HYDROTHERMAL EVENTS IN THE VALLE-DE-TENA (SPANISH WESTERN PYRENEES) AS EVIDENCED BY FLUID INCLUSIONS AND TRACE-ELEMENT DISTRIBUTION FROM FLUORITE DEPOSITS

This paper provides further evidences from fluorite and calcite geoche mistry and from fluid inclusion studies for the origin of the Valle de Tena fluorite deposits. The Valle de Tena, Spanish Western Pyrenees, contains two kinds of fluorite mineralizations: (1) vein-type deposits located in the vicinity of the Panticosa granite and enclosed by Devo nian carbonate facies; and (2) carbonate-hosted mineralizations on hig hly silicified Lower Carboniferous limestones. Based on geological evi dences the latter deposits can be referred to as Permo-Triassic. Micro thermometrical measurements on two-phase, water-rich inclusions with h igh liquid to vapor ratios yield homogenization temperatures ranging f rom 100 degrees to 200 degrees C for the two deposit-types. Salinities range from 4.0 to 11.6 eq wt% NaCl for carbonate-hosted deposits and from 12.5 to 21.3 eq wt% NaCl for vein mineralizations. REE contents a re variable and highest abundances are found in the fluorite from Lanu za and Tebarray (green fluorite),These later fluorite mineralizations have primary REE patterns with positive Eu anomalies which possibly re flect the alteration of feldspar. The REE distribution patterns of flu orites and calcites from the carbonate-hosted mineralizations are diff erent from those occurring as veins; the decrease of LREE in the forme r resulted in roof-shaped REE patterns. The negative Eu anomalies as w ell as the trace-element distribution allow us to deduce that the flui d from which these later Ca-minerals were formed was probably equilibr ated with the sedimentary country rocks. The fluid inclusion, geochemi cal, geologic and preliminary stable isotope data support two temporal ly distinct hydrothermal systems accounting for the fluorite formation and suggest a sedimentary basin source for the ore fluids, High-salin ity fluids (basement brines) are involved in the formation of the vein -type deposits, whereas the subsequent carbonate-hosted mineralization s were formed by mobilization of the fluorite veins by formation water s. The most likely fluorite deposition mechanism is cooling with minor contribution of fluid-rock interaction. In such context, magmatic act ivity is considered as heat source, The above mineralization events po ssibly span a time from Permian to Triassic which is in close agreemen t with the timing of hydrothermal processes documented throughout the Hercynian Europe.