Selected supergene uranium minerals from the Tachov ore area (Czech Republic)
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Abstract
The occurence of three uranyl minerals (uranophane-beta, metauranocircite, metatorbernite) was found at the Tachov ore area (western Bohemia, Czech Republic). Uranophane-beta was determined at abandoned uranium deposit Vítkov II. It forms dark to orange yellow crystalline aggregates up to 1 × 3 cm in size and rare idiomorphic prismatic crystals up to 3 mm in length. It is monoclinic, space group P 21/a, the unit-cell parameters refined from X-ray powder diffraction data are: a 13.960(1), b 15.468(1), c 6.6318(8) Å, β 91.41o and V 1431.6(2) Å3. Chemical analyses of uranophane-beta correspond to the empirical formula (Ca1.00Co0.01Ni0.01)Σ1.02(UO2)2.00(SiO3OH)2.00·5H2O. Metauranocircite and metatorbernite was found at material from small open pit at Ostrov near Tachov. Metauranocircite forms yellow crystalline coatings up to 2 × 3 cm in size on quartz gangue or older metatorbernite composed by tabular crystals up to 2 mm in size. It is monoclinic, space group P 21/a, the unit-cell parameters refined from X-ray powder diffraction data are: a 9.783(2), b 9.885(2), c 16.878(2) Å, γ 89.93o and V 1632.3(4) Å3. Chemical analyses of metatorbernite correspond to the empirical formula (Ba1.04Ca0.02Co0.01Ni0.01)Σ1.08(UO2)2.04[(PO4)1.99(AsO4)0.01]Σ2.00·6H2O. Metatorbernite occurs as green crystalline coatings up to 2 × 2 cm in size on quartz gangue composed by tabular crystals up to 3 mm in size. It is tetragonal, space group P 4/n, the unit-cell parameters refined from X-ray powder diffraction data are: a 6.9702(9), c 17.329(2) Å and V 841.8(2) Å3. Chemical analyses of metatorbernite correspond to the empirical formula (Cu0.77Co0.01)Σ0.78(UO2)2.03[(PO4)1.84(AsO4)0.16]Σ2.00·8H2O. The origin of studied mineral association is interpreted as product of in-situ supergene alteration of primary uranium mineralization in environment under of present surface.
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References
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