Abstract

This work describes the mineralogical and geochemical features of the heavy mineral assemblage within a very fine- to medium-grained black sand occurrence along the Uruguayan Atlantic coast. Mineralogical analysis focused on the valuable heavy minerals’ varieties bearing TiO₂, LREE, and ZrO₂ using a SEM/EDS instrument. The total concentration of valuable heavy minerals (ilmenite, zircon, and monazite) increases from 21% in the raw black sand sample to 65% after concentrating and sieving within the very fine to fine grain-size fraction (63 to 180μm). This concentrated fraction comprises 46% ilmenite, 19% Ti-magnetite, 2% leucoxene and rutile, 5% monazite, and 14% zircon, alongside other non-valuable heavy minerals and light minerals (gangue). Average geochemical microanalysis (n=557) show that the ilmenites are composed of 54% TiO₂, 42% FeO, 1.6% MnO and 0.9% MgO. Ti-magnetites are composed of 36% TiO₂, 58% FeO, 0.7% MnO, 1.8% MgO, 0.7% Al₂O₃, 0.9% SiO₂ and 1.1% CaO. Ce-monazite yields 35% CeO₂, 15.5% La₂O₃, 13.2% Nd₂O₃, 8.8% Th₂O, 1.3% U₃O₈, and 25.7% P₂O₃. Zircon is composed of 65.6% ZrO₂ and 33.1% SiO₂.

Keywords:SEM-EDS; Mineralogy; Geochemistry; Black sands; Ilmenite; Monazite; Uruguay