Abstract
Bauxites in southern France (Provence and Languedoc) have been exploited since the beginning of the last century. Though most of the deposits are now subeconomic or mined-out, these bauxites represent model analogs for other economic bauxites of the world. These Cretaceous karst-type deposits lie directly on Jurassic carbonates, and have been formed through a combination of different processes: in-situ alteration of siliciclastic sediments deposited on carbonate platforms, and reworking of early bauxites in the karst network. In this study, we present preliminary bulk rock geochemical and in-situ laser ablation (LA) -ICP-MS analyses on Al- and Fe-oxy-hydroxides of Provence (Les Baux-de-Provence) and Languedoc (Villeveyrac, Loupian) bauxites, with the aim of evaluating the concentrations of rare earth elements (REEs) and their deportment in these minerals. REEs have total average concentrations of 700 mg/kg in the analyzed samples, which are mostly composed of boehmite, γ-AlO(OH), and Fe-oxy-hydroxides (hematite and goethite). Maximum REEs concentrations are commonly associated with positive Ce anomalies in chondrite-normalized patterns. In contrast with other examples from the literature, it has been observed that high REE concentrations also occur in samples apparently devoid or poor of REE-minerals. In these samples, the total amount of REEs is positively correlated with that of Ga (commonly contained in boehmite). LA-ICP-MS trace element analyses on boehmite and Fe-oxy-hydroxides have shown that while the Al-hydroxide contains the suite of REEs, goethite and hematite are preferentially enriched only in Ce. Considering that Al-hydroxides are digested during the Bayer process, an interesting issue to develop in the future is whether (and how) REEs released during Al-hydroxide digestion could be recovered together with Al from the pregnant leach liquor, as routinely done for Ga.
Highlights
Bauxite deposits are economic concentrations of aluminum, representing residual products of weathering and leaching of aluminosilicate parent rocks
We present bulk rock geochemical and in-situ laser ablation-inductively coupled plasma mass spectrometric (LA-inductively coupled plasma-mass spectrometry (ICP-MS)) analyses on Al- and Fe-oxy-hydroxides hosted in bauxite deposits in southern France with the aim of evaluating rare earth elements (REEs) concentrations and deportment of in these minerals
The bauxite clasts are predominantly composed either of boehmite or hematite (Figure 3a)
Summary
Bauxite deposits are economic concentrations of aluminum, representing residual products of weathering and leaching of aluminosilicate parent rocks. The main advantage of the Bayer process is that the soda dissolution treatment affects aluminum-containing minerals, and minimizes the dissolution of other mineral phases [5] This digestion is achieved in a strongly alkaline solution at temperatures above 100 ◦ C (the reaction for boehmite-rich bauxite is carried out at more than 240 ◦ C), so that minerals such as gibbsite and boehmite are dissolved to produce (Al(OH)4 )− (aluminate) ions in solution [5]. Vind et al [27] have shown that the most abundant phase containing REEs in the residue of Greek bauxites is a LREE ferrotitanate [(REE,Ca,Na)(Ti,Fe)O3 ] compound, considered to have formed during the digestion of precursor LREE-minerals during the Bayer process. 32], and can be considered as model analogs of economic karst bauxites located in other regions of platforms These deposits mainly contain a boehmite-gibbsite mineralization [30,31,32], and can the world. Of the old bauxite mines object of sampling (https://maps‐for‐free.com)
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