NATURAL FLUID PHASES AT HIGH-TEMPERATURES AND LOW-PRESSURES

Gas phases at low pressures and high (magmatic) temperatures have cert ain peculiar properties. The fluid is mainly water vapour, which is us ually observed during discharging of crystal magmatic melts. At > 700 degrees C and < 100 bar these peculiar properties include: formation o f near 'dry' salt melts as second fluid phase, very strong fractionati on of hydrolysis products between vapour and melts, subvalence state o f metals during transport processes, and high sensitivity of the gas t o conditions of sublimate precipitation. Phase diagram analysis as wel l as results of field and laboratory experiments are presented in this article. The processes could be a model for industrial technologies t o clean wastes from toxic, rare and heavy metals. Transport forms of s ome elements in volcanic gases are very similar to the species which w ere formed first in the protosolar nebula. (C) 1998 Elsevier Science B .V. All rights reserved.