Sources of some heavy minerals and their association with gold-bearing stream sediments in the Gagare Drainage Basin, Wonaka Schist belt northwestern Nigeria

No Abstract.

Mineralization Characterization of Psammitic Rocks in Efon-Alaaye and Environs using Remote Sensing and Field Studies

This paper analyses remotely sensed data over a part of the Psammitic Rocks in Efon-Alaaye and Environs to elucidate its geology and structural framework as well as delineate the potential zones of mineralization. The study area belongs to the Precambrian Basement Complex terrain of Southwestern Nigeria and lies within the eastern unit of the Ilesha schist belt. The lithologic units comprise schistose quartzites, quartz schists, quartz-mica-schists, and granitic gneisses. Landsat 8 satellite imagery and Shuttle Radar Topography Mission imagery (SRTM), both of path 190 and row 055, were used for the purpose of this study. A total of 138 lineaments of total length of 147.948 Km, were automatically extracted from both data. Rose diagram showed that the lineaments are bi-directional, with major lineaments trending NE-SW, E-W and the subsidiary ones in the NW-SE direction. These lineaments are mostly mapped on the schistose quartzites. Also, N-S trending faults were mapped from the Digital Elevation Model map generated from the SRTM data which was confirmed to be reverse fault based on field studies. The mineral alteration map generated revealed signatures of gold, iron oxides and silica minerals, while the mineralization potential map was done with reference to established geological settings of the area in conjunction with the structural elements such as folds, faults, joints and fractures mapped and measured on the field. These structures are typical of gold mineralization and associated metallic minerals in the Ilesha schist belt. This study also confirmed that mineralization in the study area is structurally controlled and type of mineralization is epigenetic in nature as a result of favorable ground preparation.

Pedogeochemical survey for uranium mineralization in parts of Igarra Schist belt, Southwestern Nigeria

Pedogeochemical survey for uranium mineralization in Dagbala-Atte district, Igarra schist belt, southwestern Nigeria was carried out. The concentrations of As, Au, Fe, Mn, Mo, Ni, Pb, Se, U and V in the residual soils were subjected to univariate and multivariate analyses and plotted on geochemical distribution maps to delineate possible U-mineralization areas. Histograms and box plots showed the elements are log-normally distributed with threshold values of 9.47 %, 10.8, 1589, 2.98, 45.6, 31.0, 0.68, 8.59, 122 ppm and 10.6 ppb, respectively for Fe, As, Mn, Mo, Ni, Pb, Se, U, V and Au. Correlation matrix revealed a strong correlation between U and each of Fe, Mo and Pb indicating close primary association among these four elements. Factor analysis revealed association of U, Mo and Pb implying possible occurrence of U in the granitic rocks of the area. Geochemical maps showed that the strongest U anomaly occurred in the northeastern part of the district that is underlain by granitic gneisses with numerous unmapable granite-pegmatite veins, which possibly are the host of the U mineralization. Copious geological study of these granite-pegmatite veins is recommended. Keywords: Anomaly, box plots, correlation matrix, geochemical distribution map, uranium mineralization.

Geochemistry and Sr-Nd isotopic studies of Palaeoproterozoic (ca. 2.3 Ga) meta-lamprophyre from Rapuru area, Nellore Schist Belt, Southern India: Implication for back-arc basin magmatism and its relevance to the Columbia Supercontinent assembly

Present study reports two lamprophyre dykes from the Rapuru area along the margin of Eastern Dharwar Craton (EDC) and Nellore Schist Belt (NSB). The Rapuru lamprophyre (RL) dykes are situated along southern extension of the Prakassam Alkaline Province (PAP). The Rapuru lamprophyre (RL) dykes are deformed yet preserves the porphyritic-panidiomorphic texture with mica phenocrysts and amphibole and feldspars in the groundmass. The geochemically RL have low Mg# (0.28-0.37), Ni (30 ppm - 60 ppm) and Cr (119 ppm - 228 ppm) concentration indicates their evolved nature like other reported lamprophyre from PAP and EDC. Which is a further supported Sr-Nd isotopic ratios shows affinity towards MORB-OIB like signature and juvenile magmatic nature. The RL seems to have inherited by two major influences, namely, primary source region: which is geochemically juvenile similar to the compositional field of enriched-MORB, and the continental lithosphere. Such magmas are known to have formed in the back-arc-basin environment. The initial 87 Sr/ 86 Sr ratio (∼0.7012-0.7045) and initial εNd (3.13 to 7.93) ratios are in line with the Back-Arc Basin Basalts (BABB) recorded in other parts of the world. The field observation and bulk-rock Sr-Nd radiogenic isotope in the present study support Palaeoproterozoic nature of RL. This concurrence of juvenile radiogenic isotopes and fluid-related trace element compositions apparently suggest dehydration of a subducted slab triggered metasomatism of the overlying mantle wedge in subduction related geodynamic setting. Such intrusive lamprophyre rocks of the older ages are limited in India as well as other part of the world. The rocks of 2.1 and 1.8 Ga, are widely considered to be the ages of initial accretion and final breakup of an erstwhile Columbia Supercontinent assembly. We argue that the RLs were formed in Palaeoproterozoic period during the waxing stages of the Columbia Supercontinent Assembly in BAB environment; most probably due to low degree of partial melting of asthenosphere and lithospheric interaction by the introduction of influx of subduction component into arc-back arc basin system.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5598266