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 formation of which are linked to a Namurian-Westfalian emersion episode and to post-Hercynian hydrothermal systems similar to those occurring elsewhere in Hercynian Europe. In this study, strontium isotopes were used to determine the source(s) of strontium, and by inference calcium, of the fluorite mineralizations, as well as the nature of the ore-forming 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 Tebarray 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 limestones. 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 sequence and in granites from the study area. Volcanic rocks are ruled out as a significant Sr source for the fluorite deposits. The observed trend in Sr-87/Sr-86 versus 1/Sr support a fluid-rock interaction model which satisfactorily reproduces the marked Sr-87-enrichment in the fluorites and calcites from the deposits.