Identification and implications of fight hydrocarbon fluid inclusions from the Proterozoic Bidjovagge gold-copper deposit, Finnmark, Norway

Carbonic fluid inclusions were observed in quartz-bearing veins at the Proterozoic Bidjovagge AuCu deposit within the Kautokeino greenstone belt in Norway, where mineralization occurred in oxidation zones of graphitic schists. A primary fluid inclusion zonation was observed with C0₂-rich fluid inclusions in the structural footwall of the deposit, and CH₄-rich inclusions within the ore zone in the oxidation zone. Microthermometry of the primary hydrocarbon inclusions revealed 2 groups; (1) a group which homogenized between −125°C and the critical temperature of CH₄ (−82.1°C), which indicated the presence of pure CH₄, and (2) a group which homogenized between the critical temperature of CH₄ and −42°C, which indicated the presence CH₄ and higher hydrocarbons (HHC). Raman microprobe analyses of the first group confirmed the presence of CH₄. The second inclusion group were fluorescent, and Raman spectra clearly displayed CH₄,C₂H₆, and rarer C₃H₈ peaks. A typical feature of the Raman spectra were elevated baselines at the hydrocarbon peaks. Carbon peaks were also usually detected in each inclusion by Raman analysis. Bulk gas chromatography analyses of samples containing the first group (CH₄) indicated the presence of CH₄ and low concentrations of C₂H₆ and C₃H₈. Gas chromatography analyses of samples containing the second group (CH₄ and higher hydrocarbons) confirmed the presence of CH₄, and higher hydrocarbons such as C₂H₆ and C₃H₈ and also butanes. Based on the spacial zonation of hydrocarbons and the estimated PT conditions of 300 to 375°C and 2 to 4 kbars, the authors suggest an abiotic origin for the hydrocarbons. It is suggested that the hydrothermal fluids oxidized the graphitic schist, precipitated Cu and Au and formed light gas hydrocarbons.     

酸溶-电感耦合等离子发射光谱法测定密西西比型铅锌矿床矿石中的铅

密西西比型(MVT)铅锌矿床的主要矿物有方铅石、闪锌矿,常伴生有重晶石、萤石等矿物,使得MVT型矿石在酸处理过程中易生成不溶于水和酸的硫酸铅钡复盐,故而检测矿样中铅的含量偏低。本文建立了采用盐酸-硝酸-氢氟酸体系酸溶分解MVT型矿石,电感耦合等离子体发射光谱法(ICP-OES)测定铅含量的分析方法。实验比较了盐酸-硝酸-氢氟酸、盐酸-硝酸-氢氟酸-高氯酸、盐酸-硝酸-硫酸三种酸溶体系的溶样效果,并通过X射线衍射论证了方法的可行性。结果表明,盐酸-硝酸-氢氟酸体系克服了复盐硫酸铅钡和硫酸铅沉淀的生成,适量的氢氟酸促进了Pb SO4的溶解,X射线衍射表征也表明此种酸溶体系的沉淀中不含有Pb SO4,可更彻底地分解MVT型矿石。本方法精密度(RSD)为0.3%~0.6%,实际样品的加标回收率为96.0%~99.2%,铅的最佳检测范围为0.01%~20.0%。     

Flotation of galena. Influence of grain size,of pulp deoxygenation,and of cleaning with ammonium acetate

The flotation of < 10, 10–20, and 20–40 μm galena fractions was studied. For uncleaned galena a given collector coverage produced better floatability with increasing grain size. Nitrogen had a detrimental effect only for the < 10 μm fraction, producing at a given collector coverage a recovery smaller than that obtained with air.Galena cleaned with 400 g/l ammonium acetate had very poor floatability, although xanthate abstraction was fairly high; this confirms that strong xanthate adsorption is necessary for flotation. Formation of monothiocarbonate was small in all cases, which points to a very minor influence, if any, of this compound in the flotation process.In blank flotation tests, or for very low residual xanthate concentrations, a peak at 208 nm and a shoulder at 255 nm were observed. The former was assigned to the uncomplexed Pb²⁺ ion, and the latter was tentatively attributed to the PbOH⁺ ion.Lead in solution results from dissolution of the oxidation products of galena, as galena itself has an exceedingly low solubility. The curve for total lead in solution vs. initial xanthate concentration, had a minimum for an initial xanthate concentration of 10^?5M, the further increase in dissolved lead is attributed to formation of complexes such as PbX⁺ (X = xanthate). Dissolved lead concentrations were nearly as high for cleaned as for uncleaned galena, which indicates a high oxidation rate of the mineral.     

Lattice dynamics and Raman spectroscopy of protoenstatite Mg2Si2O6

Enstatites (Mg₂Si₂O₆) are important rock forming silicates of the pyroxene group whose structures are characterised by double MgO₆ octahedral bands and single silicate chains. Orthoenstatite transforms to protoenstatite above 1273 K with a doubling of the a axis and a rearrangement of the silicate chains with respect to the Mg₂₊ ions. Lattice dynamical calculations based on a rigid-ion model in the quasi-harmonic approximation provide theoretical estimates of elastic constants, long wavelength phonon modes, phonon dispersion relations, total and partial density of states and inelastic neutron scattering cross-sections of protoenstatite. The computed elastic constants are in good agreement with experimental data. The computed density of states of a chain silicate such as protoenstatite is distinct from that of olivines (forsterite, Mg₂SiO₄ and fayalite, Fe₂-SiO₄) with isolated silicate tetrahedra. The band gaps in the density of states in forsterite are largely due to the separation in the frequency ranges of the external and internal vibrations of the isolated silicate group, whereas in protoenstatite these gaps are filled by the vibrations of the bridging oxygens of the silicate chain. The computed density of states is used to calculate the specific heat, the mean square atomic displacements and temperature factors. Validity of these calculations are supported by Raman scattering measurements. Polarised and unpolarised Raman spectra are obtained from small single crystals of protoenstatite (Li,Sc)_0.6Mg_1.4Si₂O₆ stable at room temperature using the 488 nm or 514.5 nm lines of an Ar⁺ ion laser and a micro-Raman spectrometer with backscattering geometry. The Raman spectra were analysed and interpreted based on the lattice dynamical model. The experimental Raman frequencies and mode assignments (based on polarised single crystal spectra) are in good agreement with those obtained from lattice dynamical calculations.     

The aqueous oxidation of complex sulfide concentrates in hydrochloric acid

Complex sulfides containing sphalerite, galena, chalcopyrite, and small amounts of silver in a matrix of pyrite can be decomposed at 120°C and oxygen pressure of 1000 kPa in 1–2 N HCl for 90 min to yield > 97% of the zinc and > 95% of the copper in solution while about 83% of the lead remains in the residue as PbCl₂ and PbSO₄ and 85% of the silver, together with most of the pyrite. The recovery of elemental sulfur is nearly 100% with respect to ZnS, PbS, and CuFeS₂. Leaching in HCl is faster than in H₂SO₄ at the same acid normality, and the process is diffusion-controlled (strongly dependant on agitation speed and having an activation energy of 3.6 kcal/mole). Lead jarosite, Pb_0.5Fe₃ (SO₄)₂?(OH)₆, is mainly formed when H₂SO₄ is used as a leaching agent.     

Influence of pH on mineral speciation in a bioreactor simulating acid mine drainage

Mineral precipitates formed under conditions representative of acid mine drainage were prepared by oxidizing 0.1 M FeS0₄ · 7H₂0 solutions at 24°C and pH 2.3, 2.6, 3.0, 3.3 and 3.6 using a bioreactor and a strain ofThiobacillus ferrooxidans. The oxidation of dissolved Fe²⁺ was monitored colorimetrically and was completed within 90 to 120 h at all pHs. Schwertmannite, Fe₈O₈(OH)₆SO₄, was a major component of the precipitates and was the only phase formed at pH 3.0. Jarosite, (H,Na,K)Fe₃(OH)₆(SO₄)₂, increased in abundance with decreasing pH whereas goethite, α-FeOOH, appeared at pH 3.3 and 3.6. A similar relationship between pH and mineralogy has been reported in natural specimens of mine drainage ochres.     

Galvanic interactions between galena–sphalerite and their reactivity

The galvanic effect between the main associated mineralogical phases in a mineral sphalerite concentrate was evaluated using an alternative methodology. Comparative voltammetric studies were performed between high purity galena mineral (94.65%) and sphalerite concentrate (content of 78.11% sphalerite, ZnS; 13.64% galena, PbS; 0.57% chalcopyrite, CuFeS₂; 0.41% cadmium sulfide, CdS; and 0.11% arsenopyrite, FeAsS) using carbon paste electrodes (CPE) in order to identify galvanic interactions that affect their reactivity. The electrolyte was an aqueous solution of 0.1 M NaNO₃ (pH 6.5). The results showed that, in sphalerite concentrate, the electrochemical reactivity of the galena was diminished and displaced to more positive potentials with respect to the high purity galena mineral response. This behavior can be attributed to the galvanic protection offered by the sphalerite on the galena, thereby avoiding its free oxidation. On the other hand, sphalerite oxidation was diminished by the formation of a passive products film that is dissolved to more positive potentials which provokes oxidation of other minerals like CuFeS₂, (Zn,Cd)S and FeAsS present in a minor proportion in the sphalerite concentrate.     

Thermodynamic calculations on sulfide flotation systems, II. Comparisons with electrochemical experiments on the galena-ethyl xanthate system

Extensive thermodynamic calculations have been carried out to study the oxidation of galena and its flotation by potassium ethyl xanthate (KEX). In order to include some kinetic effects, three cases have been considered by assuming that sulfur oxidation can proceed as far as the formation of sulfate, thiosulfate and elemental sulfur.The results of these calculations have been compared with those of linear sweep voltammetry and intermittent galvanostatic polarization experiments conducted on galena at pH 9.2. Analysis of the experimental data indicates that in xanthate-free solutions, galena is oxidized primarily to PbO and S⁰ and, to a lesser extent, S₂O₃²⁻, rather than to the thermodynamically most favored PbOH⁺ and SO₄²⁻. Tests carried out in the presence of collector confirm the previous finding (Woods, 1971) that the interaction of xanthate with the mineral begins with chemisorption by a one-electron reaction. This cannot, of course, be predicted by calculations based on bulk thermodynamics.     

Extending the applicability of the Raman carbonaceous‐material geothermometer using data from contact metamorphic rocks

The degree of graphitization of carbonaceous material (CM) has been widely used as an indicator of metamorphic grade. Previous work has demonstrated that peak metamorphic temperature (T) of regional metamorphic rocks can be estimated by an area ratio (R2) of peaks recognized in Raman spectra of CM. The applicability of this method to low‐pressure (<3 kbar) contact metamorphism was tested using Raman spectroscopic analyses of samples from two contact‐metamorphic aureoles in Japan (Daimonji and Kasuga areas). A suitable measurement procedure allows the dependence of the geothermometer on sample type (thin section, chip) and incident angle of laser beam relative to the c‐axes of CM to be tested. Two important general results are: (i) in addition to standard thin sections, chips are also suitable for spectral analysis; and (ii) the incident angle of the laser beam does not significantly affect the temperature estimation, i.e. spectral measurements for the geothermometer can be carried out irrespective of the crystallographic orientation. A laser wavelength of 532 nm was used in this study compared with 514.5 nm in an independent previous study. A comparison shows that the use of a 532‐nm laser results in a slightly, but systematically larger R2 ratio than that of a 514.5‐nm laser. Taking this effect into account, our results show that there is a slight but distinct difference between the R2–T correlations shown by contact and regional metamorphic rocks: the former are slightly better‐crystallized (have slightly lower R2 values) than the latter at the same temperature. This difference is interpreted as due to the degree of associated deformation. Despite the slight difference, the results of this study coincide within the estimated errors of ±50 °C with those of the previously proposed Raman CM geothermometer, thus demonstrating the applicability of this method to contact metamorphism. To facilitate more precise temperature estimates in regions of contact metamorphism, a new calibration for analyses using a 532‐nm laser is derived. Another important observation is that the R2 ratio of metamorphosed CM in pelitic and psammitic rocks is highly heterogeneous with respect to a single sample. To obtain a reliable temperature estimate, the average R2 value must be determined by using a substantial number of measurements (usually N > 50) that adequately reflects the range of sample heterogeneity. Using this procedure (with 532‐nm laser) and adapting our new calibration, the errors of the Raman CM geothermometer for contact metamorphic rocks decrease to ～±30 °C.     

An ultraviolet laser microprobe for the in situ analysis of multisulfur isotopes and its use in measuring Archean sulfur isotope mass-independent anomalies

A laser fluorination microprobe system has been constructed for high-accuracy, high-precision multisulfur isotope analysis with improved spatial resolution. The system uses two lasers: (a) a KrF excimer laser for in situ spot analysis by ultraviolet (UV) photoablation with λ = 248 nm and (b) a CO₂ laser for whole-grain analysis of powdered samples by infrared heating at λ = 10.6 μm. A CO₂ laser is necessary for the analysis of interlaboratory isotope reference materials because they are supplied as powders. The δ³⁴S and δ³³S compositions of reference materials measured with a CO₂ laser fluorination system agree (±0.2‰, 1σ) with the recommended values by the Sulfur Isotope Working Group of the International Atomic Energy Agency [Ding et al 2001] and [Taylor]. The precision of replicate analyses of powdered sulfide minerals with the CO₂ laser is typically ±0.2‰ (1σ) for δ³⁴S.The in situ fluorination of sulfides with a KrF excimer laser (λ = 248 nm) was validated by comparison of measurements of side-by-side laser craters and powders excavated from drill holes. Powders from drill holes were analyzed with the CO₂ laser. In situ laser craters and drill hole powders give the same δ³⁴S_V-CDT and δ³³S_V-CDT values within 0.2‰. The δ³⁴S_V-CDT and δ³³S_V-CDT values of both powders and in situ analyses are independent of F₂ gas pressure over a range of 15 to 65 torr. No dependence of δ³⁴S_V-CDT and δ³³S_V-CDT values on UV laser energy fluence has been observed. Mineral-specific fractionation of sulfur isotopes in analyzing pyrite, sphalerite, galena, troilite, and chalcopyrite has not been observed with a KrF excimer laser (λ = 248 nm). Test analyses with an ArF excimer laser (λ = 193 nm), however, gave fractionated sulfur isotope ratios.A range of Δ³³S anomalies of from - 1.5 to +3.0‰ in Archean samples from the North Pole district, Pilbara Craton, Australia, and from black shale of the Lokamonna Formation, South Africa, were verified by in situ analysis of individual pyrite grains with a KrF excimer laser. These results show that a combination of high-accuracy, high-precision analyses with improved spatial resolution permits locating and analyzing host minerals of non-mass-dependent sulfur isotope anomalies.     

Bismuthoan Galena—A New Variety of Galena

Bismuthoan galena is a variety of galena, resulting from the replacement of Bi for some Pb in galena.This mineral occurs in the No.11 orebody of the Lamo skarn-type Zn-Cu deposit in the Dachang ore field ,but only the No,11 orebody of the Lamo deposit is developed such bismuthoan galena.This is closely related to such a geochemical background that the No.11 orebody contains high Bi and Bi-sulfosalt minerals are well developed there.Eight electron microprobe analyses of five samples give 60.17-70.20%Pb(66.94% on average),10.00-16.06%Bi (12.47%),4.83-8.97%Ag(6.39%)and 13.25-13.98% S(13.65%).Its molecular formula is Pb0.76,Bi0.14,Ag0.13,1.03S.No galena so high in Bi has been reported in the literature and this is the first report in China.     

Terrestrial heat flow around the aseismic front of the Japanese Island Arc

Very few data on heat flow are available in the area around the aseismic front of the Japanese Islands. In order to remedy this situation, measurements of the terrestrial heat flow were made at three locations in the eastern part of Fukushima Prefecture, northeastern Honshu, Japan. The observed values of heat flow were 37 mW/m² (0.88 μcal/cm²·s) at Soma, 52 mW/m² (1.25 μcal/cm²·s) at Kashima and 19 mW/m² (0.46 μcal/cm²·s) at Naraha, respectively. These data partially fill the gaps in the terrestrial heat flow data on land in northeastern Honshu, Japan. These values are considerably lower than the average heat flow over the world, but agree well with the previous estimation for the area.     

Solution mechanisms of silicate in aqueous fluid and H2O in coexisting silicate melts determined in-situ at high pressure and high temperature

The structure of H₂O-saturated silicate melts, coexisting silicate-saturated aqueous solutions, and supercritical silicate liquids in the system Na₂O·4SiO₂–H₂O has been characterized with the sample at high temperature and pressure in a hydrothermal diamond anvil cell (HDAC). Structural information was obtained with confocal microRaman and with FTIR microscopy. Fluids and melts were examined along pressure-temperature trajectories defined by the isochores of H₂O at nominal densities, ρ_fluid, (from EOS of pure H₂O) of 0.90 and 0.78 g/cm³. With ρ_fluid = 0.78 g/cm³, water-saturated melt and silicate-saturated aqueous fluid coexist to the highest temperature (800 °C) and pressure (677 MPa), whereas with ρ_fluid = 0.90 g/cm³, a homogeneous single-phase liquid phase exists through the temperature and pressure range (25–800 °C, 0.1–1033 MPa). Less than 5 vol% quartz precipitates near 650 °C in both experimental series, thus driving Na/Si-ratios of melt + fluid phase assemblages to higher values than that of the Na₂O·4SiO₂ starting material.Molecular H₂O (H₂O°) and structurally bonded OH groups were observed in coexisting melts and fluids as well as in supercritical liquids. Their OH/(H₂O)-ratio is positively correlated with temperature. The OH/(H₂O)° in melts is greater than in coexisting fluids. Structural units of Q³, Q², Q¹, and Q⁰ type are observed in all phases under all conditions. An expression of the form, 12Q³ + 13H₂O2Q² + 6Q¹ + 4Q⁰, describes the equilibrium among those structural units. This equilibrium shifts to the right with increasing pressure and temperature with a ΔH of the reaction near 425 kJ/mol.     

P-T-X parameters of metamorphogene and hydrothermal fluids,isotopy and age of the Bogunai gold deposit,southern Yenisei Ridge (Russia)

Fluid inclusions in quartz, sulfides from quartz veins, and quartz, garnet, plagioclase, and orthoclase from granulites of the Bogunai gold deposit located in the granulites of the Angara-Kan block of the Yenisei Ridge were studied by thermobarometry, gas chromatography, chromato-mass-spectrometry, Raman spectroscopy, and mass spectrometry with inductively coupled plasma. The formation temperatures (850-950 °C) and pressures (8.5-9.0 kbar) of minerals of the granulite metamorphic facies are much higher than the crystallization temperatures (220-420 °C) and pressures (0.1-1.6 kbar) of gold-quartz veins of the Bogunai deposit. These veins formed with the participation of H₂O-CO₂-hydrocarbon fluids with a salt (predominantly MgCl₂) concentration of 2-19 wt.% NaCl equiv. The gas phase of fluid inclusions from quartz, pyrite, chalcopyrite, galena, and sphalerite contains not only H₂O, CO₂, CH₄, and N₂ but also the first found compounds of sulfur (CS₂, O₂S, COS, C₂H6S₂) and nitrogen (C3H₇N, C3H₇NO, C₄H8N₂O) and numerous hydrocarbons of different classes (paraffins, arenes, naphthenes, alcohols, aldehydes, ketones, carbonic acids, and furans). The age of the Krasnoyarsk mineralized zone, one of the sites of the Bogunai deposit, is 466 ± 3.2-461.6 ± 3.1 Ma, which is almost 1400 Ma younger than the age of granulite metamorphism and 255 Ma younger than the age of diaphthoresis but is close to the age of the Lower Kan granitoid pluton (455.7 ± 3.4 Ma). The sulfur isotope ratios (5³⁴S) of sulfides (pyrite, chalcopyrite, sphalerite, and galena) are close to the mantle values, 0.8 to 3.5%c, and are in the range of the granitoid values, which indicates the crustal source of the fluid sulfur. Gold of the Bogunai deposit accumulated with the participation of H₂O-CO₂-hydrocarbon fluids generated both in deep-fault zones and in granitoid intrusions.     

铅锌硫化矿物从铅-锌-还原型硫热液系统中晶出时的硫同位素分馏规律

本文试图在Pinckney及Rafter(1972)工作的基础上讨论闪锌矿和方铅矿同时从铅锌-还原型硫热液系统中晶出时的硫同位素分馏规律。     

Dissolution of lead- and lead-arsenic-jarosites at pH 2 and 8 and 20 °C: Insights from batch experiments

Lead- and Pb-As-jarosites are minerals common to acidic, sulphate-rich environments, including weathering zones of sulphide ore deposits and acid rock or acid mine drainage (ARD/AMD) sites, and often form on or near galena. The structures of these jarosites are based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, comprised of slightly distorted FeO₆ octahedra and SO₄²⁻ (-AsO₄³⁻ in Pb-As-jarosites) tetrahedra. To better understand the dissolution mechanisms and products of the break down of Pb- and Pb-As-jarosite, preliminary batch dissolution experiments were conducted on synthetic Pb- and Pb-As-jarosite at pH 2 and 20 °C, to mimic environments affected by ARD/AMD, and at pH 8 and 20 °C, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)₂). All four dissolutions are incongruent. Dissolution of Pb-jarosite at pH 2 yields aqueous Pb, Fe and SO₄²⁻. The pH 8 Pb-jarosite dissolution yields aqueous Pb, SO₄²⁻ and poorly crystalline Fe(OH)₃, which does not appear to resorb Pb or SO₄²⁻, possibly due to the low solution pH (3.44-3.54) at the end of the experiment. The pH 2 and 8 dissolutions of Pb-As-jarosite result in the formation of secondary compounds (poorly crystalline PbSO₄ for pH 2 dissolution; poorly crystalline PbSO₄ and Fe(OH)₃ for pH 8 dissolution), which may act as dissolution inhibitors after 250 to 300 h of dissolution. In the pH 2 dissolution, aqueous Fe, SO₄²⁻ and AsO₄³⁻ also form, and in the pH 8 dissolution, Fe(OH)₃ precipitates then subsequently resorbs aqueous AsO₄³⁻. The dissolutions probably proceed by preferred dissolution of the A- and T-sites, which contain Pb, and SO₄²⁻ and AsO₄³⁻, respectively, rather than Fe, which is sterically remote, within the T-O-T Pb- and Pb-As-jarosite structures. These data provide the foundation necessary for further, more detailed investigations into the dissolution of Pb- and Pb-As-jarosites.     

Oxygen isotope evidence for sorption of molecular oxygen to pyrite surface sites and incorporation into sulfate in oxidation experiments

Experiments were conducted to investigate (i) the rate of O-isotope exchange between SO₄ and water molecules at low pH and surface temperatures typical for conditions of acid mine drainage (AMD) and (ii) the O- and S-isotope composition of sulfates produced by pyrite oxidation under closed and open conditions (limited and free access of atmospheric O₂) to identify the O source/s in sulfide oxidation (water or atmospheric molecular O₂) and to better understand the pyrite oxidation pathway. An O-isotope exchange between SO₄ and water was observed over a pH range of 0–2 only at 50 °C, whereas no exchange occurred at lower temperatures over a period of 8 a. The calculated half-time of the exchange rate for 50 °C (pH = 0 and 1) is in good agreement with former experimental data for higher and lower temperatures and excludes the possibility of isotope exchange for typical AMD conditions (T  25 °C, pH  3) for decades.Pyrite oxidation experiments revealed two dependencies of the O-isotope composition of dissolved sulfates: O-isotope values decreased with longer duration of experiments and increasing grain size of pyrite. Both changes are interpreted as evidence for chemisorption of molecular O₂ to pyrite surface sites. The sorption of molecular O₂ is important at initial oxidation stages and more abundant in finer grained pyrite fractions and leads to its incorporation in the produced SO₄. The calculated bulk contribution of atmospheric O₂ in the dissolved SO₄ reached up to 50% during initial oxidation stages (first 5 days, pH 2, fine-grained pyrite fraction) and decreased to less than 20% after about 100 days. Based on the direct incorporation of molecular O₂ in the early-formed sulfates, chemisorption and electron transfer of molecular O₂ on S sites of the pyrite surface are proposed, in addition to chemisorption on Fe sites. After about 10 days, the O of all newly-formed sulfates originates only from water, indicating direct interaction of hydroxyls from water with S at the anodic S pyrite surface site. Then, the role of molecular O₂ is as proposed in previous studies: acting as electron acceptor only at the cathodic Fe pyrite surface site for oxidation of Fe(II) to Fe(III).     

Raman spectra and X-ray diffraction of tuite at various temperatures

High-temperature Raman spectra and thermal expansion of tuite, γ-Ca₃(PO₄)₂, have been investigated. The effect of temperature on the Raman spectra of synthetic tuite was studied in the range from 80 to 973 K at atmospheric pressure. The Raman frequencies of all observed bands for tuite continuously decrease with increasing temperature. The quantitative analysis of temperature dependence of Raman bands indicates that the changes in Raman frequencies for stretching modes (ν₃ and ν₁) are faster than those for bending modes (ν₄ and ν₂) of PO₄ in the present temperature range, which may be attributed to the structural evolution of PO₄ tetrahedron in tuite at high temperature. The thermal expansion of tuite was examined by means of in situ X-ray diffraction measurements in the temperature range from 298 to 923 K. Unit cell parameters and volume were analyzed, and the thermal expansion coefficients were obtained as 3.67 (3), 1.18 (1), and 1.32 (3) × 10^?5 K^?1 for V, a, and c, respectively. Thermal expansion of tuite shows an axial anisotropy with a larger expansion coefficient along the c-axis. The isothermal and isobaric mode Grüneisen parameters and intrinsic anharmonicity of tuite have been calculated by using present high-temperature Raman spectra and thermal expansion coefficient combined with previous results of the isothermal bulk modulus and high-pressure Raman spectra.     

Reduced sulfur and iron species in anoxic water column of meromictic crater Lake Pavin (Massif Central, France)

The vertical distribution of reduced sulfur species (RSS including H₂S/HS⁻, S⁰, electroactive FeS) and dissolved Fe(II) was studied in the anoxic water column of meromictic Lake Pavin. Sulfide concentrations were determined by two different analytical techniques, i.e. spectophotometry (methylene blue technique) and voltammetry (HMDE electrode). Total sulfide concentrations determined with methylene blue method (∑H₂S_MBRS) were in the range from 0.6 µM to 16.7 µM and were substantially higher than total reduced sulfur species (RSS_V) concentrations determined by voltammetry, which ranged from 0.1 to 5.6 μM. The observed difference in the sulfide concentrations between the two methods can be assigned to the presence of FeS colloidal species.Dissolved Fe was high (> 1000 µM), whereas dissolved Mn was only 25 µM, in the anoxic water column. This indicates that Fe is the dominant metal involved in sulfur redox cycling and precipitation. Consequently, in the anoxic deep layer of Lake Pavin, “free” sulfide, H₂S/HS⁻, was low; and about 80% of total sulfide detected was in the electroactive FeS colloidal form. IAP calculations showed that the Lake Pavin water column is saturated with respect to FeS_am phase. The upper part of monimolimnion layer is characterized by higher concentrations of S(0) (up to 3.4 µM) in comparison to the bottom of the lake. This behavior is probably influenced by sulfide oxidation with Fe(III) oxyhydroxide species.     

Some new lead oxide minerals and murdochite from T. Khuni Mine,Anarak, Iran

Four new lead oxide minerals together with ample murdochite (PbCu₆O₈) were found at the T. Khuni mine in the Anarak area of Central Iran. The formulae and proposed names are: Khuniite (Pb_1.6Zn_0.2Cu_0.2)CrO₅, Chrominium 2 PbO·CrO₃, Plumangite (Cu_0.85Zn_0.15)O·PbMn₄O₁₆ and a mineral X with the formula Pb₉O₁₆. These results were obtained by combined microscopic, X-ray and microprobe analyses.

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Zusammenfassung Vier neue Bleioxyd-Minerale, die mit reichlich Murdochit (PbCu₆O₈) verwachsen sind, wurden in der T. Khuni-Grube im Anarakgebiet in Zentralpersien gefunden. Ihre Eigenschaften und ihre Paragenese werden beschrieben. Es sind: Khuniit (Pb_1.6Zn_0.2Cu_0.2)CrO₅, Chrominium 2 PbO·CrO₃, Plumangit (Cu_0.85Zn_0.15)O·PbMn₄O₁₆ und ein Mineral X von der Zusammensetzung Pb₉O₁₆.Diese Mitteilung beruht auf Beobachtungen im Mikroskop, auf Röntgendaten und Mikrosondenuntersuchungen.