Uranium- and thorium-rich vesuvianite from the Seward Peninsula, Alaska
1980; Mineralogical Society of America; Volume: 65; Linguagem: Inglês
ISSN
1945-3027
AutoresGlen R. Himmelberg, Thomas P. Miller,
Tópico(s)Clay minerals and soil interactions
ResumoVesuvianite rich in U, Th, and REE occurs in a syenite and nepheline syenite in southeastern Seward Peninsula, Alaska. The vesuvianite occurs as large (up to 1.5 cm) tabular crystals; in thin section it is brownish-yellow and commonly zoned with an isotropic (metamict) core and an anisotropic (non-metamict) rim. The chemical composition can be approximated by the formula (Ca,Na,La,Ce,Pr,Nd,U,Th)/sub 18/ /sub 1/(Al, Ti, Fe, Mn, Mg)/sub 12/ /sub 9/Si/sub 18/(O, OH, F)/sub 76/ UO/sub 2/ content ranges from 0.39 (non-metamict) to 0.84 weight percent (metamict), and ThO/sub 2/ ranges from 0.72 (non-metamict) to 2.70 weight percent. Coexisting allanite has UO/sub 2/ and ThO/sub 2/ contents that range from 0.29 to 0.40 and 0.77 to 1.30 weight percents, respectively. The vesuvianite probably formed by metasomatic activity prior to intrusion of subsilicic alkaline dikes.
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