Lithogeochemistry and fluid flow in the epithermal Veta Rublo base metal-silver deposit, Chonta Mine (Huancavelica, Perú)

The Chonta Mine (75º00’30” W & 13º04’30”S, 4495 to 5000 m absl), owned by Compañía Minera Caudalosa, operates a polymetallic Zn-Pb-Cu-Ag vein system of the low sulphidation epithermal type, hosted by cenozoic volcanics of dacitic to andesitic composition (Domos de Lava Formation). Veta Rublo, one of the main veins of the system, is worked underground to nearly 300 m. It strikes 60-80º NE and dips 60-70º SE; its width varies between 0.30 and 2.20m, and it crops out along 1 km, but is continued along strike by other veins, as Veta Caudalosa, for some 5 km. Typical metal contents are 7% Zn, 5% Pb, 0.4% Cu and 3 oz/t Ag, with quartz, sericite, sphalerite, galena, pyrite, chalcopyrite, fahlore as main minerals, and minor carbonate and sulphosalts.

Geothermometry, ore geochemistry and fluid flow in the Esperanza Vein, Huachocolpa District (Huancavelica, Peru)

The Esperanza Zn-Pb-Ag vein, owned by Compañía de Minas Buenaventura S.A.A., lies over 4000 to 4650 masl in the Western Cordillera of the Peruvian Central Andes. The Esperanza low sulphidation epithermal vein trends ~E-W along 1500 m; it dips to the South and can be followed to 350 m depth. As other veins of the district, like Teresita and Bienaventurada, it is hosted by intermediate to felsic volcanics (andesitic to dacitic compositions) of the Huachocolpa Group (Middle Miocene to Upper Pliocene). The mineralisation occurs mostly as open space filling related to fracture development during the Quechua III deformational event. Main ore minerals are sphalerite, galena, tetrahedrite, pyrite, chalcopyrite and Ag and Pb sulfosalts; quartz, barite and calcite are the main gangue minerals. Current production grades are ~5% Zn, ~8Oz/t Ag, ~3% Pb; usually very low Cu (mean ~0.04%).

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.

Microtermometría, direcciones de flujo hidrotermal y metalogenia del yacimiento de tungsteno de Pasto Bueno (Ancash, Perú)

El yacimiento de Pasto Bueno se localiza en el extremo nordeste del Batolito de la Cordillera Blanca, comprende diversas vetas, generalmente subverticales, asociadas al stock cuarzomonzonitico de Consuzo, datado como Terciario Superior, que intruye a las pizarras de la fm. Chicama y cuarcitas de la fm. Chimu. Las principales vetas discurren con direccion N-S cortando al stock, aunque tambien existen sistemas NE-SW asi como NW-SE encajados sobre las rocas metamorficas. La mineralogia de mena reconocida comprende wolframita (hubnerita), tetraedrita/tenantita, esfalerita y galena, en una ganga de cuarzo, fluorita, sericita, pirita y carbonatos, ademas de molibdenita, calcopirita, bornita, arsenopirita, enargita (luzonita), stolzita, scheelita, zinnwaldita, topacio, tungstita y arsenico nativo. Estudios previos han caracterizado Pasto Bueno como un yacimiento con una gran componente de greisen, con una evolucion de las vetas desde un episodio temprano esteril de 400 oC, depositando la mineralizacion economica en torno a los 220-250 oC y con un evento postumo de 175-220 oC rico en CO2. La precipitacion de la wolframita se produjo a partir de un fluido netamente hidrotermal, sin embargo, dicha precipitacion estuvo controlada por el aporte al sistema de aguas externas meteoricas y/o metamorficas. El trabajo llevado a cabo ha consistido en la realizacion de un estudio microtermometrico de las 3 principales estructuras del distrito: Consuelo, Alonso-Fenix y Chabuca, para caracterizar la evolucion del fluido mineralizador desde el stock (veta Consuelo) hacia las rocas metasedimentarias de las fm. Chicama y Chimu (manto Alonso-Fenix y veta Chabuca). Para ello se realizo un muestreo sobre el evento principal de mineralizacion. Dichas muestras se sometieron a un estudio petrografico de lamina gruesa para seleccionar las muestras optimas para el posterior estudio microtermometrico. Previamente a la obtencion de las medidas de temperatura de fusion del hielo (criotermometria) y de homogenizacion del fluido; se realizo un estudio de petrografia de inclusiones fluidas para caracterizarlas y seleccionar las representativas. La interpretacion de los resultados ha permitido confirmar la existencia de un episodio previo de alta temperatura, superior a 282 oC y un evento mineralizador con temperaturas en torno a los 200-240 oC. Sin embargo, las salinidades obtenidas son mucho menores que las previamente publicadas, en torno al 5 % peso eq. NaCl, frente a 11-17 % peso eq. NaCl. Tambien se ha observado un fluido postumo rico en CO2, pero de temperatura superior, en torno a los 270 oC. Los gradientes isotermicos muestran dos focos para dichos fluidos hidrotermales: el primero asociado al stock en la veta Consuelo, y el segundo en la veta Chabuca, asociado a la zona de cabalgamiento de las pizarras de la fm. Chicama sobre las cuarcitas de la fm. Chimu. Este segundo foco puede corresponder con los aportes externos de aguas metamorficas. Para finalizar, se dan una serie de pautas para guiar las futuras exploraciones en el yacimiento. ABSTRACT The Pasto Bueno deposit is located at the northeastern end of the Cordillera Blanca Batholith. It comprises several veins, generally subvertical, associated with the quartz-monzonite stock of Consuzo, dated as Tertiary, which intrudes the Chicama fm. slates and the Chimu fm. quartzites. The main veins trend N-S cutting the stock, although there are also NE-SW and NWSE systems, hosted by the metamorphic rocks. The ore mineralogy comprises wolframite (hubnerite), tetrahedrite/tennantite, sphalerite and galena in a gangue of quartz, fluorite, sericite, pyrite and carbonates, and minor molybdenite, chalcopyrite, bornite, arsenopyrite, enargite (luzonite), stolzite, scheelite, zinnwaldite, topaz, tungstite and native arsenic. Previous studies have characterized Pasto Bueno as a deposit with a large component of greisen, with an evolution of the veins from an early barren 400 oC event , followed by economic mineralization of about 220-250 °C and a late event of 175 -220 oC rich in CO2. Wolframite precipitation occurred from a purely hydrothermal fluid; however, this precipitation was controlled by an external flux of meteoric and/or metamorphic waters. Microthermometric studies of the 3 main structures of the district (Consuelo, Alonso-Fenix and Chabuca veins) have been carried out to depict the evolution of the mineralizing fluid coming from the stock (Consuelo vein) into the metasedimentary rocks of the Chimu and Chicama fm. (Alonso-Fenix and Chabuca veins). The sampling was performed over the main event of mineralization. These samples were subject to a quick plate petrography study in order to select the optimal samples for further microthermometry studies. Before the freezing/heating measures, a fluid inclusion petrography study was done to characterize and select the representative F.I. Interpretation of results has confirmed the existence of a previous episode of higher temperature, over 282 °C, and a mineralizing event with temperatures of about 200-240 °C. However, obtained salinities, about 5 wt% NaCl equivalents, are much lower than those previously reported, about 11-17 wt% NaCl equivalents. A last fluid, rich in CO2, but of higher temperature, about 270 oC, has been characterized. Isothermal gradients show two foci for the hydrothermal fluids: the first one associated to the Consuzo stock as shown in the Consuelo vein, and the second one related to the thrust fault which places the Chicama fm. slates over the Chimu fm. quartzites in the Chabuca vein area. This second focus may correspond to an external input of metamorphic waters. Finally, some guidelines have been given to guide future explorations.

3D Frangi-based lung vessel enhancement filter penalizing airways

This paper describes a fully automatic simultaneous lung vessel and airway enhancement filter. The approach consists of a Frangi-based multiscale vessel enhancement filtering specifically designed for lung vessel and airway detection, where arteries and veins have high contrast with respect to the lung parenchyma, and airway walls are hollow tubular structures with a non negative response using the classical Frangi's filter. The features extracted from the Hessian matrix are used to detect centerlines and approximate walls of airways, decreasing the filter response in those areas by applying a penalty function to the vesselness measure. We validate the segmentation method in 20 CT scans with different pathological states within the VESSEL12 challenge framework. Results indicate that our approach obtains good results, decreasing the number of false positives in airway walls.

Pulmonary Artery-Vein Segmentation in Real and Synthetic CT Images = Segmentación Arteria-Vena Pulmonares en Imágenes de CT Reales y Sintéticas

La tomografía axial computerizada (TAC) es la modalidad de imagen médica preferente para el estudio de enfermedades pulmonares y el análisis de su vasculatura. La segmentación general de vasos en pulmón ha sido abordada en profundidad a lo largo de los últimos años por la comunidad científica que trabaja en el campo de procesamiento de imagen; sin embargo, la diferenciación entre irrigaciones arterial y venosa es aún un problema abierto. De hecho, la separación automática de arterias y venas está considerado como uno de los grandes retos futuros del procesamiento de imágenes biomédicas. La segmentación arteria-vena (AV) permitiría el estudio de ambas irrigaciones por separado, lo cual tendría importantes consecuencias en diferentes escenarios médicos y múltiples enfermedades pulmonares o estados patológicos. Características como la densidad, geometría, topología y tamaño de los vasos sanguíneos podrían ser analizados en enfermedades que conllevan remodelación de la vasculatura pulmonar, haciendo incluso posible el descubrimiento de nuevos biomarcadores específicos que aún hoy en dípermanecen ocultos. Esta diferenciación entre arterias y venas también podría ayudar a la mejora y el desarrollo de métodos de procesamiento de las distintas estructuras pulmonares. Sin embargo, el estudio del efecto de las enfermedades en los árboles arterial y venoso ha sido inviable hasta ahora a pesar de su indudable utilidad. La extrema complejidad de los árboles vasculares del pulmón hace inabordable una separación manual de ambas estructuras en un tiempo realista, fomentando aún más la necesidad de diseñar herramientas automáticas o semiautomáticas para tal objetivo. Pero la ausencia de casos correctamente segmentados y etiquetados conlleva múltiples limitaciones en el desarrollo de sistemas de separación AV, en los cuales son necesarias imágenes de referencia tanto para entrenar como para validar los algoritmos. Por ello, el diseño de imágenes sintéticas de TAC pulmonar podría superar estas dificultades ofreciendo la posibilidad de acceso a una base de datos de casos pseudoreales bajo un entorno restringido y controlado donde cada parte de la imagen (incluyendo arterias y venas) está unívocamente diferenciada. En esta Tesis Doctoral abordamos ambos problemas, los cuales están fuertemente interrelacionados. Primero se describe el diseño de una estrategia para generar, automáticamente, fantomas computacionales de TAC de pulmón en humanos. Partiendo de conocimientos a priori, tanto biológicos como de características de imagen de CT, acerca de la topología y relación entre las distintas estructuras pulmonares, el sistema desarrollado es capaz de generar vías aéreas, arterias y venas pulmonares sintéticas usando métodos de crecimiento iterativo, que posteriormente se unen para formar un pulmón simulado con características realistas. Estos casos sintéticos, junto a imágenes reales de TAC sin contraste, han sido usados en el desarrollo de un método completamente automático de segmentación/separación AV. La estrategia comprende una primera extracción genérica de vasos pulmonares usando partículas espacio-escala, y una posterior clasificación AV de tales partículas mediante el uso de Graph-Cuts (GC) basados en la similitud con arteria o vena (obtenida con algoritmos de aprendizaje automático) y la inclusión de información de conectividad entre partículas. La validación de los fantomas pulmonares se ha llevado a cabo mediante inspección visual y medidas cuantitativas relacionadas con las distribuciones de intensidad, dispersión de estructuras y relación entre arterias y vías aéreas, los cuales muestran una buena correspondencia entre los pulmones reales y los generados sintéticamente. La evaluación del algoritmo de segmentación AV está basada en distintas estrategias de comprobación de la exactitud en la clasificación de vasos, las cuales revelan una adecuada diferenciación entre arterias y venas tanto en los casos reales como en los sintéticos, abriendo así un amplio abanico de posibilidades en el estudio clínico de enfermedades cardiopulmonares y en el desarrollo de metodologías y nuevos algoritmos para el análisis de imágenes pulmonares. ABSTRACT Computed tomography (CT) is the reference image modality for the study of lung diseases and pulmonary vasculature. Lung vessel segmentation has been widely explored by the biomedical image processing community, however, differentiation of arterial from venous irrigations is still an open problem. Indeed, automatic separation of arterial and venous trees has been considered during last years as one of the main future challenges in the field. Artery-Vein (AV) segmentation would be useful in different medical scenarios and multiple pulmonary diseases or pathological states, allowing the study of arterial and venous irrigations separately. Features such as density, geometry, topology and size of vessels could be analyzed in diseases that imply vasculature remodeling, making even possible the discovery of new specific biomarkers that remain hidden nowadays. Differentiation between arteries and veins could also enhance or improve methods processing pulmonary structures. Nevertheless, AV segmentation has been unfeasible until now in clinical routine despite its objective usefulness. The huge complexity of pulmonary vascular trees makes a manual segmentation of both structures unfeasible in realistic time, encouraging the design of automatic or semiautomatic tools to perform the task. However, this lack of proper labeled cases seriously limits in the development of AV segmentation systems, where reference standards are necessary in both algorithm training and validation stages. For that reason, the design of synthetic CT images of the lung could overcome these difficulties by providing a database of pseudorealistic cases in a constrained and controlled scenario where each part of the image (including arteries and veins) is differentiated unequivocally. In this Ph.D. Thesis we address both interrelated problems. First, the design of a complete framework to automatically generate computational CT phantoms of the human lung is described. Starting from biological and imagebased knowledge about the topology and relationships between structures, the system is able to generate synthetic pulmonary arteries, veins, and airways using iterative growth methods that can be merged into a final simulated lung with realistic features. These synthetic cases, together with labeled real CT datasets, have been used as reference for the development of a fully automatic pulmonary AV segmentation/separation method. The approach comprises a vessel extraction stage using scale-space particles and their posterior artery-vein classification using Graph-Cuts (GC) based on arterial/venous similarity scores obtained with a Machine Learning (ML) pre-classification step and particle connectivity information. Validation of pulmonary phantoms from visual examination and quantitative measurements of intensity distributions, dispersion of structures and relationships between pulmonary air and blood flow systems, show good correspondence between real and synthetic lungs. The evaluation of the Artery-Vein (AV) segmentation algorithm, based on different strategies to assess the accuracy of vessel particles classification, reveal accurate differentiation between arteries and vein in both real and synthetic cases that open a huge range of possibilities in the clinical study of cardiopulmonary diseases and the development of methodological approaches for the analysis of pulmonary images.