Thermochemical Reduction Research Articles

Textural and geochemical analysis of celestine and sulfides constrain Sr-(Pb-Zn) mineralization in the Shizilishan deposit, eastern China

Breccia-hosted Sr-(Pb-Zn) mineralization from the Shizilishan deposit (Edong district, eastern China) is located at the contact between a Lower Cretaceous (∼139 Ma) quartz diorite porphyry stock and Triassic evaporite-bearing limestone/dolomite sequences. Backscatter electron imaging, electron probe microanalysis, and laser ablation (multicollector-) inductively coupled-plasma mass spectrometry constrain ore genesis based on the textural evolution and trace element and isotope geochemistry in multiple stages of celestine and sulfides (pyrite and marcasite). Complex growth and/or dissolution and/or recrystallization textures of celestine and superposition of pyrite and marcasite are suggestive of evolving fluid compositions and physicochemical conditions during which pH first decreased (favorable for marcasite precipitation) and then increased, facilitating precipitation of Ba-rich celestine and As-rich pyrite. Sphalerite is characterized by enrichment in structurally-bound Sb, Cu, Ag, As, and Tl. Celestine displays Sr and S isotope signatures comparable to Middle Triassic seawater, indicating derivation of both elements from evaporite sequences. Decreasing δ34S in sulfides through the paragenetic sequence may reflect multiple sulfur sources produced by thermochemical reduction of sulfate and/or bacterial sulfate reduction processes. This research highlights that low to moderate salinity fluids, expected to carry significant concentrations of Sr, are able to form large celestine deposits through extensive water–rock interaction when fluid flow is either protracted, or there are superimposed episodes of fluid introduction with high Sr/Ba ratios and moderate dissolved sulfate. The Shizilishan deposit shares some alteration features and geochemical signatures with low-temperature Carlin-type Au deposits (e.g., relative enrichment in As and Tl in ore-stage pyrite) and Fe-poor MVT-type Pb-Zn ores (e.g., high content of Ga and Ge but low Fe, Mn, and In in sphalerite).

A universal chemical-induced tensile strain tuning strategy to boost oxygen-evolving electrocatalysis on perovskite oxides

Exploring effective, facile, and universal tuning strategies to optimize material physicochemical properties and catalysis processes is critical for many sustainable energy systems, but still challenging. Herein, we succeed to introduce tensile strain into various perovskites via a facile thermochemical reduction method, which can greatly improve material performance for the bottleneck oxygen-evolving reaction in water electrolysis. As an ideal proof-of-concept, such a chemical-induced tensile strain turns hydrophobic Ba5Co4.17Fe0.83O14-δ perovskite into the hydrophilic one by modulating its solid–liquid tension, contributing to its beneficial adsorption of important hydroxyl reactants as evidenced by fast operando spectroscopy. Both surface-sensitive and bulk-sensitive absorption spectra show that this strategy introduces oxygen vacancies into the saturated face-sharing Co-O motifs of Ba5Co4.17Fe0.83O14-δ and transforms such local structures into the unsaturated edge-sharing units with positive charges and enlarged electrochemical active areas, creating a molecular-level hydroxyl pool. Theoretical computations reveal that this strategy well reduces the thermodynamic energy barrier for hydroxyl adsorption, lowers the electronic work function, and optimizes the charge/electrostatic potential distribution to facilitate the electron transport between active sites and hydroxyl reactants. Also, this strategy is reliable for other single, double, and Ruddlesden–Popper perovskites. We believe that this finding will enlighten rational material design and in-depth understanding for many potential applications.

Solar Carbo-Thermal and Methano-Thermal Reduction of MgO and ZnO for Metallic Powder and Syngas Production by Green Extractive Metallurgy

The solar carbo-thermal and methano-thermal reduction of both MgO and ZnO were performed in a flexible solar reactor operated at low pressure through both batch and continuous operations. The pyro-metallurgical process is an attractive sustainable pathway to convert and store concentrated solar energy into high-value metal commodities and fuels. Substituting fossil fuel combustion with solar energy when providing high-temperature process heat is a relevant option for green extractive metallurgy. In this study, a thermodynamic equilibrium analysis was first performed to compare the thermochemical reduction of MgO and ZnO with solid carbon or gaseous methane, and to determine the product distribution as a function of the operating conditions. The carbo-thermal and methano-thermal reduction of the MgO and ZnO volatile oxides was then experimentally assessed and compared using a directly irradiated cavity-type solar reactor under different operating conditions, varying the type of carbon-based reducing agent (either solid carbon or methane), temperature (in the range 765–1167 °C for ZnO and 991–1550 °C for MgO), total pressure (including both reduced 0.10–0.15 bar and atmospheric ~0.90 bar pressures), and processing mode (batch and continuous operations). The carbo-thermal and methano-thermal reduction reactions yielded gaseous metal species (Mg and Zn) which were recovered at the reactor outlet as fine and reactive metal powders. Reducing the total pressure favored the conversion of both MgO and ZnO and increased the yields of Mg and Zn. However, a decrease in the total pressure also promoted CO2 production because of a shortened gas residence time, especially in the case of ZnO reduction, whereas CO2 formation was negligible in the case of MgO reduction, whatever the conditions. Continuous reactant co-feeding (corresponding to the mixture of metal oxide and carbon or methane) was also performed during the solar reactor operation, revealing an increase in both gas production yields and reaction extent while increasing the reactant feeding rate. The type of carbon reducer influenced the reaction extent, since a higher conversion of both MgO and ZnO was reached when using carbon with a highly available specific surface area for the reactions. The continuous solar process yielded high-purity magnesium and zinc content in the solar-produced metallic powders, thus confirming the reliability, flexibility, and robustness of the solar reactor and demonstrating a promising solar metallurgical process for the clean conversion of both metal oxides and concentrated solar light to value-added chemicals.

In English

The addition of silver ions or nanoparticles to impart antimicrobial properties to polymeric or other materials is a widely used method. However, it should be noted that the antiviral and antimicrobial effect of silver nanoparticles that come into contact with the environment, associated with their size, with a decrease in the size of nanoparticles, their effectiveness increases sharply. In the present work, we used a biodegradable polymer polylactide (PLA), which is obtained by condensation of lactic acid or ring-opening polymerization of lactide. These studies will further contribute to the development of new safe materials, in particular for food packaging, which is undoubtedly an urgent problem. The work aims is to obtain the silver-containing polymer composites based on polylactide by thermochemical reduction of Ag+ ions using natural (chitosan) and synthetic (polyethyleneimine (PEI)) polymers and to study the structure, morphology, thermomechanical and antimicrobial properties of the obtained nanocomposites. Thermochemical reduction of Ag+ ions in the bulk of polymer films, containing PLA, silver palmitate as a precursor of Ag NP and reducing agent (PEI or chitosan), has been performed by keeping them at 100–170 °C within 5 minutes. The polymeric film composites, cast from chloroform solution, were heated in an oven using precise thermal regulator VRT-3. As a result of reduction, the films get attained silver color, the Ag content in the bulk of films varied from 1 to 4 wt. %, and the thickness of the films was 110 μm. Structure, morphology, thermomechanical and antimicrobial properties of two types of nanocomposites – PLA-Ag-PEI and PLA-Ag-chitosan, formed by the thermochemical reduction of Ag+ in polymer films have been studied using wide-angle X-ray scattering (WAXS) (a DRON-4-07 diffractometer), a transmission electron microscope (TEM) (JEM-1230 JEOL, Japan), and thermomechanical analysis (a UIP-70M device). Antimicrobial activity of the obtained nanocomposites was investigated applying reference strains of opportunistic bacteria Staphylococcus aureus and Escherichia coli. It has been found that thermochemical reduction of Ag+ ions in the bulk of polymer films, when using synthetic or natural polymers (PEI or chitosan) as a reducing and stabilizing agent of silver nanoparticles occurs at 160 °C during 5 minutes. It has been found that the average size of Ag nanoparticles in the polymeric matrix is equal to ~ 7 and ~ 4 nm for PEI and chitosan, respectively. It has been shown that PLA-Ag-chitosan nanocomposites have much higher antimicrobial activity against S. aureus and E. coli strains as compared to PLA-Ag-PEI nanocomposites.

Genetic model for early Cambrian reef limestone-hosted Pb-Zn deposits in the world-class Huayuan orefield, South China: New insights from mineralogy, fluorite geochemistry and sulfides in situ S-Pb isotopes

The Xiangxi-Qiandong metallogenic belt (>300 Mt sulfide ores @∼4.0 wt% Pb + Zn), located at the southeastern margin of the Yangtze Block, is one of the important Pb-Zn producers in China. Although carbonate-hosted Pb-Zn deposits in this district have attracted great attention during past decades, many issues, particularly the ore genesis and geodynamic setting, remain unclear. In this study, we take the Limei and Yutang deposits as typical case studies, using detailed geology, rare earth elements and yttrium (REY) geochemistry of fluorite and sulfides in situ S-Pb isotopes, to propose a new model for early Cambrian reef limestone-hosted Pb-Zn deposits in the district. REY contents (0.47 to 8.67 ppm; mean = 3.99 ppm) in fluorite from Limei and Yutang slightly deplete in LREE and HREE relative to MREE, indicating that the REEs and metals were transported predominantly as chloride complexes in a low-temperature (<200 °C) hydrothermal fluid with high saline. New δ34S values of sulfides (+27.66 to + 35.46‰ in Limei and + 24.80 to + 36.07‰ in Yutang) imply that S2- was originated from evaporite sulfate within ore-hosting strata via thermo-chemical reduction (TSR) as the presence of reducing agents (bioclastic limestone and organic matter). In situ δ34S values show a slightly large range (variation up to 11.27‰) and vary significantly within single grain (up to 4.60‰), which may be inherited from the S composition of H2S in the original fluid. In situ Pb isotopic ratios of sulfides from Limei (206Pb/204Pb = 18.001–18.269, 207Pb/204Pb = 15.645–15.796 and 208Pb/204Pb = 38.243–38.597) and Yutang (206Pb/204Pb = 18.135–18.384, 207Pb/204Pb = 15.714–15.924 and 208Pb/204Pb = 38.347–38.874) positively correlates in Pb-Pb diagrams, indicating the mineralizing metals are mainly derived from Proterozoic basement rocks with an amount of contribution from early Cambrian sedimentary rocks. Mineralogy, fluorite REY geochemistry and sulfides in situ S-Pb isotopes together with previously reported mineralization ages suggest that the mixing of metal-rich fluid from basement rocks and the H2S-rich fluid originated from ore-hosting strata plays an important role in forming the Pb-Zn deposits of Limei and Yutang. This study provides a typical example for better understanding the genesis and geodynamic setting of MVT deposits in the foreland basin, South China.

Application of Porous Materials for CO2 Reutilization: A Review

CO2 reutilization processes contribute to the mitigation of CO2 as a potent greenhouse gas (GHG) through reusing and converting it into economically valuable chemical products including methanol, dimethyl ether, and methane. Solar thermochemical conversion and photochemical and electrochemical CO2 reduction processes are emerging technologies in which solar energy is utilized to provide the energy required for the endothermic dissociation of CO2. Owing to the surface-dependent nature of these technologies, their performance is significantly reliant on the solid reactant/catalyst accessible surface area. Solid porous structures either entirely made from the catalyst or used as a support for coating the catalyst/solid reactants can increase the number of active reaction sites and, thus, the kinetics of CO2 reutilization reactions. This paper reviews the principles and application of porous materials for CO2 reutilization pathways in solar thermochemical, photochemical, and electrochemical reduction technologies. Then, the state of the development of each technology is critically reviewed and evaluated with the focus on the use of porous materials. Finally, the research needs and challenges are presented to further advance the implementation of porous materials in the CO2 reutilization processes and the commercialization of the aforementioned technologies.

Nanocomposites based on polylactide and silver nanoparticles and their antimicrobial and antiviral applications

Novel antimicrobial and antiviral silver-containing nanocomposites (PLA-Ag-PEI) based on polylactide (PLA) have been created by the thermochemical reduction of Ag+ ions in the polymer films. Structure-properties relationships of nanocomposites were investigated using FTIR, WAXS, TEM, DSC, TGA. It was found that thermochemical reduction of Ag+ ions in presence of polyethyleneimine as a reducing agent and stabilizer occurred above 100 °C for 5 min. The optimal parameters of the Ag+ ions reduction process in the polymer films were determined, i.e. 160°С for 5 min. The average size of Ag nanoparticles in the PLA-Ag-PEI was defined to be 6.7 nm. The nanocomposites have demonstrated strong antimicrobial activity against S. aureus and E. coli strains, as well as antiviral activity against herpes simplex virus type 1, influenza A virus and adenovirus serotype 2.

Thermochemical reduction modeling in a high-temperature moving-bed reactor for energy storage: 1D model

The design of robust and efficient high-temperature thermochemical reactors and determination of operating conditions are critical steps toward enabling high-efficiency long-duration solar energy storage. This work presents a computational model for the thermal reduction of a metal oxide material (Mg-Mn-O) up to 1450 °C and the coupled complex transport phenomena in a novel tubular thermal reactor design that features the capability for a high extent-of-reduction (high energy storage density) and inherent heat recuperation. A one-dimensional model coupling counter-current gas–solid flow, two-phase heat transfer, thermochemical redox reactions, and species transport in a moving-bed reactor is developed. Simplified versions of the model are validated with published results in the literature for packed beds with both inert and reactive particles; the fully coupled model is also validated with experimental measurements of a moving-bed reactor in terms of local temperatures and oxygen release at the exit. Detailed comparisons on the effects of different boundary conditions in the reaction zone (prescribed wall temperature vs. heat flux conditions) and formulations based on a simple uniform flow assumption vs. plug flow using Ergun equation for gas flow are investigated. The results are compared with experimental measurements, and for all cases, the energy flow components in the reactor system and the thermal to chemical conversion efficiency and overall system efficiency are computed. The predicted high thermal-to-chemical efficiency ∼95% and system efficiency ∼30% agree with experimental measurements.

Plasma Driven Exsolution for Nanoscale Functionalization of Perovskite Oxides.

Perovskite oxides with dispersed nanoparticles on their surface are considered instrumental in energy conversion and catalytic processes. Redox exsolution is an alternative method to the conventional deposition techniques for directly growing well-dispersed and anchored nanoarchitectures from the oxide support through thermochemical or electrochemical reduction. Herein, a new method for such nanoparticle nucleation through the exposure of the host perovskite to plasma is shown. The applicability of this new method is demonstrated by performing catalytic tests for CO2 hydrogenation over Ni exsolved nanoparticles prepared by either plasma or conventional H2 reduction. Compared to the conventional thermochemical H2 reduction, there are plasma conditions that lead to the exsolution of a more than ten times higher Ni amount from a lanthanum titanate perovskite, which is similar to the reported values of the electrochemical method. Unlike the electrochemical method, however, plasma does not require the integration of the material in an electrochemical cell, and is thus applicable to a wide range of microstructures and physical forms. Additionally, when N2 plasma is employed, the nitrogen species are stripping out oxygen from the perovskite lattice, generating a key chemical intermediate, such as NO, rendering this technology even more appealing.

Investigation of reactive perovskite materials for solar fuel production via two-step redox cycles: Thermochemical activity, thermodynamic properties and reduction kinetics

The investigation and optimization of solar fuels production by H2O and CO2 splitting reactions using non-stoichiometric redox materials as oxygen carriers relies on materials-related studies. The thermochemical cycles performance strongly rely on the thermodynamics and kinetics of redox reactions, as well as the chemical composition and morphology of the reactive redox materials commonly based on ceria and perovskites. This study focusses on the evaluation and selection of suitable non-stoichiometric metal oxides for two-step thermochemical cycles with high fuel production yields, rapid reaction rates, and performance stability. The redox activities of different A- and B-site substituted perovskite materials (ABO3) were experimentally investigated (with A = La, Sr, Y, Ca, Ce, Pr, Sm and B = Mn, Co, Fe, Mg, Al, Ga, Cr). The reactive powders were synthesized via modified Pechini methods providing a porous microstructure especially suitable for thermochemical cycles, while their redox activity was evaluated by thermogravimetric analysis. This experimental screening highlighted the difficulty to combine high reduction extent (δ) achievable by the reactive material with complete re-oxidation extent and fast reaction rates. From the redox activity study of manganite perovskites, La0.5Sr0.5Mn0.9Mg0.1O3 (LSMMg) was pointed out as a good compromise between CO2 splitting activity and thermal stability, possibly competing with ceria as a promising material for two-step thermochemical cycles. Both thermodynamic and kinetic studies were also performed to provide a better understanding of the mechanisms involved in thermochemical cycles. Thermodynamic properties derived from experimental δ(T,pO2) diagrams were used to predict the upper bounds for both reduction extent and fuel production performance at equilibrium. Regarding kinetics, the activation energy during LSMMg reduction was shown to increase with the increase of the non-stoichiometry extent.

Photochemical vapor generation combined with headspace solid phase microextraction for determining mercury species by microwave-induced plasma optical emission spectrometry

A new and simple photochemical vapor generation (PCVG) technique utilizing UVC irradiation combined with headspace solid phase microextraction (HS SPME) is developed for the unified separation and preconcentration of mercury species followed by their determination through miniaturized thermal desorption argon microwave-induced plasma optical emission spectrometry (TD–MIP–OES). Inorganic mercury (Hg2+), methylmercury, and ethylmercury are decomposed and reduced to mercury cold vapor in 2% formic acid through combined UVC irradiation and thermochemical reduction. The mercury vapor is subsequently liberated from the liquid phase and transported to the headspace. Without any tedious sample pretreatments, HS SPME using DVB/CAR/PDMS fiber affords clean and convenient one-step extraction followed by direct desorption into the injection port of the detection system. The 15 min-long UVC irradiation, thermal reduction of mercury species, and preconcentration of mercury vapor resulted in low limits of detection between 0.08 and 0.10 ng mL−1 for all mercury species. The method performance was validated by determining the total mercury and MeHg concentration in a tuna fish certified reference material (ERM CE464) and total mercury in sediment ERM CC580, and the results agreed well with the certified values.

A Wearable Patch Based on Flexible Porous Reduced Graphene Oxide Paper Sensor for Real‐Time and Continuous Ultraviolet Radiation Monitoring

AbstractReal‐time and continuous monitoring of ultraviolet (UV) radiation in daily activity is critical in diverse fields ranging from personal fitness, cosmetics, to medical aspects. Here, a wearable UV monitoring patch that can be easily fixed/removed at desired locations and provide real‐time and continuous UVA levels in daily life is developed. The wearable patch consists of a highly sensitive, flexible graphene sensor for UVA measurement and a multifunctional fabric patch integrated with commercial electronic components for signal processing, wireless transmission. To achieve a high sensitive UVA sensor with high flexibility and long‐term stability, porous reduced graphene oxide (pRGO) papers are fabricated by simple solvent evaporation followed by thermochemical reduction. The flexible UVA sensors based on pRGO papers feature a high UVA photoresponsivity of 125 mA W−1, which is comparable to that of a commercial silicon‐based UV sensor. Furthermore, the polydimethylsiloxane‐encapsulated pRGO (PDMS‐pRGO) sensors exhibit stable UVA photoresponse characteristics that is maintained under severe conditions, such as a large number of bending cycles, thermal heating, and high humidity. The use of wearable patches that enable real‐time, wireless monitoring of personal UVA levels in various practical applications are demonstrated.

Genesis of carbonate-hosted Zn-Pb deposits in the Late Indosinian thrust and fold systems: An example of the newly discovered giant Zhugongtang deposit, South China

The Sichuan-Yunan-Guizhou triangle region contains numerous economically important carbonate-hosted Zn-Pb deposits that occur in the Late Indosinian thrust and fold system rather than foreland basin. In this paper, we investigate the thrust-controlled Zhugongtang deposit (>30.0 Mt ores @ 6.76 wt% Zn and 2.27 wt% Pb) as a case study, using ore deposit geology, in-situ trace elements and isotopes in sulfides, to provide new insights into the ore genesis of the MVT deposits in the thrust belts. The sulfide orebody is structurally controlled by a kilometer-scale thrust system and occurs as open-space fillings, vein or replacement structures. Trace elements in pyrite show a low concentration of Co, Ni, Tl and Se, suggesting that the sulfides were formed under low-temperature (100–250 °C) and slightly reduced conditions. The δ13CPDB values (−7.53 to +1.73‰) in calcite lie between the marine carbonate rocks and sedimentary organic matter, and the calculated δ18Ofluid values (+3.40 to +13.36‰) are different from that of marine carbonate rocks but partly overlap with the basinal brines. Such C-O isotope signature indicates that the carbon was mainly derived from the host rocks (limestone) with additional contribution from organic carbon. The oxygen isotope values suggest mixing of the basinal brine and the limestone. The δ34S values of sulfides within Permian strata (+12.2 to +15.3‰) and Devonian strata (+18.5 to +23.8‰) are similar to the coeval seawater sulfate within the ore-hosting strata, respectively. This indicates that the reduced sulfur is originated from evaporative sulfate within host rocks by thermo-chemical reduction in the near-close system. In-situ Pb isotopic ratios of galena (206Pb/204Pb = 18.566–18.758, 207Pb/204Pb = 15.757–15.769 and 208Pb/204Pb = 39.061–39.366) are comparable with the Proterozoic basement and the country rocks, indicating the mineralizing metals were mainly derived from basement rocks and partly extracted from country rocks via fluid-rock interaction. Regional geological evidence indicates the timing of Zn-Pb mineralization of Zhugongtang is Late Triassic to Early Jurassic and related to the Indosinian orogeny. Overall, the newly obtained trace element and isotopic data together with geological evidence suggest that the Zhugongtang deposit is an MVT deposit formed in the orogenic thrust belt and that fluid mixing was critical for the ore formation.

Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with a p-type low bandgap double perovskite oxide

Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34−x Fe x O6−δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6−δ (BCNFCo), exhibited an optical absorption edge at ∼800 nm, p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm−2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.

In situ trace elements and sulfur isotope analysis of sulfides from the Akiri Cu ± (Ag) deposit, Benue Trough, North-central Nigeria: Implications for ore genesis

The Benue Trough of Nigeria is an intracratonic rift basin hosting several vein-type base metal deposits. The Akiri Cu ± (Ag) deposit represents a distinct sub-class of sediment-hosted Pb-Zn-Cu-Ba mineralization found throughout the Benue Trough. The deposit is hosted in bleached red beds of the Keana Formation and in shale-siltstones and carbonates of the Ezeaku Formation in the Middle Benue Trough, North-Central Nigeria. Mineralization at the Akiri deposit occurs as vein in-fillings in a series of NE-SW and E-W trending faults and fractures in the Early- to Late-Turonian Keana and Eze-Aku sedimentary rocks. To better constrain the sources of ore minerals and structural controls on the formation of this sediment-hosted Cu ± (Ag) mineralization, we report combined geologic, geochemical, mineralogical, and stable isotopic data for the Akiri Cu ± (Ag) deposit. Major ore-stage sulfides at Akiri are chalcopyrite and pyrite, which were accompanied by several types of alteration, including silicification, hematization, limited pyritization, and bleaching of mineralized sandstone bodies. In-situ trace element and sulfur isotopic data distinguishes early-stage pyrite (Py1) from late-stage pyrite (Py2). The late-stage Py2 co-exists with chalcopyrite suggesting coeval precipitation. Early-stage pyrite (Py1) contains lower Ag (avg. 0.04 ppm) but higher Au (avg. 3.03 ppm) than the late-stage pyrite (Py2) (avg. Ag = 2.78 ppm; Au = 0.424 ppm). The δ34S values of the early-stage sulfide (Py1) vary from 19.07‰ to 25.99‰ (avg. 22.20‰), suggesting that sulfur was largely derived from thermochemical reduction (TSR) of seawater sulfate. The δ34S values for co-existing Py2 and chalcopyrite range from 9.83‰ to 11.24‰ (avg. 10.32‰) and from 7.37‰ to 10.69‰ (avg. 8.96‰), respectively, suggesting a derivation of sulfur from TSR of seawater sulfate with contributions from magmatic sulfur. Based on structural features and ore textures, we propose that sulfide precipitation at Akiri was facilitated by sulfur-rich fluids circulating through pre-existing structures (fractures and faults) under fairly high (>200 °C) to moderate (<170 °C) temperature conditions. Geological, mineralogical, geochemical and isotopic data from this study support the classification of the Akiri Cu (+Ag) deposit as an epigenetic sandstone-hosted copper deposit.

Genesis of the Gangcha gold deposit, West Qinling Orogen, China: Constraints from Rb-Sr geochronology, in-situ sulfur isotopes and trace element geochemistry of pyrite

The Gangcha gold deposit, in the western zone of the Xiahe-Hezuo region within the West Qinling orogen of Central China, is a newly discovered medium-scale epithermal gold deposit with 19 tons of identified gold reserves. Mainly hosted in the Permian metasedimentary rocks and Triassic altered volcaniclastic rocks, and gold mineralization is closely associated with pyrite. Here we present results from field observation and geochemical studies of pyrite using electron probe microanalysis (EPMA), in-situ laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and femtosecond laser ablation coupled multi-collector inductively coupled plasma mass spectrometry (fsLA-MC-ICP-MS) analyses. Based on the results, we identified five types of pyrite in the ores and wall rocks (namely Py1, Py2, Py3, Py4 and Py5). Among these, the pre-ore Py1, which is enriched in As, shows markedly negative δ34S values of −30.99 to −17.70‰ that are assumed to be the reflection of abiotic thermochemical reduction of sulfate (TSR) related to extremely oxidized magmas that have assimilated carbonaceous sedimentary rocks. Py2, occurring in the pyrite veins, displays internal rhythmic As- and Au-enriched growth zoning, and the δ34S values of Py2 progressively increase from the cores to the outer rims that are interpreted to result from mixing between the pyrite-forming fluid and magmatic vapor that invaded the main hydrothermal system episodically. The intermediate ore stage pyrite (Py3), represented by the quartz-pyrite (±arsenopyrite) veins, is enriched in As, Sb and Au. The comparable δ34S values of Py3 (−4.59 to + 7.05‰, average + 4.46‰) and Py4 (−5.66 to + 6.50‰, average + 1.80‰) could indicate magmatic sulfur. Compared with pyrites of the earlier stages, the late ore stage pyrite (Py5) is distinctly more enriched in δ34S, and is interpreted to have formed by mixing between a magmatic fluid and meteoric water. Additionally, some of the pyrites (Py5) from Stage V, occurring as the rim of pyrite grain, are interpreted to have formed by replacement via a dissolution-reprecipitation process of the earlier-formed Py4. The Rb-Sr data of pyrites from veins of different mineralization stages yield a mean isochron age of 225.3 ± 2.6 Ma, interpreted as the age of gold mineralization. Based on a combination of geochronological and geochemical date of pyrite, we propose that the ore-forming fluids of the Gangcha gold deposit are closely associated with coeval magmatic activity during the region collisional orogenic event.

Genetic model for Jurassic shale-hosted Zn-Pb deposits of the Arak Mining District, Malayer-Esfahan metallogenic belt: Insight from sedimentological, textural, and stable isotope characteristics

The genetic model, including conditions under which mineralization formed, and relative timing of mineralization are critical questions for SEDEX (or shale-hosted massive sulfide, SHMS) deposits. There is increasing awareness that sub-seafloor replacement is an important process in the formation of some SEDEX deposits. We have studied the Hossein-Abad and Western Haft-Savaran Zn-Pb SEDEX deposits located in the Arak basin of the Malayer-Esfahan Metallogenic Belt, Iran, to address these questions of genesis. This metallotect formed in a back-arc paleotectonic setting as a result of the subduction of the Neo-Tethys oceanic plate beneath the Sanandaj-Sirjan Zone. The rocks that host the mineralization are Jurassic organic matter-bearing, fine-grained sandstones, siltstones, and shales. Asymmetric lenticular bedding, unidirectional flow (based on oblique silt lamination direction relative to horizontal bedding), graded bedding, and clay-rich interbeds indicate sediments were deposited from turbidity currents in a low-energy basin environment.There are three ore facies in the Hossein-Abad and Western Haft-Savaran Zn-Pb deposits: 1) bedded ore; 2) massive ore; 3) feeder zone. Bedded ore contains pyrite framboids and polyframboidal clusters. The size range of the pyrite framboids (3 to 6 µm in diameter) indicates they formed in the water column and not in the subsurface. Characteristic structures in bedded ore are: 1) sulfide-bearing silt injections into clay-filled burrows, 2) injection of sulfide-bearing silt into flame structures of claystone laminae, and 3) organic matter in claystone oriented obliquely relative to bedding. These structures are the result of seismic deformation induced by synsedimentary earthquakes, whereby sulfides that formed in permeable unconsolidated sediment were injected into the organic matter-bearing claystone unit.The δ18O and δ13C values of siderite, calcite and dolomite in veins from the feeder zone and massive ore range from 12.2 to 23.8‰ and −16.7 to 1.7‰, respectively. These values indicate that formational water, seawater and organic matter oxidation-decomposition all played a role in hydrothermal carbonate formation. Melting and homogenization temperatures for CO2 for CO2-bearing fluid inclusions range from −57.5 to −60 °C and 6.6 to 29.5 °C, respectively, and indicate the presence of < 15 mol percent CH4. The CO2 homogenization temperature range suggests the CO2-rich phase is a CO2-CH4 mixture. The CH4 and CO2 in the H2S-bearing fluid were likely generated by biodegradation and oxidation of organic matter via BSR and methanogenesis.The sulfur isotope compositions of pyrite, galena, sphalerite and chalcopyrite from the feeder zone and the massive ores range from δ34S −4.3 to + 7.2‰ and display equilibrium fractionations, indicating that the sulfur originated from two processes: (a) bacterial reduction of seawater sulfate (BSR) (distal from mineralization site), and (b) thermochemical reduction of seawater sulfate (TSR) (in both massive ore and feeder zone). Sulfur isotope geothermometric calculations (Δgalena-sphalerite) for two samples give temperatures in the range 209–224 °C for the massive ore facies. Such high temperatures negate a contribution of sulfur from BSR. However, BSR likely occurred in sediments distal to the feeder zone, where seawater sulfate was bacterially reduced to H2S, and this H2S migrated to the mineralization site during diagenesis. Collectively, the stable isotope data indicate mineralization formed in response to mixing occurred between ascending hot metalliferous hydrothermal fluid that rose up the fault and fracture network, with H2S-bearing fluid and sulfate-bearing percolating seawater, triggering sulfide deposition.

Rb–Sr dating and S–Sr–Nd isotopic constraints on the genesis of the Hehuashan Pb–Zn deposit in the Middle–Lower Yangtze River Metallogenic belt, China

The Hehuashan sediment-hosted Pb–Zn deposit is a large-scale (Pb + Zn＞1 Mt) deposit hosted in the Tongling mining district of the Middle-Lower Yangtze River belt (MLYB). The Pb–Zn ore bodies are composed of two main mineralization types, namely breccia type and massive type. The breccia type ore bodies are hosted by the Triassic limestone and dolostone, while the massive ore bodies are hosted by marble dolostone which are close to the diorite intrusions. The previous research showed that the Hehuashan Pb–Zn deposit is a Mississippi Valley-type (MVT) deposit formed in Middle Triassic and overprinted by late mineralization of magmatic-hydrothermal fluids in Yanshanian period. In this research, we aimed to declare the age of the late mineralization and it's relationship with diorite intrusions. The mineralization age (132.8 ± 3.1 Ma) of the massive ore rocks (late mineralization) is similar to the zircon U–Pb age of the diorite (133–130 Ma), showing that this type mineralization is contemporaneous to the Yanshanian intrusive events. Furthermore, similar initial 87Sr/86Sr values between sphalerite and diorite indicating a magmatic fluid was involved during the mineralization process and the emplacement of diorite also might have provided ore-forming materials. The heavy sulfur compositions (δ34S = +8.6‰ to +12.8‰) of the sphalerite in massive ore rocks indicate that the sedimentary sulfate may have provided reduced sulfur for sulfides precipitation by sulfate thermochemical reduction process. Sr–Nd isotopic compositions of the diorite in the Hehuashan deposit area showed that the massive Pb–Zn mineralization was related to the intrusion of diorite in an extensional tectonic setting. In summary, the Hehuashan Pb–Zn deposit composes a late Yanshanian Pb–Zn mineralization event and represents a younger Pb–Zn mineralization in the Tongling district and MLYB. The Triassic carbonates have the potential for Pb–Zn deposit exploration in the Tongling district and Middle–Lower Yangtze River belt.

SHRIMP 4-S isotope systematics of two pyrite generations in the 3.49 Ga Dresser Formation

The 3.49 Ga Dresser Formation has been considered to host evidence of the earliest microbes metabolising sulfur species on Earth. However, previous bulk analyses and in situ measurements conclude disparate metabolisms based on opposite ΔS. This study first established the generations of pyrite growth, and then measured the multiple sulfur isotopes in situ using Sensitive High Resolution Ion MicroProbe-Stable Isotope analyses. Two main generations of pyrite were revealed based on core-rim textures and multiple sulfur isotopic compositions: ΔS-positive Generation One (G1) and δS- and ΔS-negative Generation Two (G2). In the chert-barite unit, the diluted ΔS-positive and ΔS-negative photochemical products were mainly sequestered in G1 and barite, respectively. G2 were formed via the sulfide pathway with sulfur derived from sulfate reduction and magmatic HS. The δS-ΔS-ΔS systematics suggests an abiological origin for G1, and thermochemical and possible (minor) microbial sulfate reduction for G2.

Epigenic vs. hypogenic speleogenesis governed by H2S/CO2 hydrothermal input and Quaternary icefield dynamics (NE French Pyrenees)

Hypogenic caves, linked to carbonate rock dissolution due to CO2- and H2S-rich ascending deep waters, represent more than 10% of karstic networks worldwide; a proportion that increases as these systems are better constrained. However, interaction between hypogenic and epigenic processes is still poorly understood, especially since the subsequent invasion of surface water often obliterates the morphological and mineral markers of hypogenic activities. The Ariège Valley (French Pyrenean foothills) hosts significant karstic networks epigenically reworked by several episodes of glacier meltwater penetration during the successive coverage of Quaternary icefields. Among these karstic systems, the Vapeur and Ermite caves were probably initiated by a hypogenic component during the Miocene. In particular, multiple-S, Sr, H, C, and O isotopes of thermo-mineral waters and calcite-sulfate speleothems confirm that hydrothermal fluids reached the caves, and subsequently interacted with Quaternary glacial epigenic phases. Deep fluids conveyed CO2 and H2S, both produced from the thermochemical reduction of Triassic evaporites at depth. H2S oxidation and CO2 hydration in the cave atmosphere, above the water table, created sulfuric and carbonic acids responsible for an intense karstification. Interpretation of isotopic data, together with a geomorphological, mineralogical and textural study of cave minerals, allow us to propose a speleogenetic model in which the respective impact of epigenic and hypogenic processes was driven by base-level changes during successive Quaternary glacial/interglacial epochs: (i) during glacial periods, invasion of glacier meltwater within the karst led to the dilution of the hydrothermal water, and was responsible for an “epigenic mechanical-dominant” speleogenesis through water-related abrasion; (ii) interglacial epochs were marked by base-level drops and the establishment of a vadose domain in caves, favoring the widening of karstic conduits through carbonic and sulfuric acid condensation-corrosion during thermal water degassing. This “hypogenic chemical-dominant” speleogenesis was active until a new advance of glaciers, and this cycle occurred several times.