ISOTOPIC COMPOSITION AND CONCENTRATION OF INERT GASES IN MEXICAN HYDROTHERMAL SYSTEMS (Genetic and applied aspects)

Isotopic composition and concentration of inert gases in samples of hydrothermal fluids from eight discharge areas in Mexico are studied. Xe, Dr, and a large proportion of Ar and Ne are found to be of atmospheric isotopic composition. A small fraction of Ar is of radiogenic origin. All of the Mexican hydrothermal systems under study contain mantle helium (from 4 to 44 % of total He). Values of the 3He/ 4 He ratio vary along and across the strike of the Transmexican volcanic belt, these values being consisten with the geostructural pattern as well as with the petrochemical features of the Late Plionece -Quaternary volcanics. The maximum portion of mantle helium is peculiar to the "hottest" hydrothermal systems (Los Azufres and Cerro Prieto) and to the vicinity of Los Humeros caldera (Quateloluco spings). Anomalous high content of Ne is observed in the same areas. Bearing in mind the analogous peculiarity of other powerful hydrothermal systems of the world, these evidences suggest a high geothermal potential for those areas.