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[ Fingerprints of magma mingling processes within the Miocene Zebín tuff cone feeding system (Jičín Volcanic Field, Czech Republic) ]]> Rapprich V, Shields S, Halodová P, Lindline J, van Wyk de Vries B, Petronis MS, Valenta J; Vol. 62, issue 4, pages 215 - 229
A well-preserved set of partly eroded mid-Miocene scoria cones and tuff cones are exposed in the Jičín Volcanic Field, Czech Republic. Zebín Hill, a formerly quarried tuff cone with an exposed conduit and associated dikes, offers an opportunity to study magmatic processes within the high-level feeding system of a small monogenetic volcano. Two types of dikes and associated “blob-like” intrusions were observed. Pure basanite dikes predominate in the center of the cone, whereas its peripheries were intruded by mingled dikes. The mingled dikes consist of mm-scale basanitic domains enclosed in a network of trachyandesitic dikelets. Locally, hybrid domains with intermediate characteristics were observed. The basanite dikes and basanite enclaves within mingled dikes contain normally-zoned minerals (Fo90 to Fo70 olivine, Mg-rich to Mg-poor diopside, labradorite to andesine composition of plagioclase) indicative of basanite magma evolution during ascent. In contrast, the trachyandesite and hybrid enclaves in mingled dikes show reverse zoning of minerals (Mg-poor to Mg-rich diopside, sanidine to oligoclase feldspar composition) indicative of magma hybridization.
This study suggests that the Zebín Volcano did not develop from a simple monogenetic system and through a simple central axis feeder; rather, Zebín Hill evolved from a complex magma feeding/storage system and through a complex feeder network. We conclude that the simple external structure of a monogenetic volcano may sometimes hide rather complex magmatic plumbing systems encompassing compositionally contrasting rocks/magmas. ]]> Original Paper
<![CDATA[ Petrology and geochronology of felsic volcanics in the Sabga area (Bamenda Highlands): implications for age variation along the Cameroon Volcanic Line ]]> Bate Tibang EE, Suh CE, Cottle J, Ateh KI, Tiabou AF, Nche LA, Che VB, Vishiti A; Vol. 62, issue 4, pages 231 - 246
The textural characteristics of felsic lavas and ignimbrites in the Sabga area along the continental segment of the Cameroon Volcanic Line (CVL) are documented in this study. Two rhyolitic lava flows separated by mafic and rhyodacitic lava flows were dated by zircon LA-ICP-MS technique in order to constrain the timescales of successive flow emplacement as well as magma chamber processes in this volcanic field. The studied samples have rheomorphic characteristics such as eutaxitic textures defined by elongated fiamme as well as deformed and welded glass shards. They exhibit flow banding and contain spherulitic groundmass. Rhyolitic autobreccias and ignimbrites are widespread in the Sabga area, are peralkaline in nature and their ages are broadly similar at ˜23.0 ± 0.3 Ma (23.34 ± 0.34 Ma for the ignimbrite and 22.98 ± 0.28 Ma for the rhyolitic autobreccia unit). These ages suggest rapid recharge of magma into a periodically replenished and open chamber. The felsic rocks in the Sabga area and around the Bamenda Highlands are also younger compared to other felsic units along the CVL (29 Ma to 69.4 ± 0.4 Ma). ]]> Original Paper
<![CDATA[ An unusual Ni-Sb-Ag-Au association of ullmannite, allargentum, Au-rich silver and Au-bearing dyscrasite from Oselské pásmo “silver” Lode of Kutná Hora Pb-Zn-Ag ore district (Czech Republic) ]]> Pažout R, Šrein V, Korbelová Z; Vol. 62, issue 4, pages 247 - 252
A rare and unusual Ni-Sb-Ag-Au association of ullmannite, NiSbS, associated with allargentum, Ag6Sb, Au-rich silver, Au9.7Ag85.0Sb2.9, and Au-bearing dyscrasite was found in medieval mine dump material of the Oselské pásmo ”silver” lode of the historic Kutná Hora Pb-Zn-Ag ore district. Ullmannite is the first and only Ni sulphide found in the base-metal paragenesis of otherwise exclusively Ag-(Cu)-(Pb)-Sb sulphosalts. No other nickel mineral is known from this base-metal ore district. The mineral was identified in two polished sections of one sample as anhedral grains up to 50 µm across enclosed in allargentum. The average chemical composition of ullmannite Ni 26.76-27.17, Sb 57.80-59.17, S 15.14-15.28 wt. % corresponds to the empirical formula Ni0.98Sb1.01As0.01S1.00 on the basis of Ni + Sb + S = 3 apfu, i.e. it is close to the ideal formula o with only trace contents of As. Au-rich silver with 15.52-16.34 wt. % of gold was found in association with freibergite and pyrargyrite as an anhedral inclusions up to c. 5 µm across. The chemical composition corresponds to Au9.7Ag85.0Sb2.9 on the basis of 100 apfu. One more gold-containing phase was determined: Au-bearing dyscrasite with ˜0.7 wt. % of Au. The sample also produced an example of Ag-rich “bonanza” with stephanite, acanthite, pyrargyrite and miargyrite. The likely source of nickel and gold were the serpentinized ultrabasic bodies, cut by the “silver” lodes in the South of the ore district. The serpentinites contain 2000 ppm of Ni and low but stable contents of Au. Penetration of hydrothermal fluids could have caused the mobilization of nickel and gold in serpentinites and in earlier ore mineralization (arsenopyrite). This process resulted in the breakdown of earlier silver minerals while allargentum, dyscrasite and stephanite crystallized. The discovery of Ni-Sb-Ag-Au association in Kutná Hora ore district sheds new light on the elemental variability of this hydrothermal vein-type deposit of Variscan age. ]]> Original Paper
<![CDATA[ A novel sheet topology in the structure of kamitugaite, PbAl[(UO2)5(PO4)2.38(AsO4)0.62O2(OH)2](H2O)11.5 ]]> Plášil J; Vol. 62, issue 4, pages 253 - 260
Kamitugaite is a rare supergene uranyl phosphate of aluminum and lead occurring at the Kobokobo pegmatite in the Sud-Kivu Province, Democratic Republic of Congo; its structure has remained unknown until now. Based on single-crystal X-ray diffraction data carried out on the type specimen of kamitugaite (no. 13986, Royal Museum for Central Africa, Tervuren), it is triclinic, space group P-1, with a = 9.0296(8), b = 10.9557(8), c = 15.8249(15) Å, α = 89.585(7)°, β = 85.349(8)°, γ = 84.251(7)°, V = 1552.5(2) Å3 and Z = 2. The structure was refined from diffraction data to R = 0.1074 for 2697 unique observed reflections. The structure of kamitugaite is based upon infinite sheets of uranyl and phosphate polyhedra, stacked perpendicular to c; these sheets result from edge-sharing of UO7 and UO8 bipyramids, forming chains approximately parallel to b, which are linked by (P,As)O4 tetrahedra. Such a sheet has not been observed in minerals or synthetic compounds and is related to the phosphuranylite topology; the ring symbol is 61544334. There are two distinct interlayer complexes in kamitugaite: one involving Pb2+ and H2O groups and another involving octahedrally coordinated Al3+ and isolated H2O groups. Adjacent sheets are linked a) through the Pb2+-O and H-bonds, and b) via H-bonds only in case of the interlayer with Al, the bonding differences being largely attributable to the very different stereochemistry of Pb2+ compared to Al3+. The unique combination of these two elements is probably a key reason for the scarcity of kamitugaite. ]]> Original Paper
<![CDATA[ Babánekite, Cu3(AsO4)2 ∙ 8H2O, from Jáchymov, Czech Republic - a new member of the vivianite group ]]> Plášil J, Škácha P, Sejkora J, Škoda R, Novák M, Veselovský F, Hloušek J; Vol. 62, issue 4, pages 261 - 270
Babánekite, Cu3(AsO4)2∙8H2O, a new member of the vivianite group was found in material originating from the Geister vein, Rovnost mine, Jáchymov, Western Bohemia, Czech Republic. It occurs as a supergene alteration mineral in association with members of the lindackerite supergroup (veselovskýite, hloušekite, pradetite and lindackerite), lavendulan, gypsum and an X-ray amorphous Cu-Al-Si-O-H phase. Crystals of babánekite are pinkish to peach-colored, elongated, prismatic and up to 2 mm in length. They exhibit the forms {010}, {100}, {110}, {101} and less frequently also {001}. Crystals are transparent to translucent with a vitreous luster. The mineral has a light pinkish streak. Estimated Mohs hardness is between 1.5 and 2. The cleavage is perfect on {010}. The calculated density is 3.192 g/cm3. Electron-microprobe analysis yielded CoO 8.89, NiO 4.06, CuO 15.31, ZnO 10.87, P2O5 0.16, As2O5 39.79, SO3 0.13, H2O 24.78 (calc.), total 103.99 wt.% yielding the empirical formula (Cu1.12Zn0.78Co0.69Ni0.32)Σ2.91[(AsO4)2.01(PO4)0.01(SO4)0.01]Σ2.03∙8H2O based on 16 O apfu. The ideal end-member formula of babánekite is Cu3(AsO4)2 ∙8H2O, which requires CuO 38.95, As2O5 37.52, H2O 23.53, total 100.00 wt.%. Babánekite is monoclinic, C2/m, with a = 10.1729(3), b = 13.5088(4), c = 4.7496(1) Å, β = 105.399(2)°, V = 629.28(3) Å3 and Z = 2. The eight strongest X-ray powder diffraction lines are [dobs Å(I)(hkl)]: 7.936(11)(110), 6.743(100)(020), 3.231(14)(13-1), 2.715(11)(041), 2.3331(10)(15-1), 2.0819(5)(350), 1.6862(16)(080) and 1.6107(4)(55-1). The crystal structure of babánekite, refined to R1 = 2.18 % for 864 unique observed reflections, confirmed that the atomic arrangement is similar to other members of the vivianite group of minerals. The mineral is named for Ing. František Babánek (1836-1910), Czech mining and geological expert, who worked in the Jáchymov and Příbram mines. ]]> Original Paper
<![CDATA[ Molecular structure of the phosphate mineral koninckite - a vibrational spectroscopic study ]]> Jirásek J, Čejka J, Vrtiška L, Matýsek D, Ruan X, Frost RL; Vol. 62, issue 4, pages 271 - 279
We have undertaken a study of the mineral koninckite from Litošice (Czech Republic), a hydrated ferric phosphate, using a combination of scanning electron microscopy with electron probe micro-analyzer (wavelength-dispersive spectroscopy) and vibrational spectroscopy. Chemical analysis shows that studied koninckite is a pure phase with an empirical formula Fe3+0.99(PO4)1.00∙2.75 H2O, with minor enrichment in Al, Ca, Ti, Si, Zn, and K (averages 0.00X apfu). Raman bands and shoulders at 3495, 3312, 3120, and 2966 cm-1 and infrared bands and shoulders at 3729, 3493, 3356, 3250, 3088, 2907, and 2706 cm-1 are assigned to the ν OH stretching of structurally distinct differently hydrogen bonded water molecules, A Raman band at 1602 cm-1 and shoulders at 1679, 1659, 1634, and 1617 cm-1 and infrared bands at 1650 and 1598 cm-1 are assigned to the ν2 (δ) H2O bending vibrations of structurally distinct differently hydrogen bonded water molecules. Raman shoulders at 1576, 1554, 1541, 1532, and 1520 cm-1 and infrared shoulders at 1541 and 1454 cm-1 may be probably connected with zeolitically bonded water molecules located in the channels. Raman bands and shoulders at 1148, 1132, 1108, 1063, 1048, and 1015 cm-1 and an infrared band and shoulders at 1131, 1097, 1049, and 1017 cm-1 are assigned to the ν3 PO43- triply degenerate antisymmetric stretching vibrations. A Raman band and a shoulder at 994 and 970 cm-1, respectively, and an infrared band and a shoulder at 978 and 949 cm-1, respectively, are assigned to the ν1 PO43- symmetric stretching vibrations. Infrared shoulders at 873, 833, and 748 cm-1 are assigned to libration modes of water molecules. Raman bands and shoulders at 670, 648, 631, 614, 600, 572, and 546 cm-1 and infrared bands at 592 and 534 cm-1 are assigned to the ν4 (δ) PO43- triply degenerate out-of-plane bending vibrations; weak band at 570 cm-1 may coincide with the δ Fe-O bending vibration. Raman bands and shoulders at 453, 443, 419, and 400 cm-1 are assigned to the ν2 (δ) PO43- doubly degenerate in-plane bending vibrations. Raman bands at 385, 346, 324, 309, 275, 252, and 227 cm-1 are assigned to the ν Fe-O stretching vibrations in FeO6 octahedra. Raman bands at 188, 158, 140, 112, 89, and 73 cm-1 are assigned to lattice vibrations. ]]> Original Paper