GSL March ?Booksale
Advertisement

Lyell Collection
Geochemistry: Exploration, Environment, Analysis
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Figures Only
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Web of Science (6)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Arthur, R. C.
Right arrow Articles by Ota, K.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Geochemistry: Exploration, Environment, Analysis; 2006; v. 6; issue.1; p. 33-48;
DOI: 10.1144/1467-7873/05-081
© 2006 Geological Society of London

Original Article

Geochemical constraints on the origin and stability of the Tono Uranium Deposit, Japan

Randolph C. Arthur*1, Teruki Iwatsuki2, Eiji Sasao2, Richard Metcalfe3, Kenji Amano2 & Kunio Ota2

1 Monitor Scientific, LLC, 3900 S. Wadsworth Blvd, Suite 555, Denver, Colorado 80235, USA(*e-mail: rarthur@monitorsci.com)
2 Japan Atomic Energy Agency, Mizunami Geoscience Academy, 1-64, Yamanouchi, Akeyo, Mizunami,Gifu 509-6132, Japan
3 Quintessa Limited, Queen's Tower A 7-707, 2-3-1 Minatomirai, Nishi-ku, Yokohama, 220-6007, Japan

Data characterizing the mineralogy, hydrochemistry and geomicrobiology of the Tono region of central Japan were used to interpret geochemical constraints on the origin and stability of the Tono Uranium Deposit. The derived constraints are compatible with models of deposit formation, which call for leaching of uranium from the upper weathered zone of the Toki Granite by relatively oxidizing groundwaters that are near-neutral to moderately alkaline and carboniferous. The oxidizing groundwaters then migrate into mudstones and sandstones of the overlying Toki Formation, where the uranyl species is reduced by water–rock–microbe interactions to uranous species, sorbed by various detrital and authigenic phases and eventually precipitated as uraninite, coffinite and the metastable, amorphous hydrous oxide, UO2(am).

Formation of the Tono deposit may have been more or less continuous up to the present time. The modern hydrochemical system, upon which the genetic model is based, began to evolve about 15 Ma when seawater was flushed out of the sedimentary cover and basement granite by fresh, meteoric waters during a period of uplift and erosion preceding Pliocene to Pleistocene sedimentation. Recharge with meteoric water continued to the present, which suggests that palaeohydrochemical conditions were probably similar to those observed in the region today when the Tono deposit began to form about 10 Ma.

Redox environments in the Tono region inferred from in-situ Eh measurements in deep boreholes and calculated potentials for the SO42–/HS– redox couple appear to be controlled by heterogeneous reactions involving Fe(III)-oxyhydroxides. Metastable equilibria and particle-size effects associated with these reactions produce a range of possible redox environments that are equally compatible with both the relatively oxidizing and reducing groundwaters of the Toki Granite. This compatibility extends to sedimentary porewaters, where the redox environment is also controlled by microbially mediated sulphate reduction, oxidation of organic matter and precipitation of sulphide minerals. Redox conditions have been stable during at least the past several tens of thousands of years based on palaeoredox indicators interpreted from the trace element contents of fracture calcites. The pH and carbonate contents of palaeogroundwaters and modern groundwaters of the Tono region were, and are, controlled mainly by calcite equilibrium.

Key Words: uranium • natural analogue • palaeoredox




This article has been cited by other articles:


Home page
 American MineralogistHome page
H. Sugimori, T. Iwatsuki, and T. Murakami
Chlorite and biotite weathering, Fe2+-rich corrensite formation, and Fe behavior under low PO2 conditions and their implication for Precambrian weathering
American Mineralogist, 2008; 93: 1080 - 1089.
[Abstract] [Full Text] [PDF]

Home page
 Geochemistry: Exploration, Environment, AnalysisHome page
E. Sasao, K. Ota, T. Iwatsuki, T. Niizato, R. C. Arthur, M. J. Stenhouse, W. Zhou, R. Metcalfe, H. Takase, and A. B. Mackenzie
An overview of a natural analogue study of the Tono Uranium Deposit, central Japan
Geochemistry: Exploration, Environment, Analysis, 2006; 6: 5 - 12.
[Abstract] [Full Text] [PDF]

Home page
 Geochemistry: Exploration, Environment, AnalysisHome page
R. Metcalfe, H. Takase, E. Sasao, K. Ota, T. Iwatsuki, R. C. Arthur, M. J. Stenhouse, W. Zhou, and A. B. Mackenzie
A system model for the origin and evolution of the Tono Uranium Deposit, Japan
Geochemistry: Exploration, Environment, Analysis, 2006; 6: 13 - 31.
[Abstract] [Full Text] [PDF]

Home page
 Geochemistry: Exploration, Environment, AnalysisHome page
Y. Kanai, H. Kamioka, T. Nakajima, and H. Tsukamoto
Characterization and geochemical behaviour of uranium series nuclides in sandy sediments at Kanamaru area, Yamagata and Niigata Prefectures, Japan
Geochemistry: Exploration, Environment, Analysis, 2006; 6: 57 - 67.
[Abstract] [Full Text] [PDF]