Absence Of Gold Research Articles

Implications for metallogenic evolution of the Balong gold deposit, East Kunlun metallogenic belt: Insights from in-situ trace elements and S isotopes of sulfides

The Balong gold deposit is one of numerous lode gold deposits in the East Kunlun metallogenic belt. Gold mineralization is hosted in Triassic granitoids, typified by auriferous quartz veins. Hydrothermal alteration includes sericite, quartz, sulfide, chlorite, and calcite. Pyrite, as the most abundant sulfide in the ore, is sometimes seen in the company of arsenopyrite. Three types of pyrite have been identified. The porous Py1 exhibits low Co and Ni contents, with an absence of gold. Subhedral Py2-1 shows higher Co (median 80 ppm) and Ni (median 10.5 ppm) contents and contains various Cu-Pb-Zn-Ag mineral inclusions. Py2-2 shows an increase in As (median 17, 073 ppm) and Au (median 3.79 ppm), exhibiting obvious distinctions between Py2-1 and Py2-2.Gold in the Balong deposit consists of both visible and invisible gold. Gold occurs within micro-fractures of pyrite and arsenopyrite, appearing as irregular inclusions or as infillings. Apart from visible gold grains, the majority of invisible gold hosted in Py2-2 occurs as solid solutions (Au+). Coupled dissolution-reprecipitation reactions of early pyrite are a key factor for visible gold precipitation and later invisible gold enrichment. Pyrite records a narrow range of δ34S values from −1.6 to 5.4 ‰, reflecting sulfur from a deep magmatic source. These findings indicate a connection between the ore-forming materials and the evolved magmatic-hydrothermal fluids.

Devonian intrusions of southwestern New Brunswick, Canada: U-Pb geochronology, petrogenesis and genetic constraints on gold mineralization

ABSTRACT The Clarence Stream intrusion-related gold deposit is hosted within metasedimentary and metavolcanic sequences of the Ordovician Cookson and Silurian Mascarene groups that were intruded by several phases of the Late Silurian to Early Devonian Saint George Plutonic Suite. Based on geochemical and geochronological data, the intrusive rocks in the deposit are categorized into three distinct suites, including gabbroic, granitoid, and Whittier Ridge Granite (WRG). The gabbroic suite is the same as the East Branch Brook metagabbro intrusion, which exhibits a subalkaline mafic composition fractionated from a depleted mantle in a suprasubduction zone setting. The granitoid suite shows the same geochemical characteristics and age as the metaluminous to slightly peraluminous Magaguadavic Granite and its fractionated phases. The WRG suite reflects characteristics of calc-alkaline, metaluminous to peraluminous I-type granites in the area, such as Sorrel Ridge and Mount Douglas granitic plutons. In situ U-Pb zircon geochronology yielded an age of 419.5 ± 3.8 Ma for a monzodiorite from the gabbroic suite. Porphyritic granite and alkali granite from granitoid suite yielded U-Pb zircon age of 402.4 ± 1.8 Ma and 394.3 ± 3.8 Ma, respectively. Geochronologic data from the WRG suite reflect two different crystallization ages of 383.8 Ma (382.4 ± 3.1 to 385.1 ± 4) and 372.4 Ma (367.4 ± 1.3 to 377.1 ± 1.9). Several pieces of evidence demonstrate that the gold mineralizing events occurred after the emplacement of the East Branch Brook metagabbroic dykes and are linked to the various intrusive phases of the nearby syntectonic Early Devonian Magaguadavic Granite. The absence of gold and sulphide mineralization in felsic dykes related to the WRG confirms that this plutonic body formed adjacent to the gold zones after the main gold mineralizing event.

Investigating the Chaperoning Effect of Nanoparticles in Chemically Denatured zDHFR: An in vitro Study

Maintenance of native structure and function of the protein is a major concern for industrial production of aggregation prone therapeutically important recombinant proteins. Aggregation may results due to change in the native conformation of proteins under different stress conditions. To overcome the problem of protein aggregation, role of silver and gold nanoparticles have been investigated. The nanoparticles owing to their affirmative interaction with the proteins possess chaperoning activities and protect the native state from denaturation. In the present study, through performing chemical denaturation of zebrafish dihydrofolate reductase using denaturants like guanidine hydrochloride and urea in the presence and absence of gold and silver nanoparticles and monitoring the process through enzyme activity assay and intrinsic tryptophan fluorescence, we have demonstrated the impact of nanoparticles in maintaining native conformation of proteins. Further, the outcome of refolding studies of DHFR protein with nanoparticles monitored by UV-visible spectroscopy was also reported.

Prospects and possibilities of using ash and slag wastes of power enterprises of Primorsky Krai as technogenic mineral raw materials

The results of an investigation of ash and slag wastes (ASW) of enterprises of the energy sector of Primorsky Krai are presented. The averaged contents of the main elements and mineral complexes in Primorsky Krai are given. It is shown that the mineral composition of the ASW data makes it possible to separate the primary raw materials into fractions with different compositions. A scheme is proposed for dividing the initial ash extractors into separate mineral fractions by the particle size and by their physical properties. The predominant concentration of gold, platinum, rare earth elements (REE) and a number of other valuable components in the heavy non-magnetic fraction isolated from the primary ASW was detected. Almost complete absence of gold, noble metals and REE in underburning of coal, magnetic and micro-dispersed fractions of ASW has been demonstrated. A device was offered for complex processing of ash and slag wastes of enterprises of the power industry of Primorsky Krai, which makes it possible to divide the initial ASW into mineral fractions, being raw materials for various industries.

Low resistance copper-based ohmic contact for AlGaN/GaN high electron mobility transistors

Ti/Al/Ni/Cu ohmic contact for AlGaN/GaN structure has been fabricated. The Ni layer played an important role in achieving low specific contact resistance (rc), smooth morphology, and excellent edge acuity. With a 50-Å Ni layer, a rc of 1.35 × 10−6 Ω-cm2 and a root-mean-square roughness of 7.65 nm have been realized. The characterization results indicated that no evidence of Cu diffusion into the semiconductor layers. The formation of Al-Cu and Ti-Cu alloys might have confined the Cu within the ohmic metal. In the absence of gold, the surface roughening caused by Au-Al alloy in conventional Ti/Al/Ni/Au structure was also prevented.

Influence of supported gold particles on the surface reactions of ethanol on TiO2

The adsorption and reactions of ethanol on the surfaces of TiO2 and TiO2-supported gold samples were investigated by infrared (IR) spectroscopy and mass spectrometry. IR spectra measured as the samples were treated in flowing ethanol at room temperature indicate that the alcohol was adsorbed both molecularly and dissociatively in the form of ethoxy species bonded to Ti4+ sites. Our results suggest that the presence of neighboring gold particles facilitates cleavage of the β-CH bond of the ethoxy species at increasing temperature, leading to the formation of acetaldehyde linearly bonded to Ti4+ sites, which is readily desorbed. In the process, hydrogen adatoms are recombined on gold particles to give H2. In absence of gold, Ti4+ sites abstract hydrogen atoms from the ethoxy species to give titanium hydride species, which react with hydroxyl groups to produce water and leave oxygen vacancies on the TiO2 surface. Acetaldehyde is formed in the process and it is adsorbed in a bidentate configuration on the oxygen vacancies, where it undergoes reductive coupling to give butene. Our data show that the ability of gold particles to abstract and recombine hydrogen atoms prevents the formation of oxygen vacancies on the support and, in consequence, hinders the subsequent reactions of the produced acetaldehyde.

Anticancer studies of drug encapsulated polyethylene terephthalate-Co-polylactic acid nanocapsules

Objectives:The purpose of this study was to investigate the anticancer activity of anticancer drugs (5-fluorouracil and 6-thioguanine) in polymeric nanocapsules in the presence and in the absence of gold and iron oxide nanoparticles toward Hep2 cancer cells.Materials and Methods:MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay was used for quantitative measurements for the anticancer cell activity. Encapsulated drug in polyethylene terephthalate-polylactic acid copolymer (PET-co-PLA) nanocapsules in the presence and absence of gold and iron oxide nanoparticles were prepared via the W/O/W emulsification solvent-evaporation method. Morphology of the nanoparticles was characterized by transmission electron microscopy and scanning electron microscopy.Conclusion:The average size of the polymeric nanocapsules, gold nanoparticles, and iron oxide nanoparticles were found to be in range of 230-260, 18 -20 nm, 5-10 nm, respectively. The findings in this study inferred that incorporated drug in polymeric nanocapsules with gold nanoparticles and iron oxide nanoparticles show better anticancer activity when compared with encapsulated drug in polymeric nanocapsules.

How Gold Particles Suppress Concentration Quenching of Fluorophores Encapsulated in Silica Beads

Increasing the luminescence of silica particles encapsulating fluorescein by increasing fluorescein concentration is a promising strategy which is unfortunately limited by the phenomenon of self-quenching. In this paper, we demonstrate that this quenching can be almost entirely suppressed by the presence of gold inclusions within silica. Precisely, in core(gold)/shell(polysiloxane) particles incorporating fluorescein molecules, the quantum yield attains 80% of that of isolated fluorescein for an interdye distance of 3 nm whereas it is less than 15% in the absence of gold. From systematic measurements of quantum yield and lifetime, we proved that, contrary to all literature expectations, the reduction of self-quenching does not originate from the enhancement of the radiative decay rate but from a dramatic decrease of the nonradiative one: the presence of metal inclusions impeding energy transfers to fluorescein H-type dimers that act as traps for light.

Adsorption of Thiol-Protected Gold Nanoparticles on TiO2 and Their Behavior under UV Light Irradiation

A combination of in situ attenuated total reflection infrared (ATR-IR) spectroscopy, UV-vis spectroscopy and transmission electron microscopy was used to study the adsorption of thiol-protected gold nanoparticles on TiO2 films and the behavior of the resulting composite films upon UV irradiation. The gold nanoparticles were covered by charged thiols N-acetyl-L-cysteine and L-glutathione and had a mean core diameter of about 1 nm. The TiO2 film was prepared by deposition of a slurry of TiO2 nanoparticles with a particles size of 21 nm. The combination of the two spectroscopic techniques showed that the adsorption of the gold nanoparticles onto the TiO2 films is significantly limited by intrafilm diffusion. Upon illumination the IR spectra revealed the removal of the adsorbed thiolates and the appearance of sulfates. These species were also observed when N-acetyl-L-cysteine adsorbed on TiO2 was illuminated, i.e., in the absence of gold. In the latter case oxalate was observed in large quantity on the TiO2 surface, in contrast to the illumination of the N-acetyl-L-cysteineprotected gold particles. This indicates a different pathway for the decomposition of the adsorbed thiol when adsorbed on the gold or directly on the TiO2 surface. In situ UV-vis spectroscopy also shows the formation of larger particles upon illumination, which is confirmed by transmission electron microscopy.

A Luminescent Supermolecule with Gold(I) Quinoline-8-thiolate: Crystal Structure, Spectroscopic and Photophysical Properties

The trinuclear complex [(8-QNS)(2)Au(AuPPh(3))(2)].BF(4) (8-QNS = quinoline-8-thiolate), with intramolecular gold(I)...gold(I) distances of 3.0952(4) and 3.0526(3) A, is aggregated to form a novel hexanuclear supermolecule, ([(8-QNS)2(Au(AuPPh3)2])2.(BF4)2, via a close intermolecular gold(I)...gold(I) contact of 3.1135(3) A. The beautiful hexanuclear supermolecule has an inversion center, and the six metal centers can be viewed as roughly coplanar. Six gold(I) ions are embedded in an ellipse and surrounded by 4 quinoline and 12 phenyl rings. The title compound shows interesting spectroscopic and luminescence properties dependent on the solvent polarity; i.e., it emits at ca. 440 and 636 nm in CH(2)Cl(2) and only at ca. 450 nm in CH(3)CN. The long-lived emission at ca. 636 nm (16.2 micros) in CH(2)Cl(2) is quenched by polar solvents such as CH(3)CN and CH(3)OH with quenching constants as 1.00 x 10(5) and 3.03 x 10(4) s(-1) M(-1), respectively, which is suggested to be related to the presence or absence of gold(I)...gold(I) interactions due to scrambling of the [AuPPh(3)]+ units, isolobal to H+.

Optical and Chemical Observations on Gold−Mercury Nanoparticles in Aqueous Solution

The γ-radiolytic reduction of Hg2+ in aqueous solution in the presence of 0.3 M 2-propanol first leads to Hg22+ (e237 nm = 3.2 × 104 M-1 cm-1), and later to colloidal mercury. When the reduction is carried out in the presence of colloidal gold nanoparticles, Hg22+ does not appear as an intermediate, and Hg22+ formed in the absence of gold does not react with added gold colloid. These effects are understood in terms of the reaction of a precursor, Hg+, with the gold particles. The optical absorption spectra of the resulting mercury containing gold particles are reported for various Au/Hg ratios. The plasmon absorption band of gold is blue-shifted and damped, and a broad absorption band develops around 360 nm with increasing mercury content. The mercury of the composite particles is slowly reoxidized upon exposure of the solution to air. Excess Hg2+ ions in solution extract adsorbed mercury in the form of Hg22+. Both the absorption spectra and electron micrographs of the gold particles are interpreted by a ...

The preparation and coordination chemistry of substituted benzenethiols. Triphenylphosphine gold(I)complexes of sterically demanding and nondemandingarenethiols. The absence of gold(I)–gold(I) interactions

Novel substituted benzenethiols can be easily prepared via aryl thiocyanates or arylbromides. Reaction of [(Ph 3P)AuCl] with the sterically-non demanding benzenethiols HSC 6H 4NMe 2- p and HSC 6H 4NMe 3 +- p and with the sterically-demanding benzenethiols HSCMe 2H 2NMe 2- p, HSC 6Me 4H- p and in the presence of triethylamine yields the monomeric gold(I) complexes [(Ph 3P)Au(SAr)], which are analogous to the gold-based antiarthritic drug Auran of in. Reaction with the sterically demanding dithiol HSC 6Me 4SH- p in the presence of NEt 3 yields the dimeric complex 0{(Ph 3P)Au} 2( μ-SC 6Me 4S- p)].Spectrochemical and electrochemical data are reported. The crystal structures of [(Ph 3P)Au(SC 6H 4NMe 2- p)] and [(Ph 3P)Au(SC 6H 4NMe 3- p)]PF 6 have been solved: both complexes are monomeric in the solid state, lacking the short gold–gold interaction which is commonly found in gold(I) complexes of soft ligands, e.g., [(Ph 3P)Au(SPh)] 2.

Measuring diagnostic accuracy in the absence of a "gold standard".

As the nation debates issues of national health care reform, psychiatrists seek equal status with other medical colleagues. To defend psychiatry in the national arena, the accuracy of psychiatric diagnoses must be measured. Indexes of accuracy such as sensitivity and specificity provide valuable information, yet they are rarely computed because there is no "gold standard" with which to compare them. The goal of this article is to show how this problem can be overcome and to encourage nosologists to use accuracy statistics in assessing the adequacy of psychiatric diagnoses. The authors reviewed the literature on medical decision making to find methodological approaches to assessing diagnostic accuracy in the absence of gold standards. A lack of such standards is not unique to psychiatry and has been addressed with a variety of novel analytic procedures. Although these methods differ in many respects, each recognizes that the conventional 2 x 2 table of interrater agreement does not provide enough data for estimating diagnostic accuracy. After defining the data needed, each method provides a mathematical model that estimates accuracy statistics and the prevalence of a disorder. Most of these methods are variants of latent class analysis. The authors reanalyzed data from one of the reviewed papers to show that similar inferences about accuracy of diagnoses could be drawn from a conventional latent class analysis. There are potential pitfalls in using latent structure methods, but their cautious use would provide valuable information for psychiatric nosology. These methods supplement, but do not replace, data about outcome, family history, laboratory studies, and other validating criteria in making accurate diagnoses.

Distinguishing barren and auriferous veins in the Sigma Mine, Val-d'Or, Quebec

The Sigma Mine is an Archean lode gold deposit located in the Abitibi greenstone belt, Quebec. Barren quartz veins occur subparallel to auriferous veins within the mine and also occur north of the mine. The quartz and auriferous veins exhibit a similar mineralogy and alteration and are indistinguishable except for the presence or absence of gold. This study determines differences between (i) a vein that may be auriferous but lacks gold at that location and (ii) a barren vein that formed from fluids that never had the capability of carrying gold. Microthermometry distinguishes two distinct salinities within aqueous inclusions in the barren veins, compared to high salinities only reported in the auriferous veins. The CO2–H2O fluid inclusions within barren veins are remarkably similar to their counterparts in auriferous veins in composition, homogenization temperature, and CO2 effervescence. The most significant difference between the two vein types, and a potential exploration tool, is observed in the CO2-rich inclusions. Tight clustering of first melting temperatures between −57.4 and −56.4 °C and Raman spectroscopy indicate the presence of only CO2 in the barren veins. These results contrast sharply with the −62.5 to −56.0 °C range of first melting temperatures and the presence of H2S indicated by Raman spectroscopy in auriferous veins. Lack of CH4 and H2S gases in the barren CO2-rich inclusions reflects the oxidation state of the fluids, which was too high to permit transport of gold as a reduced complex.

Grand Designs The Peace Plans of the Late Renaissance

The frustration of intellectuals who attempt to cure mankind of its follies is perennial and proverbial. Reactions to this frustration, at all times, range from resignation to revolution. In the sixteenth century resignation received philosophical expression in Neostoicism which taught the wise man how to survive in adversity and preserve his peace of mind and moral rectitude, and as an extreme example of revolutionary reaction one could cite the Munsterite attempt to establish a New Jerusalem by force. In between these two poles lies the field of utopias: literary descriptions of things as they should be, visions to be aspired to but often without a prescription as to how they are to be attained. For this weakness the absence of a precise bridge leading from reality to ideal utopias are frequently dismissed as ' 'melancholic sighs which are not calls for action. Yet not all utopists were armchair intellectuals indulging in day dreams, and one of the tantalizing aspects of the study of their visions is the attempt to deduce the means by which they hoped to realize the dream, or, in other words, what they considered to be possible agents of change. Most Renaissance utopias were blueprints for a single perfect community existing within an unreformed world. Thus their authors had to contend with the question of the relations of their ideal society with the rest of the still-imperfect world. In certain cases the problem was solved by locating the Utopian country in such a remote place that it would be cut off from the rest of civilization, hidden and protected from its evils; other utopists imagined their perfect community as strong enough to repel any invader and even, when necessary, to conquer neighbours and impose upon them the ideal way of life; and some visionaries claimed that the security of their land would be assured since its Utopian simplicity, austerity and absence of gold would deflect the envy and greed of potential enemies. Yet in none of the

Inhibition of antigen- and mitogen-induced human lymphocyte proliferation by gold compounds.

Gold sodium thiomalate (GST) inhibited in vitro antigen- and mitogen-triggered human lymphocyte DNA synthesis. Inhibition of responsiveness was observed with concentrations of GST equivalent to gold levels found in serum or tissues of patients receiving chrysotherapy, Inhibition was dependent upon the gold ion itself since GST and gold chloride were both inhibitory whereas thiomalic acid was not. Inhibition could not be explained by nonspecific killing of cells or by an alteration in the kinetics of the responses. GST inhibited mitogen-induced proliferation most effectively when present from the initiation of culture and could not inhibit the responsiveness of cells which previously had been activated by concanvalin A. These findings indicated that GST blocked a critical early step in lymphocyte activation. The degree of GST-induced inhibition of proliferation was increased in cultures of cells partially depleted of monocytes. Moreover, inhibition was reversed by supplementation of these cultures with purified monocytes. These observations suggested that GST blocked thymus-derived (T)-lymphocyte activation by interfering with a requisite function of the monocyte population in initiating such responses. Prolonged incubation of peripheral blood mononuclear cells with GST resulted in diminished mitogen responsiveness upon subsequent culture in the absence of gold. The addition of fresh monocytes restored responsiveness to these populations. Furthermore, preincubation of purified monocytes with GST rendered them deficient in their ability to support mitogen-induced T-lymphocyte proliferation on subsequent culture. These observations indicate that the major effect of GST results from interference with the functional capability of the monocyte population.