Silicothermal fluid: a novel medium for mass transport in the lithosphere

New experimental data from synthetic fluid-inclusion studies in the system K 2 O-CO 2 -SiO 2 -H 2 O (KCSH) show that a potassic, silica-rich (≈ 90 wt% SiO 2 ) fluid can coexist immiscibly with a supercritical, alkaline, aqueo-carbonic fluid and quartz from temperatures as low as 300 °C to more than 750 °C at relatively low geologic pressures ( 2 -rich fluids, if they form in the lithosphere, are likely to be important in the mobilization and transport of silica and large ion lithophile elements (e.g., K, Cs, Ba) and metals of economic significance (e.g., Au, Ag, U).