STRONTIUM AND SULFUR ISOTOPE GEOCHEMISTRY OF LOW-TEMPERATURE BARITE FLUORITE VEINS OF THE CATALONIAN COASTAL RANGES (NE SPAIN) - A FLUID MIXING MODEL AND AGE CONSTRAINTS

Sulphur and strontium isotope analyses from the low-temperature barite-fluorite veins of the Catalonian Coastal Ranges (NE Spain) reveal the nature and source of the ore-forming fluids and constrain the ages of the mineralizations. Sulphur isotope values in the barite deltaS-34 = +15 to +20 parts per thousand) are similar to those of sulphates in nearly Triassic-Jurassic evaporites deltaS-34 = +11 to +19 parts per thousand). Sr-87/Sr-86 isotopic composition ratios of barites and fluorites are 0.7094-0.7167. The variation of Sr-87/Sr-86 within individual veins suggests that the Sr had two different sources: granites rocks in the Hercynian basement and seawater or evaporites of Triassic-Early Jurassic age. Vein formation is modelled as a two-component mixing process in which the S and Sr isotopic composition of the end-members change with time. The observed difference in mean S and Sr isotopic compositions among the veins is interpreted to reflect differences in mineralization age. Ore deposition occurred between 225 and 195 Ma (Triassic to Early,Jurassic) in all cases except the Berta mine which may be as young as Miocene.