Petrography, compositional characteristics and stable isotope geochemistry of the Ewekoro formation from Ibese Corehole, eastern Dahomey basin, southwestern Nigeria

Subsurface samples of the predominantly carbonate Ewekoro Formation, obtained from Ibese core hole within the Dahomey basin were used in this study. Investigations entail petrographic, elemental composition as well asstable isotopes (carbon and oxygen) geochemistry in order to deduce the different microfacies and depositional environment. Petrographic study reveals the presence of dolomite, biomicrite, sandy biomicrite, and  biosparite facies. Preserved pore types such as; intercrystaline, moldic and vuggy pores were observed as predominant conduits for fluids. The major element oxides ranges are; CaO (39.79 - 53.98wt. %), SiO2 (1.29-25.37 wt. %), Al2O3 (0.43-3.77 wt. %), K2O (0.04-0.27wt. %), Fe2O3 (0.74-2.35 wt. %), and Na2O (<0.01-0.05 wt. %). Cross correlation of the major oxidecontents shows that Al2O3, K2O, Na2O, TiO2, Fe2O3, and P2O5 are  associated with aluminosilicates and their low concentrations indicates that the basin was free of suspended clays and other aluminosilicates materials during carbonate sedimentation. The relatively high concentration of SiO2 and its interrelationship with other major oxides, suggests SiO2 has strictly influenced the sedimentation of the carbonate hence would have been contributed as free silica, probably from beaches and not as  aluminosilicates. The Mn/Sr ratio reveals an influence of diagenesis on the mineralogy of the carbonates. The Mg/Ca ratio ranges from 0.02 and 0.1(av. 0.04), with an outlier value of 0.1, indicating a strong diagenetic influence and the precipitation of dolomite in the mixing zone. The isotopic composition of δ13C (-1.9‰ to 0.79‰) shows a discrepancy from modern carbonate sediments. The average estimated formational temperature of the limestone is 32.50C. The δ13O versus δ18O bivariate diagram indicates that the limestone is predominantly average marine limestone with chalk and late cement. The values of depositional setting (Z), estimated from δ13O and δ18O composition support a diagenetic influence on the Ewekoro Formation. The U/Th ratios (~0.25 to 2.3; av. 1.2) and Ce anomaly (0.70 - 0.94, av. 0.85) indicate a predominantly oxygenated environment with little fluctuation in bottom water oxygen level

Preliminary investigation on industrial properties of the Olode-Falansa pegmatite, Southwestern Nigeria

In Olode-Falansa area, which is part of the southwestern basement complex of Nigeria near Ibadan, the major rock types are granite gneiss, quartzite, medium-grained granite and pegmatite. In particular, the pegmatites which occur as low-lying bodies, with a mineralogy dominated by pinkish-white microcline perthite, quartz, muscovite and plagioclase plus accessory constituents of garnet, beryl and tourmaline have been investigated for their distribution, physical, chemical and mineralogical characteristics in order to evaluate their industrial qualities. Chemical analysis shows variations in the major elements contents of the main minerals. In particular, quartz samples have 94.02 to 97.30% SiO2; 0.86 to 2.60% Al2O3; 0.05 to 1.02% K2O; and 0.13 to 1.29% Fe2O3, while the feldspar samples are 61.37 to 67.83% SiO2; 16.85 to 18.40% Al2O3; 11.35 to 14.32% K2O and 0.04 to 0.11% Fe2O3 respectively. The total alkalis (Na2O+K2O) indicate K-feldspar composition. The specific gravity for quartz ranges from 2.60 – 2.63, while that of feldspar is from 2.55 –2.58. Water absorption capacity is higher for quartz (25.10 – 27.10%) than feldspar (4.61 – 5.80%). Compressive strength of selected pegmatite minerals indicates values from 133.24 to 223.84MN/m2. This investigation shows that the pegmatites have good potential for industrial uses. They can be used directly as raw materials or after beneficiation. In particular, the quartz and feldspars can find application in the refractory, glass, ceramic and abrasive industries. They can also be found useful in minor construction works especially in homes and offices. Muscovite can be used as thermal and electrical insulators, while the beryl can be useful as ornaments. The associated rocks such as gneisses, quartzites and granites can be useful in interior and exterior decorations as well as in tiles manufacturing. KEY WORDS: Olode Pegmatite; K-feldspar; Quartz; Raw Materials Global Journal of Geological Sciences Vol.2(2) 2004: 255-26

A study on the interpretation of spontaneous potential and resistivity logs in layered aquifer sequence of Pondicherry Region, South India

Geophysical logs provide a strong mechanism for interpretation and determination of the depositional environments, facies and also help in interpretations of hydrogeologic units. Spontaneous potential (SP) and resistivity logs can be used as an indicator of textural parameters. Pondicherry region has a complicated geology and with formation of different ages. The boreholes (BH) of this region are examined for litholog, SP and resistivity from four different BH locations, viz, Ariyankuppam, Chinnaverampattinam, Thavalakuppam and Nallavadu. These locations were studied and interpreted by using the shapes of the curves to identify the depositional environments, and this was later compared with the vertical litholog profile. Comparing the variation of these logs, the lateral variation of sedimentary facies was also attempted. The average resistivity values of Ariyankuppam, Chinnaverampattinam, Thavalakuppam and Nallavadu are 42.4, 30.4, 50.4 and 28.3 Ωm, respectively. Majority of the resistivity values corresponds from fine- to medium-grained sand, clayey pebbles, fine to very coarse sand and clayey sand with lignite. Frequency of resistivity values in each BH were identified for determining the dominant representative grain size. The study has pointed out the lithological variation of the system laterally and vertically using geophysical well logs