Scheelite bearing quartz veins from Poblet (Catalonian Coastal Ranges): Characterisation of fluid inclussions and genetic model

Scheelite-bearing quartz veins from Poblet, trending in a NE-SW direction, are hosted by calcic granitoids of Late Hercynian age in the southern part of the Catalonian Coast Range. Fluid inclusions from quartz and scheelite have been characterized using microthermometry, Raman microspectrometry and Scanning Electron Microscopy. Except for type I inclusions (not observed in scheelite), similar inclusions have been observed in both minerals. One recognizes, in order of formation : Type I inclusions containing brine, daughter phases (halite, sylvite and sometimes iron chloride) and incidentally trapped minerals (ankerite, siderite, muscovite, K-felspar and unidentified species). Type II(L) inclusions have a low salinity (1 to 6 % eq. NaCl) and homogenize in the liquid phase in the range of 300-400 °C or under critical conditions near 400 °C. Type II(V) are low density, CO2-poor aqueous inclusions, homogenizing in the gas phase in the range of 350-420 °C. Type II(V') have higher CO2 contents. Type II inclusions appear as samples of an initially hypercritical fluid, trapped at different stages of its evolutions towards two subcritical fluids. Type III inclusions indicate later circulation of a colder, low-salinity solution (Th : 150 to 300 °C ; salinity : 0 to 3.5 % NaCl wt %). Abundant iron contents in type I inclusions suggest some interaction at elevated temperature (400 to 600°C) with a biotite granite (Whitney et al., 1985). P-T conditions compatible with measurements performed on type II inclusions are about 400 °C and 0.8 kbar, in a range similar to that determined for the Djbel Aouam occurrence in Hercynian Morocco (Cheilletz, 1984). Equivalent conditions have been postulated for scheelite precipitation at Poblet

Immunological impact of an additional early measles vaccine in Gambian children: responses to a boost at 3 years.

BACKGROUND: Measles vaccine in early infancy followed by a dose at 9 months of age protects against measles and enhances child survival through non-specific effects. Little is known of immune responses in the short or long term after booster doses. METHODS: Infants were randomized to receive measles vaccine at 9 months of age (group 1) or 4 and 9 months of age (group 2). Both groups received a boost at 36 months of age. T-cell effector and memory responses using IFN-γ ELIspot and cytokine assays and antibody titres using a haemagglutination-inhibition assay were compared at various times. RESULTS: Vaccination at 4 months of age elicited antibody and CD4 T-cell mediated immune responses .Two weeks after vaccination at 9 months of age group 2 had much higher antibody titres than group1 infants; cell-mediated effector responses were similar. At 36 months of age group 2 antibody titres exceeded protective levels but were 4-fold lower than group 1; effector and cytokine responses were similar. Re-vaccination resulted in similar rapid and high antibody titres in both groups (median 512); cellular immunity changed little. At 48 months of age group 2 antibody concentrations remained well above protective levels though 2-fold lower than group 1; T-cell memory was readily detectable and similar in both groups. CONCLUSIONS: An additional early measles vaccine given to children at 4 months of age induced a predominant CD4 T-cell response at 9 months and rapid development of high antibody concentrations after booster doses. However, antibody decayed faster in these children than in the group given primary vaccination at 9 months of age. Cellular responses after 9 months were generally insignificantly different

L'ALTERATION DES VERRES : DONNEES DE L'ANALYSE DE SURFACE

L'étude de la composition superficielle des verres soumis à altération a été abordée par spectrométrie XPS (ou ESCA), sonde ionique (SIMS) et microscopie électronique (transmission et balayage). Les matériaux choisis sont des verres industriels et naturels ; les milieux de corrosion sont l'eau douce, l'eau de mer et des solutions d'ions métalliques. La température est de 90°C, le milieu est non agité et non renouvelé. Tous les essais ont été réalisés sur des esquilles. Les principaux résultats sont les suivants : - le comportement de l'aluminium se manifeste par la formation d'un dépôt très mince riche en Al et par l'enrichissement en cet élément du verre sous-jacent. - lors de l'altération en eau douce, le comportement du fer et son influence sur l'altération sont nettement fonction de la concentration initiale en cet élément. - dans l'eau de mer, il se développe des phases hydroxycarbonatées qui sont les précurseurs de phyllosilicates caractéristiques de l'altération sous-marine des verres.The study of the superficial composition of altered glasses has been investigated by XPS (or ESCA), secondary ion mass spectrometry (SIMS) and electron microscopes (TEM and SEM). The selected materials were industrial and natural glasses ; the solutions were fresh water, sea-water and metal-bearing diluted solutions. The temperature was 90°C, the bulk was neither stirred nor replenished. All runs were performed on hand-fractured sections of glasses. Amongst the results obtained, one may quote the formation of a superficial Al-rich layer with an increase of Al into the hydrated underlying glass. Another results show : 1) during the alteration in fresh water, the behaviour of iron and its influence on the alteration process can be related to the initial iron concentration ; 2) in sea-water, hydroxycarbonates were detected ; these phases are the precursors of phyllosilicates characteristic of marine alteration of glasses

Jabali, a Zn-Pb-(Ag) carbonate-hosted deposit associated with Late Jurassic rifting in Yemen

International audienceThe Jabali deposit (3.8 Mt at 16% Zn, 2% Pb and 132 g/t Ag) is hosted by dolomitized platform carbonates of Kimmeridgian age at the southwestern edge of the oil-producing Wadi al Jawf rift basin in northern Yemen. Paleogeographical reconstructions demonstrate that tensional synsedimentary tectonic activity from the Late Jurassic to Early Cretaceous was responsible for the thick accumulation of argillaceous and evaporitic sediments in the subsident rift basin, the unstable margin of which was the site of rapid facies changes, local disconformities and periods of emergence, as well as of dolomitization along the WNW- and NNW-striking boundary fault system. In the Jabali area, the upper part of the Jurassic sequence underwent two stages of dolomitization before emergence and deep karstic erosion. Solution cavities and depressions in the eroded surface were filled by dolomite sand and black pyritic mudstone prior to a last marine transgression of limited extent. Subsequent ore deposition and associated late dolomitization sealed the network of solution cavities, impregnating the dolomite sands and the host dolomites. Sphalerite I and wurtzite, followed by silver-bearing zoned sphalerite II associated with galena, crystallized from a cyclic influx of low-temperature (75-100°C) saline solutions. Lead isotope geochemistry indicates that the lead, zinc and silver probably originated from an Early Proterozoic basement. The dissolved metals were likely derived from the basal aquifer (detrital material of basement origin) of the evaporite-bearing sequence filling the Wadi al Jawf trough. Migrating metalliferous brines from the basin to the uplifted Jabali area, where ore deposition was favoured by a reducing environment, were probably channelled by the boundary fault system during the last stages of synsedimentary tectonic activity

Recherches preliminaires sur la relation entre la taille et la toxicite de l'amiante chrysotile

CNRS-CDST / INIST-CNRS - Institut de l'Information Scientifique et TechniqueSIGLEFRFranc