Hg Alloys Research Articles

Morphology and chemistry of placer gold in the Bagrote and Dainter streams, northern Pakistan: Implications for provenance and exploration

The Bagrote and Dainter valleys in Gilgit Baltistan Pakistan, belonging to the Kohistan island arc and southwestern domain of the Karakorum metamorphic complex, respectively, are a location of regional placer gold mining. However, no in situ hydrothermal gold deposits have been discovered in this region. Here, we report the textural, morphological, and geochemical characteristics of placer gold from the stream sediments of the Bagrote and Dainter valleys with a view to trace the provenance. The morphological features of the studied gold grains indicate proximal source mineralization. The gold grains display a microtexture typical of mechanical abrasion rather than chemical activity. Their chemical composition of most of the grains from each stream falls in a restricted range (minor alloying elements mainly Cu) with high fineness (1,000 Au/(Au + Ag)), suggesting derivation from a homogeneous source or limited number of mineralization types. The high Cu content of the gold grains from the Bagrote stream suggests that the gold here might be associated with previously undiscovered porphyry gold mineralization, whereas the Au–Ag–Hg alloys from the Dainter stream suggest a genetic linkage with undiscovered fault‐controlled auriferous veins of epithermal origin in the southwestern part of the Karakorum metamorphic complex. The chemical composition of both streams placer gold in triangular diagram in terms of Au–Ag–Cu shows all the gold grains from Dainter stream were derived from epithermal type of mineralization, and most of the plots of Bagrote stream fall on the domain of porphyry epithermal type of deposits which are also in consistent with a continental arc setting in the study area. The mechanically developed microtexture, homogeneous chemical composition in individual grains from core to rim, and absence of high fineness rims of the gold grains from both streams, suggest the absence of any supergene regrowth and direct transfer from the primary source through glacier to the fluvial system. The Gilgit Baltistan province, dominated by dry temperate climate and glacial environment having steep geomorphology, precluding any significant supergene processes such as silver leaching and addition of authigenic gold on detrital gold grains.

Visual sensing of Hg2+ using unmodified Au@Ag core–shell nanoparticles

In this work, we have developed a novel visual Hg2+ sensor in aqueous solution using unmodified Au@Ag core–shell nanoparticles at room temperature, based on a redox reaction between Ag-shell and Hg2+. The prepared Au@Ag core–shell nanoparticles exhibited good monodispersity. In the presence of Hg2+, Hg2+ was reduced into Hg (0) by Ag-shell, and deposited on the surface of Au-core to form Au–Hg alloys and caused nanoparticles aggregation, leading to the color changes of the solution from yellow to purplish red, and the surface plasmon resonance spectra of Au@Ag core–shell nanoparticles red shift. Under the optimal conditions, the visual sensor could selectively detect Hg2+ as low as 0.4 µM with the naked eye and 5.0 nM by UV–vis spectra analysis methods. The designed sensor had several advantages: (1) the nanoparticles surface need not be functionalized. (2) The color change of the solution was in 2 s and could easily be observed with naked eyes. The visual sensor had been applied to detection of Hg2+ in tap and lake water, which obtained satisfied result.

Supergene enrichment of precious metals by natural amalgamation in the Las Cruces weathering profile (Iberian Pyrite Belt, SW Spain)

Natural Au–Ag–Hg alloys occur in the Las Cruces ore deposit, in the eastern part of the Iberian Pyrite Belt. They are mainly concentrated in the lower part of the gossan profile including a sheared black shale level where the gossan makes contact with a barren pyrite zone within the supergene Cu-rich mineralization.Drill core analyses show a heterogeneous distribution of Au, Ag, and Hg within the weathering profile, with mean values of 5.1ppm, 155ppm, and 52ppm, respectively. In general, the absolute tenures increase towards the bottom of the weathered profile. Mineralogical studies conducted on samples from the active mine workings indicate that Hg and precious metals occur mainly as Au–Ag–Hg alloys. These associations constitute the best potential resource for precious metals at the Las Cruces deposit.This paper describes how this unusual precious metal enrichment is produced along the weathering profile by supergene processes. Combining paragenetic information, mineral chemistry and the data pertaining to the solubilities of Au, Ag, and Hg in a weathering profile, we suggest a two-stage genetic model for the formation of the Las Cruces Au–Ag–Hg mineralization: (1) release of Au, Ag, and Hg from the massive sulfide deposit by weathering processes during the gossan formation. At pH<5.5 and Eh>0.9V conditions, Au, Ag and Hg are mobilized downward through the weathering profile as chloride complexes and fixed as elemental Au, halides, oxides, and sulfates; and (2) remobilization of Hg, Ag, and Au in the gossan after the deposit was buried beneath the Neogene carbonate-rich sedimentary cover. The buffering capacity of the percolating fluids due to their interaction with the carbonate-rich sedimentary pile leads to significant mineralogical and geochemical changes. At near-neutral conditions (pH=6–7; Eh≈0V), Hg, Ag, and Au are newly-remobilized as thiosulfate, sulfate, and hydroxide complexes and newly-fixed by sorption during ferric hydroxide formation and as sulfates. Several cycles of dissolution–precipitation of Au, Ag, and Hg near the redox front occur by oscillations in the water table and changes in the pH–Eh conditions. The interaction of downward migrating fluids with high reductant lithologies (black shales and massive sulfides) seems to be responsible for the reduction of different complexes and for the precipitation of cinnabar, Ag-sulfides and sulfosalts as well as the precipitation of Au–Ag–Hg amalgams.

Estimation of Maximum Solid Solubility in Mg&amp;ndash;Hg Alloys by the Lever Rule

The microstructures of Mg­Hg alloys with 1.1­2.9mass% Hg were investigated in this paper. Under the non-equilibrium solidification condition, the examined Mg­Hg alloys had a two-phase structure consisting of a solid solution phase and a spheroidal-graphite iron-like divorced eutectic. Eutectic i-Mg and eutectic Mg3Hg formed separately, so the proportion of eutectic Mg3Hg could be accurately measured. A method was proposed to estimate the maximum solid solubility of Hg in Mg under the non-equilibrium solidification condition by measuring the area fraction of Mg3Hg in metallographes. The maximum solid solubility of Mg­2.4mass% Hg was 0.81 and 0.69mass%, with cooling rates of 0.67 and 2.0K/s, respectively. The maximum solid solubility decreased as the cooling rate increased and increased as the Hg content increased. [doi:10.2320/matertrans.M2012272]

Influence of Ga Content on Electrochemical Behavior of Mg-5 at%Hg Anode Materials

The effects of Ga content on the electrochemical behavior of Mg-5 at%Hg alloys which contain a small amount of Ga was investigated by the measurement of polarization curves and galvanostatic test. The microstructure of the alloys and the surface of the specimens corroded in galvanostatic test were observed by using scanning electron microscopy, energy spectrum analysis and X-ray diffraction analysis. It can be concluded that with the content of Ga increasing, the alloys come into Mg-Mg 3 Hg, Mg-Mg 7.2 (Hg, Ga) 2.8 and Mg-Mg 5 Ga 2 binary phase fields sequentially. The best electrochemical activity occur in the Mg-5 at%Hg -1 at%Ga alloy, with open circle potential -2.124V and mean potential -1.992 V. The corrosion resistance of the alloys is in the sequential order from big to small: Mg-5 at%Hg-5 at%Ga, Mg-5 at%Hg-22 at%Ga, Mg-5 at%Hg-1 at%Ga, Mg-5 at%Hg. The lowest corrosion current density is 0.418 mA·cm -2 . The activation mechanism of the magnesium alloy produced by Hg and Ga was concluded: the dissolution of Hg and Ga atoms leads to the back accumulation of liquid Hg and Ga, which makes a true metallic contact with a-Mg. Magnesium atoms diffuse through the liquid mercury and gallium to form magnesium amalgam and undergo severe oxidation at the amalgam/electrolyte interface. The reaction produces pure Hg and Ga again which continue the activation process.

Influence of Ga and Hg on microstructure and electrochemical corrosion behavior of Mg alloy anode materials

The effects of Hg and Ga on the electrochemical corrosion behavior of Mg-5%Hg (molar fraction) alloys were investigated by the measurement of polarization curves and galvanostatic test. The microstructure of the alloys and the corroded surface of the specimens were investigated by scanning electron microscopy, X-ray diffractometry and emission spectrum analysis. It can be concluded that the addition of 1%Ga (molar fraction) reduces corrosion current density from 26.98 mA/cm2 to 2.34 mA/cm2; while the addition of 1%Hg (molar fraction) increases corrosion current density. The addition of Ga and Hg both promotes the electrochemical activity of the alloys and the influence of Ga is more effective than Hg. Mg-5%Hg-1%Ga alloy has the best electrochemical activity, showing mean potential of -1.992 V. The activation mechanism of the magnesium alloy produced by Hg and Ga was put forward. Magnesium atoms are dissolved in liquid Hg and Ga to form amalgam and undergo severe oxidation at the amalgam/electrolyte interface.

Liquid structure of Rb–Hg alloys studied by neutron diffraction

The structures of liquid Rb–Hg alloys were studied as a function of composition by neutron diffraction. In the intermediate Rb concentration range, the obtained structure factors show a small prepeak, which may be an evidence of the formation of Hg polyanion units in liquids. The Reverse Monte Carlo (RMC) analysis was applied to separate the total radial distribution function into the corresponding partial radial distribution functions. Up to 10at.% Rb, no obvious changes are found for the first peak position of the partial radial distribution functions of the Hg–Hg pair and that of the Hg–Rb pair. The first peak position between the Hg–Rb pairs increases above 20at.% Rb. In addition to the first peak, a subpeak between Hg–Hg pairs can be seen in the large distance. At 60at.% Rb, the nearest neighbor distance between Hg atoms shows the closest value in the concentration range studied. These results indicate that with the progress of charge transfer the solvation structure in the dilute Rb concentration range changes into the structure containing polyanions composed of Hg species.

Gold and sulphide minerals in Tertiary quartz pebble conglomerate gold placers, Southland, New Zealand

Auriferous quartz pebble conglomerates (QPC) formed during Tertiary sedimentary recycling in the Waimumu district, Southland, New Zealand. These sediments contain fine-grained gold of detrital origin with abundant surface textures and gold-forms associated with authigenic gold remobilisation. Most authigenic gold contains no detectable silver and occurs as overgrowths on detrital Au–Ag and Au–Ag–Hg alloys that contain up to 13 wt.% Ag, and 9 wt.% Hg. Fine-grained Au–Ag and Au–Ag–Hg alloys are compositionally heterogeneous, exhibiting both well-defined silver-depleted and silver-enriched rims. Rare coarse Au–Ag alloy is intergrown with quartz and is homogenous. Discrete grains of authigenic, porous, sheet-like gold occur in carbonaceous mudstone within a QPC sequence. Some QPC contain abundant sulphide minerals. Some of these sulphides (pyrite and arsenopyrite) are of long-distance detrital origin, presumably from the Otago Schist, whereas the bulk of the sulphide suite is marcasite of variably transported diagenetic origin, derived from the erosion of QPC and underlying Tertiary sediments. There has also been authigenic deposition of sulphide minerals in the QPC themselves. These diagenetic sulphides include framboidal and anhedral marcasite, and framboidal and euhedral pyrite. Sulphur isotope data for the sulphide minerals range from − 45‰ to + 18‰ (relative to VCDT). Sulphur isotope data for euhedral detrital pyrite and arsenopyrite range from − 9‰ to − 1‰ and are most likely derived from the Otago Schist to the north. Both framboidal and anhedral marcasite have lower values (< − 20‰) reflecting microbial sulphate reduction as a source for the precursor hydrogen sulphide. Anhedral marcasite contains elevated concentrations of Ni, Co, As and Cr, commonly with compositional banding of these metals. Both the gold and diagenetic sulphides from the Belle-Brook QPC are compositionally similar to gold and sulphides from Archaean QPC. Porous, sheet-like authigenic gold is morphologically similar to gold associated with carbonaceous material in the Witwatersrand. In addition, Southland marcasite textures resemble the rounded and banded pyrite in Witwatersrand QPC placers. There is abundant evidence from these Tertiary QPC in southern New Zealand for sedimentary transport of sulphide minerals and post-depositional sulphide mineralisation in the surficial environment despite an oxygen-rich atmosphere. These young deposits thus provide an example of authigenic gold and sulphide textures formed during diagenesis in unmetamorphosed placers. Many of these textures are similar to those commonly ascribed to metamorphic processes in Archaean auriferous QPC.

Atomic force microscopy of [formula omitted] alloy formation on thin Au films

Atomic force microscopy was applied to the study of thin Au films deposited under ultra-high vacuum conditions on a glass support maintained at 78 K. A variety of thin gold film structures were thus determined and characterized ranging from (i) nanometric isolated gold islands, (ii) nanometric gold structures, to (iii) continuous gold films, all depending on the amount of Au deposited. The influence of the amalgamation process on the thin Au films topography was studied. The fundamental importance of surface defects on the rate of amalgamation was clearly seen. The movement of small Au islands on glass obtained as the result of thermal decomposition of Au Hg alloys was observed.

The electrochemical behaviour of AlZnIn and AlZnHg alloys in aqueous halide solutions

The electrochemical behaviour of 99.99% aluminium, an Al-Zn-In and Al-Zn-Hg alloy was investigated, and compared, in aqueous halide, sulphate and perchlorate solutions using electrochemical and surface analytical techniques. Localized attack was observed for pure aluminium and the two alloys (but at more electronegative potential values) in chloride, bromide, iodide and perchlorate solutions but attack of the mercury-containing alloy was observed, also, in sulphate and fluoride solutions. This was attributed to the additional effects of oxide detachment induced by mercury giving rise to large potential oscillations, approaching potential values close to the theoretical potential of aluminium, for immersion in sulphate solutions. The precipitation of oxyfluoride complexes in fluoride solutions leads to the observation of more passive behaviour in fluoride media. The major difference, in the electrochemical behaviour of pure aluminium and the alloys, lay in the extent of metastable attack, as evidenced by the higher frequency of current and potential fluctuations observed with the alloys, before complete breakdown of the passive films occurred.

Electronic properties of liquid mercury alloys

The thermoelectric power, Q, of liquid RbHg and the electrical resistivity, ϱ, of liquid KHg and RbHg alloys were measured. A deep minimum of Q is present at 5 at.% Rb. At this alkali content, the temperature coefficient of Q shows a minimum for liquid RbHg, and the temperature coefficient of ϱ shos a maximum for liquid KHg and RbHg. The resistivity shows a maximum value at 60 at.% alkali for liquid KHg and RbHg alloys. Two types of chemical short-range order (CSRO) seem to be present in liquid alkali-Hg alloys and features of these CSROs are discussed on the basis of the information available on the electronic properties.

The anodic dissolution of dental amalgams studied with abrasive stripping voltammetry

AbstractThe recently described technique abrasive stripping voltammetry was used to study the corrosion behavior of five commercial dental amalgams. Abrasive stripping voltammetry of these amalgams reveals details of the anodic dissolution of the alloys that are not accessible by other methods. Systematic studies of SnHg alloys, SnAg alloys, and dental amalgams lead to a method that allows the identification of the γ2‐phase in dental amalgams. It can be shown that the non‐γ2 amalgams have a higher stability than γ2‐containing amalgams only in solutions of very low complexation ability. In cases of more aggressive solutions such as lemon juice, non‐γ2 and conventional amalgams exhibit identical behavior during the anodic oxidation.

Corrosion protection of galvanized steel pipe in acidic media by surface amalgamation

AbstractA procedure for corrosion protection of galvanized steel in slightly acidic media has been proposed, based on surface amalgamation by contact with Hg2+ solutions. The treatment procedure and the changes it effects in the morphology of the Fe–Zn alloyed layers of galvanized coatings are described. The amalgamated layer reaches a thickness of 75 μm and includes the η and ζ layers, penetration into the ζ layer being by grain boundary diffusion. A reduction in the corrosion rate of surface amalgamated galvanized pipe in contact with slightly acidic media, ranging from ten fold at pH 4–6 to one hundred fold at pH <4, is due to cathodic control resulting from the high overvoltage for hydrogen discharge on Zn–Hg alloys.

The Concentration and Temperature Dependence of the Magnetic Susceptibility of Liquid Mercury Alloys

The molar magnetic susceptibility, χ M of liquid Hg–Na and Hg–In alloys was measured from room temperature to 723 K using the Faraday method. The concentration dependence curve (CDC) of χ M for liquid Hg–In alloys shows positive deviations from the linear law. The results of liquid Hg–Na alloys have a positively enhanced tendency in the intermediate concentration range, though the overall concentration dependence remains to be slightly negative (“W shape”); this type of CDC of χ M is similar to that of liquid Hg-Cs alloys. Such a tendency of deviations has been discussed in terms of the nearly free electron theory for χ M of liquid alloys. Maxima at a few at.% solute (In or Na) found in the CDC of the temperature coefficient of χ M , dχ M /d T , appear to indicate an evidence of higher order correlation effects, as observed in many liquid Hg alloys.

The volume and thermal expansion coefficients of liquid Hg-In and Hg-Sn alloys-evidence for higher-order correlation effects in liquid Hg alloys

The molar volumes VM and the thermal expansion coefficients alpha p of liquid Hg-In and Hg-Sn alloys were measured as detailed functions of composition in the range of dilute solute (In or Sn) concentration (below 15 at.% In and 10 at.% Sn). The excess molar volume Delta VM for each kind of alloy decreases monotonically with increasing concentration of solute (In or Sn) atoms. On the other hand, the concentration dependences of alpha p differ; a slight hump exists at a few at.% In for liquid Hg-In alloys, while no anomalous behaviour of alpha p is found for liquid Hg-Sn alloys. These results are closely related to the fact that there is a minimum in the curve of the thermoelectric power Q plotted against concentration for Hg-In but not for Hg-Sn, and appear to show the importance of higher-order correlation effects in liquid Hg-In alloys. It is also pointed out that similar anomalies can be found in the literature values of the partial molar excess entropy of solute component in liquid Hg-In and Hg-Tl systems.

The Magnetic Susceptibility and Its Temperature Dependence of Liquid Hg–Tl and Hg–Cs Alloys

The molar magnetic susceptibility χ M of liquid Hg–Tl and Hg–Cs alloys was measured from room temperature to 748 K using the Fraday method. The observed χ M of liquid Hg–Tl alloys shows positive deviations from the linear concentration dependence. For liquid Hg–Cs alloys a positively enhanced tendency of χ M is found around 40 at.%Cs, though deviations from the linear law remain to be negative as a whole (“W shape”). Such a concentration dependence of χ M is discussed in terms of the nearly free electron model. Positive deviations or positively enhanced tendencies (“W shape”) of χ M in these liquid Hg alloys seem to be explained by taking into account electron-ion interactions. The temperature coefficient of χ M , or dχ M /d T , is discussed from the point of view of higher order ion-ion correlation effects recently found for some liquid mercury alloys.

A reply to Faber's question about the minimum in the thermoelectric power of liquid mercury alloys

The “minimum in Q” of liquid Hg alloys has been a curious and unresolved problem. For example, in his book (Introduction to the Theory of Liquid Metals, Cambridge 1972), Faber questioned why the addition of small quantities of In increases |Q| while adding small quantities of Sn decreases it though their effect on the resistivity ϱ is the same. In order to reply to his question, the ϱ of liquid Hg-In and Hg-Sn alloys was measured accurately as detailed functions of composition. It is concluded that there exists a difference in the temperature dependence of ϱ between liquid Hg-In and Hg-Sn alloys. This indicates that the “minimum in Q” of liquid Hg-In alloys seems to be related to higher order correlation function effects.

Higher-order correlation effects on thermodynamic and electronic properties of liquid alloys

The higher-order atom-atom correlation function effect, which has been recently revealed to be related to the origin of the minimum in the thermoelectric power Q of liquid Hg alloys, is discussed in some detail. New experimental results of the electrical resistivity ϱ and Q of liquid HgLi alloys are included in this discussion. The relation between the higher order correlation function effects and the thermodynamic function of liquid Hg alloys (the heat of mixing ΔH M) is stressed. The charge transfer effect, which can been clarified by the modified Miedema's plot, seems to produce the local structural change which can be seen as the higher order correlation effect.

Precious metal alloys and organic matter in the Zechstein copper deposits, Poland

Au-and PGE-bearing samples1 from organogenic limestone located in the western part of the Lubin mine have been investigated. They contain: Au−Ag−Pt−Hg alloys, native Pd, sobolevskite (PdBi), native lead and plumbian gold which is related to an admixture of AuPb2, electrum (Ag2Au). Clausthalite also occurs in this association and contains up to 1% Ir. Kerogen is an important member of the association and contains, among others, 700 ppm Pt, 400 ppm Pd, 600 ppm Ir and 1100 ppm Au.

On the behaviour of the Cd d bands in Au, Ag and Hg alloys

The valence band densities of states of selected HgCd alloys have been studied using 40.81 eV HeII photoelectron spectroscopy. The binding energies, splittings and widths of the Hg 5d5/2, 3/2 and Cd 4d5/2, 3/2 peaks have been studied for various alloy concentrations and are discussed in conjunction with previous work on AuCd and AgCd alloys and with the results of self-consistent bandstructure calculations. It has been found that the increase in full width at half maximum of the valence d bands with increasing concentration varies approximately as Z/R2, where Z is the like-atom coordination number and R is the like-atom nearest-neighbour distance.