著者

平野 伸夫 竹之下 愛 土屋 範芳

出版者

一般社団法人 日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.38, no.5, pp.198-207, 2009 (Released:2009-11-26)

参考文献数

28

被引用文献数

2 2

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Carbonate hot spring is a natural chemical reaction field for understanding CO2 geological sequestration as a natural analogue. Natural analogue studies are particularly important to understand the kinetics of mineral precipitation which has potential difficulties in experimental investigations. Carbonate sinter is frequently formed in and around carbonate hot spring, which can be suitable to elucidate mechanisms of carbonate precipitation associated with flushing CO2.   Oku-Okuhachikuro hot spring, located in Kosaka town, Akita Prefecture, NE Japan, is an artificial hot spring after drilling of exploration for the Kuroko-deposits, and it is still active where carbonate sinter has still been forming continuously for more than thirty years after drilling. The temperature of spring water is 44 °C and water pH is 6.2, with discharge rate of 0.08 m3/min. The average chemical compositions of sinter correspond about 80 wt% CaCO3, and 4 wt% Fe2O3, associated with minor (<1 wt% each) SiO2, MnO, MgO, Na2O and K2O. Carbonate sinter is mainly composed of aragonite with a small amount of calcite; an intimate occurrence of these two forms of CaCO3 is the most characteristic feature of this locality. However, mineral assemblage, texture and structure of carbonate sinter are different in relation to the distance from the blowout point. Near the blowout point, the sinter is well solidified and shows laminar structure having both of calcite and aragonite. Thickness of Ca-rich laminar ranges from 20 to 150 μm and Fe-rich one is from 10 to 80 μm. Calcite and aragonite assemblage is mainly observed in Ca-rich layer. The Fe-rich layer, however, is composed only of aragonite. The sinter along downstream becomes porous and is monomineralic having aragonite as CaCO3. The observed relations on the special distribution of aragonite/calcite and the possible stability relations of these phases through EPMA and TG-DTA analyses suggest an importance of minor elements (Fe, etc.) in the precipitation of metastable carbonates: this possible effect of the precipitation of metastable phases should be taken into account in the consideration of geochemical processes of CO2 mineral trapping.

著者

平野 伸夫 竹之下 愛 土屋 範芳

出版者

一般社団法人 日本鉱物科学会

雑誌

岩石鉱物科学 (ISSN:1345630X)

巻号頁・発行日

vol.38, no.5, pp.198-207, 2009-09-30

参考文献数

28

被引用文献数

1 2

---

&nbsp;&nbsp;Carbonate hot spring is a natural chemical reaction field for understanding CO₂ geological sequestration as a natural analogue. Natural analogue studies are particularly important to understand the kinetics of mineral precipitation which has potential difficulties in experimental investigations. Carbonate sinter is frequently formed in and around carbonate hot spring, which can be suitable to elucidate mechanisms of carbonate precipitation associated with flushing CO₂.<br> &nbsp;&nbsp;Oku-Okuhachikuro hot spring, located in Kosaka town, Akita Prefecture, NE Japan, is an artificial hot spring after drilling of exploration for the Kuroko-deposits, and it is still active where carbonate sinter has still been forming continuously for more than thirty years after drilling. The temperature of spring water is 44 &deg;C and water pH is 6.2, with discharge rate of 0.08 m³/min. The average chemical compositions of sinter correspond about 80 wt% CaCO₃, and 4 wt% Fe₂O₃, associated with minor (<1 wt% each) SiO₂, MnO, MgO, Na₂O and K₂O. Carbonate sinter is mainly composed of aragonite with a small amount of calcite; an intimate occurrence of these two forms of CaCO₃ is the most characteristic feature of this locality. However, mineral assemblage, texture and structure of carbonate sinter are different in relation to the distance from the blowout point. Near the blowout point, the sinter is well solidified and shows laminar structure having both of calcite and aragonite. Thickness of Ca-rich laminar ranges from 20 to 150 &mu;m and Fe-rich one is from 10 to 80 &mu;m. Calcite and aragonite assemblage is mainly observed in Ca-rich layer. The Fe-rich layer, however, is composed only of aragonite. The sinter along downstream becomes porous and is monomineralic having aragonite as CaCO₃. The observed relations on the special distribution of aragonite/calcite and the possible stability relations of these phases through EPMA and TG-DTA analyses suggest an importance of minor elements (Fe, <i>etc.</i>) in the precipitation of metastable carbonates: this possible effect of the precipitation of metastable phases should be taken into account in the consideration of geochemical processes of CO₂ mineral trapping.<br>