Grain-size fractionation and Rare Earth Element distribution in a lateritic-saprolitic nickel profile, Camarioca Este deposit, Eastern Cuba

Nickel laterites constitute strategic resources that host rare earth elements (REEs) and scandium (Sc)—critical metals for the energy transition. However, the distribution of these elements within lateritic–saprolitic profiles remains insufficiently characterized, limiting their recovery as mining byproducts. This study investigates the influence of grain size on REE distribution in the Camarioca Este deposit (eastern Cuba), aiming to establish reproducible analytical techniques applicable to lateritic profiles developed over ultramafic rocks in other tropical regions, such as the Caribbean, South America, Africa, and Southeast Asia.

Two complete weathering profiles (limonite, enriched limonite, and saprolite) were sampled using standardized channels, yielding eight representative samples. Each sample was partitioned into three grain-size fractions (0.105 mm, 0.074 mm, and <0.074 mm), in addition to elutriated fractions. Major elements were determined by ICP OES, and trace elements by ICP MS; both analyses were performed at Activation Laboratories in Canada. Mineralogy was characterized via XRD and SEM Raman spectroscopy.

Total REE concentrations range from 10.4 to 68.1 ppm, with saprolite reaching 35–65 ppm—values that exceed those reported for oxide-type profiles in western Moa (1–3 ppm). Scandium correlates with Fe₂O₃ (r = 0.60) and reaches up to 92 ppm in the fine fractions. The elutriated fractions concentrate the highest REE values, averaging 49.6 ppm, along with 75 ppm of Sc. Cerium anomalies reach values of up to 12.7 ppm in the coarse fractions, indicating the concentration of Ce⁴⁺ in Fe–Mn oxides, whereas the fine fractions exhibit flatter patterns (LREE/HREE ~3.8–5.5). 

The distribution of rare earth elements (REE) in the fine and elutriated fractions of these lateritic–saprolitic profiles represents a promising target for the recovery of critical metals as byproducts of nickel mining in eastern Cuba.