Uranium- and thorium-rich vesuvianite from the Seward Peninsula, Alaska

• Main Authors: Gibn R. Hnrauelnnnc, U. S. Geological Survey, Nno Tnouas P. Miller
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Seward Peninsula; Alaska
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.505.3214; http://rruff.info/doclib/am/vol65/AM65_1020.pdf

Vesuvianite rich in U, Th, and REE occurs in a syenite and nepheline syenite in south-eastern 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 (meta-mict) core and an anisotropic (non-metamict) rim. The chemical composition can be approxi-mated by the formula (Ca,Na,La,Ce,Pr,Nd,U,Th)re r(Al,Ti,Fe,Mn,Mg)t2 rSi,6(O,OH,F)t6. UO, content ranges from 0.39 (non-metamict) to 0.84 weight perc€nt (metamict), and ThOt ranges from 0.72 (non-metamict) to 2.70 weight percent. Coexisting allanite has UO, and ThO2 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.