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