New insights into the distribution and speciation of nickel in a Myanmar laterite

Because ferromanganese oxides can host significant amounts of Ni during the weathering, the Fe- and Mn-oxide are resultantly considered as the important Ni-bearing minerals. However, little is known about the role of Mn species to influence the Ni behavior during this process. In this study, we employed the techniques of ICP-MS, XRF, XRD, XAFS (XANES and EXAFS), and μ-XRF to interpret the Ni behavior along a laterite profile in Myanmar. Nickel concentrations in the saprolite developed on peridotites can reach up to 11 wt% Ni mainly because of Ni precipitation as fracture-fillings and thin coatings on joints, which produce a promisingly and importantly economic mineral resource of this territory. In the peridotites, Fe and Mn species predominantly consisted of olivine (96%) and biotite (74%), respectively. Nickel XANES spectra indicated that Ni was primarily hosted by olivine (86%) in the protolith under reduction condition, lizardite (90%) and Ni-bearing goethite (10%) in the lower garnierite vein under strong oxidation condition, and lizardite (37%) and Ni-bearing goethite (63%) in the upper saprolite under medium oxidation condition. Accordingly, minerals of Fe and Mn were progressively oxidized toward Fe3+ and Mn4+, which occurred primarily as Fe3+-bearing goethite and Mn4+-bearing birnessite. The occurrence of Fe- and Mn-oxide plays an important role in Ni species and suggests that birnessite maybe facilitate the formation of Fe oxide precipitations by means of the oxidation of Fe2+ in the olivine to Fe3+ in the goethite. The results are of relevant importance, as it fills a gap in the knowledge of ore-formation processes occurring in Myanmar