Gold in Ophiolites

Ophiolites, as a class, have been currently under-estimated as potential gold targets, although they have been the subject of major scientific research. Their resources have also attracted investors producing Cr, Cu (massive sulphides), Co, Ni (laterites), industrial rocks and minerals (serpentinites, emeralds), etc. They are also potential PGE sources.

Gold Ores Related to Shear Zones, West Santa Comba Fervenza Area (Galicia, NW Spain): A Mineralogical Study

Recent research has discovered high-grade Au ores in NNE-SSW trending shear zones in metamorphic proterozoic and palaeozoic terranes, some 40 km NW of Santiago de Compostela (NW Spain). The orebodies are bound to late-stage Hercynian structures, mainly due to brittle deformation, which are superimposed on earlier ductile shear zones, cutting through various catazonal lithologies, including ortho- and paragneisses, amphibolites, eclogites, and granites. Ore mineralogy, alteration, and ore textures define a frame whose main features are common to all prospects in the area. Main minerals are arsenopyrite and pyrite - accompanied by quartz, adularia, sericite, + (tourmaline, chlorite, carbonates, graphite), as main gangue minerals - with subordinate amounts of boulangerite, bismuthinite, kobellite, jamesonite, chalcopyrite, marcasite, galena, sphalerite, rutile, titanite, scheelite, beryl, fluorite, and minor native gold, electrum, native bismuth, fahlore, pyrrhotite, mackinawite, etc., defining a meso-catathermal paragenesis. Detailed microscopic study allows the author to propose a general descriptive scheme of textural classification for this type of ore. Most of the ores fill open spaces or veins, seal cracks or cement breccias; disseminated ores with replacement features related to alteration (mainly silicification, sericitization, and adularization) are also observed. Intensive and repeated cataclasis is a common feature of many ores, suggesting successive events of brittle deformation, hydrothermal flow, and ore precipitation. Gold may be transported and accumulated in any of these events, but tends to be concentrated in later ones. The origin of the gold ores is explained in terms of hydrotherreal discharge, associated with mainly brittle deformation and possibly related to granitic magmas, in the global tectonic frame of crustal evolution of West Galicia. The mineralogical and textural study suggests some criteria which will be of practical value for exploration and for ore processing. Ore grades can be improved by flotation of arsenopyrite. Non-conventional methods, such as pressure or bacterial leaching, may subsequently obtain a residue enriched in gold.

40ar/39ar Dating of alunite from the Pueblo Viejo Gold-Silver District, Dominican Republic

New 40Ar/39Ar ages for alunite from the Moore and Monte Negro deposits in the Pueblo Viejo district, as well as from a newly discovered alunite-bearing zone on Loma la Cuaba west of the known deposits, are reported here. The ages range from about 80 to 40 Ma, with closely adjacent samples exhibiting very different ages. Interpretation of these results in the context of estimated closure temperatures for alunite and the geologic and tectonic evolution of Hispaniola does not lead to a simple conclusion about the age of mineralization. The simplest interpretation, that mineralization was caused by a buried Late Cretaceous (~80 Ma) intrusion, is complicated by lack of intrusions of this age in the area and absence of alteration in overlying limestone. The alternative interpretation, that mineralization was formed during Early Cretaceous (~110 Ma) magmatism and that the 40Ar/39Ar ages were completely reset by Late Cretaceous thrusting, is complicated by a lack of information on the timing and thermal effects of thrusting in central Hispaniola. Alunite studies have yielded similar unclear results in other pre-Cenozoic ore systems, notably those of the Lachlan fold belt in Australia

Tunable Fano resonance in symmetric multilayered gold nanoshells

Fano resonances (FRs) are produced when a discrete state is coupled with a continuum. In addition to fundamental scientific interests, FRs in plasmonic systems give rise to the so-called plasmon-induced transparency. In this work we have studied the evolution of dipole-dipole all-plasmonic FRs in symmetric multilayered nanoshells as the function of their geometrical parameters. We demonstrate that symmetry breaking is not mandatory for controlling the Fano resonance in such multilayered nanoshells. Generation of FRs in these symmetric nanostructures presents clear advantages over their asymmetric counterparts, as they are easier to fabricate and can be used in a wider range of technological applications.

Tunable Fano resonance in symmetric multilayered gold nanoshells

We have studied the evolution of dipole–dipole all-plasmonic Fano resonances (FRs) in symmetric multilayered nanoshells as a function of their geometrical parameters. We demonstrate that symmetry breaking is not mandatory for controlling the Fano resonance in such multilayer structures. By carefully selecting the geometrical parameters, the position of the FR can be tuned between 600 and 950 nm and its intensity can be increased up to four fold with respect to the non-optimized structures. Generation of FRs in such symmetric nanostructures presents clear advantages over their asymmetric counterparts, as they are easier to fabricate and can be used in a wider range of technological applications.

Photoacoustic effect measurement in aqueous suspensions of gold nanorods caused by low-frequency and low-power near-infrared pulsing laser irradiation

When aqueous suspensions of gold nanorods are irradiated with a pulsing laser (808 nm), pressure waves appear even at low frequencies (pulse repetition rate of 25 kHz). We found that the pressure wave amplitude depends on the dynamics of the phenomenon. For fixed concentration and average laser current intensity, the amplitude of the pressure waves shows a trend of increasing with the pulse slope and the pulse maximum amplitude.We postulate that the detected ultrasonic pressure waves are a sort of shock waves that would be generated at the beginning of each pulse, because the pressure wave amplitude would be the result of the positive interference of all the individual shock waves.

Probabilistic meta-analysis of risk from the exposure to Hg in artisanal gold mining communities in Colombia

Colombia is one of the largest per capita mercury polluters in the world as a consequence of its artisanal gold mining activities. The severity of this problem in terms of potential health effects was evaluated by means of a probabilistic risk assessment carried out in the twelve departments (or provinces) in Colombia with the largest gold production. The two exposure pathways included in the risk assessment were inhalation of elemental Hg vapors and ingestion of fish contaminated with methyl mercury. Exposure parameters for the adult population (especially rates of fish consumption) were obtained from nation-wide surveys and concentrations of Hg in air and of methyl-mercury in fish were gathered from previous scientific studies. Fish consumption varied between departments and ranged from 0 to 0.3 kg d?1. Average concentrations of total mercury in fish (70 data) ranged from 0.026 to 3.3 lg g?1. A total of 550 individual measurements of Hg in workshop air (ranging from menor queDL to 1 mg m?3) and 261 measurements of Hg in outdoor air (ranging from menor queDL to 0.652 mg m?3) were used to generate the probability distributions used as concentration terms in the calculation of risk. All but two of the distributions of Hazard Quotients (HQ) associated with ingestion of Hg-contaminated fish for the twelve regions evaluated presented median values higher than the threshold value of 1 and the 95th percentiles ranged from 4 to 90. In the case of exposure to Hg vapors, minimum values of HQ for the general population exceeded 1 in all the towns included in this study, and the HQs for miner-smelters burning the amalgam is two orders of magnitude higher, reaching values of 200 for the 95th percentile. Even acknowledging the conservative assumptions included in the risk assessment and the uncertainties associated with it, its results clearly reveal the exorbitant levels of risk endured not only by miner-smelters but also by the general population of artisanal gold mining communities in Colombia.

A method to obtain the thermal parameters and the photothermal transduction efficiency in an optical hyperthermia device based on laser irradiation of gold nanoparticles

Optical hyperthermia systems based on the laser irradiation of gold nanorods seem to be a promising tool in the development of therapies against cancer. After a proof of concept in which the authors demonstrated the efficiency of this kind of systems, a modeling process based on an equivalent thermal-electric circuit has been carried out to determine the thermal parameters of the system and an energy balance obtained from the time-dependent heating and cooling temperature curves of the irradiated samples in order to obtain the photothermal transduction efficiency. By knowing this parameter, it is possible to increase the effectiveness of the treatments, thanks to the possibility of predicting the response of the device depending on the working configuration. As an example, the thermal behavior of two different kinds of nanoparticles is compared. The results show that, under identical conditions, the use of PEGylated gold nanorods allows for a more efficient heating compared with bare nanorods, and therefore, it results in a more effective therapy.

Probabilistic assessment of risk from the exposure to mercury in artisanal gold mining communities in Colombia

Colombia is one the largest per capita mercury polluters as a consequence of its artisanal gold mining operations, which are steadily increasing following the rising price of this metal. Compared to gravimetric separation methods and cyanidation, the concentration of gold using Hg amalgams presents several advantages: the process is less time-consuming and minimizes gold losses, and Hg is easily transported and inexpensive relative to the selling price of gold. Very often, mercury amalgamation is carried out on site by unprotected workers. During this operation large amounts of mercury are discharged to the environment and eventually reach the fresh water bodies in the vicinity where it is subjected to methylation. Additionally, as gold is released from the amalgam by heating on open charcoal furnaces in small workshops, mercury vapors are emitted and inhaled by the artisanal smelters and the general population

Evaluation of the bioaccumulation kinetics of gold nanorods in vital mammalian organs by mean of TXRF spectrometry

This work presents the first application of total-reflection X-ray fluorescence (TXRF) spectrometry, a new and powerful alternative analytical method, to evaluation of the bioaccumulation kinetics of gold nanorods (GNRs) in various tissues upon intravenous administration in mice. The analytical parameters for developed methodology by TXRF were evaluated by means of the parallel analysis of bovine liver certified reference material samples (BCR-185R) doped with 10 μg/g gold. The average values (n = 5) achieved for gold measurements in lyophilized tissue weight were as follows: recovery 99.7%, expanded uncertainty (k = 2) 7%, repeatability 1.7%, detection limit 112 ng/g, and quantification limit 370 ng/g. The GNR bioaccumulation kinetics was analyzed in several vital mammalian organs such as liver, spleen, brain, and lung at different times. Additionally, urine samples were analyzed to study the kinetics of elimination of the GNRs by this excretion route. The main achievement was clearly differentiating two kinds of behaviors. GNRs were quickly bioaccumulated by highly vascular filtration organs such as liver and spleen, while GNRs do not show a bioaccumulation rates in brain and lung for the period of time investigated. In parallel, urine also shows a lack of GNR accumulation. TXRF has proven to be a powerful, versatile, and precise analytical technique for the evaluation of GNRs content in biological systems and, in a more general way, for any kind of metallic nanoparticles.

Uso de técnicas de minería de texto para la identificación de ensayos clínicos en nanomedicina

La nanotecnología es el estudio que la mayoría de veces es tomada como una meta tecnológica que nos ayuda en el área de investigación para tratar con la manipulación y el control en forma precisa de la materia con dimensiones comprendidas entre 1 y 100 nanómetros. Recordando que el prefijo nano proviene del griego vavoc que significa enano y corresponde a un factor de 10^-9, que aplicada a las unidades de longitud corresponde a una mil millonésima parte de un metro. Ahora sabemos que esta ciencia permite trabajar con estructuras moleculares y sus átomos, obteniendo materiales que exhiben fenómenos físicos, químicos y biológicos, muy distintos a los que manifiestan los materiales usados con una longitud mayor. Por ejemplo en medicina, los compuestos manométricos y los materiales nano estructurados muchas veces ofrecen una mayor eficacia con respecto a las formulaciones químicas tradicionales, ya que muchas veces llegan a combinar los antiguos compuestos con estos nuevos para crear nuevas terapias e inclusive han llegado a reemplazarlos, revelando así nuevas propiedades diagnósticas y terapéuticas. A su vez, la complejidad de la información a nivel nano es mucho mayor que en los niveles biológicos convencionales y, por tanto, cualquier flujo de trabajo en nano medicina requiere, de forma inherente, estrategias de gestión de información avanzadas. Muchos investigadores en la nanotecnología están buscando la manera de obtener información acerca de estos materiales nanométricos, para mejorar sus estudios que muchas veces lleva a probar estos métodos o crear nuevos compuestos para ayudar a la medicina actual, contra las enfermedades más poderosas como el cáncer. Pero en estos días es muy difícil encontrar una herramienta que les brinde la información específica que buscan en los miles de ensayos clínicos que se suben diariamente en la web. Actualmente, la informática biomédica trata de proporcionar el marco de trabajo que permita lidiar con estos retos de la información a nivel nano, en este contexto, la nueva área de la nano informática pretende detectar y establecer los vínculos existentes entre la medicina, la nanotecnología y la informática, fomentando así la aplicación de métodos computacionales para resolver las cuestiones y problemas que surgen con la información en la amplia intersección entre la biomedicina y la nanotecnología. Otro caso en la actualidad es que muchos investigadores de biomedicina desean saber y comparar la información dentro de los ensayos clínicos que contiene temas de nanotecnología en las diferentes paginas en la web por todo el mundo, obteniendo en si ensayos clínicos que se han creado en Norte América, y ensayos clínicos que se han creado en Europa, y saber si en este tiempo este campo realmente está siendo explotado en los dos continentes. El problema es que no se ha creado una herramienta que estime un valor aproximado para saber los porcentajes del total de ensayos clínicos que se han creado en estas páginas web. En esta tesis de fin de máster, el autor utiliza un mejorado pre-procesamiento de texto y un algoritmo que fue determinado como el mejor procesamiento de texto en una tesis doctoral, que incluyo algunas pruebas con muchos de estos para obtener una estimación cercana que ayudaba a diferenciar cuando un ensayo clínico contiene información sobre nanotecnología y cuando no. En otras palabras aplicar un análisis de la literatura científica y de los registros de ensayos clínicos disponibles en los dos continentes para extraer información relevante sobre experimentos y resultados en nano medicina (patrones textuales, vocabulario en común, descriptores de experimentos, parámetros de caracterización, etc.), seguido el mecanismo de procesamiento para estructurar y analizar dicha información automáticamente. Este análisis concluye con la estimación antes mencionada necesaria para comparar la cantidad de estudios sobre nanotecnología en estos dos continentes. Obviamente usamos un modelo de datos de referencia (gold standard) —un conjunto de datos de entrenamiento anotados manualmente—, y el conjunto de datos para el test es toda la base de datos de estos registros de ensayos clínicos, permitiendo distinguir automáticamente los estudios centrados en nano drogas, nano dispositivos y nano métodos de aquellos enfocados a testear productos farmacéuticos tradicionales.---ABSTRACT---Nanotechnology is the scientific study that usually is seen as a technological goal that helps us in the investigation field to deal with the manipulation and precise control of the matter with dimensions that range from 1 to 100 nanometers. Remembering that the prefix nano comes from the Greek word νᾶνος, meaning dwarf and denotes a factor of 10^-9, that applyied the longitude units is equal to a billionth of a meter. Now we know that this science allows us to work with molecular structures and their atoms, obtaining material that exhibit physical, chemical and biological phenomena very different to those manifesting in materials with a bigger longitude. As an example in medicine, the nanometric compounds and the materials in nano structures are often offered with more effectiveness regarding to the traditional chemical formulas. This is due to the fact that many occasions combining these old compounds with the new ones, creates new therapies and even replaced them, reveling new diagnostic and therapeutic properties. Even though the complexity of the information at nano level is greater than that in conventional biologic level and, thus, any work flow in nano medicine requires, in an inherent way, advance information management strategies. Many researchers in nanotechnology are looking for a way to obtain information about these nanometric materials to improve their studies that leads in many occasions to prove these methods or to create a new compound that helps modern medicine against powerful diseases, such as cancer. But in these days it is difficult to find a tool that searches and provides a specific information in the thousands of clinic essays that are uploaded daily on the web. Currently, the bio medic informatics tries to provide the work frame that will allow to deal with these information challenge in nano level. In this context, the new area of nano informatics pretends to detect and establish the existing links between medicine, nanotechnology and informatics, encouraging the usage of computational methods to resolve questions and problems that surge with the wide information intersection that is between biomedicine and nanotechnology. Another present case, is that many biomedicine researchers want to know and be able to compare the information inside those clinic essays that contains subjects of nanotechnology on the different webpages across the world, obtaining the clinic essays that has been done in North America and the essays done in Europe, and thus knowing if in this time, this field is really being exploited in both continents. In this master thesis, the author will use an enhanced text pre-processor with an algorithm that was defined as the best text processor in a doctoral thesis, that included many of these tests to obtain a close estimation that helps to differentiate when a clinic essay contains information about nanotechnology and when it does not. In other words, applying an analysis to the scientific literature and clinic essay available in both continents, in order to extract relevant information about experiments and the results in nano-medicine (textual patterns, common vocabulary, experiments descriptors, characterization parameters, etc.), followed by the mechanism process to structure and analyze said information automatically. This analysis concludes with the estimation, mentioned before, needed to compare the quantity of studies about nanotechnology in these two continents. Obviously we use a data reference model (Gold standard) – a set of training data manually annotated –, and the set of data for the test conforms the entire database of these clinic essay registers, allowing to distinguish automatically the studies centered on nano drugs, nano devices and nano methods of those focus on testing traditional pharmaceutical products.