Genesis and mineralogical classification of Ni-laterites, Oman Mountains

The laterite profiles investigated in the present study developed after the emplacement of a slab of oceanic crust and upper mantle sequence (the Semail ophiolite) onto the East Arabian margin during the Late Cretaceous. The laterites formed as a result of prolonged weathering of the ophiolitic assemblage under tropical to subtropical conditions.Nine laterite profiles have been examined for their Ni potential along a NW-SE segment of the Oman Mountains. The profiles show a vertical succession from bedrock protolith through saprolite, oxide laterite, to clay laterite.A significant enrichment in Ni and Co occurred as a result of the lateritization process. Ni concentrations average 0.63% (Ibra), 0.72% (3 profiles, East Ibra), 0.67% (3 profiles, Al-Russayl), and 0.33% (2 profiles, Tiwi). Electron microprobe analyses showed that goethite, chlorite, kaolinite, serpentine and talc are the main Ni-bearing minerals. This study showed that the Ibra, East Ibra and Tiwi laterites are similar to the other hydrous Mg-silicates (type A) Ni deposits, where nickel-bearing talc (willemseite) or chlorite, and serpentine (nepouite, chrysotile, and antigorite) are the main constituents. Al-Russayl laterite is however, similar to the oxide type (Type C), where most likely the nickel is included in the oxyhydroxides (mainly goethite) minerals.