Nicolas Meisser

Contribution to the mineralogy of acid drainage of Uranium minerals: Marecottite and the zippeite-group

Abstract Sulfate-rich acid waters produced by oxidation of sulfide minerals enhance U mobility around U ores and U-bearing radioactive waste. Upon evaporation, several secondary uranyl minerals, including many uranyl sulfates, precipitate from these waters. The zippeite-group of minerals is one of the most common and diverse in such settings. To decipher the nature and crystal chemistry of the zippeite-group, the crystal structure of a new natural hydrated Mg uranyl sulfate related to Mgzippeite was determined. The mineral is named marecottite after the type locality, the La Creusaz U prospect near Les Marécottes, Western Swiss Alps. Marecottite is triclinic, P1, with a = 10.815(4), b = 11.249(4), c = 13.851(6) Å, a = 66.224(7), b = 72.412(7), and g = 69.95(2)°. The ideal structural formula is Mg3(H2O)18[(UO2)4O3(OH)(SO4)2]2(H2O)10. The crystal structure of marecottite contains uranyl sulfate sheets composed of chains of edge-sharing uranyl pentagonal bipyramids that are linked by vertex-sharing with sulfate tetrahedra. The uranyl sulfate sheets are topologically identical to those in zippeite, K(UO2)2(SO4)O2·2H2O. The zippeite-type sheets alternate with layers containing isolated Mg(H2O)6 octahedra and uncoordinated H2O groups. The uranyl sulfate and Mg layers are linked by hydrogen bonding only. Magnesium-zippeite is redefined as Mg(H2O)3.5(UO2)2(SO4)O2, based on comparison of the powder X-ray diffraction pattern of micro-crystalline co-type material with the pattern of a synthetic phase. Magnesium-zippeite contains zippeite-type uranyl sulfate sheets with Mg located between the layers, where it is in octahedral coordination. In Mg-zippeite, distorted Mg octahedra are linked by sharing vertices, resulting in dimers. The apices of the Mg octahedra correspond to two O atoms of uranyl ions, and four H2O groups. Magnesium-zippeite and marecottite co-exist, sometimes in the same sample, at Lucky Strike no. 2 mine, Emery County, Utah (type locality of Mg-zippeite), at Jáchymov, Czech Republic, and at La Creusaz. This study provides insight into the complexity of the zippeite-group minerals containing divalent cations, where different arrangements in the interlayers result in different unit cells and space groups.

Spriggite, Pb3 [(UO2)6O8(OH)2] (H2O)3, a new mineral with β-U3O8 –type sheets: Description and crystal structure

Abstract Spriggite, Pb3[(UO2)6O8(OH)2](H2O)3, is a new hydrated Pb uranyl oxyhydroxide found near Arkaroola, Northern Flinders Ranges, South Australia. The new mineralʼs name honors geologist and conservationist Reginald Claude Sprigg (1919-1994), founder of the Arkaroola Tourist Station. Together with beta-uranophane, soddyite, kasolite, Ce-rich francoisite-(Nd), metatorbernite, billietite, Ba-bearing boltwoodite, schoepite, metaschoepite, and weeksite, spriggite results from the supergene alteration of U-Nb-REE-bearing hydrothermal hematite breccia. Spriggite forms prismatic crystals up to about 150 μm in length and up to 40 μm across. It is transparent, bright orange in color with vitreous luster, biaxial, nmin= 1.807; nmax = 1.891 (NaD, 22.5 °C), non-fluorescent, brittle with an uneven fracture. It has a pale orange streak, Mohsʼ hardness ~4, good cleavage along (100) and Dcalc = 7.64(6) g/ cm3. The empirical formula is (Pb2.77Ca0.06Ba0.04)Σ2.87U6O19.9(OH)2⋅3H2O, and the simplified formula is Pb3[(UO2)6O8(OH)2](H2O)3. Spriggite is monoclinic, C2/c, a = 28.355(9), b = 11.990(4), c = 13.998(4) Å, β = 104.248(5); V = 4613(3) Å3, Z = 8. The strongest eight lines in the powder X-ray diffraction pattern are [d in Å (I)(hkl)]: 6.92(60)(400), 6.02(30)(112̅;020), 3.46(80)(800), 3.10(100)(204;6̅04;33̅2;5̅32), 2̅.74(30)(4̅40), 2.01(30)(336̅), 1.918(60)(10.04̅;14.04̅;11.3̅2;1̅3̅-.31), 1.738(30)(53̅6;1̅1̅.36). The structure has been solved from a crystal twinned on (001) and refined to R1 = 9.7%. The structure is based upon the [(UO2)6O8(OH)2]6+ sheets of uranyl polyhedra of the β-U3O8 anion topology with Pb2+ cations and H2O groups in the interlayer. Billietite and spriggite contain only hexavalent U in the uranyl sheets, whereas the similar sheets in β-U3O8 contain U5+ and U6+, and those in ianthinite U4+ and U6+. Spriggite has the highest Pb:U ratio among the known hydrated Pb uranyl oxyhydroxide minerals.

Xocolatlite, Ca2Mn24+Te2O12·H2O, a new tellurate related to kuranakhite: Description and measurement of Te oxidation state by XANES spectroscopy

Abstract Xocolatlite, Ca2Mn4+2 Te6+2O12·H2O, is a rare new mineral from the Moctezuma deposit in Sonora, Mexico. It occurs as chocolate-brown crystalline crusts on a quartz matrix. Xocolatlite has a copperbrown streak, vitreous luster, and is transparent. Individual crystals show a micaceous habit. Refractive indices were found to be higher than 2.0. Density calculated from the empirical formula is 4.97 g/cm3, and immersion in Clerici solution indicated a density higher than 4.1 g/cm3. The mineral is named after the word used by the Aztecs for chocolate, in reference to its brown color and provenance. The crystallographic characteristics of this monoclinic mineral are space group P2, P2/m, or Pm, with the following unit-cell parameters refined from synchrotron X-ray powder diffraction data: a = 10.757(3) Å, b = 4.928(3) Å, c = 8.942(2) Å, β = 102.39(3)°, V = 463.0(3) Å3, and Z = 2. The unavailability of a suitable crystal prevented single-crystal X-ray studies. The strongest 10 lines of the X-ray powder diffraction pattern are [d in Å (I) (hkl)]: 3.267(100)(012), 2.52(71)(303̄), 4.361(51) (002), 1.762(39)(323̄), 4.924 (34)(010), 2.244(32)(313̄), 1.455(24)(006), 1.996(21)(014), 1.565(20) (611), and 2.353(18)(411̄). XANES Te LIII-edge spectra of a selection of Te minerals (including xocolatlite) and inorganic compounds showed that the position of the absorption edge can be reliably related to the oxidation state of Te. XANES demonstrated that xocolatlite contains Te6+ as a tellurate group. Water has been tentatively included in the formula based on IR spectroscopy that indicated the presence of a small amount of water. Raman, IR, XANES, and X-ray diffraction data together with the chemical composition show a similarity of xocolatlite to kuranakhite. A possible series may exist between these two species, xocolatlite being the Ca-rich end-member and kuranakhite the Pb-rich one.

Pseudojohannite from Jáchymov, Musonoï, and La Creusaz : A new member of the zippeite-group

Abstract Pseudojohannite is a hydrated copper(II) uranyl sulfate described from Jáchymov, Northern Bohemia, Czech Republic (type locality). Pseudojohannite also occurs at the Musonoï quarry near Kolwezi, Shaba, Congo, and the La Creusaz prospect, Western Swiss Alps. At all three localities, pseudojohannite formed through the interaction of acid sulfate mine drainage waters with uraninite (Jáchymov and La Creusaz) or uranyl silicates (Musonoï). Pseudojohannite forms moss green, non UV-ß uorescent aggregates consisting of irregularly shaped crystals measuring up to 25 μm in length and displaying an excellent cleavage parallel to (.101). dmeas is 4.31 g/cm3, dcalc 4.38 g/cm3, and the refractive indices are nmin = 1.725 and nmax = 1.740. A high-resolution synchrotron powder diffraction pattern on the material from Musonoï shows that pseudojohannite is triclinic (P1 or P1̅), with a = 10.027(1) Å, b = 10.822(1) Å, c = 13.396(1) Å, α = 87.97(1)°, β = 109.20(1)°, γ = 90.89(1)°, V = 1371.9(5) Å3. The location of the uranium and sulfur atoms in the cell was obtained by direct methods using 1807 reflections extracted from the powder diffractogram. Pseudojohannite contains zippeite-type layers oriented parallel to (.101). The empirical chemical formula calculated for a total of 70 O atoms is Cu6.52U7.85S4.02O70H55.74, leading to the simplified chemical formula Cu6.5[(UO2)4O4(SO4)2]2(OH)5·25H2O. The distance of 9.16 Å between the uranylsulfate sheets in pseudojohannite shows that neighboring layers do not share O atoms with the same CuΦ6 [Φ = (O,OH)] distorted octahedrons, such as in magnesium-zippeite. Rather, it is expected that CuΦ6 forms a layer bound to the zippeite-type layers by hydrogen bonding, as in marécottite, or one apex of the CuΦ6 polyhedron only is shared with a zippeite-type layer, as in synthetic SZIPPMg. The higher number of cations in the interlayer of pseudojohannite (Cu:S = 1.6:1) compared to marécottite (3:4) and SZIPPMg (1:1) indicates that pseudojohannite has a unique interlayer topology. Ab-initio powder structure solution techniques can be used to obtain important structural information on complex micro-crystalline minerals such as those found in the weathering environment. Pseudojohannite represents a new member of the zippeite group of minerals, and further illustrates the structural complexity of zippeite-group minerals containing divalent cations, which have diverse arrangements in the interlayer. Peudojohannite and other divalent zippeites are common, easily overlooked minerals in acid drainage environments around uranium deposits and wastes.

Paulscherrerite from the Number 2 Workings, Mount Painter Inlier, Northern Flinders Ranges, South Australia: “Dehydrated schoepite” is a mineral after all

Abstract Paulscherrerite, UO2(OH)2, occurs as an abundant dehydration product of metaschoepite at the Number 2 Workings at Radium Ridge, Northern Flinders Ranges, South Australia. The mineral name honors the contribution of Swiss physicist Paul Scherrer (1890-1969) to mineralogy and nuclear physics. Individual paulscherrerite crystals are tabular, reaching a maximum of 500 nm in length. Paulscherrerite has a canary yellow color and displays no fluorescence under UV light. Chemically, paulscherrerite is a pure uranyl hydroxide/hydrate, containing only traces of other metals (<1 wt% in total). Bulk (mg) samples always contain admixtures of metaschoepite (purest samples have ~80 wt% paulscherrerite). A thermogravimetric analysis corrected for the presence of metaschoepite contamination leads to the empirical formula UO3·1.02H2O, and the simplified structural formula UO2(OH)2. Powder diffraction shows that the crystal structure of paulscherrerite is closely related to that of synthetic orthorhombic α-UO2(OH)2. However, splitting of some X-ray diffraction lines suggests a monoclinic symmetry for type paulscherrerite, with a = 4.288(2), b = 10.270(6), c = 6.885(5) Å, β = 90.39(4)°, V = 303.2(2) Å3, Z = 4, and possible space groups P2, P21, P2/m, or P21/m. Paulscherrerite-like material was synthesized using various methods, including heating metaschoepite in water at 150 °C and slow hydration of UO3(am) in air; material synthesized using hydrothermal techniques displayed peak splitting indicative of monoclinic symmetry. Paulscherrerite has been reported under the name “dehydrated schoepite” as an early weathering product of uraninite/pitchblende in several deposits, such as Shinkolobwe, Zaire; Nopal I deposit, Mexico; and the granitic pegmatites of New Hampshire, U.S.A.

Sulfur isotope analysis of cinnabar from Roman wall paintings by elemental analysis/isotope ratio mass spectrometry – tracking the origin of archaeological red pigments and their authenticity

The most valuable pigment of the Roman wall paintings was the red color obtained from powdered cinnabar (Minium Cinnabaris pigment), the red mercury sulfide (HgS), which was brought from mercury (Hg) deposits in the Roman Empire. To address the question of whether sulfur isotope signatures can serve as a rapid method to establish the provenance of the red pigment in Roman frescoes, we have measured the sulfur isotope composition (δ(34)S value in ‰ VCDT) in samples of wall painting from the Roman city Aventicum (Avenches, Vaud, Switzerland) and compared them with values from cinnabar from European mercury deposits (Almadén in Spain, Idria in Slovenia, Monte Amiata in Italy, Moschellandsberg in Germany, and Genepy in France). Our study shows that the δ(34)S values of cinnabar from the studied Roman wall paintings fall within or near to the composition of Almadén cinnabar; thus, the provenance of the raw material may be deduced. This approach may provide information on provenance and authenticity in archaeological, restoration and forensic studies of Roman and Greek frescoes.

Mineralogy and crystal structure of bouazzerite from Bou Azzer, Anti-Atlas, Morocco: Bi-As-Fe nanoclusters containing Fe3+ in trigonal prismatic coordination

Abstract Bouazzerite, Bi6(Mg,Co)11Fe14[AsO4]18O12(OH)4(H2O)86, is a new mineral occurring in “Filon 7” at the Bou Azzer mine, Anti-Atlas, Morocco. Bouazzerite is associated with quartz, chalcopyrite, native gold, erythrite, talmessite/roselite-beta, Cr-bearing yukonite, alumopharmacosiderite, powellite, and a blue-green earthy copper arsenate related to geminite. The mineral results from the weathering of a Variscan hydrothermal As-Co-Ni-Ag-Au vein. The Bou Azzer mine and the similarly named district have produced many outstanding mineral specimens, including the world’s best erythrite and roselite. Bouazzerite forms monoclinic prismatic {021} crystals up to 0.5 mm in length. It has a pale apple green color, a colorless streak, and is translucent with adamantine luster. dcalc is 2.81(2) g/cm3 (from X-ray structure refi nement). The new mineral is biaxial with very weak pleochroism from yellow to pale yellow; the refractive indices measured on the (021) cleavage face range from nmin = 1.657 to nmax = 1.660; the Gladstone-Dale relationship provides a value of 1.65. The empirical chemical formula is Bi6.14Fe12.6Mg8.45Co0.48Ni0.12Ca0.23(As17.0Cr0.64Si0.32)Σ=18.0O174.6H184. Bouazzerite is monoclinic, P21/n, Z = 2, with a = 13.6322(13) Å, b = 30.469(3) Å, c = 18.4671(18) Å, β = 91.134(2)°, and V = 7669.0(13) Å3. The eight strongest lines in the X-ray powder diffraction pattern are [d in Å (I)(hkl)]: 11.79(100)(021̅), 10.98(80)(101/1̅01), 10.16(80)(1̅20), 7.900(80)(022̅), 12.45(70)(11̅0), 15.78(60)(01̅1), 3.414(40)(333/400), 3.153(40)(353/22̅5). The crystal structure of bouazzerite is based upon [Bi3Fe7O6(OH)2(AsO4)9]11- anionic nanoclusters that are built around [trigonal prismaticFe3+(octahedralFe3+3(OH)O12)2]29- groups, containing one Fe3+ ion in trigonal prismatic coordination and six Fe3+ ions in octahedral coordination. The nanoclusters have a diameter of about 1.3 nm and are linked together by chains of Mg(O,H2O)6 octahedra. The resulting arrangement displays channels down [100] that contain structural water. Bouazzerite is the fi rst mineral based upon Bi- and As-containing ferric nanoclusters. Its discovery provides a unique insight into transport mechanisms of toxic elements in the oxidation zones of sulfi de mineral deposits in the form of complex Fe-As nanoparticles.

Cleusonite, (Pb,Sr) (U4+, U6+) (Fe2+, Zn)2 (Ti,Fe2+,Fe3+)18 (O, OH)38, a new mineral species of the crichtonite group from the western Swiss Alps

Cleusonite, (Pb,Sr)(U4+,U6+) (Fe2+,Zn)2 (Ti,Fe2+,Fe3+)18 (O,OH)38, is a new member of the crichtonite group. It was found at two occurrences in greenschist facies metamorphosed gneissic series of the Mont Fort and Siviez-Mischabel Nappes in Valais, Switzerland (Cleuson and Bella Tolla summit), and named after the type locality. It occurs as black opaque cm-sized tabular crystals with a bright sub-metallic lustre. The crystals consist of multiple rhombohedra and hexagonal prisms that are generally twinned. Measured density is 4.74(4) g/cm3 and can be corrected to 4.93(12) g/cm3 for macroscopic swelling due to radiation damage; the calculated density varies from 5.02(6) (untreated) to 5.27(5) (heat-treated crystals); the difference is related to the cell swelling due to the metamictisation. The empirical formula for cleusonite from Cleuson is (Pb0.89Sr0.12)Σ = 1.01 (U+40.79U+60.30)Σ = 1.09 Fe+32.33V+50.19Mn0.08 Al0.07)Σ = 17.90 [O35.37(OH)2.63]Σ = 38. Cations were measured by electron microprobe, the presence of structural (OH) was confirmed by infrared spectroscopy and the U6+/U4+ and Fe2+/Fe3+ ratios were determined by X-ray photoelectron spectroscopy. Cleusonite is partly metamict, and untreated crystals only show three major X-ray diffraction peaks. Because of this radiation-damaged state, the mineral appears optically isotropic and shows a light-grey to white colour in reflected polarized light. Cleusonite is trigonal, space group R 3, and unit-cell parameters are varying from a = 10.576(3), c = 21.325(5) A (untreated crystal) to a = 10.4188(6), c = 20.942(1) A (800°C treatment) and to a = 10.385(2), c = 20.900(7) A (1000°C treatment). The three cells give a common axial ratio 2.01(1), which is identical to the measured morphological one 2.04(6). The name cleusonite also applies to the previously described “uranium-rich senaite” from Alinci (Macedonia) and the “plumbodavidite” from Huanglongpu (China).

Fluid inclusion, stable isotope and Ar-Ar evidence for the age and origin of gold-bearing quartz veins at Mont Chemin, Switzerland

SummaryA new Swiss gold occurrence at Mont Chemin, comprising gold-bearing quartz veins, displays many characteristics that are typical of mesothermal gold deposits within the Alps and globally. The most notable of these features are: i) the presence of NaCl-H2O-CO2-bearing fluid with an XCO2 of approximately 0.016 and NaCl equivalents in the range 4.6 to 10.6 weight percent, ii) greenschist formational temperatures and pressures in the range 265-285 °C and 700-1400 bars; and iii) the proximity of the occurrence to the Rhone-Simplon Line, a deep crustal structure in the Swiss Alps.Corrected Ar-Ar data for hydrothermal adularia, considered to be contemporaneous with mineral deposition from the gold-bearing fluid, yields an age of 9.9 ±1.0 Ma. Geothermal gradients and uplift rates derived from the Ar-Ar age data and the geothermometry are in agreement with existing data for this region, and indicate that the hydrothermal activity at the Mont Chemin gold occurrence records one of the last Alpine metamorphic events in the northeastern Mont Blanc massif.Temperature estimates from fluid-muscovite-quartz-feldspar equilibrium and oxygen isotope thermometry of coexisting adularia and quartz are combined with the fluid inclusion isochores to derive depositional pressures. These data yield geothermal gradients on the order of 50 °C/km and uplift rates of 0.44 mm/a for the NE portion of the Mont Blanc massif.ZusammenfassungEin neues Schweizer Goldvorkommen am Mont Chernin, es handelt sich um Goldführende Quarzgänge, zeigt viele Charakteristika, die für mesothermale Goldlagerstätten der Alpen und weltweit typisch sind: i) Die Anwesenheit von NaCl-H2O-CO2 Fluiden mit einem XCO2 von ca. 0.016 und NaCl zwischen 4.6 und 10.6 Gew. % Äquiv.ii) Grünschieferfazielle Bildungstemperaturen und -drucke von 265-285°C bzw. 7001400bar. iii) Die Nähe der Vorkommen zur Rhone-Simplon Linie, einer tiefgreifenden Struktur in der Kruste der Schweizer Alpen.Korrigierte Ar-Ar Daten von hydrothermalem Adular, der als zeitgleich mit den Minerallagerstätten gebildet, angesehen wird, ergaben ein Alter von 9.9 ± 1.0 Ma. Die aus aus den Ar-Ar Daten bestimmten geothermalen Gradienten und Hebungsraten und die Ergebnisse der Geothermometrie stimmen mit bisher existierenden Daten aus dieser Region überein und zeigen, daß die hydrothermale Aktivität in den Goldvorkommen des Monte Chemin eines der letzten alpidischen metamorphen Ereignisse im nordöstlichen Mont Blanc Massiv darstellt.Temperaturabschätzungen aus Fluid-Muscovit-Quarz-Feldspat Gleichgewichten und Sauerstoffisotopen-Thermometrie an koexistierendem Quarz und Adular werden mit den Isochoren der Flüssigkeitseinschlüsse kombiniert, um die Bildungsdrucke abzuleiten. Diese Daten ergeben geothermische Gradienten in der Größenordnung von ca. 50 °C/km und Hebungsraten von 0.44 mm/Jahr für den Nordostteil des Mont Blanc Massives.

Scheuchzerite, Na(Mn,Mg)9[VSi9O28(OH)](OH)3, a new single-chain silicate

Abstract Scheuchzerite, Na(Mn,Mg)9[VSi9O28(OH)](OH)3, is a new mineral from the metamorphosed synsedimentary exhalative Mn deposit of Fianel, Val Ferrera, Central Alps, Switzerland. It is dedicated to the Swiss naturalist Johann Jakob Scheuchzer (1672.1733). Scheuchzerite is associated with saneroite and tiragalloite in veins resulting from the remobilization of ore components during retrograde Tertiary Alpine metamorphism. Scheuchzerite forms yellow-orange, transparent acicular crystals up to 0.5 mm in length with yellow-orange streak and vitreous luster, Mohs. hardness ~2.5, dcalc 3.47 (electron microprobe) to 3.52 g/cm3 (structure refinement); dmeas 3.50(2) g/cm3, good cleavage parallel to fiber elongation. Scheuchzerite is biaxial positive, nmin = 1.74 and nmax = 1.75; nmean (Gladstone-Dale) 1.74; weakly pleochroic, X = brown yellow, Y = pale yellow. The empirical chemical formula is Na0.97(Mn7.79Mg0.95Zn0.16Ni0.04Ca0.03Al0.01)Σ=8.98 (V0.95As0.02Si9.08)Σ=10.05O32.05H4. Scheuchzerite is triclinic, P1̅, a = 9.831(5) Å, b = 10.107(5) Å, c = 13.855(7) Å, α = 86.222(10)°, β = 73.383(9)°, γ = 71.987(9)°; V = 1254.2(10) Å3; Z = 2. The crystal structure was solved with direct methods on the basis of 1616 unique reflections with I > 4σF and refined to R1 = 9.4%. The crystal structure consists of tetrahedral layers separated by layers containing chains of edge-sharing [Mn(O,OH)6] octahedra as well as [NaO8] polydedra. The tetrahedral layers consist of [Si9O25(OH)] loop-branched chains of corner-sharing silicate tetrahedra extending along [011]. The loops contain 6 tetrahedra and are separated by 3 tetrahedra in a broken 4-loop arrangement. A hydrogen atom is probably shared by two O atoms (symmetrical hydrogen bond), replacing the missing silicon atom. A vanadate (VO4)3. tetrahedron branches off the 6-tetrahedra loop, and hence the overall formula of the tetrahedral chains is [VSi9O28(OH)]. In the notation of Liebau (1985), scheuchzerite is a single chain silicate (monopolysilicate) {olB1∞}[VSi9O28(OH)]. The topology of the scheuchzerite structure is reminiscent of that of the double-chain silicates of the amphibole group, but scheuchzerite contains a new type of silica chain.