Petrography and chemistry of tungsten-rich oxycalciobetafite in hydrothermal veins of the Adamello contact aureole, northern Italy
| Autor: | Timothy E. Payne, P.J. McGlinn, Reto Gieré, Gregory R. Lumpkin, C. Terry Williams |
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| Rok vydání: | 2017 |
| Předmět: |
Zirconolite
Mineral 010504 meteorology & atmospheric sciences Geochemistry Mineralogy engineering.material 010502 geochemistry & geophysics 01 natural sciences Silicate Hydrothermal circulation Petrography chemistry.chemical_compound Betafite Geophysics chemistry Geochemistry and Petrology Batholith engineering Vein (geology) 0105 earth and related environmental sciences |
| Zdroj: | Mineralogy and Petrology. 111:499-509 |
| ISSN: | 1438-1168 0930-0708 |
| Popis: | Tungsten-rich oxycalciobetafite occurs in complex Ti-rich hydrothermal veins emplaced within dolomite marble in the contact aureole of the Adamello batholith, northern Italy, where it occurs as overgrowths on zirconolite. The betafite is weakly zoned and contains 29–34 wt% UO2. In terms of end-members, the betafite contains approximately 50 mol% CaUTi2O7 and is one of the closest known natural compositions to the pyrochlore phase proposed for use in titanate nuclear waste forms. Amorphization and volume expansion of the betafite caused cracks to form in the enclosing silicate mineral grains. Backscattered electron images reveal that betafite was subsequently altered along crystal rims, particularly near the cracks. Electron probe microanalyses reveal little difference in composition between altered and unaltered areas, except for lower totals, suggesting that alteration is primarily due to hydration. Zirconolite contains up to 18 wt% ThO2 and 24 wt% UO2, and exhibits strong compositional zoning, but no internal cracking due to differential (and anisotropic) volume expansion and no visible alteration. The available evidence demonstrates that both oxycalciobetafite and zirconolite retained actinides for approximately 40 million years after the final stage of vein formation. During this time, oxycalciobetafite and zirconolite accumulated a total alpha-decay dose of 3.0–3.6 × 1016 and 0.2–2.0 × 1016 α/mg, respectively. |
| Databáze: | OpenAIRE |
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