The low level of Mn in the Ga’ara ironstone indicates the deposition from the fresh water (Canavan et al., 2007; Rigaud et al., 2013). The Mn/Fe ratio (Table 2) is low which reflects high separation between the two elements in the hydromorphic environment. They are both mobile in reducing conditions, but Mn requires a higher oxidation potential to precipitate than Fe2+ (Canavan et al., 2007).