Preliminary data on cadmium and arsenic geochemistry for some phosphorites in Egypt

Phosphorite deposits in Egypt, contained in the Duwi Formation, are a part of the Middle Eastern to North African phosphogenic province of Late Cretaceous to Paleogene age. They are mainly composed of phosphatic, structureless pelloids and bioclasts of francolite composition. Three localities were sampled. Results of inductively coupled plasma (ICP) analyses indicate that the cadmium contents range from 0.37 to 11.55 ppm with an average of 3.2 ppm. Arsenic contents range from 0.1 to 2.1 ppm with an average of 0.95 ppm. Red Sea phosphorites show higher cadmium contents compared with the Nile Valley and Abu-Tartur phosphorites. The Abu-Tartur phosphorites show higher arsenic contents compared with the Red Sea and Nile Valley phosphorites. Nile Valley phosphorites have the lowest cadmium and arsenic contents. Lack of correlation between Cd and As suggests different sources and/or diagenetic behavior. Correlation between both elements and Al2O3 is also lacking, suggesting that both Cd and As do not have a detrital origin. Lack of correlation between Cd and As and CaO and P2O5 indicates there is no genetic relationship between Cd and As and francolite. Lack of correlation between Cd and TOC suggests that Cd does not have an organic origin, while the relatively strong positive correlation between As and TOC indicates that As contents may be related to the organic fraction. Relatively strong positive correlation between As and S is suggestive for the occurrence of As as sulfide. The geochemistry of Cd and As is completely different and diagenesis seems to be the most important controlling factor of their distribution. (c) 2005 Elsevier Ltd. All rights reserved.