Laterization Process of Ultramafic Rocks in Siruka, Solomon Islands

The paper was reported in the 6th International Symposium on \u22Novel Carbon Resource Sciences\u22 Nov. 12-13, 2010Silica and magnesia in the bed rock and the saprolitic zones have been removed and only the residual elements (iron, chromium, aluminium, manganese, cobalt and nickel) remain in the limonitic zone. These elements are relatively concentrated by the removal of the soluble elements. However, nickel becomes unstable and is leached towards the lower part of the profile and concentrated at the saprolitic zone. Nickel is combined with silica and magnesia, as lizardite or mixed gels (garnierite nickel ore) at the weathering front. Significant supergene nickel enrichment occurring in the decomposed zone, indicating that water had percolated downward to a very low water table at depth during the wearhering process. Cobalt and manganese are concentrated in the limonitic part of the profiles (~3-6m depth) of which are poorly protected against erosion and mechanical transportation. The behavior of nickel is contradictory to that of cobalt and manganese and its relative mobility is a little higher than them. It is leached out of contradictory to that of cobalt and manganese and its relative mobility is a little higher than them. It is leached out of the limonitic concretions, where it id first concentrated with Co and Mn, and largely migrates to the bottom part of the profiles. The structure and mineralogy of the weathering profile indicate environmental conditions likely to have been dominated by alternating wet and dry periods