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[ Single-crystal structure refinement of bukovite, (Cu3Fe)Σ4Tl2Se4 ]]> Sejkora J, Mauro D, Biagioni C; Vol. 68, issue 3, pages 179 - 184
Single-crystal X-ray diffraction study of bukovite, ideally (Cu3Fe1)Σ4Tl2Se4, was performed using a specimen from the Ústaleč uranium deposit, 15 km west of Horažďovice, SW Bohemia, Czech Republic. In the studied specimens, bukovite occurs in calcite gangue with uraninite associated with bytízite, chaméanite, clausthalite, hakite-(Hg) and umangite. Electron microprobe analysis gave (in wt. % - average of 20 spot analyses): Cu 19.90, Tl 41.21, Fe 5.55, S 0.31, Se 31.60, total 98.57. On the basis of 10 atoms per formula unit, the empirical formula of bukovite is (Cu3.06Fe0.97)Σ4.03Tl1.97(Se3.91S0.09)Σ4.00 (Z = 1). Unit-cell parameters are a = 3.9694(8), c = 13.694(3) Å, V = 215.77(10) Å3, space group I4/mmm. The crystal structure was refined by single-crystal X-ray diffraction data to R1 = 0.0264 for 92 unique reflections with Fo > 4σ(Fo) and 10 refined parameters. The crystal structure of bukovite can be described as formed by single mackinawite-like {001} layers of edge-sharing (Cu,Fe)-centered tetrahedra, with Tl atoms hosted in eight-fold cubic coordinated sites intercalated between these tetrahedral layers. The role of Fe is discussed and the chemical formula (Cu3Fe)Σ4Tl2Se4 is proposed. ]]> Original paper
<![CDATA[ Chemical composition of tourmalines from the Manjaka pegmatite and its exocontact, Sahatany Valley, Madagascar ]]> Gadas P, Novák M, Vašinová Galiová M, Pezzotta F; Vol. 68, issue 3, pages 185 - 202
Chemical compositions and mineral assemblages of tourmalines from the elbaite-subtype Manjaka pegmatite in the Sahatany Valley, central Madagascar, and its exocontact were examined using EPMA and LA-ICP-MS. Several textural, compositional and paragenetic types of tourmalines were recognized in the individual pegmatite units and in the zones located towards the host rock in the order: wall pegmatite unit → border pegmatite unit → contact zone → recrystallization zone; the latter zone evidently originated after the host Mg-rich calc-silicate rock (Di + Tr + Qz > Pl + Kfs ˃ Phl + Dol ˃ Cal). Zoned prismatic crystals from the border unit evolved from the core Tur Ia (dravite < Fe-rich elbaite), Tur Ib (Mn,Fe-rich to Mn-rich fluor-elbaite > elbaite), to the crystal rims Tur II (elbaite > darrellhenryite) via the substitutions: (1) 2YR2+ = YLiAl, (2) YMnWF = YFe2+WOH, (3) YLi0.5WOH = YAl0.5WO, and (4) YLiTAlWOH3 = YAlTSiWO3. The contact zone, ˜2 mm thick, contains abundant Tur IV (Li,Fe,Al-enriched dravite > oxy-dravite), and the recrystallization zone, ˜1.5 cm thick, common Tur V (fluor-uvite > dravite > fluor-dravite, magnesio-lucchesiite, uvite) via the substitutions: (1) 2YR2+ = YLiAl and (5) YR2+WOH = YAlWO, (6) XNaWOH = XCaWO and (7) XNaYAl = XCaYR2+. The chemical compositions of the individual types of tourmalines suggest that the mobility of elements between calc-silicate rock and pegmatite was low. Only weak influx of Mg, V and Cr into pegmatite and Li and Al from the pegmatite to the host rock - recrystallization zone, respectively, were observed. The existence of thin B-rich contact zone with dominant Tur IV suggests low influx of B into the host rock in early magmatic stage. High contents of F in Tur V from the recrystallization zone were very likely triggered by influx of B,F-enriched residual pegmatite fluids. Very high a(B2O3), but low a(H2O) and a(F) in the pegmatite melt constrained very low degree of external contamination of the pegmatite. Compositional evolution in tourmalines from Manjaka was compared with the pegmatites and their exocontact at Stoffhütte, Koralpe, Austria, and Bližná I, Moldanubian Zone, Czech Republic. ]]> Original paper
<![CDATA[ Perthite in nepheline syenite from the kakortokite unit in the Ilímaussaq Complex, south Greenland ]]> Schønwandt HK, Barnes GB, Ulrich T; Vol. 68, issue 3, pages 203 - 211
Petrographic investigations of white kakortokite (nepheline syenite) reveal two structurally different types of perthite grains, herein called type A and B. Type A is more common and consists of an intimate intergrowth of microcline and albite. Microcline in type A perthites consists of two irregular penetrative individuals which appear as elongated pointed bodies parallel to (010) intergrown with polysynthetic twinned albite, which occurs as serrated bodies elongated parallel to (010). In type B perthites, K-feldspar (microcline) shows tiled structure and albite appears as microcrystalline equigranular veinlets, penetrating the perthite grain often perpendicular to (010). A great compositional variation of the type A grains (from nearly 100% microcline to almost pure albite) excludes exsolution to be the main process responsible for the structure. On the other hand, a replacement process controlled by a simultaneous dissolution-precipitation can explain the structure of type A, which means that widespread Na-metasomatism (albitization) had to have taken place in the kakortokite. Due to the different twinning structure of K-feldspar (microcline) in type B, the albitization in these grains occurred by albite veining of the grains. ]]> Original paper
<![CDATA[ New type of epithermal manganese mineralization from the Banská Hodruša precious and base metal deposit at the Rozália mine, Hodruša- Hámre, Slovakia ]]> Rybárik M, Števko M, Koděra P, Prcúch J; Vol. 68, issue 3, pages 213 - 228
The newly discovered unusual epithermal manganese mineralization was found at the 18th level of the Rozália mine in the Štiavnica stratovolcano and it is hosted by a NE-SW oriented fault dipping 55° to SE. Based on its structural setting and cross-cut relationship to a pre-caldera vein it belongs to a large system of post-caldera veins related to horst uplift in the central zone of the stratovolcano. The vein occurs in andesite and consists of two contrasting parts, including a part dominated by white coarse-grained calcite and Mn-rich part represented by abundant johannsenite, younger rhodonite and Mn-carbonates (rhodochrosite, Mn-calcite), in association with minor quartz, calcite, adularia, chlorite, and clinozoisite. Ore minerals are represented by sphalerite, galena, pyrite, chalcopyrite and rare inclusions of acanthite and can be found exclusively in the Mn-rich part of the vein. Johannsenite forms greenish-blue, greenish-brown or brown radial aggregates reaching up to 7 cm in size. Its average empirical formula is Ca0.96(Mn0.97Mg0.07Fe0.03)1.07(Si1.98Al0.02)2.00O6. Rhodonite shows a significant compositional variation of Ca and Mn contents, ranging from Ca0.48Mn4.56(Si5O15) to Ca1.58Mn3.41 (Si5O15) as well as minor amounts of Fe (up to 0.32 apfu), Mg (up to 0.14 apfu) and Al (0.06 apfu). Microthermometry of fluid inclusions hosted by johannsenite, rhodonite, sphalerite, calcite and Mn-calcite determined that the mineralization precipitated from fluids of low salinity (1.4 to 5.3 wt. % NaCl eq.) and moderate homogenization temperatures (187-318 °C), with a trend of simultaneous decrease in salinity and temperature, interpreted as mixing of fluids. Boiling of fluids was recorded in early calcite at temperatures from 275 to 279 °C, corresponding to pressure from 58 to 62 bars and paleodepth from 704 to 752 m. These values are similar to data from other post-caldera veins in the vicinity of the mine, as well as from other johannsenite-bearing epithermal deposits in the world. ]]> Original paper
<![CDATA[ Deformation pattern of the Lower Triassic sedimentary formations of the Silica Nappe: Evidence for dynamics of the Western Carpathian orogen ]]> Vojtko R, Lačný A, Jeřábek P, Potočný T, Gerátová S, Kilík J, Plašienka D, Lexa O; Vol. 68, issue 3, pages 229 - 248
The Lower Triassic formations of the Silicic Unit were studied by structural geology methods to unravel its deformation history and chronology of nappe transport. The nappe sheet of this unit is the highest representative thin-skinned thrust in the Western Carpathians. The Silicic Unit spreads in the broader area of the Variscan consolidated Gemeric and the Veporic crystalline basements. Geological and palaeotectonic evidence indicate that the Silicic nappe pile is more than one km and at some places up to 3 km thick. The nappe is abundant in the inner zones of the Western Carpathians and overlaps all other structural units in the area, in particular it covers the margin of the Gemeric Unit. Based on the structural analysis, geometry and overprinting criteria of secondary planar structures (cleavages or fold axial surfaces) and fold axes indicate the presence of three main deformation events. Generally, the first group of structures is related to ≈ W-E shortening (AD1), which is interpreted in association with closure of the Meliata Ocean. The younger direction of the Silicic nappe system shortening (AD2) shows top-to-the-NNW thrusting and is related to the Early to Late Cretaceous Eoalpine convergence. This stage also comprises folds with steep north dipping axial surfaces and occasionally also flat-lying axial surfaces forming fan-like structure of fold axial planes. The last observed structures refer to the W-E shortening (AD3) characterised by the symmetric gentle to open folds with subvertical axial surfaces locally with few pronounced top-to-the-east asymmetries. ]]> Original paper
<![CDATA[ Navrotskyite, K2Na10(UO2)3(SO4)9·2H2O, a new sodium and potassium uranyl-sulfate mineral from the Blue Lizard mine, Red Canyon, White Canyon District, San Juan County, Utah ]]> Olds TA, Kampf AR, Perry SL, Guo X, Marty J, Rose TP, Burns PC; Vol. 68, issue 3, pages 249 - 259
Navrotskyite (IMA 2019-026), K2Na10(UO2)3(SO4)9·2H2O, is a new potassium-sodium-uranyl-sulfate mineral from the Blue Lizard mine, San Juan County, Utah, USA. The new mineral occurs on sandstone and asphaltite matrix in close association with belakovskiite, blödite, bobcookite, changoite, fermiite, ferrinatrite, ilsemannite, ivsite, meisserite, pseudomeisserite-(NH4), seaborgite and tamarugite. Navrotskyite is orthorhombic, space group Pbcm (#57), with unit cell parameters a = 5.4456(13), b = 21.328(5), c = 33.439(8) Å, V = 3883.8(2) Å3 and Z = 4. Crystals are acicular tapered needles up to about 1 mm in length, typically occurring as radial sprays and tightly intergrown aggregates resembling fibre-optic bundles. Crystals are elongated on [100] and exhibit only the {012} prism form, resulting in diamond-shaped cross-sections. The terminations are generally not well-formed, but broken crystals are truncated by good {100} cleavage. No twinning was observed. Navrotskyite is pale greenish yellow in color, has a white or very pale-yellow streak and fluoresces neon yellow green under both long- and short-wave UV. It is transparent with vitreous to silky luster. The mineral exhibits a splintery, uneven fracture and has a Mohs hardness of about 2. The calculated density based on the empirical formula is 3.46 g/cm3. The mineral is optically biaxial (-), with α = 1.520(2), β = 1.557(2) and γ = 1.565(2) (white light). The measured 2V is 48.2(5)° and the calculated 2V is 48.9°. Dispersion is imperceptible and no pleochroism was observed. The optical orientation is X = a, Y = c, Z = b. The empirical formula is K2.06Na9.98U3.02S8.98O44H3.97 based on 44 O apfu. The eight strongest powder X-ray diffraction lines are [dobs Å(I)(hkl)]: 5.28(100)(110), 3.050(44)(049, 119), 10.70(43)(020), 3.845(36)(046,134,116), 3.225(30)(153), 3.533(29)(060,061,136), 2.822(29)(139) and 5.59(27)(006). The crystal structure of navrotskyite (R1 = 0.0289 for 4032 reflections with I > 2σI) contains infinite [(UO2)(SO4)3]4- chains that extend along [100] and that link to neighbouring chains via a complex network of K-O and Na-O bonds. Related topologies based on the same UL3-type chain are also observed in the minerals fermiite, meisserite and pseudomeisserite-(NH4), all of which occur in the same general assemblage as navrotskyite. ]]> Original paper