Search

Tetrahedrite-(Cd), Cu6(Cu4Cd2)Sb4S13, is a new IMA-approved mineral species from Radětice near the Příbram deposit, Czech Republic. It occurs as black metallic anhedral grains, up to 200 µm in size in quartz–calcite gangue, associated with galena, bournonite, sphalerite, pyrite, geocronite, silver, stromeyerite, tetrahedrite-(Zn), tetrahedrite-(Fe), tetrahedrite-(Cu), and an unknown Pb-rich tetrahedrite-like phase. In reflected light, tetrahedrite-(Cd) is isotropic and grey with greenish tints. Reflectance data for the four COM wavelengths in air are as follows (λ (nm) : R (%)): 470 : 30.8, 546 : 31.1, 589 : 31.1 and 650 : 28.8. Electron microprobe analysis gave (in wt % – average of 13 spot analyses) Cu 34.85, Ag 2.09, Fe 0.18, Zn 0.26, Cd 11.03, Hg 0.75, Pb 0.31, Sb 28.07, and S 23.38, with a total of 100.92. On the basis of ΣMe = 16 atoms per formula unit, the empirical formula of tetrahedrite-(Cd) is Cu9.65Ag0.34Cd1.73Zn0.07Hg0.07Fe0.06Pb0.03Sb4.06S12.84. Tennantite-(Cd) is cubic, I4‾3m, with unit-cell parameters a=10.504(3) Å, V=1158.9(9) Å3, and Z=2. Its crystal structure was refined by single-crystal X-ray diffraction data to a final R1=0.0252 on the basis of 257 unique reflections with Fo>4σ(Fo) and 23 refined parameters. Tetrahedrite-(Cd) is isotypic with other tetrahedrite-group minerals. Its crystal chemistry is discussed, and previous findings of Cd-rich tetrahedrite-group minerals are briefly reviewed.

The mineralogical, fluid inclusion, and stable isotope (C, O) study was conducted on a Late Variscan Zn-Pb vein Bt23C, Příbram uranium and base-metal district, Bohemian Massif, Czech Republic. The vein is hosted by folded Proterozoic clastic sediments in exo-contact of a Devonian-to-Lower-Carboniferous granitic pluton. Siderite, dolomite-ankerite, calcite, quartz, baryte, galena, sphalerite, V-rich mica (roscoelite to an unnamed V-analogue of illite), and chlorite (chamosite) form the studied vein samples. The banded texture of the vein was modified by the episodic dissolution of earlier carbonates and/or sphalerite. Petrographic, microthermometric, and Raman studies of fluid inclusions proved a complicated fluid evolution, related to the activity of aqueous fluids and to an episode involving an aqueous–carbonic fluid mixture. Homogenization temperatures of aqueous inclusions decreased from ~210 to ~50 °C during the evolution of the vein, and salinity varied significantly from pure water up to 27 wt.% NaCl eq. The aqueous–carbonic fluid inclusions hosted by late quartz show highly variable phase compositions caused by the entrapment of accidental mixtures of a carbonic and an aqueous phase. Carbonic fluid is dominated by CO2 with minor CH4 and N2, and the associated aqueous solution has a medium salinity (6–14 wt.% NaCl eq.). The low calculated fluid δ18O values (−4.7 to +3.6‰ V-SMOW) suggest a predominance of surface waters during the crystallization of dolomite-ankerite and calcite, combined with a well-mixed source of carbon with δ13C values ranging between −8.2 and −10.5‰ V-PDB. The participation of three fluid endmembers is probable: (i) early high-temperature high-salinity Na>Ca-Cl fluids from an unspecified “deep” source; (ii) late low-salinity low-temperature waters, likely infiltrating from overlying Permian freshwater partly evaporated piedmont basins; (iii) late high-salinity chloridic solutions with both high and low Ca/Na ratios, which can represent externally derived marine brines, and/or local shield brines. The source of volatiles can be (i) in deep crust, (ii) from interactions of fluids with sedimentary wall rocks and/or (iii) in overlying Permian piedmont basins containing, in places, coal seams. The event dealing with heterogeneous CO2-bearing fluids yielded constraints on pressure conditions of ore formation (100–270 bar) as well as on the clarification of some additional genetic aspects of the Příbram’s ores, including the reasons for the widespread dissolution of older vein fill, the possible re-cycling of some ore-forming components, pH changes, and occasionally observed carbon isotope shift due to CO2 degassing.

The new mineral grimmite, NiCo2S4, was found in siderite–sphalerite gangue at the dump of shaft no. 9, one of the mines in the abandoned Příbram uranium and base-metal district, central Bohemia, Czech Republic. The new mineral occurs as rare idiomorphic to hypidiomorphic grains up to 200 µm × 70 µm in size or veinlet aggregates. In reflected light, grimmite is creamy grey with a pinkish tint. Pleochroism, polarising colours and internal reflections were not observed. Reflectance values of grimmite in the air (R %) are 42.5 at 470 nm, 45.9 at 546 nm, 47.7 at 589 nm and 50.2 at 650 nm). The empirical formula for grimmite, based on electron-microprobe analyses (n= 13), is Ni1.01(Co1.99Fe0.06Pb0.01Bi0.01)Σ2.07S3.92. The ideal formula is NiCo2S4; requires Ni 19.26, Co 38.67, and S 42.07; and totals 100.00 wt %. According to the single-crystal X-ray diffraction data (Robs=0.0489), grimmite is cubic, Fd–3m, a=9.3933(9), with V=828.81(14) Å3 and Z=8. The calculated density is 4.96 g cm−3. The strongest reflections of the calculated powder X-ray diffraction pattern [d, Å (I)(hkl)] are 3.3210 (75) (220), 2.7116 (7) (222), 2.3483 (81) (400), 1.9174 (27) (422), 1.6605 (100) (440), 1.4852 (11) (620) and 1.3558 (15) (444). Grimmite is named after Johann Grimm (24 June or 24 July 1805 to 26 June 1874), the former director of the Příbram Mining College. The association of sulfides and sulfarsenides was found with grimmite. Essentially non-zoned coarse-grained siderite encloses idiomorphic crystals and/or aggregates of red sphalerite I and zoned skutterudite-group minerals. Skutterudites (skutterudite, niklskutterudite and ferroskutterudite) are usually strongly corroded and replaced by younger phases. Relics of skutterudite are rimmed by nickeline and later on by gersdorffite with rare domains of glaucodot and arsenopyrite, whereas completely leached parts of skutterudite crystals are filled up by quartz containing small isolated grains and aggregates of pyrite, sphalerite II, grimmite, galena, ullmannite, bismuthinite, parkerite and jaipurite, the latter being rarely enclosed in grimmite.

This mineralogical and fluid inclusion study was conducted on an Au-bearing quartz–sulfide vein encountered in the deep parts of the Bytíz deposit in the Příbram uranium and base-metal district, Bohemian Massif, Czech Republic. The samples were taken where the Au-bearing vein is crosscut by the common base-metal Zn-Pb ore vein Bt23C. The early mineralization of the Au-bearing vein is composed mainly of quartz (Q-1 to Q-3), illite–muscovite, Fe-Mg chlorite, arsenopyrite, and Au-Ag alloys, showing a wide range of compositions (4–69 at. % Ag) and a decrease in Au/(Au + Ag) ratios during vein evolution. Younger hydrothermal processes led to the crystallization of nests and veinlets composed of late quartz (Q-4), carbonates (siderite, dolomite–ankerite and calcite), base-metal sulfides (galena, sphalerite, chalcopyrite, and tetrahedrite), a suite of Ag and Bi-tellurides, and acanthite. The input of Sb is manifested by the partial to complete replacement of some gold grains by aurostibite and an unnamed (Ag,Au)-Sb oxide with a composition close to AuSbO3. The fluid inclusion study, combined with chlorite thermometry and arsenopyrite thermometry, showed that the early mineralization crystallized from progressively cooled (from 300 to 400 °C down to ca. 180 °C), diluted (1.2–7.0 wt. % NaCl eq.) aqueous solutions. The late portion of the mineralization formed from aqueous fluids with highly variable salinity (0.2–23.4 wt. % NaCl eq.) and homogenization temperatures decreasing from ca. 250 °C to < 50 °C, which compare well with the base-metal mineralization of the vein Bt23C and other base-metal veins of the Příbram ore area. Our study illustrates the nature and intensity of the processes of the reworking of the early gold mineralization mediated by the younger Ag,Sb-rich base-metal fluids, giving rise to Příbram’s typical late-Variscan vein Zn-Pb mineralization.

Uraninite-coffinite vein-type mineralisation with significant predominance of uraninite over coffinite occurs in the Příbram, Jáchymov and Horní Slavkov ore districts and the Potůčky, Zálesí and Předbořice uranium deposits. These uranium deposits are hosted by faults that are mostly developed in low- to high-grade metamorphic rocks of the basement of the Bohemian Massif. Textural features and the chemical composition of uraninite, coffinite and ningyoite were studied using an electron microprobe. Collomorphic uraninite was the only primary uranium mineral in all deposits studied. The uraninites contained variable and elevated concentrations of PbO (1.5 wt %⁻5.4 wt %), CaO (0.7 wt %⁻8.3 wt %), and SiO2 (up to 10.0 wt %), whereas the contents of Th, Zr, REE and Y were usually below the detection limits of the electron microprobe. Coffinite usually forms by gradual coffinitization of uraninite in ore deposits and the concentration of CaO was lower than that in uraninites, varying from 0.6 wt % to 6.5 wt %. Coffinite from the Jáchymov ore district was partly enriched in Zr (up to 3.3 wt % ZrO2) and Y (up to 5.5 wt % Y2O3), and from the Potůčky uranium deposit, was distinctly enriched in P (up to 8.8 wt % P2O5), occurring in association with ningyoite. The chemical composition of ningyoite was similar to that from type locality; however, ningyoite from Potůčky was distinctly enriched in REE, containing up to 22.3 wt % REE2O3.

Selenium-rich Au⁻Ag mineralization has been discovered in the Kremnica ore district, central Slovakia. The mineralization is hosted by a single quartz⁻dolomite vein hosted by Neogene propyllitized andesites of the Kremnica stratovolcano. Ore mineralogy and crystal chemistry of individual ore minerals have been studied here. The early base-metal ore mineralization composed of pyrite, sphalerite, and chalcopyrite lacks selenium, whereas the superimposed Au⁻Ag paragenesis is Se-enriched. The Au⁻Ag alloys, uytenbogaardtite, minerals of the galena⁻clausthalite series, acanthite⁻naumannite series, diaphorite, miargyrite, pyrargyrite⁻proustite, polybasite group, minerals of the tetrahedrite group and andorite branch (andorite IV, andorite VI, Ag-excess fizélyite), freieslebenite, and rare Pb⁻Sb sulphosalts (scaiinite, robinsonite, plagionite) have been identified here. Besides selenides, the most Se-enriched phases are miargyrite, proustite⁻pyrargyrite, and polybasite⁻pearceite, whose Se contents are among the highest reported worldwide. In addition, one new phase has been found, corresponding to a Se-analogue of pearceite containing 2.08⁻3.54 apfu Se. The style of mineralization, paragenetic situation, and chemical trends observed in individual minerals are comparable to those of Au⁻Ag low-sulphidation epithermal Au⁻Ag mineralizations of the Kremnica and neighboring Štiavnica and Hodruša-Hámre ore districts. However, the pronounced enrichment in selenium is a specific feature of the studied vein only.

Selenium mineralization in the Příbram uranium and base-metal district (Central Bohemia, Czech Republic) bound to uraninite occurrences in calcite hydrothermal veins is extremely diverse. The selenides antimonselite, athabascaite, bellidoite, berzelianite, brodtkorbite, bukovite, bytízite, cadmoselite, chaméanite, clausthalite, crookesite, dzharkenite, eskebornite, eucairite, ferroselite, giraudite, hakite, klockmannite, naumannite, permingeatite, příbramite, sabatierite, tiemannite, and umangite were found here, including two new mineral phases: Hg-Cu-Sb and Cu-As selenides. Those selenides—and in some cases their sulphidic equivalents—are characterized using wavelength-dispersive spectroscopy, reflected light, powder X-ray diffraction, single crystal X-ray diffraction, Raman spectroscopy, and electron backscatter diffraction. The selenide mineralization in the Příbram uranium district is bound to the border of the carbonate-uraninite and subsequent carbonate-sulphidic stages. Selenides crystallized there at temperatures near 100 °C in the neutral-to-weakly-alkaline environment from solutions with high oxygen fugacity and a high Se2/S2 fugacity ratio.

Hakite, ideally Cu10Hg2Sb4Se13, is a Se-dominant member of the tetrahedrite group occurring at only a few localities in the World. A new occurrence of this mineral in the Pribram uranium and base-metal ore district, Central Bohemia, Czechia, is reported in this paper. Hakite was found to be locally abundant and was identified in several samples with Se mineralization. Three chemically distinct types of hakite were distinguished based on electron microprobe study, Hg-rich hakite (hakite sensu stricto), Zn-rich hakite and Cd-rich hakite. Hg-hakite dominates among the samples studied. Its average empirical formula based on 29 apfu (n = 54) is (Cu5.61Ag0.39)∑6.00Cu400(Hg1.61Zn0.20Cu0.19Cd0.15Fe0.04)∑2.19(Sb3.85As0.28)∑4.13(Se11.55S1.14)∑12.69. Less common is the Zn-hakite, (Cu5.80Ag0.20)∑6.00Cu4.00(Zn1.33Hg0.42Cd0.22Cu0.18Fe0.01)∑2.16(Sb3.85 As0.26)∑4.11(Se10.92S1.81)∑12.73(n = 22), and rare Cd-hakite has an empirical formula (n = 7) of (Cu5.84 Ag0.16)∑6.00Cu4.00(Cd1.27Zn0.60Cu0.10Hg0.07Fe0.02)∑2.06(Sb4.00As0.19)∑4.19(Se12.14S0.61)∑12.75. The refined unit cell of Hg-hakite from Příbram, obtained from powder X-ray diffraction data, is a = 10.8783(3) Å with V= 1287.3(1) Å3 (Z= 4, for the cubic space group I4̅3m). Structure refinement from the precession electron diffraction data collected on the transmission electron microscope (R = 24.4% for 424 observed reflections), confirmed that hakite is isostructural with tetrahedrite. The evolution of hydrothermal fluids, from which Se mineralization formed, suggests a distinct enrichment in sulfur and depletion in selenium over the time span of crystallization. [ABSTRACT FROM AUTHOR]

Hloušekite, (Ni,Co)Cu4(AsO4)2(AsO3OH)2(H2O)9, is a new supergene arsenate mineral from the Geister vein (Rovnost mine), Jáchymov (St Joachimsthal), Western Bohemia, Czech Republic. It was found along with veselovskýite, pradetite, lavendulan, arsenolite, babánekite and gypsum on the surface of strongly altered ore fragments containing dominant tennantite and chalcopyrite. Hloušekite forms thin, lath-like crystals, locally elongated reaching up to 3 mm across. It is transparent, has a pale green colour with vitreous lustre, has a greyish-white streak and it is very brittle with an uneven fracture. It does not fluoresce under shortwave or longwave ultraviolet radiation. Cleavage on {010} is perfect; the Mohs hardness is 2-3. The calculated density is 3.295 g cm-3. Hloušekite is optically biaxial with α′ = 1.653(2) and γ′ = 1.73. The estimated optical orientation is γ′ vs. elongation (c) = 14(1)°. In larger grains it is weakly to moderately pleochroic (α = colourless, β = pale green to green). Hloušekite is triclinic, space group P1̅, a = 6.4010(6), b = 8.0041(6), c = 10.3969(14) Å, α = 85.824(8), β = 79.873(9), γ = 84.655(7)° and V = 521.23(10) Å3, with Z = 1, a:b:c = 0.800:1:1.299. The eight strongest lines in the powder X-ray diffraction (XRD) pattern [d in Å (I)(hkl)] are 10.211(100)(001), 7.974(9)(010), 3.984(6)(020), 3.656(5)(11̅2), 3.631(5)(02̅1), 3.241(5)(022), 3.145(5)(200) and 3.006(5)(210). Chemical analysis by electron microprobe yielded MgO 0.20, FeO 0.10, NiO 5.79, CoO 1.80, CuO 29.53, ZnO 0.66, Al2O3 0.14, P2O5 0.11, As2O5 45.01, H2O 17.71 (calc.), for a total of 101.05 wt.%. The resulting empirical formula, calculated by stoichiometry (9H2O + 2OH), obtained from the crystal structure, is (Ni0.79Co0.25)Σ1.04(Cu3.78Zn0.08Mg0.05Al0.03Fe0.01)S3.95 (AsO4)1.98(PO4)0.02(AsO3OH)2.00(H2O)9.00. The ideal endmember formula , NiCu4(AsO4)2(AsO3OH)2(H2O)9.00, requires NiO 7.23, CuO 30.81, As2O5 44.51, H2O 17.45, total 100.00 wt.%. The crystal structure of hloušekite was solved by charge flipping from single-crystal XRD data and refined to R1 = 0.0599 for 1441 reflections with [Iobs > 3σ(I)]. Hloušekite is a new member of the lindackerite group (also including lindackerite, pradetite and veselovský ite) of the lindackerite supergroup. The ondrušite group of the lindackerite supergroup includes ondrušite, chudobaite, geigerite and klajite. The establishment of these two groups reflects the difference between the crystal structures of their members, mainly in the coordination environment of the Me cations. [ABSTRACT FROM AUTHOR]

Revisiting the structure of uranyl arsenate mineral hügelite provided some corrections to the available structural data. The previous twinning model (by reticular merohedry) in hügelite has been corrected. Twinning of the monoclinic unit cell [a = 7.0189 (7) Å, b = 17.1374 (10) Å, c = 8.1310 (10) Å and β = 108.904 (10)°], which can be expressed as a mirror in [100], leads to a pseudo-orthorhombic unit cell (a = 7.019 Å, b = 17.137 Å, c = 61.539 Å and β = 90.02°), which is eight times larger, with respect to the unit-cell volume, than a real cell. Moreover, the unit cell of chosen here and the unit cell given by the previous structure description both lead to the same supercell. A new structure refinement undertaken on an untwinned crystal of hügelite resulted in R = 4.82% for 12 864 reflections with I obs > 3σ(I) and GOF = 1.12. The hydrogen-bonding scheme has been proposed for hügelite for the first time., (open access.)

Bayleyite is a highly hydrated uranyl tricarbonate mineral containing eighteen water molecules per formula unit. Due to this large water content, the correct description of its crystal structure is a great challenge for the first principles solid state methodology. In this work, the crystal structure, hydrogen bonding, mechanical properties and infrared spectrum of bayleyite, Mg 2 [UO 2 (CO 3 ) 3 ] · 18 H 2 O, have been investigated by means of Periodic Density Functional Theory methods using plane wave basis sets and pseudopotentials. The computed unit-cell parameters, interatomic distances, hydrogen bonding network geometry and the X-ray powder diffraction pattern of bayleyite reproduce successfully the experimental data, thus confirming the crystal structure determined from X-ray diffraction data. From the energy-optimized structure, the elastic properties and infrared spectrum have been determined using theoretical methods. The calculated elastic properties include the bulk modulus and its pressure derivatives, the Young and shear moduli, the Poisson ratio and the ductility, hardness and anisotropy indices. Bayleyite is shown to be a very isotropic ductile mineral possessing a bulk modulus of B ~28 GPa. The infrared spectrum of bayleyite is obtained experimentally from a natural mineral sample from the Jáchymov ore district, Czech Republic, and determined employing density functional perturbation theory. Since both spectra show a high degree of consistence, the bands in the observed spectrum are assigned using the theoretical methodology. The atomic vibrational motions localized in the uranyl tricarbonate units are described in detail, using appropriate normal coordinate analyses based on accurate vibrational computations, since the vibrational normal modes have not been hitherto studied for any uranyl tricarbonate mineral., Competing Interests: Declaration of competing interest There are no conflicts of interest to declare., (Copyright © 2020 Elsevier B.V. All rights reserved.)