Nickel Dispersion at the Bottom of the Regolith: Formation of Pimelite Target-Like Ores in Rock Block Joints in Koniambo Ni Deposit (New Caledonia)

Abstract : In New Caledonian Ni deposits, kerolite ore occur in fractures within saprolite level, generally several tens of meters to one hundred meters below the present-day relief. They are affected by active dissolution precipitation processes when rocks reach a certain depth close to the surface, e.g. within the water table oscillation zone. Fracture-related kerolite ore account for rather local high Ni-grades, much above the average exploited grade. Close to this kerolite veins occurs pimelite target like characterized by their chemical and mineralogical zoning with an outer green pimelite rim around a white inner zone consisting in Mg-kerolite. These target-like are precipitated in open spaces, particularly in narrow joints. This work presents a mineralogical and chemical characterization of the target-like and proposes a model where alternate periods of hydration and drying, induced by water table movements, lead to the extensive dispersion of nickel and its re-precipitation as target-like.