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[ A word of the retiring Editor-in-Chief & A word of the newly-coming Editor-in-Chief: (Not such) significant changes in the editorial board ]]> Janoušek V, Plášil J; Vol. 65, issue 3, page: 139
]]> Editorial
<![CDATA[ Stangersite, a new tin germanium sulfide, from the Kateřina mine, Radvanice near Trutnov, Czech Republic ]]> Sejkora J, Makovicky E, Balić-Žunić T, Berlepsch P; Vol. 65, issue 3, pages 141 - 152
The new mineral stangersite was found in the burning waste dump of abandoned Kateřina coal mine at Radvanice near Trutnov, northern Bohemia, Czech Republic. The new mineral occurs as well-formed, flattened, acicular crystals with a cross-section of 2-5 × 20-40 μm and up to 1 cm in length. They constitute random or fan-shaped clusters on rock fragments and on crumbly black ash in association with greenockite, herzenbergite, unnamed GeS2 and GeAsS. Stangersite was also observed as irregular grains, up to 100 μm in size, in the multicomponent aggregates on which the above-described crystals grow. These aggregates are formed, beside stangersite, by minerals of Bi-Sb, Bi2S3-Sb2S3 and Bi2S3-Bi2Se3 solid solutions, Bi3S2, Bi-sulfo/seleno/tellurides, tellurium, unnamed PbGeS3, Cd4GeS6, GeAsS, GeS2, Sn5Sb3S7, greenockite, cadmoindite, herzenbergite, teallite and Sn- and/or Se-bearing galena. Stangersite formed under reducing conditions by direct crystallization from hot gasses (250-350 °C) containing Cl and F, at a depth of 30-60 cm under the surface of the dump. The mine dump fire started spontaneously and no anthropogenic material was deposited there. Stangersite is brittle (aggregates) or elastic, to flexible (acicular crystals). It is orange to yellowish red with a very light yellowish brown streak, translucent to transparent in transmitted light, and has vitreous to adamantine luster. Cleavage is perfect in two directions: perpendicular and oblique to elongation of crystals. The VHN microhardness is 55 kp·mm-2 (539 MPa) and corresponds to Mohs hardness about 2; the calculated density is 3.98 g·cm-3. In the reflected light, stangersite is light greyish white. Bireflectance and pleochroism were not observed due to distinct orange-brown internal reflections. Anisotropy under crossed polars is strong with dark brownish grey to reddish-brown or brownish violet rotation tints. The empirical formula, based on electron-microprobe analyses of acicular crystals of stangersite, is Sn1.02Ge0.94(S2.93Se0.10)Σ3.03. The ideal formula is SnGeS3, which requires Sn 41.29, Ge 25.25, S 33.46, total 100 wt. %. The chemical composition of stangersite from multicomponent aggregates shows an extensive PbSn-1 substitution covering nearly the whole field of stangersite in the SnGeS3-PbGeS3 solid solution. Stangersite is monoclinic, P21/c, a = 7.2704(15), b = 10.197(2), c = 6.8463(14) Å, β = 105.34(3)°, with V = 489.5 Å3 and Z = 4. The strongest reflections of the powder X-ray diffraction pattern [d, Å/I(hkl)] are: 7.006/100(100), 4.135/49(120), 3.077/47(130), 2.776/38(022), 2.699/69(211), 2.1213/31(320), and 1.7239/35(41-2; 410). Stangersite has a layered structure, with corrugated (100) layers of Sn2+S5 coordination pyramids and with interspaces filled by lone electron pairs of Sn2+ and [001] chains of Ge4+S4 coordination tetrahedra. The Raman spectrum of stangersite with tentative band assignments is given. We named the mineral after its chemical constituents: Sn (stannum), Ge (germanium) and S (sulphur). ]]> Original paper
<![CDATA[ Beryllium minerals as monitors of geochemical evolution from magmatic to hydrothermal stage; examples from NYF pegmatites of the Třebíč Pluton, Czech Republic ]]> Zachař A, Novák M, Škoda R; Vol. 65, issue 3, pages 153 - 172
Mineral assemblages of primary and secondary Be-minerals were examined in intraplutonic euxenite-type NYF pegmatites of the Třebíč Pluton, Moldanubian Zone occurring between Třebíč and Vladislav south of the Třebíč fault. Primary magmatic Be-minerals crystallized mainly in massive pegmatite (paragenetic type I) including common beryl I, helvite-danalite I, and a rare phenakite I. Rare primary hydrothermal beryl II and phenakite II occur in miarolitic pockets (paragenetic type II). Secondary hydrothermal Be-minerals replaced primary precursors or filled fractures and secondary cavities, or they are associated with ,,adularia” and quartz (paragenetic type III). They include minerals of bohseite-bavenite series, less abundant beryl III, bazzite III, helvite-danalite III, milarite-agakhanovite-(Y) III, phenakite III, and datolite-hingganite-(Y) III. Chemical composition of the individual minerals is characterized by elevated contents of Na, Cs, Mg, Fe, Sc in beryl I and II; Na, Ca, Mg, Fe, Al in bazzite III; REE in milarite-agakhanovite-(Y) III; variations in Fe/Mn in helvite-danalite and high variation of Al in bohseite-bavenite series. Replacement reactions of primary Be-minerals are commonly complex and the sequence of crystallization of secondary Be-minerals is not defined; minerals of bohseite-bavenite series are mostly the latest. Beryl usually occurs in pegmatites with rare tourmaline, whereas helvite-danalite bearing pegmatites are tourmaline-rich. Abundant tourmaline in pegmatites with helvite-danalite and its scarcity in beryl-bearing pegmatites indicate that early tourmaline crystallization affected activity of Al in the parental medium and thus may have controlled formation of primary Be-minerals (beryl - higher Al, helvite-danalite - lower Al) which crystallized later. Secondary Be-minerals with dominant minerals of bohseite-bavenite series and milarite suggest high activity of Ca in fluids. Variations in chemical composition (Al contents) of bohseite-bavenite series were controlled by the chemical composition of the precursor. High variability of primary magmatic Be-minerals within a single pegmatite district is exceptional and it is constrained by variable activities of Si and mainly Al, divalent cations - Ca, Mn, Fe, Zn and Mg, trivalent cations - REEs, Sc, and B, S, and fO2 in the individual pegmatites. ]]> Original paper
<![CDATA[ Pošepnýite, a new Hg-rich member of the tetrahedrite group from Příbram, Czech Republic ]]> Škácha P, Sejkora J, Plášil J, Makovicky E; Vol. 65, issue 3, pages 173 - 186
The new mineral pošepnýite was found in the mine dump of shaft No. 16 Háje, one of the mines in the Příbram uranium and base-metal district, central Bohemia, Czech Republic. Pošepnýite is associated with příbramite, dzharkenite, ferroselite, hakite-(Hg), tetrahedrite-(Zn), antimonselite and uraninite in a calcite-dominant gangue. The new mineral occurs as idiomorphic to hypidiomorphic grains up to 100 μm in size. Pošepnýite is steel-grey and has a metallic lustre. Mohs hardness is ca. 3.5-4; the calculated density is 6.23 g cm-3. In reflected light, pošepnýite is light brown. No bireflectance, pleochroism, anisotropy or internal reflections were observed. The average empirical formula, based on electron-microprobe analyses (62 spot analyses), is (Cu3.33Ag0.28)Σ3.61 (Hg3.43Cu2.50Zn0.03Cd0.03Fe0.01)Σ6.00 (Sb3.88As0.12)Σ4.00 (Se10.83S1.29)Σ12.12. The ideal formula is (Cu+3+x3-x)Σ6 (Hg2+4-xCu+2+x)Σ6Sb4 (Se12.50.5)Σ13, 0 ≥ x << 2, which requires Cu 12.25, Hg 30.93, Sb 18.77 and Se 38.05, total 100.00 wt. % (for x = 0) or Cu 17.65, Hg 23.87, Sb 19.32, Se 39.16, total 100.00 wt. % (for x = 1). Pošepnýite is cubic, I-43m, a = 10.964(1) Å, with V = 574.82(15) Å3 and Z = 2. The strongest reflections of the calculated powder X-ray diffraction pattern are [d, Å (I) (hkl)] are: 3.165(100) (222), 2.930(24) (321), 2.0017(16) (521), 1.9381(65) (440), 1.6528(31) (622)]. According to the single-crystal X-ray diffraction data (Robs = 0.051), pošepnýite is isostructural with minerals of the tetrahedrite group. The cubic structure of pošepnýite is a tetrahedral framework with cavities and a part of tetrahedra replaced by SbSe3 coordination pyramids. It has one type of pyramidal Sb position, one type of tetrahedrally coordinated cation position M1 occupied by (Hg, Cu), and one type of partly vacant cation site M2 with triangular coordination. The main anion site Se1 participates in all of these cation coordination polyhedra. Minority anion ’Se2’ ties the six coordination triangles of Cu2 in the cavity of the tetrahedral framework into one cluster. Pošepnýite is named after the František Pošepný, a famous 19th-century geologist, often regarded as the father of the modern economic geology. ]]> Original paper
<![CDATA[ Nickel-(Bi,Ag) sulphide mineralization from NYF Vepice pegmatite, Milevsko pluton, southern Bohemia (Czech Republic) - a reflection of the parental granite chemistry ]]> Sejkora J, Litochleb J, Novák M, Cícha J, Dolníček Z; Vol. 65, issue 3, pages 187 - 199
Unusual high- to low-T sulphide mineralization with Ni-(Bi, Ag) phases was examined at the NYF intragranitic pegmatite No. III from Vepice near Kovářov enclosed in the Milevsko Pluton, Moldanubian Zone, Southern Bohemia. Zoned pegmatite dike, up to 30 cm thick, has transitional contact with host durbachite and its internal structure includes transitional unit, border granitic unit, graphic unit, blocky unit (Kfs+Qz), quartz core and small miarolitic pocket. Sulphide mineralization locally associated with calcite and fluorite is represented by common pyrite with minor galena, accessory chalcopyrite, sphalerite, marcasite, native Bi and Ni-(Bi, Ag) minerals - argentopentlandite, parkerite and pentlandite. It is developed in small miarolitic pockets and on pegmatite fractures cutting all pegmatite units. Irregular anhedral grains and aggregates of argentopentlandite, < 200 μm in size, associated with chalcopyrite, have empirical formula Ag0.97(Fe4.88Ni3.10Cu0.04Co0.01)Σ8.03 (S7.96As0.03)Σ7.99. Zoned irregular aggregates of parkerite, 20-30 μm in size, are typically associated with pentlandite, or overgrow galena and yield empirical formula (Ni3.02Fe0.02Co0.01)Σ3.06(Bi1.73Sb0.05As0.04)Σ1.92S2.02. Pentlandite is present in two morphological forms: rare lenticular to isometric anhedral grains, ≥ ˜200 μm in size, and numerous small tabular crystals, ≥ 20 μm in length, in subparallel arrangement rimming aggregates of other sulphides. Empirical formula is (Ni4.57Fe4.14Co0.25)Σ8.96(S8.01As0.02)Σ8.03. Evaluation of relative chronology of the sulphide minerals is complicated mainly due to complex textural relations. Pyrite + marcasite are likely pseudomorphs after pyrrhotite likely the earliest phase whereas pentlandite and native Bi are among the latest. Early sulphides (pyrrhotite, chalcopyrite, sphalerite, argentopentlandite) crystallized at T < ˜550-400 °C, whereas pyrite, marcasite, galena, parkerite, and native Bi at T < 240 °C. Cooling of the system below T ˜200 °C appeared soon after transformation of pyrrhotite to pyrite+marcasite aggregates. Sulphides manifest that concentrations of Ni in residual pegmatite melt and exsolved fluids were high enough to facilitate saturation of Ni-sulphides. Very high Ni/Co ratio in sulphides reflects a much lower concentration of cobalt in durbachite. The examined Ni-(Bi, Ag) sulphides manifest that high concentrations of highly compatible Ni in parental granite may be reflected in accessory minerals from its pegmatite. ]]> Original paper
<![CDATA[ The petrostructural characteristics and 207Pb/206Pb zircon data from the Ngomedzap-Akongo area (Nyong complex, SW-Cameroon) ]]> Owona S, Mvondo Ondoa J, Tichomirowa M, Ekodeck GE; Vol. 65, issue 3, pages 201 - 219
Herein, we constrain the Ngomedzap-Akongo geodynamic evolution in the eastern part of the Nyong complex (NyC) in SW Cameroon that belongs to the Paleoproterozoic West Central African Fold Belt (WCAF) through petrostructural field observations, laboratory analyses, and 207Pb/206Pb zircon geochronology. It consists of magnetite bearing quartzite, metagranodiorite, meta-anorthosite, metagabbro, and metasyenites that have recorded a polyphase D1-D3 deformation. D1, likely a pure shear-type, has been strongly overprinted by the D2 transpression flow regime that emplaced the Nyong tectonic nappe, transported top - to the East onto the Congo shield. This nappe is dissected by D3 blastomylonitic shear-zones. Both the D2 and D3 have controlled the actual geometry of the Nyong belt, later crosscut by D4 multiple brittle tectonic styles, likely post-orogenic. Zircon geochronology yielded 207Pb/206Pb zircon geochronology protolith Archean mean ages of 2764 ± 26 Ma (MSWD = 0.81) in metagranodiorite; 2816 ± 34 Ma (MSWD = 1.3) and 2789 ± 13 Ma (MSWD = 0.28) in metasyenites. These new data corroborate old ones and, together, document the Archean origin of the NyC as details of the Nyong fold-and-thrust belts that of WCAFB and South American homologous due to the colliding Congo-San Francisco shields associated with Eburnean/Trans Amazonian orogeny (2400-1800 Ma). ]]> Original paper