Distribution of germanium in rocks and minerals of the Ilímaussaq alkaline complex, South Greenland

Abstract

In the agpaitic nepheline syenites of the Ilímaussaq complex, analyses by X-ray fluorescence spectrometry reveal that Ge is largely held in arfvedsonite (2.4–4.3 ppm) and aegirine (2.5–4.3 ppm) and has abnormally low contents (down to < 0.2 ppm) in microcline. This distribution is discussed in relation to three controls: (1) increased ratios of octahedral to tetrahedral Ge in Na-rich, Ge-bearing melts and in high-pressure melts, (2) increased ratios of bivalent to quadrivalent Ge in highly reduced melts and (3) reduced admittance of Ge into the structurally ordered low microcline which crystallised in the low-temperature agpaitic magmas.