Opaline chert nodules in maar lake sediments from Camp dels Ninots (La Selva Basin, NE Spain)

Chert nodule samples from three different well cores (CC, CP1 & CA) from the lacustrine infill of the Camp dels Ninot maar-diatreme (La Selva Basin) have been studied by means of X-ray diffraction, and optical and electron microscope technique. The chert nodules replace diatomites and carbonates layers, and varies in mineralogy between opal-A to opal-A/CT. The microtexture of the opal-A rich nodules is characterized by smooth microspheres of ~2μm in diameter that forms aggregates of amalgamated microspheres. Commonly, the nodules contain diatoms and their moulds when replacing diatomites, and dolomite or ankerite crystals and their moulds when replacing carbonates. The opal-A/CT rich nodules exhibit a microtexture consisting of microspheres of ~8μm in diameter that form aggregates with botryoidal and finger-like morphologies. Results indicate that the early diagenetic transformation of opal-A to opal-CT is not complete in the studied sediments.Peer Reviewe

L\u27evolution historique de la privilege au premier saisissant et la conception francais de la egalite des creanciers

The Mayari-Baracoa Ophiolitic Belt (MBOB, eastern Cuba) is composed of two large, chromite-rich massifs: Mayari-Cristal and Moa-Baracoa. The chromitites and hosting dunites were firstly affected by a regional serpentinization event, a subsequent episode of hydrothermal alteration (chloritization mainly) and, finally, these already altered bodies were crosscut by thin calcite-dominated veins. Analysed serpentines from serpentinized chromitites and dunites present very similar isotopic compositions (delta(18)O= + 4.7 parts per thousand to + 6.3 parts per thousand and deltaD = - 67 parts per thousand to - 60 parts per thousand), suggesting that the serpentinization process took place at moderate temperatures, in an oceanic environment. Serpentine formation by interaction with ocean water is also supported by the isotopic composition of chlorite and calcite. These results suggest that the serpentinization, chloritization and fracture filling processes of the Mayari-Baracoa Ophiolite Belt took place in a subocean floor scenario and, thus, that the Mayari-Baracoa serpentines represent a good example of serpentine formed during interaction with seawater. The oceanic origin of the serpentines from serpentinized chromitites and dunites from the MBOB indicate that the serpentinization of the mantle sequence occurred pre-thrusting (pre-emplacement in age). (C) 2003 Elsevier Science B.V. All rights reserved

Dolomitization at the base of the «Landete Dolostones» formation in Sierra de Espadán (Castellón province): isotopic geochemistry (C, O and Sr) and fluid inclusion data

The dolomitization affecting the basal facies of the «Landete Dolostone» Formation in Sierra de Espadán (Castellón Province, Iberian Ranges) has been studied using fluid inclusions, stable (C and O) and radiogenic (Sr) isotopes. Two different processes have been found: (1) a pervasive epigenetic dolomitization originated by mixing of two different fluids of contrasted composition, and (2) the generation of «zebra»-llke rhythmic textures formed from hot (215 °C), high salinity (20-24 wt% eq NaCI) connate fluids equilibrated with the enclosing dolostone ( 8 18O H2O= + 13.0%o). A link between this high temperature event and the presence of a Hg deposit in the area is propose

Geochemistry of fluids associated to Mesozoic veins of the Talayuelas anticline (Cuenca, Iberian Ranges)

In the Talayuelas anticline (Cuenca province, Iberian Ranges) many quartz-siderite and barite ± quartz veins associated to Mesozoic faulting are found. They reflect an intense hydrothermal activity dominated by upwelling hot fluids of ultimate surficial origin (150 to 160 °C and up to 25% NaCI eq. salinity) that mixed with colder, less saline, descending solutions. Barite sulfate is related to the leaching of evaporites of Triassic to Jurassic age. The fluid circulation was probably enhanced by the high geothermal gradient related to the graben stage during the development of the Iberian rift

Molten sulphur-dominated fluids in the origin of a native sulphur mineralization in lacustrine evaporites from Cervera del Rio Alhama (Cameros Basin, NE Spain)

During the regional and petrologic study of the Cameros Basin, vein deposits containing native sulphur, gypsum, quartz and rare sphalerite were found enclosed in lacustrine evaporites. The fluid inclusion study of the coeval quartz crystals revealed that the aqueous fluids were extremely scarce during vein formation. Surprisingly, die textural study, microthermometry and qualitative Raman analyses of these inclusions proved that the main fluid-trapped during vein formation was a mixture of molten sulphur and volatiles (N-2, CO2 and H2S). As far as we know, this is the first time that an almost pure sulphur-bearing fluid is described to occur in sulphur deposits. (C) 2000 Elsevier Science B.V. All rights reserved

Origin of vein hydrothermal carbonates in triassic limestones of the Espadan Ranges (Iberian Chain, E Spain)

Dolomitization and Hg bearing veins in the lower Triassic limestones of the Espadan Ranges (Iberian Chain, E of Spain) are related to a hydrothermal event that occurred during the Santonian (late Cretaceous). Sr-87/Sr-86 ratios of unaltered regional dolostones range from 0.70829 to 0.70945, higher than those expected for Triassic diagenetic dolostones. Vein filling is constituted by a brown cloudy calcite (CC1), quartz, saddle-dolomite, mercurian tetrahedrite ("schwatzite") and a late blocky calcite (CC2). Low delta C-13 values of CC1 (-3.7 to -6.1 parts per thousand PDB) calcites resulted from the incorporation of light CO2 liberated from the destruction of organic matter within the vein system due to a temperature increase (up to 240 degreesC-270 degreesC), well above the gas generation window. Quartz has high delta O-18 values, ranging from 18.4 to 22.5 parts per thousand (SMOW). Saddle dolomites have low delta O-18 values (20.2 to 17.6 parts per thousand), with also low delta C-13 values, which is consistent with an effervescence of previously formed volatiles (CO2, N-2, H2S). Finally, the isotopically light carbon in late calcites (-6.3 to -10.6 parts per thousand) suggests a source related to the oxidation of organic matter whereas the heavy delta O-18 (23.5 to 25.4 parts per thousand) composition reflects O-18 buffering by the host carbonates. The small variations of Sr-87/Sr-86 ratios in hydrothermal calcites and dolomites (0.7082 to 0.7089) indicate that strontium isotope composition of the fluids were also buffered by the enclosing limestones. (C) 2001 Elsevier Science B.V. All rights reserved

[Dataset] The hydrochemical evolution of alkaline volcanic lakes: a model to understand the South Atlantic Pre-salt mineral assemblages

Supersaturaton due to mixing: the “algebraic effect” and Single-crystal and polycrystalline calcite growthPeer reviewe