Ba Pb Research Articles

Theoretical prediction and experimental synthesis of a Ba0.5Pb0.5S alloy via the molecular precursor route

We synthesized Ba–Pb–S chalcogenide compounds with tunable bandgap properties using a discrete molecular precursor strategy. Ba0.5Pb0.5S has a 1.77 eV optical bandgap, p-type characteristics, and shows great potential for optoelectronic applications.

Trace Element Analysis of Pyrite and Arsenopyrite Using the LA-ICPMS Technique in Pulai, Central Belt of Peninsular Malaysia

The Pulai gold deposit is one of the most promising gold prospects in the Central Belt of Peninsular Malaysia. It is found within the Permian-Triassic Gua Musang sequence of metasediments and metavolcanics and in a structurally controlled NE-SW major fault. Various ore minerals, including pyrite, arsenopyrite, chalcopyrite, sphalerite, pyrrhotite, and galena are typically associated with this deposit. Four types of pyrite (Pyrite 1, Pyrite 2, Pyrite 3, and Pyrite 4) and two types of arsenopyrite (Arsenopyrite 1 and Arsenopyrite 2) were characterised based on their morphological and textural differences. In this region, gold occurs as refractory gold in the nanoparticle form and in the state of Au+ within the structure of sulphides of variable concentrations. Through the detailed laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) trace element mapping analysis of pyrite and arsenopyrite, the main Au-bearing sulphides were found within vein-hosted Pyrite 4 and Arsenopyrite 2 during late phase mineralisation, while Pyrite 3 had the lowest Au concentration. Two phases of Au enrichment were recorded in Pyrite 4, mainly in the core (2 to 11.7 ppm; average 1.4 ppm) and margin of the grain (0.3 to 8.8 ppm; average 1.2 ppm), whereas the highest Au content was detected in the core of Arsenopyrite 2 (0.3 to 137.1 ppm; mean 31.9 ppm). The enrichment of Au is associated with As, forming a zoning elemental pattern distribution. Other trace elements, including Co, Ni, Sb, Pb, Bi, Cu, and Zn, show systematic variation in their composition between the various types of pyrite and arsenopyrite. For early-phase sulphides, the Au enrichment localised at the margin of Pyrite 2 and Arsenopyrite 1, together with Co–Ni, Pb–Bi–Sb, and Ag in the same oriented pattern, suggesting the remobilisation and redistribution of Au in sulfides. Meanwhile, the late crystallisation phase of vein-hosted sulphides formed a rich Au–As ore zoning pattern in the core of Arsenopyrite 2 and Pyrite 4. The second phase of Au enrichment continued at the margin of Pyrite 4 through the remobilisation and precipitation of Au together with Ni, Co, Sb, Pb, Bi, Ag, and Cu. Subsequent deformation then reactivated the late fluid system with the enrichment of Sr, Ba, Rb, Ag, and Zn along the fractures and outermost rim of Pyrite 4 and Rb–Sr–Ba–Pb–Bi along the rim of Arsenopyrite 2. The Pulai gold prospect is interpreted as an orogenic-style gold mineralisation where arsenic can be used as an indicator for proximity to ore mineralisation in exploration.

The effect of pH on heavy metals availability on crude oil remediated and non-remediated soil, Nkeleoken Community Eleme, Rivers State, Nigeria

This study was aimed at examining the influence of pH on heavy metals availability in polluted and non-polluted soils. The findings showed that metal availability depends on soil solution which is pH dependent. The values of pH in Nkeleoken remediated soil (RSENa, RSENb, RSENc) in dry season were 6.01, 5.87, 5.78 and 6.64, 5.77, 5.68 in wet season with mean values of 5.89±0.05 and 6.03±0.53 while the pH of the contaminated soil ranged between 4.31 – 4.41. The mean values of heavy metals in Nkeleoken remediated soil are; Se (318±9.88; 326±11.6 mg/kg), Cd (3.65; 3.82±1.09 mg/kg), V (1095±71.05; 1189±149 mg/kg), Ba (8.98±1.53; 9.40±1.89 mg/kg), Cu (8.19±0.08; 8.84±0.14 mg/kg), Ni (0.02±0.01 mg/kg), As (5.52±2.35; 10.3±2.38mg/kg), Pb (1.73±0.32; 2.70±1.38 mg/kg) and Cr (23.1±4.05; 23.1±4.05 mg/kg). The results revealed that V and Se had the highest concentration level followed by As while the least concentrations were observed in Cd, Ba, Pb and Cr in both dry and wet season. The concentrations of heavy metals in the non-remediated soil ranged from 866 – 868 mg/kg, 1356 – 6332 mg/kg, 211 – 218 mg/kg, 73.6 – 79.0, and 866 – 868 mg/kg for Se, V, Ba Pb and as in dry and wet seasons. However, Cr concentrations ranged from 6.03 – 7.02 mg/kg. The concentrations of V and Se in the non-remediated soils (NRSENx - NRSENz) during dry and wet seasons were higher than their corresponding in the remediated soils likewise the recommended values set by DPR (2012).

The Eocene Poshteh Ba–Pb–Zn–Cu deposit, Iran: geological, mineral–chemical, fluid inclusion, and S–O isotopic analysis of a Kuroko-type VMS deposit with paleo-hydrothermal vent chimneys

The Poshteh deposit is the first documented paleo-hydrothermal chimney-bearing volcanogenic massive sulfide (VMS) deposit in Iran. It occurs in the form of well-developed lensoid orebodies within the Eocene volcano-sedimentary sequence, and comprises of laminated, brecciated, banded, massive, and disseminated textures. The stratiform part of this deposit is approximately 500 m long and up to 20 m thick, and consists of massive to semi-massive sulfides and barites, some of which are banded, which are overlain by barite and siliceous exhalites. The stringer zone stratigraphically underlies the stratiform mineralization. Veins within the stringer zone are composed of quartz, barite, pyrite, galena, sphalerite, and chalcopyrite. Three thin layers of exhalative Mn–Fe-bearing chert overlies the sulfide–sulfate orebodies. Four types of fluid inclusions were recognized in barite and quartz encompassing monophase vapor, monophase liquid, two-phase liquid-rich inclusions, and two-phase vapor-rich fluid inclusions. The homogenization temperatures of fluid inclusions mainly vary between 86.2 and 241.9 °C, whereas their salinities focus on 0.99–21.23 wt.% NaCl equiv. The ore-forming fluids of the barite and quartz minerals are characterized by low-to-medium temperature and low-to-medium salinity. The δ34S values of barite associated with the stratiform and stringer barite orebody range from 8.37 to 21.83 ‰, indicating that the sulfur was derived from the seawater. The sulfur isotope values of sulfide (− 5.18 to 9.33 ‰) are similar to those of VMS deposits from other parts of the world. The δ18O data suggest that the ore-forming fluids of the Poshteh deposit were mainly derived from deep subseafloor circulation of seawater. The well-preserved chimneys typically contain distinct concentric outer and inner sulfide- and axial sulfate-rich zones. The outer zones of the chimneys contain mainly pyrite and chalcopyrite. The sulfides within the inner zone consist predominantly of sphalerite, argentite, and galena. The axial conduits are commonly dominated by barite and calcite. The sulfide-rich chimney zones are also characterized by significantly higher metal contents. The presence of paleo-hydrothermal vent chimneys in the Poshteh Kuroko-type deposit and their trace-element contents also provides significant data for understanding the physicochemical conditions of VMS mineralization.

Hair mineral analysis in the population of students living in the Lower Silesia region (Poland) in 2019: Comparison with biomonitoring study in 2009 and literature data

The paper presents a comparative analysis of biomonitoring research results using hair mineral analysis today and 10 years ago. The aim of the present work was to examine the impact of individual factors, on the content of elements in human hair. The mineral analysis of 115 hair samples was carried out using ICP-OES and AAS technique. It was shown that calcium, barium, copper, mercury, magnesium, manganese and selenium content depend on gender and is higher for women. Statistically significant synergistic correlations were identified between the following pairs of elements: (Ca–Mg), (P–S), (Mo–Sb) and (Ba–Pb). The results of the present work were compared with the previous assessment in 2009 on students of the same age. The content of most of the heavy metals in hair was reduced significantly, which is a sign of the improving state of the local environment. The greatest decrease was recorded for silver (96.6%), arsenic (93.4%), mercury (45.1%), lead (67.7%), antimony (55.2%), thallium (10 times) and cobalt (93.7%). The level of the following elements increased: Ba: 27.3%, Cu: 28.5%, Ni: 22.4%, Ti: 191%, Zn: 11.0%. Changes in the content of most heavy metals in hair have been noted, as well as changes of reference ranges, which may indicate an improvement in the state of the environment in Wrocław, Lower Silesia (Poland) over the last 10 years. These results were confirmed by biomonitoring studies carried out with human hair, which was shown to be a reliable biomarker of human exposure to toxic elements.

Synsedimentary to early diagenetic rejuvenation of barite-sulfides ore deposits: Example of the Triassic intrakarstic mineralization in the Lodève basin (France)

The exhumed Lodève Basin (Hérault, France) provides a rich suite of outcrops showing diagenetic Ba–Pb–Fe–Cu fronts trapped in karst system in Cambrian dolomites during the Triassic post-rift exhumation of the basin. The sedimentological analysis on 10 sites in the basin reveals that barites-sulfides fronts formed during humid-arid climate fluctuations and the emplacement of a shallow lake environment. The fabric of ore deposits, the microthermometry of fluid inclusions entrapped within barites and the strontium/sulfur isotopic compositions of barite-sulfides associations indicate two distinct groups of mineralizations, Type I and Type II, which are contemporaneous but resulting from different processes. The synsedimentary mineralization of the Type I, the presence of only primary single-phase liquid fluid inclusions within barite crystals and the gradual increase of δ34S for both barites and chalcopyrites with depth (from −7 to +18.9‰ V-CDT) suggest ore precipitation close to the vadose zone under bacterial sulfate reduction (BSR) in a confined sulfate-rich playa lake aquifer. The similar 87Sr/86S ratios between barites and the overlying Triassic evaporites indicate that the barium and strontium derived directly from the overlying sulfate-rich lake. For the Type II, the high homogenization temperature of fluid inclusions entrapped within barite (modal Th between 60 and 80 °C) and the association with hydrocarbon markers, confirm the participation of deeper basinal brines in addition to downward percolating sulfates derived from the lake environment. The high positive values of δ34S for both barites and sulfides are typical of a precipitation linked to the combined action between anaerobic oxidation of methane and sulfate reduction (AOM-SR) at the sulfate-methane transition zone (SMTZ) during hydrocarbon migration. Similar 87Sr/86Sr ratios between Middle Triassic barites and previous Late Permian barites confirm that the source of metals precipitated at the SMTZ originated from the dissolution of anterior ore deposits located in the sulfate-depleted zone. This study links very shallow metallogenesis processes to reworking of MVT ore deposits by the action of sulfate-reducing bacteria around hydrocarbon seeps in a karstic environment.

P-T-X reconstruction for ore deposits using petroleum-rich fluid inclusions in fluorite: A case study in the Bou Jaber diapir-related Ba–Pb–Zn–F deposit, Northern Tunisia

The Bou Jaber ore deposit is one of the numerous diapir-related Pb–Zn–F–Ba deposits of the Dome Zone in Northern Tunisia. Its location is controlled by the regional NE-SW Tajerouine Fault.Ore minerals are hosted in the Late Aptian limestones (Serdj Formation) as open space filling and stratabound replacement bodies. According to Bouhlel et al. (2016), the poly-phase mineralization resulted from the successive activity of three mineral systems, a Pb–Zn, then a barite, and eventually a fluorite deposition system. The latter, from the Late Miocene, is demonstrated in the present study.The fluorite system is characterized by the involvement of oil in the hydrothermal fluids. This oil was produced in the local environment of the deposit from the thermal maturation of the Albian Fahdene black shale source-rock at temperature range of~140 °C–~100 °C. Two brines were involved in the fluorite hydrothermal system. The first one (L1) is a Ca-rich brine (≥20 wt % bulk salinity), with Na/Ca ≤ 0.18, which is thought to have long resided in the basement, before its transfer into the Jurassic reservoir (Upper Nara Formation) and its eventual mobilization at the time of ore deposition. The second brine (L2), less saline (≤14 wt % bulk salinity) is more sodic, with Na/Ca up to 0.53, and represents unmodified brine originated from the nearby Triassic salt. The L1 brine was F-bearing, whereas the L2 brine was associated with oil. Fluorite deposition occurred at the estimated shallow depth of 1.7 km from cooling of the L1 brine due to the first isobaric cooling from ~160 °C to 135 °C under sub-lithostatic conditions (36 MPa). This stage is followed by mixing with the newly incoming L2 brines (transporting oil) along a sub-isochoric decompression path (down to the hydrostatic pressure at 17 MPa) and continuously cooling from 135 °C to 125 °C. The cooling and mixing caused fluorite deposition after which a transient heat advection episode (up to 145 °C) caused late calcite deposition prior to the end of hydrothermal circulation.

Geodynamic conditions of formation of massive sulfide deposits in the Magnitogorsk Megazone, Southern Urals, and prospection criteria

The zoned composition changes of the massive sulfide deposits in the major massive sulfide zone of the Southern Urals such as the Magnitogorsk Megasynclinorium are considered. The zoning is expressed as the trend of Ni–Co–Cu → Zn–Cu → Cu–Zn → Au–Ba–Pb–Cu–Zn. This trend is related to two basic factors: (1) the subduction process with the slab’s eastward subsidence preconditioned the formation (from the west to the east) of the following massive sulfide zones: accretionary prism, frontal island arc, developed island arc, inter-arc spreading zone, split back arc, and back-arc spreading; (2) the longitudinal zoning of the massive sulfide paleovolcanic belts related to changes in the thickness of the crust’s basaltic layer and an inclination of the subducting plate in transverse blocks of the belt. The first factor affects the general paleovolcanic and metallogenic latitudinal zoning of the studied region, while the second factor defines the local meridional zoning. The composition of ore-bearing solutions is dependent on the formation depth of the subduction fluids, magma differentiation type, and the ratio of deep fluids to solutions of near-surface convective cells. The combination of the geodynamic factors expressed in the composition of ore-bearing volcanic complexes and the specific geological settings defines the massive sulfide mineralization composition and productivity criteria. The most productive structures include the frontal island-arc and inter-arc spreading zones and within them, the central-type volcanic edifices whose basalts are referred to as the island-arc tholeiite series and are characterized by the minimum TiO2 and Zr content and low La/Yb ratios.

Ecotoxicological risks of the abandoned F-Ba-Pb-Zn mining area of Osor (Spain).

Due to its potential toxic properties, metal mobilization is of major concern in areas surrounding Pb-Zn mines. In the present study, metal contents and toxicity of soils, aqueous extracts from soils and mine drainage waters from an abandoned F-Ba-Pb-Zn mining area in Osor (Girona, NE Spain) were evaluated through chemical extractions and ecotoxicity bioassays. Toxicity assessment in the terrestrial compartment included lethal and sublethal endpoints on earthworms Eisenia fetida, arthropods Folsomia candida and several plant species, whereas aquatic tests involved bacteria Vibrio fischeri, microalgae Raphidocelis subcapitata and crustaceans Daphnia magna. Total concentrations of Ba (250-5110mgkg-1), Pb (940 to >5000mgkg-1) and Zn (2370-11,300mgkg-1) in soils exceeded intervention values to protect human health. Risks for the aquatic compartment were identified in the release of drainage waters and in the potential leaching and runoff of metals from contaminated soils, with Cd (1.98-9.15µgL-1), Pb (2.11-326µgL-1) and Zn (280-2900µgL-1) concentrations in filtered water samples surpassing US EPA Water Quality Criteria (2016a, b). Terrestrial ecotoxicity tests were in accordance with metal quantifications and identified the most polluted soil as the most toxic. Avoidance and reproduction tests with earthworms showed the highest sensitivity to metal contamination. Aquatic bioassays performed in aqueous extracts from soils confirmed the results from terrestrial tests and also detected toxic effects caused by the mine drainage waters. Algal growth inhibition was the most sensitive aquatic endpoint. In view of the results, the application of a containment or remediative procedure in the area is encouraged.

Spectral properties of chlorines and electron transfer with their participation in the photosynthetic reaction center of photosystem II

Structural factors that provide localization of excited states and determine the properties of primary donor and acceptor of electron in the reaction center of photosystem II (PSII RC) are studied. The results of calculations using stationary and time-dependent density functional theory indicate an important role of protein environments of chlorophylls PA, PB, BA, and BB and pheophytins HA and HB in the area with a radius of no greater than ≤10 A in the formation of excitonic states of PSII RC. When the neighboring elements are taken into account, the wavelength of long-wavelength Qy transition of chlorophyll molecules is varied by about 10 nm. The effect is less developed for pheophytin molecules (Δλ ≅ 2 nm). The following elements strongly affect energy of the transition: HisA198 and HisD197 amino-acid residues that serve as ligands of magnesium atoms affect PA and PB, respectively; MetA183 affects PA; MetA172 and MetD198 affect BA; water molecules that are located above the planes of the BA and BB macrocycles form H bonds with carbonyl groups; and phytol chains of PA and PB affect BA, BB, HA, and HB. The analysis of excitonic states, mutual positions of molecular orbitals of electron donors and acceptors, and matrix elements of electron transfer reaction shows that (i) charge separation between BA and HA and PB and BA is possible in the active A branch of cofactors of PSII RC and (ii) electron transfer is blocked at the BB - HB fragment in inactive B branch of PSII RC.

REE and isotope (Sr, S, and Pb) geochemistry to constrain the genesis and timing of the F–(Ba–Pb–Zn) ores of the Zaghouan District (NE Tunisia)

The F–(Ba–Pb–Zn) ore deposits of the Zaghouan District, located in NE Tunisia, occur as open space fillings or stratabound orebodies, hosted in Jurassic, Cretaceous and Tertiary layers. The chondrite-normalized rare earth element (REE) patterns may be split into three groups: (i) “Normal marine” patterns characterizing the wallrock carbonates; (ii) light REE (LREE) enriched (slide-shaped) patterns with respect to heavy REE (HREE), with small negative Ce and Eu anomalies, characteristic of the early ore stages; (iii) Bell-shaped REE patterns displaying LREE depletion, as well as weak negative Ce and Eu anomalies, characterizing residual fluids of subsequent stages. The 87Sr/86Sr ratios (0.707654–0.708127±8), show that the Sr of the epigenetic carbonates (dolomite, calcite) and ore minerals (fluorite, celestite) are more radiogenic than those of the country (Triassic, Jurassic, Cretaceous, lower Miocene) sedimentary rocks. The uniformity of this ratio, throughout the District, provides evidence for the isotopic homogeneity and, consequently, the identity of the source of the mineralizing fluids. This signature strongly suggests that the radiogenic Sr is carried by Upper Paleozoic basinal fluids.The δ34S values of barite, associated to mineralizations, are close to those of the Triassic sea water (17‰). The δ34S values of sulfide minerals range from −13.6‰ to +11.4‰, suggesting two sulfur-reduced end members (BSR/TSR) with a dominant BSR process.Taking account of the homogeneity in the Pb-isotope composition of galenas (18.833–18.954±0.001, 15.679–15.700±0.001 and 38.690–38.880±0.004, for the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios respectively), a single upper crustal source for base-metals is accepted. The Late Paleozoic basement seems to be the more plausible source for F–Pb–Zn concentrated in the deposits. The genesis of the Zaghouan District ore deposits is considered as the result of the Zaghouan Fault reactivation during the Late Miocene period.

Petrogenesis of a Palaeoproterozoic S-type granite, central Wuyishan terrane, SE China: implications for early crustal evolution of the Cathaysia Block

We present zircon U–Pb ages, Hf isotopes, and whole-rock geochemistry of the Xiaochuan gneissic granite intrusion, SE China, to constrain its petrogenesis and provide insights into early crustal evolution of the Cathaysia Block. LA-ICP-MS zircon U–Pb dating of a representative sample yields a weighted mean 206Pb/207Pb age of 1839 ±16 Ma, interpreted as the emplacement age of the Xiaochuan granite. Zircons have ϵHf(t) values ranging from –8.1 to 2.7 and T DM2 model ages from 2.23 to 3.03 Ga. The granites are strongly peraluminious (A/CNK = 1.14–1.41), with relatively high FeOt, TiO2, and CaO/Na2O, and low CaO, Al2O3/TiO2, and Rb/Sr values. In addition, they show strongly negative Ba, Sr, Nb, and Ta and positive Th and Pb anomalies in the primitive mantle-normalized spider diagram, similar to other Cathaysia Palaeoproterozoic S-type granites. The geochemical and Hf isotopic signatures suggest that the Xiaochuan gneissic granites were generated by partial melting of Archaean crustal materials in an intraplate extensional setting. Our results, combined with existing geochronological data, further demonstrate that the Wuyishan terrane is underlain by Palaeoproterozoic crystalline basement.

Structural and electrical transport properties of proficient Ba–Pb nanoferrites

The excellent combination of magnetic and dielectric properties of hexaferrites makes these materials suitable for use in high-frequency applications. Ba–Pb nanocrystalline ferrites having the general formula Ba1−xPbxFe12O19 (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were prepared by the co-precipitation method. X-ray powder diffraction (XRD) patterns of all prepared samples indicated the formation of the required phase. The crystallite size, lattice parameters and porosities of samples were measured from XRD data. Scanning electron microscopy was carried out to observe the morphology of the synthesized Ba–Pb ferrites. Temperature-dependent dc electrical resistivity, dielectric constant, dielectric loss tangent and the ac electrical conductivity of nanocrystalline Ba ferrites were investigated as a function of frequency and Pb concentration. The effect of Pb doping on dielectric and electric properties of Ba nanoferrites was explained on the basis of cation distribution in the crystal structure.

The Mississippi Valley-type fluorite ore at Jebel Stah (Zaghouan district, north-eastern Tunisia): Contribution of REE and Sr isotope geochemistries to the genetic model

The fluorite district of Zaghouan, north-eastern Tunisia, is characterized by F-(Ba–Pb–Zn) ore deposits. Mineralization occurs within stratabound to stratiform bodies, either within Jurassic back-reef limestone uplifted blocks, or along unconformity surfaces that separate them from the overlying sequence. Fluorite mineralization also occurs within fractures crosscutting the uplifted limestone blocks and their overburden. Despite the similarity of the Liassic series throughout the major part of the district, stratabound fluorite deposits formed subsequent to a strong epigenetic dolomitization (Souissi et al., 1998), and occurring along the Lower–Middle Liassic unconformity, are known only at Jebel Stah and at the adjacent Jebel Kohol. Four petrographic types of fluorite are recognized: the finely-laminated karst deposits (Fl1a), the macrogranular fluorite (Fl1b), resulting from the recrystallization of Fl1a, and the megacrystalline fluorite (Fl2) associated to calcite in lodes, and fluorite in geodes (Fl3). This study gives new arguments in terms of the genetic model of the fluorite ore of Jebel Stah and by using trace metal elements (MTE), rare earth elements (REE) and Sr isotope geochemistry. The MTE geochemistry shows, that the epigenetic dolomites and the fluorite Fl1a bear higher concentrations in Mn and Zn, with respect to the fluorites Fl1b, Fl2 and Fl3, while the latter are depleted in all MTE, but enriched in Co. The similarity of their REE patterns indicates that the latter are coeval, and that Fl1a fluorite may be considered as the early ore generation. The same argument confirms that this geochemical imprint has been inherited from a hydrothermal fluid that had remained in equilibrium with shales at depth. Fluorite deposition appears related to an oxidized fluid derived from a sedimentary basin. Fluid circulation may have been triggered in response to hydraulic fracturing within a high geothermal gradient setting, especially along the major structural trends. Fl1b, Fl2 and Fl3 fluorites have been generated from the residual fraction of the ore fluid at later stages of mineralization and in a closed system. Both mineralization and the epigenetic dolomites are characterized by Sr isotope ratios that are higher than the barren Lower–Middle Liassic rocks, indicating that the Sr cannot be derived from the wallrocks. However, these ratios are higher than the Triassic seawater; yet consistent with those of the Paleozoic period. Thus, the fluorite ore of Jebel Stah, is believed to be remobilized from primary ore deposits which are suspected to be hosted in the late series within this period.

Lead isotope systematics in the Långban deposit and adjacent sulphide mineralisations in western Bergslagen, Sweden

The Långban mines and the investigated sulphide deposits are situated in the westernmost part of the Bergslagen ore province, where it borders the voluminous, younger intrusives of the Transscandinavian igneous belt (TIB) in south-central Sweden. We report thermal ionisation mass spectrometer (TIMS) lead isotope data from the Långban Mn–Fe–(As–Ba–Pb–Sb) deposit and from Pb–Zn–(Cu–Fe–As–Ag) sulphide mineralisations in the region. Based on a systematic study of lead isotopic compositions of minerals from different assemblages and paragenetic stages (galena, native lead, arsenates, arsenites, oxychlorides, silicates, carbonates) from Långban, we propose that c.1.89–1.88 Ga (Svecofennian) volcanic-hydrothermal processes supplied the predominating lead component to this complex deposit. Regional amphibolite facies metamorphism, the intrusion of younger granitoids, as well as a succession of ductile to brittle deformation episodes, led to multiple stages of remobilisation of the pre-existing, syngenetic components. During these stages, variable mixing with a minor component of presumed sedimentary origin, comparatively rich in 207Pb and 208Pb, resulted in a temporally unsystematic variability in lead isotopic compositions in the Långban deposit. Contrary to previous suggestions, our lead isotope data suggest that a significant input from, or overprinting by, fluids derived from post-Svecofennian granitic magmatism is unlikely to have affected the Långban mineralisation. By contrast, such processes were probably locally significant in sulphide ± oxide deposits situated in the immediate vicinity of 1.78 Ga intrusives (e.g. at Lahäll and northern Myssberget). Here, the lead isotopic compositions of galena are more radiogenic, which is interpreted to be the result of mixing between Svecofennian ore ± evolved host-rock lead and a later overprinting lead component related to the intrusion of c.1.78 Ga granitoids (Filipstad-type TIB, Hyttsjö intrusive suites). Presently, we cannot unambiguously distinguish whether the source of the major overprinting lead component in some of the sulphide mineralisations was derived from the 1.78 Ga magmas themselves, or from evolved Svecofennian metasupracrustal whole-rock lead remobilised at that time, although our data lean towards the latter.

A thermodynamic modelling of the Ba–Pb system

The thermodynamic modelling of the Ba–Pb binary system was carried out with the help of CALPHAD (CALculation of PHAse Diagram) method. The liquid phase has been described with the association solution model with ‘ Ba 1Pb 1’ associated complex. Ba 2Pb,Ba 5Pb 3,BaPb,αBa 3Pb 5_HT,βBa 3Pb 5_LT and BaPb 3 have been treated as stoichiometric compounds and a sublattice model has been used for the description of the bcc and fcc phases. Due to incompatible experimental phase diagram and thermodynamic data, two sets of thermodynamic parameters have been optimized and discussed. They differ mainly by the optimized value of the entropy of formation of the associated complex and by the entropies of the intermetallic compounds.

Enthalpy of formation of Ca–Pb and Ba–Pb alloys

The enthalpies of formation of liquid and solid Ca–Pb and Ba–Pb alloys have been measured by using high temperature solution calorimetry and direct calorimetry. The enthalpies of mixing of liquid Ca–Pb alloys have been measured at 1020 K and, for the Ba–Pb alloys, in the temperature range of 1070–1150 K. For the liquid alloys, a very strong compound forming tendency has been noticed. Formation and melting enthalpies have been measured for the different intermetallic compounds. For the solid alloys, the most exothermic values in the two systems are Δ f H m 0 (kJ mol −1 of atom, 300 K): Ca 2Pb −62±2 and BaPb −73±2, respectively.

Inherent instabilities of some W 5Si 3-type binary phases with large electropositive metal atoms: Six examples in the Ba–Pb, Ca–Sn–Mg,Cu,Zn, and La–Ga–Al,Zn systems

A particular pathology of certain W 5Si 3-type A 5 B 3 structures ( I4/ mcm) appears to arise because of unduly close approaches of the A1-type atoms on the cell faces at 1 2 , 0, ( 1 4 , 3 4 ) that occur with the larger and more electropositive A and/or in the presence of smaller B atoms. A structure refinement of binary Ba 4.81Pb 3 indicates such a marginal stability in that the Ba atoms in the facial Ba 0.81 chains exhibit an extreme displacement ellipsoid along c ⇒ . Although Ca 5Sn 3 and La 5Ga 3 binaries are unknown in this structure type, five stable ternary derivatives of these have been synthesized via substitution reactions and characterized by single crystal X-ray diffraction means: Ca 4Sn 3.223(4)Mg 0.777, Ca 4Sn 3Cu 1.30(4), Ca 4.66(6)Sn 3Zn 0.704(4), La 4.81(1)Ga 1.38(2)Al 1.62, and La 4.762(5)Ga 1.5(1)Zn 1.5. Only the Ca–Sn–Zn phase exhibits lower symmetry, P4/ mbm. The problematic A1 sites exhibit diverse changes in these, whereas the surrounding B2 tetrahedra are largely unaltered. The Ca–Sn results are, respectively: direct Mg/Sn substitution at the Ca1 site; mixed fractional distribution of the smaller Cu at two sites around the A1 position with an unresolved disorder; a pair of apparently independent modes, fractional Ca in the normal position and fractional Zn rectangles thereabout. The two La–Sn phases contain normal Ga,Al (Ga,Zn) tetrahedral chains with pairs of fractional disordered La atoms along 1 2 , 0, z. Each can be rationalized in terms of a reasonable incommensurate structure. Electronic effects may also be operable.

Synthesis of New Visible Light Active Photocatalysts of Ba(In1/3Pb1/3M1/3‘ )O3 (M‘ = Nb, Ta): A Band Gap Engineering Strategy Based on Electronegativity of a Metal Component

We have synthesized new, efficient, visible light active photocatalysts through the incorporation of highly electronegative non-transition metal Pb or Sn ions into the perovskite lattice of Ba(In(1/3)Pb(1/3)M'(1/3))O3 (M = Sn, Pb; M' = Nb, Ta). X-ray diffraction, X-ray absorption spectroscopic, and energy dispersive spectroscopic microprobe analyses reveal that tetravalent Pb or Sn ions exist in the B-site of the perovskite lattice, along with In and Nb/Ta ions. According to diffuse UV-vis spectroscopic analysis, the Pb-containing quaternary metal oxides Ba(In(1/3)Pb(1/3)M'(1/3))O3 possess a much narrower band gap (E(g) approximately 1.48-1.50 eV) when compared to the ternary oxides Ba(In(1/2)M'(1/2))O3 (E(g) approximately 2.97-3.30 eV) and the Sn-containing Ba(In(1/3)Sn(1/3)M'(1/3))O3 derivatives (E(g) approximately 2.85-3.00 eV). Such a variation of band gap energy upon the substitution is attributable to the broadening of the conduction band caused by the dissimilar electronegativities of the B-site cations. In contrast to the ternary or the Sn-substituted quaternary compounds showing photocatalytic activity under UV-vis irradiation, the Ba(In(1/3)Pb(1/3)M'(1/3))O3 compounds induce an efficient photodegradation of 4-chlorophenol under visible light irradiation (lambda > 420 nm). The present results highlight that the substitution of electronegative non-transition metal cations can provide a very powerful way of developing efficient visible light harvesting photocatalysts through tuning of the band structure of a semiconductive metal oxide.

Triplet state in photosystem II reaction centers as studied by 130 GHz EPR

Abstract The triplet state in the reaction centers of photosystem II was studied by high-field/high-frequency (130 GHz) EPR in the temperature range 50–90 K. At 50 K, the zero-field splitting parameters of the EPR spectrum correspond well to those of a chlorophyll monomer, in agreement with earlier studies. In the high magnetic field of 4.6 T employed in this study, the g-anisotropy of the triplet state becomes apparent and leads to a shift of the canonical positions of the triplet EPR spectrum. Assuming that triplet g- and zero-field tensors are coaxial, the principal values of the triplet g-tensor are determined to be 2.00324, 2.00306 and 2.00231 with an error of ±0.00004. Lifting this assumption results in higher g-anisotropy. At higher temperatures, the shape of the spectra changes significantly. Triplet excitation hopping involving the accessory chlorophyll BA and PA or PB (equivalents of the special pair bacteriochlorophylls of the bacterial reaction centers) can partially explain those changes, but the most prominent features indicate that also the electron acceptor IA (a pheophytin molecule) must be involved.