FLUID INCLUSION MICROTHERMOMETRY AND GAS CHEMISTRY IN GEOTHERMAL SYSTEM, JAPAN AND ITS APPLICATION FOR THE STUDY OF FLUID EVOLUTION - Energy Research Developments: Tidal Energy, Energy Efficiency and Solar Energy - page 164

bubble was observed in six liquid-rich inclusions longer than 30μm. Based on the gas
composition of individual liquid-rich inclusion obtained by QMS as mentioned in section
3.2.2, the dominant non-condensable gas in the inclusion is CO 2 . Upon crushing, the vapor
bubble gradually expanded until they filled the entire volume of two primary (T h of 229 ºC)
and three secondary inclusions (T h of 223 to 236 ºC). This behavior suggests that the CO 2
content in these inclusions exceeded 0.2 mol%. Whereas, the bubble fills 80 % of the
inclusion volume in one other primary inclusion (T h of 227 ºC), suggesting CO 2 content
ranges from 0.1 to 0.2 mol%. According to Hedenquist and Henley (1985), dissolved CO 2
will contribute to the depression of the freezing-point in an inclusion. If the ice-melting
temperatures (T m ) of the inclusions depend solely on their CO 2 contents, their maximum
possible CO 2 contents can be calculated from their T m values. In the case of the secondary
inclusions in anhydrite from a depth of 916 m, their T m values of - 0.8 and - 0.9 ºC correspond
to CO 2 content of 0.9 mol% (Sasada et al., 1992). The CO 2 contents of the secondary
inclusions, therefore, range in 0.2 to 0.9 mol%. They are in good agreement with CO 2 content
of 0.4 mol% (table 3) in the inclusions in the anhydrite analyzed by the QMS.

Table 2. Bubble behavior on crushing and estimated CO 2 contents of liquid-rich
inclusions from the Matsukawa and Kakkonda geothermal fields

Well Depth

(m)

Mineral Type Bubble behavior CO 2 (mol%)

Th ( ) Tm ( )

Matsukawa
M11 916 AH Pr fill the inclusion (2)* 229 0.2 ≦

3.0 to 4.5

Pr expand,but not fill the

inclusion (1)

227

3.8 0.1 0.2

Sc fill the inclusion (3)

223 236 0.8 to 0.9 0.2 0.9

Kakkonda
Well-12 650 QZ Pr fill the inclusion (1) 254

0.9 0.2 0.9

Sc ditto (1)

229 231 0.4 0.2 0.4

Sc expand,but not fill the

inclusion(1)

229 231 0.4 0.1 0.2

Well-73 50 CA Sc fill the inclusion (2) 0.1

150 157 0.1

Well-42 600 CA Pr fill the inclusion (2)

275 302 0.4 to 0.7 0.2 0.8

* Number in parenthesis shows percentage.

The similar method by the crushing run was performed on hydrothermal quartz and
calcite from three production wells in the Kakkonda geothermal field. The CO 2 content is
0.1mol% for two secondary inclusions in calcite from Well-73 and range in 0.2 to 0.8 mol%
for two primary inclusions in calcite from Well-42. On the other hand, the CO 2 contents of
the primary and secondary inclusions in quartz from 650 m of Well-12 range in 0.2 to 0.9 and
0.1 to 0.4 mol%, respectively. The CO 2 content of 0.11 mol% (table 3) in the inclusions
analyzed by the QMS for quartz from 500m depth of Well-13 is the lowest of these ranges.
According to Sasada et al. (1992) and Sawaki et al. (1997), the CO 2 contents of fluid
inclusions estimated for quartz and anhydrite by microthermometry and crushing technique
are consistent with those obtained by the QMS analysis at the Sengan, Yuzawa, Kurikoma,
Hohi, Hishikari, Broadlands and Kirishima geothermal fields.