La composición isotópica del azufre en sulfuros (8 34S) de las mineralizaciones tipo sedimentario-exhalativo del Ordovícico superior del valle de Arán (Pirineos Centrales) varía entre +3,5 y +15,1 %0 en los encajados en carbonatos y entre -2,7 y +5,5 %0 en los encajados en materiales detríticos. Estos valores sugieren que dichos depósitos se formaron a partir de dos fuentes de azufre distintas: una originada por reducción de sulfato de origen marino y otra por lixiviación de materiales detríticos y/o volcánicos de edad cambro-ordovícica. El metamorfismo Hercínico no ha afectado significativamente las composiciones isotópicas originales de los sulfuros y las variaciones de la 8 34S de los mismos en cada una de las dos litologías encajantes, podrían explicarse por pequeños cambios en la f0 2, temperatura o pH durante la formación de los depósitos. La composición isotópica del plomo de 6 galenas analizadas presenta las relaciones siguientes: 18,02 ::; ABSTRACTThe sulfur isotopic composition of sulfides from sedex-type deposits enclosed within Upper Ordovician rocks in the valle de Arán (Central Pyrenees) ranges from +3.5 to + 15.1 %0 in mineralizations enclosed in carbonates and from -2.7 %0 to +5.5 in mineralizations enclosed in detritic rocks. These values suggest two different sources of sulfur: a heavy source of crustal origin, probably related to the reduction of seawater sulfate, and a lighter one, resulting from leaching of underlying detritic and/or volcanic rocks of cambro-ordovician age. Hercynian metamorphism has not significantly altered the original sulfur isotopic composition of sulfides and their variation at the deposit scale can be explained by changes in T, pH or f0 2 during sulfide deposition. Lead isotope composition of 6 galena samples have the following ratios: 18.02::; 206Pbp04Pb ::; 18.08; 15.66 ::; 207PbP04Pb::; 15.70 and 38.16 s 208PbP04Pb ::; 38.29, similar to those reported by Marcoux (1987) in the Pierrefitte deposits (Central Pyrenees, France). These values are very homogeneous and suggest alead source situated within the upper crust. Calculated ages based on Cumming and Richards (1975) lead evolution model range from 422 to 452 m.a. (Upper Ordovician), which is the age of the enclosing rocks. These data confirm the hypothesis of a sedimentary-exhalative origin of the deposits.

The chemical composition of tourmaline has been used as a host environment register as well as a potential exploration tool for mineral deposits. In this study, the textural and chemical composition of tourmalines associated with Zn-Pb mineralizations around the Murguía diapir (Basque Cantabrian Basin, N Spain) are examined to verify if they record the mineralizing events in the area. Petrographically, tourmalines have been differentiated between inherited and authigenic. Colorless authigenic tourmalines are present as halos partially around green and pleochroic detrital grains or as individual crystals. Inherited and authigenic tourmalines are also chemically distinct. Authigenic tourmalines show different X-site occupancies, a Mg/(Mg+Fe) ratio above 0.77, and are aluminum rich and plot to the right of the povondraite-oxidravite join, above the schorl-dravite join. Inherited tourmalines plot within the alkaline (Na+K) group field, and have a Mg/(Mg+Fe) ratio below 0.77. These data suggest that authigenic tourmalines grew under reducing conditions, compatible with the hydrothermal event responsible for the ore deposition and caprock formation during the diapir ascent.Tourmaline. Salt diapir. Zn-Pb deposits. Basque Cantabrian Basin. KEYWORDS