2.2. Olší uranium deposit

2.1. Rožná uranium deposit

52 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

The Rožná uranium deposit occurs in the uppermost Gföhl unit of the Moldanubian Zone. The host rocks of this ore deposit are formed predominantly by biotite paragneisses, amphibolites and small bodies of calc-silicate rocks, marbles, serpentinites and pyroxenites. The uranium mineralisation is bounded on the longitudinal shear zones (R1–R4). The main part of disseminated uranium mineralisation hosts the Rožná 1 (R1) and Rožná 4 (R4) shear zones. In the less strongly mineralised Rožná 2 (R2) and Rožná 3 (R3) shear zones, numerous pinnate carbonate veins occur. Longitudinal shear zones are segmented by NW-SE and SW-NE faults, which host

Uranium mineralisation could be divided into (1) disseminated coffinite > uraninite > U-Zrmineralisation evolved in altered rocks (aceites) of the mineralised shear zones (R1–R4), (2) uraninite > coffinite mineralisation in carbonate veins, (3) disseminated coffinite > uraninite in aceites adjacent to main shear zones (R1, R4) and (4) mostly coffinite mineralisation bound to the intersection of shear zones with an younger NW-SE and SW-NE faults. Ore lenses of disseminated uranium mineralisation in fault zones R1 and R4 are 3.5-m thick on average, ore grade is around 0.5% U, up to 10% U locally. Ore bodies in ore zones R2 and R3 host a large number of carbonate veins up to 2-m thick with U-mineralisation of the average grade 0.6% U. Ore bodies in aceites with predominance of coffinite on uraninite and U-Zr silicate have U-mineralisation of

post-uranium carbonate-quartz-sulphide mineralisation (Figure 3) [1].

Figure 3. Schematic cross section of the Rožná uranium deposit, modified from [1].

The Olší uranium deposit is also evolved in the NE part of the Moldanubian Zone. The host rocks of this uranium deposit consist mainly of plagioclase-biotite and amphibole-bearing paragneisses with small lenses of K-rich granitoids and serpentinites. Longitudinal N-S and NNW-SSE striking ductile shear zones (O1, O2 and O3) dip to W at an angle of 45–70. Longitudinal shear zones are crosscut by ductile to brittle NW-SE and SW-NE striking fault zones that host lenses of contrasted uranium mineralisation. The main uranium ore bodies are evolved on the N-S longitudinal shear zones. The Variscan calcite-chlorite-uraninite association and the Mesozoic albite-chlorite-coffinite association represent the uranium mineralisation. Total mine production of the Olší ore deposit was 2922.2 tons U with average grade of 0.10% U, mined from 1959 to 1989 [7].
