Ley 25.675: Ley General del Ambiente

1

Izabella Rebeka Márkus#

1 _{Institute of Mineralogy and Geology, University of Miskolc,} #_{[email protected]}

Key words: REE content of bauxite, REE-phosphates, xenotime-(Y), baddeleyite

INTRODUCTION

Halimba is situated in the south-western part of the Bakony-mountains in Central- Hungary. This is a well known region for its numerous karst-bauxite deposits (Halimba is one of them). Our aim was the identification of REE containing mineral phases, their relationships with textural elements and the possibility of their enrichment in size fractions obtained by wet sieving.

GEOLOGICAL BACKGROUND

The karst-bauxite deposit from Halimba covers an area of 8 km2, being the largest continuous karst-bauxite deposit in Europe (Bárdossy 2007). The substrata of the deposit varies, the Norian dolomites of the Haupt Dolomite Formation being the most frequent, which is partially overlain by the upper Rhetian-Norian carbonates and marls of the Kössen Formation and the carbonates of the same age of the Dachstein Limestone Formation (Pataki 2002). The bauxite was deposited in a fluvial-floodplain environment, and it is enriched in bauxite extraclasts. The texture can be characterized as bauxitic-wackstone or packstone with iron rich ooids, pisoids and intraclasts (Juhász 1988, Bárdossy 2007). The cover of the bauxite deposit is the Santonian conglomerates and marls of

the Csehbánya Formation, the Jákó Marl Formation and the Ugod Limestone Formation.

MATERIALS AND METHODS

The samples were prevailed from the Halimba-subterranean mine. Based on the previous bulk rock ICP-MS results, we selected a sample with high REE content on which we made detailed mineralogical investigations. We studied the whole, unprocessed sample and also the different size fractions obtained with wet sieving. The applied methods were X-ray powder diffraction (quantitative data was obtained by Rietveld-refinement), X-ray fluorescence spectrometry and scanning electron microscopy combined with energy dispersive X-ray spectrometry.

RESULTS AND DISCUSSION

On the whole sample based on XRD results we identified boehmite, hematite, anatase, rutile and kaolinite. In the fractions > 1 mm and 500 μm obtained with wet sieving, the mineralogical composition was slightly different. We identified boehmite, hematite, anatase, rutile and zircon. Kaolinite was absent. In the fractions > 212 μm, >125 μm and > 63 μm the zircon was absent. In the fractions > 45 μm and < 45 μm beside the boehmite,

98 hematite, anatase and rutil the kaolinite appeared. The amount of kaolinite in the original sample was 3-5 %, in the > 45 μm fraction 5-4 % and in the < 45 μm fraction 11-8 %, showing that the clay mineral content of the bauxite can be decreased efficiently by wet sieving. The amount of zircon was around 0.2-0.5 wt % in both sample. During the Rietveld-refinement a residual peak persisted at 6.118 Å, which we identified as lepidocrocite (200) with Al-substitution. Although it is considered a rare mineral in bauxites, the solid solution between bohmite-lepidocrocite is known (Wolska et al. 1992), but this case needs further investigations.

We made SEM observations on the whole sample and the fractions > 500 μm, > 45 μm, < 45 μm. The original sample showed a specific oolitic, pisolitic wackstone texture. We identified monazite and xenotime-(Y) enriched in REE. The xenotime was enriched in Gd, Dy, Er, Yb, while the monazite in Nd, La and Sm. The xenotime grains were angular, xenomorph, appearing always inside the ooides. The monazite is more frequent, it can be found in the ooids and their matrix too. Beside these two minerals, we observed a large quantity of zircon in the ooid/pisoids and the matrix too, and in few cases baddeleyite. In the > 500 μm fraction we identified monazite and xenotime with similar REE enrichment like in the first sample, except few grains of monazite in which beside Nd, La, Sm the Eu and some Th and Ca could also be observed. Also in this sample we found xenotime with very low REE content. In the > 45 μm fraction size sample, we identified the above- mentioned REE containing minerals. We also observed U containing xenotime grains, which could not be observed in other samples. In the < 45 μm sample we identified monazite with La, Nd Sm enrichment, Ca is also present, but based on other EDX measurements made on the ground mass, Ca could be observed to, so it is possible to be simply enrichment of the ground mass. We also observed the

presence of Cr and Na in the groundmass. The xenotime grains showed similar composition like in other samples. The xenotime and monazite grains in all samples were around 5-10 μm in size. In the case of the last two samples we could not determine if the grains were part of the ground mass or in the ooids/pisoids because the samples size fraction is smaller than the size of these (20-30 μm).The REE containing mineral grains were more abundant in the coarser fraction.

Based on XRF analyses Al2O3 content

decreased with the size fraction, while the SiO2 content increased. This can be

explained with the increasing amount of kaolinite. The MgO and CaO content was the highest also in the < 45 μm fraction. Sr and Zr also shoved enrichment in the smaller grain sizes, while the Cr has a decreasing tendency.

Acknowledgement: The research was carried out as part of the TÁMOP-4.2.2.A- 11/1/KONV-2012-0005 project as a work of Center of Excellence of Sustainable Resource Management, in the framework of the New Széchenyi Plan.

REFERENCES

BÁRDOSSY, G. (2007): The Halimba bauxite deposite. 119 p.

JUHÁSZ, E. (1988): Sedimentological features of the Halimba bauxite and paleogeographic reconstruction. Acta Geol.

Hungarica, 31/1-2, 111-136.

WOLSKA, E., SZAJDA, W., PISZORA, P. (1992): Determination of solid solution limits based on the thermal behaviour of aluminium substituted iron hydroxides and oxides. Journal of Thermal Analysis, 38, 2115-2122.

Pataki, A. (2002): Geological results of the research between 1995-2001 on the Halimba bauxite deposit. Földtani Kutatás,

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LIANDRATITE FROM KARKONOSZE PEGMATITES,