ABSTRACT

In order to extract fluid inclusions in minerals, a new type ball-mill made of Pyrex glass designed by Kita (1981) was used. Samples used in this study were hydrothermal vein quartz, fluorite and arsenopyrite. Under suitable conditions, gases in primary inclusions could be extracted with little contribution of secondary inclusions. The conditions found adequate for quartz and fluorite samples from the Takatori mine are as follows; 1) initial grain size of the sample is 6 ∼ 10 mesh, and the amount of sample is about 4g, 2) preheating temperature of sample is set at the filling temperature of primary inclusions, and the preheating period is more than 12h in vacuum, 3) the duration period of crushing using an alumina ball for 30 ∼ 60min is necessary, and 4) the duration of gas-recovery procedure for more than 3h with the heating of the mill at the same temperature of preheating is necessary for the recovery of gasses adsorbed on the powdered sample. For quartz and fluorite samples, isotopic compositions of extracted gases including H₂O, CO₂ and CH₄ were reproduced well. The CO₂/H₂O ratio obtained for fluid inclusions in quarts from the Takatori tungsten mine, Japan, varied considerably according to the difference in the condition of ball-milling. For arsenopyrite sample the isotopic results were scattered widely because SO₂ was evolved during crushing even at room temperature, which may be due to the reaction between arsenopyrite and H₂O. When this method is applied to extracting fluid inclusions in minerals, the experimental conditions such as 1) and 2) should be changed depending on the nature of samples, especially the filling temperature of primary inclusions is important to set the preheating temperature. Disadvantages inherent in the ball-milling method are, 1) incomplete extraction of fluid inclusions and 2) the adsorption of gases onto the powder surface. The latter can be overcome by heating the powdered sample during the recovery process of gases, which was proven by the simulation test. As far as the isotopic compositions of H₂O, CO₂ and CH₄ extracted from fluid inclusions are concerned, disadvantages given above have no effect on the result.