2.3. Okrouhlá Radouň uranium deposit

The Okrouhlá Radouň uranium deposit is situated in a NNW-SSE striking shear zone on the NE margin of the Klenov pluton, which is a part of the Moldanubian plutonic complex. The host rock series comprises partly migmatised biotite paragneisses and sillimanite-biotite paragneisses of the Moldanubian Zone and two-mica leucogranites of the Klenov pluton. Granites that formed a series of the NE-SW to NNE-SSW elongated sheets or larger irregular bodies with sheeted margins intruded into the high-grade metasediments. The sheets are mostly parallel to the foliation in the metasediments.

The most significant mineralised structure in this area, the Radouň shear zone, was explored along a strike length of approximately 3 km and to a depth of 650 m. The highest grade uranium mineralisation was developed at depths of 250–400 m beneath the present surface. The thickness of the mineralised shear zone is highly variable, ranking from 30 cm to approximately 7 m. The thickest portion of this zone was observed in the southern part of the uranium deposit, where a shear zone was developed in altered two-mica leucogranites and in highly hydrothermally altered, partly migmatised biotite paragneisses. The shear zone is infilled with cataclasites formed by host rock breccias, which were altered to clay-mineral-rich and chlorite-rich assemblages containing a disseminated uranium mineralisation comprising mainly coffinite and lesser amounts of uraninite. Total mine production of the Okrouhlá Radouň uranium deposit was 1339.5 tons U with average grade of 0.084% U, mined from 1972 to 1990 [7].

#### 2.4. Zadní Chodov uranium deposit

The Zadní Chodov uranium deposit, which is located in the northern tectonic block of the Bor pluton, was developed by mine workings down to a level of 1250 m with a length of over 2.5 km. The host rock series are formed by migmatised biotite paragneisses of the Moldanubian Varied

Group with intercalations of quartzites, amphibolites, calc-silicate rocks and crystalline limestones. Uranium mineralisation is associated with N-S trending zones of the Zadní Chodov fault in areas of their intersection with NW-SE trending fault structures. The shear zones are infilled by highly chloritised and arigilitised host rocks.

2.6. Vítkov II uranium deposit

2.7. Lhota uranium deposit

3. Analytical methods

average grade of 0.124% U, mined from 1961 to 1990 [7].

18 m. The mineralised shear zones comprise coffinite and brannerite.

and average grade of 0.120% U was identified [7].

study the internal structure of mineral aggregates.

The Vítkov II uranium deposit occurs in the central part of the Bor pluton. Its main mineralised shear zones are zone 0–30 in the east and the Vítkov zone in the west. The thickness of the shear zones varies from 5 to 7 m to several tens of metres. Both the shear zones are infilled by crushed altered rocks, quartz and carbonates. Rich accumulations of U-minerals often occur in their vicinity. The pennate NW-SE faults evolved between both shear zones are infilled by dykes of biotite and two-mica granites and aplites. Granites of the Bor pluton in the area of the Vítkov II uranium deposit are usually intensely altered to aceites. The ore bodies comprise coffinite, uraninite and brannerite finely disseminated in the surrounding altered granites. The ore bodies are grouped into four ore pipes, which are accumulated in environs of the shear zone 0–30. Total mine production of the Vítkov II uranium deposit was 3972.6 tons U with

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 Lhota uranium deposit is situated in the central block of the Bor pluton. Uranium mineralisation is evolved in altered coarse-grained biotite granites, accompanied by smaller bodies of amphibole-biotite granodiorites and tonalites. All these granitoids are overlain by remnants of the Moldanubian high-grade metasediments. The NW-SE, partly also N-S trending aplite dykes, pierces this rock complex. The two ore bearing shear zones (Os-2 and Os-17) strike NW-SE and dip steeply NE. The thickness of these mineralised shear zones are 5–

This uranium deposit has been verified between 1953–1967 and 1975–1989 by five exploration shafts down a depth of 250 m and by numerous boreholes down to levels of 300–600 m. During these two exploration stages, uranium mineralisation with the total amount of 158 t U

The rock-forming (chlorite, plagioclase) and uranium minerals were analysed in polished thin sections using CAMECA SX-100 electron probe micro-analyser (EPMA) operated in WDX mode. The contents of selected elements were determined using an accelerating voltage and beam current of 15 keV and 20 or 40 nA, respectively, with a beam diameter of 2–5 μm. The raw data were converted into concentrations using appropriate PAP-matrix corrections [9]. The detection limits were approximately 400–500 ppm for Y, 600 ppm for Zr, 500–800 ppm for REE and 600–700 ppm for U and Th. Back-scattered electron (BSE) images were acquired to

The whole-rock composition of the selected, unaltered and altered high-grade metasediments and granitic rocks from investigated uranium deposits is based on analyses of 50 samples. The selected trace elements (U, Th, REE, Y and Zr) were determined by ICP-MS (a Perkin Elmer Sciex ELAN 6100 ICP mass spectrometer) at Activation Laboratories, Ltd., Ancaster, Canada.

The thickness of main mineralised shear zones (CH-1, CH-4 and CH-11) ranges from 30 cm to approximately 1–2.5 m. Their total thickness is about 50–150 m (Figure 4). The high-grade uranium mineralisation was developed at the depths of 440–960 m beneath the present surface. The most common uranium minerals are coffinite (65 vol.%), uraninite (25 vol.%) and brannerite (10 vol.%). Total mine production of the Zadní Chodov uranium deposit was 4150.7 tons U with average grade of 0.195% U, mined from 1952 to 1992 [8].

#### 2.5. Dyleň uranium deposit

The Dyleň uranium deposit was located in high-grade metasediments of the Moldanubian Zone (migmatised biotite, biotite-sillimanite and quartzitic paragneisses with intercalations of quartzites). The main tectonic zone in the area of the Dyleň ore deposit is N-S trending zone of the Dyleň fault, dip to W at an angle of 60–70. However, the uranium mineralisation is associated with NW-SE trending shear zones, dip to SW at an angle of 70–90. The W-E striking faults crosscut both shear zone structures. All these shear zones and faults are infilled by chlorite-enriched aceites. Highly disseminated apatite-brannerite-coffinite association with up to 90 vol.% of coffinite represents the Variscan uranium mineralisation. Main part of uranium mineralisation is bounded on highly altered biotite paragneisses. Total mine production of the Dyleň uranium deposit was 1100.5 tons U with average grade of 0.14% U, mined from 1965 to 1991 [7].

Figure 4. Schematic cross section of the Zadní Chodov uranium deposit, modified from [8].
