Framboidal pyrite and bacterio-morphic goethite at transitional zones between Fe–Ni-laterites and limestones: Evidence from Lokris, Greece

The Fe–Ni laterite deposits at the Lokris area of Greece, which are a major source of nickel, are characterized by multistage erosion/re-deposition and intense tectonic activities. This study is focused on certain mineralogical and geochemical features observed in the transitional zones above and below the laterite ore in both the Nissi and Patitira (Lokris) Ni-laterite deposits. The upper transition zone is characterized by an association of framboidal pyrite with organic matter, and the lower zone by the occurrence of goethite, which differs compared to the common type of rounded and angular fragments of goethite and limonite containing detrital grains of quartz, chromite, and chlorite. These differ from typical goethite and limonite in many ways including (a) size, (b) shape, and (c) trace element content. currence and association of Fe-mineral assemblages (pyrites and Fe-oxides) with fossilized microorganisms and the negative δ34S values for sulfide-bearing samples are indicative of organic matter involvement in the metal and metalloid cycling. The paucity of P, As, and REE within typical Fe-Ni laterite ore and the preferential occurrence of REE-minerals along with Ni, Co, and Mn (asbolane and silicates) towards the lowermost part of the laterite ore suggest their deposition was controlled by physicochemical conditions rather than the precursor rocks.