Ktenasit a jeho minerální asociace z ložiska Zlaté Hory - východ (Česká republika)

Abstract

The rare Cu-Zn sulphate, ktenasite, was found in the association with schulenbergite, serpierite, gypsum and brochantite at abandoned stope of the Modrá štola adit, the ore deposit Zlaté Hory - East, Czech Republic. Ktenasite occurs there as two different (color, morphology) types, the first is olive green to dark green columnar crystals up to 4 mm in length which forms radially arranged groups or rich crystalline coatings. The second type is represented by blue to greenish blue crystalline coatings or hemispherical or fan-shaped aggregates formed by thin tabular crystals. The X-ray powder diffraction data, Raman spectra and chemical composition of both types are almost identical. Ktenasite is monoclinic, space group P21/c, the unit-cell parameters refined from X-ray powder diffraction data are: a 5.610(2), b 6.123(2), c 23.827(9) Å, β 95.27(3)o and V 815.0(4) Å3. Its chemical analyses correspond to the empirical formula Zn1.00(Cu3.13Zn0.96Mg0.07Al0.01)Σ4.17(SO4)1.98(PO4)0.01(SiO4)0.01(OH)6.32·6H2O. Schulenbergite most often occurs only as an admixture in blue-green crystalline aggregates of ktenasite, sometimes together with serpierite. More rarely, its blue tabular crystals with a pearly luster up to 0.4 mm in size were also observed. Schulenbergite is trigonal, space group R-3, the unit-cell parameters refined from X-ray powder diffraction data are: a 8.187(3), c 7.012(4) Å and V 410.5(3) Å3. Its chemical analyses correspond to the empirical formula (Cu4.96Zn2.34)7.30(SO4)1.92(SiO4)0.05(PO4)0.02 (OH)10.47·6H2O. Serpierite is relatively abundant in the studied mineral association, usually forms light blue fine crystalline coatings, its fan-shaped aggregates up to 4 mm in size formed by elongated tabular crystals have also been found more rarely. Its chemical analyses correspond to the empirical formula (Ca1.14Mn0.03Mg0.02)Σ1.19(Cu3.08Zn0.73)Σ3.81(SO4)1.99 (PO4)0.02(OH)5.97·3H2O. Abundant brochantite forms bright green crystalline coatings and tiny dark green to black-green crystals. Its chemical analyses correspond to the empirical formula (Cu3.80Zn0.17Al0.02)Σ3.99(SO4)0.99(PO4)0.01(OH)6.00. The origin of studied mineral association is connected with sub-recent weathering of primary sulphides (pyrite, pyrrhotite, sphalerite and chalcopyrite) in the conditions of abandoned mine space.