Determination of Trace Elements in Zoned Beryl by Laser and Ion Microprobe Analyzers

Abstract

Trace elements in beryl from Homret Mukpid pegmatite, Egypt, were determined by laser microprobe spectroscopy (JOEL JLM-200) and ion microprobe mass analysis (HITACHI IMA-2). The beryl shows growth zoning which is parallel to {1010}. Analyzed points in the beryl crystal correspond to five zones indicated in Fig.1. Point 1 is almost colorless, points 2 and 4 are light blue, and points 3 and 5 show bulish tint.
Eight elements (Si, Ti, Al, Fe, Be, Mn, Mg and Ca) were detected by both analytical methods, and six more elements (Zr, Cr, Na, K, Li and Cs) by the latter (Table 2 and Fig. 2). The following is the results by microprobe analyses (Table 1 and Fig. 2): (i) the composition of the beryl scarcely differs from its ideal formula, (ii) especially, that of the central zone (point 1) is almost ideal, (iii) a part of Al is replaced by Fe³⁺, (iv) the deeper colored zones (points 2 and 4) are rich in Ti, Mn, Mg, Ca, Na and K, as compared with the pale parts, (v) Zr and Cr con-centrate in the central and marginal zones (points 1 and 5), and (vi) the content of Li is high in the center, while Cs in the margin.
These results indicate that laser and ion microprobe analyses are very useful for the determination of trace elements in small areas. The writers believe that both apparatuses would contribute to the mineral exploration as well as mineralogy, geology and geochemistry.