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Mineralogy of Egyptian Bentonitic Clays II: Geologic Origin
- Mohamed A. Agha, Ray E. Ferrell, George F. Hart, Mohamed S. Abu El Ghar, A. Abdel-Motelib
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- Journal:
- Clays and Clay Minerals / Volume 61 / Issue 6 / December 2013
- Published online by Cambridge University Press:
- 01 January 2024, pp. 551-565
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Reconstructing the origin of bentonitic clays is often a challenging and rather complicated undertaking, but the analysis of certain predictor clay minerals is proving to be an excellent method to simplify this process. The goal of the present investigation was to use abundance changes of five X-ray diffraction (XRD) predictor minerals to determine the relative contributions of weathering and parent-rock changes to the origin of clay minerals in Egyptian bentonitic clays as the test case. The XRD predictor minerals, selected in an earlier discriminant function analysis of quantitative abundances of 14 minerals, provided a simpler approach to the interpretation of clay-mineral origins because they are the minerals that were most responsible for statistically significant differences among the samples. Changes in mineral composition were basically a function of parent-rock lithology, drainage, and climate interactions. A Paleo-Climate Index (CI; the ratio of coarsely crystalline kaolinite to Fe-rich smectite), and a Parent-Rock Index (PI; the ratio of the illitic phases and quartz abundances to pure smectite) were established to track the paleo-climate and parent-rock changes, respectively. Low CI values indicated that a long, seasonally dry climate prevailed during the Middle Eocene, uppermost Eocene, Lower Miocene, and Upper Pliocene bentonitic clay deposition. Lowermost Upper Eocene and the Middle Miocene bentonitic clays were produced when a wet climate prevailed throughout the year. Moderate to high PI values suggested derivation of the clays from the acidic basement crystalline rocks at Uweinat-Bir Safsaf uplift and Lower Paleogene shales during the Middle Eocene and lowermost Upper Eocene. The youngest Upper Eocene and Lower Miocene materials contained abundant Fe-smectite and low PIs indicating derivation from tholeiitic basalts. Diagenetic and sedimentary segregation modifications were not apparent. Direct evidence for in situ derivation from volcanic precursor materials was lacking in general, but volcanic eruptions were common in the region. The minerals in the Egyptian bentonitic clays formed as weathering products on land and have been transported by north-flowing streams and rivers to the sites of accumulation.
Mineralogy of Egyptian Bentonitic Clays I: Discriminant Function Analysis
- Mohamed Agha, Ray E. Ferrell, George F. Hart
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- Journal:
- Clays and Clay Minerals / Volume 60 / Issue 4 / August 2012
- Published online by Cambridge University Press:
- 01 January 2024, pp. 387-404
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The purpose of the present investigation was to apply a discriminant function analysis (DFA) to quantitative mineralogical data from 124 Paleogene and Neogene bentonitic clays from the northern Western Desert of Egypt in order to establish an objective procedure for grouping the samples at three distinctly recognizable, but partially overlapping, levels of classification. These levels were province or geographic region, geologic age, and quarry. Quantitative mineralogical data were obtained by means of X-ray diffraction procedures employing least-squares fitting of simulated and standard mineral patterns with those from the laboratory. All data were transformed by a log-ratio procedure prior to the DFA. Fe-rich smectite (Feoct-1.4 a.p.f.u.), coarsely crystalline kaolinite, Fe-poor I-S (random with 60% S layers), quartz, and illite were the most important discriminator minerals. S-moderate I-S (random with 70% S), S-rich I-S (random with 80% S), two varieties of finely crystalline kaolinite, feldspar, and amorphous matter were also present. Calcite and gypsum were present in some samples. The median wt.% values for Fe-rich smectite, coarsely crystalline kaolinite, Fe-poor I-S, quartz, and illite in all samples were 16.6, 16.0, 15.2, 4.2, and 3.7, respectively. Abundances of quartz and feldspar have a good positive correlation, and finely crystalline kaolinite and Fe-rich smectite are negatively correlated. Other specific mineral associations are difficult to interpret visually because of the numbers of classes and variables employed in the investigation; however, DFA was successful in identifying statistically significant differences amongst the groups.
At the province level, the back-classification of the samples was successful 92% of the time at the highest probability level, or 100% if the first plus second probability results were utilized. For samples of the same age, 80% of the first-choice assignments were correct and >90% were correct when the second choice was included. At the quarry level, the predictability rate ranged from 76 to >90%. Using both probability results, only seven of the samples were misclassified. In a blind test of quarry samples, the DFA assignment was 80% correct. These tests confirm the objective reliability of class assignments based on DFA. Results based on this data set can be used to classify new samples in future geologic interpretations and economic exploitation of the deposits in the region.
Experience with balloon pulmonary valvuloplasty and predictors of outcome: a ten-year study
- Sonia A. El-Saeidi, Hala S. Hamza, Hala M. Agha, Mohammed M. Soliman, Wael A. Attia, Rania El-Kaffas, Faten Abdel-Aziz, Osama Abdel-Aziz, Sahar Shaker, Amira Esmat, Rasha Ammar, Aya Fattouh, Khalid Mohi-eldin, Amal M. El-Sisi
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- Journal:
- Cardiology in the Young / Volume 30 / Issue 4 / April 2020
- Published online by Cambridge University Press:
- 19 February 2020, pp. 482-488
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Background:
Balloon pulmonary valvuloplasty is the treatment of choice for patients with moderate to severe pulmonary valve stenosis.
Methods:An observational retrospective cross-sectional study including neonates, small infants, and children who underwent balloon pulmonary valvuloplasty in the period from 2007 to 2016 in the cardiac catheterisation unit of the paediatric cardiology department in Cairo University. Multivariable models were built to report the predictors of the outcome of balloon pulmonary valvuloplasty and its complications.
Results:A total of 1200 patients were included in the study and divided according to age into 3 groups: neonates and early infants (n = 282), infants (n = 362), and children (n = 556). Procedural success, defined as a drop pressure gradient across the pulmonary valve to less than or equal to 50% of the baseline measurements, was achieved in 82.7% of the patients. Multivariate analysis revealed that only infundibular pulmonary stenosis (p value 0.032), supravalvular in association with valvular pulmonary stenosis (p value <0.001), and pulmonary valve diameter by angiogram (p value <0.001) were significant predictors of success. The presence of supravalvular in association with valvular pulmonary stenosis (p value <0.001) was associated with a lower weight (p value 0.007) and higher right ventricular pressure before the intervention (p value <0.001), and a minor immediate drop in the pressure gradient post-intervention (p value <0.001) was found to be the most significant predictor of the occurrence of complications.
Conclusion:The absence of infundibular and supravalvular stenosis and a large pulmonary valve diameter were the most significant predictors of success.