Geochemistry of Cadmium in Mesozoic Phosphorites of the East European Platform

Cadmium is the most toxic admixture in mineral fertilizers. The Cd concentration in Mesozoic phosphorites, which are widespread in the East European Platform, has not been investigated. The present study was stimulated by the scanty and contradictory nature of the published data on this issue. We determined Cd concentration in 21 phosphorite samples from major deposits and checked the reliability of obtained results by external replicate analyses. It has been established that the Cd concentration in phosphorites varies from 5 ppm in the Late Jurassic–Early Cretaceous basin to 2 ppm in the Late Cretaceous basin. Cadmium does not enter the structure of phosphate and sulfide minerals. The Cd concentration is independent of the phosphorus abundance. However, all studied samples show a positive correlation of Cd with organic matter mainly contained in phosphates, supporting the biophilic nature of Cd. Mesozoic phosphorites of the East European Platform accumulated in epicontinental basins. They are significantly depleted in Cd relative to Mesozoic–Cenozoic phosphorites in pericontinental basins of the southern margin of the Tethys Ocean. The Cd concentration is more stable in Mesozoic phosphorites than in Mesozoic–Cenozoic deposits.