Geothermobarometry based on pyrrhotite composition and fluid inclusion studies: application to the scheelite-bearing deposit of Salau (Pyrénées, France)
Dubessy, Jean; Schellen, Anne-Dominique; Claude, Jean-Marie
European Journal of Mineralogy Volume 2 Number 2 (1990), p. 235 - 244
published: Apr 17, 1990
manuscript accepted: Nov 21, 1989
manuscript received: Aug 25, 1989
ArtNo. ESP147050202009, Price: 29.00 €
Abstract The equilibrium between sulphur in pyrrhotite and sulphur in a H2S-bearing fluid is used to determine the P-T-fO2-fS2 conditions for the formation of the scheelite-bearing ore of Salau. Microthermometry and Raman microspectrometric analyses provide V-X properties of the fluid inclusions ; the pyrrhotite compositions are determined by X-ray diffraction (Fe0.907S on average). The obtained T-fO2-fS2 values (335 < T(°C) < 365 ; -33 < log fO2 < -29 ; -8.4 < log fS2 < -8.1) are consistent with those determined from the paragenesis hedenbergite + pyrite -I- pyrrhotite + quartz + calcite ± andradite. This agreement shows that pyrrhotite composition was not significantly modified during cooling and that homogeneous molecular C-O-H equilibria still control the redox state of the fluid at 350 °C.