Precipitation of lead–zinc ores in the Mississippi Valley‐type deposit at Trèves,Cévennes region of southern France

The Trèves zinc–lead deposit is one of several Mississippi Valley‐type (MVT) deposits in the Cévennes region of southern France. Fluid inclusion studies show that the ore was deposited at temperatures between approximately 80 and 150°C from a brine that derived its salinity mainly from the evaporation of seawater past halite saturation. Lead isotope studies suggest that the metals were extracted from local basement rocks. Sulfur isotope data and studies of organic matter indicate that the reduced sulfur in the ores was derived from the reduction of Mesozoic marine sulfate by thermochemical sulfate reduction or bacterially mediated processes at a different time or place from ore deposition. The large range of δ³⁴S values determined for the minerals in the deposit (12.2–19.2‰ for barite, 3.8–13.8‰ for sphalerite and galena, and 8.7 to ?21.2‰ for pyrite), are best explained by the mixing of fluids containing different sources of sulfur. Geochemical reaction path calculations, based on quantitative fluid inclusion data and constrained by field observations, were used to evaluate possible precipitation mechanisms. The most important precipitation mechanism was probably the mixing of fluids containing different metal and reduced sulfur contents. Cooling, dilution, and changes in pH of the ore fluid probably played a minor role in the precipitation of ores. The optimum results that produced the most metal sulfide deposition with the least amount of fluid was the mixing of a fluid containing low amounts of reduced sulfur with a sulfur‐rich, metal poor fluid. In this scenario, large amounts of sphalerite and galena are precipitated, together with smaller quantities of pyrite precipitated and dolomite dissolved. The relative amounts of metal precipitated and dolomite dissolved in this scenario agree with field observations that show only minor dolomite dissolution during ore deposition. The modeling results demonstrate the important control of the reduced sulfur concentration on the Zn and Pb transport capacity of the ore fluid and the volumes of fluid required to form the deposit. The studies of the Trèves ores provide insights into the ore‐forming processes of a typical MVT deposit in the Cévennes region. However, the extent to which these processes can be extrapolated to other MVT deposits in the Cévennes region is problematic. Nevertheless, the evidence for the extensive migration of fluids in the basement and sedimentary cover rocks in the Cévennes region suggests that the ore forming processes for the Trèves deposit must be considered equally viable possibilities for the numerous fault‐controlled and mineralogically similar MVT deposits in the Cévennes region.     

Chemical and isotopic signatures of Na/HCO3/CO2‐rich geofluids,North Portugal

Geochemical and isotopic studies have been undertaken to assess the origin of CO₂‐rich waters issuing in the northern part of Portugal. These solutions are hot (76°C) to cold (17°C) Na–HCO₃ mineral waters. The δ²H and δ¹⁸O signatures of the mineral waters reflect the influence of altitude on meteoric recharge. The lack of an ¹⁸O‐shift indicates there has been no high temperature water–rock interaction at depth, corroborating the results of several chemical geothermometers (reservoir temperature of about 120°C). The low ¹⁴C activity (up to 9.9 pmC) measured in some of the cold CO₂‐rich mineral waters (total dissolved inorganic carbon) is incompatible with the presence of ³H (from 1.7 to 4.1 TU) in those waters, which indicates relatively short subsurface circulation times. The δ¹³C values of CO₂ gas and dissolved inorganic carbon range between ?6‰ and ?1‰ versus Vienna‐Peedee Belemnite, indicating that the total carbon in the recharge waters is being diluted by larger quantities of CO₂ (¹⁴C‐free) introduced from deep‐seated (upper mantle) sources, masking the ¹⁴C‐dating values. The differences in the ⁸⁷Sr/⁸⁶Sr ratios of the studied thermal and mineral waters seem to be caused by water–rock interaction with different granitic rocks. Chlorine isotope signatures (?0.4‰ < δ³⁷Cl < +0.4‰ versus standard mean ocean chloride) indicate that Cl in these waters could be derived from mixing of a small amount of igneous Cl from leaching of granitic rocks.     

Children,social capital and health: increasing the well‐being of young people in rural Wales

This paper explores the usefulness of employing the concept of social capital within a research project investigating the best ways of meeting the health and well‐being needs of young people living in rural Wales. The first part of the paper provides an overview of some of the current research exploring the relationship between social capital, health and young people. The second part provides an overview of findings from an action research project to illustrate how social capital is conceived and applied in this context. It concludes by stating that children and young people do actively generate, draw upon and negotiate their own social capital, and that this is an under‐utilised resource in terms of promoting health and well‐being.     

Homelessness,poverty, and risks to health: beyond at risk categorizations of street children1

Homeless and street children are commonly portrayed in the academic and welfare literature as a prime category of ‘children at risk’. They have attracted world‐wide attention due to rising numbers in cities of the Western and developing world coupled with a discourse of childhood that ascribes risk to poor urban children unaccompanied by adults on the streets. This paper presents a critique of views about homeless and street children that rest upon an unhelpful blanket generalization of risk and, more specifically, that adopt polemical or categorical statements about homelessness as the most salient risk factor for poor health. Current research is distancing itself from a discourse that sets global characteristics for a ‘street lifestyle’, aiming instead to contextualize research on street children. Many studies have also questioned the stereotypical expectation that homeless children are the most vulnerable in deprived environments, arguing that poverty, not homelessness per se, carries the most significant risks to children's health. A risk discourse is unhelpful where it promotes a stereotype of vulnerability about children, resulting in further discrimination and social exclusion; it is most helpful when it focuses attention on ways to negotiate adverse situations. Some challenging academic and practical questions need to be raised regarding risk assumptions and risk assessment.     

PIGMENT IDENTIFICATION IN GREEK POTTERY BY RAMAN MICROSPECTROSCOPY*

Raman microspectroscopy (RMS) is now established as a key technique for the identification of pigments of archaeological pottery that permits the in situ study of art objects by a non‐destructive procedure. The information obtained represents a great aid to restoration and conservation techniques. In this work, the chemical nature of the red, black and white pigments of five samples of Greek pottery from the end of the fifth century and the first half of the fourth century bc , exhumed from the Iberian necropolis of Cabezo Lucero (Guardamar del Segura, Alicante, Spain), has been identified. The black and the red pigments are found to be magnetite (Fe₃O₄) and hematite (α‐Fe₂O₃), respectively. The white pigment is found, for the first time, to be composed of alumina (α‐Al₂O₃ and γ‐Al₂O₃) probably yielded by the thermal decomposition of Greek bauxite.     

GEOCHEMICAL CHARACTERIZATION OF ARCHAEOLOGICAL LIME MORTARS: PROVENANCE INPUTS*

Chemical and mineralogical analyses were carried out on historical lime mortars from the parish church of Santa María La Real (Guipúzcoa). The study included various periods ranging from Roman to modern times and allowed the identification of various types of raw materials. In order to obtain pure binder, free of carbonate aggregates and charcoal particles, an innovative binder separation method was implemented. The chemical composition of the binder allows discrimination of different provenance areas for the raw materials, although those areas do not correlate with specific historical periods. In addition, the influence of burial processes on the primeval chemical features has been assessed and reveals that modern mortars display greater chemical modification than the Roman mortars.     

UNOFFICIAL COINAGE IN THE THIRD CENTURY ad IN THE GALLO‐ROMAN WORLD: CHEMICAL AND PHYSICAL ANALYSES FOR DETERMINING THE LOCALIZATION OF THE WORKSHOP*

The third century ad was a complex period of crisis in the Roman world. In this paper, official and unofficial antoniniani, and double sestercii and sestercii, were analysed by fast neutron activation analysis (FNAA) to determine the alloys used by the craftsmen for producing forgeries. Moreover, at Châteaubleau, archaeologists discovered antoniniani and bronze forgeries from Postumus. Similar materials have been found in other hoards. They are believed to have been produced by a workshop called ‘atelier II’ by numismatists. The question was whether it is possible to differentiate the Châteaubleau production from the atelier II production.