Mercury (Hg) is a highly volatile element whose behaviour at high temperatures is difficult to measure experimentally but which is nevertheless geologically important as a potential indicator of large-scale volcanism. Due to its low levels in volcanic samples, little is known about how Hg partitions during magmatic evolution. This experimental study was therefore aimed at obtaining better understanding of how Hg behaves during magmatic processes.

We began with experiments in vertical atmospheric furnace (1 bar and 1300°C) in which a starting basaltic composition doped with 1000ppm of Hg as HgO was mounted on Pt wire. However, all Hg was lost before the basalt reached the liquidus temperature. We therefore switched to using a "closed" system experimental setup: sealed silica glass tubes. In order to compare the volatility of Hg with other elements, the Icelandic basalt used as starting material was doped with other volatile trace elements (e.g., Ag, Cd, Co, Cu, Ni). This global composition was fused, ground and then doped with 93ppm Hg as HgO in order to reach significant mercury partial pressures (pHg) in the silica tubes. Experiments were then performed in a muffle furnace at 1250, 1300 and 1400°C for times of 5 to 1440 minutes and finally air quenched. Major oxides and trace elements were analysed on glass chips by electron microprobe and laser Ablation ICP-MS, respectively. Hg contents were measured on ground glass with a Direct Mercury Analyzer. As expected, almost all Hg (> 99%) was lost in the first minutes generating an essentially constant pHg in the gas of ~0.0015 bar. At 1400°C the Hg content of the glass declines to 38ppb within 60 minutes and remains essentially at this level. The corresponding "plateau" level at 1300°C is ~110ppb. These concentrations are similar to those found in natural igneous rocks.