Abstract
This paper investigates and reports the lithological and compositional features of Igue marble deposit in southwestern Nigeria. The deposit occurs as low-lying heterogeneous units under a humus-laden dark brown tropical soil within Igarra Schist Belt on south eastern flank of basement complex of southwestern Nigeria. The marble deposit occurs as lenses sandwiched between quartz-biotite schist, calc-silicate gneiss and polygenetic metaconglomerate intercalated with mica schist and quartzite all resting on ancient migmatite gneiss. The three colour variants of the marble which are white, grey, and foliated have average SiO2 contents of 2.92, 1.72 and 4.04% respectively. In the same order, average CaO contents are 60.76, 59.35 and 51.7%; MgO contents are 1.62, 1.42 and 2.57% indicating the marble is calcitic in nature. The oxides P2O5, TiO2 and MnO altogether constitute 0.09, 0.11 and 0.41% of the bulk chemistry of the white, grey, and foliated marble, respectively. Average loss on ignition (LOI) in white marble (33.46%), grey marble (36.12%) and foliated marble (33.49%) are relatively high suggesting high volatile contents. Chemical features of the marble deposit are comparable to similar rock types in Obajana and Ososo areas in Southwestern Nigeria. The marble differs significantly from Igbeti marble deposit which is dolomitic in nature. Marble deposits from different parts of Nigeria basement exhibits variable geochemical features that are influenced by their protoliths, mode of formation and associated lithologies and forms the basis for various economic uses. Key words: Igue marble, lithological and compositional features, Igarra Schist Belt, Nigeria, calcitic.
Highlights
Carbonate rocks occur as carbonatites, limestone, dolostone or marble
The chemical composition of any marble deposit will depend on the original limestone from which it is formed and the physicochemical conditions during such transformations
Even though the Igue marble occurs at a relatively shallow depth, the thin gritty overburden has been scraped by a bulldozer to further expose the marble
Summary
Carbonate rocks occur as carbonatites, limestone, dolostone (dolomite) or marble. The first is related to igneous activities; the two are sedimentary while marble is a metamorphic product of carbonaceous sediments subjected to high temperature and pressure. In the presence of chemically active fluids, sedimentary carbonates are progressively transformed into marble through recrystallization starting at the grain boundaries. Under the influence of increased temperature and pressure, calcite in limestone changes to recrystallized interlocking minerals. The chemical composition of any marble deposit will depend on the original limestone from which it is formed and the physicochemical conditions during such transformations.
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