Au Mn Research Articles

Genesis of tungsten mineralization in the Yangla copper-polymetallic deposit, northwest Yunnan, China: Evidence from in situ U-Pb dating, trace elements, Sr isotopes, fluid inclusions, and H-O isotopes of scheelite

Scheelite is one of the main ore minerals in tungsten deposits, and its geochemical features can be used to examine and constrain tungsten mineralization. The Yangla deposit is one of the most important Cu-polymetallic skarn-porphyry deposits in the “Sanjiang” polymetallic metallogenic domain, Southwest China, hosting 150 Mt of Cu ores with economic concentrations of Pb, Zn, and Sb. The newly discovered tungsten mineralization in the Yangla deposit remains poorly understood. Hence, in order to ascertain the timing of tungsten mineralization, investigate its genetic relationship with magmatism and ore genesis, and elucidate the source, nature, and evolution of the ore-forming fluids, we performed a combined study of geochronology, in-situ trace elements, fluid inclusions, H-O isotopes, and in-situ Sr isotopic compositions of scheelite. In-situ U-Pb dating of scheelite showed that the timing of tungsten mineralization was 30 Ma. This mineralization age is significantly later than the published Cu mineralization age (∼230 Ma), skarn (∼231 Ma), and granitoid emplacement age (∼230 Ma) in the Yangla ore district. In-situ trace element analyses revealed that scheelite is depleted in Mo, Mn, and Ta and slight enriched in Sr, Y, REEs, and Au. It is also characterized by HREE-depleted chondrite-normalized patterns with strongly positive Eu anomalies. Our data reveal that 3Ca2+ = (2REE)3++□Ca (site vacancy) is the main substitution mechanism that controls REEs in scheelite. The low concentrations of Mo, negative Ce anomalies, and positive Eu anomalies of scheelite indicate a reduced condition. Preliminary REEs features indicate that the genesis of scheelite may be related to vein-type W (Au) deposits. The homogenization temperatures for fluid inclusions present a strongly decreasing trend (328 to 173 ℃), indicate that cooling is the predominant mechanism for the formation of scheelite. The δD and δ18Ofluid values from fluid inclusions of scheelite vary broadly from −161.70 ‰ to −133.30 ‰ and from 6.32 ‰ to 9.80 ‰, respectively, indicating a mixture of magmatic and meteoric water, with possible involvement of magma degassing and fluid–rock interaction. The initial 87Sr/86Sr ratios of scheelites (0.71931– 0.72117) are significantly higher than those of the granodiorite (0.71149 – 0.71990) and basalt (0.70562 – 0.70995) in the Yangla ore district, indicating that the Oligocene magmatism and Devonian marble with radiogenic Sr isotopic compositions contributed to tungsten mineralization. The fluid-rock interaction between the ore-forming fluids derived from the concealed granitoids and the Devonian wall rocks may play an important role in tungsten mineralization and provide significant Ca for scheelite precipitation. Thus, the tungsten mineralization should be associated with Oligocene magmatism, ruling out the genetic relationship with Late Triassic magmatism and being significantly different from the skarn-porphyry Cu-Pb-Zn mineralization at Yangla.

High Promoting of Catalytic Cracking of Light Diesel by Au–Mn Modified ZSM-5 for Propylene Production

High Promoting of Catalytic Cracking of Light Diesel by Au–Mn Modified ZSM-5 for Propylene Production

Neutron activation analysis of meteorites at the VR-1 training reactor

Samples of space objects were characterized using instrumental neutron activation analysis (NAA) combined with conversion electron Mössbauer spectrometry. Fragments of Moldavites, Muonionalusta meteorite and Sikhote-Alin meteorite were irradiated in the thermal neutron field of the low-power VR-1 training reactor operated by the Czech Technical University in Prague. Activated samples were investigated by means of nuclear gamma-spectrometry technique (semiconductor HPGe detector). Qualitative analysis revealed the occurrence of Na, Al, Mg, Cl, K, Ti, V, Mn, Fe, Sr, and Ba in Moldavites, Na, Cl, Mn, Fe, Co, Cu, Ni, As, and Au in Muonionalusta iron meteorite, and Ni, Co, Fe, and Mn in Sikhote-Alin iron meteorite. Employing the comparative NAA, the concentration of Na, Al, K, Ti, V, Fe, and Sr in Moldavite, concentration of Na, Fe, Ni, and Au in Muonionalusta meteorite, and concentration of Ni in Sikhote-Alin meteorite was determined. Moreover, Muonionalusta meteorite structure was investigated using the conversion electron Mössbauer spectrometry at room temperature, and α-(Fe, Ni) phase and γ-(Fe, Ni) phase were identified. The obtained results clearly show that the low-power VR-1 research reactor (80 W) is an excellent tool for NAA experiments, and that nuclear-analytical techniques can provide useful data for other scientific branches.

Ab initio investigation of supported Au–Mn nanowires

We present an ab initio study of surface supported Au–Mn nanowires. Three different substrates are discussed: Cu(110), stepped Cu(111) and Si(001) surface. The emergence of stable antiferromagnetic (AFM) solutions in Au–Mn nanowires was found in all three cases. We found the nonzero magnetic moments of Mn atoms, however, the bulk of manganese is paramagnetic. The critical temperature of the Au–Mn wires is calculated by means of kinetic Monte Carlo simulation. The strong size-effect of the critical temperature is demonstrated.

Unusual magnetic properties of Au–Mn nanowires on copper and silicon substrates

The quantum properties of bimetallic supported Au–Mn nanowires on copper and silicon substrates were studied. As a result of ab initio calculations it was found that Au–Mn nanowires are antiferromagnetic in the ground state. The strong dependence of magnetic properties of supported Au–Mn nanowires on the substrate geometry and component composition was revealed. Analysis of wire geometry shows that Mn atoms are embedded into the silicon substrate. Results of our study show the strong suppressing of exchange interaction in Au–Mn nanowire on nonmetal silicon substrate in comparison to copper ones. A significant decrease was found for the energy difference ΔE between antiferromagnetic and ferromagnetic states of the supported Au–Mn nanowires in comparison to freestanding nanowires as the result of nanowire–substrate interaction.

Electrochemical fabrication of nanoporous gold decorated with manganese oxide nanowires from eutectic urea/choline chloride ionic liquid. Part III − Electrodeposition of Au–Mn: a study based on in situ Sum-Frequency Generation and Raman spectroscopies

In two previous papers (C. Mele, M. Catalano, A. Taurino, B. Bozzini. Electrochim. Acta 87 (2013) 918; B. Bozzini, A. Gianoncelli, C. Mele, M. Kiskinova. Electrochim. Acta 114 (2013) 889), we have: (i) fabricated high-capacitance materials consisting of nanoporous gold (NPG)-supported MnO2 nanowires (NW), by electrochemical etching of single-phase Au–Mn alloys electrodeposited from a deep eutectic solvent (DES) electrolyte and (ii) investigated some aspects of the precursor Au-Mn alloy electrodeposition process by following it in situ with space-resolved soft X-ray fluorescence (XRF) and absorption (XAS) microspectroscopies: this study has allowed to single-out the peculiarities of elemental and chemical-state distribution that contribute to the nanostructure fabrication. The present paper completes the electrodeposition study by investigating the potential-dependent interfacial composition of the growing Au-Mn alloys by complementary in situ linear (Raman) and non-linear (Sum-Frequency Generation − SFG) vibrational spectroscopies. The results regarding alloy electrodeposition are compared to those obtained with a pure Au bath. In situ spectroscopy during electrodeposition reveals that both choline cation and urea are present at the growing metal/DES interface, coadsorbed with CN− resulting from the decomposition of the Au complex. Electrostatic adsorption controls the surface coverage scenario at the Au/DES interface, while Mn favours the relative surface coverage with urea. Moreover, the interaction of urea with the metal film is modified by the addition of Mn, switching from solid-like to liquid-like at the Mn-alloying potential threshold. Also the CN− adsorption scenario is sensitive to surface alloying: the Mn-containing interface shows two adsorption sites with lower degree of metal-adsorbate charge transfer. Finally, the degree of surface enhancement correlates well on the one hand with the applied potential and the interfacial chemistry, and on the other hand with the crystallite morphology induced by alloying Au with Mn. The correlation among the spectroelectrochemical scenario, the potential-dependent alloy composition and the crystallite shape expressed by this investigation fits within the framework set by recent modelling of dynamic electrodeposition morphochemistry and opens up novel opportunities for improving the control over the functional properties of net-shape electrodeposited materials.

Magnetic characteristics of Au–Mn nanowires

The quantum properties of Au–Mn nanowires are analyzed theoretically from first principles. The emergence of magnetic properties in these nanowires, consisting of nonmagnetic elements, is demonstrated. It is shown that the manganese atoms carry fairly large magnetic moments (∼4.3 μB), although crystalline Mn is a paramagnet. Analysis of the electronic structure of these bimetallic nanowires indicates that the magnetic moments at the Mn atoms arise owing to the formation of a complicated structure of hybrid orbitals. Furthermore, it is found that the antiferromagnetic state in Au–Mn nanowires is stabilized by the occurrence of indirect exchange interaction between Mn atoms.

First-principles investigations of chirality in trimetallic alloy clusters: AlMnAun (n = 1-7).

Chirality, also called handedness, plays a crucial role in function ranging from biological self-assembly schemes, organic polymer functionalities, to optical material designs. In this Article, we demonstrated a first-principles investigation of chirality in magnetic AlMnAun(0/+1/-1) (n = 1-7) clusters. Optimized structures of the AlMnAun clusters exhibit configurational combinations between AlAun+1 and MnAun+1 clusters, indicating a subtle but equal competition between Au-Al and Au-Mn interactions in the alloy clusters. High magnetic moments are equal to or greater than 4μB in AlMnAun clusters due to the presence of the Mn dopant. Chirality turns up with the forms of right-handed and left-handed in stable AlMnAu5, AlMnAu6, and AlMnAu7 clusters. As a result, reflection symmetries are found in vibrational Raman and circular dichroism spectra of these chiral pairs. The present study shows that chiral magnetic clusters can be composed by doping two heteroatoms with one intrinsic magnetic dopant into small gold clusters.

Electrochemical fabrication of nanoporous gold decorated with manganese oxide nanowires from eutectic urea/choline chloride ionic liquid. Part II – Electrodeposition of Au–Mn: A study based on soft X-ray microspectroscopy

Abstract In a previous paper (C. Mele, M. Catalano, A. Taurino, B. Bozzini. Electrochim. Acta 1 (2013) 918), we demonstrated the possibility of growing high-capacitance hybrid materials consisting of nanoporous gold (NPG)-supported MnO 2 nanowires (NW) for supercapacitors, by electrochemical etching of electrodeposited single-phase Au–Mn alloys. The present paper concentrates on the electrodeposition of Au–Mn alloys from urea/choline-chloride ionic liquid solutions: the precursors of the high-capacitance hybrid material. The electrodeposition process, giving rise to alloys with 4–26% Mn content, was followed by space-resolved soft X-ray fluorescence (XRF) and absorption (XAS) microspectroscopy, complemented with electrochemical (cyclic voltammetry), structural (X-ray diffraction) and morphological (scanning electron microscopy) characterisations. The purposely developed electrochemical cells, exhibiting a specifically designed current density distribution, have allowed the quasi-in situ mapping of the local morphology-composition changes at the electrodes. Supersaturated Au–Mn solid solutions were obtained in the whole investigated compositional range under mass transport control of Mn. Variations in the Mn oxidation state were evidenced comparing low- and high-Mn content regions. It was found that, notwithstanding the heterogeneity of the current density, the morphologically compact high-Mn regions of the particular alloys with 20–26% Mn show a notable compositional homogeneity, rendering this material ideally suited for the fabrication of the target hybrid.

Electrochemical fabrication of nanoporous gold-supported manganese oxide nanowires based on electrodeposition from eutectic urea/choline chloride ionic liquid

In this study an electrochemical approach is proposed for the fabrication of nanoporous gold (NPG)-supported manganese oxide nanowires. This method consists in: (i) electrodepositing an Au–Mn alloy, (ii) selectively corroding Mn under electrochemical control, forming simultaneously the NPG support and the functional Mn-oxide decorating the nanopores. The electrodeposition process is carried out from a bath based on eutectic urea/choline chloride ionic liquid. The electrochemical dealloying/oxidation step is performed in an aqueous solution. The oxidation process, performed by cyclic voltammetry (CV) in aqueous solution, has been monitored in situ by visible reflectivity measurements. The crystal structure and the morphology of the electrodeposited Au–Mn alloy have been examined by XRD and SEM, respectively. The 3D morphology of the nanostructure has been characterised by FIB/FEG-SEM. The specific capacity of NPG-supported nanostructured Mn-oxide has been measured by CV and found to be notably better than that of unsupported electrodeposited Mn-oxide nanowires.

DETERMINATION OF ko-FACTORS FOR ko-INAA OF SOME ELEMENTS BY NEUTRON ACTIVATION WITH Am-Be ISOTOPE SOURCE

In neutron activation analysis based on the ko standardization method (ko INAA), the ko-factor is a combination of nuclear constants and it was measured by experiments. It plays an important role in the accuracy of ko-INAA method. Therefore, it is necessary to measure the ko-factors in many different neutron sources and compare the results. In this paper, the ko- factors to gold of manganese (ko, Au(Mn)), cadmium ((ko, Au(Cd)), Chromium ((koAu(Cr)), Zinc ((ko, Au(Zn)), Arsenic ((ko, Au(As)), Vanadium ((ko,Au(V) by neutron activation with the Am-Be isotope neutron source were measured. The comparision between our results and the results of Decorter et. al. showed relative differences of less than twenty percents. Among which, our most accurate result was found in (ko, Au(Mn) with only 1.18 percents relative difference.

Calibration of the isomer shift for the 77.34 keV transition in A197u using the full-potential linearized augmented plane-wave method

The isomer shift calibration constant has been calculated for the 77.34 keV Mossbauer transition connecting the ground state of the (197)Au nucleus with the first excited state of this nucleus. The full-potential linearized augmented plane-wave method was used in the fully relativistic approach, albeit without taking into account the spin-orbit coupling. The final assignment of the calibration constant was based on calculations performed for AuCN, AuCl(3), AuBr(3), KAuCl(4), KAuBr(4), and metallic gold. It is found that the calibration constant takes on the following value alpha = +0.0665(4) mm s(-1) a.u.(3). The error quoted is due to the linear regression fit, and the real error might be as large as 10%. The spectroscopic electric quadrupole moment for the ground state of the (197)Au nucleus was calculated as the by-product. It was found that this moment equals Q(g) = +0.566(1)b in fair agreement with the accepted value based on the muonic hyperfine spectroscopy results. The error quoted is again due to the linear regression fit and the real error might be as large as 10%. The final assignment of the value for the quadrupole moment is based on the calculations for the following compounds: AuCl, AuBr, AuI, AuCN, and AuMn(2). Results for the magnetically ordered Au(2)Mn were applied to determine the sign of the quadrupole moment.

Magnetic and transport measurements in Au(1−)Mn alloys in the cluster glass regime

Abstract A detailed study of magnetization and magnetoresistance has been carried out on a series of Au 1− x Mn x alloys (0.10⩽ x ⩽0.18) in the temperature range 4.2–300 K and in magnetic fields up to 9 T. The dc magnetization measurements show an irreversibility between the zero-field-cooled and field-cooled data while a fairly large negative magnetoresistance is observed in the alloys. These results are indicative of a cluster glass behaviour as has been observed in the AuFe alloys.

The Ternary System Au—Mn—Sb and the AuMnSn1‐xSbx Phase.

Abstract The phase relations in the Au–Mn–Sb system have been studied by powder X-ray diffraction, metallography, electron microprobe analysis, and thermal analysis. The condensed phases occurring, tie-lines, and tie-triangles are presented for an isothermal section of the phase diagram at 400 °C. At this temperature the solid solubility of the third component in the binary phases is generally limited to a few percent. The phase relations are relatively complex in regions which involve the numerous binary gold–manganese phases. The only genuine ternary phase, AuMnSb, has a very narrow composition range around Au 35 Mn 30 Sb 35 and is stable up to 575±5 °C, where it decomposes peritectically. The AuMnSb phase is ferromagnetic with a Curie temperature of 135±10 K. The solid-solution phase AuMnSn 1− x Sb x exhibits ferromagnetic properties throughout the entire homogeneity range with the Curie temperature ranging between 625±100 and 135±10 K.

The ternary system Au–Mn–Sb and the AuMnSn 1− xSb x phase

The phase relations in the Au–Mn–Sb system have been studied by powder X-ray diffraction, metallography, electron microprobe analysis, and thermal analysis. The condensed phases occurring, tie-lines, and tie-triangles are presented for an isothermal section of the phase diagram at 400 °C. At this temperature the solid solubility of the third component in the binary phases is generally limited to a few percent. The phase relations are relatively complex in regions which involve the numerous binary gold–manganese phases. The only genuine ternary phase, AuMnSb, has a very narrow composition range around Au 35Mn 30Sb 35 and is stable up to 575±5 °C, where it decomposes peritectically. The AuMnSb phase is ferromagnetic with a Curie temperature of 135±10 K. The solid-solution phase AuMnSn 1− x Sb x exhibits ferromagnetic properties throughout the entire homogeneity range with the Curie temperature ranging between 625±100 and 135±10 K.

Effect of Drying Conditions of Au–Mn Co-Precipitates for Low-Temperature CO Oxidation

Au–Mn co-precipitates were dried at different temperatures and in different atmospheres. The co-precipitates were tested for low-temperature CO oxidation without any additional thermal treatment. While samples dried at 120°C in air exhibited the highest activity for CO oxidation, samples dried at room temperature under vacuum were less active. The catalytic properties of most fresh samples improved after the first light-off test, during which a temperature of 400°C was reached. To investigate the physical and chemical state of gold and manganese support, dried samples were examined by 197Au Mössbauer spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The 197Au Mössbauer spectra showed that gold existed only in metallic form and was produced during the co-precipitation procedure. XRD and XPS analyses demonstrated that fresh samples contained manganese carbonate and oxides such as MnO2. The carbonate was converted to manganese oxides after the light-off test. TEM analysis indicated that the manganese support was present in plate-like shapes and the shape of gold particles was rectangular with rounded corners. Au particle sizes were in the range 4.5–6.5 nm before the light-off test. After heat treatment at 400°C, catalytic activity improved and a strong interaction between gold particles and the MnOx support was induced.

The ternary system Au–Mn–Sn

The phase relations in the Au–Mn–Sn system have been studied by powder X-ray diffraction, metallography, electron microprobe analysis, and thermal analysis. The condensed phases occurring, tie-lines and tie-triangles are presented for an isothermal section of the phase diagram at 400°C. At this temperature the solid solubility of the third component in the binary phases is generally limited to a few percent. The numerous phases in the binary Au–Mn system, are reflected in relatively complex phase relations in certain parts of the Au–Mn–Sn system. The only genuine ternary phase, AuMnSn, has a narrow composition range between Au 35Mn 31Sn 34 and Au 33Mn 35Sn 32 and is stable up to ca. 470°C were it decomposes peritectically.

A shift-lattice description of some face centred cubic alloy superstructures

Both metal atom components of a number of binary alloy structures, mainly occurring in the Au-rich region of the Au–Mn system, have been analysed as shift-lattices. It is shown that both atom types lie upon separate complementary shift-lattices. All the structures can be reproduced by a smooth variation of the shift-lattice parameters. Those found experimentally form only a small set of the infinite family of commensurate and incommensurate structures which can be constructedvia the shift-lattice method. The diffraction patterns of these phases can readily be derived and the relationship of the diffraction patterns observed to the separate components from each of the contributing shift-lattices is described.

Thermal expansion anomalies at the magnetic transition temperatures of Au 4Mn and Au 2Mn

Measurements of the thermal expansion and specific heat are carried out for the ferromagnetic ordered alloy Au 4Mn and the antiferromagnetic one Au 2Mn at temperatures including the Curie temperature T c and Néel temperature T N. The pressure effect on T C and T N is also measured. It is found that both Au 4Mn and Au 2Mn have positive exchange strictions and d T C/d p and d T N/d p are positive. The results are discussed in terms of the MnMn distance dependence of the exchange interactions in AuMn alloys.

Effect of magnetic impurities of universal conductance fluctuations

Experiments performed on mesoscopic systems made of dilute magnetic alloys ( Au Mn and Au Cr) show the effect of magnetic impurities on the Universal Conductance Fluctuations. The magnetic field allows us to switch from a low field state where the impurities are free and destroy the phase coherence to a high field state where the magnetization is saturated and the phase coherence is conserved along the whole sample. The results are interpreted by a molecular field approach in the spin glass state. However, we do not observe any jump of the conductance with time induced by spin flip in the zero field spin glass state. An explanation of the absence of jump is proposed.