Chik

Ijolite-urtites make up several bodies cutting Upper Proterozoic marbles. The northeastern part of the main intrusion is a banded complex consisting of alternating bands of ijolite-urtite, ijolite and melteigite with amongst them intensively altered marble xenoliths. The thickness of the bands varies from several centimetres to several tens of metres and the bands differ in grain size with some variably grained and others medium- to coarse-grained and sometimes pegmatitic. The primary rock-forming minerals are nepheline, which in urtites comprise up to 90% of the rock, and fassaite. The southeastern part of the principal body contains calcite-bearing urtite, calcite-nepheline rocks and pure calcite rocks that look like carbonatites, but the calcite gives Ù18Oo/oo SMOW values from +14.7 to +16.4and Ù13Co/oo PDB from -0.9 to -2.0. Near the boundary of fassaite ijolites and urtites with calcite-bearing nepheline rocks melanite ijolites are found. They comprise nepheline, melanite and Na-hedenbergite and show evidence that fassaite has been replaced by melanite + Na-hedenbergite. In calcite-bearing urtites and calcite-nepheline rocks the role of secondary minerals is of greater importance with the replacement of nepheline by cancrinite (3-4%) and thomsonite. Apatite is the most common accessory mineral.