Application of Cathodoluminescence to Geothermal Exploration. Preliminary Case Studies of the Kakkonda and Mori Geothermal Fields.:Preliminary Case Studies of the Kakkonda and Mori Geothermal Fields

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The purpose of the paper is to clarify the application of cathodoluminescence (CL) to geothermal exploration such as detection of a productive fracture. The CL of anhydrites and calcites in the different origins or stages in the Kakkonda and Mori geothermal fields has been studied using the Luminoscope (ELM-3R) and the CL mode of a scanning electron microscope (CL-SEM). The CL images of natural hydrothermal anhydrite have brown, pale green colors and colorless. The CL images with brown and pale green colors result from both Sm3+ and Dy3+ emissions, and Mn2+ emission, respectively. Calcite in the three different origins or stages such as natural hydrothermal calcite, calcite scale and limestone shows CL images with red color, resulting from Mn2+ emission. Intensity of the CL spectrum of Mn2+ in the calcites suggests that Mn content in limestone is lower than that in other calcites. Based on these investigations, it is concluded that the CL of anhydrite and calcite is a useful method to discern the different origins or stages of these minerals, and to detect productive fractures in geothermal fields. Moreover, this method provides us important information for mixing degree of magmatic fluid with geothermal fluid in reservoir.
日本地熱学会の論文