Abstract
The geology, petrography and geochemistry of the Federal Capital Territory (FCT), marbles were investigated with the view to establishing marble occurrences and their geochemical characteristics. Crystalline rocks of the Nigerian Basement Complex (migmatite – gneiss complex) underlie the area. Ten marble bodies were mapped. The marbles are metasedimentary in origin and were deposited in a structurally controlled basin. They maintain a consistent NNE/SSW (N26° E – N35° E) strike similar to strikes of major regional structures. The marbles are interbedded with mica schist, which is suggestive of periodic variation during their depositional history. The marbles have fine (0.2 – 1.0mm) to medium (1.5 – 4.0mm) calcite and dolomite grains, and exhibit porphyroblastic texture. The calcite and dolomite grains are uniformly distributed and constitute 97.00 – 99.78% of the marbles. The carbonate grains are idiomorphic to subhedral with triple junctions at angles of 110° – 130°, which is suggestive of an equilibrium and stable environment of crystallization. The mineral paragenesis (hornblende – plagioclase – garnet – wollastonite – tremolite – silimanite – zircon – orthoclase – apatite) is suggestive of amphibolite facies of metamorphism to which the marble host rocks have been subjected. It is here suggested that the organic matter of the FCT marbles were destroyed during metamorphism resulting in the production of garnet, biotite and hornblende. The marbles are dolomitic (MgO, 16.05 – 21.65%) and have average Mg/Ca ratio of 2:3. The Na2O and K2O contents are low (0.053% and 0.007% respectively), which is suggestive of a shallow marine depositional environment for the initial limestone material. The environment was rich in Mg and Ca and the Mg co-precipitated with Ca due to poisoning effect of Mg on calcite. The initial environment of limestone precipitation was of moderate temperature, hypersaline with respect to Ca and Mg and precipitation was influenced by microbial activity. The associated MgO was, therefore, precipitatory in origin and not replacement during metamorphism.KEY WORDS: marble, dolomitic, geochemistry, precipitatory and Abuja
Highlights
The marbles of the Federal Capital Territory (FCT) are found in the eastern part of Kuje (Fig 1)
The low values of Na2O of the FCT marbles would suggest a shallow, near shore, low energy “clean water” marine environment of deposition for the original carbonate material that was later metamorphosed to marbles during the Pan African Orogeny, as the marble are associated with basement rocks
It is clear that the initial limestones from which the FCT marbles were formed were deposited in a shallow, anoxic, hyper saline marine environment under moderate temperatures, with micro fauna and flora playing a vital role
Summary
The marbles of the Federal Capital Territory (FCT) are found in the eastern part of Kuje (Fig 1). The marble localities include Burum, Taka-Lafia, Dibe Fadama, Dibe Kassa, Kasada and Kusaki (Fig. 2). The occurrence of marbles in this area was, first examined and studied at Burum (Burum East Deposit) and described as dolomitic (Trustwell, 1956). In early 1962, a reconnaissance map of the area to the west (Burum West Deposit) was prepared by Bell (1963), including a further deposit of approximately 365.8 metric tones. A total indicated reserves of 4,927,000 metric tones of marble was established for the Burum West and East Deposits after a drilling programme by the Geological Survey of Nigeria in 1962 (MacLeod, 1963). E.C. Ashano, Department of Geology and Mining, University of Jos. Nigeria
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
