ISOTOPIC COMPOSITION OF STRONTIUM IN THE VALLE DE TENA (SPANISH CENTRAL PYRENEES) FLUORITE DEPOSITS - RELEVANCE FOR THE SOURCE OF ELEMENTS AND GENETIC SIGNIFICANCE

The fluorite deposits of the Valle de Tena, Central Pyrenees, include stratabound (Portalet) and vein (Lanuza and Tebarray) deposits the for mation of which are linked to a Namurian-Westfalian emersion episode a nd to post-Hercynian hydrothermal systems similar to those occurring e lsewhere in Hercynian Europe. In this study, strontium isotopes were u sed to determine the source(s) of strontium, and by inference calcium, of the fluorite mineralizations, as well as the nature of the ore-for ming fluids. Fluorite and calcite from each deposit have similar Sr-87 /Sr-86 ratios (Portalet 0.7085-0.7108; Lanuza 0.7086-0.7104 and Tebarr ay 0.7086-0.7101). In all deposits, the Sr isotope composition of most of the Ca-minerals is more radiogenic than that of the host limestone s. This indicates that the Ca-minerals contain a mixture of Sr derived locally from the host limestones and (87) Sr-enriched Sr leached from silicate minerals in the siliciclastic portion of the basement sequen ce and in granites from the study area. Volcanic rocks are ruled out a s a significant Sr source for the fluorite deposits. The observed tren d in Sr-87/Sr-86 versus 1/Sr support a fluid-rock interaction model wh ich satisfactorily reproduces the marked Sr-87-enrichment in the fluor ites and calcites from the deposits.