GROUND GEOPHYSICAL PROSPECTING ON ZOG EL-BOHAR AREA, SOUTHWEST OF QUSEIR, EASTERN DESERT, EGYPT
Islam Mohammed Hosain Khalel;
Abstract
Zog El-Bohar area is a part of the Central Eastern Desert of Egypt and located about 15 Km to the Southwest of Quseir Town on the Red Sea Coast betwen latitudes 25o 57′ 49.29″ N & 25o 58′ 27.91″ N and longitudes 34o 17′ 25.92″ E & 34o 18′ 11.31″ E. Topographically, the study area is relatively not rugged with low to moderate hills of 79m to 123m above Sea level.
Field observations proved the simple geology of the area since it consists of metagabbro, younger granite, Duwi Formation, Dakhla shales, Tarawan Formation and Quaternary sediments. The Precambrian rocks in the area are represented mainly by the metagabbro and younger granites. The phosphates of the Duwi Formation conformably overlie the Quseir variegated shale and underlie the Dakhla Shale. A carbonate bed equivalent to the Tarawan Chalk overlies the Dakhla Formation in this area. The Quaternary sediments bound the different rock units in the study area and fill the main wadies.
Ground spectrometric and magnetic surveys were carried out along 26 parallel profiles striking to the N-S, with line spacing 50 m and station separation 25m along traverse lines. Besides, seven vertical electrical sounds (VES) using shlumberger array and four 2-D Earth resistivity imaging (2-D ERI) profiles using Wenner array were executed in the study area.
The ground gamma-ray spectrometric data of the area involves Total Count (T.C) in Ur, equivalent Uranium (eU) in ppm, equivalent Thorium (eTh) in ppm and Potassium (k) in %. The spectrometric measurements of this area recorded 52.6 Ur for Total Count, 51 ppm equivalent Uranium, 14 ppm equivalent Thorium (eTh) and 4.2 % for Potassium. The ratios of the three radioelements are calculated and mapped as (eU/eTh), (eU/K) and (eTh/K). It is found that the high radiometric levels are mainly attributed to the phosphates of the Duwi Formation and more or less the granites whereas, the low radiometric values are in accordance with the metagabbro and wadi sediments. The data were analyzed and processed using effective analysis techniques such as factor analysis, ternary composite imaging as well as the statistical treatments.
The Factor analysis technique reduced the seven radiometric variables into three principle components PC1, PC2 and PC3 to form three factors with different contributions of each variable in these factors. The correlation matrix shows that the total count (T.C.) is highly correlated positively with eU (62.3 %) and weakly correlated with eTh, K, eU/eTh, eU/K, eTh/K as 37.5, 32.6, 37.4, 45.5 and 12% respectively. The equivalent uranium (eU) is highly correlated with their ratios; eU/eTh and eU/K as 74 and 77 % and moderately correlated with eTh/K with 50 %. It is observed that eU is reversely correlated with the K and eTh where they recorded -51 and -33 % respectively. The eU/K is positively correlated with eU/eTh where the ratio reaches to 66 %. Manual and automatic matching of the three factors with each other enables the interpreter to recognize five interpreted litho-radiometric units which are highly correlated with the surface geologic units of the area.
Ternary composite images are used to provide a view of the overall pattern of the three radioactive elements which are related to various lithologies. Therefore, this technique assisted in delineating and recognizing the radioactive lithologic units in the area. The quantitative interpretation of the spectrometric data in the present area is discussed on the light of these two techniques and the statistical treatment of the data.
Statistical computation was applied to the original spectrometric data without applying any transformation. In the present work, the spectrometric data were statistically examined to identify and outline significant eU anomalies on the basis of exceeding two and three standard deviation levels above the mean for single points, which show local enrichment of eU over eTh and K % in terms of statistically high eU/eTh and eU/K % values. This type of statistical treatment of data provides a mean of searching for areas showing high uranium anomaly content within each unit. Accordingly, a local point anomaly map is generated showing the location and magnitude of deviation from the mean for eU, eTh, eU/eTh and eU/K. It also shows the anomalies that their values exceed (X + 2S) and (X + 3S). It is observed from the map that, there are two zones of uranium occurrences in the area under consideration are related to the Duwi Formation of Phosphatic composition. Nevertheless, there are another radiometric anomalies are attributed to the eTh which have values exceeding than X+2S and X+3S related generally to the granitic rocks.
The ground magnetic survey provides total magnetic intensity map which in turn reduced to the North magnetic pole and hence generation the RTP map of the area. The RTP map transformed to frequency domain in such a way to separate the deep seated (regional component) from the near surface (residual component) magnetic sources. It is found from the application of filtering techniques that, the shallow magnetic sources are at depth about 92m, while that of deep-seated are at 148m. The RTP data also, processed and analyzed with some advanced techniques involving horizontal gradient, 3-D Euler Deconvolution and the source parameter index (SPI).
Field observations proved the simple geology of the area since it consists of metagabbro, younger granite, Duwi Formation, Dakhla shales, Tarawan Formation and Quaternary sediments. The Precambrian rocks in the area are represented mainly by the metagabbro and younger granites. The phosphates of the Duwi Formation conformably overlie the Quseir variegated shale and underlie the Dakhla Shale. A carbonate bed equivalent to the Tarawan Chalk overlies the Dakhla Formation in this area. The Quaternary sediments bound the different rock units in the study area and fill the main wadies.
Ground spectrometric and magnetic surveys were carried out along 26 parallel profiles striking to the N-S, with line spacing 50 m and station separation 25m along traverse lines. Besides, seven vertical electrical sounds (VES) using shlumberger array and four 2-D Earth resistivity imaging (2-D ERI) profiles using Wenner array were executed in the study area.
The ground gamma-ray spectrometric data of the area involves Total Count (T.C) in Ur, equivalent Uranium (eU) in ppm, equivalent Thorium (eTh) in ppm and Potassium (k) in %. The spectrometric measurements of this area recorded 52.6 Ur for Total Count, 51 ppm equivalent Uranium, 14 ppm equivalent Thorium (eTh) and 4.2 % for Potassium. The ratios of the three radioelements are calculated and mapped as (eU/eTh), (eU/K) and (eTh/K). It is found that the high radiometric levels are mainly attributed to the phosphates of the Duwi Formation and more or less the granites whereas, the low radiometric values are in accordance with the metagabbro and wadi sediments. The data were analyzed and processed using effective analysis techniques such as factor analysis, ternary composite imaging as well as the statistical treatments.
The Factor analysis technique reduced the seven radiometric variables into three principle components PC1, PC2 and PC3 to form three factors with different contributions of each variable in these factors. The correlation matrix shows that the total count (T.C.) is highly correlated positively with eU (62.3 %) and weakly correlated with eTh, K, eU/eTh, eU/K, eTh/K as 37.5, 32.6, 37.4, 45.5 and 12% respectively. The equivalent uranium (eU) is highly correlated with their ratios; eU/eTh and eU/K as 74 and 77 % and moderately correlated with eTh/K with 50 %. It is observed that eU is reversely correlated with the K and eTh where they recorded -51 and -33 % respectively. The eU/K is positively correlated with eU/eTh where the ratio reaches to 66 %. Manual and automatic matching of the three factors with each other enables the interpreter to recognize five interpreted litho-radiometric units which are highly correlated with the surface geologic units of the area.
Ternary composite images are used to provide a view of the overall pattern of the three radioactive elements which are related to various lithologies. Therefore, this technique assisted in delineating and recognizing the radioactive lithologic units in the area. The quantitative interpretation of the spectrometric data in the present area is discussed on the light of these two techniques and the statistical treatment of the data.
Statistical computation was applied to the original spectrometric data without applying any transformation. In the present work, the spectrometric data were statistically examined to identify and outline significant eU anomalies on the basis of exceeding two and three standard deviation levels above the mean for single points, which show local enrichment of eU over eTh and K % in terms of statistically high eU/eTh and eU/K % values. This type of statistical treatment of data provides a mean of searching for areas showing high uranium anomaly content within each unit. Accordingly, a local point anomaly map is generated showing the location and magnitude of deviation from the mean for eU, eTh, eU/eTh and eU/K. It also shows the anomalies that their values exceed (X + 2S) and (X + 3S). It is observed from the map that, there are two zones of uranium occurrences in the area under consideration are related to the Duwi Formation of Phosphatic composition. Nevertheless, there are another radiometric anomalies are attributed to the eTh which have values exceeding than X+2S and X+3S related generally to the granitic rocks.
The ground magnetic survey provides total magnetic intensity map which in turn reduced to the North magnetic pole and hence generation the RTP map of the area. The RTP map transformed to frequency domain in such a way to separate the deep seated (regional component) from the near surface (residual component) magnetic sources. It is found from the application of filtering techniques that, the shallow magnetic sources are at depth about 92m, while that of deep-seated are at 148m. The RTP data also, processed and analyzed with some advanced techniques involving horizontal gradient, 3-D Euler Deconvolution and the source parameter index (SPI).
Other data
| Title | GROUND GEOPHYSICAL PROSPECTING ON ZOG EL-BOHAR AREA, SOUTHWEST OF QUSEIR, EASTERN DESERT, EGYPT | Other Titles | استكشافات جيوفيزيائية أرضية تفصيلية على منطقة زج البهار، جنوب غرب القصير، الصحراء الشرقيه، مصر | Authors | Islam Mohammed Hosain Khalel | Issue Date | 2014 |
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