The Cr and V are associated with Fe because of their similar geochemical behavior during accumulation, but both Cr and V become depleted during the deferruginization development in the hydromorphic environment (Boulange et al., 1990). The relatively high Cr/Ni ratio in pisolite and matrix is due to the association of Cr with kaolinite and this is supported by the positive correlation between Al2O3 and Cr in the pisolites and its matrix (Tables 3 and 4).