Weathering alteration and related REE concentration in the Catalمo I carbonatite complex, central Brazil

REE geochemistry and mineralogy was investigated in a lateritic profile derived from the weathering alteration of the Catalão I complex. From bottom to top of the weathering profile the fresh rock (FR) changes gradually into an altered rock, an isalteritic saprolite (IS) and an alloteritic saprolite (AS). The FR is a phoscorite cut by abundant carbonatitic veins. In the IS apatite is the most abundant mineral, occurring together with goethite, quartz, and small amounts of a secondary Al-phosphate belonging to the plumbogummite-group minerals. AS is formed of goethite, plumbogummite-group minerals, and quartz. Within the FR, carbonatitic veins are richer in REE (REE2O3=0.32%) than phoscorite (REE2O3=0.13%). Both parent rocks are characterized by LREE enrichment, but LREE/HREE ratio is higher for carbonatite. REE concentration tends to intensify with weathering, being REE2O3=0.6–0.8% for IS and 1.3–1.9% for AS. REE fractionation in the vertical direction is very weak, being the general pattern of REE distribution essentially inherited from the fresh rock. In addition to the REE-laterites, an extremely REE rich silicified facies within the IS (REE2O3=2.48–4.83%) was also investigated.