Alkaline Rocks and Carbonatites of the World

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Occurrence number: 
Longitude: -49.05, Latitude: 61.08

In an area southwest of Frederikshab a swarm of northwest-trending, Mesozoic dolerite dykes is paralleled by fewer and generally thinner lamprophyric carbonatite dykes which range from a few mm to about 1 m in thickness. The rocks consist of a matrix of calcite, and less commonly dolomite or ankerite, and magnetite with megacrysts of phlogopite, salite, hornblende and olivine. Analyses indicate SiO2 values of 14-30%, CO2 16-19%, and generally K2O > Na2O (Walton and Arnold, 1970, Table 1). Most are ne normative with normative ac and lc in some. Nodules up to 6 cm in diameter are found, including olivine crystals thought to be of upper mantle origin, various types of granulites, and some with sodic amphibole, aegirine-augite and biotite which textural evidence would suggest are of metasomatic origin.

K-Ar on biotite from one dyke gave 162±5 Ma (Larsen and Moller, 1968a, p. 86).
LARSEN, O. and MOLLER, J. 1968a. Potassium-argon age studies in West Greenland. Canadian Journal of Earth Sciences, 5: 683-91. WALTON, B.J. and ARNOLD, A.R. 1970. Plutonic nodules in lamprophyric carbonatite dykes near Frederikshab, south-west Greenland. Meddelelser om Gronland, 190(5): 1-26
Fig. 100 Location of lamprophyric carbonatite dykes in the Iluilarssuk area (after Walton and Arnold, 1970, Fig. 1).
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