petrography

Structural, Petrographical and Geochemical Characterization of Tin-Tantalum Bearing Pegmatites from Chessu Area, North Central, Nigeria (Published)

Granodiorite, medium grain granite gneiss, medium grain banded gneiss with pegmatite intrusion, comprise the Basement Complex rocks of Chessu. The primary geological structures that emerge from the Pan Africa ductile and brittle deformation stages are fold, strike slip fault, dextral shear plane and fractures in Chessu and environs.  Tin and tantalum containing pegmatites are found in the main E-W and NE-SW fault.  Field observation demonstrate NE-SW, NNE-SSW and N-S structural trend with dipping values ranging between 19^°-52^° in accordance with data collected, displayed on rose plots and equally supported by lineaments. In terms of petrography, medium grained banded gneiss, medium grain granite gneiss and granodiorite all contain quartz, plagioclase, biotite and muscovite. Pegmatite contains muscovite, biotite, quartz and orthoclase among other opaque minerals. The protoliths of the gneisses, which may be from granite are revealed by the geochemical data used on Middlemost plots (Na₂O + K₂O vs SiO₂), which suggest that the rocks are members of the granitoid family. The Harker’s variation Plots of SiO₂ vs Na₂O, K₂O, CaO, MgO, TiO₂, P₂O₅, reveals intense alteration and contamination during fractionation of the rock, as displayed by the scattered/non-linear trends.  The primitive mantle (spider plot) indicates the depletion of some compatible less mobile elements (Ti, Y, Zr and Sr) and enrichment of incompatible elements (Th, Rb, Nb, Ta, Sr and Pb), which reveal the mineralization potential in these incompatible elements. The enriched elements Th, Nb, Ta and Pb are used as the pathfinder elements for Tin and Tantalum mineralization in Chessu area.  The deformation processes and structures created in the latter phase of Pan Africa Orogenic event resulted in the pegmatite emplacement, this could infer a connection between the mineralizing fluid and the rocks. 

Keywords: Chessu, enrichment, geochemical, mineralization, petrography

Petrology and Petrochemistry of Basement Rocks in Ila Orangun Area, Southwestern Nigeria (Published)

From field studies, six (6) lithological units were identified to be common around the study area which includes quartzites, granites, granite gneiss, porphyritic granites, amphibolite and pegmatites. The results of petrographical analyses show the mineral assemblages of the various rock types in the area which include quartzites as containing quartz, biotite, muscovite and myrmekite. Granite gneiss contains quartz, biotite, orthoclase, myrmekite, microcline, nepheline, hornblende and plagioclase. Pegmatite contains quartz, myrmekite, plagioclase, hornblende, microcline and muscovites. Porphyritic granites were observed to contain quartz, biotite, microcline, orthoclase and tourmaline. Granite contains quartz, biotite, hornblende, plagioclase and orthoclase while Amphibolite schist contains quartz, biotite, hornblende and muscovites. For the purpose of this study twenty (20) pulverized rock samples were taken to the laboratory for geochemical analysis with their results used in the classification as well as suggest the geochemical attributes of the rocks. Geochemical results obtained and interpreted using various geochemical plots or discrimination plots all classified the rocks in the area as belonging to both the peralkaline metaluminous and peraluminous types. Results for the major oxides ratios produced for Na₂O/K₂O, Al₂O₃/Na₂O + CaO + K₂O and Na₂O + CaO + K₂O/Al₂O₃ show the excess of alumina, Al₂O₃ over the alkaline Na₂O +CaO +k₂O thus suggesting peraluminous rocks. While the excess of the alkali over the alumina suggests the peralkaline metaluminous rock type. The results of correlation coefficient show a perfect strong positive correlation which shows that they are of same geogenic sources while negative correlation coefficient values indicate a perfect weak negative correlation suggesting that they are of heterogeneous geogenic sources. The result of the factor analysis show the elemental association of the trace elements and heavy metals represented as variables in the statistical analysis. Hence, establishing the elemental association of Component 1 as consisting of Ag-As-Ba-Cd-Co, Component 2 as Cr-Cu-Ni, Component 3 as Pb-Rb, Component 4 as Zn-Fe-V and Component 5 as U-Mn. Component 1 suggest the possibilities of sulphide and gold mineralization. Component 2 suggesting pathfinder elements while Components 3, 4 and 5 suggest weathered or dispersed elements. Hence, the occurrence of heavy metallic minerals in the rocks will serve huge economic significance with focus on the pegmatites in the area.

Keywords: Ila Orangun, Pegmatites, Petrochemistry, peraluminous, petrography