Fluorite genesis in sedimentary basins: A review

The available data on the dissolved fluoride content and the saturation degree by fluorite in waters of the world ocean and large continental reservoirs were critically reviewed. It was shown that evaporative concentrating of dissolved salts in the autonomous marine basins cannot cause chemogenic fluorite precipitation, which can occur only with additional supply of fluoride from external sources (river runoff, volcanic exhalations, and terrigenous aerosols). The contribution of external fluoride sources should be at least 1.5–4 times of the mass of fluoride supplied with seawater. As such, saturation of waters by CaF2 and the fluorite formation is possible in large drying continental reservoirs of the arid zone that have no direct connection with the world ocean. An assumption about a two-stage mechanism of authigenic fluorite formation in carbonate rocks was made. At the first stage, freshly formed finely dispersed carbonate sediments uptake fluoride from seawater as a result of sorption and coprecipitation. In the second stage, during the recrystallization of the primary solid phase, its partial purification occurs, which is accompanied by the release of some of the uptaken fluoride into the pore solutions. This causes an increase in the dissolved fluoride concentration in the pore waters to values sufficient for fluorite precipitation.