Concentration of rare earth elements in the Faixa Placha tin deposit, Pedra Branca A-Type Granitic Massif, central Brazil, and its potential for ion-adsorption-type REE-Y mineralization

Abstract

The Goiás Tin Province (GTP) in Brazil has great potential for rare earth elements (REE) deposits associated with A-type granites, such as the Pedra Branca Massif, which contains several Sn deposits and REE anomalies, hosted in its cupola and fracture greisens. The Faixa Placha is the most important tin deposit in the Pedra Branca Massif and has high REE-Y concentrations, both in the Sn ore and parent biotite granite, as well as greisenized granites and greisens, with the potential to be economically used as a byproduct of tin. The values exceed 1000 ppm in light rare earth elements (LREEs) and 500 ppm in heavy rare earth elements (HREEs) + Y in the parent granite. REE concentrations in greisenized granites and greisens are similar to that of the parent granite, indicating that the enrichment in REE is due to the presence of REE-bearing primary minerals and that greisenization did not affect the original magmatic primary REE content. The REE-bearing minerals in the parent granite are allanite, monazite, xenotime, thorite, apatite, and zircon. These minerals, except zircon, are altered to secondary monazite, silicates, fluorcarbonates, and oxyfluorides, which are responsible for the concentration of REE in greisenized granites and greisens and the availability of these metals for the clay fraction of saprolites and soils. Ion exchange analyses in the saprolites and soils of a Faixa Placha profile show that the extractions in the clay fraction are more enriched in REE-Y compared to the whole soil extractions, with values between 3425 and 36,762 ppm and between 2804 and 21,689 ppm, respectively. The REEs are more enriched in the basal part of the profile, especially the LREEs. These exchangeable REE-Y concentrations indicate the potential of the Faixa Placha and nearby areas to constitute an important REE-Y deposit of the ion-adsorption-type.