Evolution of the Piauí Laterite, Brazil: Mineralogical, Geochemical and Geomicrobiological Mechanisms for Cobalt and Nickel Enrichment

The Piauí laterite (NE Brazil) was initially evaluated for Ni but also contains economic concentrations of Co. Our investigations aimed to characterise the Co enrichment within deposit; by understanding mineralogy we can better design mineral processing target recovery. is heterogeneous on mineralogical and lithological scale differing from classic schematic profiles nickel laterites, while there a clear transition saprolite more ferruginous units, deposit lateral vertical variations that are associated with both original intrusive complex nature fluid flow, redox cycling fluctuating groundwater tables. well described following six geochemical units: SAPFE, clay bearing saprolite; SAPSILFE, silica dominated SAPMG, green magnesium rich chlorite SAPAL, white-green high aluminium, low saprock, serpentine serpentinite protolith. Not all these units ‘ore bearing’. concentrated in range nickeliferous phyllosilicates (0.1–25 wt%) including serpentines, talc pimelite, goethite (up 9 wt%), magnetite (2.8–14 Mn oxy-hydroxides (0.35–19 wt%). Lower levels present ilmenites, chromites, distinct small horizons 3 wt% Ni). With respect Co, only significant chemical correlation Mn, contain up 14 Cobalt when present, grains an average 0.19 maximum 0.65 other main minerals (0.41–1.89 0.45 ilmenite 0.35 Chemically three types oxy-hydroxide, asbolane, asbolane-lithiophorite intermediates romanechite. Spatially resolved X-ray absorption spectroscopy analysis suggests primarily as octahedrally bound Co3+ substituted directly into MnO6 layers intermediates. However Co2+ evident intermediates, structurally along interlayer between successive layers. microbial community prokaryotes few fungi, highest abundance diversity closest ground level. Microorganisms capable metal were identified be microcosm experiments different demonstrated stimulated biogeochemical did not contribute mobilisation. Correlations likely relic parent rock weathering rather than due processes; conclusion agrees associations.