Manometric and mass spectrometric analysis of fluids in geological materials

Abstract

A procedure of volatile analysis in rocks which permits quantitative estimation of all the volatile species of any geological interest is presented and illustrated by several examples. Gas extraction is performed either by vacuum crushing or heating. A separation line using cold traps, oxidation (CO to CO2) and reduction (H2O to H2) furnaces permits to separate several fractions. At the end of each separation phase the pressure in the line is measured with a capacitance manometer before analysis of the gas mixture with a mass spectrometer. Calibration is done periodically using standard gases stored in gauged bottles. The detection limits are 0.5 to 1. x 10-7mol H20, 0.3 x 10-7 mol CO2 and about 0.2 ×10-7mol for H2, N2, CO, CH4 and Ar. Further species like organic compounds, SO2and H2S are detected but not determined. In the case of H2O and CO2 the reproducibility is better than 4%. The conjunction of vacuum crushing, stepwise heating and size fraction analysis permits to separate components like: dissolved, adsorbed and vesicle trapped. In particular, effects of adsorption have been evaluated: it is a serious problem for species like CO2 and H2O with finely crushed material. H2 and CO detected after thermal extraction when organic compounds are present in the sample reflect organic decomposition rather than any thermodynamic equilibrium attained upon rock formation. © 1988, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.