Geochemical And Petrographic Studies Of The Newly Exposed Facies In The Ibese Quarry, Dahomey Basin

ABSTRACT

Limestone, glauconite, ferruginized sandstone and shale samples were obtained from

the mapped newly exposed part of the Dangote Cement quarry located in Ibese,

eastern Dahomey Basin, Nigeria. The Paleocene-Eocene Akinbo and Ewekoro

Formations were studied, logged and sampled from the Northern (NM) and

Southwestern (SWM) sections quarried to depths of about 12m and 23m respectively.

Twelve samples taken from these sections have been examined in an attempt to

determine the geochemical characteristics of the sediments, mineralogical

composition and provide petrographic interpretation in order to understand the

associated diagenetic processes and depositional conditions. A combination of

analytical techniques including: geochemical analysis for major and trace elements,

X-ray diffraction (XRD), thin section and scanning electron microscopy (SEM) were

used in this study. Results show that the major elements present in the analyzed

samples include CaO, SiO2 , SO3, Al2O3, Fe2O3, P2O5, MgO, K2O, TiO2 and MnO

respectively. CaO is the dominant oxide with concentration ranging from 4.13 -

94.67wt.% (Av. 65.85wt.%), followed by SiO2 with values ranging from 1.38 -

59.78wt. % (Av. 30.58 wt.%). The high Ca/Mg ratio defines a high calcite purity,

which is significant in cement production. LOI values range from 5.13 - 12.20% and

trace elements are generally below 0.7ppm in all the samples. Calcite (56.69 -

57.96%) dominates the mineralogy followed by quartz, dolomite and kaolinite.

Petrographic observations identify four facies: unsorted biosparite, sparse biomicrite,

fossiliferous micrite, and packed biomicrite, which have been affected by various

diagenetic processes such as cementation, neomorphism, micritization, compaction,

dissolution and dolomitization. Due to the presence of fossils such as sponges,

molluscs, the limestones are typically deposited in a freshwater environment,

probably upper deltaic (non-marine) environment or brackish water, (probably lower

deltaic (marginal-marine) environment). The studied limestones are suitable for cement production based on the elemental composition.