The carbonatite-alkaline rock suites are quite unique for hosting high grade critical metals including rare earth elements (REE), niobium (Nb), tantalum (Ta), thorium (Th) and uranium (U). Most of these rock suites are generally associated with continental rifting in overthickened Precambrian cratonic environments. In Turkey, despite majority of magmatism is quite young, a few number of carbonatite intrusions were identified in Central Anatolian Crystalline block. However, the scientific literature which focused on the magmatic activities of NW Anatolia with its numerous articles involving magmatic intrusions and their extrusive counterparts lacked genuine magmatic carbonatite data until the present day. The Ar & imath;kl & imath; carbonatite intrusion is the first magmatic carbonatite identified in NW Anatolia, and also interesting for its unusual mineralogical and geochemical features. The carbonatite body is generally composed of multiple phases of calcite and apatite mineralizations. Carbonatitic rocks of Ar & imath;kl & imath; show a highly evolved nature with considerable Mg and Ca contents accompanied by Th (up to 0.36 wt%), U (up to 373.6 ppm) and heavy rare earth elements (HREE) (up to 194.7 ppm). The delta 13C (PDB) and delta 18O (SMOW) values show that fractional crystalization and hydrothermal activities effected the composition of initial carbonatitic melt. The metasomatic halo of Ar & imath;kl & imath; carbonatites are enriched in terms of K (up to 12 wt%), P (up to 9 wt%), Th (248 ppm), and U (up to 0.27 wt%). However, the LREE values of both carbonatites and metasomatic rocks are pretty low compared to other carbonatite-fenite complexes. The effects of magmatic and post-magmatic events (partial melting, fractional crystalization, liquid immiscibility, and fenitization) played an important role in the formation of Ar & imath;kl & imath; carbonatite intrusion.