The geochemical behaviour of the rare earth elements (REE) during the supergenic evolution of the rocks is not yet well known. This paper deals with the REE behaviour in ferralitic alteration profiles of the residual phosphate and titanium deposit of Tapira, originated from pyroxenites and peridotites containing apatite and perovskite. This study was carried out on a rock constituted essentially of apatite, perovskite and titaniferous magnetite, with diopside and phlogopite as accessory minerals. The analysis of a microfractured and silicified fresh rock has shown perovskite as the main bearing REE primary mineral (1.5 to 2.0% RE 2 O 3). The alteration of this rock occuring on a first stage with preservation of the volume (isovolume) leads to: 1. total removal of silica (opal and quartz); 2. partial dissolution of primary apatite along the fractures and neoformation of secondary apatite, enriched in fluor and depleted in REE; and 3. total transformation (pseudomorphose) of perovskite into microbothroidal anatase in the voids of which a crystal association (geodes) of rare earth and Ca phosphate of rhabdophane group is neoformed. On a second alteration stage it is observed that: 1. all the apatite is dissolved leaving behind important assembly of voids; 2. the phosphate of the rhabdophane group is partially dissolved and replaced by a phosphate of the crandallite group rich in REE; 3. a certain Ti mobilization occurs in the interior of the anatase (corrosion gulf; titaneous cutans) followed by its partial epigenization by ferruginous products and an initial alteration of the titaniferous magnetite. The study seems to indicate that in Tapira: 1. the phosphorous has a fundamental role on trapping the REE released by hydrolysis of the bearing primary minerals; 2. the REE remain in the alterites and are fixed in mineralogical phases of a sequence of REE phosphates richer in aluminium; 3. the REE and the Ti remain closely associated in the studied weathering phases.

Some bauxitic profiles, developed from alkaline rocks of the Poços de Caldas, Minas Gerais, Brazil complex were studied. The preliminary results show that nearly 40% of the total zirconium existing in the rock was leached out of the profile during the bauxitization process. On the other hand, it became evident that only a small part of the bauxitic residual zirconium is tied to zircon. Most of it is associated with the bauxitic ferruginous phase as colloidal hydroxides mixtures.