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48 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

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Additional information is available at the end of the chapter Miloš René

http://dx.doi.org/10.5772/intechopen.71967 Additional information is available at the end of the chapter

#### Abstract

The Bohemian Massif hosts a significant quantity of uranium deposits bound by brittle shear zones developed in high-grade metamorphic rocks (Rožná, Okrouhlá Radouň, Zadní Chodov and Dyleň) and/or granites (Vítkov II and Lhota). According to the international atomic energy agency (IAEA) uranium deposits classification, these deposits are classified as metamorphic deposits. For shear zone-hosted uranium mineralisation, the no direct relationship between ore mineralisation and granite bodies is significant. Ore lenses and/or disseminated ore mineralisation form the shear zone-hosted uranium deposits. The host rocks of these deposits are transformed in aceites. Aceites are defined as low-temperature alkaline metasomatic rocks, which are closely associated with uranium mineralisation. Complex coffinite-uraninite or coffinite-uraninite-brannerite assemblages form the shear zone mineralisation with predominance coffinite about uraninite.

Keywords: uranium, shear zone, aceite, coffinite, uraninite, brannerite, Bohemian Massif

## 1. Introduction

The Bohemian Massif as part of the Central European Variscan belt hosts a high quantity of uranium mineralisation [1, 2]. The shear zone-hosted uranium mineralisation is recently classified as metamorphic uranium deposits (e.g., Ace Fay, Canada) [3]. In the Bohemian Massif, the Rožná, Olší, Okrouhlá Radouň and Zadní Chodov ore deposits in the high-grade metamorphic rocks of the Moldanubian Zone and the Vítkov II and Lhota ore deposits in granitoids of the Bor pluton represent this group of uranium deposits. Apart from the predominant veintype uranium deposits in the Ore Mts. (Niederschlema-Alberoda, Jáchymov) and the Příbram ore deposit, these deposits show no direct genetic relationship between mineralisation and granitic plutons (Figure 1).

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

2. Geological setting

pluton, fill N-S faults. (Figure 2) [6].

Figure 2. Geological map of the Bor pluton, modified from [6].

In high-grade metamorphic rocks of the Moldanubian Zone are evolved the Rožná, Olší, Okrouhlá Radouň, Zadní Chodov and Dyleň uranium deposits. The high-grade metamorphic rocks are represented by biotite paragneisses with intercalations of amphibolites, calc-silicate

Shear Zone-Hosted Uranium Deposits of the Bohemian Massif (Central European Variscan Belt)

http://dx.doi.org/10.5772/intechopen.71967

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The Vítkov II and Lhota uranium deposits occur in granitoids of the Bor pluton. An N-S trending, 35-km long magmatic body forms the Bor pluton, which is emplaced in the fault zone, which is a part of regional West Bohemian shear zone. The most voluminous rocks in the Bor pluton are coarse-grained biotite, usually porphyritic biotite granites. In the northern block, older amphibole-biotite granodiorites, tonalites and quartz diorites were also observed. Dykes of two-mica monzogranites, aplites, which predominates in the southern part of the Bor

rocks, marbles and lenses of partly serpentinised ultrabasic rocks (dunites).

Figure 1. Simplified geological map of the Bohemian Massif with the most significant hydrothermal uranium deposits.

The shear zone-bounded uranium deposits consist of peneconcordant lenses or highly disseminated uranium mineralisation evolved in brecciaed shear zones and/or in fractures. The host rocks of these deposits are strongly altered in aceites, exhibiting extensive albitisation, chloritisation and hematitisation of the host rock series. In the recent classification of metamorphic and metasomatic rocks, these metasomatic rocks are named as aceites [4].

According to their mineral composition, the aceites are very similar to episyenites developed in uranium deposits of theMassif Central and the ArmoricanMassifin France, linked toleucogranitic plutons. Episyenites are defined as igneous-like rocks of syenite composition; displaying cavities produced by hydrothermal dissolution of quartz grains than can ultimately host uranium ore deposits [5]. Both rock types are products of low-temperature alkaline metasomatism associated with a significant input of Na2O and the loss of SiO2. Distinctly different mineral compositions have metasomatic deposits, which originated by high-temperature alkali metasomatism (e.g., Central Ukraine). Metasomatic facies in these uranium deposits include albitites, aegirinites and alkali-amphibole-rich rocks. In the recent international union of geological sciences (IUGS) classification of metamorphic rocks, these metasomatites are classified as fault-related metasomatites, which are common in the Precambrian shields [4]. The aim of this chapter is to present the detailed petrology,mineralogy and geochemistry of aceites and associated uraniummineralisation evolved in shear zone-hosted uranium ore deposits of the Bohemian Massif.
