Gamma-Ray Data Processing and Integration for Lode-Au Deposits Exploration

A large number of mineral deposits are associated with hydrothermal processes, especially auriferous deposits. In such processes, studies on percolating fluids may indicate the presence of potash (K), among other elements. In this study, aerogammaspectrometric data-processing methodologies are evaluated, especially those methods based on the suppression of the primary contribution of potassium, the result of lithological and soil variations, and to environmental conditions. Resulting maps point out the contribution of hydrothermal K. This processing procedure was used because of the association of hydrothermal K and auriferous mineralizations according to the deposit model defined for the studied region. Intensity maps locate the areas with great influence of hydrothermal K. Data integration required to improve a change in the gammaspectrometric data processing in order to positively correlate hydrothermalised areas. Data integration could distinguish high and medium favorable targets for mineral exploration of lode-Au deposits in the studied region.     

Effect of fire on growth of three perennial grasses from central semi-arid Argentina

The effect of fire on growth of Piptochaetium napostaense, Stipa tenuis, and Stipa gynerioides, three important native perennial grasses in the semi-arid region of central Argentina, was evaluated under different fire temperature regimes: 300–400°C (low temperature regime), 500–600°C (high temperature regime) and no fire (control). Fire treatments were applied with a portable propane plant burner in April and December 1994, May 1995, and January 1996. Overall results indicate that during the first months after fire occurrence, average total green length of S. tenuis, P. napostaense and S. gynerioides tillers was severely reduced (p<0.05) by fire. This effect was more pronounced in plants burned with the high temperature treatment. The observed patterns of response to fire for height of tillers were very similar to those already reported for total green length of tillers. Towards the end of each growth cycle, the number of green leaves per tiller of burned plants of P. napostaense, S. tenuis, and S. gynerioides were similar or greater (p<0.05) than the number of green leaves on tillers of control plants. Relative growth rates for total green length and for height in tillers of burned plants of S. tenuis, P. napostaense and S. gynerioides were greater than in tillers of control plants. Our results indicate that fire affected differentially the growth of the studied species; S. gynerioides was more affected by fire than P. napostaense and S. tenuis. The species most tolerant to fire was P. napostaense.     

蛇绿岩套中超基性岩体的岩石组合:蛇纹岩、异剥钙榴岩和蛇绿碳酸岩——以西阿尔卑斯Zermatt-Saas蛇绿岩为例

蛇纹岩、异剥钙榴岩和蛇绿碳酸岩是蛇绿岩套中超基性单元特有的3类岩石组合,该套岩石组合的形成过程复杂,经历了从地幔岩浆结晶分异、洋脊变质作用改造和俯冲-仰冲构造过程,记录了从地幔岩浆侵位到造山带形成、演化的全程信息。蛇纹岩由方辉橄榄岩、二辉橄榄岩和纯橄岩通过水化和氧化过程而形成;异剥钙榴岩由含水石榴石、符山石、绿帘石族矿物、透辉石和绿泥石等含水和含钙的硅酸盐矿物组成,是由基性岩经历钙交代和水化作用而形成;蛇绿碳酸岩则由高度破碎变形的蛇纹岩角砾和碳酸岩基质(方解石、白云石或菱镁矿)共同组成,碳酸钙主要来自海水参与蛇纹岩化过程产生的富钙热液。阿尔卑斯西部的Zermatt-Saas蛇绿岩体中这3种岩石的组合研究表明:蛇纹岩化过程发生在大洋变质时期,超基性岩体在海水的作用下形成蛇纹岩。蛇纹岩化过程中释放出主要来自斜方辉石和单斜辉石的钙,与水共同作用交代超基性岩体中的基性岩脉,从而形成异剥钙榴岩。蛇绿碳酸岩形成于俯冲变质之前或俯冲变质的早期。这3类岩石一经形成,都经历了其后的叠加变质作用,进而表明Zermatt-Saas蛇绿岩经历了大洋变质、与俯冲、折返和抬升有关的高压变质和区域变质、绿片岩相变质和晚期热液变质作用的pT轨迹演化,代表着西阿尔卑斯从洋脊变质作用到俯?     

Characterization of polysomatism in biopyriboles: Double-/triple-chain lamellar intergrowths

As a first step towards accurate quantification of the polysomatic states of biopyriboles, we have studied the polysomatic transformation between amphibole and hydrous triple-chain silicate (TCS) in the synthetic system Na₂O-MgO-SiO₂-H₂O (NMSH). The reaction is: 4Na₂Mg₄Si₆O₁₆(OH)₂ TCS 3Na_2.67Mg_5.33Si₈O_21.33(OH)_2.67. Amphibole We have characterised a polysomatic intergrowth of amphibole and TCS (synthesized at 2 kbar/(653° C) by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), infrared spectroscopy and ²⁹Si magic-angle-spinning (MAS) NMR spectroscopy. The sample is a fine-scale lamellar intergrowth of double- and triple-chain structures; lamellae are 27 Å to hundreds of Ångströms wide. The ²⁹Si MAS NMR spectrum of the intergrowth is explicitly a superposition of the individual amphibole and TCS spectra. By ensuring that the recycle delay time used considers the longest spin-lattice relaxation time (ca. 900 s), the relative amounts of double- and triple-chain structures can be quantified by simple deconvolution of the spectrum. The relative amounts of double- and triple-chain structures are 42 ± 5 and 58 ± 5 mol%, respectively. With regard to quantifying populations of chain multiplicities in biopyriboles, we believe that ²⁹Si NMR is more accurate than the conventional HRTEM fringe-counting method (Maresch and Czank 1983, 1988), and is far superior to XRD and infrared spectroscopy, which suffer from high sensitivity to particle size and calibration problems. ²⁹Si MAS NMR can provide an accurate means of monitoring the progress of polysomatic reactions in biopyriboles. It is likely to be most effective for samples containing only a few different chain multiplicities (e.g. m = 1, 2, 3 and perhaps 4), such as occur in natural pyroxenes and amphiboles.     

Analysis of the pressure variations at sea-level

Summary First of all the tendency equation at sea-level is deduced from the equation of continuity and the classical condition of quasi-static equilibrium along the verticals. This equation is then shown to be insufficient for the analysis and forecast of pressure variations. Accordingly, the equation of motion is combine with the tendency equation and the result of this operation is a partial differential equation for the field of pressure at sea-level. The analysis of its coefficients shows that it can be reduced to a partial differential equation for the height-integral of pressure which can also be written as a linear integro-differential equation. The solution of this last equation can be expanded in a series of rotating fields with positive constant angular velocities, the axis of rotation being the earth's polar axis and the spectrum of angular velocities being given by the eigenvalues of a symmetric kernel associated with theGreen's function of the geoid surface. Finally, the solution of the integro-differential equation leads to the determination of the sea-level pressure by the tendency equation.

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Résumé On déduit tout d'abord l'équation des tendances au niveau de la mer de l'équation de continuité et de la condition classique d'équilibre vertical quasi-statique. On montre ensuite que cette équation est insuffisante pour l'analyse et la prévision des variations de pression. En conséquence, on associe l'équation du mouvement à l'équation des tendances et le résultat de cette opération est une équation aux derivées partielles pour le champ de pression au niveau de la mer. L'analyse des coefficients de cette équation montre qu'elle peut être réduite à une équation aux dérivées partielles pour l'intégrale de la pression suivant la verticale, ou encore à une équation intégrodifférentielle linéaire. La solution de cette dernière équation est une série de champs en rotation dont les vitesses angulaires sont constantes et positives, leurs axes de rotation se confondant avec l'axe des pôles et le spectre des vitesses angulaires étant déterminé par les valeurs propres d'un noyau symétrique associé à la fonction deGreen de la surface du géoide. Finalement, la solution de l'équation intégro-différentielle conduit à la détermination de la pression au niveau de la mer par léquation des tendances.

     

Suspended-sediment response to pulses in river flow and semidiurnal and fortnightly tidal variations in a mesotidal estuary

The effects of the tidal regime and high river flows on the suspended sediment concentration field have been separated and the retention time of fluvial sediment has been determined. The study was carried out in the upper Sado estuary, Portugal, and included surveys at high and low tide in different semidiurnal tide ranges every month for 1 year, including contrasting freshwater discharge. DDT and its metabolites (DDD and DDE) were determined in the suspended sediment and in the whole soft tissues of oysters, and they have been used as tracers of the derived flood material in the upper estuary. The tide is responsible for the relatively slow relaxation time following a winter runoff event.     

Reconstructions of the Mediterranean Outflow Water during the quaternary based on the study of changes in buried mounded drift stacking pattern in the Gulf of Cadiz

Contourite deposits in the central sector of the middle slope of the Gulf of Cadiz have been studied using a comprehensive acoustic, seismic and core database. Buried, mounded, elongated and separated drifts developed under the influence of the lower core of the Mediterranean Outflow Water are preserved in the sedimentary record. These are characterised by depositional features in an area where strong tectonic and erosive processes are now dominant. The general stacking pattern of the depositional system is mainly influenced by climatic changes through the Quaternary, whereas changes in the depositional style observed in two, buried, mounded drifts, the Guadalquivir and Huelva Drifts, are evidence of a tectonic control. In the western Guadalquivir Drift, the onset of the sheeted drift construction (aggrading QII unit) above a mounded drift (prograding QI unit) resulted from a new Lower Mediterranean Core Water hydrodynamic regime. This change is correlated with a tectonic event coeval with the Mid Pleistocene Revolution (MPR) discontinuity that produced new irregularities of the seafloor during the Mid- to Late-Pleistocene. Changes in the Huelva Drift from a mounded to a sheeted drift geometry during the Late-Pleistocene, and from a prograding drift (QI and most part of QII) to an aggrading one (upper seismic unit of QII), highlight a new change in oceanographic conditions. This depositional and then oceanographic change is associated with a tectonic event, coeval with the Marine Isotope Stage (MIS) 6 discontinuity, in which a redistribution of the diapiric ridges led to the development of new local gateways, three principal branches of the Mediterranean Lower Core Water, and associated contourite channels. As a result, these buried contourite drifts hold a key palaeoceanographic record of the evolution of Mediterranean Lower Core Water, influenced by both neotectonic activity and climatic changes during the Quaternary. This study is an example of how contourite deposits and erosive elements in the marine environment can provide evidence for the reconstruction of palaeoceanographic and recent tectonic changes.     

Adaptation to metal toxicity: a comparison of hydrothermal vent and coastal shrimps

Rainbow vent field is one of the most metal‐contaminated hydrothermal sites on the Mid‐Atlantic Ridge near the Azores region. Two hydrothermal shrimp species dominate the fauna at the Rainbow site along with the mussel Bathymodiolus azoricus. Although the levels of essential and non‐essential metals in these shrimps have been studied, the biological consequences of a metal‐rich environment are still largely unknown. Therefore, the aim of this study was to determine the levels of metal‐binding proteins – metallothioneins (MT) and the activities of antioxidant enzymes – superoxide dismutase, catalase, total glutathione peroxidase and selenium‐dependent glutathione peroxidase in two hydrothermal vent shrimps (Mirocaris fortunata and Rimicaris exoculata) collected from the Rainbow site and to compare them with two coastal shrimps (Palaemon elegans and Palaemonetes varians) from a south Portugal lagoon (Ria Formosa) to evaluate their different adaptation strategies towards metals in their environment. Results show significant differences in MT levels and antioxidant enzymatic activities between vent and coastal shrimps and also between shrimp species collected from the same site. This suggests that biochemical responses in both vent and coastal shrimps are affected not only by the environmental characteristics but also by inter‐specific differences. Nevertheless, these responses apparently confer successful adaptation for survival in a metal‐extreme environment.     

Circulation modelling

Summer upwelling on the continental shelf north of Cape Canaveral, Florida, has been previously observed to result from wind forcing. A two-layer, finite element model reproduces reasonably well the characteristics of the wind-driven upwelling in respect to location and magnitude. Model investigation also shows that upwelling results from offshore current forcing which is imposed through an along-shelf sea level slope. This sea level slope, which has been found to be of the order of −10⁻⁷, represents a mean Gulf Stream effect. The results suggest that the strongest upwelling events near Cape Canaveral occur when the wind and Gulf Stream forcings act together.     

Wave-power absorption by a periodic linear array of oscillating water columns

This paper describes a theoretical analysis of the ocean wave energy absorption by a periodic linear array of oscillating water columns (OWCs) of arbitrary planform. The analysis is based on classical linear water wave theory and uses the expressions for the wave field resulting from time-harmonic pressure distributions on the free surface. The water depth is assumed finite and constant. The cases of oblique and normal incidence are analysed. A linear power take-off mechanism is assumed, but a complex characteristic constant (allowing for phase control) and air compressibility are considered. Special analytical expressions are derived for OWCs of rectangular and circular planforms. Numerical results for circular chambers show that the hydrodynamic interaction can substantially change the maximum energy absorption, depending on array and chamber geometry and on angle of incidence.