Gold Sulfide Research Articles

SPHERICAL MICROPARTICLES FROM GOLD–BEARING QUARTZ VEINS OF THE IROKINDA DEPOSIT, WESTERN TRANSBAIKALIA

We have studied the material composition of ore microparticles extracted from gold concentrates of operating quartz vein No. 30 located in the Irokinda deposit, Western Transbaikalia. We consider the origin of such microparticles in connection with our observation data and the previously published structural and geological features revealed in formation of the ore field, as well as tectonophysical conditions of formation of many gold-bearing quartz veins, including vein No. 30. Gold-quartz veins, located in the allochthonous plate thrusted onto the Kelyano-Irokinda belt (Fig. 1), infill the NE-striking fault zones. E.A. Namolov conducted the tectonophysical analysis of the “elementary fracture – ore-bearing suture/joint” system, which provided a genetic explanation of the morphology of ore quartz veins (including vein No. 30) and conditions for formation of their host fault zones. Ore-bearing fractures are combinations of shear and cleavage cracks that occur in case of certain positions of the strain ellipsoid in conditions of horizontal compression. Due to repeated intra-mineralization displacements, the texture of the ores is strappy, and the quartz matrix of the veins contains numerous inclusions of host rocks. The spherical particles have zonal structures and consist of metal nodes and external continuous or discontinuous shells, which thickness ranges from 10 to 400 microns (Fig. 2, Fig. 3). The nodes are composed mainly of native Fe with admixtures of Fe, Mn, Al (Table), the contents of which are typically less than 1.0–1.5 wt %. Characteristic features of the mineral composition of shells of the spheroidal microparticles: – The widespread graphite matrix consisting of minerals of different classes, except for native; – Pyrite in the group of ore oxides of Fe, Mn, Cr, Ti; – A large group of carbonate minerals; – Feldspars and natrosilite among silicates; – The mineral with CaBr 2 composition; – Mono-mineral quartz rims. The consequence of metamorphism, i.e. deformational or mechano-chemical transformations of rocks in Irokinda, as well as the autochthon (the rock bed of the Kelyano-Irokinda belt), is the gas-water (‘hydrothermal’) system capable of forming the spherical ore particles with low-temperature mineral rims. The main feature of the structure of the spherical microparticles in Irokinda is a sharp contrast of the crystallization conditions of the metal nodes and their rims. Similar conditions leading to formation of contrasting mineral associations, that are similar in compositions to the discussed spherules, are characteristic of the gas-water-lithoclastitic and gas-water stages of mud volcanoes. For these stages, we suggest the cavitation mechanism of formation of spherical metal particles of Fe, Fe–Cr and other compositions, which is accompanied by combustion (pyrogenic melt) and pyrolysis of hydrocarbon components of the fluid. This mechanism, with the exception of the origin of the melt (in this case, of the friction type) seems to most closely correspond to the actual data. The spheroids are likely to have formed in the pre-ore stage of formation of the quartz veins. The high-temperature metal spherical microparticles revealed in our study can be regarded as specific indicators showing conditions in which the ore-forming system of the dynamo-metamorphic type was functioning to produce gold mineralization on the Irokinda deposit. The structure and composition of these microparticles differ from those of the microspherules from other gold deposits in Transbaikalia (black shale formation in Sukhoi Log, and low–sulphide gold–quartz ore formation in Pervenets), which also belong to the dynamogenic genetic type. However, the ore-forming systems of the compared deposits have two common factors that contribute to formation of spherical microparticles – high tectonic activity manifested by repeated (impulse-type) tectonic movements, and the associated unstable pressure conditions. The consequence of the latter is heterogenization of the gas-water fluid, which, in turn, leads to the cavitation and froth flotation mechanisms.

Au-S Bonding Revealed from the Characterization of Diatomic Gold Sulfide, AuS.

Gold monosulfide, AuS, has been detected and characterized in the gas phase using optical spectroscopy. The symmetries of the ground and low-lying electronic excited states have been determined by application of a synergy of hot and cold laser excitation techniques. The electronic spectra are assigned to progressions in four band systems associated with excitations from the X(2)Πi ((2σ)(2)(2π)(3)) ground state to the A(2)Σ(+) state arising from the (2σ)(1)(2π)(4) configuration and to the a(4)Σ(-), B(2)Σ(-), and C(2)Δi states arising from the (2σ)(2)(2π)(2)(3σ*)(1) configuration. The bond length and dissociation energy of the ground X(2)Πi state are determined to be 2.156(2) Å and 298 ± 2 kJ/mol, respectively. A molecular orbital correlation diagram is used to rationalize the energy ordering of the excited states and the associated harmonic frequencies.

Biooxidation of Carbonaceous Refractory Gold Ores by an Iron-Sulfur-Oxidizing Mixotrophic Bacterium at Neutral pH

The ability of an iron-sulfur-oxidizing mixotrophic bacterium to treat two types of sulfide-rich carbonaceous refractory gold concentrates from Sulawesi and Sumatra in Indonesia was studied in comparison with an acidophilic chemolithotrophic bacterium Acidithiobacillus ferrooxidans. Over the course of the biooxidation experiments, the pH of the solution tended to rise (pH>5) due to the high content of acid-consuming minerals such as carbonates in both concentrates. Ferric ions were frequently observed to precipitate due to high solution pH. The BIOXskc employed in this study was able to increase the gold extraction from low sulfidic carbonaceous refractory gold concentrates by ~15% higher than that by using At. ferrooxidans. It was also capable of treating carbonaceous matters which causes preg-robbing effect and retaining iron in ionic form due presumably to the production of extracellular polymeric substances (EPS) under high solution pH. Nevertheless, BIOXskc also reduced the gold extraction yield of high sulfidic gold concentrates because of passivation effect. It is suggested that the precipitation of iron and sulfur on the surface of sulfide minerals during biooxidation may prevent cyanide ion contact with gold.

The Microbial Ecology of Moderately Thermophilic Mineral Leaching Reactors: The Effect of Solids Loading and Organic Carbon Supplementation on Reactor Performance

Tank bioleaching of refractory sulphidic gold ores is well established, with potential to expand application to base metal concentrates. With increasing commercial tank bioleaching operations, understanding their microbial consortia is essential for process robustness. Recently, it has been shown that the consortia implicated in tank mineral bioleaching of gold-containing pyritic ores are dynamic, responding to the leaching environment. Factors driving the microbial dynamics of these consortia are under investigation, with emphasis also placed on determining the metabolic role of the key players in these consortia. Here, the combined influence of solids loading and organic carbon availability on microbial community dynamics and performance has been studied in agitated, aerated slurry bioreactors at 45°C. The control (autotrophic) and experimental (organic carbon added) reactors performed comparably at low solids loadings (4%, 7% and 10%). At 20% solids loadings, higher ferric iron concentrations (31 g/L vs 25g/L) and sulphide oxidation (66% vs 45%) were observed in the experimental reactor over the control. Under operating conditions used, a shift from bacterially-dominated cultures with L.ferriphilum as major species towards increasing archaeal abundance was observed. Archaeal abundance was higher in the organic carbon supplemented reactor at all solids loadings. The increased microbial diversity with organic supplementation appears to contribute to increased community robustness and associated leaching with increasing stress.

Удаление сорбционно-активных углеродистых веществ из упорных золотосульфидных руд и концентратов месторождения Майское

Удаление сорбционно-активных углеродистых веществ из упорных золотосульфидных руд и концентратов месторождения Майское

Abstract 3681: Facile fabrication of MRI-capable and NIR-resonant core-satellite nanomediators for photothermal therapy

Abstract Although many techniques exist for fabricating near-infrared (NIR)-resonant and magnetic resonance imaging (MRI)-capable nanomediators for photothermal cancer therapy, preparing them in an efficient and scalable process remains a significant challenge. In this report, we develop two facile methods to fabricate both NIR-resonant and MRI-capable nanomediators utilizing well developed polysiloxane-containing polymer-coated iron oxide nanoparticles (IONPs). One of the methods is to attach multiple NIR-resonant nanoparticles onto a thiol-modified IONP core through one-step mixing with gold sulfide nanoparticles (Au2S NPs) to fabricate a core-satellite nanomediator. The other strategy is to covalently attach a NIR organic dye onto intact polysiloxane-containing polymer-coated IONPs through facile mixing with siloxane-modified IR820. The successful decoration with either Au2S NPs or IR820 is demonstrated for the resultant nanomediators by absorption spectra and transmission electron microscopy (TEM) images. It is estimated that 10 Au2S NPs and 2×104 dye molecules (loading capacity: 4.5 mg IR820/mg Fe) are attached onto the polymer-coated IONPs, respectively. The hydrodynamic sizes of these novel multifunctional nanomediators are ∼57.5 nm for IONP-Au2S NP and 28.2 nm for IONP-IR820, which are much smaller than traditional gold nanoshell-based designs. The photothermal efficiency of the IONP-Au2S NP and IONP-IR820 nanocomposite solutions under the irradiation of 885 nm NIR laser light is significantly enhanced compared to IONPs alone. The enhancement in photothermal efficiency by the newly developed nanomediators is also investigated in nude mice bearing SUM-159 tumor xenografts. The biodistribution data measured by inductively coupled plasma optical emission spectrometry (ICP-OES) reveal that ∼1% injection dose (ID) of IONP-Au2S NPs and ∼9% ID of IONP-IR820 accumulate into tumor tissue 24 h post intravenous injection at a dose of 20 mg Fe/Kg mouse body weight. The average tumor surface temperature recorded by an infrared camera is increased by 10.8 ± 1.2 °C for the mice administered with IONP-Au2S NPs and 25.7 ± 3.6 °C for the group injected with IONP-IR820, compared to 4.8 ± 0.5 °C for the PBS-injected control mice after laser irradiation with a power of 0.5 W for 10 min. Furthermore, our data reveal that the fabrication will not compromise the IONP core capability as an MRI contrast agent. Taken together, we demonstrate a facile technique to generate NIR-resonant and MRI-capable nanomediators from a polysiloxane-containing polymer-coated IONP platform. The as-developed dual functional nanomediators hold great promise for translatable MRI-guided photothermal cancer therapy. Citation Format: Hongwei Chen, Xiaoqing Ren, Hayley Paholak, Joseph Burnett, Feng Ni, Duxin Sun. Facile fabrication of MRI-capable and NIR-resonant core-satellite nanomediators for photothermal therapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3681. doi:10.1158/1538-7445.AM2015-3681

Experimental constraints on gold and silver solubility in iron sulfides

Experiments were performed to determine crystallization of Fe,S-melts (pyriti≿ and troilitic with molar ratio S/Fe ratios of 2 and 1, respectively) containing traces of gold and silver at (Ag/Au)wt ratios varying from 10 to 0.1. The solid products were studied by optical microscopy, scanning electron microscopy, X-ray powder diffraction (XRD), microprobe analysis, and X-ray photoelectron spectroscopy (XPS) in order to reveal the concentration limits of “invisible” gold and silver in magmatic iron sulfides, and to determine the influence of sulfur on forms of precious metals in the Fe–S system with different Ag/Au ratios.Au–Ag phases do not form inclusions but instead concentrate on the grain boundaries in the synthetic pyrrhotite and troilite, while pyrite comprises micro- (1–5 μm) and macroinclusions of Au–Ag alloys and Au–Ag sulfides. In “pyriti≿” systems, the fineness of alloys increases from 650 to 970‰ and the composition of sulfides changes from acanthite (Ag2S) to uytenbogaardtite (Ag3AuS2) and petrovskaite (AgAuS) as the Ag/Au ratio decreases. The concentrations of “invisible” precious metals revealed in troilite were 0.040 ± 0.013 wt.% Au and 0.079 ± 0.016 wt.% Ag. Measured concentrations in pyrite and pyrrhotite were <0.024 wt.% Au and <0.030 wt.% Ag. The surface layers of iron sulfides probed with XPS were enriched in the precious metals, and in silver relative to gold, especially in the systems with Fe/S = 1, probably, due to depletion of the metallic alloy surfaces with gold. Au- and Ag-bearing iron sulfides crystallized primarily from melts may be the source of redeposited phases in hydrothermal and hypergene processes.

Effects of dissolved oxygen and carbon dioxide under oxygen-rich conditions on the biooxidation process of refractory gold concentrate and the microbial community

Biomining microorganisms obtain energy from the oxidation of reduced sulfur and iron (II) by using dissolved oxygen (DO) as the electron acceptor. Carbon dioxide, the carbon source for biomining microorganisms, is essential for biooxidation. However, to date, no published reports exist regarding the effect of reactive oxygen species (ROS) and the CO2 content in an oxygen-rich condition (when oxygen is sufficient) on the biooxidation process. In this study, a microbial community was used to oxidize refractory sulfide gold concentrate in a 1.5L experimental stirred tank reactor. The effects of DO in a slurry and the CO2 content in the intake gas on the biooxidation process, bacterial growth and microbial community were investigated. It was found that the biooxidation efficiency increased at first and then decreased as the DO level elevated, while the content of ROS significantly increased within the bacteria cells. Under an oxygen-rich condition, the biomass increased as the CO2 content increased, while the biooxidation efficiency first increased and then decreased. These changes revealed that the oxidation activity of biomining microorganisms was inhibited by a high CO2 content and that bacterial growth and energy utilization were decoupled. Leptospirillum ferriphilum-like bacteria and Sulfobacillus thermosulfidooxidans were the dominate strains in the experiment. As the DO increased, the relative proportion of L. ferriphilum-like bacteria in the bacteria community first increased and then decreased, while S. thermosulfidooxidans showed the opposite trend. With an increasing CO2 content in the intake gas, the relative proportion of S. thermosulfidooxidans increased, while that of L. ferriphilum-like bacteria decreased.

Facile Fabrication of Near-Infrared-Resonant and Magnetic Resonance Imaging-Capable Nanomediators for Photothermal Therapy.

Although many techniques exist for fabricating near-infrared (NIR)-resonant and magnetic resonance imaging (MRI)-capable nanomediators for photothermal cancer therapy, preparing them in an efficient and scalable process remains a significant challenge. In this report, we exploit one-step siloxane chemistry to facilely conjugate NIR-absorbing satellites onto a well-developed polysiloxane-containing polymer-coated iron oxide nanoparticle (IONP) core to generate dual functional core-satellite nanomediators for photothermal therapy. An advantage of this nanocomposite design is the variety of potential satellites that can be simply attached to impart NIR resonance, which we demonstrate using NIR-resonant gold sulfide nanoparticles (Au2SNPs) and the NIR dye IR820 as two example satellites. The core-satellite nanomediators are fully characterized by using absorption spectra, dynamic light scattering, ζ potential measurements, and transmission electron microscopy. The enhanced photothermal effect under the irradiation of NIR laser light is identified through in vitro solutions and in vivo mice studies. The MRI capabilities as contrast agents are demonstrated in mice. Our data suggest that polysiloxane-containing polymer-coated IONPs can be used as a versatile platform to build such dual functional nanomediators for translatable, MRI-guided photothermal cancer therapy.

Characterization of Conventional One-Step Sodium Thiosulfate Facilitated Gold Nanoparticle Synthesis.

Gold-gold sulfide nanoparticles are of interest for drug delivery, biomedical imaging, and photothermal therapy applications due to a facile synthesis method resulting in small particles with high near-infrared (NIR) absorption efficiency. Previous studies suggest that the NIR sensitivity of these nanoparticles was due to hexagonally shaped metal-coated dielectric nanoparticles that consist of a gold sulfide core and gold shell. Here, we illustrate that the conventional synthesis procedure results in the formation of polydisperse samples of icosahedral gold particles, gold nanoplates, and small gold spheres. Importantly, through compositional analysis, via UV/vis absorption spectrophotometry, transmission electron microscopy (TEM), and energy dispersive x-ray spectroscopy (EDS), we show that all of the nanoparticles exhibit identical face center cubic (FCC) gold crystalline structures, thus suggesting that sulfide is not present in the final fabricated nanoparticles. We show that icosahedrally shaped nanoparticles result in a blue-shifted absorbance, with a peak in the visible range. Alternatively, the nanoplate nanoparticles result in the characteristic NIR absorbance peak. Thus, we report that the NIR-contributing species in conventional gold-gold sulfide formulations are nanoplates that are comprised entirely of gold. Furthermore, polydisperse gold nanoparticle samples produced by the traditional one-step reduction of HAuCl4 by sodium thiosulfate show increased in vitro toxicity, compared to isolated and more homogeneous constituent samples. This result exemplifies the importance of developing monodisperse nanoparticle formulations that are well characterized in order to expedite the development of clinically beneficial nanomaterials.

Improving gold recovery of Pb–Zn sulfide ore by selective activation with organic acid

Free gold and gold wrapped in sulfides are considered as the object of gold floatation. However, floatation of free gold exhibits more variables in practice. In this study, improving gold recovery of a Pb–Zn sulfide ore from Yunnan Province, China, was investigated. The results show that free gold and auriferous sulfides account for 94.99 % of total gold. Without adding organic acid in floatation, only 82 % recovery of gold could be obtained. Gold recovery in Au/Pb concentrates increases by 9.29 % with oxalate added and by 7.35 % with citric acid added, respectively, while performances of lead and arsenic nearly keep a constant. A possible reason is that free gold is of wonderful selectivity against pyrite with organic activators. A new method to enhance gold recovery is proposed.

The use of continuous centrifugal gravity concentration in grinding circuit. Modified approach for improved metallurgical performance and reduced grinding requirements

The use of centrifugal gravity concentration in the closed-grinding circuit of a gold-containing massive sulphide ore was tested on classifier underflow and overflow. A continuous Knelson CVD6 was retrofitted to the hydrocyclone underflow for recovery of Au and Pb at a coarser feed size. The objective of treatment of overflow was recovering unliberated Au prior to flotation. The tests were performed in actual operating conditions at Nyrstar's Myra Falls Mine. The results of the tests on the cyclone underflow revealed that both liberated and unliberated Au and Pb were recovered by the Centrifugal Variable Discharge (CVD) concentrator. Concentrate grades <60g/Mg Au were attainable at a more than 20% recovery. This application also allowed early and increased Pb recovery before it became gravity unrecoverable by over-grinding. Other benefits included capturing middlings for regrinding as well as potential coarser grinding and increase in mill throughput. A coarse grind also corresponds to a reduction in deformation of Au-particles, and is beneficial for increased Au recovery in downstream processing. Treatment of cyclone overflow by the CVD also provided favourable results. The outcomes included capturing unliberated gold prior to flotation and potentially reducing pumping requirements and reagent consumption. A comparison of the metallurgical performances showed that CVD application on classifier underflow was more effective. The CVD was capable of recovering unliberated gold in sulphides and performed better at a coarser particle size. Therefore, when used with the grinding circuit, a coarser grind can be applied and the CVD could be used to reject gangue at a coarser size.

On a role of liquid intermediates in nucleation of gold sulfide nanoparticles in aqueous media.

Previously, we found a series of fluid nanoscale intermediates preceding nucleation of gold sulfide in the reaction between aqueous HAuCl4 and sodium sulfide. Here, the effects of temperature, addition of an inert electrolyte and some other factors on characteristics of the "dense liquid" intermediates and the formation of solid nuclei were studied using UV-vis absorption spectroscopy, DLS, zeta-potential measurements, and SAXS. It was revealed, in particular, that the negatively-charged interfaces of the dense liquid species critically impede their fusion into large enough dense droplets in which nucleation can take place. The nucleation and following coagulation of poorly crystalline gold sulfide proceed not instantly but progressively as the dense liquid droplets arise, with the process being sharply accelerated by the injection of NaCl or temperature increase.

Synthesis of Dumbbell‐Like Gold–Metal Sulfide Core–Shell Nanorods with Largely Enhanced Transverse Plasmon Resonance in Visible Region and Efficiently Improved Photocatalytic Activity

The metallic nanostructures with unique properties of tunable plasmon resonance and large field enhancement have been cooperated with semiconductor to construct hetero‐nanostructures for various applications. Herein, a general and facile approach to synthesize uniform dumbbell‐like gold–sulfide core–shell hetero‐nanostructures is reported. The transformation from Au nanorods (NRs) to dumbbell‐like Au NRs and coating of metal sulfide shells (including Bi2S3, CdS, CuxS, and ZnS) are achieved in a one‐pot reaction. Due to the reshaping of Au core and the deposition of sulfide shell, the plasmon resonances of Au NRs are highly enhanced, especially the about 2 times enhancement for the visible transverse plasmon resonance compared with the initial Au NRs. Owing to the highly enhanced visible light absorption and strong local electric field, we find the photocatalytic activity of dumbbell‐like Au–Bi2S3 NRs is largely enhanced compared with pure Bi2S3 and normal Au–Bi2S3 NRs by testing the photodegradation rate of Rhodamine B (RhB). Moreover, the second‐layer sulfide can be coated and the double‐shell Au–Bi2S3–CdS hetero‐nanostructures show further improved photodegradation rate, especially about 2 times than that of Degussa P25 TiO2 (P25) ascribing to the optimum band arrangement and then the prolonged lifetime of photo‐generated carriers.

Gold in Egypt: Does the future get worse or better?

Within the Eastern Desert of Egypt, there are more than a hundred vein-type gold deposits and occurrences. Gold was mined in the Dynastic and Roman periods of the Egyptian history and most of the attention was focused entirely on the near-surface high grade parts of these veins. Currently, besides the more problematic sulfide-rich quartz veins, which generally occur in the lower levels of the worked out auriferous quartz veins, some targets including wall-rock alteration, listwaenite, dumps and tailings of ancient mines, by-product gold hosted in volcanogenic massive sulfide deposits and gold-bearing Algoma-type BIF, as well as alluvial gold constitute the new targets for gold in the Eastern Desert of Egypt. In most of these targets, gold displays a bimodal distribution; occurring both as free-milling gold and in the form of sub-microscopic or “invisible” gold in refractory sulfides and sulfoarsenides such as pyrite, chalcopyrite, arsenopyrite, gersdorffite and pentlandite minerals.Characterizing gold in an ore is important in extraction metallurgy. Free-milling gold can be efficiently recovered by crushing, grinding and cyanidation without additional processing. In refractory ores, on the other hand, conventional milling can liberate the sulfides from the gangue allowing a low content of concentrate to be produced by a process such as flotation. However, direct leaching of the concentrate results in poor gold extractions as the cyanide lixiviant is unable to contact the gold locked within the refractory host. Oxidative pretreatment is required for such ores and the methods available for oxidation are roasting (calcination), pressure oxidation, and bacterial oxidation; all oxidize the refractory minerals in the ore to render the gold amenable to cyanidation. While such oxidative methods are capable of achieving reasonable recoveries, they increase the capital and operating costs. An alternative, applicable to the liberation of gold from the refractory host, is to continue the grinding process to reduce the particle size of the host mineral thereby exposing a part of the gold surface for contact with the cyanide solution. A benefit of this technique is that the environmental aspects of the oxidation reaction products are avoided, however the ultra fine grinding also adds more operating costs.Metallurgical studies carried out on some gold deposits, dumps and tailings of ancient gold mines in Egypt, proved that these ores are amenable to percolation leaching (concentration of KCN varies between 0.5 and 1g/L) for the (−10mm) grain size, and consequently heap leaching is a successful technique as the results of these laboratory scale column tests show. In most of these studies, a marked improvement in the percent of gold recovery was gained when the crushed ore is agglomerated by the addition of water, lime and/or cement particularly in ores containing significant quantities of clay minerals and clay-forming minerals (e.g. sericite and muscovite), and by addition of kerosene which passivates the adsorption surfaces on the graphite.Placer gold is recovered by gravity methods utilizing the large difference in specific gravity between gold and commonly associated minerals such as quartz and feldspar. The equipments range from a simple pan to more complex devices used in gold recovery plants and dredges.Modern studies in Egypt point to the presence of different targets of gold; diverse in their gold content, mode of occurrence of gold and the metallurgical treatments required for extracting gold. With the advance of modern techniques such as Electron Microprobe Analyses (EMPA), laser Ablation Microprobe Inductively Coupled Plasma Mass Spectroscopy (LAM-ICP-MS), gold ores in Egypt should be re-characterized precisely to know the specifications of these ores and consequently predict the metallurgical regime required, and with the high world gold price, it has become necessary to take into consideration the presence of refractory gold ores as one of these targets in Egypt. Generally speaking, laboratory experiments conducted on gold processing in Egypt are encouraging to some extent; however the gold extraction rates of the free milling ores with conventional cyanidation and refractory ores with direct and pretreatment techniques can be improved by modifying the conditions of extraction to be consistent with the results obtained from the re-characterization stage. Otherwise any target for gold and whatsoever the mode of occurrence of gold in this target (i.e. free-milling and/or refractory) could be recovered directly by heap leaching technique and we should accept less than ideal gold recovery for any target when weighed against the capital expenditure required for processes such as roasting, and the continuous grinding processes which might improve recoveries by only a small percentage.

“Invisible” gold in covellite (CuS): Synthesis and studies by EPMA, LA-ICP-MS, and XPS techniques

Samples of covellite CuS(cr) containing up to 0.3 wt % of gold in “invisible” form were obtained by means of hydrothermal synthesis (450–475°C, 1 kbar) and synthesis in eutectic chloride melts (495°C). The studies using EPMA and LA-ICP-MS techniques showed that gold was uniformly dispersed within the volume of covellite grains and Au content increased with increasing of sulfur fugacity. The XPS-analysis of the samples obtained showed no chemical shift of the Au-4f 7/2 line compared to Au and Au2S, whereas a positive chemical shift of this line was revealed for mixed Au-Ag sulfides and tellurides. The obtained data allow one to assume that gold does not occur in covellite as an isomorphous admixture (solid solution) but forms nanoparticles of Au or gold sulfide.

Ammoniacal thiosulfate leaching of pressure oxidized sulfide gold concentrate with low reagent consumption

Ammoniacal thiosulfate leaching of pressure oxidized sulfide gold concentrate received from a gold mine is studied. The main chemical composition of the concentrate was Au 32g/t, Ag 12g/t, Fe 59%, S 21% and As 19%. The experimental variables studied were ammonia concentration, thiosulfate concentration, copper concentration, and temperature. The highest gold extraction (89%) was achieved with the following leaching solutions: 0.2molS2O3/L, 0.2molNH3/L, and 0.1gCu/L; and with the following conditions: solids, 30m-%; pressure, 1atm; continuous aeration (0.2L/min); temperature, 30°C; and leaching time, 6h. Measured thiosulfate and copper concentrations after 6h of leaching were 0.19M and 0.08g/L, respectively. The results from the leaching experiments showed that the pressure oxidized gold concentrate was effectively leached in an ammoniacal thiosulfate leaching solution with minimal reagent consumption. The study shows that the widely reported problem of high reagent consumption can be circumvented in leaching of pressure oxidized sulfide gold concentrate by the use of low reagent concentrations. The results indicate good premises for gold recovery by ion-exchange resins, since minimal thiosulfate consumption also ensures low polythionate concentration, which is an important issue in gold recovery with ion-exchange resins. The minimal reagent consumption also indicates that there are good possibilities to circulate the leaching solution for re-use in the leaching stage after gold recovery and solid–liquid separation.

Abstract 5380: Near-infrared-resonant IONP/Au2S core/satellites hybrid nanocomposite for imaging-guided photothermal therapy

Abstract Abstract: Photothermal therapy (PTT) using near-infrared-resonant nanomaterials including multifunctional probes with both therapeutic functions and imaging capabilities has gained great attention in recent years. However, various challenges still exist including the large size of gold nanoshells, the “melting” effect of gold nanorods, lack of imaging capability, and tedious multiple steps for making imaging-capable multifunctional probes. Consequently, it is desired to develop an effective PTT mediator with the following criteria: small size, photo stability, facile synthesis, low toxicity, and imaging capability. We report the design of a core/satellites hybrid nanocomposite with a highly crystallized iron oxide nanoparticle (IONP) core (10-20 nm) and multiple gold sulfide (Au2S) nanoparticle satellites (1-2 nm) attached to the IONP polysiloxane-containing polymer coating for imaging-guided photothermal cancer therapy. In this nanostructure, the multiple satellites (Au2S) enhance PTT, while the IONP core serves as both a photothermal mediator and magnetic resonance imaging (MRI) contrast agent to localize the tumor. To make these core/satellites nanocomposites we first modify the IONP polymer coating with (3-mercaptopropyl) trimethoxysilane followed by mixing with Au2S nanoparticles, which are made by mixing sodium sulfide (Na2S) and chloroauric acid (HAuCl4) at the designed ratio. After purification using a magnet, the TEM image shows that around 8-10 Au2S nanoparticles (1-2 nm average diameter) were attached to each IONP (15 nm in diameter). This core/satellites nanocomposite has obvious absorption in the near infrared (NIR) range and the absorption peak can be adjusted by the molar ratio of Na2S to HAuCl4. The developed nanocomposite exhibits an enhanced photothermal effects without any quenching under NIR laser light. Benefitting from the anti-biofouling polysiloxane-containing polymer coating for in vivo applications, the core/satellites nanocomposites effectively accumulate to xenograft tumor tissue (SUM-159, triple-negative breast tumor cell line) through the enhanced permeability and retention effect after tail vein injection. MRI imaging is used to locate the tumors. NIR triggered PTT, which is enhanced by the core/satellites nanoparticles within the tumor site, destroys the tumor cells, while the tumor tissues in control mice do not show any change under the same laser light irradiation. Our in vitro and in vivo data reveal that NIR-resonant IONP/Au2S core/satellites nanocomposites can be used as effective MRI imaging-guided photothermal cancer therapy. Correspondence should be addressed to: Duxin Sun, PhD, or Hongwei Chen, PhD, Department of Pharmaceutical Sciences, College of Pharmacy, The University of Michigan, 428 Church Street, Ann Arbor, MI 48109, Email: duxins@umich.edu (D. Sun); or hongweic@umich.edu (H. Chen) Citation Format: Hongwei Chen, Joseph Burnett, Xiaoqing Ren, Feng Ni, Yi Wei, Hayley Paholak, Duxin Sun. Near-infrared-resonant IONP/Au2S core/satellites hybrid nanocomposite for imaging-guided photothermal therapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5380. doi:10.1158/1538-7445.AM2014-5380

Infrared microthermometric and noble gas isotope study of fluid inclusions in ore minerals at the Woxi orogenic Au–Sb–W deposit, western Hunan, South China

The Woxi Au–Sb–W deposit, hosted by the Neoproterozoic low-grade metamorphic clastic rocks, is located in a brittle-ductile shear zone within the Xuefengshan Range, South China. Orebodies are predominantly banded quartz veins, which are strictly controlled by bedding faults and display significant vertical extents (up to 2km) without obvious vertical metal zoning. Fluid inclusions hosted in quartz, scheelite, and stibnite from quartz–scheelite and quartz–sulfide–gold veins have been studied using conventional and infrared microscopy, respectively. Four types of fluid inclusions were identified based on petrography, including type I (two-phase, liquid-rich aqueous inclusions), type II (two- or three-phase, CO2-rich inclusions), type III (two-phase, vapour-rich aqueous inclusions), and type IV (single-phase aqueous inclusions). The fluid inclusions in ore minerals (scheelite and stibnite) and their coexisting quartz largely share similar characteristics in terms of their types, homogenization temperatures and salinities. This is consistent with the fact that these ore minerals are always intergrown with quartz. Microthermometric and laser Raman data indicate a low-to-moderate temperature (140–240°C), low salinity (<7.0wt.% NaCl equiv.), CO2-rich, N2-bearing aqueous ore-forming fluid. Such fluid is further identified as a deeply non-magmatic crustal fluid rather than a mantle-source fluid by the significantly low 3He/4He ratios (0.002–0.281Ra), and a small amount of meteoric water or host-rock-buffered fluid could be involved. W ore precipitation was probably associated with mixing between a deeply-originated crustal fluid and host-rock-buffered fluid based on the fluid inclusion features in scheelite and quartz-I. However, Au and Sb ore deposition probably resulted from boiling which was caused by the marked pressure drop. Geological features (such as banded structure and crack-sealing structure) also indicate that fluid pressure fluctuation induced by fault-valve mechanism occurred during ore precipitation. These characteristics of the ore-forming fluids in the Woxi deposit are in good agreement with the definition of orogenic gold deposits and the Woxi Au–Sb–W deposit is probably an atypical orogenic gold deposit for its unique ore-forming element association.

Characterization of the silicon nanopillar-surface filled and grafted with nanomaterials

This paper reports the characterization of the silicon nanopillar-surface filled and grafted with nanomaterials. Usually a silicon nanopillar-surface contains nanopillars and air among them. The air is not a good medium to absorb and trap the incoming photons. In order to improve this capability, the air should be replaced with other material. To this end, copper sulfide–gold (CuS–Au) core–shell nanostructures and silver nanoplates are used as two representative substitutes for air among the nanopillars. Experiments find that the reflectance of the nanomaterial-coated nanopillar-surface can be reduced at least 50% compared to that of the bare nanopillar-surface. Different nanomaterial-coated nanopillar-surface can tune the optical reflectance and absorption profile, thereby trapping photons in different wavelength ranges.