The bauxite-bearing lateritic profile of the Jequié Complex, São Francisco Craton, Brazil: potential for rare earth elements mineralization and insights on the mineral system

Abstract

The Jequié Block is located at the northeastern portion of the São Francisco Craton and represents the Archean tectonic paleoplate that hosts the Jequié Complex. The rocks of the Jequié Complex are cogenetic, enderbitic-charnockitic plutons, which were intruded by gabbros, norites and anorthosites, and subsequently all these rocks were re-equilibrated in granulite facies. Three bauxite occurrences were mapped at the southeastern portion of the Jequié Block, named Itaji (ITJ), Casa de Farinha (CDF) and Valentim (VLT), which are hosted by the bedrock of the units Poço Preto and Santa Inês – Volta do Rio. The Poço Preto Unit is composed of granulitic granodiorites to tonalities, while Santa Inês – Volta do Rio is composed of granulitic granites to granodiorites. The stream sediment results highlighted good geographic correlation between the content of Al, Fe, REE+Y+Sc and Ce in the catchments at the mineralized area. On the ITJ, the vertical profile indicates a lateritic sequence composed of the bedrock (i), saprock (ii), saprolite (iii) and pedolith (iv), while the upper part is the lateritic duricrust (v). The results of petrography, X-ray powder diffraction and whole rock geochemistry, supports the lateritic evolution. This vertical profile was later redeposited through surficial process in a proximal place. The breakdown of K-feldspar and plagioclase into kaolinite started at the weathering front and was continuously intensified towards the saprolite, as well as the transformation of the biotite and amphibole into goethite. The halloysite was identified as an intermediate mineral between the K-feldspar and kaolinite. The kaolinite locally was represented by its polymorph dickite. The transformation of the kaolinite into gibbsite happened between the saprolite and the pedolith, the main reaction in terms of the mineralization was the pseudomorphic feldspar replacement by gibbsite. The presence of the nordstrandite at CDF could be related to local conditions of the weathering, and/or to the bedrock geochemical composition in the region.The bauxite-bearing lateritic profile of the Jequié Complex, São Francisco Craton, Brazil: potential for rare earth elements mineralization and insights on the mineral system1. IntroductionThe Brazilian Federal Government released a list with the strategic minerals to the Brazilian economy, and both aluminum ore and the rare earth elements are stated therein Oliveira (2021). The bauxites are the main raw material of the aluminum industry, which are rocks composed of aluminum hydroxide minerals (Retallack 2010). The Brazil has eleven bauxite mines under operation and the largest productions are placed in the Amazon region (Costa 2016). The laterite (or residual) ores, including bauxite, are among the most relevant non-conventional deposits for the production of REE (Wang et al. 2011). There are no mines currently exploiting REE in Brazil, and the most advanced research projects are targeting REE mineralization hosted by carbonatite complexes, such those from Alto do Paranaíba Igneous Province (Takehara et al. 2015).During the first decade of the 2000’s, the Rio Tinto mining company developed the Amargosa Bauxite Project, currently with limited activity, targeting gibbsite mineralization in the regolith of the Jequié Complex granulites (Costa 2016; Stausholm 2021). Fernandes (1996 and references therein)