Lateritic weathering of pyroxenites at Niquelandia, Goias, Brazil; the supergene behavior of nickel

Two typical lateritic weathering profiles (Jacuba and Angiquinho) from the Niquelandia Ni deposits, Brazil, were studied in order to establish the petrological relationship between the supergene Ni products and the parental pyroxenes. From the base to the top of the profiles, pyroxenes are replaced by goethite and kaolinite through a series of transitional Ni-bearing phyllosilicates. The mineralogy and the chemical composition (especially the Ni content) of these clay minerals depends on the degree of fracturing and serpentinization of the pyroxenite and the location of the pyroxenite with respect to neighboring dunite. Within the Jacuba profile, smectite and pimelite pseudomorphs after pyroxene are especially Ni rich, and in fact, are the most Ni-enriched clay minerals now known in lateritic weathering profiles.