Journal of GEOsciences Table of Contents for the Journal of GEOsciences. List of articles from the latest print issue.http://www.jgeosci.orgen-US Journal of GEOsciences <![CDATA[ Compositional, structural and vibrational spectroscopic characteristics of feldspar megacrysts in alkali basalts from southern Slovakia ]]> Huraiová M, Lengauer CL, Abart R, Hurai V; Vol. 63, issue 3, pages 215 - 226
Feldspar megacrysts in Late Miocene-Pliocene maars, diatremes and basaltic lava flows in the northern part of the Pannonian Basin span the compositional range from Na-sanidine, through anorthoclase to oligoclase and andesine. Newly formed An82 plagioclase (bytownite) crystallized within composite melt inclusions hosted by the oligoclase. Powder X-ray diffraction data indicate strong structural disorder diagnostic of the high albite-high sanidine series typical of magmatic feldspars. The magmatic origin is also corroborated by chemical compositions, which plot along the 700 ± 50 °C solvus, with the exception of the most sodic Ab79 plagioclase megacryst projecting along the 600 °C isotherm. Vibrational spectroscopic records document that the basic groups of magmatic feldspars can be identified by the specific pattern of the group I and IV bands in the 350-600 cm-1 range. The IVa band at 560-570 cm-1 is diagnostic for triclinic feldspars. The anorthite and orthoclase contents can be inferred from the 506-515 cm-1 (Ia) and 473-486 cm-1 (Ib) peak separation values combined with the Ia bandwidth. ]]> Original paper
<![CDATA[ Felsic diapirism beneath the high-grade terrains in the eastern Bohemian Massif - refraction tomography evidence ]]> Novotný M; Vol. 63, issue 3, pages 227 - 251
Unlike standard ray-based tomographies, the Depth-Recursive Tomography on Grid (DRTG) method assesses the travel-time fit at each model grid node using a regular network of refraction rays. This concept allows estimating the lateral resolution achieved in the velocity image that regards the chosen confidence levels and the strength of velocity anomalies. Recently, The DRTG has been applied to the S01 and CEL09 refraction profiles imaging major crustal structures of the Bohemian Massif in enhanced resolution. Now, similar enhanced velocity models are derived along the S04, S02 and S03 profiles mapping the Sudetic and Moldanubian regions. The S02 and S03 and the transverse CEL09 and S04 velocity sections particularly imaged the subsurface of the Moldanubian high-grade belts to the 15-20 km depth. Their common interpretation revealed the signatures of exhumation processes from upper-mantle depths assumed in this region. Particularly, the S02 and S03 sections map large volumes of high-grade metamorphic rocks forming low-velocity (LV) diapirs that are surrounded by 7000-6400 m/s high-velocity (HV) elevations. The S03 section images the coupled HV-LV-HV anomalies beneath the high-grade complexes of the Orlica-Śnieżnik Dome (OSD) and the Góry-Sowie Unit (GSU). The central gradient-free LV (5800-6000 m/s) cores of these triplets apparently correspond to the OSD or GSU felsic granulites/gneisses that ascended to supra-crustal levels.
The Bouguer anomaly map suggests that the S02 and S03 profiles intersect the felsic sheets formed along the transverse Sudetic faults. Along the western belt of Moldanubian high-grade rocks, the S02 section revealed an extensive HV body shallowly emplaced beneath the high-grade Gföhl and Ostrong assemblages. Three mid-crustal HV elevations, correlating with local magnetic anomalies, obviously represent the deep sources of this HV mafic body and indicate its autochthonous nature. Finally, the DRTG also detected a shallowly emplaced HV layer beneath the Saxonian Granulite Massif at the S04 section. The mid-crustal HV-LV-HV diapiric triplets and shallowly emplaced HV bodies are likely typical of the high-grade terrains. The observed patterns resulted from contemporaneous intrusion of mafic and, more viscous, felsic magmas during continental collision. The inferred structural features of subduction-exhumation processes are suggested to further constrain their thermo-mechanic modeling. ]]> Original paper
<![CDATA[ Complex magmatic and subsolidus compositional trends of columbite-tantalite in the beryl-columbite Šejby granitic pegmatite, Czech Republic: role of crystal-structural constraints and associated minerals ]]> Novák M, Chládek Š, Uher P, Gadas P; Vol. 63, issue 3, pages 253 - 263
The simply zoned Šejby pegmatite of beryl-columbite subtype is enclosed in migmatitized gneisses - country rocks of the southern part of the Central Moldanubian Plutonic Complex, Bohemian Massif, Czech Republic. The columbite-group minerals (CGM) occur mostly in blocky K-feldspar unit. Primary magmatic CGM [columbite-(Fe)—tantalite-(Fe)], show an interesting compositional and textural evolution. Subhomogeneous cores of columbite-(Fe)—tantalite-(Fe) (A) are surrounded by heterogeneous intermediate zones (B) and (C) with irregular to oscillatory zoning and mutually comparable compositions. Zone (B) contains grains of tapiolite-(Fe) and inclusions of pyrite decomposed into a mixture of secondary jarosite-group minerals. In the next zone (C), irregular Mn-enriched patches occur and in the outermost thin zone (D) CGM exhibit fine oscillatory zoning typically developed at crystal terminations. The late, subsolidus CGM include patchy-zoned Mn-enriched columbite-(Fe) and late columbite-(Fe) veinlets both formed at the expense of their magmatic precursors in the zone C; the veinlets are also present in the zone D. Similar but fine patches and veinlets are developed around jarosite pseudomorphs after pyrite. The compositional evolution of CGM shows a slight increase in Ta/Nb and Mn/Fe in the zones A and B followed by a reverse trend to elevated Nb and Fe in the zone C and, in particular, in the zone D. Complex subsolidus fluid-melt interactions that generated patches and veinlets caused only minor changes in Ta/Nb and slight Mn-enrichment. Tantalum depletion in veins close to jarosite pseudomorphs after pyrite indicates higher mobility of Ta in acidic low-temperature fluids. ]]> Original paper
<![CDATA[ Horákite, a new hydrated bismuth uranyl-arsenate-phosphate mineral from Jáchymov (Czech Republic) with a unique uranyl-anion topology ]]> Plášil J, Kampf AR, Sejkora J, Čejka J, Škoda R, Tvrdý J; Vol. 63, issue 3, pages 265 - 276
Horákite, ideally (Bi7O7OH)[(UO2)4(PO4)2(AsO4)2(OH)2]·3.5H2O, is a new uranyl mineral discovered on a specimen originating from Jáchymov, Czech Republic (most probably from the Geister vein, Rovnost mine). It occurs as a supergene alteration mineral in association with phosphuranylite (overgrowing older metatorbernite-metazeunerite) in a quartz gangue with abundant tennantite. Horákite forms greenish-yellow to pale yellow prismatic crystals clustering to acicular aggregates, up to 1 mm across. Crystals are transparent to translucent with a vitreous luster. The mineral has a light yellow streak. Estimated Mohs’ hardness is ˜2. The cleavage is perfect on {100}. The calculated density is 6.358 g/cm3. Horákite is optically biaxial (+), α ≈ 1.81, β ≈ 1.84, γ ≈ 1.88 (measured in white light); 2Vobs. is 78(1)°, 2Vcalc. is 83°; non-pleochroic. The optical orientation is X = b, Zc. Electron-microprobe analysis yielded the empirical formula (Bi7.01Pb0.14)O7OH[(U1.01O2)4(P1.03O4)2(As0.74Si0.23O4)2(OH)2]·3.5H2O based on 37.5 O apfu. Horákite is monoclinic, C2/c, a = 21.374(2), b = 15.451(3), c = 12.168(2) Å, β = 122.26(1)° and V = 3398.1(10) Å3, Z = 4. The eight strongest X-ray powder-diffraction lines are [dobs Å(I)(hkl)]: 11.77(100)(110), 6.21(23)(-202), 5.55(23)(310, -112), 4.19(27)(-331), 3.54(61)( 510, -423), 3.29(20)( 331), 3.14(58)(241, 023) and 3.02(98)(150, 113, -533, mult.). The crystal structure refinement of horákite, refined to R = 5.95 % for 1774 unique observed reflections, revealed a novel sheet structure. It consists of topologically unique [(UO2)4(PO4)2(AsO4)2(OH)2] sheets (i.e., horákite topology), and an interstitial {(Bi7O7OH)(H2O)3.5} complex. Sheets result from the polymerization of UO7 bipyramids by sharing edges to form tetrameric units; tetrahedrally coordinated sites are linked to the UO7 both monodentately (T1 to U1) and bidentately (T2 to U2). The mineral is named after František Horák (1882-1919), the mining engineer in Jáchymov, and his grandson, Vladimír Horák (born 1964), an amateur mineralogist and expert on the mining history of the Jáchymov ore district. ]]> Original paper
<![CDATA[ Initial replacement stage of primary uranium (UIV) minerals by supergene alteration: association of uranyl-oxide hydroxy-hydrates and “calciolepersonnite” from the Krátka Dolina Valley (Gemerská Poloma, Gemeric Unit, Western Carpathians, Slovakia) ]]> Ferenc Š, Biroň A, Mikuš T, Spišiak J, Budzák Š; Vol. 63, issue 3, pages 277 - 291
Mineral association with uranyl-oxide hydroxy-hydrates and uranyl carbonate-silicates was found in J-1 quartz vein containing U-Au mineralization at Krátka Dolina Valley (Rožňava district, Slovakia). The vein penetrated Lower Palaeozoic graphitic phyllites and metalydites (Vlachovo Fm., Gemeric Unit).
Among minerals identified at the site, becquerelite I is characterized by the highest Ca content and its composition is close to the ideal . On the other hand, becquerelite II is characterized by increased K at the expense of Ca. The average chemical composition of both types of becquerelite can be expressed by the empirical formulae: (Ca0.85K0.04Na0.01Fe0.02Zn0.02Ba0.01Pb0.01)Σ0.96[(UO2)6O4(OH)5.84]·8H2O (becquerelite I), and (Ca0.36K0.27Na0.01Fe0.02Zn0.02Pb0.01Bi0.01)Σ0.78[(UO2)6O4(OH)5.29]·8H2O (becquerelite II). Vandendriesscheite with unusual chemical composition imitates a transition phase between gauthierite and vandendriesscheite. Negative correlation of K vs. Pb indicates that in the studied mineral phase lead is partially replaced by potassium (and other cations). An average chemical composition of the studied vandendriesscheite can be expressed as: (K0.49Na0.02)Σ0.51(Pb1.20Fe0.05Zn0.04Ba0.03Sr0.02Al0.02)Σ1.36[(UO2)10O6(SiO4)0.05(PO4)0.02(OH)10.86]·11H2O. A leesite-like phase with an average composition (K0.72Sr0.01Ba0.02Fe0.03Zn0.01Pb0.02Al0.02)Σ0.83(H2O)2[(UO2)4O2(SiO4)0.01(OH)5,00]Σ11,01·3H2O, was found only rarely. An unnamed mineral phase, with chemical composition close to lepersonnite-(Gd), designated as “calciolepersonnite”, is younger at the studied site then uranyl-oxide hydroxy-hydrates. Compared to the ideal lepersonnite-(Gd) formula, there is a lower REE content at the cationic position, an increased Ca and there are also monovalent cations (especially K) entering the structure. An average “calciolepersonnite” chemical composition is: (K0.62Na0.09)Σ0.71(Ca2.08Mg0.04Sr0.02Ba0.02Fe0.05Zn0.05Pb0.03)Σ2.30(Y + REE)Σ0.92[(UO2)23.76{(SiO4)3.19(PO4)0.11(AsO4)0.02(SO4)0.02}Σ3.34(CO3)8(OH)26.37]·46.82H2O.
In the supergene zone of J-1 vein at Gemerská Poloma, three stages of development can be defined: (I) formation of uranyl-oxide hydroxy-hydrates that directly, partially or completely, replace UIV minerals; (II) formation of uranyl carbonate-silicates (i.e., “calciolepersonnite”) that replace uranyl-oxide hydroxy-hydrates, apparently indicating shift to relative acid environment (but still remaining alkaline to neutral pH) and (III) formation of uranyl phosphates/arsenates of the autunite group (“uranium micas”) that precipitated relatively far from accumulations of primary (UIV) minerals (in cracks and cavities of the gangue, or in the surrounding non-mineralized rocks). Their origin documents the change of alkaline-neutral to acidic environment, due the more advanced weathering of vein sulphides. Given the absence of Y + REE in older uranyl-oxide hydroxy-hydrates that directly replace brannerite, most of these elements required for “calciolepersonnite” formation were probably released from the host rocks and not from the primary, hydrothermal uranium minerals. ]]> Original paper