Increase In Gold Content Research Articles

Geology, hydrothermal alteration and mineralization of the Carlin-type gold deposit at South Ratatotok, Southeast Minahasa Regency, North Sulawesi Province, Indonesia

South Ratatotok in North Sulawesi, Indonesia is one of the regions that was once a gold-producing region in North Sulawesi. Mesel gold deposit in this region is approved as Carlin type gold deposit with a total of resources of 12.25 Mt @5.21 g/t Au. Near the Mesel deposit, gold mineralization is currently discovered prospects such as Leon, Bulex Hill, Heind’s Find and Monkey Forest. This study is aimed to elucidate the types and distribution of hydrothermal alteration and ore mineralization encountered in these four prospect areas. Research methods including field work (including geological and hydrothermal alteration mapping, rocks and ore sampling) and various laboratory works consisting of petrographic analysis, ore microscopy, X-Ray Diffraction (XRD) and fire assay were performed. As a result, the study area is composed of several lithological units including limestone, volcanic breccia, porphyritic andesitic intrusion units as well as colluvial deposit. The wall rocks have been suffered by various hydrothermal alteration as follows: silicification in limestone, carbonatization in volcanic breccia, argillic alteration in volcanic breccia and propylitic alteration developed in porphyritic andesitic intrusion, minor decarbonatization associated with limestone and minor oxidation in volcanic breccia. Gold mineralization is present as a replacement type in very fine size of sulphides and gold is closely associated with silicified limestone. Ore chemistry by fire assay analysis indicates that gold and silver contents vary from 0.012 g/t to 2.41 g/t Au, and <0.5 g/t to 2.1 g/t Ag, respectively. The increase of gold content is geochemically followed by high values of Ag, As, Sb, Cu, Pb, Zn and by low value of Hg because of oxidation. Supergene process was also the key factor in the enrichment of gold where the oxidized ore has relatively higher gold grade than in non-oxidized ore.

Formation of quasi-spherical Au48-198 clusters in anodic titania nanotubes grown on Ti-Au alloys

The effect of alloying sputter-deposited Ti with 2 at.% of Au on the growth of anodic nanotubes was studied in monoethylene glycol electrolyte containing 1.0 mol dm−3 of water and 0.1 mol dm−3 of ammonium fluoride. The classic shape of nanotubes modified with quasi-spherical clusters of Au48-198 was obtained on Ti-Au (2 at.%). The results were compared to the formation of a barrier-type anodic film which suggested that gold located at the alloy/anodic film interface is enriched as a consequence of the preferential oxidation of titanium during the prior anodizing period and transported to the cell boundary region of the nanotubular film in the form of quasi-spherical clusters of Au48-198. A consequence of the inclusion of Au48-198 in the structure of the nanotubes was a reduction in the rate of nanotubular film growth due to the generation of oxygen catalysed on the clusters. A further increase in gold content up to 8 at.% in the alloy resulted in the formation of sponge-like or nanoporous anodic layers, with the structure depending on electrolyte composition.

Reduction of preg-robbing activity of carbonaceous gold ores with the utilization of surface blinding additives

The carbonaceous matter present in some gold ores adsorbs the gold cyanide complexes from the leached solution and transport them to tailings, resulting in loses and preventing the recovery of the metal – a phenomenon known as preg-robbing. The present work aims at evaluating the capacity of 8blinding additives to deactivate/passivate the carbonaceous matter present in mineral coals and in gold ores. Initially, adsorption experiments with 3 mineral coals at different levels of maturation (anthracite, bituminous and lignite) were carried out to simulate the complex carbonaceous matrix of the gold ores. The coal presenting the best adsorptive capacity was selected for the experiments with the blinding additives. Different concentrations of additives (562–28,125 g/tcoal) and conditioning times (5, 30 and 120 min) were investigated. The blinding additives presenting satisfactory results were used in the deactivation/passivation carbonaceous gold ore experiments. Adsorption experiments showed that the anthracite coal adsorbed gold cyanide while bituminous and lignite coal failed to do so. It is believed that the difference in the adsorptive capacity presented by the mineral coals owes to the structure of the carbonaceous material, and also that the anthracite coal structure is similar to what is found in the carbonaceous gold ores presenting preg-robbing activity. The deactivation/passivation experiments indicated that the additives A1, A2, A3, A4 and A5 suppressed the adsorptive capacity of the anthracite by 60–85% in concentrations varying from 562 to 28,125 g/tcoal respectively. The additive presenting the best performance was A2. Experiments with a carbonaceous gold ore indicated that the use of 350 and 1000 g/tgold ore of additive A1 presented the best recoveries, 90.12 and 90.69%, resulting in the lowest presence of gold contents in the tailings, 1.17 and 1.25 g/t respectively. These values are very close to what was reported for CIL leaching (89.89% and 1.30 g/t) and considerably higher than values observed in the conventional leaching (83.79% and 2.10 g/t). Despite presenting the best deactivation/passivation performance when used with the anthracite coal, additive A2 did not reduce the preg-robbing activity of the carbonaceous matter of the ore, resulting in an increase in gold content in the tailing. The use of additives in the industrial process will demand a simpler and less expensive operational facility and the performance will be similar to the CIL technique.

Dye-sensitized Solar Cell utilizing Gold Doped Reduced Graphene Oxide Films Counter Electrode

This work is concerned with the use of gold doped reduced graphene oxide (rGO) films as counter electrode in a dye-sensitized solar cell (DSSC). The effect of gold content on the photovoltaic parameters of the device has been studied. The samples are crystalline, indicated by the presence of rGO phase. It was found that the short-circuit current density (JSC) decreases with the increase in gold content. The DSSC utilizing the sample prepared using 2.0 wt.% gold demonstrated the highest JSC, Voc and η of 0.989 mA cm-2, 0.692 V and 0.175%, respectively. The highest efficiency (η) of the device is due to the lowest leak current and charge transfer resistance (Rct).

Selective oxidation of n-octanol on unmodified and La-modified nanogold catalysts: Effect of metal content

We investigated the influence of metal loading in gold catalysts supported on titania, either unmodified or La-modified, on their catalytic performance and the formation of active sites for selective oxidation of n-octanol under mild conditions. Catalysts were characterized by BET, EDX, ICP, HRTEM, FTIR CO and XPS. Gold content had a significant effect on the catalytic properties of unmodified catalysts: activity of Au/TiO2 increased by increasing the metal load. However, in the case of a lanthanum-modified support samples, an increase of gold content from 0.5 to 4 wt.% had no effect on its activity (ca. 40% conversion after 6 h for all catalysts). This catalytic behavior is due to a change in the surface concentration of Au+ ions. For the unmodified catalysts, the surface concentration of Au+ ions increased with increasing gold loading, and, as a consequence, a significant increase in activity was observed. For La-modified catalysts, the surface concentration of Au+ ions is almost the same for all gold concentrations; as a result, no increase in activity was observed with the increase in gold content. It points to Au+ ions as the most probable active sites for the studied reaction.

Gold recycling and enrichment beneath volcanoes: A case study of Tolbachik, Kamchatka

Magmas supply metals to hydrothermal ore deposits, although typical arc basalts may be unable to produce a gold-rich ore-forming fluid, as such basalts rarely exceed 5 ppb Au. Consistent with this, the occurrence of native gold of magmatic origin is extremely rare, and only a few finds of micron-sized gold particles in unaltered basalts have been documented. Surprisingly, some lava flows and scoria cones of the historic basaltic eruptions of Tolbachik volcano (Kamchatka) are unusually gold-rich. Tolbachik basalts contain up to 11.6 ppb Au based on whole rock analyses, nuggets of gold (electrum) up to 900 μm in size and native gold droplets up to 200 μm, plus numerous vapor-deposited gold crystals within fumarolic incrustations and directly on surfaces of basaltic lapilli. Our results demonstrate that the gold nuggets in Tolbachik basalt are of hydrothermal origin and were physically scavenged from epithermal veins hosted by country rocks during intrusion of mafic magmas. Depending on the melt temperature and/or time span of the melt-rock interaction, gold was ejected by the erupting volcano either in the form of abraded nuggets or liquid droplets, or was fully assimilated (dissolved) into the shallow long-lived magma chamber to provide a 4-fold increase in gold content over background concentration of 2.7 ppb Au, characteristic of mafic volcanic rocks in Kamchatka. Upon the end of the eruption, the continued discharge of volcanic vapors enriched in gold deposited abundant crystals of gold on cooling lava and scoria. Similar to Tolbachik, recycling of metals from prior accumulations (ore deposits) in the shallow crust may take place in other long-lived magma reservoirs, thus upgrading the gold and other metal contents and contributing to the ore-forming potential of a magma.

Investigations of structure and nonlinear optical properties of gold doped germanium–gallium–sulfur chalcogenide glasses

Chalcogenide glass in molar composition of Ga10Ge25S65 (GGS) and same glasses doped with various amount of gold were prepared. Both density and refractive index of the glasses increased with increase of gold content. Optical band gap (Eopg) of the GGS glasses was obtained by Tauc and Menth's method, and the Eopg value decreased with increase of gold content. Analysis of Raman spectra informed that the main frame of the glasses was constructed by [GeS4] tetrahedra and no characteristic band belonging to gold was observed, indicating that gold behaved as a glass modifier for the GGS glasses. To investigate the influence the gold has on third-order optical nonlinearities of the GGS glasses, femtosecond Z-scan measurements were conducted at the wavelength of 800nm. The results showed that the performance of third-order optical nonlinearities of the GGS glasses was improved by introduction of gold.

Nanogold Particles Produced by NaBH4Reduction of Gold Salt in the Presence of Laponite Sol

In the last few decades, there has been considerable effort in preparing and characterizing nanostructured materials. Layered inorganic solids such as polysilicates, double hydroxide, perovskites and clay minerals are important constituents of these assemblies because of their ability to provide interlamellar space, and their large active surface area. Laponite is a synthetic polycrystalline clay similar in structure and composition to natural hectorite of the smectite group. The sodium ions in the central layer of laponite are exchangeable, and in aqueous dispersions, these ions diffuse into the water, and plate-like particles with negatively charged faces are formed. Among nanoparticles, colloidal metal or metal oxide particles have been intensively studied because of their unique optical and catalytic properties and their biomedical applications. There have been many reports on the synthesis of nanoparticle/clay composites. Metal hydroxides of iron, chromium, cobalt, manganese and cerium in acetic acid solutions were used to exchange the sodium ions in laponite, and their corresponding nanometal oxidelaponite composite products were obtained by calcination of adsorptions of these precursor solutions at 500 C in air. The preparation and characterization of nanogold/laponite composite were examined in this study. For this purpose, gold(III) chloride solution in dilute HCl was reduced with sodium borohydride in the presence of laponite. UV-vis spectra of different concentrations of nanogold sols are shown in Figure 1. In Figures 1(a) and (b), very broad absorption peaks are observed, and apparent surface plasmon resonance absorptions of nanogold particles are not observed due to the very low concentration of nanogold particles. Alternatively, characteristic surface plasmon resonance absorption of nanogold particles can be observed at about 520 nm in high concentrations of nanogold (Figures 1(c), (d) and (e)). With the increase of gold content, the absorption peak position is shifted toward higher wavelength, from 518 nm to 521 nm. This red shift can be related to the growth of nanogold particles with the increase of gold content. It is known that the surface plasmon resonance absorption of gold nanoparticles is very sensitive to particle aggregation and variations in surroundings, and strongly influenced by chemical modifications of the particle surfaces. The growth of nanogold particles has also been observed in TEM micrographs, as shown in Figure 2. The particle size is changed from about 3 nm to about 15-20 nm. With a low concentration of nanogold particles, not many particles were observed, and these results agree well with those of UV-vis spectra, Figure 1. UV-vis absorption spectra of gold colloids in the presence of laponite as a function of HAuCl4 concentrations: (a) 0.05, (b) 0.25, (c) 0.50, (d) 2.5, (e) 5.0 mmol.

Synthesis and characterization of Ag/Au alloy and core(Ag)–shell(Au) nanoparticles

Bimetallic silver–gold nanoparticles (NPs) with different structures were prepared. Namely, silver–gold alloy and core(Ag)–shell(Au) type nanoparticles were synthesized at various Ag/Au ratios using only sodium citrate as reductant without any stabilizers. The synthesized NPs were characterized by different structure analysis methods. The unique optical properties of these NPs were studied by UV–vis spectroscopy. For Ag/Au alloy NPs the λmax values are linearly tunable from ∼408nm to 525nm depending on the composition. The plasmon band of core–shell NPs can be shifted to higher wavelengths by depositing a gold shell with increasing thickness. The HRTEM images clearly confirm the two different structures of the NPs. We found that the size of alloy nanoparticles decrease from d ∼15nm to d ∼8nm with the increase in gold content. In contrast, core(Ag)–shell(Au) type NPs with progressively increasing size (d=13–16nm) along with separately formed smaller gold NPs were formed.

Tunable synthesis and acetylation of dendrimer-entrapped or dendrimer-stabilized gold–silver alloy nanoparticles

In this study, amine-terminated generation 5 poly(amidoamine) dendrimers were used as templates or stabilizers to synthesize dendrimer-entrapped or dendrimer-stabilized Au–Ag alloy nanoparticles (NPs) with different gold atom/silver atom/dendrimer molar ratios with the assistance of sodium borohydride reduction chemistry. Following a one-step acetylation reaction to transform the dendrimer terminal amines to acetyl groups, a series of dendrimer-entrapped or dendrimer-stabilized Au–Ag alloy NPs with terminal acetyl groups were formed. The formed Au–Ag alloy NPs before and after acetylation reaction were characterized using different techniques. We showed that the optical property and the size of the bimetallic NPs were greatly affected by the metal composition. At the constant total metal atom/dendrimer molar ratio, the size of the alloy NPs decreased with the gold content. The formed Au–Ag alloy NPs were stable at different pH (pH 5–8) and temperature (4–50°C) conditions. X-ray absorption coefficient measurements showed that the attenuation of the binary NPs was dependent on both the gold content and the surface modification. With the increase of gold content in the binary NPs, their X-ray attenuation intensity was significantly enhanced. At a given metal composition, the X-ray attenuation intensity of the binary NPs was enhanced after acetylation. Cytotoxicity assays showed that after acetylation, the cytocompatibility of Au–Ag alloy NPs was significantly improved. With the controllable particle size and optical property, metal composition-dependent X-ray attenuation characteristics, and improved cytocompatibility after acetylation, these dendrimer-entrapped or dendrimer-stabilized Au–Ag alloy NPs should have a promising potential for CT imaging and other biomedical applications.

Preparation and characterization of polyurethane–gold nanocomposites prepared using encapsulated gold nanoparticles

AbstractGold nanoparticles (GNPs) have been widely studied due to their unique properties. Although many research groups have developed the synthesis of GNPs using various polymers as stabilizing or reducing agents, the effects of GNPs on the structures and properties of polymer matrices have been less reported. We propose a new design for the preparation of polyurethane–gold (PU–Au) nanocomposites. 11‐Mercapto‐1‐undecanol‐coated GNPs acted as the chain extenders and reacted with isocyanates to form covalent bonds between PU and GNPs. PU–Au nanocomposites were successfully synthesized, and the effects of multifunctional GNPs on the structures, morphology and properties of poly(ester urethane) were investigated. Scanning electron microscopy images suggested the GNPs can be dispersed uniformly in the PU matrix. Maltese‐cross of spherical crystals was observed in the PU–Au nanocomposites, and the size of the crystals decreased with an increase in gold content. As the gold content increased, the thermal decomposition temperature and the temperature of the maximum decomposition rate increased. The glass transition temperature, crystal melting temperature and melting enthalpy of the soft segment also increased progressively. The results showed that multifunctional GNPs concentrated hard segments and resulted in an increase of heterogeneous nucleation, phase separation and elasticity. Copyright © 2010 Society of Chemical Industry

架橋ＣＲの分子運動性と金超微粒子充てん効果

The molecular mobility of vulcanized chloroprene rubber (CR) was examined by 1H pulsed NMR. The spin-spin relaxation time (T2) of 1H showed that the vulcanized CR consisted of three components of rubber molecules. The component with the longest T2 (M3 component) appeared at above 90°C, and its molecular mobility was similar to that of liquid. The M3 component was thought to be composed of branch structures such as dangling chains and endchains. For the CR filled with ultrafine gold particles, the temperature at which the M3 component appeared became higher with the increase of gold content. The molecular mobility of the branch structures was reduced by the interaction between the surface of the gold particles and the end groups of rubber molecules such as the metal-sulfur bond. The gold particles did not change the stress-strain and the viscoelastic behaviors of CR, but improved its fatigue property at higher temperature.

Gold doping effects on swelling of teflon-like thin films

We report on the swelling process in gold-doped teflon-like films as a function of metal concentrations. The film thickness variation, measured in low-pressure acetone vapour using an ellipsometric technique, shows, with a range of 0.001–9 mbar, a linear increase in gold content. This trend disappears for metal percentages near to the percolation threshold, an effect which is also evident from the time evolution of the swelling process at constant pressure.

Properties of PdAu and PtCu alloy surfaces for the adsorption and catalytic reduction of O 2 and NO by H 2

The adsorption and catalytic properties of PdAu and PtC alloy surfaces were investigated under low pressure conditions, with the real surface composition being monitored using Auger electron spectroscopy. Flash desorption experiments on O 2 and NO, and steady state kinetic experiments involving the reduction of these substances by H 2 were performed on polycrystalline alloy surfaces. For the PdAu system, O 2 desorption was promoted by gold, as shown by the shift of O 2 desorption toward lower temperature and a linear decrease in the saturated amount of O 2 adsorption with increase in gold content. For the PtCu system, O 2 desorption was retarded by copper i.e. the O 2 desorption temperature shifted upward with increase in copper content. In both the alloy systems, catalytic activities for the above reactions were significantly suppressed by the addition of gold or copper to the platinum group metals. The drop was more pronounced for NO reduction, suggesting that a larger ensemble of active platinum group metal atoms are necessary for NO dissociation.

Mechanism of gold transfer and deposition in a supergene environment

The possibility of gold mobility in supergene environments is suggested by numerous indirect observations of gold particles. However, presently there are no dissolution or transport data based on the chemistry of actual weathering solutions. We have investigated models of gold transport by studying the water chemistry of a stream where weathering of auriferous minerals is occurring under supergene conditions in a temperate climate. Dissolved gold concentrations in the auriferous zone are forty times higher (200 pmolL −1) than in non-auriferous zones (5 pmolL −1). We have examined the potential gold ligands: thiosulfate, hydroxide, and chloride. Speciation calculations using the field data show that gold solubility is controlled by a gold thiosulfate complex: Au(S 2O 3) 2 3−. The oxidation of the thiosulfate ligand induces the destabilization of the aurothiosulfate complex. Gold is then reduced to the metallic state as submicronsized suspended particles. This conclusion is supported by the measured increase in gold content of suspended particulates. Mass balance calculations performed with both dissolved and paniculate gold data permit the quantification of gold deposition along the stream.

Palynological assessment of organic tissues and metallic minerals in the Jerritt Canyon gold deposit, Nevada (U.S.A.)

Organic tissues and metallic minerals were studied in acid residues and thin section of the Jerritt Canyon (Bell Mine) gold deposit. The purpose was to compare gold-bearing and gold-free rocks, characterize their differences, and assess a possible relationship between the invisible gold and the organic tissues in these early Paleozoic, carbonaceous limestones, dolomites, and claystones. The most visually abundant acid-resistant component in the sooty, unoxidized, gold-bearing rocks is a black, rectangular, carbon-bearing mineraloid. In X-ray diffraction, it is poorly crystalline; in nuclear magnetic resonance, it is a highly aromatized structure. The increase in gold content that accompanies the increase in content of this protographite suggests that it may be the major gold-bearing compound. Less abundant among the acid-resistant residues are uncarbonized organic tissues that are typical of marine settings. The tissues not in the vicinity of silicified veins are medium to dark brown. The dominant tissues are the amorphous remains of algae and their zooplankton predators. These uncarbonized indigenous tissues indicate that temperatures were lower than those determined by geochemical and fluid inclusion methods. The presence of different kinds of carbon-bearing compounds could account for the discrepancy between the palynological and geochemical data. The uncarbonized organic tissues comprise such a small percentage of these rocks that they could be easily missed by bulk analytical methods. The presence of uncarbonized tissues helps to constrain the duration of the high heat flow that is shown by the fluid inclusion data. The presence of mixed signals suggests that the protographite may be the product of chemical rather than thermal reactions.

Geomorphological control of gold distribution and gold particle evolution in glacial and fluvioglacial placers of the Ancocala-Ananea basin - Southeastern Andes of Peru

Gold placers are formed as a result of surficial processes but glacial and fluvioglacial systems are generally considered to be unfavourable for placer genesis. Nevertheless, some important glacial and fluvioglacial placers have been discovered and are currently being exploited in the Andes of Peru and Bolivia. In the Plio-Pleistocene Ananea-Ancocala basin (4300–4900 m above sea-level), the gold content of the various formations indicates that only glacial and fluvioglacial sediments related to the Ancocala and Chaquiminas Glaciations (middle and upper Pleistocene) contain gold in any notable quantity. Local concentrations of economic interest occur only where a glacier has cut through a primary mineralized zone. Glacial erosion of dispersed primary mineralizations does not produce high-content placers of the kind found in fluviatile environments. Gold distribution in tills is more irregular than in fluviatile sediments and no marked enrichment at bedrock occurs. The transition from a glacial to a fluvioglacial environment is characterized by an increase in gold content due to a relative concentration of the biggest gold flakes and by the appearance of a gold distribution pattern similar to that found in a fluviatile environment. During their transport by glacial and fluvioglacial processes, gold particles acquire specific features; the size and morphology of a gold flake population are determined by the sedimentological and geomorphological environment in which the flakes are carried.

Formation and stability of amorphous alloys of Au-Ge-Si

Alloys of Au-Ge-Si in a narrow composition range near the eutectic were prepared in amorphous solid form with splat quenching techniques. The glass transition temperature, T g , decreases slightly with increase in gold content of the alloy but the reduced glass temperature, gt g = kT g h v was nearly independent of composition and ~0.006. It was found that the addition of gold to the eutectic alloy increases the resistance of the amorphous alloy to crystallization. This is attributed to a decreasing rate of crystallization of the metastable γ phase with excess of gold. A splat of Au 0.789Ge 0.124Si 0.087 alloy remained amorphous without appreciable crystallization up to 13°K above its T g with a heating rate of 20°K/min.