Rare-earth-element geochemistry in soils developed in different geological settings of Cuba

Abstract

The increased exploitation of rare-earth elements (REEs) over the past few decades and the disposal of various products containing these elements have prompted numerous environmental studies and the need to establish regulatory guidelines. We determined the concentration of REEs in topsoil samples of 33 soil profiles collected from areas of different geological settings in Cuba. The average REE concentrations revealed the following chemical abundances in decreasing order: Ce>Nd>La>Pr>Sm>Er>Yb>Dy>Tb>Lu>Ho>Gd>Eu>Tm. The significant variation in REE levels reflects the geological diversity of Cuba. The highest REE concentrations were observed in Typic Rhodudalf and Rhodic Eutrodox, which are derived from hard limestone. In contrast, the lowest REE concentrations were detected in the Typic Kandiustalf, which originated from mica schist. The lower light REE (LREE) contents in Cuban soils compared with soils from other countries is related to the low abundance of felsic rocks on the island. We also observed a strong positive correlation between REEs and some major elements in soils. This finding implies that the distribution of REEs in soils is partly governed by phosphates and aluminosilicates. The low fractionation between LREEs and heavy REEs is likely related to the predominance of soils developed from carbonates. This finding was also supported by the low LaN/SmN and GdN/YbN ratios and principal component analysis. The spatial distribution of REEs normalized to Upper Continental Crust coupled with univariate and multivariate statistical techniques indicated that parent materials control the prevalence of REEs in Cuban soils. The data presented here represent the first national-wide survey of REEs in Cuban soils.