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The scarce carbonate record on the Martian surface is one of the fundamental unsolved issues for paleoclimate and environmental evolution. Whether carbonates first formed and then dissolved due to a transition in global environments or whether Mg–Fe carbonates never extensively formed due to geochemical kinetics thresholds remains unknown. In this study, we experimentally examined the preservation potential of siderite in Mars‐relevant fluids, including ultrapure water, H2O2, NaClO4, NaClO3, NaCl, Na2SO4, NaHCO3, and Na2SiO3 solutions, at 277 K. The effects of the water/rock ratio at WR10 and WR100 on dissolution rates were also investigated. We found that siderite dissolution and subsequent oxidation and hydrolysis of leached Fe did not substantially acidify the solutions. The siderite dissolved relatively rapidly in the chloride and chlorate solutions and slowly in the silica or bicarbonate solutions. In a circum‐neutral to slightly alkaline aqueous environment with oxidative species, the mobility of leached Fe was limited, leading to the formation of goethite or lepidocrocite, which clustered on the siderite surface. The longest lifetime of 1‐mm siderite grains was found in the Na2SiO3 solution at WR100, which was estimated to range from 198 ka to 198 Ma. Water‐limited, silica‐rich, and oxidative aqueous environments benefit siderite preservation on the Martian surface. Our results support that the lack of voluminous siderite on Mars may be primarily due to the inhibition of its formation rather than alteration and dissolution after its presence, consistent with the recent detection of Mg–Fe carbonate at Gale Crater and Jezero Crater. Plain Language Summary: Despite the predominant carbon dioxide atmosphere, the distribution of carbonate outcrops on Mars detected to date is very limited. The discrepancy between the CO2‐dominant atmosphere and scarce carbonate records is one of the key issues for understanding the paleoclimate and environmental evolution of Mars. We experimentally investigated the preservation potential of siderite in eight Mars‐relevant fluids under water‐limited versus water‐abundant scenarios at 277 K. We found that water‐limited conditions, silica‐rich environments, and the presence of oxidants in aqueous environments generally benefit siderite preservation. The longest lifetime of 1‐mm siderite grains is present in silica‐rich solutions, estimated to range from 198 ka to 198 Ma. In a neutral to alkaline aqueous environment with oxidative species, the mobility of leached iron is limited, and the Fe precipitates are mainly in the form of goethite or lepidocrocite, accumulating on the siderite surface. Martian aqueous environments can efficiently preserve siderite. Therefore, the lack of voluminous siderite on Mars may be because siderite was never extensively formed rather than altered and dissolved after its presence. Key Points: Siderite dissolves relatively fast in chloride‐ and chlorate‐fluids and slowly in silica‐ and bicarbonate‐fluidsWater‐limited, silica‐rich, and oxidative aqueous environments favor siderite preservation on the Martian surfaceThe scarcity of voluminous siderite on Mars may be due to the inhibition of its formation rather than its dissolution after its presence [ABSTRACT FROM AUTHOR]

A distinct layer of Ironic oolitic siltstone stratum is observed at the lower part of the Benxi Formation of the Middle Carboniferous in Liujiang Basin, exhibiting prominent lithological characteristics and consistent thickness within the region. According to the observation of rock thin sections and scanning electron microscopy, ironic oolites exhibit a diameter ranging from 0. 1 to 1. 0 mm, characterized by a ring structure with indistinct boundaries consisting of 3 to 5 layers enclosing fine quartz silt particles. According to the results of energy spectrum analysis, the oolite exhibits varying elemental compositions including Fe, Si, Al, O, K, C, and Ti in distinct regions. Through comprehensive analysis, it is determined that the predominant mineral constituents comprise limonite, hematite, quartz, and clay minerals. Through the analysis of trace elements, it is inferred that during the initial sedimentation of the Benxi Formation, the region was characterized by a relatively warm and semi-humid climate, a partially enclosed reducing environment bay, and brackish water conditions. After a prolonged period of weathering and erosion, the surface underwent deposition, resulting in a relatively enriched residual Fe element. Subsequently, through sedimentation and runoff processes, it was transported into the bay. The participation of organic carbon facilitated the formation of siderite (FeCO3) through its combination with Fe2O3. This resulted in the gradual deposition of siderite layers around suspended small quartz particles in the water body, which eventually settled on the seabed as particle concentration increased. Siderite undergoes diagenesis, leading to its instability and subsequent decomposition into Fe3O4. This process is further accompanied by oxidation, ultimately resulting in the transformation of siderite into limonite [FeO(OH)·H2O]. Additionally, under extremely arid and hot conditions during later stages, siderite readily oxidizes into hematite, thereby giving rise to the coexistence of limonite and hematite within irony ooids. [ABSTRACT FROM AUTHOR]

Large-scale subsurface hydrogen storage is critical for transitioning towards renewable, economically viable, and emission-free energy technologies. Although preliminary studies on geochemical interactions between different minerals, aqueous ions, and other dissolved gasses with H2 have helped partially quantify the degree of hydrogen loss in the subsurface, the long-term changes in abiotic hydrogen–brine–rock interactions are still not well understood due to variable rates of mineral dissolution/precipitation and redox transformations under different conditions of reservoirs. One of the potentially understudied aspects of these complex geochemical interactions is the role of iron on the redox interactions and subsequent impact on long-term (100 years) hydrogen cycling. The theoretical modeling conducted in this study indicates that the evolution of secondary iron-bearing minerals, such as siderite and magnetite, produced after H2-induced reductive dissolution of primary Fe3+-bearing phases can result in different degrees of hydrogen loss. Low dissolved Fe2+ activity (<10−4) in the formation water can govern the transformation of secondary siderite to magnetite within 100 years, eventually accelerating the H2 consumption through reductive dissolution. Quantitative modeling demonstrates that such secondary iron mineral transformations need to be studied to understand the long-term behavior of hydrogen in storage sites. [ABSTRACT FROM AUTHOR]

Mesozoic oceanic anoxic events were characterized by relatively low seawater sulphate concentrations ([SO42−]), which likely regulated the development and evolution of these major palaeoceanographic phenomena. However, there is little reliable sedimentary evidence for low [SO42−] in ancient marine waters and understanding of how such a seawater chemistry potentially impacted oceanic anoxic events is limited. This study presents an integrated sedimentological, mineralogical and geochemical investigation of the mineral siderite hosted in dark grey shale and sideritic concretions of Early Aptian (coeval with Oceanic Anoxic Event 1a) from the Tibetan Himalaya. Siderite is present throughout the section and possesses similar morphological characteristics whether in dark grey shale or concretions. Siderite can be present as disseminated and rhombic crystals formed during early diagenesis, or minor spherical crystals formed during late diagenesis. The evidence from redox elements, middle rare‐earth element bulge patterns and extremely low carbon‐isotope values of the sideritic concretions indicates that the iron carbonate was formed in the Fe‐reduction zones by the process of dissimilatory iron reduction. This process would have required conditions of low [SO42−], reducing environment, abundant iron and high alkalinity. Additionally, the coexistence of siderite and pyrite may indicate that dissimilatory iron reduction occurred close to the microbial sulphate reduction zone, with seawater [SO42−] hovering around the tipping point at which pyrite could form once seawater sulphate increased. Such an increase during Oceanic Anoxic Event 1a could have resulted from basalt–seawater interaction and associated enhanced continental weathering, and/or hydrothermal activity. This study's observations support the previous hypothesis that low [SO42−] for Oceanic Anoxic Event 1a was probably caused by massive gypsum burial in the proto‐South Atlantic. Subsequently, enhanced sulphate input could have promoted microbial sulphate reduction and accompanying oxidation of organic matter, which likely further enhanced nutrient recycling, increased primary productivity and organic‐carbon burial, leading to more oxygen consumption and expansion of oxygen minimum zones, as reconstructed for many oceanic anoxic events. [ABSTRACT FROM AUTHOR]

Large-scale subsurface hydrogen storage is critical for transitioning towards renewable, economically viable, and emission-free energy technologies. Although preliminary studies on geochemical interactions between different minerals, aqueous ions, and other dissolved gasses with H2 have helped partially quantify the degree of hydrogen loss in the subsurface, the long-term changes in abiotic hydrogen–brine–rock interactions are still not well understood due to variable rates of mineral dissolution/precipitation and redox transformations under different conditions of reservoirs. One of the potentially understudied aspects of these complex geochemical interactions is the role of iron on the redox interactions and subsequent impact on long-term (100 years) hydrogen cycling. The theoretical modeling conducted in this study indicates that the evolution of secondary iron-bearing minerals, such as siderite and magnetite, produced after H2-induced reductive dissolution of primary Fe3+-bearing phases can result in different degrees of hydrogen loss. Low dissolved Fe2+ activity (−4) in the formation water can govern the transformation of secondary siderite to magnetite within 100 years, eventually accelerating the H2 consumption through reductive dissolution. Quantitative modeling demonstrates that such secondary iron mineral transformations need to be studied to understand the long-term behavior of hydrogen in storage sites.

Abstract Past and present habitability of Mars have been intensely studied in the context of the search for signals of life. Despite the harsh conditions observed today on the planet, some ancient Mars environments could have harbored specific characteristics able to mitigate several challenges for the development of microbial life. In such environments, Fe2+ minerals like siderite (already identified on Mars), and vivianite (proposed, but not confirmed) could sustain a chemolithoautotrophic community. In this study, we investigate the ability of the acidophilic iron-oxidizing chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans to use these minerals as its sole energy source. A. ferrooxidans was grown in media containing siderite or vivianite under different conditions and compared to abiotic controls. Our experiments demonstrated that this microorganism was able to grow, obtaining its energy from the oxidation of Fe2+ that came from the solubilization of these minerals under low pH. Additionally, in sealed flasks without CO2, A. ferrooxidans was able to fix carbon directly from the carbonate ion released from siderite for biomass production, indicating that it could be able to colonize subsurface environments with little or no contact with an atmosphere. These previously unexplored abilities broaden our knowledge on the variety of minerals able to sustain life. In the context of astrobiology, this expands the list of geomicrobiological processes that should be taken into account when considering the habitability of environments beyond Earth, and opens for investigation the possible biological traces left on these substrates as biosignatures.

Two accretionary sediment sequences from Sites 1245 and 1252 recovered during Ocean Drilling Program (ODP) Leg 204 at southern Hydrate Ridge were investigated to explore the response of geochemical partitioning of iron and sulfur isotopic composition of authigenic pyrite to non-steady-state depositional and diagenetic scenarios. Five iron species were characterized by a modified sequential extraction procedure that covers almost all iron-bearing minerals in sediment cores, including: (1) iron-bearing carbonates, mainly siderite; (2) ferric (hydr)oxides, probably ferrihydrite and/or lepidocrocite; (3) magnetite; (4) iron-bearing silicates; and (5) pyrite. Highly reactive iron has been accumulated for a long-term steady-state history and its pyritization, to varying degrees, is limited by availability of dissolved sulfide. This causes pyrite and siderite occurred in the same sedimentary layer and shows an inverse relationship between their concentrations. From this, their proportions to highly reactive iron can be chosen for evaluating the degree of sulfidization. A significant change in sulfur isotopic composition of pyrite (-42.4 to +16.8‰ VCDT) indicates that the steady-state conditions are dramatically limited, where the d34S values higher than -20‰ may result from an upward shift of SMT zone close to the seafloor or a sudden, massive depositional event. To explain the downcore sulfidization effects and pyrite d34S values, we developed two categories of conceptual scenarios based on variations in sedimentation rate and methane flux. The geochemical features similar to those derived from each scenario were searched in the sediment columns and the non-steady-state events behind the scenarios were proved to be consistent with the real observations. Thus, iron species and pyrite d34S values can be regarded as a proxy to differentiate different non-steady-state depositional and diagenetic controls on the sedimentary record. [ABSTRACT FROM AUTHOR]

Structured marine clay is commonly encountered in offshore engineering projects and engineers are concerned about its impact on the engineering properties of marine clay as well as its correlation with index properties. Current research has emphasized the role of soil structure in these aspects of marine clay. In this study, we investigated the influence of depositional environment and oxidation-induced evolution of clay microstructure on the formation of clay structure in structured clay from Zhanjiang area, a coastal city located in South China. The distinct soil structure observed in marine-terrigenous clay deposited under different environments exhibited sensitivity ranging from 1.6 to 8.9 at varying moisture content levels. The wide range of sensitivity observed in structured marine-terrigenous clay was attributed to free iron oxide derived from siderite present in an acidic environment. Compared to other regions, Zhanjiang marine clay demonstrated favorable mechanical properties but poor physical properties due to its unique clay structure characteristics. Based on these findings, we proposed a modified approach for correlating index properties with engineering properties that yielded good predictions. [ABSTRACT FROM AUTHOR]

Siderite is a typical iron-bearing carbonate mineral, which is characterized by thermal instability. In this study, the thermal decomposition of natural siderite with magnesium (Mg) isomorphous substitution was performed in a flowing air atmosphere. During the thermal decomposition, X-ray diffraction, Mössbauer spectroscopy, transmission electron microscope, and vibrating sample magnetometer were employed to characterize the samples. Results indicated that siderite primarily transformed into maghemite and Mg–Fe spinel in oxidation decomposition, and no magnetite was detected. The synthetic spinel phases were highly stable and difficult to oxidize even at a roasting temperature of 700 °C because of the magnesium substitution. Owing to the ferrimagnetism of maghemite and Mg–Fe spinel, the magnetism of samples significantly improved during the oxidation decomposition. [ABSTRACT FROM AUTHOR]

Pyrite is a ubiquitous sulfide mineral found in diverse geological settings and holds great significance in the formation of Au deposits as well as the safe utilization of groundwater due to its remarkable ability to incorporate substantial amounts of As. However, despite its importance, there remains a dearth of fundamental data on the partitioning of As between pyrite and fluid, which is key for accurately modeling the As distribution in these environments. Here, we present new insights into the partitioning behavior of As between pyrite and fluid at conditions that mimic natural fluid systems. Pyrite was synthesized by replacement of natural siderite in hydrothermal experiments at 200 °C and pH 5 applying a wide range of fluid As concentrations, spanning from 0.001 to 100 µg/g. The As distribution and concentration in synthetic pyrite was analyzed by quantitative LA-ICP-MS mapping providing a high spatial resolution and sensitivity at 2–3 µm image pixel size at a detection limit of ∼1 µg/g at the single pixel scale. Pyrite-fluid partitioning coefficients (D As (py/fluid)) between synthetic pyrite and experimental fluid agree with previously published data for high fluid As concentrations of 1 µg/g to 100 µg/g (D As < 2000). However, at low As concentrations in the experimental fluid (<1 µg/g), a steep increase in the D As (py/fluid) values of up to ∼30,000 was detected, demonstrating even stronger As partitioning into pyrite. This is confirmed by the analyses of natural pyrite that precipitated from As-poor fluids (0.3–0.4 ng/g) within a deep anoxic aquifer in SE Sweden. The discovery holds significant implications for the mobility and scavenging of As, which in turn is important for understanding the formation and fingerprinting of mineral deposits as well as for the secure utilization of groundwater resources. [ABSTRACT FROM AUTHOR]

Past and present habitability of Mars have been intensely studied in the context of the search for signals of life. Despite the harsh conditions observed today on the planet, some ancient Mars environments could have harbored specific characteristics able to mitigate several challenges for the development of microbial life. In such environments, Fe2+ minerals like siderite (already identified on Mars), and vivianite (proposed, but not confirmed) could sustain a chemolithoautotrophic community. In this study, we investigate the ability of the acidophilic iron-oxidizing chemolithoautotrophic bacterium Acidithiobacillus ferrooxidans to use these minerals as its sole energy source. A. ferrooxidans was grown in media containing siderite or vivianite under different conditions and compared to abiotic controls. Our experiments demonstrated that this microorganism was able to grow, obtaining its energy from the oxidation of Fe2+ that came from the solubilization of these minerals under low pH. Additionally, in sealed flasks without CO2, A. ferrooxidans was able to fix carbon directly from the carbonate ion released from siderite for biomass production, indicating that it could be able to colonize subsurface environments with little or no contact with an atmosphere. These previously unexplored abilities broaden our knowledge on the variety of minerals able to sustain life. In the context of astrobiology, this expands the list of geomicrobiological processes that should be taken into account when considering the habitability of environments beyond Earth, and opens for investigation the possible biological traces left on these substrates as biosignatures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mineral-activated perxymonosulfate (PMS) shows dewaterability and triclosan removal. • Iron-rich minerals are more economical than traditional sources of Fe2+. • Rheological test demonstrates that siderite/PMS can promote sludge fragmentation. • Siderite could release Fe2+ more sustainably to persistently produce free radicals. High water and pharmaceutical and care products (PPCPs) bounded in sludge flocs limit its utilization and disposal. The advanced oxidation process of perxymonosulfate (PMS) catalyzed by iron salts has been widely used in sludge conditioning. In this study, two iron-rich minerals pyrite and siderite were proposed to enhance sludge dewatering performance and remove the target contaminant of triclosan (TCS). The permanent release of Fe2+ in the activation of PMS made siderite more effective in enhancing sludge dewater with capillary suction time (CST) diminishing by 60.5 %, specific resistance to filtration (SRF) decreasing by 79.2 %, and bound water content (BWC) dropping from 37.1 % to 2.6 % at siderite/PMS dosages of 0.36/0.20 mmol/g-TSS after 20 min of pretreatment. Pyrite/PMS performed slightly inferior under the same conditions and the corresponding CST and SRF decreased by 51.5 % and 71.8 % while the BWC only declined to 17.8 %. Rheological characterization was employed to elucidate the changes in sludge dewatering performance, with siderite/PMS treated sludge showing a 48.3 % reduction in thixotropy, higher than 28.4 % of pyrite/PMS. Oscillation and creep tests further demonstrated the significantly weakened viscoelastic behavior of the sludge by siderite/PMS pretreatment. For TCS mineralization removal, siderite/PMS achieved a high removal efficiency of 43.9 %, in comparison with 39.9 % for pyrite/PMS. The reduction in the sludge solids phase contributed the most to the TCS removal. Free radical quenching assays and EPR spectroscopy showed that both siderite/PMS and pyrite/PMS produced SO 4 -· and ·OH, with the latter acting as the major radicals. Besides, the dosage of free radicals generated from siderite/PMS exhibited a lower time-dependence, which also allowed it to outperform in destroying EPS matrix, neutralizing the negative Zeta potential of sludge flocs, and mineralizing macromolecular organic matter. [ABSTRACT FROM AUTHOR]

We have conducted electrical conductivity measurements of FeCO3 siderite under high pressure up to 63 GPa in order to understand the nature and effect of iron spin transition and its influence on the geophysical properties of siderite, which is an end-member of major carbonate minerals. The results from Raman and Mössbauer spectroscopic measurements show that the high- to low-spin transition of iron occurs at around 50 GPa in agreement with previous studies. A sharp decrease of the electrical conductivity was also observed at around 50 GP, which is associated with the spin transition in iron. Although the stability of FeCO3 siderite may be limited under high-temperature conditions along with the mantle geotherm, solid solutions in the MgCO3-FeCO3 system, Mg1-xFexCO3, could be stable up to the pressure-temperature condition of the lowermost mantle. The pressure-temperature range of the spin transition in Mg1-xFexCO3 is narrower than those of the major lower mantle minerals, ferropericlase and bridgmanite, and thus the drop of the electrical conductivity induced by the spin transition could be clearer under lower mantle conditions. Therefore, the existence of Mg1-xFexCO3 may affect the observed heterogeneity of electrical conductivity in the mid-lower mantle. [ABSTRACT FROM AUTHOR]

Stable isotope, trace element, and cathodoluminescence analyses were performed on gastropods and matrix from rock cores of the Middle to Upper McMurray Formation (Lower Cretaceous/Aptian, Northwestern Alberta, Canada) to characterize the extent to which pristine material remained from which depositional environmental conditions could be estimated. Aragonitic gastropod shells retain their original depositional chemistry, and along with other closely associated authigenic carbonate components, indicate that the Middle to Upper McMurray Formation was deposited in a freshwater environment that was part of a continent-scale river system. [ABSTRACT FROM AUTHOR]

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The tailings of JISCO have a large amount of resources and high iron grade, with BaO content of about 8%. It is a secondary resource with important recovery value. In order to realize the efficient recovery and utilization of iron and barium in the tailings of JISCO, a systematic process mineralogy study was carried out on the tailings, and the recovery of iron minerals and barium resources was explored. The results show that the grade of TFe is 23.56%, the grade of Ba is 6.68%, and the content of SiO2 is 20.86%. The main metal minerals are hematite (speculate, limonite) and siderite, with contents of 22.23% and 16.17% respectively, and a magnetite content of 7.72%. The main non-metallic minerals are quartz and barite, with contents of 21.85% and 13.18% respectively. The particle size of hematite (speculate, limonite), siderite and barite in the tailings is coarse, and the distribution rate of +75 µm is greater than 60%. The liberation degree of hematite (specularite, limonite) and siderite is not high, mainly in form of rich intergrowths, and the liberation degree of barite is as high as 72.85%. Magnetite/hematite is associated with siderite and quartz in the form of adjoining and wrapping. Nearly half of siderite is closely associated with magnetite/hematite, followed by intercalating with quartz. Barite is mainly adjacent to quartz and magnetite/hematite. The iron minerals and barite were preliminarily separated from the tailings of JISCO by low-intensity magnetic separation and high-intensity magnetic separation. The mixed magnetic separation concentrate was subjected to hydrogen-based mineral phase transformation and low-intensity magnetic separation to obtain an iron concentrate with a TFe grade of 58.77% and an operating recovery of 78. 46%. The barite concentrate with BaSO4 grade of 91. 30% and operation recovery of 90.28% was obtained from the magnetic separation tailings by shaking table gravity separation and flotation roughing. The research provides a reference for the formulation of beneficiation process and comprehensive utilization of iron and barium resources in the tailings of JISCO. [ABSTRACT FROM AUTHOR]

The article introduces a digitized siderophore information database called SIDERITE, which contains 649 unique structures of siderophores. Siderophores are secondary metabolites that bind and chelate iron, playing a vital role in microbial survival and growth. The database provides a comprehensive overview of siderophores, including their biosynthetic pathways, sources, and chemical characterizations. Using this database, the authors developed a functional group-based method to predict new iron-binding molecules and identified 3199 potential siderophore candidates. The study aims to accelerate the discovery of novel iron-binding molecules and enhance our understanding of siderophores. The researchers used a rule-based approach to discovering siderophores, which are molecules that bind to iron. The researchers used a database of known siderophores to develop rules for identifying potential siderophore candidates. They then applied this method to a large chemical database and identified thousands of molecules with potential iron-binding activities. The researchers also conducted experiments to verify the predictions and found a high positive rate for iron-binding activity. The study highlights the structural diversity of siderophores and the potential for further exploration in this field. The researchers have also created a comprehensive database of siderophores for future research. [Extracted from the article]

Concentrically zoned pyrite aggregates (CZPA) are common in sediment‐hosted massive sulfide (SHMS) deposits and have been widely used to interpret the ore‐forming processes. There is considerable uncertainty, however, over the formation of aggregates that are oscillatorily zoned and contain randomly‐orientated pyrite microcrystals. Guided by the results of examination of the micro‐textures of CZPA and in‐situ chemical analyses, we conducted a quantitative diffusion‐reaction simulation to assess the mechanism of CZPA formation. Our study shows that oscillatory zoning results from the feedback between the diffusion of reactants and the nucleation‐growth of Fe‐sulfides. Externally derived Fe2+ diffuses into the early diagenetic sediments containing decomposing organic matter (2CH2O + SO42− = 2HCO3− + H2S) and reacts with H2S to form a pyrite layer via an intermediate pathway (Fe2+ + H2S → FeS + 2H+, FeS + H2S → FeS2 + H2). This growth of pyrite layers depletes the local concentration of reactants and suppresses nucleation until the diffusive reaction front advances and another layer is formed. Intermediate phases, for example, mackinawite, nucleate instead of pyrite, because of their greater ease of nucleation due to the low surface tension, and lead to the domination of nucleation over growth. The nucleation of mackinawite and occurrence of siderite in the CZPA are consistent with a low temperature, high pH, anoxic early diagenetic environment. Our study demonstrates that CZPA in SHMS deposits are formed by intrinsic self‐organizational processes rather than by extrinsic changes of ore‐forming fluids. The CZPA in SHMS deposits are thus indicative of their diagenetic origin with Fe2+ infiltrated and diffused from hydrothermal fluids into the sediments. Plain Language Summary: Oscillatory zoning patterns are a phenomenon commonly encountered in scientific disciplines that include biology, geology, chemistry and atmospheric physics. To decipher these patterns, we employ a unifying principle that leverages a reaction‐diffusion approach and successfully replicate the textures observed in a massive sulfide deposit, via numerical simulations. In addition, we show that factors such as the concentration, distribution, and mobility of reactant species, such as the iron ion, sulfide, and organic matter in sediments, influence the texture of patterns at both the millimeter and nanometer scales. Our proposed numerical models yield results that closely align with the oscillatory zoning patterns observed in pyrite‐siderite from the Xinqiao massive sulfide deposit in Central China. The broader impact of this work lies in the development of a computer simulation‐based protocol, which sheds light on the processes forming massive sulfide deposits. This, in turn, has the potential to significantly aid the exploration for new metal and sulfide resources beneath the surface of the Earth. Key Points: Reactive‐diffusion simulations of the formation of concentrically zoned pyrite aggregates in sediment‐hosted massive sulfide depositsThe ore textures were the result of an intrinsic self‐organized process rather than extrinsic changes of chemical compositionsProtocols for deciphering diagenetic environments affected by the infiltration of Fe2+‐rich hydrothermal fluids [ABSTRACT FROM AUTHOR]

Ni-based catalysts play a fundamental role in catalytic CO2 methanation. In this study, the possibility of using siderite ore as a catalyst or catalytic support material for nickel-based catalysts was investigated, aiming at the exploitation of an abundant natural resource. The catalytic performance of Ni-based catalysts with reduced siderite ore as a support was evaluated and compared to MgO as a support material. MgO is known as an effective support material, as it provides access to bifunctional catalysts because of its basicity and high CO2 adsorption capacity. It was shown that undoped and Ni-doped reduced siderite ore have comparable catalytic activity for CO2 hydrogenation (20−23%) at 648 K, but show limited selectivity toward methane (<20% for sideritereduced and 60.2% for Ni/sideritereduced). When MgO was added to the support material (Ni/sideritereduced/MgO), both the CO2 conversion and the selectivity toward methane increased significantly. CO2 conversions were close to the thermodynamic equilibrium, and methane selectivities of ≥99% were achieved. [ABSTRACT FROM AUTHOR]

Rhenium (Re) is an extremely rare element, with a crustal abundance of approximately 0.4 parts per billion (ppb) and a sea water concentration of 8.3 parts per trillion (ppt). However, Re concentrations in anoxic marine sediments range from 2 to 184 ppb, which is attributed to reduction of the highly soluble perrhenate ion (Re(VII)O4−) to insoluble Re(IV) species. Anoxic sediments typically contain Fe(II) and sulfide species, which could potentially reduce Re(VII) to Re(IV). In this study, we examined the interactions of KReO4 with magnetite (Fe3O4), siderite (FeCO3), vivianite (Fe3(PO4)2•8H2O), green rust (mixed Fe(II)/Fe(III) layered double hydroxide), mackinawite (FeS), and chemically reduced nontronite (NAu-1) using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy to determine the valence state and speciation of Re. Uptake of Re by green rust was rapid, with ~50% associated with the solids within 2 days. In contrast, there was <10% uptake by the other Fe(II) phases over 48 days. Reduction of Re(VII) to Re(IV) was only observed in the presence of green rust, producing clusters of bidentate-coordinated Re(IV)O6 octahedra.. These results suggest that except for green rust, the potential for other Fe(II)-bearing minerals to act as reductants for ReO4− in sedimentary environments requires further investigation. [ABSTRACT FROM AUTHOR]

Aiming at the problems of high sulfate concentration in effluent from conventional filter media of autotrophic denitrification technology and inability to remove phosphorus synchronously, the denitrification and dephosphorization performance of composite mineral sources filter media (MSAD) is explored through batch experiments, and the denitrification and dephosphorization effects of pyrite (FeS2) and siderite (FeCO3) at different mass ratios are analyzed. The results show that, compared with single FeS2 as electron donor, the composite mineral sources (FeS2 and FeCO3) possess higher nitrate removal rate, lower sulfate concentration and more stable pH value. On the 4th day of stable operation after domestication, the system with m(FeS2) ∶ m(FeCO3) = 2 ∶ 1 exhibitsd supreme denitrification performance (removal rate of NO3--N is 93%, and TN is 86%). The removal efficiency of total phosphorus in the system with m(FeS2) ∶ m(FeCO3) = 1 ∶ 1 is the highest (65%). Species analysis show that the microbial species responsible for sulfide autotrophic denitrification are dominant in the composite mineral source. This study provides a theoretical reference for the selection of mineral sources in engineering practice of autotrophic denitrification technology. [ABSTRACT FROM AUTHOR]

Arsenic-alkali slag (AAS) is one of the most hazardous solid wastes generated by the antimony smelting process, posing a significant environmental risk. However, the economic method for effective As immobilization in AAS is still lacking. In this study, we proposed an economical and novel method for the removal of As from AAS using siderite (FeCO3). After the sodium carbonate is recovered from the AAS leaching liquor, the process continues. Aqueous As(V) is immobilized as scorodite via continuous dissolution–oxidation of siderite (FeCO3) by air injection. The residual As(V) is immobilized via Fe-As coprecipitation by lime neutralization. The dissolution–oxidation of siderite produces Fe(III), ensuring continuous Fe(III)-As(V) coprecipitation and scorodite crystallization. The results showed that the removal efficiency of As from AAS reached 99.98%. The mixture of scorodite and Fe-As coprecipitation demonstrated good As stability in the Toxicity Characteristic Leaching Procedure (2.6 mg/L) and at pH 4 (1.84 mg/L), pH 6 (2.13 mg/L), and pH 8 (3.20 mg/L) in a 50-d long-term stability test. Combined results from chemical analysis, X-ray diffraction, and infrared spectroscopy revealed that the existence of high ionic strength Na+ and Cl– were the critical factors in the dissolution of siderite and the crystallization of scorodite. This study provides an effective treatment method for the removal and fixation of arsenic in metallurgical AAS. [ABSTRACT FROM AUTHOR]

Outcrops of the coal-bearing Tankhoi Formation (Oligocene–Pliocene), traced along the southern shore of Lake Baikal, submerge under its Southern Basin, where several hydrate-bearing zones of the focused hydrocarbon fluid discharge have been found. To test the hypothesis that coals of the Tankhoi Formation can be the sources of hydrocarbon gases in these zones, we collected coal samples from the Shakhterskaya Gorka outcrop. Experiment on gas generation from the selected samples was carried out in a special autoclave at a temperature of 90°C for eight months. This paper presents the obtained results, which confirm an important role of the process of gas generation from coals in the formation of fluids in the Kedr mud volcano. The further migration of gases was accompanied by the biodegradation and formation of secondary microbial methane due to CO2 reduction. This was one of the reasons for the carbon isotopic pattern observed in methane (heavier than –50‰ VPDB) and carbon dioxide (positive values) taken from the near-surface sediments and hydrates of the Kedr mud volcano, as well as for the significant enrichment of authigenic siderites in the heavy 13C isotope. [ABSTRACT FROM AUTHOR]

A generalization of unpublished and published data since 1985 on biogeochemical, hydrogeochemical, geochemical, mineralogical studies and soil geochemistry at uranium deposits of the Khiagda ore field in the Vitim uranium ore district made it possible to reveal a genetic relation of deep cold carbonated hydrocarbonate–magnesium groundwater containing dissolved hydrocarbons (HCs) to uranium mineralization and ore preservation. The through penetration of epigenetic HCs was traced from the disintegration zone of basement granitoids through overlying sedimentary ore-bearing and volcanosedimentary rocks up to overlying fractured basalts. The assemblage of clarified rocks–HCs–siderites–uranium phosphates U(IV) was commonly found. Carbonated hydrocarbonate–magnesium groundwater and anomalous HC contents in soils can be additional criteria for identifying the Vitim-type uranium deposits in the Trans-Baikal region. [ABSTRACT FROM AUTHOR]

The thermal conductivity of natural monoliths of calcite, dolomite marble, and limestone from various deposits was measured using the absolute stationary method of longitudinal heat flow in the temperature range of 50–300 K and the dynamic method in the range of 323–573 K. A majority of calcite marbles were inferior in thermal conductivity to dolomite marbles. At room temperature, the thermal conductivity coefficients of all studied samples were lower k = 5 W/(m K). The obtained data were compared with the literature data. The diversity of experimental data from different authors on the thermal conductivity of carbonates is associated with qualitative differences in the samples studied

The gas hydrate‐bearing structure—mud volcano Kedr‐1 (Lake Baikal, southern basin)—is located near the coal‐bearing sediments of the Tankhoy formation of Oligocene–Miocene age and can be an ideal source of gas‐saturated fluid. A significant amount of siderite minerals (FeCO3) were collected from sediments at depths ranging from 0.5 to 327 cm below the lake floor (cmblf). An important feature of these carbonate minerals is the extremely strong enrichment in the heavy 13C isotope, reaching values of +33.3‰ VPDB. The δ13C of the siderite minerals, as well as their morphology and elemental composition, and the δ13CDIC of the co‐existing pore water, differed across layers of the core, which implies at least two generations of siderite formation. Here, we leverage mineralogical and geochemical data with 16S rRNA data from the microbial communities in sediments surrounding layers containing siderite minerals. Statistical data reveal the formation of three clusters of microbial communities based on taxonomical composition, key taxa among bacteria and archaea, and environmental parameters. Diversity and richness estimators decrease with sediment depth, with several similar prevailing clades located at the bottom of the core. Most of the taxa in the deep sediments could be associated with putative metabolisms involving organotrophic fermentation (Bathyarchaeia, Caldatribacteriota, and Chloroflexota). Various groups of methanogens (Methanoregulaceae, Methanosaetaceae, and Methanomassiliicoccales) and methanotrophic (Methanoperedenaceae) archaea are present in the sediment at variable relative abundances throughout the sampled depth. Based on the physicochemical characteristics of the sediment, carbon isotope analysis of carbonate minerals and DIC, and phylogenetic analysis of individual taxa and their metabolic potential, we present several models for subsurface siderite precipitation in Lake Baikal sediments. [ABSTRACT FROM AUTHOR]

The kinetics of atmospheric hydrochloric acid leaching of the iron-containing slime formed during quartz–leucoxene sandstone beneficiation is studied. The calculated activation energies indicate two temperature ranges of the slime leaching: a diffusion kinetic region at 40–70°C (Ea = 35.79–36.56 kJ/mol) and a kinetic region at 70–80°C (Ea = 48.68 kJ/mol). A steplike character of the development of slime during the leaching of iron-containing minerals from it is revealed, which is caused by the consecutive processes of siderite and hematite decomposition and a change in the process rate as the solution is saturated with iron ions. [ABSTRACT FROM AUTHOR]

The article describes the theoretical and experimental research data on possibility to improve the quality of the end concentrates of float-and-sink, X-ray luminescent, adhesive and froth separation. The method of nitride hardening is proposed for ferrosilicium grain surface with the hardened layer depth in the range of 30–60 nm for reducing ferrosilicium corrosion rate by 2.7 times at the preserved process properties. The necessity of adding the primary float-and-sink flotation circuit with two-stage magnetic separation to decrease the yield of rough concentrates and to improve their quality owing to removal of 29–95% of siderite. The optimized composition of luminophore-bearing modifying agent ensures complete recovery of earlier unrecoverable diamonds in concentrate at the maximum kimberlite yield of 2.5%. The workbench test processing of difficult diamond-bearing raw materials proves the possibility of incremental diamond concentration in adhesive and froth separation (by 14.0% and 12.7%, respectively), and in the cycle of finishing operations in X-ray luminescent separation (by 25.3%) owing to modification of surface properties of diamond crystals using physicochemical methods and energy deposition. [ABSTRACT FROM AUTHOR]

Siderite (FeCO3) is an important ferrous iron carbonate in the geochemical cycling of iron, as it is a sink for iron under reducing conditions. However, its detection is not straightforward with classical analytical approaches because in natural samples it is often fine‐grained and/or occurs in low concentrations. In this study, we explore the analytical potential of low‐temperature magnetometry. Synthetic siderites with a limited amount of associated ferric iron of up to 5 mol% and some natural siderites were subjected to investigation. Maxima in the cooling curves in a 5 T magnetic field shows that the Néel temperature of siderite is at 37 K in agreement with literature data. Those maxima appear at a higher temperature in the synthetic siderites with associated/sorbed ferric iron; it is 45 K for the 5 mol% Fe3+ synthesis. With the increasing amount of ferric iron, the synthetic siderites show an increasingly prominent remanence tail beyond the nominal Néel temperature in field‐cooled (FC) and zero‐field‐cooled (ZFC) warming curves of the remanent magnetization acquired in 5 T at 5 K. Fine‐grained siderite alters in air on laboratory time scales which is manifested by more pronounced remanence tails up to higher temperatures. Siderite's presence is best diagnosed by evaluating a combination of FC warming curves and a FC/ZFC remanence ratio >3 at 5 K. Standard addition experiments of FC warming curves enable the determination of siderite down to 0.1 wt%. Plain Language Summary: Siderite (FeCO3) is a foremost reservoir of iron, an important biogeochemical element, in sediments under reducing conditions. Therefore, determining how much siderite is present in a sediment is important but not so straightforward: X‐ray diffraction (XRD) is not that sensitive when dealing with fine particles, siderite's typical mode of occurrence. Here, we explore the analytical potential of low‐temperature magnetometry (a sensitive technique) by taking advantage of the magnetic properties of siderite. We document siderite's magnetic properties in the 4–300 K temperature range by studying several synthetic siderites that contain up to a few percentage of associated or sorbed ferric iron and some natural siderites. The temperature below which siderite becomes magnetic, the Néel temperature nominally at 37 K, rises with the ferric iron amount, while exposure to air also rises the temperature, hinting at the development and growth of a surface coating. Low‐temperature magnetometry enables detection of siderite down to 0.1%, that is, the technique is much more sensitive than XRD. Key Points: Fine grained siderites with a limited amount of ferric iron sorbed onto them were synthesizedWarming curves of 5 K remanences of these siderites show a tail beyond its nominal Néel temperature, an effect of the surface coatingFine grained siderite can be detected down 0.1 wt% by processing field‐cooled warming curves [ABSTRACT FROM AUTHOR]

The Late Permian strata of the Xuanwei Formation in the eastern Yunnan region exhibit extensive diverse morphological features within siderite deposits. These variations in siderite deposits suggest potential differences in their formation processes. In this study, fieldwork and comprehensive indoor studies revealed four distinct forms of siderite deposits: stratiform-laminated, lens-like nodule, sandstone cementation, and fracture filling. The stratiform-laminated siderite, varying in color from bluish-grey to dark grey, is composed of uniformly sized microcrystalline to fine-grained siderite along with detrital matter, displaying precise layering and banding structures that suggest direct deposition from cyclic iron-rich seawater under reducing conditions. Lens-like-nodule siderite, which appears grey-yellow, is composed of mud microcrystalline siderite, medium to coarse-grained pseudo-ooids, and glauconite. It shows conformable distribution characteristics resulting from the diagenetic differentiation of iron-rich sediments under reducing conditions during the diagenetic and early diagenetic periods. Siderite as sandstone cementation exhibits a yellow-brown color and consists of dispersed colloidal siderite and cemented siderite clumps that fill intergranular pores of detrital particles. It precipitated under reducing conditions within those intergranular pores. Siderite filling fractures typically appear as vein-like or network-like structures intersecting bedding at large angles. They exhibit grain structures with significant variations in size. These siderite deposits exhibit exceptional purity and result from siderite dissolution during sedimentary periods, followed by reprecipitation within regional extensional fractures during the diagenetic phase. The primary occurrence of siderite deposits in the study area is within coal-bearing strata, as revealed by the integration of sedimentary profiles and sedimentary facies analysis. The coal-bearing strata, influenced by the Emeishan large igneous province, underwent iron enrichment during and after volcanic eruptions while developing a reducing environment, which was facilitated by abundant vegetation. Consequently, geological processes led to siderite layers, lens-like siderite nodules, and siderite cementation. The Yanshan orogeny induced extensive high-angle fracture development in epigenetic coal-bearing strata, facilitating fluid circulation and the redistribution of soluble siderite. This geological activity resulted in the formation of vein-like structures composed of siderite. [ABSTRACT FROM AUTHOR]

In order to clarify the cause of formation of siderite cement, and study the influence of siderite cement on reservoir and its geological model, and explore the influence of siderite-bearing reservoir on oilfield development and production, the study of the cause of formation of siderite cement and its influence on physical properties was carried out. Based on conventional core analysis, thin section analysis and X-ray analysis, statistics on the types and characteristics of cements in middle-shallow reservoirs in the Enping oil area, Pearl River Mouth Basin, reveal that siderite cement is abundant. The redox state and sedimentary environment of the paleo-ocean were used to study the genetic mechanism of siderite and quantitatively study the influence of siderite on middle-shallow reservoir quality. The results show that siderite in the reservoir is the product of the combination of CO2 produced by the degradation of organic matter and Fe2+ enriched in pore water during diagenesis. It formed in the early diagenetic stage when the primary pores of sandstone developed, which has a positive significance for the preservation of the overall pores of the reservoir. However, the local cementation of siderite (mostly developed in thin argillaceous belts) is destructive to the reservoir because it occupies a large proportion of the primary pore space. The "permeability control" effect of siderite cement makes the vertical permeability of the muddy strip much lower than that in other directions, thus greatly increasing the shielding effect of the muddy thin layer on the bottom water, which is conducive to reservoir development. Due to the blocking of argillaceous belts, the reservoir geological pattern will change from bottom water reservoir to edge water reservoir and edge water reservoir to multilayer edge water reservoir, which can be exploited by corresponding development measures. The development of siderite leads to differences in the energy supply in the top, middle and edge of the reservoir, which can guide water injection and improve the well pattern strategy. The research results were applied in Oilfield B, where the horizontal strip interlayer of fulling siderite cements resulted in insufficient energy supply in the high position. By injecting hot water to increase energy, oil field production is doubled, and reservoir recovery is greatly improved.

Stable isotope, trace element, and cathodoluminescence analyses were performed on gastropods and matrix from rock cores of the Middle to Upper McMurray Formation (Lower Cretaceous/Aptian, Northwestern Alberta, Canada) to characterize the extent to which pristine material remained from which depositional environmental conditions could be estimated. Aragonitic gastropod shells retain their original depositional chemistry, and along with other closely associated authigenic carbonate components, indicate that the Middle to Upper McMurray Formation was deposited in a freshwater environment that was part of a continent-scale river system.

Abstract Siderite (FeCO3) is an important ferrous iron carbonate in the geochemical cycling of iron, as it is a sink for iron under reducing conditions. However, its detection is not straightforward with classical analytical approaches because in natural samples it is often fine‐grained and/or occurs in low concentrations. In this study, we explore the analytical potential of low‐temperature magnetometry. Synthetic siderites with a limited amount of associated ferric iron of up to 5 mol% and some natural siderites were subjected to investigation. Maxima in the cooling curves in a 5 T magnetic field shows that the Néel temperature of siderite is at 37 K in agreement with literature data. Those maxima appear at a higher temperature in the synthetic siderites with associated/sorbed ferric iron; it is 45 K for the 5 mol% Fe3+ synthesis. With the increasing amount of ferric iron, the synthetic siderites show an increasingly prominent remanence tail beyond the nominal Néel temperature in field‐cooled (FC) and zero‐field‐cooled (ZFC) warming curves of the remanent magnetization acquired in 5 T at 5 K. Fine‐grained siderite alters in air on laboratory time scales which is manifested by more pronounced remanence tails up to higher temperatures. Siderite's presence is best diagnosed by evaluating a combination of FC warming curves and a FC/ZFC remanence ratio >3 at 5 K. Standard addition experiments of FC warming curves enable the determination of siderite down to 0.1 wt%.

Siderite (FeCO3) is an iron-bearing carbonate mineral that is the most abundant sedimentary iron formation on Earth. Mineralogical alteration of four siderite samples annealed at temperatures 200 °C, 300 °C, 400 °C, 500 °C, 750 °C, and 1000 °C in an O2 and a CO2 atmosphere were investigated using such tools as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), the X-ray fluorescence (XRF) method, differential scanning calorimetry and thermogravimetric analysis (DSC/TGA), and Mössbauer spectroscopy measurements. The decomposition of three siderite samples with similar iron content in the oxygen atmosphere took place in the temperature range of 340–607 °C. This process begins at approximately ~100 °C higher under a reducing atmosphere, but it is completed just above 600 °C, which is a temperature comparable to decomposition in an oxidizing atmosphere. These processes are shifted toward higher temperatures for the fourth sample with the lowest iron but the highest magnesium content. Magnetite, hematite, and maghemite are products of siderite decomposition after annealing in the oxygen atmosphere in the temperature range 300–500 °C, whereas hematite is the main component of the sample detected after annealing at 750 °C and 1000 °C. Magnetite is the main product of siderite decomposition under the CO2 atmosphere. However, hematite, maghemite, wüstite, and olivine were also present in the samples after annealing above 500 °C in this atmosphere. [ABSTRACT FROM AUTHOR]

The mineral association of siderite with Cu–Fe sulfides, cronstedtite, and goethite were first recognized when studying the Mikheevskoe Cu(Mo,Au)–porphyry deposit. This association is confined to fault zones, where it fills a network of mineralized fractures developed on porphyry- and argillizite-type ores. Minerals of this association were also identified in some argillizite samples of this deposit. The formation conditions of this mineral association and its relation to the evolution of the Late Paleozoic porphyry system or other endogenic–exogenic processes manifested during the subsequent geological history of the study area were studied. The integrated research included microprobe analysis and the measurement of O and C stable isotopes in minerals of the studied association in the "Geoanalitik" (Yekaterinburg) and "Geonauka" (Syktyvkar) Centers for Collective Use. The study of mineral compositions and their relationships indicates that the studied mineral association deposited at temperature of about 70°C from neutral or low-acid solutions with varying , HS–, and aSiO2 (aq) contents. The measurements of δ13C (from –5.5 to –18.2‰) and δ18O (from 20.4 to 33.4‰) values in siderite made it possible to calculate the composition of a mineral-forming fluid. It was established that such a fluid has the following parameters: δ18O H2O from –3 to +10‰ and δ13C CO2 from 15 to –28‰. It could correspond to magmatogenic water fluids mixed with Corg-bearing surface water. Based on the obtained results, it is suggested that this mineral association is related to argillizites, the development of which occurred at the last stage of endogenic mineral formation at the Mikheevskoe deposit. Nevertheless, it is not excluded that it may be related with other low-T hydrothermal processes at the stage of Meso-Cenozoic tectonomagmatic activation of the Urals. There is no evidence of the relation of the studied mineral association with weathering crusts. [ABSTRACT FROM AUTHOR]

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The physicochemical properties of siderites (FeCO3) of different origin have attracted attention due to challenges in the diagnostics with the aim of evaluating the involvement of bacteria in the formation of iron-rich sedimentary deposits. A comparative study of siderites of chemical and bacterial origin was performed by Mӧssbauer spectroscopy, X-ray diffraction, and scanning electron microscopy for the purpose of determining the possible characteristics, which will allow the identification of biogenic siderite. It was found that all the characterized siderites have significant differences in the crystal morphology associated with the physicochemical conditions of their formation. Siderites of bacterial origin are characterized by a smaller crystal size compared to siderites of hydrothermal or sedimentary origin. The inhomogeneity of the nearest environment of the iron atoms, which was found for siderites of bacterial origin and which is manifested in the Mӧssbauer spectra as a larger width of the quadrupole shift distribution, can be used as a diagnostic indication of biogenic siderites. [ABSTRACT FROM AUTHOR]

Hydrothermal alteration with bleaching of host rocks is the most important prospecting indicator for gold deposits in the Jiangnan Orogen Belt. The alteration has been identified as pre-ore carbonate (siderite)-sericitization and the Fe of siderite in the alteration zone is derived from the host rocks rather than fluids. In addition, such alteration decreases in intensity and width with depth and gold mineralization also occur in the non-bleached rocks, casting doubt on the reliability of the prospecting indicator. Detailed petrographic work and SEM analysis on the Wangu deposit indicate that there are two types of siderites, i.e., Sd1 and Sd2. Among them, Sd1 grains are relatively small and distributed along the planes of unaltered host rocks, while Sd2 grains, only occurring in the altered slates, are commonly larger. Both types of siderites were altered by auriferous fluids, producing porous cores and minerals such as pyrite, quartz, and ankerite. Compared with unaltered parts, the altered parts have lower Fe, but higher U, Pb, and REE. In addition, Sd1 and Sd2 are similar in Mn, Na, V, and Sr concentrations but different in Fe and Mg. The occurrence and geochemical compositions of both siderites indicate that Sd1 could be transformed into Sd2 by pre-mineralization alteration through dissolution-reprecipitation. Chlorite is another important Fe-bearing mineral in the host rocks, and EPMA analysis suggests that it is ripidolite with relatively high Fe contents. Consequently, chlorite can also provide Fe to form the pre-ore carbonate(siderite)-sericitization. Geochemical modeling demonstrates that both ripidolite and siderite can result in sulfidation and therefore gold precipitation. As a result, this study demonstrates that pre-ore alteration with characterized bleaching is not a prerequisite for gold mineralization despite of its prominent features. Due to the presence of Fe-bearing Sd1 and chlorite, gold mineralization could still occur through sulfidation in the unaltered rocks. [ABSTRACT FROM AUTHOR]

Multiple siderite beds developed in the first member of the Lower Cretaceous Nantun Formation (K1n1) in the basin. The results show that the siderites in K1n1 of the study area are mostly stratiform or massive, with three micromorphological features (dense micronized crystals, bands, and paragenesis with quartz and calcite). The siderite beds are mainly composed of siderite, clay, quartz, calcite, and feldspar. Under the microscope, charcoal, algal fossils, granular pyrite crystals, vein-like siliceous bands, etc., were observed. The oxides in the siderite beds include Fe2O3, SiO2, Al2O3, etc. The trace elements are typically characterized by high Mn and Be contents; low Sr/Ba, Th/U, and Al/Ti ratios; and high V/Cr ratios. These indicate weakly reducing, freshwater depositional paleoenvironments. The δ13Cv-PDB and δ18Ov-PDB values of siderite are −0.20–1.11‰ (mean: 0.62‰) and −18.22‰ to −10.14‰ (mean: −14.23‰), respectively, which shows that the carbon in siderite came mainly from carbonate dissolution. The Fe-bearing rocks in the source area migrated to the basin after undergoing physical and chemical weathering, and when the resultant Fe2+ concentration reached saturation, Fe2+ combined with CO32− in the water bodies to form authigenic siderite. [ABSTRACT FROM AUTHOR]

The article presents results of the biostratigraphic and U–Pb geochronological (detrital zircon) studies of the volcanoterrigenous lacustrine member of the upper subformation (Lower Paleozoic Oldynda Formation), which contains polymetallic massive sulfide ores of the Ozernoe deposit (Kurba–Eravna ore district, western Transbaikalia). The first, second, and "crystalline tuff" horizons of the first ore-bearing level of the Ozernaya member were studied. It is represented by an alternation of tuffs, calcareous, siliceous, carbonaceous tuffites, pelitomorphic limestones, calcareous gravelstones with interlayers and lenses of mineralized tuffaceous conglobreccia and layers of banded siderite pyrite ores. For the first time, bryozoans, algae, and palynoflora were recorded in calcareous tuffaceous siltstones and limestones of the second and "crystalline tuff" productive horizons. These data indicate the Early Carboniferous (Tournaisian) time of sediment accumulation. Results of the U–Pb geochronological studies of detrital zircons from the mineralized tuffaceous conglobreccia of the third productive horizon suggest that the lower boundary of rock formation is not older than Late Cambrian. [ABSTRACT FROM AUTHOR]

Transitional shale gas layers are widely distributed in China, but no significant exploration breakthrough has been made so far. This paper investigates and analyzes the characteristics and gas-bearing mechanisms of transitional shale gas reservoirs in detail, aiming to clarify the shale gas accumulation mechanism of transitional shale and provide theoretical support for the selection of favorable intervals. The transitional shale gas layer is characterized by a thin single-layer thickness, rapid lithological change, low brittle mineral content, and poor kerogen type. The lack of organic matter (OM) sponge pore development process from the oil-generation stage results in limited numbers of OM nanometer-scale pores. Shale pore space is dominated by pores and fractures related to clay minerals. The measured gas content is well consistent with the theoretically calculated gas content for marine organic-rich shales. However, the actual measured gas content is far lower than the theoretically calculated gas content for the transitional shale gas reservoir. The main mechanisms are summarized to be (1) the high hydrocarbon expulsion efficiency of the "sandwich" space structure of the sandstone--shale--coal association, which gives rise to most natural gas migrating into nearby sandstone, and (2) high water saturation resulting in insufficient storage space for free gas in the shale reservoir. Unlike marine shale gas, natural gas in the transitional shale reservoir is primarily dominated by adsorbed gas in kerogen, and free gas is relatively low. The favorable lithofacies types are organic-rich siliceous/calcareous shales. Multiple layers of siderite-bearing shales/siderites are developed vertically and continuously distributed horizontally in transitional strata, particularly in flat-lagoon facies. It is easy to form a "micro-trap" to store gas in siderite-bearing shale, and siderite-bearing shale has strong sealing properties due to low porosity, low permeability and high breakthrough pressure. This property can form overpressure and trap shale gas inside the shale, providing a new research perspective for the optimization of vertical favorable intervals, as well as exploration breakthrough in transitional shale gas. Further research should strengthen the systematic sedimentological study of transitional facies, reveal shale gas occurrence state and dynamic transformation, and optimize favorable interval evaluation systems to clarify the feasibility of coalmeasure gas commingled production. [ABSTRACT FROM AUTHOR]

The manganese ferrite has been processed by mechanosynthesis, using reactive siderite and MnO 2 powder mixtures, with and without subsequent heat treatment. Taguchi planning was used to assess the impact of milling conditions (rotational speed and time) and subsequent calcination temperature on conversion of precursors, based on integrated intensities of the main XRD peaks of precursor phases FeCO 3 (104) and MnO 2 (110), and spinel phase (311), using Ni as internal pattern. Thermogravimetry provided additional information on the residual contents of reactants in the as-milled samples. The best conditions for complete conversion to spinel phase of as-milled samples were obtained by milling at 650 rpm, for 6 h ( I 311 , s p / I 111 , N i = 2.41) , and for calcined samples were obtained after milling at 650 rpm, for 3 h, and calcination at 650 °C (I 311 , s p / I 111 , N i = 2.35). The impact of processing conditions on structural features of the spinel phase was accounted by the contributions to variance of intensity of its (311) reflection, which were 90% ascribed to rotational speed and only 4% ascribed to milling time, for as-milled samples, or 58%, 15% and 16% ascribed to rotational speed, milling time and calcination temperature, for calcined samples. Readier conversion of FeCO 3 relative to MnO 2 occurred during the milling stage, at low or intermediate rotational speed, with impact on M n : F e ratio in the spinel phase, as revealed by changes in lattice parameter of as-milled samples, in the range of 0.8424–0.8464 nm. Subsequent calcination minimized or eliminated traces of secondary phases. The incorporation of magnesium oxide and possibly other secondary components of the siderite precursor also induced structural changes in the resulting spinel phase, mainly in calcined samples (a o = 0.8370–0.8434 nm). Partial oxidation also contributed to structural changes in calcined samples, as revealed by differences between samples calcined in inert and oxidising atmospheres. [ABSTRACT FROM AUTHOR]

Compared with synthetic materials, natural mineral materials have the advantages of low cost and easy availability. In the present study, magnetite was prepared by calcination of natural siderite under an N2 atmosphere and utilized as a heterogeneous material for sulfamethazine (SMT) degradation via peroxydisulfate (PDS) activation. Various characterizations demonstrated that the S600 (siderite calcinated at 600 °C for 1 h) had a high specific surface area (57.18 m2/g) and high electron transfer ability. Under 1 g/L S600 and 1 mM PDS, 99.9% and 50% of SMT (5 mg/L) and TOC were eliminated in 2 h, with a kinetic constant of 0.026 min−1. Increasing the S600 dosage and PDS concentration favored SMT degradation, while inorganic anions and natural organic matter had the opposite effect. Besides this, Electron spin resonance (ESR) analysis and scavenger experiment results demonstrated that hydroxyl radicals (about 62.3%) and sulfate radicals (about 20.2%) played a major role, while Fe(IV) (about 16.5%) played a minor role in SMT degradation. Moreover, various intermediates for SMT degradation were put forward based on the LC–MS/MS results and their toxicity was predicted to decrease. This work provides a vision for water treatment based on natural mineral materials and presents a new idea for the comprehensive utilization of siderite. © 2023 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Magnetization roasting is one of the most effective way of utilizing low-grade refractory iron ore. However, the reduction roasting of siderite (FeCO3) generates weakly magnetic wüstite, thus reducing iron recovery via weak magnetic separation. We systematically studied and proposed the fluidized preoxidation-low-temperature reduction magnetization roasting process for siderite. We found that the maghemite generated during the air oxidation roasting of siderite would be further reduced into wüstite at 500 and 550°C due to the unstable intermediate product magnetite (Fe3O4). Stable magnetite can be obtained through maghemite reduction only at low temperature. The optimal fluidized magnetization roasting parameters included preoxidation at 610°C for 2.5 min, followed by reduction at 450°C for 5 min. For roasted ore, weak magnetic separation yielded an iron ore concentrate grade of 62.0wt% and an iron recovery rate of 88.36%. Compared with that of conventional direct reduction magnetization roasting, the iron recovery rate of weak magnetic separation had greatly improved by 34.33%. The proposed fluidized preoxidation-low-temperature reduction magnetization roasting process can realize the efficient magnetization roasting utilization of low-grade refractory siderite-containing iron ore without wüstite generation and is unlimited by the proportion of siderite and hematite in iron ore. [ABSTRACT FROM AUTHOR]

In this study, low-cost siderite was used to activate peroxydisulfate (PDS, S2O82-)-inactivated Enterococcus faecalis to study the inactivation characteristics and mechanism of siderite/PDS. The results showed that the siderite/PDS had a better inactivation effect on Enterococcus faecalis at pH 3. The sterilization effect increases with the increase of siderite dosage, PDS concentration and temperature. The inactivation rate is decreased with the increase of initial bacterial concentration. Inorganic ions and natural organic matter (NOM) can inhibit the inactivation effect of this technology, and the inhibition intensity is NOM > HCO3− > NO3−. The free radical quenching test shows that HO• is the main oxidizing substance in the sterilization process of siderite/PDS technology. In addition, the main disinfection mechanism is highly reactive oxygen species destroying the cell wall of bacteria and releasing organic compounds in cells. After siderite was reused for four times, simply washing siderite would recover almost 80% of the removal of Enterococcus faecalis in siderite/PDS, indicating that siderite has the potential of recycling. HIGHLIGHTS Enterococcus faecalis (Gram-positive bacteria), a typical disinfection residue bacteria, was used as the indicator microorganism.; The economic and efficient natural siderite was used as the activator of persulfate, and the reusability and structural stability of the recovered siderite are also analyzed.;

• The natural siderite and simulated synthetic siderite were used as PDS activator to remove 2-CP in soils. • Both radical pathway and non-radical pathway were found in the three catalytic systems. • The nZVI can promote the circulation of electronic transfer and dechlorination. • The reaction mechanism and degradation pathway were proposed. Natural siderite (FeCO 3), simulated synthetic siderite and nZVI/FeCO 3 composite were used as green and easily available iron-based catalysts in peroxydisulfate activation for remediating 2-chlorophenol as the target contaminant and this technique can effectively degrade organic pollutants in the soil. The key reaction parameters such as catalysts dosage, oxidant concentration and pH, were investigated to evaluate the catalytic performance of different materials in catalytic systems. The buffering property of natural soil conduced satisfactory degradation performance in a wide pH range (3-10). Both the main non-radical of 1O 2 and free radicals of SO 4 · − and O H · were evidenced by quenching experiment and electron paramagnetic resonance. The reduction of nZVI on FFC surface not only has the advantage for electronic transfer to promote the circulation of Fe(III) to Fe(II), but also can directly dechlorinate. Furthermore, the intermediates were comprehensively analyzed by GC-MS and a potential removal mechanism of three oxidant system for 2-CP soil degradation was obtained. Briefly, this research provides a new perspective for organic contaminate soil treatment using natural siderite or simulated synthetic siderite as efficient and environmental catalytic material. [Display omitted] [ABSTRACT FROM AUTHOR]