Distribution of rare alkali metals in chamber pegmatites as criterion in prospecting for optical fluorite and piezoquartz

The distribution of rubidium and cesium in microcline-perthite was studied in five topaz- and fluorite-bearing zoned pegmatites. Determinations of mineral paragenesis aided in the interpretation of the results of the rare alkali metal determinations. The study lead to the following conclusions: 1) The Rb content in zoned fluorite and topaz pegmatites increases by a factor of 2.4–3.0 from the contact zone toward the core. Cs in microcline-perthite varies systematically with position in some pegmatites, but not in others. 2) Biotite from fluorite-bearing pegmatites shows a much higher content of F, Rb, Cs and Li than biotite from fluorite-free pegmatites. This criterion (plus a higher Rb content in the block microcline-perthite near the pegmatite core) is considered as exploration aid for fluorite and piezoquartz pegmatites. — R.D. DeRudder.