Barite Dissolution Research Articles

Using barium isotopes to distinguish metamorphic and magmatic fluids for the gold deposits

The orogenic and intrusion-related gold deposits represent the two most significant types of gold reserves globally, collectively accounting for over half of the total and are formed associated with metamorphic and magmatic hydrous fluids, respectively. Theoretically, gold deposits should be a result of activities of the metamorphic and magmatic hydrous fluids that sourced, carried, and reserved gold. However, distinguishing differences between the metamorphic and magmatic fluids proves challenging mainly due to overlapping of trace elements, S, and Re-Os isotopes of sulfides and C, H, O, He, and Ar isotopes of the ore-forming fluids. Barium, as a fluid sensitive cation, is believed to faithfully record the sources and evolution of fluids. In this work, we presented the Ba isotopes of various ore-rocks from the Hadamen and Haoyaoerhudong gold deposits along the northern margin of the North China Craton. These two deposits have been well-defined the ore-forming fluids that originated from crystal-melt separation in alkaline granitic magma and dehydration of chlorite and mica from the black sales during metamorphism, respectively. The Ba isotopes exhibit significantly fractionation among the various ore-rocks from above two gold deposits. With increasing SiO2 content, δ138/134Ba values increased from −0.28 ‰ in the potassium silicate alteration zone, crossed −0.21 ‰ ∼ −0.19 ‰ in the potassium silicate alteration zone filled with sulfide-quartz veins, to −0.13 ‰ ∼ +0.01 ‰ in the sulfide-quartz veins. This suggests that the heavier Ba isotopes were preferentially incorporated into the evolving magmatic fluids primarily due to the crystallization of K-feldspar and barite. In contrast, δ138/134Ba values decreased from the carbonaceous slate (+0.73 ‰ ∼ +0.95 %) to sulfide veins (−0.28 ‰ ∼ +0.07 ‰), then increased to sulfide-quartz veins (+0.01 ‰). This phenomenon results from the continuously enhanced dissolution of diagenetic barite accompanying metamorphism and the crystallization of barite during evolution of metamorphic fluids. The microstructural characteristics also support that crystallization and dissolution of barite control significant Ba isotope fractionation in two types of fluids with different features. Furthermore, the magmatic and metamorphic fluids exhibit relative positive and negative relationships between Ba content and δ138/134Ba values, respectively. These geochemical features are also useful in defining the origin of the ore-forming fluids. Therefore, we propose that Ba isotope composition will be a new tool for deciphering the evolution of the Au-bearing ore-forming fluids and distinguishing the origin of the ore-forming fluids.

Sugarcane straw biochar: effects of pyrolysis temperature on barite dissolution and Ba availability under flooded conditions

AbstractReductive dissolution of barium (Ba) sulfate in wetland soils may increase Ba bioavailability in the environment, yet no information is available regarding Ba remediation using biochar. This study investigated the effectiveness of sugarcane (Saccharum officinarum) straw biochar pyrolyzed at 350 °C (BC350), 550 °C (BC550), and 750 °C (BC750) in inhibiting barite dissolution and, consequently, Ba availability in a soil artificially spiked with barite and flooded for 365 days. Increasing pyrolysis temperature alters the carbon structure, and increases dehydration and depolymerization, resulting in more stable biochar that releases less DOC (8.6-fold decrease from BC350 to BC750). Additionally, high-temperature biochar (BC750) had 1.7 times higher carbon (C) content, 2.4 times higher ash content, and a 13.1 times greater specific surface area (SSA) than low-temperature biochar (BC350). Amending soil with BC750 increased pH but did not promote reducing conditions, and thus did not promote barite dissolution. Conversely, greater DOC in low-temperature biochar, particularly BC350, favored reducing conditions and increased barite dissolution by 23%, with BC550 also showing an 18% increase. This enhancement led to a greater pool of Ba sorbed into more labile exchangeable sites. In summary, pyrolysis temperature affects biochar attributes, which in turn influences the soil geochemical environment and Ba speciation. Low-temperature biochar (BC350) shows potential as an amendment to increase the bioavailable Ba pool in assisted remediation programs, such as biochar-assisted phytoremediation. Graphical Abstract

Dolostone-barite-phosphorite sequence in the basal Doushantuo Formation: Origin and implications for post-Marinoan ocean chemistry and phosphogenesis

Barite (BaSO4) represents a major component of many post-Marinoan cap dolostones worldwide, recording important information on climate upheavals during the terminal Neoproterozoic. However, its origins and relations with other lithofacies remain to be explored. Here we report new occurrences of barite in the basal Ediacaran Doushantuo Formation at a major phosphate mine in Weng'an, South China, and present results of detailed petrographic and geochemical investigations on the barites and related phases. At the outcrop scale, barite is mainly present as a 1–2 cm-thick layer at the contact of the cap dolostones and overlying phosphorites. Detailed petrographic observations reveal a lithofacies transition from dolostone through a mixture of barite, dolomite and apatite to barite and finally to granular phosphorite. The barites can be categorized into three generations in stratigraphic order, which are present as loose, randomly-oriented blades (B1), dense aggregates (B2), and radially aligned crystal fans (B3), respectively. B1 is dispersed in a matrix of apatite and dolomite, which has an average δ13Ccarb of −0.61‰. This, along with the common presence of organic matter (OM) in this barite, point to a possible source of Ba from organic degradation. B3 forms a centimeter-scale layer of barite fans that laterally extends over the entire mining pit, whereas B2 is locally distributed between B1 and B3, and occurs as relatively unoriented aggregates. δ34S values of B3 show a narrow range between +25.9‰ and +30.9‰, which is similar to that of contemporaneous seawater and indicate a seawater source of sulfate in barite. Based on the present investigation and a compilation of published data, we propose that B1 is diagenetic barite with a main source of Ba from degradation of organic matter and possibly also from dissolution of previous pelagic barite, whereas B2 and B3 represent seafloor precipitates that resulted from interactions between deep, anoxic Ba-rich waters and oxic, sulfate-rich surface waters during the post-glacial transgression. This episode of barite precipitation was immediately followed by massive accumulations of phosphorites in Weng'an and many areas of South China. The consecutive deposition of cap dolostone, barite and phosphorite signifies the transition from an alkalinity-rich, stagnant anoxic ocean to a dynamic marine regime featuring oxygenated surface waters and upwelling currents. These pH and redox changes likely facilitated the cycling and enrichment of phosphate in the shallow waters that was necessitated by the unprecedented accumulation of Ediacaran phosphorites in South China.

Kinetics of In-Situ Calcium Magnesium Carbonate Precipitation and the Need for Desulfation in Seawater-Flooded Carbonate Reservoirs

Summary Mixing of incompatible injection and formation brines leads to the deposition of inorganic sulfate scales such as barite, celestite, and anhydrite in and around production wells. This process is well documented in seawater-flooded clastic reservoirs. One technique to avoid the resulting formation damage is to remove sulfate from seawater before injection using nanofiltration; however, this process is costly. We identify in this paper that it may not always be necessary in higher-temperature carbonate reservoirs. In this paper, we describe the use of reactive transport reservoir simulation to investigate the impact of carbon dioxide (CO2) partitioning and changes in pH, ionic concentrations, and temperature on carbonate reactivity and the sulfate scaling risk in waterflooded carbonate reservoirs. Dissolution and precipitation of calcite, dolomite, gypsum, anhydrite, barite, and celestite are all modeled and found to be coupled through (various) common ion effects. The produced brine compositions are used to calculate the saturation ratios (SRs) and mass of precipitate that may form in the production system. Sensitivity to mineral reaction kinetics, particularly for the dolomite reactions, is accounted for. Results identify that there is a strong relationship between calcite dissolution and dolomite (or other calcium/magnesium carbonate mineral) precipitation reactions, which drive each other and are affected by the availability of CO2 in the residual oil phase. This evolves over time, and as the thermal front propagates, impacts the concentration of calcium and magnesium in the brines traversing the reservoir. Temperature changes around the injection wellbore impact CO2 and mineral solubilities. The concentration of calcium in the displaced brine mix is thus determined more by contact with rock and temperature than by mixing between injection and formation brines. Depending on location relative to the thermal front, this may lead to gypsum or anhydrite precipitation, thereby stripping sulfate out of the injection brine. Thus, the sulfate scaling risk at the production wells is significantly reduced by this sulfate depletion process: The sulfate is stripped out of the seawater as it warms up in the reservoir before it mixes extensively with the formation water and significantly before any mixture of the two brines reaches the production zone. Thus, any loss of permeability is restricted to deep within the reservoir, where the pore volume (PV) that can accommodate mineral precipitation is very large. In this work, we identify that for carbonate reservoirs above 90–100°C, stripping of sulfate due to coupled mineral reactions may reduce or eliminate the need for use of a sulfate reduction plant (SRP). The process is modeled for the first time, accounting for the impact of CO2 partitioning and thermal front propagation. Knowledge of the kinetics of calcium/magnesium carbonate precipitation is shown to be critical in predicting the extent of sulfate depletion.

Water column barium sulfate dissolution and shielding by organic matter aggregates: Implications for the pelagic barite proxy

Pelagic barite (BaSO4) and related proxies are useful tools for reconstructing the marine carbon cycle. The factors controlling pelagic barite dissolution in the ocean water column are poorly understood, which adds uncertainty to Ba-based reconstructions. Here, we conducted static laboratory incubations to test the sensitivity of barium sulfate dissolution rate to a range of commonly occurring seawater pH, salinity, and temperature conditions. We observed relatively rapid dissolution rates ranging from 1.7 ± 0.4 to 3.4 ± 0.8 pg BaSO4 day−1 for these experiments, and we did not observe statistically significant differences in the rate of dissolution with varying pH, salinity, or temperature. The slowest dissolution rate observed in these experiments suggests that an average barium sulfate crystal would survive in the ocean water column just 6.2 ± 0.3 days. We estimate that an average isolated pelagic barite crystal would take 67 years to sink down through the water column, so our experiments imply that solitary pelagic barite crystals do not survive this transit. We conducted an additional experiment on a roller table to assess the impact of organic matter aggregates on barium sulfate dissolution. Free barium sulfate crystals incubated on the roller table dissolved even more rapidly than crystals in the static experiment (19 ± 7 pg BaSO4 day−1), but barium sulfate crystals incubated with organic matter aggregates showed little sign of dissolution over time. Our findings suggest that organic matter aggregates play a vital role in shielding pelagic barite from dissolution in the water column. This implies that pelagic barite in ocean sediments records the arrival of organic detritus to the seafloor, not just barite crystal formation in sinking organic matter in the upper water column. Additional work is needed to determine which aspects of the marine carbon cycle the pelagic barite proxy captures.

Benthic-pelagic coupling and isotopic fractionation of barium in Kiel Bight, SW Baltic Sea

Barium (Ba) isotopes are a promising new tracer for riverine freshwater input to the ocean and marine biogeochemical cycling. However, many processes that affect Ba cycling at continental margins have not yet been investigated with respect to Ba isotope fractionation. Here, we present a comprehensive data set of Ba concentration and isotope data for water column, pore water and sediment samples from Kiel Bight, a seasonally stratified and hypoxic fjord in the southwestern Baltic Sea. The surface water Ba concentration and Ba isotope inventory of the water column can generally be explained by mixing of riverine freshwater and Atlantic seawater. However, the deep-water below the seasonal pycnocline (10 - 15 m water depth) is characterized by a pronounced positive Ba concentration anomaly (up to 915 nM) that is accompanied by a δ138Ba of ~+0.25 ‰, which is lighter than expected from the seawater-freshwater mixing line (Ba: 77 nM, δ138Ba: +0.32 ‰ at a salinity of 18). Pore water profiles indicate a Ba flux across the sediment-water interface, which contributes to the enrichment in isotopically light Ba in the deep-water. Pore waters of surface sediments and deep-waters are oversaturated with respect to barite. Therefore, barite dissolution is unlikely to account for the benthic Ba flux. Water column Ba concentrations closely correlate with those of the nutrients phosphate and silica, which are removed from surface waters by biological processes and recycled from the sediment by diffusion across the sediment-water interface. As nutrient-to-Ba ratios differ among sites and from those observed in open-marine systems, we propose that Ba is removed from surface waters by adsorption onto biogenic particles (rather than assimilation) and regenerated within surface sediments upon organic matter degradation. Pore water data for subsurface sediments in Kiel Bight indicate preferential transfer of isotopically heavy Ba into an authigenic phase during early diagenesis. Quantifying the burial flux associated with this authigenic Ba phase along continental margins could potentially help to settle the isotopic imbalance between known Ba source and sink fluxes in the ocean.

Dissolution of barite using coordination chemistry: Optimization and characterization

This work included two different types of dissolving process (inorganic and organic) which used for the complete dissolving barium sulfate (barite). The inorganic solvents were involved digestion on hotplate with recipe of mixture acids with hydrogen peroxide, sulfuric acid, aqua regia, and fusion with sodium carbonate. The second set of experiments was involved organic ligands such as EDTA, DTPA and a mixture of them. Different parameters were tested in these experiments which were time, molarity of the ligand, amount of barium sulfate and pH. Barite was incompletely dissolved when inorganic solvents were used in experiment. Whilst, the organic ligands show that EDTA is the best ligand for the complete dissolving of barite comparing with DTPA and mixture of EDTA and DTPA. The optimal condition of the highest dissolution of barite by using EDTA were time for 30 h, molarity of the ligand is 2 M, amount of barium sulfate = 0.5 g, and pH = 13 at room temperature. At this condition, the dissolution of barite was 88.56%. It is worth noting that the experiments were carried out at room temperature because the study simulates the dissolution of barite scale in petroleum pipes.

Porewater geochemistry indicates methane seepage in the Okinawa Trough and its implications for the carbon cycle of the subtropical West Pacific

The Kuroshio Current, originating from the West Pacific Warm Pool and flowing through the Okinawa Trough, connects the equator and the subtropical West Pacific and plays an important role in the carbon cycle in the West Pacific Ocean. Previous studies have focused on the effects of surface export productivity and bottom redox conditions on the carbon cycle in the late Quaternary. Recent studies have demonstrated that methane seepages are very common in the Okinawa Trough, however, their significance for the carbon cycle remains not well understood. Here, methane seepages and sulfate-driven anaerobic oxidation of methane (SD-AOM) are constrained by the geochemical characteristics of porewater at site CSHC-4 (Length: 1555 cm) derived from the water depth of 934 m on the western continental slope of the Okinawa Trough. Using the △(DIC+ Ca2++ Mg2+)/△SO42− ratio, it is suggested that the sulfate reduction in the upper part of site CSHC-4 is dominated by organoclastic sulfate reduction (OSR), while that between 655 and 1055 cm is gradually dominated by SD-AOM with deepening depth. However, with the depletion of sulfate, the methanogenesis process predominates at the bottom of site CSHC-4. The depth of the sulfate-methane interface (SMI) and the methane diffusive flux of site CSHC-4 is calculated to be ∼1156 cm and ∼ 63 mmol m−2 yr−1, respectively. Near the SMI, the changes in concentrations of Ca2+, Mg2+, Sr2+ and ratios of Mg/Ca and Sr/Ca in the porewater indicate the possibility of the precipitation of authigenic high-Mg calcite in the sediments. In contrast, the increase in the concentration of Ba2+ in porewater below the SMI may imply the dissolution of barite (BaSO4). In addition, redox-sensitive elements in porewater exhibit various geochemical behaviours due to changes in redox conditions caused by SD-AOM. The above SD-AOM processes will affect the reconstruction of surface productivity and redox conditions of bottom water in the Okinawa Trough since the late Quaternary based on biogenic elements (e.g., Ca and Ba) and redox-sensitive elements (e.g., U and Cr), which requires careful evaluation. Therefore, our new findings illustrate the modern methane seepage in the Okinawa Trough and provide a reference for calculating the ancient carbon cycle in the subtropical West Pacific.

A Kinetic Monte Carlo Approach to Model Barite Dissolution: The Role of Reactive Site Geometry

Barite (Ba[SO4]) is one of the promising candidates for sequestration of radioactive waste. Barite can incorporate radium (Ra) and form ideal solid solutions, i.e., (Ba,Ra)[SO4]. Together with isostructural celestite (Sr[SO4]), ternary solid solutions, (Ba,Sr,Ra)[SO4], may exist in natural conditions. Our fundamental understanding of the dissolution kinetics of isostructural sulfates is critically important for a better risk assessment of nuclear waste repositories utilizing this mineral for sequestration. So far, the barite-water interface has been studied with experimental methods and atomistic computer simulations. The direct connection between the molecular scale details of the interface structure and experimental observations at the microscopic scale is not yet well understood. Here, we began to investigate this connection by using a kinetic Monte Carlo approach to simulate the barite dissolution process. We constructed a microkinetic model for the dissolution process and identified the reactive sites. Identification of these sites is important for an improved understanding of the dissolution, adsorption, and crystal growth mechanisms at the barite–water interface. We parameterized the molecular detachment rates by using the experimentally observed etch pit morphologies and atomic step velocities. Our parameterization attempts demonstrated that local lattice coordination is not sufficient to differentiate between the kinetically important sites and estimate their detachment rates. We suggest that the water structure and dynamics at identified sites should substantially influence the detachment rates. However, it will require more work to improve the parameterization of the model by means of Molecular Dynamics and ab initio calculations.

Marine anoxia as a trigger for the largest Phanerozoic positive carbon isotope excursion: Evidence from carbonate barium isotope record

The mid-Ludfordian Lau carbon isotope excursion (Lau CIE) represents the largest positive carbon isotope excursion in the Phanerozoic (∼9‰), coincident with the biodiversity loss of many marine animal clades. Two main explanations for the Lau CIE are enhanced organic carbon burial via increased marine productivity and preservation-driven expansion of anoxia. While these two explanations are not mutually exclusive, the main driver of Lau CIE is yet to be constrained. Here, we resolve this longstanding debate using barium isotopes (δ138Ba) of marine carbonates deposited across the Lau CIE. Our δ138Ba data from the Kosov section (Czech Republic) record a large negative excursion in correlation to the positive shift in δ13Ccarb. We suggest that the observed negative shift in δ138Ba to values as low as −0.33‰ can be best interpreted as upwelling of isotopically light Ba from deeper waters due to pelagic barite dissolution under euxinic conditions. This hypothesis is consistent with results from barium concentration data as well as the results from the sulfate mass balance modeling that indicates a contraction in the seawater sulfate reservoir, with seawater sulfate concentrations decreasing from several mM ranges before the Lau CIE to less than 100 μM during Lau CIE. Taken together, evidence for a strong negative correlation between δ138Ba and δ13Ccarb suggests that shallow water anoxia, rather than enhanced marine productivity, was a primary driver of the Lau CIE that resulted in a notable decrease in the size of seawater sulfate reservoir.

Diagenetic barite-calcite-pyrite nodules in the Silurian Longmaxi Formation of the Yangtze Block, South China: A plausible record of sulfate-methane transition zone movements in ancient marine sediments

The sulfate-methane transition zone (SMTZ) serves as an important geochemical transition especially during early diagenesis. Organoclastic sulfate reduction (OSR), sulfate-driven anaerobic oxidation of methane (SD-AOM), fermentation, and methanogenesis, the dominant diagenetic processes near the SMTZ, play key roles in marine sulfur and carbon cycling. However, the paleo-SMTZ has rarely been identified in the geologic record because of equivocal evidence. The presence of barite-calcite-pyrite assemblages (abundant nodules and pyritic laminae) concentrated over a 1-m thick interval of the Silurian Longmaxi Formation, Yangtze Block, South China, provide a unique opportunity to investigate possible vertical movements of the paleo-SMTZ in ancient sediments. The inferred paleo-SMTZ comprises nodules made up of barite (BaSO4), calcium carbonate (CaCO3), and pyrite (FeS2), and pyritic laminae. Strong 34S enrichment of barite (50 to 62.1‰ VCDT) and modestly 13C-depleted calcite (−11.4‰ to −5.3 VPDB) of the nodules associated with positive δ34S values of pyritic laminae (4 to 6.2‰ VCDT) suggest precipitation of these minerals sourced by mixed carbon and sulfur sources close to and/or within the paleo-SMTZ. Nodules from center to edge display mineral zonation that may reflect the effects of depth fluctuations of the paleo-SMTZ. Initial (stage 1) barite mineralization in nodule centers appears to have occurred within the base of the sulfate reduction zone (SRZ). By the time if stage 2 mineralization, the stratigraphic locus of precipitation had migrated closer to highly alkaline SMTZ resulting in barite dissolution and calcium carbonate precipitation. Higher proportions of calcium carbonate exhibiting some enrichment of 12C associated with cubic pyrite crystals in nodule centers are consistent with the occurrence of SD-AOM within the SMTZ. Stage 3 acicular barite mineralization along nodule edges likely took place near at the base of SRZ immediately above the SMTZ, whereas the replacement of barite by calcite during stage 4 mineralization occurred again within the SMTZ. Vertical movement of paleo-SMTZs suggested by the occurrences of barite-calcite-pyrite assemblages in the Longmaxi Formation across Yangtze Block, are likely the consequence of the complex interplay of varying sedimentation rate, organic matter quality, methane flux, and perhaps seawater sulfate concentration.

Controlling factors of groundwater chemistry and statistical analysis of the samples related to ophiolite of Nourabad-Harsin, West of Iran.

Recognizing controlling factors of groundwater chemistry in the ophiolite region of the southeastern area of Kermanshah is the aim of this study. The findings reveal that some samples' calcium, magnesium, and sodium absorption risk is higher than the standard range. Besides, statistical relationships of the data were investigated to recognize the key factors controlling water chemistry. Pearson's correlation was used to determine the elements with the same source. Saturation index (SI) and water-rock interaction helped us find the important minerals in reaction with water. Besides, the map of the spatial distribution of heavy elements was applied to prove the elements with a common source. According to these ties, the important factors controlling groundwater chemistry of the region are dissolution of gypsum as the common source of Ca, Sr, and S; dissolution and weathering of Cr-spinel mineral in peridotites as the common source of Si, Mg, and Cr; dissolution of existing Fe-Mg olivine and pyroxene in peridotite silicates as the common source of Mg and Ni, and dissolution of chalcedony, barite, and calcite as three minerals with the highest dissolution in water-rock interactionof groundwater samples.

Microscale δ34S heterogeneities in cold seep barite record variable methane flux off the Lofoten-Vesterålen Continental Margin, Norway

Authigenic carbonate and barite crusts were analyzed from recently discovered cold seeps on the Lofoten-Vesterålen (LV) continental slope, northern Norway. Carbonate phases in these crusts are methane-derived Mg-calcite and aragonite. Scanning electron microscopy (SEM) was used to petrographically characterize cold seep crusts, and secondary ion mass spectrometry (SIMS) was used to measure the microscale sulfur isotope composition (δ34S values) of authigenic barite. The mean δ34SBaSO4 value from SIMS spot analyses is 70‰ (n = 303), significantly elevated with respect to seawater sulfate (∼21‰). The δ34S values can vary more than 40‰ within individual barite aggregates (< 250 μm) and more than 50‰ within cm-scale samples. δ34SBaSO4 values in layered barite aggregates are most variable parallel to growth axes, with minimal variability in the perpendicular direction; fluctuations in δ34SBaSO4 values along growth axes are inferred to record temporal changes in sulfate distillation during barite precipitation. In layered barite aggregates, δ34SBaSO4 values frequently approach ∼90‰, but at these high δ34S values, barite dissolution features become increasingly prevalent and may reflect an upper limit for porewater 34SSO4 enrichment while maintaining barite saturation in this system. We suggest the primary forcing affecting sulfate distillation is varying activity of anaerobic oxidation of methane coupled to sulfate reduction (AOM-SR) due to temporal changes in cold seep methane flux. These findings provide the first semi-continuous geologic proxy for paleo-methane flux on the Lofoten-Vesterålen continental margin and suggest methane advection rates varied considerably over the course of carbonate-barite crust formation. In addition to systematic microscale changes in δ34SBaSO4 values, periodic intra-aggregate dissolution features indicate a dynamic seepage environment with two or more periods of enhanced methane flux in recent geological history.

Injection of Ca-depleted formation water in the Lower Triassic Bunter Sandstone Formation for seasonal heat storage in geothermal sandstone reservoirs: Effects on reservoir quality

Optimisation of the use of commonly available energy sources through seasonal storage of excess heat in hot deep aquifers is considered. The chemical effects of heating the Bunter Sandstone Formation to up to 150 °C are investigated by laboratory core flooding experiments at reservoir conditions, petrographic analysis and geochemical modelling. Experiments are performed with a Ca-depleted synthetic formation water in order to avoid loss of injectivity by calcium carbonate scaling at elevated temperatures. The synthetic formation water is injected into a Bunter Sandstone Formation sample at 25 °C, 75 °C (reservoir temperature), 100 °C and 150 °C with a velocity of 0.05 PV/h. Results show a significant increase in the aqueous concentration of calcium, silicium and barium upon heating, while the concentration of magnesium decreases. The main chemical processes taking place upon heating of the reservoir to up to 150 °C is dolomitisation, the replacement of plagioclase with albite, the dissolution of quartz and barite and the precipitation of mica. A significant portion of the cementing calcite dissolved during the experiment, and consequently the tested Bunter Sandstone sample disintegrated after the experiment, indicating that injection of heated calcium depleted Bunter brine into the Bunter Sandstone Formation may damage the reservoir. The results highlight the importance of investigating the effects that removal of selected ions may have on the reservoir properties, since the injection of modified formation water may cause new problems in the reservoir.

Acidic Polysaccharides as Green Alternatives for Barite Scale Dissolution.

Barium sulfate (barite) scale poses significant challenges for processes ranging from water treatment to fossil fuel production. Here, we identify alginate (a polysaccharide derived from brown algae) as a potent, "green" alternative to commercial barite demineralizing agents. Unlike conventional treatments of inorganic scales that require caustic conditions, alginate polymers dissolve barite at near-neutral conditions. In this study, we benchmark the demineralizing efficacy of alginate against a commercial dissolver, diethylenetriaminepentaacetic acid (DTPA), using a combination of bulk dissolution assays, scanning probe microscopy, and molecular dynamics simulations. Time-resolved rates of dissolution measured in a microfluidic device show that demineralization is enhanced more than an order of magnitude under flow. In situ atomic force microscopy reveals that alginate and DTPA exhibit distinct mechanisms of surface dissolution; and surprisingly, their binary combination in alkaline media results in a synergistic cooperativity that enhances the overall rate of barite dissolution. These studies collectively demonstrate a unique approach to demineralization using an inexpensive and abundant biopolymer that enables environmentally friendly treatment of inorganic scales.

The Mineralogical Evolution of the Clastic Dominant-Type Zn-Pb ± Ba Deposits at Macmillan Pass (Yukon, Canada)—Tracing Subseafloor Barite Replacement in the Layered Mineralization

Abstract Clastic dominant-type massive sulfide deposits are well preserved in Upper Devonian carbonaceous mudstones in the Macmillan Pass district (Yukon, Canada). The Macmillan Pass deposits have been considered to be type examples of sedimentary exhalative Zn-Pb mineralization, whereby sulfides precipitated when hydrothermal fluids were vented into a euxinic (H2S-bearing) water column. We propose a new mineralization model, documenting the mineralogical evolution of layered mineralization. We show that textures previously interpreted to form via depositional processes actually formed by subseafloor replacement of diagenetic barite. Mineral assemblages associated with barite dissolution in the layered mineralization include (1) barium carbonate phases (witherite, barytocalcite, and norsethite), which are intergrown with Zn-Pb sulfides and represent localized Ba mass transfer, and (2) barium feldspar (celsian, hyalophane) that is abundant in the mudstones surrounding the layered mineralization. The barium feldspar formed following transport of Ba in low-sulfate fluids on the margins of the subseafloor replacement system. This resulted in whole-rock Ba enrichments (up to 5 wt %) in mudstones 15 m below and above the layered mineralization. High Ba in these surrounding mudstones is coupled with decreasing K/Al ratios, indicative of secondary illite and kaolinite. The source(s) of fluids related to the diagenetic (barite, barytocalcite) and hydrothermal (ankerite) assemblages can be constrained using Sr isotopes. Whereas highly radiogenic 87Sr/86Sr values (&amp;gt;0.714) in ankerite correspond with host-rock alteration within the vent complex, the overlying barite and barytocalcite preserve lower 87Sr/86Sr values (&amp;lt;0.714), providing evidence of mixing between a radiogenic fluid (likely a formation water) and Late Devonian seawater. The complex mineralogy and paragenesis contained within the layered mineralization are linked to a protracted history of diagenetic and hydrothermal fluid events, all of which took place in and peripheral to a subseafloor replacement hydrothermal system.

A NEW SUBSEAFLOOR REPLACEMENT MODEL FOR THE MACMILLAN PASS CLASTIC-DOMINANT Zn-Pb ± Ba DEPOSITS (YUKON, CANADA)

Abstract Sedimentary exhalative (SEDEX) deposits are a subset of sediment-hosted massive sulfide deposits and provide our dominant resource of Zn. In the SEDEX model, base metals (Zn, Pb, Fe) are hydrothermally vented into sulfidic (euxinic) seawater and deposited coevally with the organic-rich mudstone host rock, resulting in laterally extensive layered mineralization. In the Selwyn Basin (Canada) at Macmillan Pass, two deposits (Tom, Jason) are well preserved in a succession of Upper Devonian mudstones and are considered type-characteristic examples of the SEDEX deposit model. As with a number of SEDEX deposits, at Macmillan Pass barite is abundant in the succession hosting hydrothermal mineralization. Early work presented a hydrothermal model for barite formation, in which barite coprecipitated with base metal sulfides in a redox-stratified water column. Recently, however, studies have both proposed an alternative diagenetic model for barite formation and provided more precise constraints on the chemistry of the hydrothermal fluid that entered the vent complexes. Here, we present a new model for Macmillan Pass in which sulfide mineralization occurred entirely within the subsurface. The introduction of hot (300°C) hydrothermal fluids into the shallow subsurface (&amp;lt;1-km depth) resulted in the thermal degradation of organic matter and generated CO2; this promoted barite dissolution, which both provided a source of sulfate for thermochemical sulfate reduction and increased the porosity and permeability within the system. Importantly, there was clear potential for the development of positive feedbacks and self-organization between diagenetic and hydrothermal processes, resulting in highly efficient ore-forming systems. In contrast to the SEDEX model, alteration footprints will be controlled by the mass transfer involved in (barite) replacement reactions rather than hydrothermal venting, and exploration criteria at a district scale should strongly favor highly productive continental margins.

The Role of Barite in the Post-Mining Stabilization of Radium-226: A Modeling Contribution for Sequential Extractions

Barite is ubiquitous and known to incorporate 226Ra through the formation of a solid-solution. In U mining mill tailings, barite is one of the dominant sulfate-binding minerals. In such environments, sequential extractions are generally used to identify the U- and 226Ra-binding phases and their associated reactivity. To better decipher the main processes governing the behavior of 226Ra during such sequential extractions, a geochemical model was developed with PHREEQC mimicking the sequential extraction of U and 226Ra from Bois-Noirs Limouzat U mine tailings, France. The model results were compared with a dataset produced by an experimental sequential extraction from the same mine tailings and including data on the solids and selective extraction results with the major elements, U and 226Ra. The simulations reproduced the results of the experimental chemical extractions accurately, with iron oxyhydroxides being the major U binding phase. However, the modeling indicated rather that barite would be the main 226Ra binding phase, instead of the iron oxyhydroxides identified by the experimental extractions. This is consistent with the 226Ra concentration measured in pore water, but in disagreement with the direct interpretation of the sequential extractions. The direct interpretation disregarded the role of barite in the geochemical behavior of 226Ra because barite was not specifically targeted by any of the extraction steps. However, the modeling showed that the dissolution of 226Ra-binding barite by reactants would lead to a 226Ra redistribution among the clay minerals, resulting in a skew in the experimental results. Similar results were achieved by referring simply to the bulk mineralogy of the tailings. This study highlights the importance of considering the mineralogy, mineral reactivity and retention capacity for more realistic interpretation of sequential extractions. Moreover, this paper provides new perspectives on the long-term consequences of these mill tailings in which barite controls the geochemical behavior of the 226Ra.

Unlocking the barite paleoproductivity proxy: A new high-throughput method for quantifying barite in marine sediments

The accumulation rate of barite (BaSO4) in marine sediments is a powerful tracer of paleo export productivity due to the refractory nature of barite in sediments and its ability to record ecosystem-wide productivity. It has been used to reconstruct past export productivity and to infer the effects of ocean circulation and nutrient supply on ocean ecosystems. However, the difficulty in generating large datasets of reliable barite accumulation rates has limited the use of this proxy. Here we present a new method for quantifying barite in marine sediments that promises a dramatic increase in sample throughput while also improving recovery of barite in a wide variety of marine sediments. This method relies on selective dissolution of barite using a chelating ligand that avoids liberating Ba from silicate phases, and it can therefore work reliably on small (~250 mg) sediment aliquots. Rigorous evaluation of the method reveals that it quantitatively extracts barite and is largely unaffected by other Ba sources. Due to the relatively simple analytical requirements of this barite extraction method and the small sample amount needed, it can also be used to rapidly generate paleoproductivity records both during and after coring expeditions. Altogether, this new technique should expand the study of the marine biologic system in the past by dramatically increasing analytical efficiency and widening the range of questions that are accessible using barite accumulation rate as a paleoproductivity proxy.

Llandovery (lower Silurian) nodular barite from the northern margin of Yangtze Block, South China, and its paleoceanographic implications

The Llandovery epoch (Early Silurian) was marked by the interruption of widespread oceanic anoxia and associated oxygenation of seawater. The first oxygenation event appears to occur near the Rhuddanian–Aeronian stages boundary. However, ventilation of the marine environments is a dynamic process, differing in timing and magnitude from place to place, basic variations in the nature of marine circulation; e.g., open shelf versus restricted shelf. The correlation of oxygenation events from open to restricted shelf environments is of significance to enhancing our understanding of marine ventilation processes. Here, we describle nodular barite that accumulated in the open marine environment near the boundary at the northern margin of the Yangtze Block, South China, emphasizing its origin and environmental implications. Petrographic evidence suggests that the nodular barite is early diagenetic. Barium was likely derived from the dissolution of biogenic barite as suggested by the 87Sr/86Sr values of the diagenetic barite. The REE + Y pattern, low Y/Ho and high Ce*/Ce values of the barite nodules demonstrate that microbial degradation of organic matter in association with Ce oxidation controlled REE composition of the nodules. PAAS-normalized positive Eu anomalies of the studied barite, however, suggest an anoxic porewater environment perhaps related to bacterial sulfate reduction or the anaerobic oxidation of methane focused within the sulfate-methane transition zone (SMTZ) as also indicated by the minor contribution of radiogenic terrigenous Sr isotopes. We infer that high marine productivity and the associated transport of biogenic barite to the sea floor was critical to the formation of the studied barite nodules. Diagenetic barite formation and preservation in Aeronian stage deposits may indicate that circulation of open marine water masses had been much ameliorated. Our results are consistent with earlier suggestions that the restricted shelf experienced a transition from anoxic or even euxinic conditions to a more oxygenated (probably suboxic) condition during the early Aeronian. The approximately contemporaneous nature of this transition and global cooling associated with the glacial pulses indicate the critical role that global climate change near the Rhuddanian–Aeronian (R-A) boundary played in the redox evolution of the Yangtze Block, South China.