PETROGRAPHIC STUDIES AND PHYSICO-MECHANICAL PROPERTIES OF BIRIMIAN GRANITOIDS – A CASE STUDY OF OYOKO GRANITOIDS COMPLEX IN KOFORIDUA

The study investigated the physico-mechanical and petrographic properties of the basin-type granitoids of the Oyoko granitoid complex, to establish their strengths for engineering properties. The results obtained from this work will therefore be necessary in knowing the competences of the rocks for various engineering construction works. The purpose of this research is to determine the physico-mechanical and microstructural features of the granitoid suites of rocks at Oyoko. Thin sections were prepared and microscope used for the petrological studies of the rocks, whilst UCS test was conducted for the strength of the rocks. The Oyoko granitoid complex rocks were petrologically identified to be biotite gneisses, pegmatite and migmatite. The rocks at the study area have received little attention in mechanical and petrographic studies. These granitoid rocks have preserved porphyritic textures and consist of mineral assemblage such as biotite, quartz, plagioclase feldspar, alkali feldspar, amphibole, clino-pyroxene, chlorite, etc. The recrystallization of the plagioclase feldspar imply that these rocks have experienced some level of deformations. The foliated granitic gneisses intruded the older rock units, some of which had been subjected to earlier tectonism. The migmatite defines the area to be closer to a contact zone. The major structural features in the migmatite rocks were ptygmatic folds. The UCS value for the biotite gneiss of 91.6 N/mm2 gives a more representation of the general rock strength of the study area. The biotite gneisses at the study area may be classified to be mechanically strong and recommended for road construction and engineering works.