PETROSTRUCTURAL AND MINERALOGICAL INVESTIGATION OF ROCKS

ABSTRACT

Petrological and mineralogical evaluation of the basement rocks around Igarra, Southwestern Basement Complex of Nigeria was carried out to investigate the petrological characteristics and mineral composition of rocks around the study area. The area is located between latitudes 7^o 15’ 00”N - 7⁰ 19’ 30”N and Longitudes 6⁰ 03’ 00”E - 6⁰ 09’ 30”E is about 36km². The investigation includes systematic geologic mapping of the rocks,laboratory analysis and interpretations of structural elements inherent in the rocks via standard geological techniques as well as petrographic study of thin sections using transmitted light microscopy. Thirty (30) rock samples were obtained from the field out of which twenty (20) fresh rock samples were selected and prepared for thin section studies using standard procedures.The granites and the metasediments were dissected by a network of quartzo-feldspathic dykes or veins of various dimensions indicative of syn to late tectonic emplacements. The metasediments had undergone polyphase metamorphism and deformation and the recent of them being the Pan African orogeny. The Pan African granite intruded the folded metasediments in N-S direction. Geologic mapping of the studied area revealed that the Pan African granites are structurally controlled intrusions in the host rock sequence. The emplacements of the granite probably reactivated the E-W fault zone and normal faulting that resulted in the down warping of the topography. The mineral assemblages are of low to intermediate metamorphic grade in the metasediments. The rocks are rich in significant amounts of essential minerals such as quartz, feldspars, biotite, hornblende and calcite and accessory minerals like chlorite, epidote. The rocks are also rich in heavy minerals such as zircon, apatite, titanite (sphene) and garnet.