Barite Crystals Research Articles

Separation and characterization of pedogenic barite crystals from petrocalcic horizon materials for future isotopic and geochronological applications

Although extensive work has been conducted on pedogenic barite in the petrocalcic soil horizons at Mormon Mesa, NV, further investigations are required to understand the mode and timing of its precipitation. Isolation of barite crystals from petrocalcic soil materials is an important first step, after which, crystal morphology can be examined. We sought a method to isolate barite and other heavy minerals to examine their feasibility for future isotopic and geochronological techniques. Using XRD, SEM with EDS and microprobe analyses, barite was analyzed for evidence of chemical or physical alteration after chemical separation procedures with HCl to remove carbonate and methylene iodide to separate minerals with specific gravities greater than and less than 3.3g/mL. After separation, barite clusters were observed within the heavy mineral separates. Barite showed no remarkable signs of physical or chemical alteration after separation and small (<1mm) clusters of barite were large enough to be hand-picked from the heavy separates. The isolation of barite from other petrocalcic soil materials is the critical first step in applying isotopic and geochronological techniques that will contribute to a better understanding of the timing and development of this unique soil system.

Rare earth elements and Nd isotopes tracing water mass mixing and particle-seawater interactions in the SE Atlantic

Distributions of dissolved and particulate rare earth elements (REEs) and seawater neodymium isotopic composition (εNd) were established in samples from the BONUS GoodHope (BGH) IPY-GEOTRACES cruise in the SE Atlantic sector of the Southern Ocean (36°S-13°E to 57°S-0°, Feb.–Mar. 2008). Close to the South African continent in the subtropical domain, particulate REEs show the highest concentrations and flat PAAS-normalized patterns, clearly tracing their lithogenic origin. Active cerium oxidation onto suspended particles is evidenced by the mirror-image relationship of the cerium anomaly between dissolved and particulate phases. Unradiogenic dissolved neodymium in surface waters (εNd= -17.1) traces the influence of old sedimentary material brought by the Agulhas current and rings to the Cape Basin area. A mass balance calculation suggests that the release of Nd from dissolution of lithogenic material corresponds to a remobilization of 154×106T of sediment per year, i.e., 5% of the total sediment delivered to the southeast African coast annually. At open ocean stations, both dissolved and particulate REEs present negative cerium anomalies, indicating that particles have acquired a marine signature. The increasing REE concentrations with depth, and the strong linear correlations of dissolved REE with silica, indicate that surface removal and deep re-mineralisation of REEs are partially related to the biogeochemical cycle of silicate, which involves biogenic silica (diatoms). Combined with marine carbonates, these authigenic phases could explain the observed REE patterns in suspended particles, except for La. We suggest that the positive La anomalies in both phases are linked to the oceanic barium cycle and the partial dissolution of barite crystals, especially in the Polar Frontal Zone.The εNd composition behaves conservatively in intermediate and deep waters, while input processes affect the isotopic signal of subtropical surface waters and Weddell Gyre bottom waters. An Indian Ocean and an Atlantic variety of AAIW have been isotopically differentiated (εNd=−9.3±0.3 and εNd=−8.0±0.5, respectively). Homogeneous signatures characterize circumpolar waters (εNd from −8.2 to −8.4 for CDW). A binary mixing model has been used to assess the contribution of undiluted NADW reaching southern latitudes.

Solid–aqueous equilibrium in the BaSO4–RaSO4–H2O system: First-principles calculations and a thermodynamic assessment

Phase relations in the BaSO4–RaSO4–H2O system are important for understanding the role of barite-type minerals in controlling the concentration of Ra2+ in natural water reservoirs. These relations are extremely sensitive to the difference in the solubility products of the end-members and to the degree of non-ideality of the solid solution phase. Experimental constraints to the standard entropy of RaSO4 and the regular interaction parameter of the barite–RaSO4 solid solution are ambiguous. This study is focused on determination of these parameters from first principles. The phonon density of states of RaSO4 is computed with the aid of the density functional perturbation theory. The regular interaction parameter in the BaSO4–RaSO4 solid solution, WBaRa, is interpreted as the slope of the enthalpy of mixing in the limit of infinite dilution (xRa=0) and is calculated from the change in the total energy of a 2×2×2 supercell of BaSO4 due to the insertion of a single substitutional defect of Ra. The method is validated by computing W values for a wider range of binary solid solutions with barite and aragonite structures. The computed value of WBaRa=2.50±1.00kJ/mol implies that the solid–aqueous equilibrium in the BaSO4–RaSO4–H2O system may have an alyotropic point in close proximity to the BaSO4 end-member. The assessment of available data on re-crystallization of barite in Ra-bearing aqueous solutions suggests that the barite crystals may fully equilibrate on the time scale of hundred days.

Precipitation of barite by marine bacteria: A possible mechanism for marine barite formation

Barite (BaSO 4 ) is found throughout the ocean, yet seawater is undersaturated with respect to barite, and organisms that could account for the abundance of barite have not yet been identifi ed. The mechanism for barite formation in seawater is not fully understood. Here we show that marine bacteria have the ability to precipitate barite through a metabolically mediated biomineralization process. We precipitated barite in laboratory experiments in the presence of several strains of marine bacteria grown on yeast media enriched with barium (Ba); barite did not precipitate under identical conditions in killed-bacteria controls. The crystals develop from amorphous, phosphorous-rich spherical precursors with fi brous internal textures, common in bacterial mineral precipitation. Bacterial mediation of barite precipitation can explain the distribution of barite in the water column and the occurrence of barite crystals in organic-rich sinking aggregates where bacteria are concentrated. This fi nding has implications for the use of barite and Ba proxies in paleoceanographic research.

Geology, mineralogy and possible origin of the copper mineralization in marble near Saldán, Córdoba (Argentina)

; refractive indices are e = 1.707(3), ω = 1.656(3), with an anomalous small 2V. Magnesium (up to 0.15 wt. % MgO) is the only significant substituent. Yellow barite crystals tabular on {001} contain traces of Sr. Quartz occurs rarely, as drusy linings. A few cases of botryoidal, opal-like quartz crusts are known. Tenorite forms dark brown masses and stringers included in marble. Very scarce grains of copper sulfides (anilite altering to spionkopite and covellite along rims and cracks) are found scattered in the marble. Copper is partially replaced by Bi (≤ 0.15 wt. % Bi) and Pb (≤ 0.16 wt. % Pb). Malachite and brochantite are alteration products of sulfides. Fluid inclusion studies indicate that the minerals precipitated from a single-phase fluid initially at a temperature above 300 oC that cooled to c. 220 oC. Salinity was very low, 0 to 2 wt. % NaCl eq. Isotopic analyses of calcite give δ 13

NON-DESTRUCTIVE IDENTIFICATION OF MICROMETER-SCALE MINERALS AND THEIR POSITION WITHIN A BULK SAMPLE

Using the conventional techniques of mineralogy, it has been a challenge to determine mineral identity, crystal orientation and spatial position of micrometer-sized crystals that are embedded in a rock, sediment or soil. Traditionally, the individual grains must be extracted and analyzed separately. Crushing or disintegrating a sample annihilates any possibility for gathering information from the texture of the porous media or the mineral assemblage close to the grains in question. A new method using three-dimensional X-ray diffraction (3DXRD) microscopy can be successfully applied to natural materials. We combined X-ray microtomography (XMT) and 3DXRD to investigate a sample of very fine-grained chalk containing fracture minerals. The XMT technique provides three-dimensional images of the particles and pore structure at very high resolution (350 nm voxel dimension) on samples less than 500 μm in diameter. The minor phases present as crystals in fractures were determined nondestructively with 3DXRD microscopy. The chalk fragment investigated is composed predominantly of randomly oriented nanometric crystals of calcite that produce powder rings where no texture can be observed. Superimposed on this pattern, Bragg diffraction peaks from the other crystalline phases were observed. Individual crystals of barite and pyrite only a few micrometers in diameter are present in the fractures. Magnetite, celestine and siderite, other minerals that might have been expected based on the XMT absorption contrast, were not identified. The crystal shape and in-fracture location, derived from the microtomograms, and the mineral identity, derived from 3DXRD, allowed us to propose that the fractures are original in these tiny drill cuttings; they were not induced by drilling and filled with drilling mud particles, thus allowing reliable estimates to be made of rock porosity and permeability.

Micromorphological investigation of pedogenic barite in Mormon Mesa petrocalcic horizons, Nevada USA: Implication for genesis

Barite crystals are identified in stage VI petrocalcic horizons at Mormon Mesa, Nevada. Their presence is significant because barite is not typically associated with arid soil processes. Barite is identified through backscatter SEM/EDS as bright white crystals with EDS peaks of high Ba, S, and O. Barite crystals are euhedral, tabular to acicular crystals ranging in size from 1 to 50μm in length and 1–20μm in diameter, and as small (2–4μm) tabular-ovoid crystals. Forty-one percent of the barite in SEM images is associated with fibers of palygorskite and/or sepiolite. Barite crystals are also associated with linear voids, circular pores, and within micropores between fibers of silicate clays. The formation of barite at Mormon Mesa is attributed to: (i) The dissolution of Ba and SO4 ions from detrital minerals and dust that are flushed into the soil profile and precipitate as barite; and/or (ii) Biomineralization of barite in micro-environments suitable for bacteria or other organisms within the petrocalcic horizon.

The origin of sulfate mineralization and the nature of the BaSO4–SrSO4 solid-solution series in the Ain Allega and El Aguiba ore deposits, Northern Tunisia

Ain Allega and El Aguiba are among the largest barite–celestite deposits attributed to the Triassic period in Tunisia. They are located in the flysch zone on the eastern edge of the Triassic diapir of Jebel Hamra. The ore body consists of dolomite intensely brecciated and surrounded by marls, clay, gypsum and dolomite which forms the hanging wall of the deposit, and rimmed by Paleocene marls. The ore minerals show a cap-rock type mineralization with various forms and types, in particular impregnation in dolomite, breccia cement, replacement of carbonate cap-rock and open space-filling in the dissolution cavities and fractures. Ore minerals include sphalerite, galena, marcasite and pyrite. Principal gangue minerals are barite, celestite, calcite, dolomite and quartz. The ore minerals are hosted by the Triassic carbonate rocks, which show hydrothermal alteration, dissolution and brecciation.The study of barite–celestite solid-solution shows a bimodal distribution in which the composition is not continuous. Some intermediate compositions are missing; 20–80% SrSO4 for the El Aguiba ore deposit and 50–70% SrSO4 for the Ain Allega ore deposit.X-ray diffraction peaks in the BaSO4–SrSO4 series display considerable broadening at intermediate compositions. The unit cell volume varies from 346.97Å3 in barite (100% BaSO4) to 308.29Å3 in celestite (100% SrSO4). This variation in cell parameters is attributed to the degree of substitution of barium by strontium since there is less variation between ionic radii of these elements. Consequently, these substitutions caused variation in morphologies, position and d-spacing of peaks (200, 011, 113, 312,122, 112, and 111). Some barite crystals have small-scale, strontium compositional banding which suggests that the crystals responded to regular fluctuations in physiochemical conditions during deposition. The degree of supersaturation in Ba2+ and Sr2+ controls the growth mechanism and consequently the surface structure, which in turn controls the mechanism of adsorption and incorporation of minor and trace elements into the growing crystal. For a solid solution, the transitional supersaturation for different growth mechanisms can be significantly different for the two end members. One of the most interesting and intriguing phenomena observed in natural crystals of the (Ba,Sr)SO4 solid solution from this study area is the development of compositional oscillatory zoning, consisting of alternating Ba-rich and Sr-rich layers.The sulfur isotope analyses show significant variability for barite and celestite (from 16.2 to 23‰). These values are interpreted as the result of the mixing of two sulfur end-members in the mineralizing fluids, corresponding to thermochemical sulfate reduction of Messinian seawater, together with Triassic sulfate, as sulfur sources.Fluid inclusion studies of celestite show that the BaSO4–SrSO4 solid-solution in both deposits was precipitated from hot saline solution (Th=190±20°C; 16.37wt.% NaCl equivalent in Ain Allega and 8.2wt.% NaCl equivalent in El Aguiba). Consequently, the precipitation could be from mixing of basinal brines with magmatic–meteoric fluid.

Infrared investigation of barite and gypsum crystallization: Evidence for an amorphous to crystalline transition

Infrared was used to monitor the progression of barite (BaSO4) and gypsum (CaSO4·2H2O) crystallization. It was found that barite crystallized with broad infrared peaks that narrowed over time. This was accentuated when an inhibitor was added. The infrared of gypsum in the early stages showed a phase that was clearly different to either bassinite or gypsum. It is hypothesised that in the absence of inhibitors, the rate-determining step for barite crystallization is the transformation from a disordered solid to a crystalline solid as little water was observed to be present during this process when inhibitors are not present. All of these findings are consistent with a non-classical model of crystallization where disordered solids eventually rearrange to a crystalline solid if not inhibited. It also suggests that water may be key to determining the “lifetime” of the disordered clusters.

Petrology and geochemistry of chert on the marginal zone of Yangtze Platform, western Hunan, South China, during the Ediacaran–Cambrian transition

AbstractThe Ediacaran–Cambrian transition was one of the most critical intervals in Earth history. During this interval, widespread chert was precipitated, commonly as a stratal wedge in carbonates, along the southern margin of the Yangtze Platform, South China. The chert wedge passes into a full chert succession further basinward to the south‐east. Four lithotypes of chert are identified across the marginal zone in western Hunan: mounded, vein, brecciated and bedded chert. The mounded chert is characterized by irregular to digitiform internal fabrics, generally with abundant original vesicles and/or channels that mostly are lined by botryoidal chalcedony cements with minor quartz and barite crystals. The host chert (or matrix) of these mounds is dominated by amorphous cryptocrystalline silica, commonly disseminated with pyrite. The vein chert, with minor quartz locally, generally cross‐cuts the overlying dolostone and chert horizons and terminates under the mounded and/or bedded chert bodies. The brecciated chert commonly occurs as splayed ‘intrusions’ or funnel‐shaped wedges and cross‐cuts the topmost dolostones. The bedded chert, the most common type, generally is thin to medium‐bedded and laminated locally; it is composed of amorphous silica with minor amounts of black lumps. Microthermometry of fluid inclusions from vein and void‐lining minerals (mainly quartz and barite) revealed homogenization temperatures from 120 to 180°C for the trapped primary fluids. Compositionally, these chert deposits generally are pure, with SiO2 &gt; 92 wt%, and only minor Fe2O3 and Al2O3 contents, most of which show positive Europium anomalies in rare earth element patterns, especially for the mounded chert. All these data suggest that the marginal zone chert deposits resulted from a low‐temperature, silica‐rich hydrothermal system, in which the mounded chert was precipitated around the releasing vents, i.e. as silica chimneys. The vein and splayed brecciated chert, however, was formed along the syndepositional fault/fracture conduits that linked downward, while the bedded chert was precipitated in the quieter water column from the fallout of hydrothermal plumes onto the sea floor. These petrological and geochemical data provide compelling evidence and a new clue to the understanding of the extensive silica precipitation; rapid tectono‐depositional and oceanic changes during the Ediacaran–Cambrian transition in South China.

17O-depleted barite from two Marinoan cap dolostone sections, South China

Distinct, non-mass-dependent 17O depletion was reported in barite from Marinoan cap dolostones (~ 635 Ma) in South China, and has been interpreted as an indication of an extremely high- pCO 2 atmosphere (Bao et al., 2008). There is a significant variation in the magnitude of the 17O anomaly even among samples from the same outcrops. Understanding the origins of this barite and particularly the source of sulfate is critical to interpreting the anomalous 17O signature and its implication on sulfur and oxygen cycles at the aftermath of Marinoan glacial meltdown. In this study, we analyzed 160 micro-sampled barite samples from 20 hand specimens collected from two cap dolostone sections in South China. Together with field, petrographic, and Sr isotope data, the expanded dataset 1) confirms the large variability in ∆ 17O (from − 0.09‰ to − 0.87‰, VSMOW), δ 18O (+ 13.3‰ to + 23.5‰, VSMOW), and δ 34S (+ 20.0‰ to + 45.5‰, VCDT) of barite; 2) demonstrates a hyperbolic relationship between the ∆ 17O and δ 34S of various barite samples with more negative Δ 17O values generally corresponding to lower δ 34S values; 3) reveals that individual barite crystal fans and fans of the same layer possess a well-clustered set of δ 18O, Δ 17O, and δ 34S values; and 4) shows, correspondingly, that barite crystal fans of different layers bear different sets of Δ 17O, δ 18O, and δ 34S values. The study suggests that 17O-depleted barite crystals were formed under supersaturation when Ba 2+ from sulfate-free deepwater came to mix with sulfate-bearing shallow water. There were multiple upwelling episodes which resulted in multiple barite layers. The large variability in sulfur and triple-oxygen isotope composition and the high 87Sr/ 86Sr ratios indicate that the two sites from South China were sufficiently close to the continent so that the isotopic composition of sulfate was easily influenced by changes in riverine flux when seawater sulfate concentration at that time was exceedingly low. Our depositional model for the barite is consistent with the proposed sequence of events after the meltdown of Marinoan glaciation in South China by Zhou et al. (2010), and is also consistent with the proposed atmospheric origin of sulfate 17O depletion by Bao et al. (2008).

Unsteady-state inhibition of crystal growth caused by solution impurities

The competitive adsorption model under unsteady state conditions (CAMUS) is presented and validated against experimental results of crystal growth inhibition in the presence of impurities. Particular emphasis is given to peculiar growth rate trends documented in the literature that are unexpected by the existing theories. These behaviours include intermittent crystal growth, increasing growth rates with time, and inverted U-shaped growth curves, which have been reported to occur in very diverse systems such as sucrose–sugarcane impurities (P. M. Martins, A. Ferreira, S. Polanco, F. Rocha, A. M. Damas and P. Rein, J. Cryst. Growth, 2009, 311, 3841–3848), barite crystals grown in the presence of carbonate ion (N. Sanchez-Pastor, C. M. Pina, L. Fernandez-Diaz and J. M. Astilleros, Surf. Sci., 2006, 600, 1369–1381) or L-glutamic acid crystals grown in the presence of L-phenylalanine (M. Kitamura and T. Ishizu, J. Cryst. Growth, 1998, 192, 225–235). The CAMUS adequately describes the experimental observations as a result of dynamic equilibrium between impurity and solute molecules, with the impurity being adsorbed first at the crystal surface and then being gradually replaced by the crystallizing solute until the steady state is reached. The set of CAMUS parameters that best fit the experimental results were determined for each case analyzed in this study.

Kinetics of crystal nucleation in ionic solutions: Electrostatics and hydration forces

Abstract The heat of precipitation, the mean crystal size and the broadness of crystal size distribution of barium sulfate precipitating in aqueous solutions of different background electrolytes (KCl, NaCl, LiCl, NaBr or NaF), was shown to vary at constant thermodynamic driving force (supersaturation) and constant ionic strength depending on the salt present in solution. The relative inversion in the effect of respective background ions on the characteristics of barite precipitate was observed between two studied supersaturation ( Ω ) and ionic strength (IS) conditions. The crystal size variance ( β 2 ) increased in the presence of background electrolytes in the order LiCl Ω = 10 3.33 and IS = 0.03 M and KCl Ω = 10 3.77 and IS = 0.09 M. At a given Ω and IS the respective size of barite crystals decreased with increasing β 2 in chloride salts of different cations and remained constant in sodium salts of different anions. We suggest that ionic salts affect the kinetics of barite nucleation and growth due to their influence on water of solvation and bulk solvent structure. This idea is consistent with the hypothesis that the kinetic barrier for barium sulfate nucleation depends on the frequency of water exchange around respective building units that can be modified by additives present in solution. In electrolyte solution the relative switchover between long range electrostatic interactions and short range hydration forces, which influence the dynamics of solvent exchange between an ion solvation shell and bulk fluid, results in the observed inversion in the effect of differently hydrated salts on nucleation rates and the resulting precipitate characteristics.

A new genus of xenophyophores (Foraminifera) from Japan Trench: morphological description, molecular phylogeny and elemental analysis

The deep-sea floor is inhabited by a number of unusual and enigmatic taxa, unknown in shallow waters. These include the xenophyophores, a group of giant protists that construct fragile agglutinated tests. Here, we describe Shinkaiya lindsayigen. et sp. nov., a new xenophyophore collected by the submersible Shinkai 6500 at a depth of 5435 m near the Japan Trench. The phylogenetic analysis performed on its complete small-subunit ribosomal DNA (SSU rDNA) sequence confirms that Sh. lindsayisp. nov. is a foraminiferan that is closely related to another xenophyophore, Syringammina corbicula Richardson, 2001, and to a monothalamous (single-chambered) foraminiferan Rhizammina algaeformis Brady, 1879. In terms of morphology, the new genus resembles Syringammina, but its test wall is thicker, softer, and more weakly cemented. Moreover, the SSU rDNA sequences of the two genera are highly divergent. Mass spectra analyses reveal unusually high concentrations of some elements, such as lead, uranium, and mercury. The granellare system (the cytoplasm and the organic sheath that encloses it) is apparently devoid of barite crystals, which are usually abundant as intracellular inclusions in xenophyophores, but is rich in mercury (with 12 times the concentration of mercury found in the surrounding sediment). Fecal pellets retained within a tubular system (stercomare) concentrate heavy metals, including lead and uranium (respectively, two and six times more than that of the sediment). Based on a comparison of the compositions of the agglutinated test wall, the granellare, the stercomare, and the surrounding sediment, we discuss the impact of xenophyophores on their habitat.

Experimental Precipitation of Barite (BaSO4) Among Streamers of Sulfur-Oxidizing Bacteria

Abstract Barite precipitation was induced by mixing sulfate and barium solutions to investigate conditions under which barite is most likely to be localized on microbial substrates, and hence most likely to preserve biogenic textures. Addition of sulfate solution to barium solution resulted in precipitation of intergrown platy, dendritic angel wing, and microgranular barite in solution. Bacterial streamers and extracellular polymeric substances (EPS) collected from a cold sulfur spring acted as loci for precipitation of euhedral bowtie, intergrown platy, and intergrown tabular barite crystals, and scalloped platy barite crystals when sulfate solution was added to barium solutions in which they were immersed. Desiccation of bacterial streamers previously exposed to barium solution also produced subhedral platy and elongate anhedral barite crystals on extracellular surfaces and EPS. Immersion of barium-exposed streamers in sulfate solution produced scalloped platy barite crystals distributed through EPS and forming radial strings around bacterial filaments. Accidental exposure of streamers to iron produced amorphous iron oxides, as well as novel single and intergrown mixed-oxygenation-state barite/FeS sandwiches. Distinct barite crystal habits and textures were observed in experiments conducted with and without bacterial streamers, suggesting that microbes have potential to influence the petrography of barite precipitated in sulfate-limited microbially colonized environments.

High‐density nitrogen inclusions in barite from a giant siderite vein: implications for Alpine evolution of the Variscan basement of Western Carpathians, Slovakia

AbstractContrasting compositions and densities of fluid inclusions were revealed in siderite–barite intergrowths of the Droždiak polymetallic vein hosted in Variscan basement of the Gemeric unit (Central European Carpathians). Primary two‐phase aqueous inclusions in siderite homogenized between 101 and 165 °C, total salinity ranged between 18 and 27 wt%, and CaCl2/(NaCl + CaCl2) weight ratios were fixed at 0.1–0.3. By contrast, mono‐ and two‐phase aqueous inclusions in barite exhibited total salinities between 2 and 22 wt%, and the CaCl2/NaCl ratios ranged from NaCl‐ to CaCl2‐dominated compositions. The aqueous inclusions in barite were closely associated with very high‐density (0.55–0.745 g cm−3) nitrogen inclusions, in some cases containing up to 16 mol.% CO2. Crystallization P–T conditions of siderite (175–210 °C, 1.2–1.7 kbar) constrained by the vertical oxygen isotope gradient along the studied vein, isochores of fluid inclusions and the K/Na exchange thermometer corresponded to minimal palaeodepths between 4.3 and 6.3 km, assuming lithostatic load and average crust density of 2.75 g cm−3. Maximum fluid pressure during barite crystallization attained 3.6–4.4 kbar at 200–300 °C, and the most dense nitrogen inclusions maintained without decrepitation the residual internal pressure of 2.2 kbar at 25 °C. Contrasting fluid compositions, increasing depths of burial (∼4–14 km) and decreasing thermal gradients (∼40–15 °C km−1) during initial mineralization stages of the Droždiak vein reflect Alpine orogenic processes, rather than an incipient Permian rifting suggested in previous metallogenetic models. Siderite crystallized at rising P–T in a closed, rock‐buffered hydrothermal system developed in the Variscan basement during the north‐vergent Cretaceous thrusting and thickening of the Gemeric crustal wedge. Variable salinities of the barite‐hosted inclusions reflect a fluid mixing in open hydrothermal system, and re‐equilibration textures (lengths of decrepitation cracks proportional to fluid inclusion sizes) correspond to retrograde crystallization trajectory coincidental with transpression or unroofing. Maximum recorded fluid pressures indicate ∼12‐km‐thick pile of imbricated nappe units accumulated over the Gemeric basement during the Cretaceous collision.

Fluid inclusion and stable isotope characteristics of the Karalar (Gazipaşa, Antalya) barite-galena deposits, Southern Turkey

The Karalar galena-barite deposits are typical examples of the carbonate-hosted barite-galena deposits widely occurring in the Central Tauride Belt. These deposits are located in Permian limestones as ore veins along fault zones that are discordant to the bedding planes and as thin veinlets within hardly brecciated bottom zones of Permian limestones. The ore deposits contain mainly barite and galena and small amounts of sphalerite, pyrite, fahlore, limonite, quartz, and calcite. Barites occur during the earlier episode of mineralization and were mylonitized before the formation of galena. Galena and other minerals occur epigenetically with barite along porous zones between brecciated barite crystals and are especially abundant in the hardly mylonitized zones. Fluid inclusion studies indicate that the ore deposits of the area were developed by hydrothermal fluids with following characteristics: they contained NaCl, CaCl2, and MgCl2; the salinity of the fluids was relatively high and their temperature was low during the crystallization of barites in the earlier episode of mineralization; and the salinity of the fluids decreased and their temperature increased during the crystallization of sulfide minerals through the later episode of mineralization. δ18O and the δD results indicate that the water in the mineralizing fluid was of meteoric origin. The deposits were formed by deep meteoric water circulating through marine sediments. Shallow circulating and slightly warmed fluids dissolved Ba and sulfate from marine sediments of the basement and transported them to the mineralization environment during the early episode, while deep circulating and more heated fluids dissolved Pb, Zn, and other elements from the basement and reached the environment during the later episode of mineralization.

Barite and barium in sediments and coral skeletons around the hydrocarbon exploration drilling site in the Træna Deep, Norwegian Sea

Barite and barium concentrations in bottom sediments and coral skeletons from the vicinity of the hydrocarbon exploration well drilled in 1992–1993 in the Traena Deep, Norwegian Sea have been studied to assess the spreading of the drilling mud and related ecological effects on Lophelia petrusa coral reefs. Sand size barite crystals derived from the drilling mud and elevated Ba concentrations in surface (0–2 cm) sediments were found up to 4 km from the exploration drilling site. 210Pb-dating results on sediment cores indicate that Ba-rich surface intervals (0–2 cm) record ca. 20 years of sedimentation history, and connect Ba enrichment with exploration drilling. The geographic distribution of Ba contents in sediments allowed the reconstruction of the drilling mud dispersal pattern showing transport eastward from the drilling site, consistent with the prevailing current directions. The presence of relatively coarse-grained sediments and barite crystals trapped in coral polyps, ca. 500 m down current from the drilling site, reflects the elevated turbulence and sediment supply during the drilling activity. This elevated sediment dispersion likely placed a stress upon the coral reefs, but due to strong currents that effectively dilute episodic drilling waste and sediment discharges, the damage does not appear significant.

Stability and direct conversion of mineral barite crystals in carbonated hydrothermal fluids

The pseudomorphic replacement of mineral barite (BaSO4) crystals into barium carbonate was investigated in the present work by using carbonated alkaline hydrothermal fluids. Hydrothermal treatments were carried out over the temperature range from 150 up to 250 °C for intervals between 1 and 192 h, with different filling ratios (40–70%), and $$ {{\text{CO}}^{{2 - }}_{3} } \mathord{\left/ {\vphantom {{{\text{CO}}^{{2 - }}_{3} } {{\text{SO}}^{{2 - }}_{4} }}} \right. \kern-\nulldelimiterspace} {{\text{SO}}^{{2 - }}_{4} } $$ molar ratios of 1, 5, and 10. The reaction products were characterized by XRD and SEM techniques. The chemical reactivity of mineral barite crystals was markedly limited at temperatures below 200 °C, and only a tiny BaCO3 layer on the surface of the original BaSO4 crystal was formed on the crystal treated for 192 h. The rate of the pseudomorphic conversion of BaSO4 into BaCO3, was accelerated by increasing the reaction temperature and the molar ratio $$ {{\text{CO}}^{{2 - }}_{3} } \mathord{\left/ {\vphantom {{{\text{CO}}^{{2 - }}_{3} } {{\text{SO}}^{{2 - }}_{4} }}} \right. \kern-\nulldelimiterspace} {{\text{SO}}^{{2 - }}_{4} } $$ . Powder X-ray diffraction results showed that under hydrothermal conditions the replacement of $$ {\text{SO}}^{{2 - }}_{4} $$ ions by $$ {\text{CO}}^{{2 - }}_{3} $$ ions, in barite crystals was completed at 250 °C with a molar ratio $$ {{\text{CO}}^{{2 - }}_{3} } \mathord{\left/ {\vphantom {{{\text{CO}}^{{2 - }}_{3} } {{\text{SO}}^{{2 - }}_{4} }}} \right. \kern-\nulldelimiterspace} {{\text{SO}}^{{2 - }}_{4} } $$ = 10 for an interval of 192 h, resulting in the Witherite structure. The morphology of the completely converted BaCO3 at 250 °C in a Na2CO3 solution for 192 h, showed that the conversion proceed without severe changes of the original shape and dimension of the original crystal, similar to that observed in mineral pseudomorphic replacement process.

On strontium and barium anomalies in the sediments of Charkadio Cave (Tilos Island, Dodekanese, Greece)

The sediments of Charkadio Cave (Island of Tilos) have been object of chemical and mineralogical investigation. Sampling the speleothems of Charkadio Cave, it is possible to look back into the island’s younger geological history. Tilos is of non-volcanic origin but neighbored to several volcanoes of the Aegean (Kos, Nisyros, and Giali). We observed a certain coincidence of increased Ba and Sr values in such samples and volcanic activity. Some of the layers of these fine-grained sediments contain volcanic particles (ash grains and lapilli). Interestingly, these strata have the highest content of Ba and Sr, as determined by neutron activation analysis. Additionally to this discovery, Sr-rich barite crystals were found in some of these layers. Thus, Ba and Sr must either exist on the surface of tephra particles in volatile and water-soluble compounds and/or were released by weathering from Ba and Sr containing feldspars (originating from pumice) in the cave sediment environment. Since other cave sediments from Tilos, which were not exposed to volcanic products, contain very much lesser quantities of Ba and Sr, we conclude that mobile Ba and Sr compounds are contributed to the sediment by volcanic fallout.