The uranium-lead mineralisation was found in the mine dump material in the locality Bezděkov (Tachov area, western Bohemia, Czech Republic). Galena occurs as coarse-grained aggregates up to 5 cm in size in quartz gangue, partly replaced by cerussite. Cerussite forms massive and powdery aggregates replacing galena. It is orthorhombic, space group Pmcn with unit-cell parameters refined from X-ray powder diffraction data: a 5.1848(2), b 8.5001(3), c 6.1478(2) Å and V 270.937(13) Å3. Kasolite forms globular aggregates covering the area up to several cm2. It is monoclinic, space group P21/c, the unit-cell parameters refined from X-ray powder diffraction data are: a 6.7133(6), b 6.9516(8), c 13.2666(14) Å, β 104.156(8)o and V 600.33(11) Å3. The chemical analyses of kasolite correspond to the empirical formula Pb1.12Fe0.03Ca0.02K0.01(UO2)1.11(SiO4)1.00·H2O on the base of Si = 1 apfu. The Bezděkov ore occurrence belongs to the shear-zone hosted uranium mineralisation. The discovered mineralization originated by the weathering of galena and uraninite in conditions of supergene zone in-situ.
The Jánská vein is one of the important veins of Březové Hory mining district (central Bohemia, Czech Republic).Base metals were mined here since 14 th century and uranium ore during late 1950's.Uranium mineralization is younger than most of the base metal mineralization according to macroscopic and microscopic study.Most specimens of uraninite, obtained from archive, contain more or less abundant galena inclusions.Galena of this type is non-radiogenic as indicated by its Pb isotopic composition (ICP-MS).Its origin can be explained by remobilisation of the older base-metal mineralization during the younger, uranium-bearing mineralization event.The amount of radiogenic Pb in uraninite fluctuates from 48 up to 89.8 %.The age of theoretical end member of uraninite, calculated statistically from all measured data (for intersection 208 Pb/ 206 Pb = 0), is 269.8 ± 20.3 Ma (2σ).The only uraninite grain without galena inclusions yielded an age of 263.2 ± 8.9 Ma by chemical dating using electron microprobe.The calculated age of the uranium mineralization is in agreement with published data for other uranium deposits genetically associated with the Central Bohemian Plutonic Complex.
Abstract Klajite, MnCu 4 (AsO 4 ) 2 (AsO 3 OH) 2 (H 2 O) 10 , the Mn-Cu-bearing member of the lindackerite group, was found in Jáchymov, Czech Republic, as the second world occurrence. It is associated with ondrušite and other arsenate minerals growing on the quartz gangue with disseminated primary sulfides, namely tennantite and chalcopyrite. Electron-microprobe data showed klajite aggregates to be chemically inhomogeneous at larger scales, varying from Mn-Ca-rich to Cu-rich domains. The chemical composition of the the Mn-rich parts of aggregates can be expressed by the empirical formula (Mn 0.46 Ca 0.22 Cu 0.07 Mg 0.02 ) ∑0.77 (Cu 3.82 Mg 0.14 Ca 0.03 Zn 0.01 ) ∑4.00 (As 1.94 Si 0.06 ) ∑2.00 O 8 [AsO 2.73 (OH) 1.27 ] 2 (H 2 O) 10 (mean of seven representative spots; calculated on the basis of As + Si + P = 4 a.p.f.u. (atoms per formula unit) and 10 H 2 O from ideal stoichiometry), showing a slight cationic deficiency at the key Me-site. According to single-crystal X-ray diffraction, klajite from Jáchymov is triclinic, P , with a = 6.4298(8), b = 7.9716(8), c = 10.707(2) Å, α = 85.737(12)°, β = 80.994(13)°, γ = 84.982(10)°, and V = 538.85(14) Å 3 , Z = 1. The crystal structure was refined to R 1 = 0.0628 for 1034 unique observed reflections (with I obs > 3σ( I )), confirming that klajite (Mn-Cu member) and ondrušite (Ca-Cu member) are isostructural. The current data-set allowed determination of the positions of several hydrogen atoms. Discussion on hydrogen bonding networks in the structure of klajite as well as detailed bond-valence analysis are provided.
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Uraninite and the supergene minerals from the Červená hydrothermal uranium vein (Jáchymov ore district, Czech Republic) were studied.These supergene minerals represent alteration products of the joint weathering of uraninite and hypogene sulfide minerals, connected to the acid-mine drainage (AMD) systems.The complex geochemistry of the hypogene mineralization provided a unique environment for formation of chemically diverse supergene phases.Among other features, the weathering system is characterized by the high activity of Cu 2+ and REE, which control the composition of the resulting supergene minerals: commonly occurring are Cu-dominant uranyl sulfates of the zippeite group (pseudojohannite, Cu-rabejacite), Cu-dominant uranyl silicates (cuprosklodowksite) or Y-and REE-containing uranyl-sulfate mineral sejkoraite-(Y).The high activity of Cu 2+ and REE is also reflected by the fact that both elements enter minerals, which are nominally Cu-or REE-free (marécottite, rabejacite, tyuyamunite, and compreignacite).The alteration association was evaluated with regard to the crystal-chemical properties of each mineral using the bond-valence approach, documenting distinct evolutionary trends during weathering.
Abstract The rare uranyl lead carbonate widenmannite, Pb 2 (UO 2 )(CO 3 ) 3 , was found at the Jánská vein, Příbram, Czech Republic, where two generations occur in several morphological types and mineral associations in hydrothermal veins. Alpha spectroscopy shows that these two generations have different ages, >220,000 and 118±12 y. ICP-MS analysis indicates that both widenmannites have a dominance of non-radiogenic Pb which originates from weathered galena. The older widenmannite I forms fine-grained, grey to beige aggregates in the highly altered supergene part of the hydrothermal ore vein in association with pyromorphite, cerussite and goethite. The younger widenmannite II occurs as white, yellow or greenish-yellow thin tabular crystals upto 0.5 mm long in association with cerussite, anglesite, limonite, kasolite and an unnamed Pb-U-O phase. Thermal analysis suggests that widenmannite decomposes in several steps, with Pb uranate as the final product. Infrared and Raman spectroscopy confirm the presence of non-equivalent (CO 3 ) 2– groups, bidentately coordinated in uranyl hexagonal polyhedra, forming the well known uranyl tricarbonate complex. Infrared spectroscopy shows conclusively that widenmannite does not contain molecular H 2 O.
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