GEOCHEMICAL PATTERNS OF A SHEARED FLUORITE VEIN, PARZAN, SPANISH CENTRAL PYRENEES

The formation of Parzan fluorite-lead <<extension-type>> vein (Spanish Central Pyrenees) is related to the post-Hercynian hydrothermal activ ity widespread not only in the Pyrenees but in Western Europe as well. The lode was later strongly deformed during the Alpine orogeny with t extural modifications and destruction of primary fluid inclusions. In order to determine if geochemical signatures of the vein were disturbe d during Alpine deformation, post-ore fluid inclusions and quartz oxyg en-isotopes have been addressed. Microthermometry and X-ray microanaly sis of frozen inclusions confirm the Na-Ca-Cl character of post-ore fl uid circulations and indicate that they were originally derived from a single source: Triassic connate waters. Oxygen isotope data on quartz formed during deformation along with trace element geochemistry sugge st that the geochemical signatures of the vein (mainly REE and Sr-87/S r-86) were apparently not reset during deformation. The REE content of fluorites is very high (up to 0.12%); the chondrite normalized REE pa tterns display a continuous decrease from La to Lu. Sulphur isotope da ta for the Parzan vein is outside the typical ''deep seated'' range, s uggesting dominantly crustal sources of sulphur for sulphides, while f ormation waters may be proposed for barite. Parzan fluorites have the most radiogenic Sr values of all the investigated fluorite deposits in Central Pyrenees. They scatter in the range of both the igneous rocks and the Cambrian-Ordovician and Triassic detrital sequences of the Pa rzan area. If REE contents and Sr-87/Sr-86 ratios reflect the primary stage of vein filling as suggested by the good correlation between bot h geochemical signatures, the linear array between Sr-87/Sr-86 and 1/S igma REE is suggestive of a mixing process. The delta(34)S, delta(18)O and Sr-87/Sr-86 parameters in barite. which postdates the fluorite, a lso provide strong evidence that barite deposition is a result of flui d mixing. Such an interpretation is in line with present-day ideas for the genesis of many of the F-Ba-Pb-Zn vein deposits in the Hercynian belt of Iberia.