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.
<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.&#160;</p><p>The degree of lateritization is determined by the Al<sub>2</sub>O<sub>3</sub>&#8211;SiO<sub>2</sub>&#8211;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.&#160; Two different genetic classification systems indicate the origin of the bauxite is mafic, basaltic igneous rocks.&#160;&#160;&#160;&#160;&#160;&#160;&#160; &#160;&#160;&#160;&#160;</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.&#160;</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,&#160; total REE content (&#8721;REE), including Y and Sc, ranges between 352 and 630 ppm (average 500 ppm) and light REE (La-Sm) to heavy REE (Eu-Lu) (&#8721;LREE/&#8721;HREE) ratios reach up to 10.2. For lower part &#8721;REE (including Y and Sc) ranges between 569 and 813 ppm (average 676 ppm) and light REE (La-Sm) to heavy REE (Eu-Lu) (&#8721;LREE/&#8721;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.&#160;</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>
Croatian bauxites are long known for their chemical and physical diversity arisen from their characteristic origin and emplacement within the area of the Adriatic–Dinaric carbonate platform (ADCP). They include eight horizons spanning the period between the Upper Triassic (Carnian) and the Miocene, formed on subaerially exposed platform paleoenvironments. The bauxite genesis is recorded in the bauxite geochemical composition as a unique signature of tectonostratigraphic evolution of the different parts of the Croatian Karst, including, for example, the forebulge unconformity typical for the Istrian area. In this work, an explanation of the typical patterns of bauxite formation is based on the construction of a discriminant function model (DFM) resulting from the compositional data (CoDa) analysis of bauxite geochemical data (major and trace elements). The model shows that the greatest part of the variation contained in the analyzed bauxite data (the first discriminant function, DF1) is associated with systematic alteration of geochemical composition in time, emphasizing characteristic decrease in clay component and gradual enrichment in heavy metals from oldest (Upper Triassic) to the youngest (Miocene) bauxites. In the general scheme, particular bauxite horizons represent standalone groups (Upper Triassic) while others form clusters showing increase and/or decrease of a particular set of elements signaling the changes in environmental conditions during the considered geological history of ADCP. Other discriminant functions (DF2 and DF3) also contribute to the all-inclusive distinction between the eight a priori defined bauxite groups discriminated by the characteristic set of geochemical variables where DF2 typically refers to the process of desilication, while DF3 to that of deferralitization.
We explored the potential incorporation of Sentinel-2A imagery for rock unit determination in the Croatian karst region dominated by carbonate rocks. The various lithological units are potential sources of both stone aggregates and dimension stone, and their spatial distribution is of high importance for mineral resource management. The presented approach included the preprocessing and processing of existing analog data (geological maps), Sentinel-2A satellite images and the United States Geological Survey spectral indices, all in combination with ground truth data. Geological mapping and digital processing of legacy maps using the K-means and random forest algorithm reduced the spatial error of the geometry of geological boundaries from 100 m and 300 m to below 100 m. The possibility of discriminating individual lithological units based on spectral analysis and discriminant function analysis was also examined, providing a tool for evaluating the geological potential for mineral resources. Despite the challenges posed by the lithological homogeneity of karst terrain, the results of this study show that the use of spectral signature data derived from Sentinel-2A satellite images can be successfully implemented in such terrains for the enhancement of existing geological maps and mineral resources exploration.
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