Monitoring rock desert formation caused by two different origins(ice-snow melting and drying)through remote sensing is crucial to our understanding of the interaction between the underlying surface of different rock d...Monitoring rock desert formation caused by two different origins(ice-snow melting and drying)through remote sensing is crucial to our understanding of the interaction between the underlying surface of different rock desert and land-atmosphere types,as well as the relationship between bare land and soil erosion.A number of achievements have been made in remote sensing monitoring of desert areas,but there is a lack of accurate classification and remote sensing identification of rock desert types based on formation mechanism.In this study,the north and south sides of the eastern Kunlun Mountains in the northern part of the Qinghai-Tibet Plateau of China were taken as the study areas.Landsat operational landscape imager,digital elevation model,and precipitation and temperature grid data were used as data sources.By identifying the bare areas based on the normalized difference vegetation index(NDVI),we used the multi-element fusion method of contours,isotherms,and isohyets to identify the rock desert types in the ice-snow melting and dry areas.The results showed that:(1)the rock desert areas identified by remote sensing based on topographic and meteorological elements were highly accurate,with an overall accuracy of 88.45%and kappa coefficient of 0.77.The multi-element fusion method of contours,isotherms,and isohyets could effectively identify the rock desert types in the ice-snow melting and dry areas;(2)the optimal segmentation range of the ice-snow melting and dry areas was 3600 m contour,-2°C-2°C isotherms,and 100-130 mm isohyets.The areas with elevation less than 3600 m,annual average temperature higher than 2°C,and average annual precipitation less than 100 mm were rock desert in the dry areas.The range of-2°C-2°C isotherms and 100-130 mm isohyets was the transition area between the ice-snow melting and dry areas.The areas with elevation higher than 3600 m,annual average temperature less than-2°C,and average annual precipitation higher than 130 mm were rock desert in the ice-snow melting areas;and(3)the identification accuracy of the bare areas based on the NDVI method was better,specifically,the identification accuracy of plain bare areas was generally better than that of mountain bare areas.The remote sensing identification method considers not only the topographic factors that have great influence on the spatial distribution of the two types of rock desert areas,but also the meteorological factors,which can provide a scientific reference for the effective identification of the two types of rock desert areas.展开更多
This work refers to the characterization of the hydrochemistry of the southern part of the Eastern Desert in Egypt, on the basis of physico-chemical properties of groundwater occurring in the fractured Precambrian roc...This work refers to the characterization of the hydrochemistry of the southern part of the Eastern Desert in Egypt, on the basis of physico-chemical properties of groundwater occurring in the fractured Precambrian rocks inland and in sedimentary formations on the coastline of the Red Sea. Thirty-five groundwater samples have been collected from the study area for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater. Several methods were used to interpret the hydrochemical data, i.e. graphical methods, principal components analysis, ions exchanges indices and saturation indices of various minerals. The results show that the major ionic relationships are Na<sup>+</sup> > Ca<sup>2+</sup> > Mg<sup>2+</sup> and Cl<sup>-</sup> > > HCO<sup>3-</sup> and that groundwater chemical characteristics are controlled by natural geochemical processes but also, to a lesser extent, by anthropogenic activities. Natural minerals dissolution, ion exchanges and evaporation play a prominent role in the ion enrichment of groundwater. A comparison of groundwater quality in relation to WHO water quality standards proved that most of the water samples are not totally suitable for drinking water purpose.展开更多
Um-Gir and El-Atshan-II areas represent important structurally-controlled radioactive anomalies and have become promising areas for U exploration. The bostonite rocks represent the most promising rock unit in the two ...Um-Gir and El-Atshan-II areas represent important structurally-controlled radioactive anomalies and have become promising areas for U exploration. The bostonite rocks represent the most promising rock unit in the two studied areas. They form the most promising rocks due to their high radioactivity and, hence uranium mineralization. Anisotropy of magnetic susceptibility (AMS) measurements was carried out for Um-Gir and El-Atshan-II bostonite rocks. The AMS results show that the mean magnitude of magnetic susceptibilities is low, of the order of 10<sup>-5</sup> S.I. units. Consequently, the bostonite rocks of the two areas are considered as non-magnetic, reflecting the presence of hematite as the main ferromagnetic mineral. These results are in agreement with the measurements of initial remnant magnetization (NRM) and the results of isothermal remnant magnetization (IRM) for the two areas. Besides, the results of magnetic anisotropy degree (<em>P</em><sup><em>J</em></sup>), refer to and concluded that the magnetic fabric of bostonite of two the areas has secondary fabric. AMS results clearly show the differences between the bostonite dyke of Um-Gir and Bostonite sill of El Atshan-II. The lineation (<em>P</em><sub><em>1</em></sub>) > foliation (<em>P</em><sub><em>3</em></sub>), and the negative values of the ellipsoid shape (<em>T</em>) of Um-Gir bostonite reflect clearly magnetic lineation (prolate ellipsoid). However, in El Atshan-II, (<em>P</em><sub><em>3</em></sub> > <em>P</em><sub><em>1</em></sub>), the values of <em>T</em> are positive, which indicate the predominance of magnetic foliation (oblate ellipsoid) over lineation. Furthermore, the foliation planes of the bostonite dyke of Um-Gir possess a shallow to moderate inclination and a nearly N-S direction, while, the foliation planes of the bostonite sill of El-Atshan-II show a shallow to moderate inclination and a NNE direction. Finally, the AMS method is a powerful tool for detecting the structures that affect the bostonite rocks of the two studied areas.展开更多
Two brecciated shear zones (NNW-SSE) are found crosscutting cataclastic rocks. The cataclastic rocks (3.0 km2) occupy the core of the granitic pluton and enclose a roof pendant of mafic-ultramafic rocks. The NNW-SSE-e...Two brecciated shear zones (NNW-SSE) are found crosscutting cataclastic rocks. The cataclastic rocks (3.0 km2) occupy the core of the granitic pluton and enclose a roof pendant of mafic-ultramafic rocks. The NNW-SSE-extending lamprophyre dykes vary in thickness from 0.5 m to 1 m and up to 800 m long, cutting the cataclastic rocks and are composed mainly of plagioclases, amphiboles, relics of pyroxenes and K-feldspar phenocrysts embedded in fine-grained groundmass. They are characterized as being peraluminous, calc-alkaline in composition (chemical trap) and enriched in calcite, sulfide and P2O5. The lamprophyres were affected by hydrothermal alteration (chlorite-carbonate alteration) while the cataclastic rocks were affected by diagenetic alteration (K-feldspar-albite alteration). Uranium mineralization is the product of hydrothermal events and has been investigated by X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), involving primary uranium minerals (U3O8) and secondary uranium minerals (uranophane and beta-uranophane, kasolite, torbernite, autonite and meta-autonite) in addition to U- bearing minerals (astrocyanite, betafite and fergusonite). The presence of different mineral parageneses associated with clay minerals indicates that the lamprophyres were subjected to acidic and alkaline mineralizing solutions. Moreover, the U-Zr/U, U-Ce/U values show negative correlations, confirming U-enrichment in both cataclastic rocks and shear zones while the Th-eU/eTh, Th-Zr/Th and Th-Ce/Th values show negative correlations, indicating that the U-bearing solutions are rich in Th in the cataclastic rocks only.展开更多
基金the Natural Science Foundation of Qinghai Province of China(2021-ZJ-905)the Second Qinghai-Tibet Plateau Scientific Expedition and Research Program of China(2019QZKK0606).
文摘Monitoring rock desert formation caused by two different origins(ice-snow melting and drying)through remote sensing is crucial to our understanding of the interaction between the underlying surface of different rock desert and land-atmosphere types,as well as the relationship between bare land and soil erosion.A number of achievements have been made in remote sensing monitoring of desert areas,but there is a lack of accurate classification and remote sensing identification of rock desert types based on formation mechanism.In this study,the north and south sides of the eastern Kunlun Mountains in the northern part of the Qinghai-Tibet Plateau of China were taken as the study areas.Landsat operational landscape imager,digital elevation model,and precipitation and temperature grid data were used as data sources.By identifying the bare areas based on the normalized difference vegetation index(NDVI),we used the multi-element fusion method of contours,isotherms,and isohyets to identify the rock desert types in the ice-snow melting and dry areas.The results showed that:(1)the rock desert areas identified by remote sensing based on topographic and meteorological elements were highly accurate,with an overall accuracy of 88.45%and kappa coefficient of 0.77.The multi-element fusion method of contours,isotherms,and isohyets could effectively identify the rock desert types in the ice-snow melting and dry areas;(2)the optimal segmentation range of the ice-snow melting and dry areas was 3600 m contour,-2°C-2°C isotherms,and 100-130 mm isohyets.The areas with elevation less than 3600 m,annual average temperature higher than 2°C,and average annual precipitation less than 100 mm were rock desert in the dry areas.The range of-2°C-2°C isotherms and 100-130 mm isohyets was the transition area between the ice-snow melting and dry areas.The areas with elevation higher than 3600 m,annual average temperature less than-2°C,and average annual precipitation higher than 130 mm were rock desert in the ice-snow melting areas;and(3)the identification accuracy of the bare areas based on the NDVI method was better,specifically,the identification accuracy of plain bare areas was generally better than that of mountain bare areas.The remote sensing identification method considers not only the topographic factors that have great influence on the spatial distribution of the two types of rock desert areas,but also the meteorological factors,which can provide a scientific reference for the effective identification of the two types of rock desert areas.
文摘This work refers to the characterization of the hydrochemistry of the southern part of the Eastern Desert in Egypt, on the basis of physico-chemical properties of groundwater occurring in the fractured Precambrian rocks inland and in sedimentary formations on the coastline of the Red Sea. Thirty-five groundwater samples have been collected from the study area for hydrochemical investigations to understand the sources of dissolved ions and assess the chemical quality of the groundwater. Several methods were used to interpret the hydrochemical data, i.e. graphical methods, principal components analysis, ions exchanges indices and saturation indices of various minerals. The results show that the major ionic relationships are Na<sup>+</sup> > Ca<sup>2+</sup> > Mg<sup>2+</sup> and Cl<sup>-</sup> > > HCO<sup>3-</sup> and that groundwater chemical characteristics are controlled by natural geochemical processes but also, to a lesser extent, by anthropogenic activities. Natural minerals dissolution, ion exchanges and evaporation play a prominent role in the ion enrichment of groundwater. A comparison of groundwater quality in relation to WHO water quality standards proved that most of the water samples are not totally suitable for drinking water purpose.
文摘Um-Gir and El-Atshan-II areas represent important structurally-controlled radioactive anomalies and have become promising areas for U exploration. The bostonite rocks represent the most promising rock unit in the two studied areas. They form the most promising rocks due to their high radioactivity and, hence uranium mineralization. Anisotropy of magnetic susceptibility (AMS) measurements was carried out for Um-Gir and El-Atshan-II bostonite rocks. The AMS results show that the mean magnitude of magnetic susceptibilities is low, of the order of 10<sup>-5</sup> S.I. units. Consequently, the bostonite rocks of the two areas are considered as non-magnetic, reflecting the presence of hematite as the main ferromagnetic mineral. These results are in agreement with the measurements of initial remnant magnetization (NRM) and the results of isothermal remnant magnetization (IRM) for the two areas. Besides, the results of magnetic anisotropy degree (<em>P</em><sup><em>J</em></sup>), refer to and concluded that the magnetic fabric of bostonite of two the areas has secondary fabric. AMS results clearly show the differences between the bostonite dyke of Um-Gir and Bostonite sill of El Atshan-II. The lineation (<em>P</em><sub><em>1</em></sub>) > foliation (<em>P</em><sub><em>3</em></sub>), and the negative values of the ellipsoid shape (<em>T</em>) of Um-Gir bostonite reflect clearly magnetic lineation (prolate ellipsoid). However, in El Atshan-II, (<em>P</em><sub><em>3</em></sub> > <em>P</em><sub><em>1</em></sub>), the values of <em>T</em> are positive, which indicate the predominance of magnetic foliation (oblate ellipsoid) over lineation. Furthermore, the foliation planes of the bostonite dyke of Um-Gir possess a shallow to moderate inclination and a nearly N-S direction, while, the foliation planes of the bostonite sill of El-Atshan-II show a shallow to moderate inclination and a NNE direction. Finally, the AMS method is a powerful tool for detecting the structures that affect the bostonite rocks of the two studied areas.
文摘Two brecciated shear zones (NNW-SSE) are found crosscutting cataclastic rocks. The cataclastic rocks (3.0 km2) occupy the core of the granitic pluton and enclose a roof pendant of mafic-ultramafic rocks. The NNW-SSE-extending lamprophyre dykes vary in thickness from 0.5 m to 1 m and up to 800 m long, cutting the cataclastic rocks and are composed mainly of plagioclases, amphiboles, relics of pyroxenes and K-feldspar phenocrysts embedded in fine-grained groundmass. They are characterized as being peraluminous, calc-alkaline in composition (chemical trap) and enriched in calcite, sulfide and P2O5. The lamprophyres were affected by hydrothermal alteration (chlorite-carbonate alteration) while the cataclastic rocks were affected by diagenetic alteration (K-feldspar-albite alteration). Uranium mineralization is the product of hydrothermal events and has been investigated by X-ray diffraction (XRD) and environmental scanning electron microscopy (ESEM), involving primary uranium minerals (U3O8) and secondary uranium minerals (uranophane and beta-uranophane, kasolite, torbernite, autonite and meta-autonite) in addition to U- bearing minerals (astrocyanite, betafite and fergusonite). The presence of different mineral parageneses associated with clay minerals indicates that the lamprophyres were subjected to acidic and alkaline mineralizing solutions. Moreover, the U-Zr/U, U-Ce/U values show negative correlations, confirming U-enrichment in both cataclastic rocks and shear zones while the Th-eU/eTh, Th-Zr/Th and Th-Ce/Th values show negative correlations, indicating that the U-bearing solutions are rich in Th in the cataclastic rocks only.
