Carbonate sinter in the Oku-Okuhachikuro hot spring, Akita prefecture - Co-existence of aragonite and calcite in calcareous sinter-

Nobuo Hirano, Ai Takenoshita, Noriyoshi Tsuchiya

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6 Citations (Scopus)


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 4wt% 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 Carich laminar ranges from 20 to 150 μ and Fe-rich one is from 10 to 80 μ. 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.

Original languageEnglish
Pages (from-to)198-207
Number of pages10
JournalJapanese Magazine of Mineralogical and Petrological Sciences
Issue number5
Publication statusPublished - 2009


  • Aragonite
  • Calcite
  • Carbonate sinter
  • Metastable phase
  • Oku-okuhachikuro hot spring


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