Geochemical and remote sensing integrated with satellite gravity data of Darhib and Atshan talc deposits, South Eastern Desert, Egypt

Abstract

The current contribution conducted new geochemical, remote sensing integrated with gravity detailed studies of talc deposits to identify the talc protolith as well as its extension, depth, and structures. There are two examined areas, distributed from north to south, Atshan and Darhib and both belong to the southern sector of the Egyptian Eastern Desert. They occur as individual lenses or pocket bodies in ultramafic-metavolcanics following NNW-SSE and E-W shear zones. Geochemically, among the investigated talc, Atshan samples have high contents of SiO₂ (av. 60.73 wt.%), and higher concentrations of transition elements such as Co (av. 53.92 ppm), Cr (781 ppm), Ni (av. 1303.6 ppm), V (av. 16.67 ppm), and Zn (av. 55.7 ppm). Notably, the examined talc deposits contain low contents of CaO (av. 0.32 wt.%), TiO₂ (av. 0.04 wt.%), SiO₂/MgO (av. 2.15), and Al₂O₃ (av. 0.72 wt.%), which is comparable with ophiolitic peridotite and forearc setting. False color composite (FCC), principal component analysis (PCA), minimum noise fraction (MNF), and band ratio (BR) have been used to distinguish talc deposits in the investigated areas. Two new proposed band ratios were created to separate talc deposits. FCC band ratios (2/4, 4/7, 6/5) and (4 + 3/5, 5/7, 2 + 1/3) have been derived to focus on talc deposits in two case studies, Atshan and Darhib areas. The application of regional, residual, horizontal gradient (HG), and analytical signal (AS) techniques to gravity data are used in interpreting the structural directions of the study area. The analysis of this technique displays several notable faults trending in NW-SE, NE-SW, NNW-SSE, and E-W directions. Two techniques of gravity depth calculation were applied in the study areas, namely source parameter image (SPI), and Euler deconvolution (EU). The analysis of these techniques reflects that the depth of subsurface sources ranges between 383 and 3560 m. Talc deposits may be attributed to greenschist facies metamorphism or to a magmatic solution that is (associated with granitic intrusions) interacted with the surrounding volcanic rocks forming metasomatic minerals.

Figure 1

(a) Location map of Atshan and Darhib areas, South Eastern Desert, Egypt (using Arc GIS 10.4 and ENVI 5.3. The acquisition date of Landsat-8 image: September 8, 2021, with path 173 and row 43. Source Landsat-8: http://earthexplorer.usgs.gov. (b) Detailed geologic map of Atshan area (using Adobe Illustrator program CS5); and (c) Detailed geologic map of Darhib area (using Adobe Illustrator program CS5).

Figure 2

Field photographs of Atshan and Darhib areas, South Eastern Desert, Egypt: (a,b) Pockets of talc deposits enclosed in ultramafic rocks; and in (c,d) metavolcanics.

Figure 3

Flowchart summarized the methodology of the current work.

Figure 4

Photomicrographs (by using polarizing microscope (Olympus X53)) of Atshan and Darhib areas, South Eastern Desert, Egypt: (a) Fine-grained talc (Tc) minerals occur as shreds in Atshan area, and (b) abundance of opaque minerals (iron oxides) in Darhib area.

Figure 5

Whole rock diagrams (by using Coreldrow program version 2012): (a) Al₂O₃ of the examined samples are compared to forearc, Pan-African serpentinites and others; (b) Al₂O₃ vs. CaO; (c) Trace elements normalized to primitive mantle; (d) SiO₂/MgO vs. Al₂O₃ binary diagram; and (e) CaO–Al₂O₃–MgO diagram.

Figure 6

(a) Landsat-8 7, 5, 3 in RGB false color composite of Atshan area, and (b) Landsat-8 7, 5, 3 in RGB false color composite of Darhib area by using Arc GIS 10.4 and ENVI 5.3.

Figure 7

The FCC of principal component analysis: (a) Landsat-8 (RGB-PC1, PC2, PC3), (b) Landsat-8 (RGB-PC4, PC2, PC1) of Atshan area. (c) Landsat-8 (RGB-PC3, PC2, PC1), and (d) Landsat-8 (RGB-PC4, PC3, PC1) of Darhib area by using Arc GIS 10.4 and ENVI 5.3.

Figure 8

The FCC of Minimum noise fraction transform: (a) Landsat-8 (RGB-MNF3, MNF1, MNF2), (b) Landsat-8 (RGB-MNF4, MNF1, MNF3) of Atshan area. (c) Landsat-8 (RGB-MNF3, MNF1, MNF2), and (d) Landsat-8 (RGB-MNF4, MNF1, MNF3) of Darhib area by using Arc GIS 10.4 and ENVI 5.3.

Figure 9

(a) OLI RGB color ratio image (6/7, 4/2 and 6/5) of Atshan area, and (b) OLI RGB color ratio image (5/4, 6/7 and 7/5) of Atshan area by using Arc GIS 10.4 and ENVI 5.3.

Figure 10

(a) OLI RGB color ratio image (2/4, 4/7 and 6/5) of Atshan area, (b) OLI RGB color ratio image (2/4, 4/7& 6/5) of Darhib area, and (c) OLI RGB color ratio image (4 + 3/5, 5/7, 2 + 1/3) of Atshan area by using Arc GIS 10.4 and ENVI 5.3.

Figure 11

(a) Regional anomaly map of the study area displays regional structural lineaments; and (b) Residual anomaly map of the study area displays shallow structural lineaments (by using Oasis Montaj software version 8.3).

Figure 12

(a) Analytical signal anomaly map of the study area; (b) Horizontal gradient anomaly map of the study areas (by using Oasis Montaj software version 8.3).

Figure 13

(a) Source parameter imaging map of the study area, (b) 3D Euler deconvolution of the study area for structural index (by using Oasis Montaj software version 8.3).

Figure 14

(a) SiO₂–Fe₂O₃–(MgO + CaO) ternary diagram. Fields of serpentinites, silica- carbonate, carbonate-rich, and silica-rich rocks^,,,; and (b) H₂O-SiO₂-MgO ternary diagram (by using Coreldrow program version 2012).