Lujavrites, melanocratic agpaitic nepheline syenites, are the most highly
evolved rocks of the Ilímaussaq alkaline complex, South Greenland. They
have elevated contents of U. U-rich occurrences at Kvanefjeld in the
northern part of the complex have been extensively drilled. Lujavrites from
other parts of the complex were examined in seven bore holes, I to VII, in
1962 in an evaluation of the U potential of the complex. The study presents
a general overview of the geology of the lujavrites, the distribution of
various types of lujavrite and the structure of the complex partly based on
the information obtained from the study of drill cores I-VII. The
lujavrites are sandwiched between the roof and floor series of the complex.
The drill cores penetrate the lower part of the roof series and present an
incomplete section through the lujavrites. The lowermost lujavrites are
dominated by aegirine lujavrites, cumulitic rocks directly succeeding the
rocks of the floor series. The overlying arfvedsonite lujavrites intrude
the lower part of the roof series.
The alternation of aegirine- and arfvedsonite-bearing lujavrites and the
formation of layering are interpreted to be caused by changes in the
physico-chemical conditions of the lujavritic magma, especially changes in
PH2O and fO2. Villiaumite, NaF, has only been found in drill cores from
high levels in the complex. Naujakasite, which is a common constitutent of
the hyper-agpaitic lujavrites at Kvanefjeld, has not been observed in drill
cores I-VII. This may be linked to its formation at higher levels in the
complex than represented by these drill cores. The lujavrites of bore holes
I-VII have with few exceptions moderate contents of U.