Manometric and mass spectrometric analysis of fluids in geological meterials.

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 per formed either by vacuum crushing or heating. A separation line using cold traps, oxidation (CO to CO2) and reduction (H20 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 mix ture 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-' mot H2O, 0.3 x 10-' mol C02 and about 0 .2 x 10' mol for H2, N2, CO, CH4 and Ar. Further species like organic compounds, S02 and H2S are detected but not determined. In the case of H2O and C02 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 .

Significance of H2 and CO release during thermal treatment of natural phyllosilicate-rich rocks

“…The newly formed H 2 O could oxidize structural Fe(II) and form H 2 by reducing H 2 O following the equation (1) as proposed by Villiéras et al (1992) to explain the release of H 2 during heating of talc and chloritite from Trimouns. In this latter study, the authors also followed the method of Zimmermann et al (1988) to recover and separate the different gases released at various temperature steps (talc: from 200 to 1100 ˚C; chloritite from pegmatite: from 280 to 1100 ˚C; chloritite from micaschist: from 300 to 1080 ˚C). The authors documented H 2 release, between 0.01 and 0.8 ppm, at low temperature (between 200 and 300 ˚C) for chloritite and talc.…”