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.