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Etude expérimentale de la distribution du fer ferrique entre spinelle chromifère et bain silicaté basique The partitioning of ferric iron between chromian spinel and basic silicate melt was studied experimentally. Runs were carried out at temperatures of 1 180-1 300 °C and oxygen fugacities of 10-3-10-9 atm, at one atmosphere total pressure. A linear relationship exists between the Fe2O3 content of chromian spinel (known by microprobe analysis) and the Fe2O3 content of the liquid (calculated from the empirical relation established by Kilinc et al., 1983). The partition coefficient, DT = (Fe2O3)sp/(Fe2O3)liq, depends on temperature, but neither on fO2 nor on the Fe total content of the melt : log DT = 4 8 13/T — 2.39. The Fe2O3 content of spinel is related to physico-chemical parameters as follows :
[formula]
It is pointed out that, at constant temperature and oxygen fugacity, (Fe2O3)sp is a linear function of the total iron content of the melt.
PERSEE Program - Tập 107 Số 1 - Trang 25-33 - 1984
The solubilities of some major and minor element minerals in ground waters associated with a sandstone-hosted uranium deposit Des échantillons d'eaux de subsurface ont été récoltés dans 41 puits atteignant les grès de base Oakville d'âge Miocène dans le Sud du Texas et ont été analysés pour les éléments majeurs et les éléments en traces afin de mesurer les variations chimiques liées à la proximité de minéralisations uranifères. L'échantillonnage s'étend sur une surface de 240 km2 qui contient plusieurs gisements d'uranium liés à des failles. Les facteurs qui influent sur le système hydrochimique de la région étudiée sont : (1) les perméabilités relativement fortes des sédiments enfouis issus de chenaux fluviatiles, (2) l'écoulement vers le haut des saumures le long de failles vivantes dans l'aquifère, (3) la formation d'une interface redox (Eh=0 volt) dans l'aquifère et (4) le climat semi-aride. Les variations des indices de saturation (SI) pour les minéraux réduits d'U, As, Mo, Se et pour les minéraux associés tels que la pyrite déterminent la position des gisements connus. Les indices de saturation tendent vers zéro (la valeur d'équilibre) lorsque l'on approche les gisements à des distances de 3 à 4-5 km en amont et décroissent de nouveau en aval. Les données de saturation pour la calcite dans les eaux de subsurface sont fortement corrélées avec la position de la limite redox actuelle. Les valeurs des indices de saturation pour les minéraux d'U, As, Mo et Se se sont révélées beaucoup plus utiles pour localiser les gisements que les concentrations des éléments prises individuellement. Les traceurs radiogéniques Ra et Rn sont fortement anomaliques dans le minerai, mais descendent rapidement au niveau du fond à de faibles distances du minerai. Une intense anomalie en hélium sous forme de traînée est observée dans la direction de circulation de l'eau de subsurface. L'approche décrite dans cet article constitue un guide d'exploration efficace à l'échelle régionale qui devrait conduire à un programme de sondages d'évaluation plus sûr.
PERSEE Program - Tập 110 Số 2 - Trang 209-226 - 1987
Anion-exchange in takovite : applications to other hydroxide minerals La takovite, un des membres du groupe des pyroaurites qui contient du nickel a été, ainsi que son minéral apparenté l'hydrotalcite, soumise à des traitements, à 25 °C, par des solutions, 0,1 M de HCl, HNO₃, H₂SO₄, NiSO₄, Al₂(SO₄)₃ et KOH. La diffraction des rayons X et la spectroscopie aux infrarouges appliquées aux matériaux traités confirment que les groupes carbonates du minéral d'origine peuvent facilement s'échanger avec les anions Cl⁻, NO₃⁻, OH⁻ et SO₄²⁻, à la température ordinaire. Les chlorures, nitrates et hydroxy˗takovites donnent des diagrammes aux rayons X pratiquement semblables à ceux du minéral non traité, avec des espacements supérieurs d'environ 0,2 Å. Les diagrammes aux rayons X des matériaux traités au sulfate donnent un espacement de 8,9 Å pour des humidités relatives inférieures à 50 % et de 10,8 Å pour des humidités relatives supérieures à 50 % contre 7,5 Å pour le matériau non traité. Si on met de la takovite traitée au sulfate dans une solution de KOH 0,01 M saturée en CO₂, pendant 18 heures à 25 °C on obtient aux rayons X et aux infrarouges les mêmes résultats que pour la takovite d'origine. On pense que les anions Cl⁻, NO₃⁻ et OH⁻ occupent une position très similaire à ceux du groupe carbonate, et la disposition du sulfate est probablement similaire à celle trouvée pour le sulfate d'hydrocalumite. Les données dont on dispose suggèrent que la carrboydite, l'honessite et la motukoreaite possèdent des structures exactement analogues à celle de la takovite sulfatée.
PERSEE Program - Tập 103 Số 2 - Trang 170-175 - 1980
Petrofabrics and microstructures of omphacites in a high temperature eclogite from the Swedish Caledonides Eclogites from the Eastern Belt of the Seve Nappes, Jämtland, Central Scandinavian Caledonides, have an LS fabric in which the foliation S and lineation L are both defined by the shape preferred orientation of omphacite.
The orientation distribution diagram of omphacite reveals a crystallographic fabric defined by [001] parallel to L and [010] in a great circle distribution perpendicular to S and L.
Optical and electron microscopy studies indicate that the eclogites have been deformed primarily by dislocation creep mechanisms operating in omphacite i.e. whilst garnets contain very low densities of dislocations and can be treated effectively as rigid bodies, omphacites contain defect structures consisting of well-ordered dislocation boundaries which delineate subgrains. The majority of dislocations in omphacite have Burgers vectors 1/2 <110> and [001].
In the absence of extensive recrystallization, the omphacite deformation fabric is explained by multiple crystallographic slip along {110} [001], (100) [001] and {110} <110> assisted by dislocation climb.
PERSEE Program - Tập 106 Số 6 - Trang 709-713 - 1983
Oxidation-reduction processes in the genesis of the uranium-vanadium tabular deposits of the Cottonwood Wash mining area (Utah, U.S.A.) : evidence from petrological study and organic matter analysis The Cottonwood Wash U-V tabular deposits are hosted by the Salt-Wash Member of the Jurassic Morrison Formation. Petrological study of ore and barren host-rocks and analysis of organic matter were conducted to test redox genetic models. Barren sandstones are mainly cemented by quartz, calcite and kaolinite. Tabular ore is cemented by U-bearing vanadiferous clays. Pitchblende and coffinite are present in some coalified logs. U and V mineralization occurred during diagenesis after interpénétration of detrital quartz grains. Two different generations of pyrite are observed. Accumulation and preservation of organic matter composed of conifers fragments were possible because of favorable paleogeographical and paleoclimatological conditions. Chemical composition of organic matter is interpreted as an oxidation event that occurred during diagenesis. This oxidation was related to the circulation of uranium-bearing, oxidizing solutions during burial. The fact that diagenetic oxidation is not strong enough to destroy organic matter supports the slow-rate oxidation identified in the genesis of secondary pyrite and suggests that the oxidizing capacity of the mineralizing fluid was lower than the reducing capacity of the hosted rocks. When these solutions encountered reduced organic-rich zones, U and V precipitated. The results indicate that Colorado Plateau tabular deposits formed from low oxygen waters compared to the solutions which formed typical roll front deposits.
PERSEE Program - Tập 110 Số 2 - Trang 145-156 - 1987
Origin of coffinite in sedimentary rocks by a sequential adsorption-reduction mechanism Coffinite is the dominant ore mineral in the tabular vanadium-uranium ores of the Tony M mine in the Henry Mountains Mineral Belt of the Colorado Plateau physiographic province of the United States. This ore body formed at a density-stratified solution interface between uranyl ion bearing-meteoric water and a saline fluid which was locally reducing. Uranium localization at this solution interface occurred by adsorption onto the surfaces of detrital minerals. This adsorption was related to the pH difference between the two fluids. New experimental evidence is presented which shows that adsorption facilitated the reduction of uranium to U(IV). This adsorbed, reduced uranium bonded with aqueous silica in the ore zone to form coffinite. Evidence is presented that in order to stabilize coffinite over uraninite, this silica was highly concentrated in the ore-forming solution, and the dominant form of this silica was as a monomeric species.
PERSEE Program - Tập 110 Số 2 - Trang 131-144 - 1987
Evolution des propriétés magnétiques lors des transformations minérales dans les roches : exemple du Jurassique Dauphinois (Alpes françaises) Magnetic mineralogy is the study of the magnetic properties of rocks related to their chemical and mineralogical composition. Here is presented a brief definition of these properties, the methods for their study and the abilities for quantitative determination of minerals, essentially iron compounds. The complicated case of the Dauphinois Jurassic calcareous shales emphasizes the various petrological applications of this kind of study and brings new constraints on alpine metamorphism.
PERSEE Program - Tập 109 Số 6 - Trang 687-696 - 1986
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