Geochemistry of uranium and thorium in phosphate deposits at the Syrian coastal area (Al-Haffah and Al-Qaradaha) and their environmental impacts

Abstract

The aim of this research was to study the geochemistry of uranium and thorium in phosphate deposits in the upper Cretaceous phosphate deposits in the Syrian coastal area. The study covered three sites, namely Ain Al-Tenah, Ain Laylon, and Al-Mhalbeh. Petrographical study showed that phosphate deposits are of nodular type with micrit to microspaite cement, containing siliceous bone residues, and green grains of glauconite, which are increasing in abundance and volume in the south toward Al-Mhalbeh, reflecting the formation of phosphate in a shallow marine environment. In addition, uranium concentration varied between 3 and 112 ppm in Ain Laylon, 4.2–17 ppm in Ain Al-Tenah and 5–61 ppm in Al-Mhalbeh. Thorium concentration varied between 0.2 and 7.5 ppm in Ain Laylon, 0.3–1.4 ppm in Ain Al-Tenah and 0.3–4.4 ppm in Al-Mhalbeh. The average Th/U ratio in the collected samples was within the range 0.04–0.08 except for five samples which exceeded the value 0.1. Moreover, the 226Ra/238U ratios are lower than unity in all samples, while the 210Pb/238U ratios ranged between 0.4 and 1.2 and the 210Pb/226Ra ratios were found to be higher than unity. On the other hand, the impact of leaching and mobility of uranium and thorium from deposits to the surrounding agriculture fields in the area has been studied using the Radium Equivalent Activity Index (Raeq). The equivalent radium activity was 102 Bq kg−1 in Ain Al-Tenah, 403 Bq kg−1 in Ain Laylon, 407 Bq kg−1 in Al-Mhalbeh and 749 Bq kg−1 in agricultural soil samples. However, the data reported in this study can be considered as a baseline data for the phosphate deposits at the coastal area.