Thrich loparite from the Khibina alkaline complex, Kola Peninsula: isomorphism and paragenesis

Th-rich (up to 18.4 wt. % ThO2) loparite occurs as an accessory phase in foyaite pegmatites at Mt. Eveslogchorr, Khibina complex, Russia. It is associated with aegirine, astrophyllite, eudialyte, lorenzenite, lamprophyllite, magnesio-arfvedsonite and gerasimovskite. Loparite crystals are zoned from...

Full description

Bibliographic Details
Main Authors: Roger H. Mitchell, Anton R. Chakhmouradian
Other Authors: The Pennsylvania State University CiteSeerX Archives
Format: Text
Language:English
Published: 1998
Subjects:
loparite
betafite
belyankinite
nepheline-syenite pegmatite
Khibina alkaline complex
Kola Peninsula
Russia
kola peninsula
Online Access:http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.578.3019
http://rruff.info/doclib/mm/vol62/MM62_341.pdf
Description
Summary:Th-rich (up to 18.4 wt. % ThO2) loparite occurs as an accessory phase in foyaite pegmatites at Mt. Eveslogchorr, Khibina complex, Russia. It is associated with aegirine, astrophyllite, eudialyte, lorenzenite, lamprophyllite, magnesio-arfvedsonite and gerasimovskite. Loparite crystals are zoned from niobian loparite (core) to niobian thorian and thorian niobian loparite (rim). Th-enrichment is accompanied by a decrease in Na, LREE, Sr and increase in A-site vacancies. The most Th-rich composition approaches (Na0.39LREE0.19Th0.12Ca0.05Sr0.02)S0.77(Ti0.76Nb0.27)S1.03O3. The mineral is partly or completely metamict and after annealing gives an X-ray diffraction powder pattern similar to that of synthetic NaLaTi2O6 and naturally occurring loparite of different composition. For the Th-rich rim sample, the five strongest diffraction lines (AÊ) are: 2.72 (100) 110, 1.575 (60) 211, 1.925 (40), 1.368 (30) 220, 1.222 (20) 310; a = 3.867(2) AÊ. The X-ray diffraction patterns do not exhibit peak splitting or other diffraction lines typical of low-symmetry and ordered perovskite-type structures. Composition determinations, infrared transmission spectroscopy and X-ray diffractometry show that thorian loparite is partly replaced by betafite with LREE and Th as dominant A-site cations (‘ceriobetafite’). Some loparite samples also exhibit thin replacement mantles of belyankinite with high LREE2O3 and ThO2 contents. Both ‘ceriobetafite ’ and belyankinite were formed due to metasomatic alteration of loparite.

Similar Items