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Caractéristiques de la phase fluide associée à la genèse des gisements d'étain d'Abbaretz et de La Villeder (Bretagne Meridionale)
Authors:B Charoy  A Weisbrod
Institution:(1) Nancy, France
Abstract:The fluid inclusions occurring in quartz of cassiterite-bearing quartz veins from two localities of Southern Brittany have been studied (microthermometry and chemical analysis). In both localities, two sorts of fluids have been recognized: 1. Early fluids, related to the precipitation of cassiterite. Those fluids are closed to a chloride-bearing aqueous solution, with very little CO2 and hydrocarbons. The salinity is rather low (6 to 9 wt % eq. NaCl). The inclusions homogenize between 150 à 300 °C. The K/Na atomic ratio is about 0,1. From these data and the mineralogical associations (muscovite + kaolinite), the physical and chemical properties of the solution at the time of cassiterite crystallization have been calculated: temperature sim350°C, pressure sim800 bars; molalities of NaCl, KCl and HCl are, respectively about 1, 0.1 and 0.01 (pH at 25 °C, 1 bar sim2, lower than 3 in any case). 2. Late fluids, related to an important kaolinization. They are generally colder, and have a either lower or higher salinity, than the early fluids.
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