3. Analytical methods

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 study the internal structure of mineral aggregates.

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 decomposition of the rock samples for ICP-MS analysis involved lithium metaborate/ tetraborate fusion.

Albite and carbonates are the main constituents of the aceites formed through hydrothermal alteration of granites and high-grade metasediments and occupy 65–85 vol.% of the bulk rocks. The quartz post-ore stage is characterised by filling of voids, created by removal of magmatic and/or metamorphic quartz, by quartz II, origin of quartz veinlets (quartz III), veinlets of

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

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The carbonate bearing post-ore stage is connected with the origin of calcite and relatively rarely sulphides, selenides and zeolites. Carbonates fill cavities in the altered rocks and/or form fine

In previous papers about shear zone-hosted uranium deposits in the Bohemian Massif [1, 10, 11], chemical composition of unaltered and altered host rocks was described in detail. Also, in those papers, detailed investigations of losses and gains during hydrothermal alteration of host rock series were performed using isocon method [12]. This chapter discusses about geochemistry of unaltered and altered rocks series concentrated on behaviour of selected trace

The chloritised high-grade metasediments from the Rožná and Okrouhlá Radouň uranium deposits without uranium mineralisation are depleted in REE. This depletion is also displayed by lower ΣREE (Rožná 69–98 ppm, Okrouhlá Radouň 106–196 ppm) and high LREE/HREE ratios (4.0–17.6) relative to the unaltered metasediments. In contrast to chloritised high-grade metasediments without uranium mineralisation, mineralised metasediments from the Rožná and Zadní Chodov uranium deposits are enriched in REE (ΣREE = 108–390 ppm), especially in

Figure 5. REE patterns of the high-grade metasediments and their hydrothermally altered equivalents from the Rožná

veinlets in highly altered granitic rocks. Occasionally, dolomite and siderite were found.

chlorite III and origin of younger hematite laths (hematite II).

4.2. Geochemistry of altered rocks

elements, especially REE, Y and Zr.

HREE (LREE/HREE 1.2–4.7) (Figures 5 and 6).

uranium deposit. Original data normalised to chondrite according to [13].
