Barite Crystals Research Articles

Quantitative visual analysis of marine barite microcrystals: Insights into precipitation and dissolution dynamics

AbstractThe accumulation rate of authigenic barite (BaSO4) in marine sediments is a promising proxy for reconstructing marine export production, but many aspects of barite precipitation and dissolution in the water column remain unknown. Here, we collected, imaged, and quantitatively analyzed 5481 barite microcrystals in bottle casts from the Eastern Pacific water column to gain a better understanding of in situ barite dynamics. Barite crystal abundance increases rapidly between the surface and 500 m in depth and then declines to predominantly low abundances below ~ 1000 m. The falloff in barite abundance between the oxygen minimum zone (OMZ) and the ocean interior suggests 60% ± 20% loss of barite by dissolution, nearly all of which is complete by water depths of 1000 m. However, there are occasional samples, as deep as 1250 m, with unusually high barite abundance that may represent marine snow deposition events. We found that microcrystals associated with organic matter substrates were smaller and less solid than free crystals, which suggests ongoing barite precipitation toward larger, more regularly shaped microcrystals within organic matter aggregates. Trends in barite microcrystal size with depth suggest that organic matter aggregates also play a role in shielding barite microcrystals from dissolution. In addition, our extensive data set raises new questions regarding marine barite nucleation and spatial heterogeneity. By helping bridge the gap between hypothesized barite dynamics and in situ observations of barite microcrystals, this study advances our understanding of water column Ba processes and the utility of sediment barite as an export production proxy.

Prediction Models of Barite Crystallization and Inhibition Kinetics: Applications for Oil and Gas Industry

Barite is one of the most common mineral scales in the oilfield and its formation can sequester toxic strontium (Sr) and radium (Ra). Various scale inhibitors are widely used to inhibit its formation. The inhibition efficiencies of 18 common inhibitors were tested using an improved kinetic turbidity method over broad oil and gas production conditions. A theoretical and a semi-empirical barite crystallization and inhibition model were developed for the 18 most used scale inhibitors. Both models can work under a broad range of production conditions and are carefully reviewed against all available experimental data. These models have shown wide applications in industrial operations, field testing, and laboratory testing. Using the new models and testing method, a novel fast inhibitor performance testing method was proposed and validated. Furthermore, the barite crystallization and inhibition models also work well to predict the inhibition performance of mixed inhibitors. This study not only advanced barite scale inhibition in an efficiency and low-cost way during oil and gas production, but also provided new insights on understanding the fate and transport of toxic Sr and Ra.

How carbonate dissolution facilitates sediment-hosted Zn-Pb mineralization

Abstract Most of the world's Zn and Pb is extracted from sediment-hosted Zn-Pb deposits. The Zn-Pb deposits hosted in carbonate rocks are hypothesized to form by mixing of acidic metal-bearing brines with reduced sulfur-bearing fluids while dissolving sedimentary carbonate. To test the role of carbonate in this process, we conducted hydrothermal experiments simulating ore formation by reacting Zn ± Pb ± Ba–bearing brines with H2S and SO42– produced by native sulfur, with and without carbonate minerals (calcite or dolomite crystals), at 200 °C and water-saturated pressure. Sphalerite, galena, and barite (or anhydrite) crystals formed only when carbonate was present in the experiment, accompanied by carbonate dissolution. The textures of sphalerite clusters are similar to those observed in ancient and modern hydrothermal deposits. Thermodynamic modeling at 150 °C and 250 °C demonstrates that mixing of metal-rich brines and H2S causes most of the Zn in solution to precipitate as sphalerite only when carbonate dissolution occurs to buffer the pH, consistent with the experimental observations. The need for a pH buffer increases with increasing temperature, and different pH buffers may play a role for different deposit types. We propose that carbonate-buffered fluid mixing is a critical process for forming post-sedimentary Zn ± Pb ± Ba deposits in sedimentary carbonate rocks.

Gold in the Farallones Block of the Shale-Hosted, Clastic-Dominated Castellanos Zinc-Lead Deposit (Northwest Cuba)

The Zn-Pb ores of the Castellanos shale-hosted, clastic-dominated deposit in northwest Cuba average nearly 1 g/t Au, with local maximum concentrations up to 34 g/t Au. This deposit is stratiform with respect to the bedding in the host black shales and shows a bottom to top zoning of ore assemblages made up of a stockwork underlying the main orebody, a basal pyrite-rich zone and a disseminated to massive Zn-Pb ore zone capped by a discontinuous, thin barite-rich zone. Petrographic data and textural relations allow distinguishing five textural types of pyrite (framboidal Py I, colloform Py IIa, euhedral Py IIb, massive Py IIc and banded colloform Py III) successively formed during ore deposition. The main Zn-Pb ore formed after the crystallization of disseminated, sedimentary framboidal pyrite (Py I) in black shales by the superimposition of several crystallization events. The crystallization sequence of the main ore-forming stage evolved from the precipitation of colloform sphalerite and pyrite (Py IIa) with skeletal galena and interstitial dolomite-ankerite to similar ore assemblages but showing subhedral to euhedral crystal habits (Py IIb) and interstitial calcite-rich carbonates. This stage ended with the development of massive pyrite (Py IIc), mainly occurring at the base of the stratiform orebody. A late fracturing stage gave way to the development of a new generation of colloform banded pyrite (Py III) just preceding the crystallization of early barite. Au is mainly concentrated in pyrite showing variable contents in the different textural types of pyrite and a bottom to top enrichment trend. Minimum contents occur in massive pyrite (Py IIc) from the basal pyrite-rich zone (0.18 ppm Au average), increasing in pyrite IIa (from 0.29 to 2.86 ppm Au average) and in euhedral pyrite (Py IIb) (from 0.82 to 9.02 ppm Au average), reaching maxima in colloform banded pyrite (Py III) formed just before the crystallization of early barite at the top of the orebody. Au enrichment in pyrite correlates with that of Sb (0.08–4420 ppm), As (0.7–35,000 ppm), Ag (0.03–1560 ppm) and to a lesser extent Cu (3–25,000 ppm), Ni (0.02–1600 ppm) and Mn (0.6–5030 ppm). Au deposition should have taken place by oxidation and, probably cooling, of reduced (H2S-dominated) fluids buffered by organic matter-rich black shales of the host sedimentary sequence. The input of such reduced fluids in the ore-forming environment most probably occurred alternating with that of the main oxidized fluids which leached Zn and Pb from the large volume of sandstones and siltstones making up the enclosing sequence, thus being responsible for the precipitation of the majority Zn-Pb ore. Supply of Au-carrying reduced fluids might progressively increase over the course of ore formation, reaching a maximum at the beginning of the late fracturing stage. This evolution of Au supply is consistent with the early crystallization of barite since Ba can also only be transported at low temperature by highly reduced fluids. These results highlight the potential of medium-sized, shale-hosted, clastic-dominated deposits to contain economic (by product) Au amounts and show that ore-forming fluids can change from oxidized (SO42+ dominated) to reduced (H2S-dominated), and vice versa, throughout the evolutionary history of a single deposit.

A Semiempirical Model for Barium-Strontium-Sulfate Solid Solution Scale Crystallization and Inhibition Kinetics at Oilfield Conditions

Summary Scale inhibitors have been widely used as one of the most efficient methods for sulfate-scale control. To accurately predict the required minimum inhibitor concentration (MIC), we have previously developed several crystallization and inhibition models for pure sulfate scales, including barite, celestite, and gypsum. However, disregarding the wide existence of barium-strontium-sulfate (Ba-Sr-SO4) solid solution in the oil field, no related models have been developed that would lead to large errors in MIC determination. In this study, the induction time of Ba-Sr-SO4 solid solution was measured by laser apparatus with or without different concentrations of scale inhibitor diethylenetriamine penta(methylene phosphonic acid) (DTPMP) at the conditions of barite saturation index (SI) from 1.5 to 1.8, temperature (T) from 40 to 70°C, and [Sr2+]/[Ba2+] ratios from 0 to 15 with celestite SI < 0. The results showed that the Ba-Sr-SO4 solid solution’s induction time increases with the [Sr2+]/[Ba2+] ratio at a fixed barite SI, T, and DTPMP dosage. That means the MIC will be overestimated if it is calculated by the previous semiempirical pure barite crystallization and inhibition models without considering the presence of Sr2+. To resolve such deviations, the novel quantitative Ba-Sr-SO4 solid solution crystallization and inhibition models were developed for the first time. The novel models are in good agreement with the experimental data. They can be used to predict the induction time and MIC more accurately at these common Ba2+ and Sr2+ coexisting scenarios. The observations and new models proposed in this study will significantly improve the barite scale management while Ba2+ and Sr2+ coexist in the oil field.

Micro-continuum approach for mineral precipitation

Rates and extents of mineral precipitation in porous media are difficult to predict, in part because laboratory experiments are problematic. It is similarly challenging to implement numerical methods that model this process due to the need to dynamically evolve the interface of solid material. We developed a multiphase solver that implements a micro-continuum simulation approach based on the Darcy–Brinkman–Stokes equation to study mineral precipitation. We used the volume-of-fluid technique in sharp interface implementation to capture the propagation of the solid mineral surface. Additionally, we utilize an adaptive mesh refinement method to improve the resolution of near interface simulation domain dynamically. The developed solver was validated against both analytical solution and Arbitrary Lagrangian–Eulerian approach to ensure its accuracy on simulating the propagation of the solid interface. The precipitation of barite (BaSO4) was chosen as a model system to test the solver using variety of simulation parameters: different geometrical constraints, flow conditions, reaction rate and ion diffusion. The growth of a single barite crystal was simulated to demonstrate the solver’s capability to capture the crystal face specific directional growth.

Hydrocarbon-bearing sulphate-polymetallic deposits at the Colipilli area, Neuquén Basin, Argentina: Implications in the petroleum system modeling

This work deals with the hydrocarbon-bearing barite-polymetallic mineralizations of the Colipilli area, located in the western sector of the Agrio Fold and Thrust Belt (Neuquén Basin, Argentina). The mineralizations consist of bed- and vein-type deposits mainly composed of barite (barite96.99%–celestine2.93%) with minor amounts of Fe-oxyhydroxides and sulfides. The bed-type deposits have zebra texture and are emplaced along the contact between Late Cretaceous–Paleocene igneous rocks (Naunauco Group) and their Early Cretaceous sedimentary host rocks (e.g., Huitrín Formation). In contrast, the vein-type deposits have breccia texture and are crosscutting the Mulichinco, Agrio and Huitrín formations or the andesitic/dioritic stocks and sills of the Naunauco Group. Different types and families of primary fluid inclusions (FI) were identified in the barite crystals. Fluorescence techniques with UV incident light and Raman spectroscopy allowed FI from completely aqueous to completely organic, including all the intermediate terms, to be identified. The organic FI have blue fluorescence and contain liquid hydrocarbons. The blue fluorescence is correlated with medium to high API gravity values (ca. 40°), indicating the presence of light hydrocarbons of advanced maturity related with the window for the generation of liquid/gaseous hydrocarbons. Microthermometry studies carried out on aqueous FI revealed that vein-type deposits formed at higher temperatures and salinities (249.7 °C and 0.5–9.3 wt % NaCl equivalent) than bed-type deposits (162.2 °C and 0.2–7.2 wt % NaCl equivalent). The heat influx provided by the Late Cretaceous–Paleocene magmatism promoted the circulation of inorganic and organic fluids of connate origin and the leaching of metallic and non-metallic elements from the sedimentary pile. During its crystallization, barite trapped fluids with variable hydrocarbon contents. The thermal anomaly associated with the magmatic activity could also have contributed with the maturation of the nearby source rocks and to the development of an atypical petroleum system.

Evaluation of Silica and Related Matrix Ion Effects on Common Scale Inhibitors

Scale inhibitors have been widely used to solve the mineral scale problems in various energy industries. The performances of scale inhibitors are influenced by different species (such as ion or chemical species) in the produced water. Silica species, one of the most ubiquitous species in the produced water, are present either by the form of silicic acid or divalent ion silicate complex/interactions (e.g., Ca,Mg silicate and Fe(II) silicate). Their impacts on common scale inhibitor performance, however, have not been systematically studied. In this study, the effects of silica and the related divalent ion silicate on the several common scale inhibitors were investigated by examining the crystallization and inhibition kinetics of barite. The results show that the presence of silica or divalent ion silicate does not show a significant effect on barite crystallization or inhibition efficiency of the polymeric inhibitors. The presence of Ca2+ and Mg2+ ions with high concentrations (e.g., 16 000 mg/L Ca2+ and 2000 mg/L Mg2+) or Fe2+ ions (e.g., 10–15 mg/L Fe2+) shows detrimental impacts on the phosphonate inhibitor diethylenetriamine penta(methylene phosphonic acid) (DTPMP). Further experimental results show that the presence of Ca,Mg silicate complex/interactions does not change the impacts of Ca2+ and Mg2+ on DTPMP, while the formation of Fe(II) silicate complex/interactions helps to partially recover the detrimental impacts of Fe2+ on phosphonate inhibitors. The mechanism of Fe(II) silicate influence on barite inhibition with DTPMP was studied by measuring the Fe2+, silica, and DTPMP concentrations in the aqueous phase before and after the experiments. The results indicate that this phenomenon is due to the Fe2+ competition between forming Fe(II)–DTPMP precipitates with DTPMP and forming Fe(II) silicate complex/interactions; silica is over 50 times higher in concentration than DTPMP. More Fe(II) silicate interaction results in less Fe(II)–DTPMP formation and more DTPMP available as scale inhibitors. Such observations inform the impact of the widely present silica species on scale inhibitor performances and provide valuable insights in oilfield scale management.

Alginate as a green inhibitor of barite nucleation and crystal growth

Combined macroscopic and microscopic experiments reveal that alginate is a potent inhibitor of both nucleation and growth of barite crystals.

Suppressing barite crystallization with organophosphorus compounds

A naturally derived phosphorous-containing molecule, phytate, functions as a dual inhibitor of barium sulfate (barite) nucleation and growth, making it a potentially viable environmentally-friendly alternative to current barite scale treatments.

Effect of crystallographic orientation on atom probe tomography geochemical data?

The recent application of atom probe tomography (APT) to minerals is becoming a powerful tool to unravel geological information from the nanoscale perspective. Yet, there are still unknown fundamental aspects of this microscopy technique for geological applications and the potential crystallographic orientation effect is a significant one. Here, the influence of the crystallographic orientation on the quality of atom probe tomography geochemical data is investigated for two minerals with the same crystal system and different morphology: spinel (isometric, hexoctahedral, octahedron morphology) and galena (isometric, hexoctahedral, cube morphology). Two separate crystals of barite (orthorhombic, dipyramidal, prism morphology) were also analyzed to test the reproducibility of APT data. Despite the general absence of expected stoichiometry, overall bulk and isotopic chemical composition are not affected by crystallographic orientation. 3D data reconstructions of the specimens showed similar spatial distribution of the ion species for each mineral and 2D density maps showed identical (barite, galena) or specular (spinel) patterns for each pair of planes analyzed. Our findings indicate a negligible effect of the crystallographic orientation in APT geochemical data for standard highly symmetric minerals but also suggest the possible influence of the crystallographic structure and composition on the mineral stoichiometry and elements spatial distribution density.

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.

Fractionation Trends and Variability of Rare Earth Elements and Selected Critical Metals in Pelagic Sediment from Abyssal Basin of NE Pacific (Clarion-Clipperton Fracture Zone)

The geochemical and mineralogical characteristics of pelagic sediments collected from the Interoceanmetal Joint Organization (IOM) claim area, located in the eastern part of the Clarion-Clipperton Fracture Zone (CCFZ; eastern tropical Pacific), are described in this paper. The concentrations of rare earth elements (REE), as well as other selected critical elements contained in 135 sediment samples of siliceous clayey silts, are presented. The vertical and spatial variabilities of elements, with particular emphasis on REE as well as metals of the highest economic interest such as Cu, Ni, and Co, are detailed. The applied methods include grain size analysis by laser diffraction, geochemistry examination using ICP-MS, XRF, AAS, and CNS spectrometry, and XRD analysis of mineral composition (Rietveld method). Additionally, statistical methods such as factor analysis (FA) and principal components analysis (PCA) were applied to the results. Finally, a series of maps was prepared by geostatistical methods (universal kriging). Grain size analysis showed poor sorting of the examined fine-grained silts. ICP-MS indicated that total REE contents varied from 200 to 577 ppm, with a mean of 285 ppm, which is generally low. The contents of critical metals such as Cu, Ni, and Co were also low to moderate, apart from some individual sampling stations where total contents were 0.15% or more. Metal composition in sediments was dominated by Cu, Ni, and Zn. A mineral composition analysis revealed the dominance of amorphous biogenic opaline silica (27–58%), which were mostly remnants of diatoms, radiolarians, and sponges associated with clay minerals (23% to 48%), mostly Fe-smectite and illite, with mixed-layered illite/smectite. The high abundance of diagenetic barite crystals found in SEM−EDX observations explains the high content of Ba (up to 2.4%). The sediments showed complex lateral and horizontal fractionation trends for REE and critical metals, caused mostly by clay components, early diagenetic processes, admixtures of allogenic detrital minerals, or scavenging by micronodules.

Three-stage formation of greenstone-hosted orogenic gold deposits in the Val-d’Or mining district, Abitibi, Canada: Evidence from pyrite and tourmaline

Orogenic gold deposits are the most widespread type of gold deposit worldwide, defining important exploration targets in Precambrian greenstone belts. Here, we refine the model for orogenic gold formation in the world-class Val-d’Or mining district (Quebec, Canada) using geochemical, isotopic and mineralogical data from quartz-tourmaline-carbonate (QTC) veins from several deposits across the district. Multi-element (Ag, As, Au, B, Ba, Co, Mg, Mo, Ni, and Pb) pyrite mapping, as well as major, trace, and rare earth element variations in tourmaline, define a three-stage paragenesis across several deposits. The first, reduced phase crystallized the quartz-carbonate-gold association in the veins; the second, oxidized phase favored tourmaline and barite crystallization (barite was not previously reported from this district); the third phase involved a reduced fluid and the crystallization of non-auriferous, As-Co-Ni-rich cubic pyrite, and tourmaline. Boron isotope ratios of tourmaline vary from −15.6 to −7.7‰, which is attributed to the mixing of at least two fluids, one related to a deep, metamorphic source and the other to shallower, possibly relict formation water. A systematic regional pattern in B-isotope variation is found, with lighter values in the volcanic rocks and heavier ones in or close to intrusions, which suggests different mixing proportions in the vein field from NE to SW.

The Formation of Barite and Celestite through the Replacement of Gypsum

Barite (BaSO4) and celestite (SrSO4) are the end-members of a nearly ideal solid solution. Most of the exploitable deposits of celestite occur associated with evaporitic sediments which consist of gypsum (CaSO4·2H2O) or anhydrite (CaSO4). Barite, despite having a broader geological distribution is rarely present in these deposits. In this work, we present an experimental study of the interaction between gypsum crystals and aqueous solutions that bear Sr or Ba. This interaction leads to the development of dissolution-crystallization reactions that result in the pseudomorphic replacement of the gypsum crystals by aggregates of celestite or barite, respectively. The monitoring of both replacement reactions shows that they take place at very different rates. Millimeter-sized gypsum crystals in contact with a 0.5 M SrCl2 solution are completely replaced by celestite aggregates in less than 1 day. In contrast, only a thin barite rim replaces gypsum after seven days of interaction of the latter with a 0.5 M BaCl2 solution. We interpret that this marked difference in the kinetics of the two replacement reactions relates the different orientational relationship that exists between the crystals of the two replacing phases and the gypsum substrate. This influence is further modulated by the specific crystal habit of each secondary phase. Thus, the formation of a thin oriented layer of platy barite crystals effectively armors the gypsum surface and prevents its interaction with the Ba-bearing solution, thereby strongly hindering the progress of the replacement reaction. In contrast, the random orientation of celestite crystals with respect to gypsum guarantees that a significant volume of porosity contained in the celestite layer is interconnected, facilitating the continuous communication between the gypsum surface and the fluid phase and guaranteeing the progress of the gypsum-by-celestite replacement.

Strontium Isotope Compositions of Hydrothermal Barite from the Yonaguni IV: Insight into Fluid/Sediment Interaction and Barite Crystallization Condition

Hydrothermal barite is a typical low-temperature mineral formed during the mixing of hydrothermal fluid and seawater. Because of its extremely low solubility, barite behaves as a close system after crystallization and preserves the geochemical fingerprint of hydrothermal fluid. In this study, the elemental contents and Sr isotope compositions of hydrothermal barites from the Yonaguni IV were determined using electron microprobe and LA-MC-ICP-MS respectively. On these bases, the fluid/sediment interaction during the hydrothermal circulation and physicochemical condition of barite crystallization were discussed. Results show that the 87 Sr/ 86 Sr values of hydrothermal barites from the Yonaguni IV are apparently higher than those of the seawater and associated volcanic rocks, indicating the sufficient interaction between the hydrothermal fluid and overlying sediment. Monomineral Sr abundance shows large variations, reflecting the changes in barite growth rate during the fluid mixing. The mineralization condition in the Yonaguni IV was unstable. During the crystallization of barite, hydrothermal fluid and seawater mixed in varying degrees, with the proportions of hydrothermal fluid varied from 36% to 72%. The calculated crystallization temperatures range from 109 to 220°C. Sediment plays a critical role during the mineralization process in the Yonaguni IV and incorporation of sediment component into hydrothermal system was prior to barite crystallization and sulfide mineralization.

Hydrothermal influence on barite precipitates in the basal Ediacaran Sete Lagoas cap dolostone, São Francisco Craton, central Brazil

Most Precambrian sediment-hosted barites have been interpreted to be diagenetic, hydrothermal exhalation, or methane-seepage in origin. Seafloor barite precipitates and void-filling barite cements in basal Ediacaran cap dolostones have been interpreted as sedimentary and early diagenetic in origin, and they have been used to infer ocean geochemistry in the aftermath of the terminal Cryogenian (or Marinoan) Snowball Earth glaciation. Barite crystals precipitated syndepositionally from seawater or authigenically from marine porewaters can potentially offer insights into Neoproterozoic ocean geochemistry. In this study, we analyzed void-filling barite cements from the basal Ediacaran Sete Lagoas cap dolostone to determine whether the barite records seawater geochemical signatures and whether it experienced post-depositional hydrothermal alteration. Sete Lagoas barite occurs as veins and major void-filling cement in multiple horizons, sometimes interbedded with carbonate fans. Barite crystals, commonly forming rosettes, grew upwards and downwards as radiating bladed crystals, isolated crystals in the matrix, and inclusions within carbonate fan crystals. Sulfur isotope compositions of coexisting barite and carbonate-associated sulfate (CAS) show similar values, suggesting a similar sulfate source, potentially seawater sulfate from a shallow marine environment. Assuming that CAS was sourced from seawater sulfate, we infer that the Sete Lagoas barite was precipitated from marine porewaters with seawater as a source of the sulfate. Carbonaceous material (CM) and fluid inclusions in barite crystals share a similar thermal history with a peak temperature in the range of 206–257 °C. CM was not detected in the host rock, possibly due to pervasive dolomitization, thermodegradation of CM or the fine-grained nature of the host rock. Estimated temperatures and salinity based on fluid inclusions are both higher than seawater, suggesting that hydrothermal activity, perhaps those related to Mississippi-Valley type mineralization in the São Francisco Craton, may have influenced the Sete Lagoas barite. Thus, although the Sete Lagoas barite may have originally precipitated from seawater or marine porewaters in communication with seawater, it may have been subsequently influenced by hydrothermal activity and therefore a more thorough diagenetic assessment must be done before the Sete Lagoas barites can be used to infer seawater geochemistry and environment in the aftermath of Marinoan Snowball Earth.

Modelling of solid formation by heterogeneous reactions through a multicomponent transport model of diluted ionic species: Simulation of barite fouling in a geothermal heat exchanger

AbstractA general model is proposed in order to describe the growth of a deposit by heterogeneous reactions. The hydrodynamics in the fluid is described by a multicomponent transport model for ionic species diluted in a solvent and heat transfer is taken into account in both liquid and solid domains. The boundary condition at the interface where the reaction takes place is described thoroughly. It involves the reaction kinetics and gives access to the velocity of the interface, ie, the mass rate of the solid deposit. The model is then applied to the case of barite crystallization in a heat exchanger. The liquid phase is therefore composed of two ionic species Ba2+ and SO42− diluted in water. The solid phase is modelled as a homogeneous barite deposit. The fully dynamic CFD simulation of the model is made using Comsol Multiphysics, in a cylindrical pipe. The solid growth is analyzed over time and space in terms of the relevant variables of the model.

Active growth of non-hydrothermal subaqueous and subaerial barite (BaSO4) speleothems in Lechuguilla Cave (New Mexico, USA)

Barite (BaSO4) speleothems have been reported from caves around the globe and interpreted to have chiefly formed in phreatic, hypogene, hydrothermal settings. Here we report two contrasting types of barite speleothems (bluish tabular crystals in a shallow pool and actively dripping greenish stalactites), which today form at lower temperatures in the non-hydrothermal and vadose environment of Lechuguilla Cave, New Mexico, USA. Scanning electron microscopy analysis, along with energy- and wavelength-dispersive X-ray spectroscopy (EDS, WDS), as well as X-ray diffraction (XRD), characterize the habit and chemical composition as barite. Fractionation of the minor element calcium is related to growth along different crystal faces whereas variations in strontium concentration are mirrored in blue color zoning of the pool crystals. Two possible modes of non-hydrothermal barite precipitation are discussed: (1) intense evaporation driven by thermal atmospheric convection cells or (2) mixing of barium-rich, sulfate-poor water with water rich in sulfate. Both processes, in isolation or in combination, lead to supersaturation and could explain formation of the investigated barite speleothems. Observations of three types of microbes on the pool barite crystals showing evidence of incrustation raises the question whether there is a potential involvement of microbial activity in the temperate barite precipitation in Lechuguilla Cave.

Barite crystallization in presence of novel fluorescent-tagged antiscalants

Barite crystallization in presence of novel fluorescent-tagged antiscalants