CO2-Bearing Fluid Inclusions from Geothermal Fields

Abstract

Three semi quantitative methods to estimate the CO2 concentration of the geothermal fluid trapped in fluid inclusions are described. The crushing method is applicable for the estimation of the low CO2 concentrations present in most geothermal fields. Intermediate CO2 is estimated from the presence of clarthrate only on freezing, and high CO2 is estimated from liquid CO2 at room temperatures or on freezing. Their concentrations are calculated within the limits where Henry's Law is obeyed. These methods are then applied to the fluid inclusions from some boiling systems. Crushing studies reveal the low CO2 of the boiling fluid at Hohi, Japan. Formation of clarthrate but not liquid CO2 on freezing inclusion from Broadlands, N.Z. suggests heterogeneous trapping of CO2 bearing boiling fluid. Liquid CO2 bearing vapor rick inclusions from Tuscany, Italy indicate formation from a local isolated hydrothermal system under more than hydrostatic pressure.