Caracterização mineral e implicações geometalúrgicas do depósito de níquel laterítico São João do Piauí.

Abstract

The nickel laterite deposit at São João do Piauí (Piauí Nickel deposit) is located in northeastern Brazil, and presents a standard oxide laterite type profile. At deposit scale, the lateritic profile (with 80 m in the studied drillholes) is composed by a silicified ferruginous laterite as the most volumetrically representative unit. In lithogeochemical analyses the general context of the lateritic horizon Fe and Si show an inverse proportional relation. Subordinate layers (~3 m) of green saprolite, enriched in MgO, Ni and REE (~7 %, 0.6 %, ~200 ppm respectively) occur intercalated in the lateritic horizons. Rietveld refinement in X-ray diffraction data determined quartz, magnetite, hematite and goethite as the most common phases in samples from the oxide horizon. Rietveld quantitative results show that in samples from the ferruginous laterite unit, goethite is the Fe mineral most enriched in trace elements, including Ni, Cu, Co, REE. Refinement of stoichiometry in magnetite-maghemite solid solution from de ferruginous laterite shows that most of the magnetite identified in the qualitative XRD analyses is in fact the isomorphic maghemite. In this context, the Rietveld analyses proved to be a powerful tool in the mineral characterization of magnetite enriched.