Trace element composition of beryl from spodumene pegmatite deposits of the Kunar Province, Afghanistan

Abstract

The study of trace element composition of beryl from the Chambalak and Digal deposits of the Darai Pech pegmatite feld of the Kunar province (Afghanistan) using secondary ion mass spectrometry (SIMS) revealed the sectoriality of the beryl crystal from the Chambalak deposit. The inner and outer parts of the profle are identifed as the pinacoid (0001) and prism (10 1 0) growth zones, respectively. At the boundary of these two simple forms, the Cs, Na, Ca, Fe, Mg, and V content strongly increases. The prism growth zone exhibits the growth pyramids: a decrease in the Na, Fe, V, Ni, and Cr content during growth towards the edge of the beryl crystal. The H2O and Mg content increases in the prism growth zone. No boundary between the pinacoid and prism growth zones is observed in beryl from the Digal deposit. There is a reason to consider its profle as the prism growth zone. A comparison of beryl based on the content of indicative elements, the increase of which corresponds to the fractionation trend of pegmatite melt (Cs, Li, and Rb), from pegmatite deposits of the Kunar province with beryl from other objects showed that pegmatite melt in the studied deposits was moderately fractionated corresponding to the initial evolution stages. It is shown that the content of some elements of beryl from the prism and pinacoid growth zones can fundamentally differ.