| Abstrakt: |
Herein, we investigated the genesis of Toungo flake graphites in the basement complex of Adamawa Massif, northeastern Nigeria, and evaluated their industrial quality. Field and laboratory evidences show that the foliated amphibolite and gneisses are the main rock unit hosting the graphite and are occasionally bordered by pegmatite. Petrographic data show that graphites in Mayo Butale (MB) and Walon Kole (WK) are associated with chlorite, suggesting a role of CO2-bearing aqueous fluids in the origin of the large and minor graphite flakes under regional greenschist facies conditions. The hydration processes related to the formation of chlorite drove the fluid composition toward CO2 saturation and graphite precipitation. The close association of the graphite with pegmatites shows that graphite precipitation occurs synchronously with melt crystallization during cooling, suggesting that C-bearing fluids exsolved from the parent melts of pegmatites. The flake sizes of Walon Kole (WK) and Mayo Butale (MB) graphites range between ~0.2 and 0.6 mm, reflective of high-quality flakes. Their light bulk densities (WK = 2.38 g/cm3; MB = 2.29 g/cm3) make them less susceptible to crushing and cracking, while their porosities (WK = 3.25–5.26%; MB = 1.4–6.88%) are suitable for use in refractory industries. Given their low moisture contents (WK = 0.27%; MB = 0.16%) and volatile matter (WK = 2.1%; MB = 4.90%), the graphites can be used to produce silicon carbides, fire-retardant additives, as well as refractory bricks, lubricants, automobile brakes, clutches, and pencil lead. Their ash contents (WK = 15%; MB = 18%) and compressive strengths (WK = 23 N/mm2; MB = 16.5 N/mm2) connote mechanical strength and good workability, thus suitable for producing crucibles, coatings of TV tube, and conductive concrete used in making cement. The graphite's thermal shock resistance is satisfactory for use in refractory industries as it withstood severe cycles of heating. Taken together, the quality of Toungo graphites conform to the minimum industrial quality standards but can be beneficiated to meet the optimum industrial grades. [ABSTRACT FROM AUTHOR] |
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