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[en] The objective of this project is the development of analyses on micro-quantities and of in-situ analyses (when necessary, with the use of lasers) and the scientific significance of the results with respect to the technical performances of the apparatus. For stable isotopes, the oxygen extraction technique from silicates and oxides has been developed for 11 different standards. The extraction line and the mode of operation are not new but improvements have allowed to lower the blanks and increase the reproducibility. For some minerals, a grain-size effect on the isotopic composition has been demonstrated. An analytic protocol has been defined and the calibration of new minerals is in progress. In-situ analyses on quartz minerals have been performed using the same method. Thanks to multi-collector mass spectrometers, the internal reproducibility reached on radiogenic lead isotope ratio determinations is below 0.01 %. However, because of the lead isotope ratio instability, the mass discrimination cannot be easily corrected. The external reproducibility has been measured on a large number of natural samples in two independent laboratories. The U/Pb ratios were measured using ICP-MS for a correction of the radiogenic lead contribution to the Pb/Pb ratio. (J.S.). 6 refs., 2 figs
[en] The isotopic composition of thermomineral waters in the Massif Central region in France has been studied extensively from 1974 until the present. The principal support for these studies has been provided by geochemical surveys of hot water for geothermal resource assessment purposes and hydrogeological studies linked to the 'Geologie profonde de la France' (GPF) scientific drilling programmes. These programmes have helped us to build a database comprising 105 dilute superficial waters (springs, rivers and shallow boreholes) and more than 200 hot geothermal waters and warm-to-cold mineralized waters. All of the samples were analysed for oxygen and hydrogen stable isotopes. The tritium content was also measured for some samples and the chemical composition of the deep water samples was studied in great detail. 5 refs, 1 fig
[en] The authors report the analysis of the oxygen isotopic composition of sulfates dissolved in 102 samples of thermal waters coming from different contexts: sedimentary (Parisian Basin), volcanic (New Mexico, West Indies, Mont Dore in France), or base (France), with the objective of a better understanding of the behaviour of oxygen isotopes of dissolved sulfates in order to use them as a geochemical tool in geothermal exploration. Some of these thermal waters contain colloids of silica, sulphur or iron which disturb oxygen extraction, and the authors therefore reconsidered handling conditions. After a recall of knowledge about the sulfate-water geo-thermometer (thermodynamic balance, kinetic parameters), the authors address mechanisms which disturb the SO4-H2O thermometer (cases of overestimated or underestimated temperature). They describe the experimental methodology: sampling, chemical processing, oxygen extraction, isotopic analysis by using a mass spectrometer. Then applications to the different studied fields are reported.
[en] This document is made of 2 progress reports and the final report of the project about Hydrothermal alteration systems as analogues of nuclear waste repositories in granitic rocks, which si part of the European Communities' MIRAGE program. The data were obtained from the study of the in-filling and hydro-thermalized walls of a mineralized vein located at Fombillou, Lot Department, in the French Massif Central. A satisfactory model of the processes generated by hydrothermal alteration then by climatic weathering such as formation of new minerals, flow of elements and variations in volume, was thus built. The mobility of elements displaying physical and chemical properties similar to those of radionuclides present in high-level radioactive waste was studied. A preliminary thermodynamic simulation of mineral transformations and transfers of matter during hydrothermal alteration was performed using the calculation code CEQCSY (Chemical Equilibrium in Complex System). This simulation is based on the values of the main physical and chemical parameters deduced from the analysis of the natural system. On the basis of the results obtained from Fombillou, an appraisal was made of the response of the granitic environment which has been disturbed by a hydrothermal system produced by heat emitted by the storage of high-level radioactive waste as well as its potential capacities of retention in case of possible leakage