The dynamic of rare earth elements in the context of multiple bauxitization cycles: Evidence in the Southern Espinhaço Range (Southeastern Brazil)

Abstract

Rare earth elements (REE) are widely used in the paleoenvironmental interpretation of bauxitic and ferruginous duricrusts as they are sensitive to the physical-chemical conditions and may record environmental changes in situations of intense weathering. In the Southern Espinhaço Range in Southeast Brazil, two bauxite targets of the scaffolded bauxitization model type evolved from hematitic phyllite and presented disparate REE behavior. In addition to the REE, the two targets have other chemical and mineralogical differences, which suggests paleoenvironmental differences during their evolution. This study investigates these differences using the mass balance of the LREE and HREE and Ce/Ce∗, La/Y, and (La/Yb)_N ratios to identify the main environmental characteristics associated with the evolution of these targets. Factorial analysis of the behavior patterns of major and trace elements, and mineralogy was used to identify cluster patterns among samples from the two targets. Contrasting behavior was found between the targets, and the REE indicate an acidic, reductive environment for one of the targets, and an alkaline/acidic, reductive environment for the other target. These differences suggest that the over layering of bauxitization cycles is responsible for adding or obliterating geochemical characteristics to make the bauxitic system complex for the interpretation of paleoenvironments.