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While conducting the National Program of Environmental Geochemistry and Medical Geology in the states of Minas Gerais and Bahia, the research team Geological Survey of Brazil – CPRM detected a large area with high levels of fluorine in the geochemical results of the soil, stream sediment and surface water. Fluorine levels were detected by an ion-selective electrode (stream sediment and soil samples) or by ion chromatography (water samples). In this low-density survey, the minimum, maximum and median fluorine grades found at the water samples were 0.005 mg/L, 7.56 mg/L and 0.05 mg/L. For the soil, the samples were 15 mg/L, 1720 mg/L and 152 mg/L, and for the stream sediment, the samples were 35 mg/L, 1076 mg/L and 262 mg/L. The region covers 25 municipalities where studies by researchers from Federal Universities of Minas Gerais and Bahia have detected a high incidence of dental fluorosis, especially where public supply is made via deep wells in the Fissure-Karst Aquifer of the Bambuí Group. Moreover, the study area is highly favorable to the mineral deposit of fluorite and secondary Pb-Zn. Because the area is much larger (99,000 km2) than the other known fluorite provinces of Brazil (Santa Catarina is 2,000 km2 and Vale do Ribeira is 5,000 km2), the designation of Geochemical Megaprovince of Fluorine in the Middle São Francisco River, Brazil, is suggested for this region.
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