Abstract
Quadruple Mass Spectrometer (QMS) is widely used for detection of very little quantity of gases. As compared with magnetic field type mass spectrometer, it can be scanned continuously and very quickly from low mass-to-charge ratio (m/e) to high m/e. Use this characteristics, heat fluid inclusions in a mineral under vaccum, they explode one by one (decrepitation), enabled to measure for gas composition of fluid inclusions for every burst temperature by introducing the emitted gas into QMS immediately. The advantage of this method is as follows,1) It does not need to grind a sample, and adsorption of the gas on the surface of a sample is made as for it to the minimum. 2) Under continuously vaccum environment, measurement in the low background (less than 4x10-6Pa) is possible. 3) Since measurement in the low background is possible, sample can be managed with small quantity (about 50mg). 4) To calculate mean ion current of each number of m/e detected by QMS during heating, it is possible to estimate for bulk gas composition. In this research, the quantitative gas analysis method of multi-composition gas established by [1] of having used QMS was applied, the new gas analysis system was built. In this system, fluid inclusions was gradually heated from 130-650 degrees C, over 30 minutes in the vaccum, and the emitted gases by decrepitation of fluid inclusions measured at intervals of 2 seconds by QMS. As a result of applying this method to gas analysis of fluid inclusion in natural pegmatitic quartz, it has checked that it was very effective to estimate quantity of water. Moreover, as for the ion current curve upon heating (gas release curve),the feature was seen for every area. Especially the area with CO2-rich fluid inclusions (Ishikawa pegmatite area and Sakihama pegmatite area) found the release curve tends to incline toward a low temperature. In near 573 degree C, the sharp peak was detected on the release curve by all quartz samples. This peak is for fluid inclusion in which inner pressure increased to cause a explode in large quantities with change of the crystal structure at the time of alpha-beta transition of quartz. The weak peak was also detected for m/e=33,34 at the temperature of alpha-beta transition of quartz. It is the evidence of existence of H2S in fluid inclusion. Reference:[1] Kamashima T.,Morikiyo T.,Jap. Mag. Min. Petr. Sci.,32,1-11(2003)
