Ag Te Research Articles

Porphyry-Style Petropavlovskoe Gold Deposit, the Polar Urals: Geological Position, Mineralogy, and Formation Conditions

Geological and structural conditions of localization, hydrothermal metasomatic alteration, and mineralization of the Petropavlovskoe gold deposit (Novogodnenskoe ore field) situated in the northern part of the Lesser Ural volcanic–plutonic belt, which is a constituent of the Middle Paleozoic island-arc system of the Polar Urals, are discussed. The porphyritic diorite bodies pertaining to the late phase of the intrusive Sob Complex play an ore-controlling role. The large-volume orebodies are related to the upper parts of these intrusions. Two types of stringer–disseminated ores have been revealed: (1) predominant gold-sulfide and (2) superimposed low-sulfide–gold–quartz ore markedly enriched in Au. Taken together, they make up complicated flattened isometric orebodies transitory to linear stockworks. The gold potential of the deposit is controlled by pyrite–(chlorite)–albite metasomatic rock of the main productive stage, which mainly develops in a volcanic–sedimentary sequence especially close to the contacts with porphyritic diorite. The relationships between intrusive and subvolcanic bodies and dating of individual zircon crystals corroborate a multistage evolution of the ore field, which predetermines its complex hydrothermal history. Magmatic activity of mature island-arc plagiogranite of the Sob Complex and monzonite of the Kongor Complex initiated development of skarn and beresite alterations accompanied by crystallization of hydrothermal sulfides. In the Early Devonian, due to emplacement of the Sob Complex at a depth of approximately 2 km, skarn magnetite ore with subordinate sulfides was formed. At the onset of the Middle Devonian, the large-volume gold porphyry Au–Ag–Te–W ± Mo,Cu stockworks related to quartz diorite porphyry—the final phase of the Sob Complex— were formed. In the Late Devonian, a part of sulfide mineralization was redistributed with the formation of linear low-sulfide quartz vein zones. Isotopic geochemical study has shown that the ore is deposited from reduced, substantially magmatic fluid, which is characterized by close to mantle values δ34S = 0 ± 1‰, δ13C =–6 to–7‰, and δ18O = +5‰ as the temperature decreases from 420–300°C (gold–sulfide ore) to 250–130°C (gold–(sulfide)–quartz ore) and pressure decreases from 0.8 to 0.3 kbar. According to the data of microanalysis (EPMA and LA-ICP-MS), the main trace elements in pyrite of gold orebodies are represented by Co (up to 2.52 wt %), As (up to 0.70 wt %), and Ni (up to 0.38 wt %); Te, Se, Ag, Au, Bi, Sb, and Sn also occur. Pyrite of the early assemblages is characterized by high Co, Te, Au, and Bi contents, whereas the late pyrite is distinguished by elevated concentrations of As (up to 0.7 wt %), Ni (up to 0.38 wt %), Se (223 ppm), Ag (up to 111 ppm), and Sn (4.4 ppm). The minimal Au content in pyrite of the late quartz–carbonate assemblage is up to 1.7 ppm and geometric average is 0.3 ppm. The significant correlation between Au and As (furthermore, negative–0.6) in pyrite from ore of the Petropavlovskoe deposit is recorded only for the gold–sulfide assemblage, whereas it is not established for other assemblages. Pyrite with higher As concentration (up to 0.7 wt %) is distinguished only for the Au–Te mineral assemblage. Taking into account structural–morphological and mineralogical–geochemical features, the ore–magmatic system of the Petropavlovskoe deposit is referred to as gold porphyry style. Among the main criteria of such typification are the spatial association of orebodies with bodies of subvolcanic porphyry-like intrusive phases at the roof of large multiphase pluton; the stockwork-like morphology of gold orebodies; 3D character of ore–alteration zoning and distribution of ore components; geochemical association of gold with Ag, W, Mo, Cu, As, Te, and Bi; and predominant finely dispersed submicroscopic gold in ore.

Thermochemical properties of silver tellurides including empressite (AgTe) and phase diagrams for Ag–Te and Ag–Te–O

This study compiles original experimental and literature data on the thermodynamic properties (ΔfG°, S°, ΔfH°) of silver tellurides (α-Ag2Te, β-Ag2Te, Ag1.9Te, Ag5Te3, AgTe) obtained by the method of solid-state galvanic cell with the RbAg4I5 and AgI solid electrolytes. The thermodynamic data for empressite (AgTe, pure fraction from Empress Josephine Mine, Colorado USA) have been obtained for the first time by the electrochemical experiment with the virtual reaction Ag + Te = AgTe. The Ag–Te phase diagrams in the T − x and logfTe2 (gas) − 1/T coordinates have been refined, and the ternary Ag–Te–O diagrams with Ag–Te–TeO2 (paratellurite) composition range have been calculated.

Stable Te isotope fractionation in tellurium-bearing minerals from precious metal hydrothermal ore deposits

The tellurium isotope compositions of naturally-occurring tellurides, native tellurium, and tellurites were measured by multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) and compared to theoretical values for equilibrium mass-dependent isotopic fractionation of representative Te-bearing species estimated with first-principles thermodynamic calculations. Calculated fractionation models suggest that 130/125Te fractionations as large as 4‰ occur at 100°C between coexisting tellurates (Te VI) and tellurides (Te −II) or or native tellurium Te(0), and smaller, typically <1‰, fractionations occur between coexisting Te(−I) or Te(−II) (Au,Ag)Te2 minerals (i.e., calaverite, krennerite) and (Au,Ag)2Te minerals (i.e., petzite, hessite). In general, heavyTe/lightTe is predicted to be higher for more oxidized species, and lower for reduced species.Tellurides in the system Au–Ag–Te and native tellurium analyzed in this study have values of δ130/125Te=−1.54‰ to 0.44‰ and δ130/125Te=−0.74‰ to 0.16‰, respectively, whereas those for tellurites (tellurite, paratellurite, emmonsite and poughite) range from δ130/125Te=−1.58‰ to 0.59‰. Thus, the isotopic composition for both oxidized and reduced species are broadly coincident. Calculations of per mil isotopic variation per amu for each sample suggest that mass-dependent processes are responsible for fractionation. In one sample of coexisting primary native tellurium and secondary emmonsite, δ130/125Te compositions were identical. The coincidence of δ130/125Te between all oxidized and reduced species in this study and the apparent lack of isotopic fractionation between native tellurium and emmonsite in one sample suggest that oxidation processes cause little to no fractionation.Because Te is predominantly transported as an oxidized aqueous phase or as a reduced vapor phase under hydrothermal conditions, either a reduction of oxidized Te in hydrothermal liquids or deposition of Te from a reduced vapor to a solid is necessary to form the common tellurides and native tellurium in ore-forming systems. Our data suggest that these sorts of reactions during mineralization may account for a ∼3‰ range of δ130/125Te values. Based on the data ranges for Te minerals from various ore deposits, the underpinning geologic processes responsible for mineralization seem to have primary control on the magnitude of fractionation, with tellurides in epithermal gold deposits showing a narrower range of isotope values than those in orogenic gold and volcanogenic massive sulfide deposits.

Multistage alteration, mineralization and ore–forming fluid properties at the Viper (Sappes) Au–Cu–Ag–Te ore body, W. Thrace, Greece.

The mineralogy of ore and hydrothermal alteration of the high-sulfidation enargite–Au–Ag–Te Viper (Thrace) orebody, and fluid inclusions, were studied in drillcore samples. The hydrothermal system has evolved through several stages from pre-ore advanced argillic I+vuggy silica alteration, ore-stage advanced argillic II+vuggy silica alteration and silicification that has developed to argillic alteration (sericite)+silicification through pH increase, and a return to acid conditions as crosscutting post-ore advanced argillic alteration III+silicification. Ore is characterized by early barren pyrite I corroded by: (i) enargite–Au± complex Pb–Bi–Cu sulfosalts, tellurides and selenides, coexisting with euhedral quartz, and (ii) zoned pyrite II distinguished by anomalous concentrations of Au, Cu, As, Te, Bi, Pb, Se, within vuggy quartz. High-grade gold ore is also intergrown with late brecciacementing and vein-type epithermal-like banded quartz+ pyrite. These alteration and mineralization observations are consistent with the changing composition, water fugacity, and density of an expanding column of metal-laden magmatic vapor, combined with changes in structural permeability. Part of the enargite─Au─ quartz assemblages have been probably quenched from sulfosalt melt at high─temperatures (&gt;575°C). End product of the enargite–sulfhide–silica crystallization sequence is the formation of high-grade epithermal quartz-gold colloformbanded ore during cooling and/or dilution/mixing down to ~200°C.

Impact of Different Conditions of Technological Process on Thermoelectric Properties of Fine-Grained PbTe

The aim of this work was to obtain PbTe material in the desired way in order to control the combined impact of lattice disorder, nanoscale precipitates and reduced grain sizes on the thermoelectric properties of this material. To achieve this, PbTe ingot doped with Ag was obtained by the Bridgman method, followed by ball-milling, cold pressing and sintering. In order to estimate crystallites diameters grain size measurements were carried out using the optical microscopy. Studies of electrical and thermoelectric properties of fine-grained material were performed. In order to analyze the morphology and the composition scanning electron microscopy and energy-dispersive X-ray spectroscopy were performed. Energy-dispersive X-ray spectroscopy analysis also revealed presence of Ag–Te precipitates.

Optical properties of Ag- and AgI-doped Ge–Ga–Te far-infrared chalcogenide glasses

Te-based glasses are ideal material for life detection and infrared-sensing applications because of their excellent far-infrared properties. In this study, the influence of Ag- and AgI- doped Te-based glasses were discussed. Thermal and optical properties of the prepared glasses were evaluated using X-ray diffraction, differential scanning calorimetry, and Fourier transform infrared spectroscopy. Results show that these glass samples have good amorphous state and thermal stability. However, Ge–Ga–Te–Ag and Ge–Ga–Te–AgI glass systems exhibit completely different in optical properties. With an increase of Ag content, the absorption cut-off edge of Ge–Ga–Te–Ag glass system has a red shift. On the contrary, a blue shift appears in Ge–Ga–Te–AgI glass system with an increase of AgI content. Moreover, the transmittance of Ge–Ga–Te–Ag glass system deteriorates while that of Ge–Ga–Te–AgI glass system ameliorates. All glass samples have wide infrared transmission windows and the far-infrared cut-off wavelengths of these glasses are beyond 25μm. The main absorption peaks of these glasses are eliminated through a purifying method.

Inherent instability by antibonding coupling in AgSbTe2

In the present paper, an inherent instability in the ternary chalcogenide compound AgSbTe2 is described from the electronic structure viewpoint. Our calculations, which are based on the cluster expansion method, suggest nine stable crystal structures involving the most stable structure with symmetry. The effective pair interactions calculated by the generalized perturbation method point out that the stability of these structures originates from the number of linear arrangements of the Ag–Te–Sb atomic bonds. Moreover, it is found that AgSbTe2 has a special electronic structure, where the dominant components of the top of the valence band are the Te-5p antibonding states. Such an antibonding contribution leads to an inherent instability, such that the system spontaneously forms various mutation phases caused by charge-compensated defect complexes. We propose that these mutation phases play an important role in the thermal conductivity and thermoelectric efficiency in AgSbTe2.

Crystallographic and optical characterizations of Ag(Ga,Al)Te2 layers grown on c ‐plane sapphire substrates by closed space sublimation

AbstractAg(Ga,Al)Te2 layers were grown by the closed space sublimation method on c ‐plane sapphire substrates. The source used was AgAlTe2/AgGaTe2 mixture or AgAlTe2/Ga2Te3 mixture. The crystallographic property of Ag(Ga,Al)Te2 layers was analyzed by X‐ray diffraction (XRD). XRD spectra of layers exhibited very strong 112 diffraction peaks regardless of the variation of the source material mixture. In addition to crystallographic characterizations, optical properties of the Ag(Ga,Al)Te2 layer were evaluated through transmittance measurements. The bandgap energy was decreased when the source mole ratio of Al to Ga was decreased. It was revealed that control regulation of x composition of Ag(Ga1‐x,Alx)Te2 was feasible by varying the source mole ratio Al/(Ga+Al). (© 2016 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Novel method for metal-oxide glass composite fabrication for use in thermoelectric devices

A novel method for thermoelectric materials fabrication using a reduction of oxide precursors in hydrogen was reported. On the example of Bi–Sb, Bi–Sb–Te and Te–Ag–Ge–Sb compounds it was shown that this simple and easy method is suitable for fabrication of two-, three- and even multicomponent thermoelectric materials. It allows controlling a composition, microstructure and even type a of electrical charge carriers. As a result of reduction of oxide precursors a layered structure with an average thickness of layers equal tens of nanometers was formed. At the near-room temperature the best material with a figure of merit (ZT) close to 0.4 was Bi0.8Sb1.2Te3Ox reduced at 340°C for 10h. At 350°C a value of ZT=0.8 was reached by the (GeTe)0.85(AgSbTe2)0.15 (TAGS85) sample reduced twice at 400°C for 10h.

Laser ablation ICPMS study of trace element chemistry in molybdenite coupled with scanning electron microscopy (SEM) — An important tool for identification of different types of mineralization

Using the example of four different types of associations from the Bohemian Massif (greisen-, gold-, base metal-, and “barren granite”-related) and of one porphyry–Cu–Mo(Au) deposit from Uzbekistan, it is shown that molybdenite from a specific type of mineralization possesses a distinct trace-element geochemical composition, which is locally influenced by the presence of relevant mineral phases occurring in the form of sub-nano-, nano- to micron-scale impurities/inclusions. It is documented that, besides typically lattice-bound elements (Re, and W) and isostructural concentrations of Se and Te (substituting for S), molybdenite can concentrate other metals (e.g., Ag, As, Au, Bi, Cu, Nb, Pb, Zn, Zr) which mostly form inclusions or impurities. Typical lattice-bound elements (W, Se, Te) can locally occur as impurities or micro-inclusions. The distribution of Re in molybdenite indicates crustal sources for the group of greisen-, base-metal-, and a few of the granite-related deposits, compared to a mixed mantle/crustal source for the Au-related and majority of granite-related deposits. Greisen-related molybdenites show the highest mean values of As (40ppm), Cu (58ppm), and Zn (45ppm), but the lowest mean Re value (0.4ppm). They contain abundant inclusions of native bismuth, which are accompanied, depending on the individual deposit, by variable quantities of Bi(Se)-, Bi(Pb)-, Pb(Bi)- and Pb–Bi–Cu-bearing phases and also bismuthinite (Bi2S3), wolframite and scheelite. Gold-related molybdenite typically has the highest mean values of Ag (464ppm), Au (24ppm), Bi (1188ppm), Sb (39ppm), and Te (112ppm) and also the highest median values of these elements. Gold mostly occurs as inclusions of native Au or in association with Bi (maldonite) and/or as Bi–Au–Te phases whereas silver is commonly present in the form of Au(Ag), and less commonly as Bi–Te–Ag, Ag–Se and Ag–Te phases. Selenium and Te are either isomorphously bound in the molybdenite structure (similarly to Re and W) and/or form micro-inclusions of different tellurides and selenides. Molybdenite from base metal associations is characterized by the highest mean Pb (3223ppm) and the highest median Ag (12ppm). These metals are present in the form of abundant micro-inclusions of galena locally accompanied by an Ag–S phase and anglesite [PbSO4] with indications of other chalcophile element sub-micro-inclusions. “Barren granite”-related molybdenites, dispersed in the rock matrix, in quartz and/or pegmatite veins and/or located in fractures, have the highest mean and median Ni values (16ppm). These molybdenites are either inclusion-free or contain micro-inclusions and also indications of sub-nano-impurities depending on the locality and a type of mineralization processes reported from the region. For example, inclusions of native bismuth, galena and anglesite occur in molybdenite from Harrachov and Bohutín where base-metal mineralization was exploited in the past. Molybdenite from the Kalmakyr porphyry–Cu–Mo(Au) deposit in Uzbekistan is characterized by the highest mean Re value (236ppm). Rhenium, Se and W have a homogeneous distribution in molybdenite from this deposit. Only galena and anglesite inclusions were identified visually in molybdenite from this type of deposit, while the presence of most likely sub-nano impurities of Cu, Zn and Ag is indicated by LA-ICPMS time-resolved depth profiles.

Combinatorial Study of Ag-Te Thin Films and Their Application as Cation Supply Layer in CBRAM Cells.

In this work, we investigate binary Ag-Te thin films and their functionality as a cation supply layer in conductive bridge random access memory devices. A combinatorial sputter deposition technique is used to deposit a graded Ag(x)Te(1-x) (0 < x < 1) layer with varying composition as a function of the position on the substrate. The crystallinity, surface morphology, and material stability under thermal treatment as a function of the composition of the material are investigated. From this screening, a narrow composition range between 33 and 38 at% Te is selected which shows a good morphology and a high melting temperature. Functionality of a single Ag(2-δ)Te composition as cation supply layer in CBRAM with dedicated Al2O3 switching layer is then investigated by implementing it in 580 μm diameter dot Pt/Ag(2-δ)Te/Al2O3/Si cells. Switching properties are investigated and compared to cells with a pure Ag cation supply layer. An improved cycling behavior is observed when Te is added compared to pure Ag, which we relate to the ionic conducting properties of Ag2Te and the preferred formation of Ag-Te phases.

ChemInform Abstract: Synthesis and Characterization of the Ternary Telluroargentate K4[Ag18Te11

AbstractThe title compound is solvothermally synthesized from a mixture of Ag(OAc), K2Te, and elemental Te in en (autoclave, 160 °C, 5 d, 30% yield).

Geochronological and He–Ar–S isotopic constraints on the origin of the Sandaowanzi gold-telluride deposit, northeastern China

Abstract Northeastern China is characterized by widespread Mesozoic volcanic rocks and Au–Cu–Mo mineral deposits with a total gold reserve of > 2000 t. Amongst those gold deposits, the newly discovered Sandaowanzi has a total reserve of ≥ 25 t of Au and an average grade of 15 g/t. This deposit is important because it is the first reported case of a dominantly Au(± Ag)-telluride deposit containing economically valuable bonanza Au- and Ag-telluride ores in the region. The Sandaowanzi quartz vein system and associated Au–(± Ag)-telluride mineralization are mainly hosted by trachyandesites and andesitic breccias. Native gold is closely associated with abundant tellurides including petzite, sylvanite, calaverite, hessite, and altaite. Twelve pyrite samples from the alteration zone yield a well defined Rb–Sr isochron age of 119.1 ± 3.9 Ma, which is in agreement with a robust Rb–Sr isochron age of 121.3 ± 2.6 Ma derived from 10 auriferous quartz samples. The obtained isochron age of ~ 120 Ma represents the formation of the Sandaowanzi gold-telluride epithermal system, which is much younger than the host trachyandesite with a zircon U–Pb age of 312.5 ± 0.5 Ma and the spatially associated monzogranite with a zircon U–Pb age of 182.2 ± 1.1 Ma. Dating results indicate a close relationship between the local Au–Ag–Te mineralization and a magmatism episode in the Early Cretaceous. Noble gas (He and Ar) isotopes obtained from telluride, sulfide and quartz and sulfur isotopes determined from sulfides including chalcopyrite, sphalerite and pyrite demonstrate clear mixing trends between crustal and mantle-derived components, confirming a significant contribution of fluid produced from mantle-derived magmas into the epithermal system. Like many Mesozoic porphyry Cu–Mo ± Au deposits, the coeval epithermal Au–Ag ± Te deposits in the region are genetically related to magmatism triggered by the subduction of the Pacific oceanic plate beneath the Eurasian continent at the time.

Geochemical and geochronological constraints on the formation of shear-zone hosted Cu–Au–Bi–Te mineralization in the Stanos area, Chalkidiki, northern Greece

Copper–gold–bismuth–tellurium mineralization in the Stanos area, Chalkidiki Peninsula, Greece, occurs in the Proterozoic- to Silurian-aged Serbomacedonian Massif, which tectonically borders the Mesozoic Circum-Rhodope metamorphic belt to the west and crystalline rocks of the Rhodope Massif to the east. This area contains the Paliomylos, Chalkoma, and Karambogia prospects, which are spatially related to regional NW–SE trending shear zones and hosted by marble, amphibolite gneiss, metagabbro, and various muscovite–biotite–chlorite–actinolite–feldspar–quartz schists of the Silurian Vertiskos Unit. Metallic minerals occur as disseminated to massive aggregates along foliation planes and in boudinaged quartz veins. Iron-bearing sulfides (pyrite, arsenopyrite, and pyrrhotite) formed prior to a copper-bearing stage that contains chalcopyrite along with galena, sphalerite, molybdenite, and various minerals in the system Bi–Cu–Pb–Au–Ag–Te. Fluid inclusion homogenization temperatures of primary aqueous liquid–vapor inclusions in stage I quartz veins range from 170.1°C to 349.6°C (peak at ~230°C), with salinities of 4.5 to 13.1wt.% NaCl equiv. Calculated isochores intersect P–T conditions associated with the upper greenschist facies caused by local overpressures during late-stage tectonic movement along the shear zone in the Eocene, which produced stretching and unroofing of rocks in the region. Values of δ34S for sulfides in the Stanos shear zone range from 2.42 to 10.19‰ and suggest a magmatic sulfur source with a partially reduced seawater contribution. For fluids in equilibrium with quartz, δ18O at 480°C varies from 5.76 to 9.21‰ but does not allow for a distinction between a metamorphic and a magmatic fluid.A 187Re–187Os isochron of 19.2±2.1Ma for pyrite in the Paliomylos prospect overlaps ages obtained previously from intrusive rocks spatially-related to the Skouries porphyry Cu–Au, the Asimotrypes Au, and the intrusion-related Palea Kavala Bi–Te–Pb–Sb±Au deposits in northern Greece, as well as alteration minerals in the carbonate-replacement Madem Lakkos Pb–Zn deposit. Ore-forming components of deposits in the Stanos area were likely derived from magmatic rocks at shallow depth that intruded an extensional shear environment at ~19Ma.

First-principles investigations of defect and phase stabilities in thermoelectric (GeTe)x(AgSbTe2)1−x

We focus on the defect and phase stabilities in the pseudo binary alloy (GeTe)x(AgSbTe2)1−x (TAGS; tellurium antimony germanium silver). TAGS is expected to be a high effective thermoelectric material because its thermal conductivity shows anomalous behavior around the concentration of x = 0.8. The origin of the anomalous thermal conductivity and the stable structure in TAGS have not been well understood. To clarify the stable structure, we calculate the formation energies of the point and complex defects. It is found that the chain structure of Ag–Te–Sb has a lower formation energy in GeTe, and the system becomes more stable by assembling the Ag–Te–Sb chain structures. Moreover, the calculated mixing energy also shows that the TAGS system tends to undergo phase separation. In such structures, the grain boundary plays an important role in inducing large phonon scattering, leading to the thermal conductivity reduction.

Synthesis and Characterization of the Ternary Telluroargentate K4[Ag18Te11

AbstractThe ternary potassium telluroargentate(I), K4[Ag18Te11], was prepared by solvothermal synthesis in ethylenediamine at 160 °C. It crystallizes in the cubic space group Fm$\bar{3}$m (no. 225) with the cell parameter a = 18.6589(6) Å. The crystal structure can be described as a [Ag18Te11]4– three‐dimensional anionic framework with the voids accommodating potassium cations. Chemical bonding analysis reveals polar covalent Ag–Te bonds and considerable Ag–Ag interactions, which support the complex anionic character of the structure. The compound is thermally stable up to 450 °C in an inert atmosphere.

Ore petrography and chemistry of the tellurides from the Dongping gold deposit, Hebei Province, China

The Dongping gold deposit is a mesothermal lode gold deposit hosted in syenite. The ore petrography and chemistry of the tellurides from the alteration zone of the deposit have been studied in detail using optical microscopy, scanning electron microscopy, electron probe micro-beam and X-ray diffraction facilities. The tellurides, consisting mostly of calaverite, altaite, petzite tellurobismuthite and tetradymite, are hosted irregularly in pyrite fractures and voids. In the ore bodies, the species and quantity of tellurides decrease from the top downwards, accompanied with lowering of gold fineness, and the existence of tellurides exhibits a positive correlation with gold enrichment. Mineral paragenesis and chemical variations suggest that during evolution of the ore-forming fluids Te preferably incorporated with Pb to form altaite, followed in sequence by precipitation of petzite, and calaverite when Ag has been exhausted, and the residue fluids were enriched in Au, giving rise to formation of native gold. Calculation with reference of the fineness of native gold coexisting with the tellurides indicates that at 300°C, log f (Te2) varied between −8.650 and −7.625. Taking account of the Au–Ag–Te mineral paragenesis, it is inferred that log ƒ (Te2) varies from −9.12 to −6.43, log ƒ (S2) −11.47 to −8.86. In consideration of the physicochemical conditions for formation of tellurides, with comparison to some known telluride deposits, it is suggested that high log ƒ (Te2) is a key factor for high fineness of native gold as well as precipitation of abundant tellurides.

Generation of Au(p)Ag(q)Te(r) clusters via laser ablation synthesis using Au-Ag-Te nano-composite as precursor: quadrupole ion-trap time-of-flight mass spectrometry.

Metal tellurides have applications in various fields of science and technology but only a few gold-silver tellurides have been reported. The laser ablation synthesis (LAS) method allows the preparation of nano-materials from solid substrates. Therefore, this method was selected to synthesise some gold-silver tellurides. Laser desorption ionisation quadrupole ion trap time-of-flight mass spectrometry (LDI QIT TOF MS) was used for the generation of new Au(p)Ag(q)Te(r) clusters. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to characterise the materials. The stoichiometry of the clusters generated was determined via collision-induced dissociation (CID) and modeling of isotopic patterns. Chemisorption of gold and silver nano-particles on tellurium powder led to the formation of a new kind of Au-Ag-Te nano-composite. The LDI of this nano-composite yielded nine unary (Ag(q), Te(r)), 40 binary (Au(p)Te(r) and Ag(p)Te(r)) and 78 ternary clusters. The stoichiometry of these novel Au(p)Ag(q)Te(r) clusters is reported here for the first time. The new Au-Ag-Te nano-composite was found to be a more suitable precursor for the generation of clusters than the mixtures of the elements. TOF MS was shown to be a useful technique for following the generation of gold-silver tellurides. Knowledge of the cluster stoichiometry could accelerate the further development of novel high-tech materials such as chalcogenide glasses.

Synthesis and antimicrobial activity of gold/silver-tellurium nanostructures.

Gold-tellurium nanostructures (Au-Te NSs), silver-tellurium nanostructures (Ag-Te NSs), and gold/silver-tellurium nanostructures (Au/Ag-Te NSs) have been prepared through galvanic reactions of tellurium nanotubes (Te NTs) with Au(3+), Ag(+), and both ions, respectively. Unlike the use of less environmentally friendly hydrazine, fructose as a reducing agent has been used to prepare Te NTs from TeO2 powders under alkaline conditions. The Au/Ag-Te NSs have highly catlaytic activity to convert nonfluorescent Amplex Red to form fluorescent product, revealing their great strength of generating reactive oxygen species (ROS). Au/Ag-Te NSs relative to the other two NSs exhibit greater antimicrobial activity toward the growth of E. coli, S. enteritidis, and S. aureus; the minimal inhibitory concentration (MIC) values of Au/Ag-Te NSs were much lower (>10-fold) than that of Ag-Te NSs and Au-Te NSs. The antibacterial activity of Au/Ag-Te NSs is mainly due to the release of Ag(+) ions and Te-related ions and also may be due to the generated ROS which destroys the bacteria membrane. In vitro cytotoxicity and hemolysis analyses have revealed their low toxicity in selected human cell lines and insignificant hemolysis in red blood cells. In addition, inhibition zone measurements using a Au/Ag-Te NSs-loaded konjac jelly film have suggested that it has great potential in practial application such as wound dressing for reducing bacterial wound infection. Having great antibacterial activitiy and excellent biocompatibility, the low-cost Au/Ag-Te NSs hold great potential as effective antimicrobial drugs.

Methods for the determination of stable Te isotopes of minerals in the system Au–Ag–Te by MC-ICP-MS

The measurement of stable isotopes in ore- and ore-related minerals can provide insight into the geochemistry and formation of metal-bearing ore systems. Currently, there are few high-precision studies of the natural variability of stable tellurium isotopes, most of which are focused on meteorites and sulfides and are related to cosmogenesis; there are no modern studies on the variability of tellurium isotopes within native tellurium and tellurides from ore-forming systems. Tellurium is an element of interest due to its common association with gold in geologic systems, as well as its rarity in the Earth's crust and increasing industrial demand for applications such as photovoltaics. This study presents a method by which tellurium can be sampled from Au–Ag tellurides and native tellurium, isolated by ion exchange chromatography, and analyzed for isotopic composition by multi collector-inductively coupled plasma-mass spectrometry (MC-ICP-MS). Using a micromill, a sufficient mass of telluride or native Te sample can be extracted from coexisting ore and gangue minerals from ∼100 μm wide by ∼50 μm deep drilled holes. Acid digestion of micromilled samples and subsequent ion exchange chromatography isolated Te from matrix metals. The chromatography procedure has Te yields of 96% and produces no net fractionation of Te isotopes. MC-ICP-MS analyses were performed using two techniques, both of which employed the doping of samples using Cd to correct for instrumental mass bias. The first method was the introduction of 100 ppb Te-bearing solutions (with 100 ppb Cd) using a desolvating nebulizer (Aridus II). The second method involved solution nebulization of 2 ppm solutions of Te (with 1 ppm Cd) into the plasma of the MC-ICP-MS. Although the wet and dry methods produce statistically identical delta values, precision is increased using the wet method. The average uncertainty (two standard deviations of the mean) using the Aridus II is ±0.20‰ for 130/125Te (dry method), whereas that for the wet method is ±0.08‰. Repeated analyses of the Te standard over a period of ∼15 months by solution nebulization yielded an external precision of ±0.10‰ for 130/125Te. Natural, hypogene tellurides (calaverite, hessite, krennerite, and sylvanite) and native tellurium samples (n = 32) have a range of 1.64‰ in the isotope composition 130/125Te, demonstrating resolvable, disparate isotope ratios between samples from different areas and between samples from the same locality (e.g., Cripple Creek, Colorado). Fractionation of Te isotopes was caused by mass-dependent geological processes.