High Ag Content Research Articles

Gas-phase electrochemical CO2 reduction on silver-copper BTC MOF in a zero-gap membrane electrode assembly

Bimetallic AgCu-BTC MOFs, derived from Cu-BTC (HKUST-1), have been synthesized by fast co-precipitation method and evaluated for CO2 reduction reaction (CO2RR) using humidified CO2 gas in a zero-gap configuration. Three compositions with varying Ag content – AgCu-1 (9.4 at.%), AgCu-2 (12.5 at.%), and AgCu-3 (16.5 at.%) – were characterized by SEM-EDS, PXRD, FTIR, and XPS. These structural analyzes confirmed the formation of a low-crystalline AgCu-BTC MOF with Ag+1 ions coordinated to the BTC framework. Electrochemical tests (CV and LSV) revealed that AgCu-3 MOF, with the highest Ag content (16.5 at.%), exhibited a more positive onset potential at -0.65 V vs Ag/AgCl compared to HKUST-1 MOF, indicating enhanced CO2RR activity, owing to Ag incorporation. Constant potential (CP) experiments showed that AgCu-3 MOF predominantly produced CO and H2, achieving faradaic efficiency of approximately 65 % for CO production and 5 % for H2 production. Moreover, lowering the relative humidity (RH%) in the inlet CO2 gas stream from 80% to 20% increased CO production by 2-fold from 6.2 µmol s-1 cm-2 to 13 µmol s-1 cm-2, simultaneously suppressing the hydrogen evolution reaction (HER). This reduction in humidity resulted in an increased local concentration of CO2 at the catalyst site, leading to an enhanced CO2RR rate. However, substantial morphological changes have been observed in the AgCu-3 MOF after the CP experiment under humid CO2 reduction conditions.

Rational one-step synthesis of porous PtAg nanowires for methanol oxidation with a CO-poisoning tolerance: An experimental and theoretical study

Binary Pt-based porous nanowires (PNWs) are highly promising for electrochemical applications owing to their high surface areas, abundant active sites, and immense durability against aggregation, but their simple template-free synthesis for methanol oxidation reaction (MOR) is rarely reported. Herein, we provide a simple and template-free method for the one-step fabrication of PtAgx PNWs via autocatalytic and oriented attachment growth mechanism in an autoclave. This drives the formation of ultra-long PtAg PNWs (∼1.5 µm length and 20 nm width) with agglutinated pores (2–10 nm), high Ag content (22–34 at%), and upshifted d-band center. These merits endowed the MOR mass activity of PtAg PNWs (2.22 mA/µgPt) by 2.26 and 2.81 times than those of Pt PNWs and commercial Pt/C catalyst, respectively, based on equivalent Pt mass besides a superior stability and CO-poisoning tolerance. The MOR activity of PtAg PNWs outperformed previously reported PtAg nanostructures. Density functional theory (DFT) simulations confirmed the bifunctional MOR mechanism with a lower energy barrier for dissociative adsorption of methanol molecules (0.49 eV) and CO oxidation on PtAg PNWs than that on Pt PNWs. This study may allow the formation of Pt-based PNWs alloys with various metals for MOR.

Synthesis and biophysical characterization of porous bi-phase calcium phosphate/gelatin-PVA scaffold: Enhanced antibacterial, osteoconductivity and anticancer activity via silver nanoparticles and methotrexate incorporation

In our relentless pursuit of advancing bone tissue regeneration, we have meticulously crafted multifunctional scaffolds that transcend traditional approaches. These freeze-dried scaffolds, composed of biphasic calcium phosphate (BCP) intricately woven into a gelatin-polyvinyl alcohol (PVA) matrix, harbor the potential to revolutionize regenerative medicine. The scaffolds are characterized with XRD, FTIR, SEM, 3D images of the SEM, mechanical properties, swelling and degradation tests, drug release, cell viability, antibacterial and anticancer tests. Our in-situ synthesis of BCP within the PVA framework yielded a biphasic structure comprising hydroxyapatite (HAp) and beta-tricalcium phosphate. These scaffolds exhibit good mechanical compressive strength (ranging from 28 to 173 kPa) and boast high porosity levels (approaching 80 %) enhance the processes of nutrition and waste removal. The incorporation of silver nanoparticles (Ag) introduces antimicrobial prowess, resulting in a complex scaffold texture characterized by well-defined pores and rugged walls. The interconnectivity within this fibrous network contributes to enhanced mechanical properties. Additionally, our scaffolds facilitate the sustained release of methotrexate (MTX), a potent anticancer agent. Within the first day, MTX is promptly delivered, potentially impacting cancer cells. These Ag-containing scaffolds effectively combat common pathogens, demonstrating significant antibacterial activity as an essential property for preventing infections at the implantation site. Notably, our scaffolds, whether infused with Ag or MTX (at a concentration of 0.25 wt%), exhibit no toxic effects on Vero and MG-63 cells within a 24-hour window. However, higher Ag content (2.0 wt%) shows cytotoxicity. In summary, our multifaceted scaffolds, poised at the intersection of science and creativity, hold immense promise for bone tissue engineering. Further investigations will explore long-term effects, broader microbial contexts, and in vivo models.

Suppression of Ag dewetting in submicron Cu@Ag particles in paste for improving sinter bondability through surface modification

Operating temperature of a wide-bandgap semiconductor-based power device can reach 300 °C, which requires a next-generation die-attach sinter material. Ag-coated Cu (Cu@Ag) particles have been considered as a low-cost filler material in pastes for sinter bonding, replacing pure Ag particles. However, there are two main problems: out-diffusion of core Cu and Ag dewetting. Although the Ag shell is sufficiently thick, Ag dewetting induces accelerated out-diffusion of the core Cu and the resultant Cu oxidation through the formation of thin Ag coating parts. Accordingly, a surface-modification method using stearic acid was developed to suppress Ag dewetting and improve the sinterability of Cu@Ag particles. Sinter-bonding characteristics were examined using pastes containing surface-modified submicron Cu@Ag particles. Sinter bonding was conducted at 250 °C under 10 MPa for 1–10 min with N2 blowing using eight types of initial and surface-modified submicron Cu@Ag particles with Ag contents of 10, 20, 30, and 40 wt% (A10, A20, A30, and A40). The shear strength of the bondline containing surface-modified A10 exhibited 17.56 MPa when bonded for 3 min, compared with 11.67 MPa of the initial A10. After a bonding time of 10 min, the shear strength increased to 20.41 MPa. Surface-modified A10 (low Ag content), with the highest efficiency in Ag dewetting suppression, exhibited sinter-bonding characteristics similar to those of Cu@Ag particles with higher Ag contents without surface treatment. Surface-modified A20 provided a sufficient strength of 20.83 MPa after 3 min of bonding.

Experimental study of corrosion rate supplied with an ab-initio elucidation of corrosion mechanism of biodegradable implants based on Ag-doped Zn alloys

Biodegradable Zn-based alloys hold great promise for biomedical implant applications, with the Zn-Ag-Cu alloy being particularly intriguing due to the additional antibacterial and antimicrobial properties. Here, to enhance the mechanical properties of the Zn-4%Ag-1Cu alloy, equal-channel angular pressing (ECAP) is employed, which is found to induce strain and lattice distortions leading to a grain size decrease and corrosion rate enhancement. To understand key factors of the surface degradation behavior on atomistic level, the density-functional theory (DFT)-based method was employed. Specifically, the study investigated the corrosion mechanism of the Zn-Ag-Cu alloy’s surface, providing valuable insights into the degradation behavior of Zn-Ag-Cu alloys. Both experiment and simulation reveal a higher corrosion resistance for the Zn-Ag-Cu alloys with higher Ag content that can be due to a homogeneous distribution of alloying induced stresses. The intermetallic component is shown to have the lowest degradation ability, which is important in terms of its contribution to dispersion hardening of the alloy. This work presents a comprehensive study shedding light on the corrosion rates of Zn-Ag-Cu alloys, providing essential knowledge concerning the mechanisms of the corrosion of Zn-Ag-Cu alloys, which is useful for the development of biodegradable implants with improved structural and degradation characteristics.

Archaeometric Investigation of a Hunnic-Period Sacrificial Assemblage from Nyergesújfalu, Hungary

Near Nyergesújfalu (Komárom-Esztergom County, Hungary), objects of a Hunnic-period sacrificial assemblage were found in 2021. The Hunnic period assemblage contains fifteen items altogether: four gold lunular mounts, six cellwork-decorated gold oval mounts, two cellwork-decorated gold suspension rings, two gold buckles and fragments of a scale-patterned gilded silver plate. The present study aims to determine the elemental composition of the metal alloy of the Hunnic-period objects and characterise the decoration techniques (gilding and garnet inlays) by using optical microscopy, handheld X-ray fluorescence spectrometry (hXRF) and scanning electron microscopy with energydispersive X-ray spectrometry (SEM-EDX). The gold objects, including their small parts such as the rivets of buckles and lunular mounts, sockets and filigree, were manufactured from a relatively goodquality gold alloy (>80 wt% Au). The fragments of the scale-patterned silver plate were manufactured from a high-quality silver alloy (>94 wt% Ag), similar to late Roman silver alloys characterised by high Ag content, and was decorated with fire (mercury) gilding. The garnets used for inlays are almandine and intermediate pyrope-almandine garnets. Based on their chemistry, the garnets belong to Group X and probably originate from the placer deposits of Sri Lanka.

Recovery of silver in the form of value-added spherical silver powder from spent Ag-Al2O3 catalyst by a novel clean method

The spent Ag-Al2O3 catalyst is an important silver secondary resource due to its high content of Ag. However, the most commonly used nitric acid leaching method produces toxic and harmful NOx gases. Herein, a novel clean method was proposed to treat the spent Ag-Al2O3 catalyst using the green leaching agent cerium ammonium nitrate instead of nitric acid to effectively avoid the generation of toxic NOx gases. More importantly, value-added monodisperse micro-sized uniform spherical particles were synthesized directly from the leaching solution by a simple chemical reduction method. The influence of leaching conditions on the leaching ratio of Ag and leaching kinetics were discussed in detail. The response surface methodology was applied to optimize the synthesis parameters of silver powder and explore the interactions between the synthesis process parameters. Under the optimal leaching parameters, the leaching ratio of Ag reached 99.69 %. The leaching kinetic analysis of leaching indicated that the leaching reaction of spent Ag-Al2O3 catalyst was controlled by chemical reaction. By the response surface methodology design, a fitted mathematical model of the particle size for silver powder and the optimum synthesis parameters of silver powder were obtained. The optimum synthesis parameters of silver powder were as follows: [Fe2+] = 1.08 mol/L, [Ag+] = 1.01 mol/L, and dispersant dosage of 2.05 wt%. The average experimental particle size of 1.337 μm was very close to the predicted value of 1.343 μm obtained from the fitted model, indicating that the fitted model of particle size for silver powders was very good. This process not only provides a clean and value-added method for recycling the spent Ag-Al2O3 catalyst, but also helps to promote the balanced and high-value utilization of high-abundance cerium.

Thermal treatments modulate short-chain fatty acid production and microbial metabolism of starch-based mixtures in different ways: A focus on the relationship with the structure of resistant starch

The physiological function of thermally treated starch-based foods was predictively analyzed by in vitro fermentation. Different thermal treatments affected the structure of resistant starch and the presence of harmful substances. The effect of these treatments on their in vitro fermentation properties was emphasized. In this study, undigested components with different structural characteristics were isolated from starch–protein–oil mixtures treated by thermal treatments (boiling, baking, and frying). The structures of digested residues from different thermally treated ternary mixtures were disrupted to varying degrees compared with the control, as evidenced by the reduction of crystalline regions, the break of inter-molecular hydrogen bonds, and damage to molecular structure of rice starch. Baking (1.381 μg/g) and frying (1.696 μg/g) resulted in higher contents of Maillard reaction products (AGEs) than boiling (1.246 μg/g). After fermentation, the content of short-chain fatty acids generated by thermally treated ternary mixtures lowered, correlating with the incomplete structure of resistant starch. By contrast, the species diversity of intestinal microbes increased in thermally treated groups because of their high intestinal pH, which favored the growth of pathogenic bacteria. In addition, the Bacteroidetes/Parabacteroides ratio of the dominant microbes in thermally treated groups was reduced, which was detrimental to the maintenance of intestinal homeostasis. In particular, the high AGE content in baking and frying groups increased the relative abundance of harmful microbes such as Proteobacteria and Pseudomonas.

Synergistic role of oxygen vacancy defect and plasmonics on modulating the photocatalytic activity of Ag/CuOx nanocomposites synthesized via solution plasma

Herein, an environmentally friendly green approach for the single-step synthesis of Ag/CuOx nanocomposite by generating plasma between two copper electrodes in an AgNO3 solution is reported. Morphological tunability of the CuOx nanoparticles from spindle to flower-like and then to wire-like is achieved by varying the concentration of the AgNO3 solution, which regulates toxic dye adsorption. Compositional analysis reveals the formation of oxygen vacancies, indicating the presence of sub-stoichiometric CuO due to the bombardment of plasma-generated species on the as-formed nanoparticle. The percentage of oxygen vacancies decreases with increasing the concentration of AgNO3 to fabricate the nanocomposites. At low Ag content in the Ag/CuOx nanocomposites, higher photocatalytic efficiency is observed than the bare CuOx nanoparticles, whereas for high Ag content, photocatalytic efficiency quenches. Electrochemical spectroscopy reveals an increase in the charge-transfer resistance with Ag content. A possible photo-degradation mechanism based on the trapping and transfer of photo-generated charge carriers between the defect-enriched CuOx and plasmonic Ag nanoparticles is presented. Charge carrier lifetime is investigated to support the photo-degradation mechanism. The effect of H2O2 on the photo-degradation by considering the band edge potential of CuOx nanoparticles is also discussed.

Characterization of laser surface-alloyed Ti-Ni-Ag coatings and evaluation of their corrosion and antibacterial performance

The novel antibacterial Ti-Ni-Ag coatings with various Ag contents (2.1 to 4.6 wt%) were successfully fabricated on TiNi substrate using laser surface alloying. Microstructure, hardness, corrosion and antibacterial properties of the laser surface-alloyed (LSAed) Ti-Ni-Ag coatings were investigated. In the alloyed layers, more Ti2Ni, β-Ti, and Ag particles are formed with a higher Ag content. The hardness of coating with 4.6 wt% Ag is increased by 109 % as compared with the TiNi substrate mainly attributed to the high Ti2Ni content. Compared with TiNi, the corrosion resistance of LSAed Ti-Ni-Ag coatings was enhanced as evidenced by a noble shift in the corrosion potential and a lower passive current density owing to the thicker and denser passive films, which was further confirmed by scanning electrochemical microscopy (SECM), X-ray photoelectron (XPS) and Mott-Schottky analyses. Also, it was found that the released Ag+ ions and Ag particles are responsible for enhancing the antibacterial efficacy of the LSAed Ti-Ni-Ag against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus).

Enhancing the Longevity and Functionality of Ti-Ag Dry Electrodes for Remote Biomedical Applications: A Comprehensive Study.

This study aims to evaluate the lifespan of Ti-Ag dry electrodes prepared using flexible polytetrafluoroethylene (PTFE) substrates. Following previous studies, the electrodes were designed to be integrated into wearables for remote electromyography (EMG) monitoring and electrical stimulation (FES) therapy. Four types of Ti-Ag electrodes were prepared by DC magnetron sputtering, using a pure-Ti target doped with a growing number of Ag pellets. After extensive characterization of their chemical composition and (micro)structural evolution, the Ti-Ag electrodes were immersed in an artificial sweat solution (standard ISO-3160-2) at 37 °C with constant stirring. Results revealed that all the Ti-Ag electrodes maintained their integrity and functionality for 24 h. Although there was a notable increase in electrical resistivity beyond this timeframe, the acquisition and transmission of (bio)signals remained viable for electrodes with Ag/Ti ratios below 0.23. However, electrodes with higher Ag content (Ag/Ti = 0.31) became insulators after 7 days of immersion due to excessive Ag release into the sweat solution. This study concludes that higher Ag/Ti atomic ratios result in heightened corrosion processes on the electrode's surface, consequently diminishing their lifespan despite the advantages of incorporating Ag into their composition. This research highlights the critical importance of evaluating electrode longevity, especially in remote biomedical applications like smart wearables, where electrode performance over time is crucial for reliable and sustained monitoring and stimulation.

Numerical evaluation of the mechanical response of Sn-Ag-Cu lead-free solders of various silver contents

PurposeThere are several lead-free solder alloys available in the industry. Over the years, the most favorable solder composition of tin-silver-copper (Sn-Ag-Cu [SAC]) has been vastly used and accepted for joining the electronic components. It is strongly believed that the silver (Ag) content has a significant impact on the solder mechanical behavior and thus solder thermal reliability performance. This paper aims to assess the mechanical response, i.e. creep response, of the SAC solder alloys with various Ag contents.Design/methodology/approachA three-dimensional nonlinear finite element simulation is used to investigate the thermal cyclic behavior of several SAC solder alloys with various silver percentages, including 1%, 2%, 3% and 4%. The mechanical properties of the unleaded interconnects with various Ag amounts are collected from reliable literature resources and used in the analysis accordingly. Furthermore, the solder creep behavior is examined using the two famous creep laws, namely, Garofalo’s and Anand’s models.FindingsThe nonlinear computational analysis results showed that the silver content has a great influence on the solder behavior as well as on thermal fatigue life expectancy. Specifically, solders with relatively high Ag content are expected to have lower plastic deformations and strains and thus better fatigue performance due to their higher strengths and failure resistance characteristics. However, such solders would have contrary fatigue performance in drop and shock environments and the low-Ag content solders are presumed to perform significantly better because of their higher ductility.Originality/valueGenerally, this research recommends the use of SAC solder interconnects of high silver contents, e.g. 3% and 4%, for designing electronic assemblies continuously exposed to thermal loadings and solders with relatively low Ag-content, i.e. 1% and 2%, for electronic packages under impact and shock loadings.

Synthesis and characterization of chitosan-corn starch-SiO2/silver eco-nanocomposites: Exploring optoelectronic and antibacterial potential

This work discusses the physicochemical and antimicrobial characteristics of chitosan-corn starch eco-nanocomposites integrated with silica@Ag nano-spheres. These composites were synthesized through sol-gel polymerization and subsequently exposed to simulated body fluid (SBF). The incorporation of Ag into the eco-nanocomposites led to a decrease in diffuse reflectance across the entire wavelength range. The dielectric permittivity exhibited an increase up to 52.1 at a frequency of 100 kHz, while the ac conductivity reached a value of 5.2 ∗ 10−6 (S cm−1) at the same frequency for the sample with the highest Ag content. The study utilized XRD and FTIR techniques to examine the materials before and after in vitro testing and evaluated the antibacterial properties of the eco-nanocomposites against several pathogenic microorganisms, including Staphylococcus haemolyticus, Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli, using the agar diffusion method. The eco-nanocomposites demonstrated bioactivity by forming a hydroxy appetite layer on their surfaces and were capable of releasing silver (Ag) at concentrations of 1.3, 1.9, and 2.5 mol%. This study suggests that chitosan-corn starch-SiO2-based doped with Ag eco-nanocomposite has the potential for various applications, including biomedical and environmental fields, where their antibacterial properties can be utilized to combat harmful microorganisms.

Mineralization process of the Mazhala Au–Sb deposit, South Tibet: Constraints from fluid inclusions, H-O-S isotopes, and trace elements

The Mazhala deposit is a typical Au-Sb deposit in the northern Himalayan orogenic belt that has increasingly attracted worldwide attentions. However, debates remain regarding the source of ore–forming fluid and its evolutionary process. Herein, we investigate the genetic and compositional evolutionary characteristics of different types of pyrite grains in order to better constrain the ore–forming fluid source and ore–forming processes by means of Using in-situ trace and sulfur isotope data of pyrite and inclusion temperature and H-O isotope data of quartz. Based on the occurrence and morphological features of pyrite, four types of pyrite (Py0, Py1, Py2, and Py3) have been identified. The framboids of pyrite Py0 have high contents of Au, Ag, Cu, Pb, and Sb, with Co/Ni < l, and their δ34S values range from −34.0‰ to −19.3‰, indicating a sedimentary-diagenetic origin. Py1 pyrite exhibits stark core-rim structure. The contents of Sn, Ti, Be and W in Py1c are higher, with Co/Ni > 1. The δ34S of Py1c ranges from 0.30 to 3.9‰ (mean = 1.7‰), indicating a magmatic hydrothermal transformation origin. Py1r, Py2, and Py3 differ greatly in pyrite morphology and trace element contents, with Co/Ni < 1, indicating as hydrothermal sedimentary transformation origin. The δ34S values of Py1r, Py2, and Py3 vary from 1.4 to 6.50‰, interpreted as the presence of metamorphic sulfur sources. The δ34S values of Py1-Py2-Py3 firstly increases and then decreases, indicatinga fluid mixing process. The Mazhala ore–forming fluid is typical of low temperature (270–291 °C), low salinity (1.1–5.0 wt%NaCl equiv) and CO2-enrichment, with H-O isotopic compositions of quartz resembling magmatic and/or metamorphic water, which makes us to infer a mixture of magmatic and/or metamorphic water source for the Mazhala ore-forming fluid. The early pyrite grains were dissolved and reprecipitated under the action of fluid. In the process of multistage hydrothermal interaction, Au and other trace elements were released from the primary pyrite lattice into the fluid, forming the gold–bearing ore–forming fluid. Separation of fluid phase coupled with significant change in the pH value of fluid prompted the co-precipitation of Au and Sb to form the Mazhala Au-Sb deposit.

Efficiency Boost of (Ag0.5,Cu0.5)(In1‐x,Gax)Se2 Thin Film Solar Cells by Using a Sequential Process: Effects of Ag‐Front Grading and Surface Phase Engineering

AbstractPost‐selenization‐fabricated (using elemental Se vapor) Cu(In,Ga)Se2 solar cell efficiency is limited by a low open‐circuit voltage, which is attributable to the Ga‐deficient surface and insufficient grain growth. In this study, a band‐grading structure is demonstrated by combining Ag‐front and Ga‐back grading in selenized (Ag,Cu)(In,Ga)Se2 (ACIGSe) absorbers with a properly designed precursor structure (Mo/CuGa/In/AgGa) and high Ag content ([Ag]/([Ag]+[Cu]) = 0.5). The phase evolution during post‐selenization reveals that the precursor structure suppresses Ag2Se formation and promotes the ACIGSe phase formed at a low temperature with enhanced grain growth. A widened surface bandgap by Ag‐front grading substantially increases the open‐circuit voltage. Furthermore, Ag addition promotes ordered vacancy compound (OVC) formation on the front surface to enlarge the valence band offset, which in turn reduces interface recombination. Furthermore, the OVC phase also assists interface passivation. Promoting surface OVC phase by Ag addition is also validated by first‐principles calculations. Furthermore, the K‐doped CuGa precursor is used for a ACIGSe absorber to address the significantly reduced carrier density by the Ag addition. With a band‐grading structure and surface OVC phase, the superior device achieves an efficiency of &gt; 19%, the highest efficiency by post‐selenization with an elemental Se source.

Study on injectable silver-incorporated calcium phosphate composite with enhanced antibacterial and biomechanical properties for fighting bone cement-associated infections

Although commonly used in orthopedic surgery, bone cements often face a high risk of post-operative infection. Developing bone cement with antibacterial capability is an effective path for eliminating implant-associated infections. Herein, the potential of silver ions (Ag+) and silver nanoparticles (AgNPs) in modifying CPC for long-term antibacterial property was investigated. Ag+ ions or AgNPs of various concentrations were incorporated in starch-modified calcium phosphate bone cement (CPB) to obtain Ag+-containing (Ag+@CPB) and AgNPs-containing (AgNP@CPB) bone cements. The results showed that all silver-containing CPBs had setting times of about 25–40 min, compressive strengths of greater than 22 MPa, high cytocompatibility but inhibitory effect on Staphylococcus aureus growth. After soaking for 1 week, the mechanical properties and the cytocompatibility of all cements revealed no significant changes, but only CPB with a relatively high content of Ag+ (H-Ag+@CPB) maintained good antibacterial capability over the tested time period. In addition, all the cements showed high injectability and interdigitating capability in cancellous bone and demonstrated augmentation effect on the cannulated pedicle screws fixation in the Sawbones model. In summary, the sustainable antibacterial capability and enhanced biomechanical properties demonstrated that Ag+ ions were more suitable for the fabrication of antibacterial CPC compared to AgNPs. Also, the H-Ag+@CPB, with good injectability, high cytocompatibility, good interdigitating and biomechanical property in cancellous bone, and sustainable antibacterial effects, bears great potential for the treatments of bone infections or implant-associated infections.

The ~1.1 Ga St. Ignace Island complex, Northern Ontario, Canada: Evidence for magma mixing and crustal melting in the generation of Midcontinent Rift-related bimodal magmas and implications for regional metallogeny

Abstract The St. Ignace Island complex in Northern Ontario is a package of dominantly felsic rocks emplaced within the upper portions of the Osler Volcanic rocks of the ~1.1 Ga Midcontinent Rift System. The Osler volcanic rocks are predominantly tholeiitic basalts intercalated with rare interflow sediments and rhyolites. The St. Ignace Island complex is a ~26 km2 stock with a felsic core of quartz-feldspar-phyric rhyolites and dacites and an outer ring of anorthosite and gabbro. Textures at a variety of scales within the rocks of the complex show clear evidence of the mingling and mixing of partially crystallized mafic and felsic liquids. Two multigrain (zircon/baddeleyite) fractions from a sample of the gabbro define a Discordia line with an upper intercept date of 1107±8.9 Ma. The core of the complex consists of dacites and rhyolites with similar REE abundances with negative Nb anomalies whereas the surrounding mafic rocks are gabbros to monzogabbros that are less LREE-enriched than the felsic rocks but with similar HREE. Felsic units have a narrow range of 87Sr/86Sri (0.7032-0.7045) and 143Nd/144Ndi (0.51051-0.51057) whereas the mafic end members have similar 87Sr/86Sri (0.7040-0.7061) but more radiogenic 143Nd/144Ndi (0.51067-0.51085). Very well-preserved silicate melt inclusions (MI), many completely glassy, were observed in quartz, clinopyroxene and some plagioclase phenocrysts from the complex. These represent some of the oldest unrecrystallized silicate melt inclusions described to date. Melt inclusions within quartz from the felsic volcanics are broadly rhyolitic in composition whereas MI from plagioclase in the mafic volcanics range from basalt to basaltic andesite; these felsic and mafic melt compositions are interpreted to represent the end-member liquids in the system and bulk rock analyses affirm mixtures of the two. Concentrations of Cu and Ag (in both mafic and felsic MI), and Mo (in felsic MI), are up to an order of magnitude higher in the mafic and felsic MI than in continental crust. Bulk rock metal concentrations are also significantly lower than in the MI, suggesting that the melt inclusions may preserve pre-eruptive metal tenors that were subsequently modified by sulfide saturation, degassing, or post-solidus hydrothermal alteration. The whole rock and MI geochemistry of the St. Ignace complex are broadly similar to the Central Osler Group and, given the broad similar ages, suggests they may have been derived from a similar mantle source, but distinct from the source of rhyolites in the Black Bay Peninsula. The negative Nb anomalies and negative εNd values for the St. Ignace complex are consistent with mixing with older continental crust during ascent and emplacement. The rocks of the St. Ignace Island complex likely formed as the result of emplacement of a large mafic magma chamber at the base of the Osler volcanic pile that triggered partial melting to generate the rhyolite end members. The felsic melts ascended to shallower levels in the crust where they mixed with mafic magmas derived directly from the deeper chamber. Generally, melt inclusions in the complex have very high Cu and Ag contents, similar to those observed in arc-related and extremely oxidized early rift-related rocks and may account for the world-class volcano-sediment-hosted Cu-(Ag) deposits within the rift and the presence of small porphyry-style deposits.

Occurrence and precipitation mechanism of silver in pyrite from chimney fragments in the Edmond hydrothermal field, Central Indian Ridge

The enrichment of precious elements including Au and Ag in submarine hydrothermal sulfide deposits attracts more and more attention. Previous studies indicate that Au and Ag combine distinctly different ligands under the physico-chemical conditions of submarine hydrothermal systems, therefore, the factors controlling their precipitation may be different. In general, silver mineralization has been much less studied than gold mineralization in submarine hydrothermal sulfide deposits. The Ag mineralization process and precipitation mechanism of submarine hydrothermal sulfide deposits formed at Mid-ocean Ridges are still poorly constrained. In this study, we studied the occurrence and precipitation mechanism of Ag in sulfide deposits of Edmond hydrothermal field, located on the intermediate-spreading Central Indian Ridge (CIR).Three ore-forming stages were identified in chimney fragments collected in the Edmond hydrothermal field. The corresponding minerals are (stage I) anhydrite + barite + colloidal/porous pyrite (Py1) + fine-grained sphalerite; (stage II) marcasite; (stage III) euhedral pyrite (Py2) + coarse-grained sphalerite + chalcopyrite + isocubanite. Py1, characterized by colloidal, porous, and micro-sized anhedral morphology, was usually overgrown by marcasite, which is, in turn, surrounded by euhedral-subhedral Py2, usually coexisting with coarse-grained sphalerite, chalcopyrite, and isocubanite. Compared to marcasite and Py2, only Py1 contains abundant native silver nanoparticles. LA-ICP-MS analyses suggest that Py1 contains higher Pb, Cu, Ag, Mn, Tl, Mo, Au, and lower Co as compared to Py2. In-situ LA-ICP-MS and nanoSIMS analyses indicate that Py1 with higher Ag contents (101–586 ppm) has larger variation in sulfur isotopic compositions (0.8 to 6.6‰) than those of Py2 with lower Ag contents (0.22–15.5 ppm; δ34S values: 2.1 to 4.8‰ for Fe-rich samples and 0 to 2.8‰ for Zn-rich samples).Texture, mineral assemblage, pyrite trace element and sulfur isotopic compositions indicate a progressive decrease on the degree of fluid-seawater mixing as the temperature gradually increases during the growth of the chimneys in Edmond hydrothermal field. Phase diagram analysis indicates that the increase in pH and in particular cooling, due to the mixing of the hot hydrothermal fluid with cold seawater, can significantly decrease the solubility of Ag and be the effective mechanisms of silver precipitation. Our results suggest that mixing of hydrothermal fluid with seawater is the main Ag precipitation mechanism for submarine hydrothermal sulfide deposits formed at Mid-ocean Ridges.

Bismuth ferrite-modified lead-free ceramics with reduced sintering temperature and improved energy storage properties

Dielectric ceramics with high polarization and low sintering temperature are important for high-performance and low-cost multilayer ceramic capacitors (MLCCs). Herein, BiFeO3 was added to a lead-free composition 0.48BaTiO3-0.4Bi(Mg0.5Hf0.5)O3-0.12SrTiO3 to lower the sintering temperature and increase the polarization simultaneously. As a result, a low sintering temperature of 950 °C and high comprehensive energy storage properties with a recoverable energy density Wrec of 5.7 J/cm3 and an energy efficiency η of 92% at 450 kV/cm were achieved. Together with the good temperature stability and cycling stability of Wrec and η, the ceramics exhibit great potential in the energy storage MLCCs with low-cost Ag-Pd electrodes with a high Ag content.

Geology and geochemistry of gold mineralization at the Namicupo prospect, Mozambique Belt, northeastern Mozambique

Auriferous quartz veins in the Namicupo gold prospect occur parallel to the foliation of metasedimentary host rocks of the Xixano Complex in northeastern Mozambique. The geochemistry and ore-forming mechanism of the Namicupo prospect have never been scientifically investigated. This study discusses the ore mineralogy, fluid inclusion, and stable isotope (S-O) characteristics of the prospect. The mineralization in the Namicupo prospect is divided into two stages. The Stage I, primary mineralization, is represented by electrum with Ag contents of 15–26 at.%, associated with pyrite and chalcopyrite. The Stage II is supergene mineralization, characterized by electrum with Ag contents of 39–46 at.%, intergrown with goethite, barite, and minium, which replaced primary sulfides. Quartz from the mineralized veins hosts three types of primary fluid inclusions coexisting in the same fluid inclusion assemblage. Type A inclusions are three-phase aqueous‑carbonic inclusions (aqueous liquid, CO2 liquid and vapor), with final homogenization temperature and salinity varying from 140 to 241 °C, and 1.0 to 7.8 wt% NaCl eq., respectively. Type B inclusions occur either as mono-phase (vapor or liquid) or two-phase (vapor and liquid) CO2-rich, N2-H2O-bearing inclusions, with homogenization temperature varying from +12.9 to +29.3 °C. The Type C inclusions are two-phase (liquid and vapor) aqueous inclusions, which homogenize to liquid phase at temperatures between 209 and 337 °C. The salinity of the Type C inclusions varies from 4.0 to 10.8 wt% NaCl eq. The sulfur isotopic ratios (δ34SCDT) of sulfides associated with Stage I mineralization and the oxygen isotopic ratios (δ18OSMOW) of water calculated from those of quartz from the quartz veins vary from −3.5 to +0.9 ‰ and −1.0 to +2.5 ‰, respectively.The primary mineralization at the prospect is classified as an orogenic-type gold mineralization, formed by aqueous‑carbonic metamorphic fluids. The precipitation of primary gold mineralization in the Namicupo prospect resulted dominantly from fluid immiscibility. The considerable amount of S up to 0.1 wt% and the high Ag contents of electrum intergrown with goethite, minium and barite suggest that the supergene mineralization in the Stage II was caused by oxidation of primary gold-bearing sulfides and Au-rich electrum under moderately acidic and oxidizing conditions, which resulted in Au and Ag liberation, likely by thiosulfate. Dissolution of primary mineralization and supergene gold enrichment in the Namicupo prospect appear to have occurred largely in situ, with little evidence of distant mobilization.