RMZ – MATERIALI IN GEOOKOLJE

356 Akinola, O. O., Talabi, A. O.In pegmatite, the feldspars exist asporphyries of microcline with its characteristicstrong cross hatched twiningand strong to weak micro perthitic intergrowth.Tourmaline crystals exhibitlong needle-like prismatic shapes withacicular habit (Figure 7).Modal analysis (Table 1) shows thatquartz is adequately represented inmost of the basement rocks withquartzite, granite, gneisses and pegmatiteshowing larger percentages whileepidiorite, amphibole schist and calcgneissrecord substantially low values.Plagioclase is well represented ingranite, pegmatite and the gneisses butwith low representation in the schistoserocks. Biotite is another mineralthat cut across most of the basementrocks. However, highest percentagesare recorded in biotite schist and biotitegneiss while calc-gneiss does notshow any trace of the mineral at all. Asregards amphibole schist, hornblendehas the highest percentage while it is ofan average value in epidiorite. Olivineand pyroxene are only represented inepidiorite while tourmaline and lepidoliteare present only in pegmatite.Results and discussionGeochemical featuresGeochemical result (Table 2) showsthat average SiO 2content of all thebasement rocks are high and rangefrom lowest value in epidiorite (55.72%) to highest value in granite (73.61%). The gneisses have average SiO 2similar to those found around Ileshaarea (Elueze, 1981). Alumina contentranges from lowest in calc-gneiss(9.23 %) to higher values in amphiboleschist (15.62 %) and highest in biotiteschist (18.03 %). The mean Al 2O 3contentof the schistose rock around Ijerois generally higher than similar rocksencountered around Ibadan (Okunlolaet al, 2009)Mean Fe 2O 3content of Epidiorite(11.16 %)) and biotite schist (8.53)are comparable. These values arehigher than biotite gneiss (7.02 %) andpegmatite (6.49 %). Low mean MnOvalue is common to all the basementrocks except quartzite (2.18 %) whichrecords the highest, and this valueis higher than calc-gneiss (1.64 %).All other basement rocks have averageMnO values that are less than 0.6%, for instance, epidiorite and biotiteschist both record 0.08 %. Mean MgOcontent of Calc-gneiss (13.49 %) isslightly lower than epidiorite (14.80%). Other rocks, amphibole schist(6.25 %), biotite gneiss (3.08 %), biotiteschist (8.94 %), quartzite (1.00 %)have low mean values while the remainingbasement rocks record lowervalues. Average CaO values of migmatitegneiss (2.51 %), biotite gneiss(2.14 %) and amphibole schist (2.04%) are comparable. However, theseRMZ-M&G 2012, 59