APPLICATION OF CATHODOLUMINESCENCE TO THE INVESTIGATION OF GRANITIC PEGMATITES

Cathodoluminescence (CL) has long been known to be an important petrologic tool for many types of geoscience materials. Cathodoluminescence is widely used in the study of sedimentary rocks and to a lesser degree, metamorphic and igneous rocks. The application of CL to the investigation of pegmatitic rocks has been meager, in part due to the limited number of pegmatite minerals for which distinct CL properties have been adequately determined. The use of CL in the examination of granitic pegmatites has been applied largely to studies of quartz, feldspar, apatite and zircon. However, the wide variety of minerals known to occur within granitic pegmatites makes them favorable candidates for much more extensive CL examination.

A collection of 50 different pegmatite minerals from several localities were examined using a cold-cathode cathodoluminescence instrument in order to define characteristic features that can be used for general petrologic studies of granitic pegmatites. The minerals examined in this study include not only common rock-forming silicates (e.g., quartz, feldspar, muscovite), but also oxides containing high-field strength elements (e.g., columbite-group minerals, cassiterite), primary and secondary phosphates (e.g., apatite, montebrasite, lazulite), halides (e.g., fluorite, cryolite) and minerals hosting the light lithophile elements, Li, Be and B (e.g., spodumene, beryl, tourmaline). CL images were captured using a CCD camera and compiled to create an atlas which will serve as the primary resource for future CL studies of granitic pegmatites.