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.

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.

An alternative pathway to β-carotene formation in plant chromoplasts discovered by map-based cloning of Beta and old-gold color mutations in tomato

Carotenoid pigments in plants fulfill indispensable functions in photosynthesis. Carotenoids that accumulate as secondary metabolites in chromoplasts provide distinct coloration to flowers and fruits. In this work we investigated the genetic mechanisms that regulate accumulation of carotenoids as secondary metabolites during ripening of tomato fruits. We analyzed two mutations that affect fruit pigmentation in tomato (Lycopersicon esculentum): Beta (B), a single dominant gene that increases β-carotene in the fruit, and old-gold (og), a recessive mutation that abolishes β-carotene and increases lycopene. Using a map-based cloning approach we cloned the genes B and og. Molecular analysis revealed that B encodes a novel type of lycopene β-cyclase, an enzyme that converts lycopene to β-carotene. The amino acid sequence of B is similar to capsanthin-capsorubin synthase, an enzyme that produces red xanthophylls in fruits of pepper (Capsicum annum). Our results prove that β-carotene is synthesized de novo during tomato fruit development by the B lycopene cyclase. In wild-type tomatoes B is expressed at low levels during the breaker stage of ripening, whereas in the Beta mutant its transcription is dramatically increased. Null mutations in the gene B are responsible for the phenotype in og, indicating that og is an allele of B. These results confirm that developmentally regulated transcription is the major mechanism that governs lycopene accumulation in ripening fruits. The cloned B genes can be used in various genetic manipulations toward altering pigmentation and enhancing nutritional value of plant foods.

Using in vitro selection to direct the covalent attachment of human immunodeficiency virus type 1 Rev protein to high-affinity RNA ligands.

We have used an in vitro selection procedure called crosslinking SELEX (SELEX = systematic evolution of ligands by exponential enrichment) to identify RNA sequences that bind with high affinity and crosslink to the Rev protein from human immunodeficiency virus type 1 (HIV-1). A randomized RNA library substituted with the photoreactive chromophore 5-iodouracil was irradiated with monochromatic UV light in the presence of Rev. Those sequences with the ability to photocrosslink to Rev were partitioned from the rest of the RNA pool, amplified, and used for the next round of selection. Rounds of photocrosslinking selection were alternated with rounds of selection for RNA sequences with high affinity to Rev. This iterative, dual-selection method yielded RNA molecules with subnanomolar dissociation constants and high efficiency photocrosslinking to Rev. Some of the RNA molecules isolated by this procedure form a stable complex with Rev that is resistant to denaturing gel electrophoresis in the absence of UV irradiation. In vitro selection of nucleic acids by using modified nucleotides allows the isolation of nucleic acid molecules with potentially limitless chemical capacities to covalently attack a target molecule.

Silica Microparticles Supported Gold and Copper Ferrite Nanoparticles: A Magnetically Recyclable Bimetallic Catalyst for Sonogashira Reaction

Novel silica supported gold and copper ferrite nanoparticles (NPs) have been synthesized, characterized and used as a separable dual catalyst in Sonogashira type reaction. These Au.CuFe2O4@Silica NPs show a high efficiency as catalyst in the alkynylation not only of aryl iodides but also aryl bromides. By using only 0.5 mol% loading and t-BuOK as base in N,N-dimethylacetamide as solvent, aryl iodides react at 115 ºC in 1 d, whereas for aryl bromides the cross-coupling takes place at 130 ºC in 2 d. The catalyst can be successfully recycled using an external magnet for four consecutive runs.

The adaptive response of humans to exercise: Impact of exercise intensity, fibre-type specific responses and molecular patterns of response

In an attempt to improve the current understanding of the adaptive response to exercise in humans, this dissertation performed a series of studies designed to examine the impact of training intensity and mode on aerobic capacity and performance, fibre-type specific adaptations to training, and individual patterns of response across molecular, morphological and genetic factors. Project #1 determined that training intensity, session dose, baseline VO2max and total training volume do not influence the magnitude of change in VO2max by performing a meta-regression, and meta-analysis of 28 different studies. The intensity of training had no effect on the magnitude of increase in maximal oxygen uptake in young healthy participants, but similar adaptations were achieved with lower training doses following high intensity training. Project # 2 determined the acute molecular response, and training-induced adaptations in aerobic performance, aerobic capacity and muscle phenotype following high-intensity interval training (HIT) or endurance exercise (END). The acute molecular response (fibre recruitment and signal activation) and training-induced adaptations in aerobic capacity, aerobic performance, and muscle phenotype were similar following HIT and END. Project # 3 examined the impact of baseline muscle morphology and molecular characteristics on the training response, and if muscle adaptations are coordinated. The muscle phenotype of individuals who experience the largest improvements (high responders) were lower before training for some muscle characteristics and molecular adaptations were coordinated within individual participants. Project # 4 examined the impact of 2 different intensities of HIT on the expression of nuclear and mitochondrial encoded genes targeted by PGC-1α. A systematic upregulation of nuclear and mitochondrial encoded genes was not present in the early recovery period following acute HIT, but the expression of mitochondrial genes were coordinated at an individual level. Collectively, results from the current dissertation contribute to our understanding of the molecular mechanisms influencing skeletal muscle and whole-body adaptive responses to acute exercise and training in humans.

ELA-ICP-MS U-Pb zircon geochronology of regional volcanism hosting the Bajo de la Alumbrera Cu-Au deposit: implications for porphyry-related mineralization

ELA-ICP-MS U-Pb zircon geochronology has been used to show that the porphyritic intrusions related to the formation of the Bajo de la Alumbrera porphyry Cu-Au deposit, NW Argentina, are cogenetic with stratigraphically well-constrained volcanic and volcaniclastic rocks of the Late Miocene Farallon Negro Volcanic Complex. Zircon geochronology for intrusions in this deposit and the host volcanic sequence show that multiple mineralized porphyries were emplaced in a volcanic complex that developed over 1.5 million years. Volcanism occurred in a multivent volcanic complex in a siliciclastic intermontane basin. The complex evolved from early mafic-intermediate effusive phases to a later silicic explosive phase associated with mafic intrusions. Zircons from the basal mafic-intermediate lavas have ages that range from 8.46 +/- 0.14 to 7.94 +/- 0.27 Ma. Regionally extensive silicic explosive volcanism occurred at similar to8.0 Ma (8.05 +/- 0.13 and 7.96 +/- 0.11 Ma), which is co-temporal with intrusion of the earliest mineralized porphyries at Bajo de la Alumbrera (8.02 +/- 0.14 and 7.98 +/- 0.14 Ma). Regional uplift and erosion followed during which the magmatic-hydrothermal system was probably unroofed. Shortly thereafter, dacitic lava domes were extruded (7.95 +/- 0.17 Ma) and rhyolitic diatremes (7.79 +/- 0.13 Ma) deposited thick tuff blankets, across the region. Emplacement of large intermediate composition stocks occurred at 7.37 +/- 0.22 Ma, shortly before renewed magmatism occurred at Bajo de la Alumbrera (7.10 +/- 0.07 Ma). The latest porphyry intrusive event is temporally associated with new ore-bearing magmatic-hydrothermal fluids. Other dacitic intrusions are associated with subeconomic deposits that formed synchronously with the mineralized porphyries at Bajo de la Alumbrera. However, their emplacement continued (from 7.10 +/- 0.06 to 6.93 +/- 0.07 Ma) after the final intrusion at Bajo de al Alumbrera. Regional volcanism had ceased by 6.8 Ma (6.92 +/- 0.07 Ma). The brief history of the volcanic complex hosting the Bajo de la Alumbrera Cu-Au deposit differs from that of other Andean provinces hosting porphyry deposits. For example, at the El Salvador porphyry copper district in Chile, magmatism related to Cu mineralization was episodic in regional igneous activity that occurred over tens of millions of years. Bajo de la Alumbrera resulted from the superposition of multiple porphyry-related hydrothermal systems, temporally separated by a million years. It appears that the metal budget in porphyry ore deposits is not simply a function of their longevity and/or the superposition of multiple porphyry systems. Nor is it a function of the duration of the associated cycle of magmatism. Instead, the timing of processes operating in the parental magma body is the controlling factor in the formation of a fertile porphyry-related ore system.

Geochronology of the Pengjiakuang and Rushan gold deposits, Eastern Jiaodong Gold Province, Northeastern China: Implications for regional mineralization and geodynamic setting

The Jiaodong gold province, the largest gold-producing district in China, is located in the jiaodong peninsula at the eastern margin of the North China craton and bounded by the continental scale Tan-Lu fault, 40 kin to the west. Previous geochronological studies suggest that pervasive gold deposition took place in the western part of the province between 122 and 119 Ma. Here we report high-quality Ar-40/Ar-39 ages of the Pengjiakuang and Rushan deposits from the eastern part of the jiaodong gold province, placing additional chronological constraints on the timing of regional mineralization. Seven sericite grains extracted from auriferous alteration assemblages at the Pengiiakuang deposit yielded well-defined plateau ages between 120.9 +/- 0.4 and 119.1 +/- 0.2 Ma (2 sigma). Three separates of igneous biotite from a sample of the Queshan gneissic granite, adjacent to the Pengjiakuang deposit, gave reproducible plateau ages of 124.6 +/- 0.6 to 123.9 +/- 0.4 Ma (2 sigma). Six sericite separates front two samples in the Rushan deposit yielded Ar-40/Ar-39 plateau ages at 109.3 +/- 0.3 to 107.7 +/- 0.5 Ma (2 sigma), whereas biotite from the Kunyushan monzogranite that hosts the Rushan deposit had plateau ages ranging from 129.0 +/- 0.6 to 126.9 +/- 0.6 Ma (3 separates front one sample). The apparent age gap between hydrothermal sericite and magmtic biotite from both deposits, together with the similar argon closure temperatures for these mica minerals, suggest that gold mineralization had no direct relationship to the granitoid magmatism. Instead, gold deposition coincided with the emplacement of mafic to intermediate dikes widespread in the jiaodong gold province, which have been dated at ca. 122 to 119 Ma and, less commonly, at 110 to 102 Ma. The new Ar-40/Ar-39 ages from the eastern jiaodong peninsula, when combined with published data from the western part suggest that gold mineralization was broadly contemporaneous throughout the district. The Early Cretaceous gold mineralization also is widely developed in four other major gold districts along the Tan-Lu fault. The temporal and spatial correlation of these gold deposits with mafic to intermediate dikes commonly found in most mineralized areas, the presence of well-documented metamorphic core complexes and half-graben basins along the Tan-Lu fault, and voluminous basalts therein, suggest that the Early Cretaceous was an important period of lithospheric extension, possibly caused by the late Mesozoic lithospheric thinning beneath the eastern block of the North China craton. Lithospheric thinning and extension could have resulted in abnormally high heat and fluid fluxes necessary for large-scaled gold mineralization.