Rare Earth Elements Enrichment in the Upper Eocene Tošići-Dujići Bauxite Deposit, Croatia, and Relation to REE Mineralogy, Parent Material and Weathering Pattern

Tošići-Dujići bauxite deposit, situated in Dalmatian inlands, Croatia, contains minor remaining bauxite reserves. The deposit lies on Lower Eocene foraminiferal limestone and is covered by Upper Eocene Promina sediments. Bauxite samples were analyzed for textural, mineralogical, and geochemical features in order to determine absolute REE abundances and their relation to mineralogy, as well as to devise the origin of REE enrichment and to trace weathering and bauxitization paths of the parent material. The samples show total REE abundances up to 3500 mg/kg with significant HREE enrichment in some cases. All samples are gibbsitic with hematite and anatase as major phases. Kaolinite occurs in most of the samples, and goethite, böhmite, and nordstrandite are minor phases. Monazite-(Ce) and xenotime-(Y) were identified as detrital REE minerals as well as authigenic florencite-(Ce). In the REE most abundant sample, REE are most likely bound to Fe- and Ti-oxide phases as suggested by correlation analysis. Chemical weathering proxies show intensive weathering. Geochemical and textural data imply that the REE enrichment is influenced by intensive weathering (CIA 97.87–99.26) of detrital material, and also by possible deposition/redeposition of residual material potentially derived and mobilized from various sedimentary rocks of the area.

Geochemical characterization of the Sutlegen bauxite deposit, SW Antalya

Purpose.The purpose is to determine geological and geochemical characteristics of the Sutlegen (Antalya, Turkey) bauxites, to identify the elements that played a major role in their formation. Methods. X-ray diffraction (XRD) mineral phase analysis, X-ray fluorescence (XRF) elemental analysis, plasma-mass spectrometry (ICP-MS), the petrographic and mineralogical analyses, and multivariate statistical methods were used. Findings. The major element content of the ore was determined as Al2O3 (60-35.2 wt%), SiO2 (39.5-0.2 wt%), Fe2O3 (48.4-19.5 wt%), TiO2 (36.9-16 wt%), and P2O5 (0.5-0.1 wt%). The Sutlegen region, which shows epirogenetic action with the uplift of the earth's crust, is generally rich in neritic carbonates. It was revealed that the bauxite ores have undergone moderate and strong laterization as a result of the deferruginization in the environment, and they were classified into four groups as lateritic, ferritic, kaolinitic, and bauxite. The increase in the aluminosilicate minerals, which were formed during the formation of bauxite in the environment was found to be directly proportional to the laterization processes. In this context, it was considered that the lateritic material that was firstly formed in the environment filled the cavities and pores of the karst-type limestones and sedimentary units in the region by superficial transfer phenomena. The bivariate diagrams of Log Cr vs. Log Ni revealed that the bauxite that formed in the region had an ultrabasic source. Originality. In literature, no scientific studies have been found on bauxite mineralization in the Sutlegen deposits that have been operated for a long period. Practical implications. In this context, the geochemical characteristics of bauxites revealed that the source of the laterization process in the region was the ultrabasic igneous rocks. The lateritic material moved by superficial transfer was accumulated on sandstone, claystone, siltstone, and limestone and in karstic cavities; then, it formed karstic bauxite (kaolinitic and bauxite) of different classifications due to the effect of metamorphism.

Geochemical characteristics of Croatian prospective Bauxite deposit Mamutovac

<p>High demand for specific chemical elements from the group of rare earth elements (REE) has led to a detailed prospection and geochemical analysis of a previously known but unexploited bauxite deposit. The Upper Eocene karst bauxite within exploitation field Mamutovac, located in the municipality of Promina in the Dalmatian Hinterland (Croatia), is such a deposit, with estimated reserves of 112,000 tone.</p><p>In order to determine REE distribution pattern in the Mamutovac Ia deposit, a 25meter core was obtained by exploration drilling, down to the deposit footwall that is composed of Upper Cretaceous rudist limestone. For this study 23 subsamples were singled out, on average, per each meter of a core. </p><p>The degree of lateritization is determined by the Al<sub>2</sub>O<sub>3</sub>–SiO<sub>2</sub>–Fe<sub>2</sub>O<sub>3</sub> composition diagram (after Schellman, 1986), and lateritization varies from moderate to strong, with a lower degree of lateritization in a lower part of the core, down from 15 m.  Two different genetic classification systems indicate the origin of the bauxite is mafic, basaltic igneous rocks.            </p><p>Main mineral phases in the bauxite core samples were determined using X-ray powder diffraction (XRPD) analysis. The mineral phases through the whole core are similar, with boehmite, gibbsite, hematite, and anatase as the main phases. Additional mineral phases determined in the core are kaolinite, goethite, and rutile. </p><p>Results of geochemical analysis obtained by inductively coupled plasma emission/mass spectrometry (ICP-ES/MS) indicate an inhomogeneous distribution of REE through the core, with two main trends: from 0-15m and from 15-25m, with some elevation of REE abundances in the lower part of the core. In the upper part of the core,  total REE content (∑REE), including Y and Sc, ranges between 352 and 630 ppm (average 500 ppm) and light REE (La-Sm) to heavy REE (Eu-Lu) (∑LREE/∑HREE) ratios reach up to 10.2. For lower part ∑REE (including Y and Sc) ranges between 569 and 813 ppm (average 676 ppm) and light REE (La-Sm) to heavy REE (Eu-Lu) (∑LREE/∑HREE) ratios are up to 9.82. Singificant enrichment of LREE compared to HREE is present due to the fact that HREE are highly mobile in an alkalic karst environment and consequently removed through drainage channels. The most abundant REE is Ce. Within interval, 0-15m Ce ranges between 149.3-264.9 ppm (average 210.7 ppm), while within the interval 15-25m Ce ranges 152.7-301.7 ppm (average 219.56 ppm).</p><p>Correlation analysis shows no correlation between Sc and other REE and no significant correlation between Ce and other REE or potential bearing oxides. The correlation between Sc and Al<sub>2</sub>O<sub>3</sub> or Fe<sub>2</sub>O<sub>3</sub> suggests that Sc is likely bound to Al-oxyhydroxides and Fe-oxyhydroxides. Correlation between REE (Sc free) and P<sub>2</sub>O<sub>5</sub> indicates REE (Sc free) are probably contained in REE-bearing phosphates. </p><p>This activity has received funding from the European Institute of Innovation and Technology (EIT), a body of the European Union, under the Horizon 2020, the EU Framework Programme and Research and Innovation.</p>