Hydrosilicate liquids in the system Na2O-SiO2-H2O with NaF, NaCl and Ta: Evaluation of their role in ore and mineral formation at high T and P

Abstract

Consideration of the existence of hydrosilicate liquids (HSL) in nature can help in understanding the accumulation and transport of some mineral and ore-forming components at the transition from magmas to hydrothermal fluids. We studied the experimental formation of HSL using a base system Na2O–SiO2–H2O with addition of NaF, NaCl and metallic Ta. The interaction between quartz and aqueous solution, performed at 1.5 kbar and 600°C and followed either by cooling or by quench, showed that the formation of HSL occurred when initial Na2O exceeded 2 wt %. Neither NaF nor NaCl have a significant effect on the formation of HSL. The HSL concentrates F, whereas Cl partitions into the aqueous fluid. With addition of Ta to the system, the HSL becomes metal-enriched. Natural analogs of experimental HSL can be found among “melt/fluid” inclusions entrapped in quartz and other minerals of miarolesin granite pegmatites and rare-metal granites. The HSL is a novel medium enabling extreme concentrations of lithophile ore metals at the magmatic-hydrothermal transition.