Search Results (8)

This paper reviews and summarizes the available information on the composition of palladian gold with various contents and sets of isomorphic impurities (Ag, Cu, Hg) at 50 deposits and ore occurrences with Au-Pd mineralization. It is revealed that Palladian gold is represented by the systems Au–Pd, Au–Pd–Hg, Au–Pd–Cu, and Au–Pd–Ag–Hg, but more frequently corresponds to Au–Pd–Ag, Au–Pd–Ag–Cu, and Au–Pd–Ag–Cu–Hg. Objects with palladian gold belong to different types of gold deposits and to the deposits at which the main components of ores are PGE, Cr, Cu, Ni, V, and Ti. We propose a classification of the types of deposits with palladian gold: (1) PGE ore deposits related to mafic–ultramafic magmatic complexes (two subtypes—(a) low-sulfide-grade (less than 2%–5% sulfides) Alaskan, and (b) high-sulfide-grade (more than 5% sulfides) Norilsk); (2) orogenic gold deposits (OG); (3) epithermal (porphyry) gold–copper deposits (EPGC); (4) iron oxide copper gold deposits (IOCG); (5) ferruginous quartzite deposits; (6) volcanic exhalation; and (7) gold-PGE placers of five subtypes corresponding to the types of 1–5 primary sources. Physicochemical conditions of the formation of palladian gold at some deposits of type 1 cover two areas—magmatic high-temperature and hydrothermal low-temperature. At the majority of deposits of types 2–4, its formation proceeds with the participation of hydrothermal fluids (300–60 °C) of various salinities (0.2–30 wt.% NaCl eq.). Palladian gold is mainly high-fineness (910‰–990‰), is less frequently medium-fineness, and contains Ag and Cu, but does not contain Hg at the deposits of types 1, 3, and 4. The only exception is the Au-Pd-Hg Itchayvayam ore occurrence (Kamchatka, Russia), for which two varieties of Pd,Hg-bearing native gold (fineness 816‰–960‰ and 580‰–660‰) are determined. Low-fineness palladian gold with the major content of Ag is typical of OGD deposits. Medium-fineness palladian gold occurs at ferruginous quartzite deposits and in volcanic exhalations. Hg, Ag, Cu-bearing high-fineness palladian gold is present mainly in placer deposits (type 7). The most common minerals in association with palladian gold are arsenides, stibioarsenides, sulfides, stannides, bismuthides, tellurides, and selenides of Pd and Pt. These are typical of deposit types 1 and 7. The minerals of Au, Ag, and Cu (tetra-auricupride, aurostibite, chalcopyrite, bornite, chalcocite, eucairite, etc.) are in association with palladian gold at OG, EPGC, and IOCG deposits. Hg minerals (cinnabar, tiemannite, coloradoite, potarite) are at some deposits (types 1, 2, 7-1, 7-4). Cu, Fe, and Pd oxides (tenorite, hematite, magnetite, PdO, (Pd,Cu)O) and Fe and Pd hydroxides (goethite, (Fe,Pd)OOH) occur at the deposits of the 3, 4, and 7 groups and indicate the highly oxidizing conditions of ore formation. The most common minerals among host minerals are quartz and muscovite, including fuchsite (Cr-Ms), chlorite, albite, K-feldspar, hornblende, and carbonates (calcite, siderite, etc.). The fineness, content, and set of impurities in palladian gold and minerals in association with it reflect the mineralogy of Au-Pd ores and allow them to be used as indicators for the deposit types. Full article

We describe a potentially new species of a platinum cupride–stannide mineral (PCSM) of composition Pt(Cu_0.67Sn_0.33). It occurs in a placer deposit in the River Bolshoy Khailyk, southern Krasnoyarskiy kray, Russia. A synthetic equivalent of PCSM was obtained and characterized. The PCSM occurs as anhedral or subhedral grains up to 15 μm × 30 μm in association with various platinum-group minerals, Rh–Co-rich pentlandite and magnetite, all hosted by a placer grain of Cu–Au–Pt alloy. Synchrotron micro-Laue diffraction studies indicate that the PCSM mineral is tetragonal and belongs to the inferred space-group P4/mmm (#123). Its unit-cell parameters are a = 2.838 (3) Å, c = 3.650 (4) Å, and V = 29.40 (10) ų, and Z = 1. The c:a ratio calculated from the unit-cell parameters is 1.286. These characteristics are in good agreement with those obtained for specimens of synthetic Pt(Cu_0.67Sn_0.33). A review on related minerals and unnamed phases is provided to outline compositional variations and extents of solid solutions in the relevant systems PtNi–PtFe–PtCu, PdCu–PdHg–PdAu, PdHg–PtHg, and AuCu–PtCu. The PCSM-bearing mineralization appears to be related genetically with an ophiolitic source-rock of the Aktovrakskiy complex of the western Sayans. The unnamed phase likely crystallized from microvolumes of a highly fractionated melt rich in Cu and Sn. Full article

Highly atypical mineralization involving Pd-Pt, Au-Ag, REE, Y, Zr, U, Th, and Cl-F-enriched minerals is found in zones with base metal sulfides (BMS; ~5 vol.% to 20 vol.%) in the eastern portion of the Oktyabrsky deposit in the Norilsk complex (Russia). The overall variations in Mg# index, 100 Mg/(Mg + Fe²⁺ + Mn), in host-rock minerals are 79.8 → 74.1 in olivine, 77.7 → 65.3 in orthopyroxene, 79.9 → 9.2 in clinopyroxene, and An_79.0 → An_3.7. The span of clinopyroxene and plagioclase compositions reflects their protracted crystallization from early magmatic to late interstitial associations. The magnesian chromite (Mg# 43.9) trends towards Cr-bearing magnetite with progressive buildups in oxygen fugacity; ilmenite varies from early Mg-rich to late Mn-rich variants. The main BMS are chalcopyrite, pyrrhotite, troilite, and Co-bearing pentlandite, with less abundant cubanite (or isocubanite), rare bornite, Co-bearing pyrite, Cd-bearing sphalerite (or wurtzite), altaite, members of the galena-clausthalite series and nickeline. A full series of Au-Ag alloy compositions is found with minor hessite, acanthite and argentopentlandite. The uncommon assemblage includes monazite-(Ce), thorite-coffinite, thorianite, uraninite, zirconolite, baddeleyite, zircon, bastnäsite-(La), and an unnamed metamict Y-dominant zirconolite-related mineral. About 20 species of PGM (platinum group minerals) were analyzed, including Pd-Pt tellurides, bismuthotellurides, bismuthides and stannides, Pd antimonides and plumbides, a Pd-Ag telluride, a Pt arsenide, a Pd-Ni arsenide, and unnamed Pd stannide-arsenide, Pd germanide-arsenide and Pt-Cu arseno-oxysulfide. The atypical assemblages are associated with Cl-rich annite with up to 7.54 wt.% Cl, Cl-rich hastingsite with up 4.06 wt.% Cl, ferro-hornblende (2.53 wt.% Cl), chlorapatite (>6 wt.% Cl) and extensive solid solutions of chlorapatite, fluorapatite and hydroxylapatite, Cl-bearing members of the chlorite group (chamosite; up to 0.96 wt.% Cl), and a Cl-bearing serpentine (up to 0.79 wt.% Cl). A decoupling of Cl and F in the geochemically evolved system is evident. The complex assemblages formed late from Cl-enriched fluids under subsolidus conditions of crystallization following extensive magmatic differentiation in the ore-bearing sequences. Full article

Core/shell-structured FeSn₂/onion-like carbon (FeSn₂/OLC) nanocapsules of confined size range of sub-50 nm are synthesized via an in-situ arc-discharge process, and are evaluated in comparison with FeSn₂ nanoparticles as an improved stannide-based electrocatalytic anode material for Li-ion batteries (LIBs). The in-situ arc-discharge process allows a facile one-pot procedure for forming crystalline FeSn₂ stannide alloy nanoparticle cores coated by defective OLC thin shells in addition to a confined crystal growth of the FeSn₂ nanoparticle cores. The LIB cells assembled using the FeSn₂/OLC nanocapsules as the electrocatalytic anodes exhibit superior full specific discharge capacity of 519 mAh·g⁻¹ and specific discharge capacity retention of ~62.1% after 100 charge-discharge cycles at 50 mA·g⁻¹ specific current. The electrochemical stability of FeSn₂/OLC nanocapsules is demonstrated from the good cycle stability of the LIBs with a high specific discharge capacity retention of 67.5% on a drastic change in specific current from 4000 to 50 mA·g⁻¹. A formation mechanism is proposed to describe the confined crystal growth of the FeSn₂ nanoparticle cores and the formation of the FeSn₂/OLC core/shell structure. The observed electrochemical performance enhancement is ascribed to the synergetic effects of the enabling of a reversible lithiation process during charge-discharge of the LIB cells by the FeSn₂ nanoparticle cores as well as the protection of the FeSn₂ nanoparticle cores from volume change-induced pulverization and solid electrolyte interphase-induced passivation by the OLC shells. Full article

Monosilicides of transition metals crystallizing in a B20 (FeSi-type) structure (space group P2 ${}_1$ 3, #198) possess a wide range of specific properties. Among them are semiconductors, metals, and paramagnetic, diamagnetic, and ferromagnetic compounds. Some of them were studied as promising thermoelectric materials. Recently, B20 monosilicides have attracted attention as a new class of topological semimetals with topological charge greater than unity. In the present work, we analyze the electronic structures of B20-type monosilicides of the fourth, fifth, and sixth periods of the Periodic Table in order to reveal their common features and peculiarities. To make this analysis more consistent, we performed a density-functional study of the electronic structures of the monosilicides in a unified manner. We reviewed the results of previous calculations and the available experimental data, comparing them with our results. The band structures of ReSi and TcSi not found in the literature were calculated and analyzed as well. The topological properties of these materials and of some isostructural germanides and stannides were investigated. Analysis reveals the current understanding of electronic structures and properties of this compound group. Full article

Two commercial hybrid coatings, cured at temperatures lower than 300 °C, were successfully used to protect magnesium silicide stannide and zinc-doped tetrahedrite thermoelectrics. The oxidation rate of magnesium silicide at 500 °C in air was substantially reduced after 120 h with the application of the solvent-based coating and a slight increase in power factor was observed. The water-based coating was effective in preventing an increase in electrical resistivity for a coated tethtraedrite, preserving its power factor after 48 h at 350 °C. Full article

The continuous substitution of tin by lead (M ${}^{\mathrm{IV}}$ ) allows for the exploration geometric criteria for the stability of the different stacking variants of alkaline-earth tri-tetrelides $A^{\mathrm{II}}{M}_3^{\mathrm{IV}}$ . A series of ternary Sr and Ba mixed tri-stannides/plumbides A ${}^{\mathrm{II}}$ (Sn ${}_{1-x}$ Pb ${}_x$ ) ${}_3$ (A ${}^{\mathrm{II}}$ = Sr, Ba) was synthesized from stoichiometric mixtures of the elements. Their structures were determined by means of single crystal X-ray data. All structures exhibit close packed ordered $A{M}_3$ layers containing M kagomé nets. Depending on the stacking sequence, the resulting M polyanion resembles the oxygen substructure of the hexagonal (face-sharing octahedra, h stacking, Ni ${}_3$ Sn-type, border compound BaSn ${}_3$ ) or the cubic (corner-sharing octahedra, c stacking, Cu ${}_3$ Au-type, border compound SrPb ${}_3$ ) perovskite. In the binary compound BaSn ${}_3$ (Ni ${}_3$ Sn-type) up to 28% of Sn can be substituted against Pb (hP8, P $6_3/$ mmc, x = 0.28(4): a = 726.12(6), c = 556.51(6) pm, R1 = 0.0264). A further increased lead content of 47 to 66% causes the formation of the BaSn ${}_{2.57}$ Bi ${}_{0.43}$ -type structure with a ${\left(\mathit{hhhc}\right)}_2$ stacking [hP32, P $6_3/$ mmc, x = 0.47(3): a = 726.80(3), c = 2235.78(14) pm, R1 = 0.0437]. The stability range of the BaPb ${}_3$ -type sequence ${\left(\mathit{hhc}\right)}_3$ starts at a lead proportion of 78% (hR36, R $\overline{3}$ m, a = 728.77(3), c = 2540.59(15) pm, R1= 0.0660) and reaches up to the pure plumbide BaPb ${}_3$ . A second new polymorph of BaPb ${}_3$ forms the Mg ${}_3$ In-type structure with a further increased amount of cubic sequences [ ${\left(\mathit{hhcc}\right)}_3$ ; hR48, a = 728.7(2), c = 3420.3(10) pm, R1 = 0.0669] and is thus isotypic with the border phase SrSn ${}_3$ of the respective strontium series. For the latter, a Pb content of 32% causes a small existence region of the PuAl ${}_3$ -type structure [hP24, P $6_3/$ mmc, a = 696.97(6), c = 1675.5(2) pm, R1 = 0.1182] with a ${\left(\mathit{hcc}\right)}_2$ stacking. The series is terminated by the pure c stacking of SrPb ${}_3$ , the stability range of this structure type starts at 75% Pb (cP4, Pm $\overline{3}$ m; a = 495.46(9) pm, R1 = 0.0498). The stacking of the close packed layers is evidently determined by the ratio of the atomic radii of the contributing elements. The Sn/Pb distribution inside the polyanion (’coloring’) is likewise determined by size criteria. The electronic stability ranges, which are discussed on the basis of the results of FP-LAPW band structure calculations are compared with the Zintl concept and Wade’s/mno electron counting rules. Still, due to the presence of only partially occupied steep M-p bands the compounds are metals exhibiting pseudo band gaps close to the Fermi level. Thus, this structure family represents an instructive case for the transition from polar ionic/covalent towards (inter)metallic chemistry. Full article

Investigations of the system Ba–In–Sn, with the objective to synthesize Ba₈In₁₆Sn₃₀ clathrate using Sn and In flux reactions, yielded instead the known BaSn₃ compound (P6₃/mmc; a = 7.228(2) Å, c = 5.469(3) Å) from Sn flux and its In-doped variant BaSn_2.8In_0.2(1) (a = 7.260(1) Å, c = 5.382(2) Å) from In flux. BaSn_3–xIn_x is the first, and up until now, the only ternary phase containing these elements. Its structure is isomorphic with the Ni₃Sn type (Pearson symbol hP8) and is apparently capable of sustaining small variations in the valence electron count by virtue of replacing Sn with the electron poorer In. Electrical resistivity measurements on single-crystals of both undoped and doped phases show different metallic-like behavior, suggesting that neither BaSn₃ nor BaSn_3–xIn_x are valence compounds. Full article