Melting behaviour and composition of aqueous fluid inclusions in fluorite and calcite: applications within the system H2O-CaCl2-NaCl
Zwart, Erik W.; Touret, Jacques L.R.
European Journal of Mineralogy Volume 6 Number 6 (1994), p. 773 - 786
published: Nov 30, 1994
manuscript accepted: May 19, 1994
manuscript received: Oct 28, 1993
ArtNo. ESP147050606014, Price: 29.00 €
Abstract In samples from Ca2 Zechstein formations in northwest Germany, aqueous liquid-vapour (LV) as well as liquid-vapour-solid (LVS) inclusions in calcite and fluorite contain high salt concentrations, particularly belonging to the system H2O-CaCl2-NaCl. Emphasis is laid on the recognition of phase transitions and compositions by sequential heating and freezing. LV inclusions clearly show a eutectic temperature close to -52°C, although the actual forming and melting of antarcticite could not be observed. Melting of ice (-27.8°C to -24.4°C) and hydrohalite (HH, -15.8°C to +15.4°C) reveal the composition (16-19 wt. % NaCl, 7-11 wt. % CaCl2) when plotted on the relevant ternary phase diagram. Melting of hydrohalite above 0.1°C is metastable. LVS inclusions belong to two categories. Type(I), with the dissolution temperature of halite lower than the homogenization temperature (Ts Th, shows non-equilibrium melting in the presence of a halite cube; the presence of LiCl and KC1 depress the eutectic point; the NaCl content can be estimated at 21 wt. %. CO2-CH4 clathrates form around the vapour phase and melt at -16.4°C to -15°C for LV inclusions and at -31°C to -28.2°C for LVS inclusions. Their nature is confirmed by Raman analyses, which also reveal traces of H2S.