@article{fdi:010093210,
  title = {{S}tudy of two alteration systems as natural analogues for radionuclide release and migration},
  author = {{I}ldefonse, {P}. and {M}uller, {J}ean-{P}ierre and {C}lozel, {B}. and {C}alas, {G}.},
  editor = {},
  language = {{ENG}},
  abstract = {{U}-deposit hosted in hydrothermally altered tuffs in {M}exico, together with weathering profiles from {C}ameroon were studied as natural analogues of radionuclide release and migration. {U}sing petrological and spectroscopic methods (infrared and electron paramagnetic resonance), we have distinguished successive secondary mineral parageneses and the behaviour of radionuclides. {I}n the {U}-deposit, the mineral parageneses show that uranium migration is mainly controlled by the redox potential and silica activity of the altering solutions. {T}he high silica content of the solutions is caused by the intense alteration of volcanic rocks. {T}wo types of secondary clay mineral parageneses are evidenced: a kaolinization, intense where uranium is accumulated in the welded tuffs, and a smectitization mainly developed in the underlying weakly welded tuffs. {S}everal types of kaolinite have been defined according to their genesis (fillings in fissures and feldspar pseudomorphs), their location relative to a breccia pipe where uranium has accumulated (core and rim of the pipe; surrounding rhyolitic tuffs), and particle morphology, structural order and substitutional {F}econtent. {I}t is shown that the variations of the concentration of paramagnetic defect centres, always more than ten times as important than those measured in weathering kaolinites, are only correlated to the location of the kaolinites. {T}he highest values correspond to the breccia pipe kaolinites, e.g. kaolinites located in the uranium accumulation zones. {M}oreover, one or two main defects centres are detected depending on the intimate association of kaolinites with uranium-bearing minerals. {B}esides, in weathering kaolinites from {U}-depleted laterites, defect centre concentrations are correlated to the total {F}e203 content in bulk samples. {T}his means that the defect centre acts as a memory of the travel of uranium when this element was sorbed onto iron gels in the first stage of weathering. {I}t is concluded that paramagnetic defect centres in kaolinites might allow an efficient fingerprint of successive irradiations in the natural analogues under study and could be an useful tool to control radionuclides migration through kaolinite-containing clayey materials such as those used for waste repository. {A} better understanding of radiation efficiency as well as accurate dose-ratekaolinite-containing clayey materials such as those used for waste reposit estimation are needed for a quantitative tracing of the migration of{A} better understanding of radiation efficiency as well as accurate dose-ratekaolin radionuclide elements. {W}ith this aim, a simulation has been undertaken withestimation are needed for a quantitative tracing of the migration of various radiations sources. {W}e have determined for each irradiation the parameters of the paramagnetic centres created in order to understand the way they are forming. {T}he knowledge of the parameters governing the formation and the stability of the radiation centres in kaolinites allow to use this mineral as a natural dosimeter.},
  keywords = {{CAMEROUN} ; {MEXIQUE}},
  booktitle = {},
  journal = {{E}ngineering {G}eology},
  volume = {29},
  numero = {4},
  pages = {413--439},
  ISSN = {0013-7952},
  year = {1990},
  DOI = {10.1016/0013-7952(90)90076-d},
  URL = {https://www.documentation.ird.fr/hor/fdi:010093210},
}