FIRST DUMORTIERITE FIND ON THE UKRAINIAN SHIELD

Abstract

While thoroughly studying drill cores, recovered during subsurface geologic mapping of the Fedorovka tectonic zone near the north edge of the Azov crystalline basement block, the authors detected and studied dumortierite, a mineral hitherto unknown on the Ukrainian shield. Studies indicate that dumortierite is a very rare, late, hydrothermal-metasomatic mineral of rare-metal pegmatite bodies, usually confined to tourmaline-bearing schists, where it was deposited in trace amounts in the closing stage of their emplacement from excess boron and aluminum that had not been totally consumed in the formation of tourmaline, sillimanite, staurolite, corundum, andalusite and the like. Under the same conditions in rare-metal pegmatite, exposed along upper reaches of the Karasu River, Turkestan Range, dumortierite was detected in 1950 by A.A. Beus. In 1982, dumortierite and muscovite were noticed among hydrothermal replacement products of andalusite that was found in association with rutile and dravite in quartz-microcline pegmatite, confined to high-alumina gneiss near the town of Katugin on the south slope of the Kalar Range, northeastern Transbaikal.