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Alteration Minerals in Granitic Rock at Ashio as Radionuclide Adsorption Materials

Published online by Cambridge University Press:  15 February 2011

S. Hamasaki
Affiliation:
Geological Survey of Japan, Higashi 1–1–3, Tsukuba 305, Japan.
K. Tsukimura
Affiliation:
Geological Survey of Japan, Higashi 1–1–3, Tsukuba 305, Japan.
K. Fujimoto
Affiliation:
Geological Survey of Japan, Higashi 1–1–3, Tsukuba 305, Japan.
K. Omura
Affiliation:
National Research Institute for Earth Science and Disaster Prevention, Tennodai 3–1, Tsukuba 305, Japan.
R. Ikeda
Affiliation:
National Research Institute for Earth Science and Disaster Prevention, Tennodai 3–1, Tsukuba 305, Japan.
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Abstract

Alteration minerals from a drill-core (maximum depth 2002 m) in the granitic rock at Ashio, central Japan, were studied by optical microscopy, X-ray diffractometry and analytical scanning electron microscopy. In the host rock, biotite is altered to chlorite and plagioclase to illite. Calcite has precipitated in veinlets and grain boundaries. The host rock close to fractures is strongly altered, whereas the rocks distant from fractures are less altered. Quartz, illite, chlorite, laumontite and calcite have precipitated on fracture walls. The alteration minerals are estimated to have formed in the range 140–200°C, higher than the present temperature (13°96°C). The chemical composition of the ground water in the granitic rock at Ashio was estimated thermodynamically from the mineral assemblage. The alteration reaction of palgioclase and the precipitation of calcite may occur simultaneously. The alteration minerals formed in the host rock and in the fractures may adsorb radionuclides effectively, and thus may inhibit radionuclide transport to biosphere.

Type
Research Article
Copyright
Copyright © Materials Research Society 1995

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References

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