Late alteration in titanite (CaTiSiO[sub 5]): Redistribution and remobilization of rare earth elements and implications for U/Pb and Th/Pb geochronology and nuclear waste disposal
- Univ. of Western Ontario, London (Canada)
Translucent, dark-colored titanites from a wide variety of geological environments are commonly partly replaced by very fine-grained aggregates of REE-rich minerals (including allanite, monazite, and bastnaesite), rutile, quartz, calcite, apatite, and chlorite along grain fractures and boundaries. The aggregates of REE-rich minerals are bordered by an irregular zone of altered titanite, which, by secondary ion mass spectrometry (SIMS), is considerably lower in REEs, U, and Th than the adjacent unaltered matrix. Light REEs and Th are differentially depleted in the altered zone and correspondingly enriched in secondary minerals. Additionally, HREEs and U have been lost to the external system, the loss of HREEs being in proportion to the increase in atomic number. Natural radiation damage was not an important factor in promoting the late alteration of titanite. Titanite which has been subjected to late hydrothermal activity would not remain a closed system in respect to either U or Th decay series and therefore cannot be used for U/Pb and Th/Pb geochronology. The observed leaching and partial dissolution of titanite under hydrothermal conditions are generally consistent with laboratory experimentation, indicating that proper isolation from any communication with hydrothermal fluids is essential in the application of titanite-based ceramics for the immobilization of radioactive waste. 42 refs., 4 figs., 3 tabs.
- OSTI ID:
- 6689711
- Journal Information:
- Geochimica et Cosmochimica Acta; (United States), Vol. 57:2; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
RADIOACTIVE WASTES
ENCAPSULATION
TITANITE
DISSOLUTION
HYDROTHERMAL ALTERATION
LEACHING
ALLANITE
APATITES
BASTNAESITE
CALCITE
CERAMICS
CHLORITE MINERALS
DAMAGE
DECAY
FLUIDS
FRACTURES
LEAD
MONAZITES
QUARTZ
RADIOACTIVE WASTE DISPOSAL
RARE EARTHS
RUTILE
THORIUM
URANIUM
ACTINIDES
CARBONATE MINERALS
ELEMENTS
FAILURES
MANAGEMENT
MATERIALS
METALS
MINERALS
OXIDE MINERALS
PHOSPHATE MINERALS
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
RADIOACTIVE WASTE MANAGEMENT
RARE EARTH COMPOUNDS
SEPARATION PROCESSES
SILICATE MINERALS
THORIUM MINERALS
WASTE DISPOSAL
WASTE MANAGEMENT
WASTES
052002* - Nuclear Fuels- Waste Disposal & Storage