Contribution à l'étude de la formation des gîtes silicatés de nickel

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Abstract
An experimental study of weathering of nickeliferous olivine and serpentine, using the « soxhlet » apparatus, shows that the two minerals behave in very different ways. While the serpentine undergoes a quasicongruent dissolution, the forsterite decays with formation of amorphous Si-enriched silico-magnesian products. Nickel shows a tendency to concentrate in such residual products. The factor of concentration is low in the case of serpentine. In the case of forsterite, the nickel percent in the amorphous products, resulting immediately from weathering, can exceed by twenty times the initial amount in forsterite. We show that these amorphous silicates behave like ions-exchangers in presence of nickel and magnesium. The high nickel amount of these products is explained by the high value, about 400, of the distribution coefficient D(Ni,Mg) = (Ni/Mg)[gel]/(Ni/Mg)[solution] ((Ni/Mg)[gel] and (Ni/Mg)[solution] are atomic ratios). These observations suggest that residual silicated ores could have undergone an amorphous stage during which nickel was concentrated by ion-exchange.

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