur, K values from 0.2 to 3.6%, eU values from 0.09 to 11.6 ppm, and eTh values from 1.1 to 30.0 ppm. Across all rock units in the research region, a normal distribution of the three radio-elements was observed (CoV% less than 100%), except for K in the Malha Formation, which exhibited a CoV value greater than 100%. This is attributed to the high heterogeneity of this rock unit, stemming from its diverse composition and proximity to the basement rocks. Notably, the alteration F-parameter demonstrated its highest value consistently over both younger and older granites, affirming the significant similarity in assumed alteration zones derived from both RS and AGS data.