MINERAL CHEMISTRY AND GEOCHEMISTRY OF HYPERSTHENE-BEARING DIORITE FROM ERUSU AKOKO, SOUTHWESTERN NIGERIA
Journal: Malaysian Journal of Geosciences (MJG)
Author: E. J. Oziegbe, V. O. Olarewaju, O. O. Ocan
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Samples of mafic intrusive rock were analyzed for their mineralogical and chemical properties. The textural relationship was studied using the petrographic microscope, elemental composition of minerals was determined using the Electron Microprobe and the whole rock chemical analysis was done using the XRF and ICP-MS. The following minerals were observed in order of abundance; pyroxene, amphibole, plagioclase, biotite, opaque minerals, quartz and chlorite, with apatite and zircon occurring as accessory mineral. Two types of pyroxenes were observed; orthopyroxene (hypersthene) and clinopyroxene. Texturally, amphiboles have inclusions of plagioclase and pyroxene. The plagioclase has undergone sericitization. The chemical composition of the pyroxene is En51.95Fs44.53Wo3.52, biotite has Fe/(Fe+Mg):0.42, Mg/(Fe+Mg):0.59, and plagioclase is Ab63.5An34.55Or1.95. Whole rock chemistry shows a chemical composition; SiO2: 45.15 %, Al2O3: 14.04 %, Fe2O3: 16.01 %, MgO: 5.65 %, CaO: 7.58 % and TiO2: 3.59 %. There is an enrichment of LREE and a depletion of HREE. Based on the minerals, mineral chemistry and the geochemistry of the studied rock, the rock is mafic and hydrous minerals formed by hydration recrystallization of pyroxene. The rock has extensively retrogressed but has not been affected by any form of deformation.