An Overview on the Classification and Tectonic Setting of Neoproterozoic Granites of the Nubian Shield, Eastern Desert, Egypt

Granites constitute the main rock components of the Earth’s continental crust, which suggested to be formed in variable geodynamics environments. The different types of granitic rocks, their compositional characteristics, tectonic settings and magma sources are outlined. Mineralogical classification of granites includes four rock types: tonalites, granodiorites, granite (monzogranite and syenogranites) and alkali-feldspar granites. Alphabetical classification subdivided granites into: I-type, S-type, A-type and M-type granites. Moreover, formation of granitic magmas requires distinctive geodynamic settings such as: volcanic arc granite (Cordilleran); collision-related granites (leucogranites); intra-plate and ocean ridge granites. The Eastern Desert of Egypt (ED) forms the northern part of Nubian Shield. Both older and younger granites are widely exposed in the ED. Old granites (OG) comprise tonalites and granodiorites of syn- to late-orogenic granitoid assemblages. They are calcalkaline, I-type, metaluminous and display island arc tectonic setting. Younger granites (YG) on the other hand, include granites, alkali-feldspar granites and minor granodiorites. They are of I- and A-type granites and of post-orogenic to anorogenic tectonic settings. The majority of the YG are alkaline, A-type granite and of within-plate tectonic setting (WPG). The A-type granites are subdivided into: A2-type postorogenic granites and A1-type anorogenic granites. Granite magma genesis involves: (a) fractional crystallization of mafic mantle-derived magmas; (b) anatexis or assimilation of old, upper crustal rocks (c) re - melting of juvenile mafic mantle – derived rocks underplating the continental crust. Generally, older I-type granitoids were interpreted to result from melting of mafic crust and dated at approximately 760–650 Ma, whereas younger granites suggested to be formed as a result of partial melting of a juvenile Neoproterozoic mantle source. Moreover, they formed from anatectic melts of various crustal sources that emplaced between 600 and 475 Ma.

Exploration for Fe-Mn Oxides Using Geochemical Signatures in Soil: A Case Study of Part of Northwestern Nigeria

Part of northwestern Nigeria was investigated with the aim of delineating concealed mineralization using geochemical signatures in soils. To achieve this, 30 selected soil samples were analysed geochemically. The result of the elemental analysis was subjected to Principal Component Analysis (PCA) and isograde plotting, while selected elements were correlated. From the geochemical result, most of the analysed elements have anomalous value in the southern part of the area, while the least values are in the southwestern. From the PCA analysis, six factor groups were distinct. The factor groups were interpreted geochemical to fingerprint mineralization in the area. The result of correlation analysis shows that Fe is negatively correlated with most of the correlated elements. The study concluded that the central part of the study area is mineralized with both manganite and goethite. In addition, manganese mineralization is indicated by elemental association: Zn+As+Be+Bi+Co+Nb+Ni+CsP+Al+Ca+Cd+Li+K, while iron mineralization is indicated with Zr+Th+Pd+Mo+V+Sn+Cr+Ce+InSc+P+Pb association.