The Origin of Fluoride in Groundwaters of the Paleozoic Sedimentary Formations of Ghana-A Preliminary Study in Gushiegu District

The occurrence of dental fluorosis and dental carries due to the occurrence of elevated fluorides in groundwaters had been identified and investigated in Gushiegu District of Northern Region of Ghana using an integrated approach involving water quality analysis and petrographical thin-section analysis of rock cuttings obtained from drilled samples from boreholes in the study area. Fluoride concentrations were found to range from 0.05 to 5.8 mg/L, with a mean concentration of 2.18 mg/L. Analysis of samples from 36 wells showed that 11.12% had fluoride concentrations below 0.05 mg/L, 44.44% had concentrations above 1.5 mg/L whilst 44.44% had concentration between 0.5-1.5 mg/L. Petrographical thin-section analyses revealed meta-mudstone, slate/meta mudstone, meta-mudstone/slate and meta-siltstone and carbonate quartz-schist as the rock types. Major rock minerals include quartz, iron oxide clay minerals, carbonates minerals, sericite and opaque whilst lithic fragments and fluorites make up minor minerals components. The range of modal composition of the major mineral components are opaque minerals (35-60%), quartz (20-60%), iron oxide (10-55%), sericite (3- 35%), clay minerals (2-33%) and carbonate minerals (10-20%) with minor mineral components (lithic fragments and fluorite) having less than 1% in all the samples. Sericite appears to be the main mineral associated with the occurrence of elevated fluoride concentration in the groundwaters with carbonate minerals playing a minor role. Dissolution of fluoride into groundwater could be due to the interactions of groundwater with rocks containing sericite and probably carbonate minerals.