Potential Pathways of Critical Elements in Fe–Ni Laterites: Insights from Skyros Island (Greece)

The occurrence of compact magnetite within peridotites of Skyros Island (Greece) has been recorded, but its origin is still uncertain. Since critical metals (Ni, Co, Sc, PGE, REE) are a growing concern on a worldwide scale and may provide evidence for the origin of ores, their investigation in magnetite ore is the objective of the present investigation. The determination of major and trace elements in representative compact magnetite from Skyros and their detailed investigation using SEM/EDS provide some evidence of genetic significance. The presence of pisolitic–oolitic texture, chromite fragments in a spatial association, with a composition ranging from high-Al to high-Cr, and flat-shaped PGE patterns indicates the origin of compact magnetite ore by metamorphism of Fe–Ni laterites rather than alteration of chromite ore. Critical elements hosted in primary minerals of ophiolites during chemical and mechanical weathering are released easily, and subsequently they are incorporated into secondary minerals and are redistributed during subsequent re-deposition and metamorphism. The relatively low content of critical elements in Skyros compact magnetite may be related to low content in the source/ parent ophiolites and re-deposition of laterite crusts onto peridotites, suggesting a lack of a pH contrast at the base (lack of carbonates) to facilitate their precipitation.