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Petrochemical Characteristics and Age of Rare Metal (Ta-Nb) Mineralization in Precambrian Pegmatites, Komu, Nigeria
No full textThe Precambrian pegmatites of Komu area intrude semi discordantly older rock types, such as biotite gneiss, amphibolites and pelitic schists. The pegmatites occur as near flat lying bodies. This study aims at elucidating the geological setting, petrography, geochemical features and age of mineralization of these pegmatite bodies, with a view to classifying them and knowing their economic potential. The petrographic analysis shows that the pegmatite samples contain mainly quartz (35%), plagioclase (15%), microcline (10%) and muscovite (12%) with accessories like tourmaline, tantalum, niobium and illmeno-rutiles. Geochemical analysis of the muscovites extracted from pegmatites show that these rocks are enriched in silica (>60%) and Al2O3 (>12%) and depleted in Fe2O3, MgO and TiO2. Trace element analysis shows that the pegmatites contain rare metals with moderately high Ta, Nb, Sn, Rb, Li and Cs values and depleted in Ti, Ba and Zr. Elemental ratios indicate low ratios of K/Cs, Th/U and K/Rb. Variation plots of Ta/(Ta+Nb) versus Mn/ (Mn+Fe) show that the pegmatites plot in the complex (beryl subtype) field. The Na/K versus Sn, Nb, Rb variation plots show that the pegmatites of Komu area are mineralized and compare favourably with those of other mineralized pegma-tite areas like Egbe and Ijero in southwestern Nigeria. The variation plots of Ta versus K/Cs, and Ta/W versus Cs, also confirm rare metal mineralization of Komu pegmatites, which plot over the mineralized line of Beus and Gordiyenko. The K/Rb versus Rb, Cs and Sn plots indicate low K/Rb ratios indicating moderate differentiation. The Rare Earth Elements (REE) show high heavy REE values and lower light REE values with prominent positive Ce anomaly and negative Eu anomaly from normalized chondrite plots. K/Ar dating of the age of mineralization of muscovites extracted from the pegmatite yielded late Pan-African ages between 502.8±13Ma and 514.5±13.2Ma. This period represents the cooling ages of the muscovite and suggests that the pegmatites may not be cogenetic with the surrounding Pan-African granitoids
Petrochemical Characteristics and Ageof Rare Metal (Ta-Nb) Mineralization in Precambrian Pegmatites, Komu,Nigeria
Get PDFThe Precambrian pegmatites of Komu area intrude semi discordantly older rock types, such as biotite gneiss,amphibolites and pelitic schists. The pegmatites occur as near flat lying bodies. This study aims at elucidating thegeological setting. petrograply, geochemical features and age of mineralization of these pegmatite bodies, with a viewto classifying them and knowing their economic potential. The petrographiic analysis shows that the pegmatite samplescontain mainly quartz (3 59%), plagioclase (15%), microcline (10%) and muscovite (12%) with accessories like tourmaline,tantalum, niobium and illmeno-rutiles. Geochemical analysis of the muscovites extracted from pegmatites show thatthese rocks are enriched in silica (>60%) and A2O3 (>12%) and depleted in Fe2O3, MgO and TIO2, Trace element analysisshows that the pegmatites contain rare metals with moderately high Ta, Nb, Sn, Rb, Li and Cs values and depleted in Ti,Ba and Zr. Elemental ratios indicate low ratios of K/Cs, Th/U and K/Rb. Variation plots of Ta/(Ta+Nb) versus Mn(Mn+Fe) show that the pegmatites plot in the complex (beryl subtype) field The Na/K versus Sn, Nb,Rb variation plotsshow that the pegmatites of Komu area are mineralized and compare favourably with those of other mineralized pegmatitc areas like Egbe and ljero in southwestern Nigeria. The variation plots of Ta versus K/Cs, and Ta/ W versus Cs, also confirm rare metal mineralization of Komu pegmatites, which plot over the mineralized line of Beus and Gordiyenko, TheK/Rb versus Rb,Cs and Sn plots indicate low K/Rb ratios indicating moderate differentiation. The Rare Earh Elements(REE) show high heavy REE values and lower light REE values with prominent positive Ce anomaly and negative Euanomaly from nonalized chondrite plos. K/Ar dating of the age of mineralization of muscovites extracted from thepegmatite yilded late Pan-African ages between 502.8 ± 13Ma and 514.54 ±13.2Ma. This period represents the coolingages of the muscovite and suggests that the pegmatites may not be cogenetic with the surrounding Pan-Africangranitoids
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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