A specially designed quartz liner effectively prevents alloying problems with noble-metal capsules during hydrothermal experiments at elevated pressures and temperatures. The liner consists of three pieces: a cylindrical container made of a single quartz crystal, a SiO2 glass plug, and a rounded closure lid made of a single quartz crystal. Soon after the final pressure and temperature have been reached, recrystallisation of the SiO2 glass plug causes the quartz cap to be tightly sealed onto the quartz container, thus producing a quartz capsule that fully isolates the charge from the surrounding noble-metal capsule. The efficiency of the method is demonstrated on experiments with Cu and S (±Fe, Ag)-bearing, NaCl-H2O dominated fluids, which are complicated by the fact that all commonly used noble metals (and -alloys) react with either of these elements. Even small amounts of added Ag are still present after the run, showing that interaction with outer gold capsules was minimal. The new method makes it also possible to study chemical systems involving compounds with low melting points, such as Sn, Bi, Te, Tl, and Hg, and it allows the surrounding noble-metal capsules to be replaced by capsules made of non-noble materials if necessary. A disadvantage of the method is that it cannot be used in conjunction with external fO2 buffers, as the fluid inclusions form before equilibrium with respect to an external fO2 buffer is reached.

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