On the state of weathering of the Upper Cretaceous red phosphorites of Eshidiya, southern Jordan

Forty samples representing the red phosphorites of Eshidiya in southeast Jordan were investigated petrographically and geochemically. Weathering of the marry limestone unit overlying the phosphorite in the Eshidiya Basin had produced a red alluvial horizon that was transported and redeposited in the study area. Clays from this alluvial horizon (kaolinite, illite/smectite mixed layer clays and palygorskite) and iron oxides physically infiltrated downwards with meteoric water through joints and invaded the phosphorites. it is this water which has mildly altered the phosphorites. This is indicated by an increase in the length of the a-axis of the francolite unit cell to 9.3501 Angstrom and also a decrease in structural CO2 to 2.48%, decreases in the CaO/P2O5 ratio to 1.32 and in the F/P2O5 ratio to 0.099, reduction in Na2O to 0.16%, SO3 to 0.77%, and Sr to 292 ppm and finally increases in Al2O3 to 2.55% and Fe2O3 to 2.12%. Comparison with other deposits of the world indicates that the red phosphorites of Eshidiya are mildly weathered. The state of weathering does not affect their commercial use, and might in fact be beneficial. (C) 1998 Elsevier Science Limited.