Tracing U mobility in deep groundwater using Ra isotopes

The mobility of natural U is compared among four boreholes in a fractured granite using Ra isotopes and geochemical modelling. Rn-222/Ra-226 activity ratios (ARs) spanning an order of magnitude underline differences in reactive surface area. (Ra-224/Ra-228)(ARs) up to 9 indicate recent changes in hydrogeochemistry, and (Ra-226/Ra-228)(ARs) 0.6-30 indicate variable deposition of U. Dissolved U is related to dissolution of a solid U(VI) phase by groundwater with HCO3- > 20 mg.L-1. U reduction is hindered by Ca2UO2(CO3)(3)(0)

Las aguas termales de Fitero (Navarra) y Arnedillo (Rioja). l. Análisis geoquímico de los estados de equilibrio-desequilibrio en las surgencias

The analysis of the different chemical features between the thermal springs of Fitero (Navarra) and Amedillo (Rioja), and between those thermal waters and other non-thermal ones in this area, has completed the geochemical characterization of both thermal manifestations. This characterization appear to confirm the existence of mixture phenomena in Fitero (in low proportions) and the narrow compositional range between the thermal springs considered in Amedillo. Taken into account the different geochemical variations of the studied waters, we have related their compositional characters with circulation through different litologies. So, thermal waters are associated to evaporitic materials (Keuper facies) with more saline characters for the Arnedillo thermal waters. On the other hand, the speciation-solubility analysis with WATEQ4F (Ba1l et al., 1987) of the spring chemical compositions and the study of associated deposits have allowed to stablish the physicochemical state at spring condition, a previous stage to determinate the thermodynamic water-rock interactions in the reservoir, at depth.El estudio de los caracteres geoquímicos diferenciales de las aguas termales de Fitero (Navarra) y Amedillo (Rioja), tanto entre ambos grupos como con respecto a otras surgencias no termales de la zona, ha permitido constatar la existencia de fenómenos de mezcla de aguas en Fitero, y las escasas variaciones composicionales entre las distintas surgencias termales de Amedillo. Los caracteres composicionales distintivos han sido relacionados con la circulación de las aguas a través de distintas litologías, 10 que ha permitido deducir que mientras que las aguas no termales se encuentran relacionadas con materiales calcáreos, las termales 10 están con materiales calcáreo-evaporiticos (facies Keuper), de carácter sulfatado en el caso de Fitero y clorurado, más salino, en Arnedillo. Por último, el análisis del quimismo de las aguas termales mediante un modelo de especiación-solubilidad, el WATEQ4F (Ball et al., 1987), en las condiciones de surgencia, así como el estudio de los depósitos asociados a las mismas, ha permitido estimar el estado fisicoquímico de los manantiales termales de Fitero y Amedi110, como paso previo al estudio de la interacción roca-fluido en el reservorio

Enclaves con espinela-corindon·sillimanita en rocas andesítico-dacíticas (Noguera, sierra de Albarracin. Teruel)

In intrusive dacitic-andesitic rocks, near Noguera de Albarrac&#237;n, Iberian Mountains (Spain), there exist metamorphic inclusions with spinel, corundum, sillimanite, biotite and other interesting minerals, many of them indicating high T-P conditions (above 800&#194;&#176; C and 5 Kb). The petrological studies indicate that such enclaves were built through a poliphasic process where various prograde and retrograde minerals were formed. A possible relationship between the metamorphic and the volcanic processes and both, metamorphic and volcanic, with the swelling-uplifting phenomenon, securely related with intrusive granitoids that took place in Albarracin area during last Hercynian times, is considered here.<br><br>En un afloramiento intrusivo, constitu&#237;do por rocas dac&#237;tico-andes&#237;ticas, al W de Noguera de Albarrac&#237;n, existen enclaves de rocas metam&#243;rficas con espinela, corind&#243;n, sillimanita y otros minerales. Los estudios petrol&#243;gicos indican que estos enclaves fueron originados en un proceso polif&#225;sico donde varias secuencias mineral&#243;gicas pr&#243;gradas y retr&#243;gradas son reconocidas. Muchas de la parag&#233;nesis indican condiciones f&#237;sicas de formaci&#243;n alrededor de los 800&#194;&#176; C y los 5 Kb. Se plantea la posibilidad de la existencia de una relaci&#243;n entre el proceso metam&#243;rfico y el volc&#225;nico, y ambos asociados con el abombamiento cortical, posiblemente en relaci&#243;n con granitoides, que tuvo lugar en la Sierra de Albarrac&#237;n durante el Paleozoico Superior

Geochemistry of saline soils in two arid zones of the mediterranean basin. 1. Geochemistry of the Chott Melghir-Mehrouane watershed in Algeria

International audienc

Géochimie des terres rares dans des solutions de sols hyper acides tropicaux. Cas du bassin versant du Rio Bocono (Andes Vénézuliennes)

Des solutions acides dont les pH sont compris entre 2,3 et 3,5 ont été prélevées dans la frange saturée de sols tropicaux se développant sur des lutites pyriteuses. Les terres rares (REE) présentent une distribution convexe asymétrique après normalisation avec le standard NASC ou la roche mère. Les terres rares intermédiaires sont relativement plus abondantes que les REE lourdes; les REE légères sont les moins abondantes. L'attaque sélective conduite avec HCI et avec l'hydroxylamine montre que c'est la distribution des REE fixées sur certains minéraux, probablement des oxydes métalliques, qui sont responsables de la convexité asymétrique observée dans les solutions. (Résumé d'auteur

Bilateral subthalamic nucleus stimulation improves balance control in Parkinson's disease

Background: Parkinson's disease (PD), the most common basal ganglia degenerative disease, affects balance control, especially when patients change balance strategy during postural tasks. Bilateral chronic stimulation of the subthalamic nucleus (STN) is therapeutically useful in advanced PD, and reduces the motor signs of patients. Nevertheless, the effects of STN stimulation on postural control are still debatable. Aims: To assess the impact of bilateral STN stimulation on balance control in PD and to determine how basal ganglia related sensorimotor modifications act on neurosensorial organisation of balance and motor postural programming. Methods: Twelve subjects aged 45–70 years underwent unified Parkinson's disease rating scale motor (part III) clinical tests, static and dynamic posturography, including sensory organisation and adaptation tests, shortly before and six months after bilateral implantation of electrodes into the STN. Results: The postoperative static test showed an improvement in postural control precision both in eyes open and eyes closed conditions. The dynamic test highlighted the decreased number of falls and the ability of the patients to develop more appropriate sensorimotor strategies when stimulated. The sensory organisation test showed an improvement of equilibrium score and, thus, a better resolution of sensorial conflicts. Conclusions: STN stimulation allowed a reduction in rigidity and therefore an improvement in the ability to use muscular proprioception as reliable information, resulting in vestibulo-proprioceptive conflict suppression. STN stimulation has a synergistic effect with levodopa for postural control. Accordingly, non-dopaminergic pathways could be involved in postural regulation and STN stimulation may influence the functioning of these pathways

Ecoulements hypodermiques et transferts de solutés dans les placages éoliens du Sahel : étude par traçage isotopique et chimique sous pluies simulées

Les placages éoliens jouent un rôle clé dans l'écologie des glacis à faible pente du Sahel burkinabé. Il s'agit d'étudier la nature des flux d'eau et de solutés par traçage artificiel isotopique (oxygène 18) et chimique (chlorure). On montre que les écoulements hypodermiques au sein de ces formations éoliennes ne représentent que 5% de l'écoulement total (écoulements de surface et hypodermique), mais qu'ils contribuent pour plus de 20% au transport de substances dissoutes. (Résumé d'auteur