Petrographical Analysis of Basement Rocks in Ila Orangun Area, Southwestern Nigeria

For the purpose of carrying out petrographical analysis on basement rocks mapped in Ila Orangun Area Southwestern Nigeria, it became expedient to use the six (6) lithological units which were identified to be common around the study area. These lithological units include quartzites, granites, granite gneiss, porphyritic granites, amphibolite and pegmatites. The aim of the research is to unravel the mineralogical assemblages in terms of % mineralogical composition under plane and cross polarized lights using modal analysis for each of the rocks that best describes the underlying lithology of the area. Methods adopted for this research include preparing the rock samples for thin sectioning. The procedure of sample preparation include cutting, trimming, lapping and mounting of the rock processed rock samples on glass slides using Canada balsam and araldites. Each glass slides are then mounted on the stage of a petrographical microscope for keen observation and petrographical studies. 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. In conclusion, results from the petrographical analysis showed that the rocks are rich in minerals of huge economic significance. Some of these include quartz (SiO 2 ) and muscovites which are both useful in the manufacturing of refractory glassware. It is however, recommended that further studies should be conducted on the microstructural investigation of these rock types which are mapped and retrieved from the study area.