Impact of weathering on REE distribution in soil-saprolite profiles developed on orthogneisses in Borborema Province, NE Brazil

Author(s)

Barros dos Santos, Jean Cheyson ^[1] ; Le Pera, Emilia ^[2] ; de Oliveira, Cybelle Souza ^[1] ; de Souza Junior, Valdomiro Severino ^[1] ; Pedron, Fabricio de Araujo ^[3] ; Correa, Marcelo Metri ^[4] ; de Azevedo, Antonio Carlos ^[5]

Affiliation

^[1] Univ Fed Rural Pernambuco UFRPE, Dept Agron, BR-52171900 Recife, PE - Brazil

^[2] Univ Calabria, Dipartimento Biol Ecol & Sci Terra, I-87036 Arcavacata Di Rende, CS - Italy

^[3] Univ Fed Santa Maria, Dept Solos, BR-97105900 Santa Maria, RS - Brazil

^[4] Univ Fed Rural Pernambuco UFRPE, Dept Ciencia Solo UAG, BR-55292270 Garanhuns, PE - Brazil

^[5] Univ Sao Paulo, Dept Ciencia Solo ESALQ, BR-13418900 Piracicaba, SP - Brazil

• Document type: Journal article
• Source: Geoderma; v. 347, p. 103-117, AUG 1 2019.
• Web of Science Citations: 1

Abstract

Rare earth elements (REEs) are a group of elements (from La to Lu) with high economic value and serve mainly as essential raw material for various high-technology items. This study explores mineral weathering and the geochemical evolution of regoliths (quaternary period) derived from orthogneisses (late Cretaceous Period) in four sites in Borborema Province, NE Brazil, providing a new contribution to the understanding of the influence of soil and saprolite attributes on the distribution of REEs in the regolith. We used optical and electron microscopy to depict the weathering of minerals in the rock, saprolite and soil microstructure, focusing on the distribution of REEs in the regolith (Depth: 3.0 m). We also determined the poorly and well-crystallized iron oxide contents, the clay fraction amount and the total organic carbon content to observe how these attributes influence the distribution of REEs in the soil and saprolite. The results allowed the classification of weathering for feldspars, micas and other primary minerals into four stages based on their degree of alteration and the consequent influence on the geochemistry of the regoliths. Advancement of the weathering stages revealed the relative increases in Fe and Ti compared with Ca, Mg, Na and K from the fresh rock up to the soil horizons, and ilmenite and xenotime were the main sources of Yb, Y, Co and P. The patterns of signatures and anomalies were different for light (LREEs), middle (MREEs) and heavy rare earth elements (HREEs) and for regoliths in different metamorphic complexes. The LREEs related well with the clay fraction amount, the poorly crystallized iron oxides and the degree of weathering, as estimated by the mineralogical index of alteration (MIA), while the HREEs related well with the total organic carbon (TOC). In particular, Ce was strongly associated with Mn oxides, possibly due to simultaneous oxidative precipitation. (AU)

• FAPESP's process: 13/03703-2 - Soil-saprolite systems in southeast and northeast Brazil: morphological characteristics, geochemical-mineralogical evolution and environmental role
• Grantee: Antonio Carlos de Azevedo
• Support Opportunities: Regular Research Grants
• FAPESP's process: 12/12711-6 - ATTRIBUTES MORPHOLOGICAL, PHYSICAL, CHEMICAL AND MINERALOGICAL OF SHALLOW SOILS AND SAPROLITE IN THE SEMI-ARID REGION OF THE PERNAMBUCO STATE
• Grantee: Jean Cheyson Barros dos Santos
• Support Opportunities: Scholarships in Brazil - Doctorate